amec tech report hydrogeological data gaps investigationinterim plan wyoming

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Ultra Resources, Inc.

F I N A L

TECHNICAL REPORT

HYDROGEOLOGIC DATA GAPS INVESTIGATION

INTERIM PLANPinedale Anticline Project Area ROD

Sublette County, Wyoming

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FINAL

TECHNICAL REPORT

HYDROGEOLOGIC DATA GAPS INVESTIGATION

INTERIM PLAN

Pinedale Anticline Project Area ROD

Sublette County, Wyoming

Prepared for:

U.S. Department of Interior, Bureau of Land Management, Pinedale Field Office

Wyoming Department of Environmental Quality, Water Quality Division

U.S. Environmental Protection Agency, Region 8

SWEPI LP (Shell)

QEP EnergyUltra Resources, Inc.

Prepared by:

AMEC Environment & Infrastructure, Inc.

1001 South Higgins Avenue, B-1

Missoula, Montana USA 59801

May 2012



FINAL Technical Report: Hydrogeologic Data Gaps InvestigationInterim Plan, PAPA ROD

AMEC Environment & Infrastructure, Inc. May 2012 i

TABLE OF CONTENTS

EXECUTIVE SUMMARY.............................................................................................................vii 1.0 INTRODUCTION .............................................................................................................. 1

1.1 Background .................................................................................................................... 1 1.2 Study Goals and Objectives .......................................................................................... 3 1.3 Report Organization ..................................................................................................... 3

2.0 HYDROGEOLOGIC DATA GAPS INVESTIGATION .................................................. 5 2.1 Geodatabase Development .......................................................................................... 5 2.2 Surface Water Flow Study ........................................................................................... 8 2.3 Surface Water Elevations Survey ................................................................................ 8 2.4 River Stage ..................................................................................................................... 9 2.5 Surface Water Quality Characterization ................................................................... 9 2.6 Characterization of Springs ......................................................................................... 9 2.7 Piezometer Installation .............................................................................................. 10 2.8 Study Well Installation ............................................................................................... 10 2.9 Well Survey and Depth to Water Measurements ................................................... 13

2.9.1 Survey of Well and Piezometer Locations.......................................................................................... 13 2.9.2 Transducer Instrumentation .................................................................................................................. 13

2.10 Groundwater Quality Sampling ................................................................................. 14 2.11 Aquifer Testing ............................................................................................................ 14 2.12 Groundwater Consumption ....................................................................................... 15 2.13 Permit Requirements for Project .............................................................................. 16

3.0 SURFACE WATER FLOW CHARACTERISTICS ....................................................... 17 3.1 Surface Water Hydrographs ...................................................................................... 17 3.2 Synoptic Flow Results ................................................................................................. 18

4.0 GROUNDWATER OCCURRENCE AND FLOW ........................................................ 19 4.1 Depth to Water ........................................................................................................... 19 4.2 Hydraulic Properties ................................................................................................... 20 4.3 Hydrogeologic Cross-Sections ................................................................................... 21 4.4 Groundwater Flow ...................................................................................................... 22

4.4.1 Horizontal Flow ........................................................................................................................................ 22 4.4.2 Vertical Flow .............................................................................................................................................. 23

4.5 Groundwater Recharge and Discharge ..................................................................... 24 5.0 WATER QUALITY .......................................................................................................... 25

5.1 Surface Water ............................................................................................................. 25




AMEC Environment & Infrastructure, Inc. May 2012 ii

5.2 Springs .......................................................................................................................... 26 5.3 Groundwater ............................................................................................................... 26

5.3.1 Alluvial HSU ............................................................................................................................................... 26 5.3.2 Wasatch HSU ............................................................................................................................................ 27

5.4

Water Quality Summary ............................................................................................ 28

5.5 Quality Assurance and Quality Control .................................................................... 28 6.0 SURFACE WATER - GROUNDWATER INTERCONNECTION .............................. 30

6.1 Water Levels and Heads ............................................................................................ 30 6.2 Surface Water Gains and Losses ............................................................................... 32 6.3 Water Quality ............................................................................................................. 32

7.0 HYDROGEOLOGIC CONCEPTUAL MODEL ............................................................. 34 7.1 Physiography of Study Area ....................................................................................... 34 7.2 Geologic Setting .......................................................................................................... 34

7.2.1 Geology of Natural Gas Resources ...................................................................................................... 35 7.2.2 Near-Surface Geology ............................................................................................................................. 35 7.2.3 Geologic Model ......................................................................................................................................... 36

7.3 Climate ......................................................................................................................... 38 7.3.1 Precipitation ............................................................................................................................................... 38 7.3.2 Evapotranspiration .................................................................................................................................... 38

7.4 Hydrology ..................................................................................................................... 39 7.5 Hydrogeology .............................................................................................................. 41

7.5.1 Hydrostratigraphic Units ......................................................................................................................... 41 7.5.1.1 Alluvium HSU .................................................................................................................................................... 42 7.5.1.2 Wasatch HSU ................................................................................................................................................... 42 7.5.1.3 Summary of Water Wells by Hydrostratigraphic Unit .......................................................................... 43

7.5.2 Groundwater Flow ................................................................................................................................... 44 7.5.2.1 Direction ............................................................................................................................................................. 44 7.5.2.2 Groundwater Gradients and Average Velocity ......................................................................................... 45 7.5.2.3 Seasonal Variability .......................................................................................................................................... 47

7.6 Water Quality ............................................................................................................. 48 7.7 Groundwater – Surface Water Interconnection ...................................................... 48 7.8 Water Balance ............................................................................................................. 49

7.8.1 Hydrologic System Water Balance ....................................................................................................... 49 7.8.1.1

Precipitation ....................................................................................................................................................... 50

7.8.1.2 Surface Water Run-On ................................................................................................................................... 50 7.8.1.3 Groundwater Underflow Into Region .......................................................................................................... 51 7.8.1.4 Surface Water Run-off ................................................................................................................................... 51 7.8.1.5 Groundwater Underflow Out of Region ..................................................................................................... 52 7.8.1.6 Groundwater Pumped for Consumptive Use ........................................................................................... 52 7.8.1.7 Evapotranspiration ........................................................................................................................................... 52

7.8.2 Steady-State Groundwater Balance ...................................................................................................... 53




AMEC Environment & Infrastructure, Inc. May 2012 iii

7.8.2.1 Recharge ............................................................................................................................................................. 53 7.8.2.2 Groundwater Underflow into Region .......................................................................................................... 54 7.8.2.3 Ditch Loss ........................................................................................................................................................... 54 7.8.2.4 Groundwater Discharge to Rivers and Streams (Base Flow) ............................................................... 55 7.8.2.5 Groundwater Underflow out of Region ...................................................................................................... 55 7.8.2.6 Groundwater Pumped for Consumptive Use ........................................................................................... 55 7.8.2.7 Evapotranspiration from Groundwater ...................................................................................................... 56

7.8.3 Summary – Groundwater Balance ........................................................................................................ 56 7.9 Conceptual Model ....................................................................................................... 57

8.0 REFERENCES CITED ...................................................................................................... 59




AMEC Environment & Infrastructure, Inc. May 2012 iv

LIST OF TABLES

Table 1 Surface Water Monitoring Stations

Table 2 Mean Monthly Discharge at USGS Gaging Stations in PAPA Region

Table 3 Mean Annual Discharge at Four USGS Gaging Stations in PAPA RegionTable 4 Survey and Water Elevation Data for Surface Water Stations

Table 5 Surface Water Quality Parameters for Laboratory Analysis

Table 6 Construction Details for Study Wells and Piezometers

Table 7 Groundwater Volumes Removed During Study Well Development and Aquifer Testing

Table 8 Survey and Water Elevation Data for Study Wells and Piezometers

Table 9 Pressure Transducers in Study Wells

Table 10 Groundwater Quality Parameters for Laboratory Analysis

Table 11 Summary of Study Well Permitting

Table 12 Summary of Aquifer Test Analysis Results

Table 13 Field Parameters Measured in 2009 at Four New Fork River Sites and Two Springs

Table 14 Synoptic Flows and Field Parameters along New Fork River and Tributaries – November2009

Table 15 Laboratory Results of Surface Water Samples Collected in 2009

Table 16 Groundwater Field Parameters Measured in June 2011

Table 17 Laboratory Results of Groundwater Samples Collected in June 2011 – Inorganic

Constituents

Table 18 Climate Data for Pinedale Area

Table 19 Geologic Unit Descriptions within the Pinedale Anticline Project Area

Table 20 Water Well Inventory

Table 21 Steady-State Groundwater Balance

Table 22 Seepage Rates and Estimated Total Ditch Loss in PAPA Region

Table 23 Estimated Base Flow Reporting to Streams/Rivers in PAPA Region




AMEC Environment & Infrastructure, Inc. May 2012 v

LIST OF FIGURES

Figure 1 Project Location Map

Figure 2 Surface Water Study Locations

Figure 3 Study Well and Piezometer Locations on Topo BaseFigure 4 Study Well and Piezometer Locations on Photo Base

Figure 5 Generalized Cross-Section of Hydrostratigraphic Units

Figure 6 Synoptic Flow Study of New Fork River November 5-6, 2009

Figure 7 NW-SE Hydrogeologic Cross-Section

Figure 8 Plan View of Hydrogeologic Cross-Section

Figure 9 Potentiometric Map Alluvium - September 2010

Figure 10 Potentiometric Map Wasatch Formation - September 2010

Figure 11 New Fork River Field Parameters

Figure 12 Piper Diagram for Surface Water

Figure 13 Surface Water Stiff Diagrams

Figure 14 Piper Diagram for Alluvial HSU GroundwaterFigure 15 Stiff Diagrams for Alluvial HSU Groundwater Study Wells

Figure 16 Piper Diagram for Wasatch HSU Groundwater

Figure 17 Stiff Diagrams for Wasatch HSU Groundwater Study Wells

Figure 18 Geology of Greater Green River Basin and Cross Sectional Diagram of Northern Green

River Basin

Figure 19 Generalized Geologic Cross Section

Figure 20 Generalized Location of Structural Features Pinedale Anticline

Figure 21 Conceptual Block Model of Geologic Units and Structure

Figure 22 Bedrock Geology

Figure 23 Surficial Geology

Figure 24 Average Annual Precipitation

Figure 25 Elevations above Mesa Spring

Figure 26 Water Balance Region

Figure 27 Entire Water Balance Components

Figure 28 Wasatch HSU Potentiometric Surface, Water Balance Region

Figure 29 Aquifer Recharge from Martin (1996)

Figure 30 Aquifer Recharge from Hammerlick and Arneson (1998)

Figure 31 Elevations above Antelope Spring

Figure 32 Conceptual Block Model and Water Balance




AMEC Environment & Infrastructure, Inc. May 2012 vi

LIST OF APPENDICES

Appendix A Piezometer Lithologic Logs

Appendix B Typical Well and Piezometer Completion Diagrams

Appendix C Study Well Lithologic LogsAppendix D Study Well As-Built Logs

Appendix E Technical Report of Aquifer Testing

Appendix F Water Balance Calculations

Appendix G Surface Water Hydrographs

Appendix H Three-Dimensional Geologic Model Technical Memorandum

Appendix I Groundwater Level Hydrographs for Study Wells

Appendix J Hydrogeologic Cross-Sections

Appendix K Quality Assurance and Quality Control Review

Appendix L Photographs of Surface Water Sites

Appendix M Photographs of Groundwater Study Wells and Piezometers




AMEC Environment & Infrastructure, Inc. May 2012 vii

EXECUTIVE SUMMARY

This report is the first of four technical reports pursuant to the Interim Groundwater/Aquifer Pollution

Prevention, Mitigation and Monitoring Plan (Interim Plan). The Interim Plan was designed to fulfill certain

requirements of the U.S. Department of Interior, Bureau of Land Management (BLM) Record of

Decision (ROD) (BLM 2008a) for the Final Supplemental Environmental Impact Statement (SEIS) for thePinedale Anticline Oil and Gas Exploration and Development Project, Sublette County, Wyoming (BLM 2008b).

The Pinedale Anticline Oil and Gas Exploration and Production Area (also known as the Pinedale

Anticline Project Area, or PAPA) is a 309-square-mile area being developed for natural gas resources

located in Sublette County, Wyoming. BLM manages 80 percent of the land within the PAPA.

The ROD required the companies developing natural gas resources in the PAPA complete additional

groundwater characterization. Data gaps in the understanding of the hydrogeologic system of the PAPA

are indentified in the Interim Plan. AMEC Environment & Infrastructure, Inc. (AMEC; previously AMEC

Geomatrix, Inc. or Geomatrix) was retained to complete a hydrogeologic data gaps investigation on

behalf of Ultra Resources, Inc. (Ultra), SWEPI LP (Shell), and QEP Energy (QEP) (known collectively as

Operators). Based on a detailed Plan of Study issued in May 2009 (AMEC 2009a), AMEC completedextensive field investigations between 2009 and 2011. This report describes results of the

hydrogeologic data gaps investigation, culminating in a revision to the hydrogeologic conceptual model

previously developed for the PAPA in 2008 (Geomatrix 2008).

Investigative work commenced in October 2009 and concluded in June 2011. Thirty study wells ranging

in depths from 15 to 795 feet, and 13 shallow piezometers, were installed throughout the PAPA to

characterize the groundwater system. Besides obtaining groundwater data (i.e. water elevations, water

quality data, and aquifer testing data), synoptic flow studies and surface water quality analysis in the New

Fork River were completed, two springs in the PAPA were characterized, and another area was

evaluated for groundwater seeps. Collectively, these data were used to:

Establish groundwater flow directions and gradients;

Designate hydrostratigraphic units;

Determine gain-loss characteristics of the New Fork River;

Evaluate surface water / groundwater interconnection;

Investigate the hydraulic connection between various water-bearing units;

Develop a lithostratigraphic geologic model of the PAPA region;

Generate a water balance for the groundwater system; and,

Revise the hydrogeologic conceptual model of the PAPA.

Our current understanding of the hydrogeologic system at the PAPA is based on findings from this

Hydrogeologic Data Gaps Investigation and review of existing hydrogeologic data and literature. The

hydrogeologic conceptual model was developed by synthesizing available geology, hydrology,

hydrogeology, and water balance data for the PAPA. This conceptual model, in turn, forms the basis for

the numerical flow model.




AMEC Environment & Infrastructure, Inc. May 2012 viii

Beneath a majority of the PAPA is the Tertiary-age Wasatch Formation, consisting primarily of fluvially-

deposited sandstone representing channel deposits, and shale/siltstone representing overbank deposits.

About one-third of the Wasatch Formation in the study area consists of sandstone, with an average

thickness of about 18 feet. About two-thirds of the Wasatch Formation consists of siltstone/shale with

an average thickness of 33 feet. Sandstone and siltstone/shale are interbedded, laterally discontinuous on

a scale of 1,000 feet, and vertical discontinuity can be on the order of 5 feet. Two other lithologic unitsare located in the PAPA, including alluvial deposits of sand and gravel present in stream valleys with

depths typically less than 100 feet, and a veneer of terrace gravel over the Mesa.

The major conduits for groundwater flow in the PAPA include: Wasatch Formation sandstones, alluvium

along the surface water courses, and glacial deposits draining the Wind River Mountains. Two

hydrostratigraphic units (HSU) are defined for the PAPA: Alluvial HSU in the valleys of the principal

rivers/streams; and Wasatch Formation (bedrock) HSU.

Groundwater in the PAPA generally flows west and south from the mountains and foothills toward the

Green River below the mouth of the New Fork River and into the center of the Green River Basin.

Groundwater in the shallow portions of the Wasatch HSU over much of the PAPA migrates verticallydown to the underlying deeper or regional portions of the Wasatch HSU. In some isolated places,

groundwater in sandstones of the Wasatch HSU may be perched. Groundwater in the Wasatch HSU

preferentially flows through higher permeability sandstone units. Although not observed during this

investigation, groundwater will flow preferentially along bedding planes and joints/fractures.

The lower New Fork River in the center of the PAPA is the major point of discharge for the Wasatch

and Alluvium HSU groundwater systems. South of this zone, groundwater flow paths are west-

southwest toward the center of the Green River Basin. Vertical groundwater gradients measured in

clustered wells of different depths support both the downward movement of groundwater in areas of

the Wasatch HSU, and vertically upward groundwater movement along the New Fork River below the

confluence of the East Fork River.

The Alluvial HSU is connected to the Wasatch HSU, receiving and transmitting water down valley and

into the New Fork River in the central PAPA. Vertical gradients in alluvium in the upper New Fork River

valley vary seasonally, but are upward most of the year. Artesian groundwater conditions in bedrock in

the central portion of the PAPA cause Wasatch HSU groundwater to discharge into alluvium and the

New Fork River.

Estimated groundwater velocity in alluvium is 30 times greater than velocities in Wasatch Formation

sandstones. Given average hydraulic property data based on aquifer tests in 12 study wells and

literature values for effective porosity, it may take groundwater 100 days to travel in alluvium the same

distance that it would take 10 years in a sandstone unit of the Wasatch Formation.

Groundwater enters and exits the PAPA study area in various ways. Most groundwater entering the

region is mountain front recharge that enters the area as underflow, while most groundwater leaving the

region occurs as groundwater discharge to the New Fork River and Green River. Only about 3 percent

of precipitation that falls within the PAPA recharges the groundwater system. Other recharge

components are infiltration of irrigation water and leakage from irrigation ditches. Groundwater is




AMEC Environment & Infrastructure, Inc. May 2012 ix

removed from the system by evapotranspiration from wetlands and riparian phreatophytes. Only a

relatively small amount of groundwater (less than one-half percent of total outflow and seven times less

than precipitation recharge) is consumed by pumping (stock wells, domestic wells, and industrial wells).

The revised hydrogeologic conceptual model presented in this report describes groundwater

occurrence, movement, and balance for the PAPA. It will support the companion investigation into thesources of low-level petroleum hydrocarbon compounds (LLPHC) detected in some groundwater

samples and become the hydrogeologic basis for the Project’s numerical groundwater model. Finally, this

revised hydrogeologic conceptual model will be used to support agency recommendations to the BLM

Field Manager for consideration in the Field Manager’s final decision regarding the appropriate design of

a long-term groundwater monitoring program to track spatial and temporal trends/changes in

groundwater conditions in the PAPA. This program will be defined in the Final Groundwater/Aquifer

Pollution Prevention, Mitigation, and Monitoring Plan for the PAPA, expected to be issued in late 2012.




AMEC Environment & Infrastructure, Inc. May 2012 1

1.0 INTRODUCTION

This report describes results of a hydrogeologic data gaps investigation of the Pinedale Anticline Oil and

Gas Exploration and Production Area (also known as the Pinedale Anticline Project Area, or PAPA)

located in Sublette County, Wyoming (Figure 1). AMEC Environment & Infrastructure, Inc. (AMEC;

previously AMEC Geomatrix, Inc. or Geomatrix) conducted the work between 2009 and 2011 on behalf

of Ultra Resources, Inc. (Ultra), SWEPI LP (Shell), and QEP Energy (QEP). The PAPA covers

approximately 309 square miles of federal, state and private land, with an approximate maximum width

of 14 miles and length of about 30 miles. The U.S. Department of Interior, Bureau of Land Management

(BLM) manages 80 percent of land within the PAPA.

A consortium of federal and state agencies and oil and gas companies prepared an Interim

Groundwater/Aquifer Pollution Prevention, Mitigation and Monitoring Plan (Interim Plan) (AMEC 2008)

that was designed to fulfill certain requirements of BLM’s Record of Decision (ROD) (BLM 2008a) for

the Final Supplemental Environmental Impact Statement (SEIS) for the Pinedale Anticline Oil and Gas

Exploration and Development Project, Sublette County, Wyoming (BLM 2008b). The consortium is comprised

of representatives and technical specialists with BLM, Wyoming Department of Environmental Quality’s

Water Quality Division (DEQ), and Region 8 of the U.S. Environmental Protection Agency (EPA), as well

as Ultra, Shell, and QEP. AMEC is providing technical support to the group on behalf of Ultra, Shell and

QEP. Collectively, the agencies are referred to herein as the ―BDE‖ (BLM/DEQ/EPA), and the three oil

and gas companies are cooperatively referred to as the ―Operators‖.

1.1 Background

To fulfill water resources inventory and monitoring requirements of BLM’s initial PAPA ROD (BLM

2000), the Operators contracted the Sublette County Conservation District (SCCD) to develop a

surface water and groundwater monitoring program, and to collect and manage resulting data. The

SCCD began collecting surface water data in 2000-2001 and groundwater data in the PAPA in 2004. The

SCCD maintains a water quality database and reports their findings to the BLM annually. SCCD’s

database contains data for domestic, stock, and industrial water supply wells located within 1 mile of

existing or proposed oil and gas development or exploration activities.

In 2007, the Operators retained AMEC to compile and analyze existing groundwater data in the PAPA

and develop a hydrogeologic conceptual model (Geomatrix 2008) that presents the following key

information:

Correlation between water-bearing units;

Groundwater flow;

Interaction between groundwater and surface water;

Variability/zonation of natural water quality; and

Relationships between domestic, stock, and industrial wells.





Based on the hydrogeologic analysis of existing information, Geomatrix (2008) identified several data

gaps, including the following:

Contemporaneous groundwater and surface water elevation data, using accurate positional and

reference elevation data;

Surface water flow data to determine influent/effluent characteristics of the New Fork River;

Data to define groundwater/surface water interconnection;

Hydraulic data to characterize hydrostratigraphic units (HSUs);

Water level data to generate surface water and groundwater hydrographs;

Water quality, flow, and elevation data to characterize springs; and

Data to investigate the hydraulic connection between each HSU.

BLM’s SEIS ROD (BLM 2008a) required characterization of the groundwater system and, as dictated by

the Interim Plan (AMEC 2008), AMEC developed a plan of study (POS) to fill identified hydrogeologicdata gaps and improve the understanding of the groundwater system in the PAPA. The BDE and

Operators approved the POS in May 2009 (AMEC 2009a).

The POS was developed to guide collecting and analyzing the additional field data identified above as

data gaps and describes the following eight tasks:

Task 1 – Establish contemporaneous water elevation data.

Task 2 – Determine gain-loss characteristics of New Fork River.

Task 3 – Evaluation surface water / groundwater interconnection.

Task 4 – Determine hydraulic properties for each hydrostratigraphic unit.

Task 5 – Establish data collection system needed to generate hydrographs.

Task 6 – Characterize Mesa, Antelope and Paradise Springs.

Task 7 – Investigate hydraulic connection between each hydrostratigraphic unit.

Task 8 – Revise hydrogeologic conceptual model.

Results from the first seven tasks are intended to support development of the revised hydrogeologic

conceptual model (Task 8), which is the culmination of this report. The revised conceptual model, in

turn, provides the hydrogeologic framework for a numerical groundwater model being developed for

the PAPA. Findings from this hydrogeologic data gaps investigation also support a companioninvestigation into the source(s) of low-level petroleum hydrocarbon compounds (LLPHC) detected in

PAPA groundwater (AMEC 2009b is the LLPHC Plan of Study). The collective outcome of studies

prescribed by the ROD and defined by the Interim Plan, and predictive analyses from the numerical

model, will be a Final Groundwater/Aquifer Pollution Prevention, Mitigation and Monitoring Plan for the

PAPA. A Draft Final Groundwater/Aquifer Pollution Prevention, Mitigation and Monitoring Plan will be

issued for agency consideration by December 2012.





1.2 Study Goals and Objectives

AMEC (2008; 2009a) identified gaps to be filled to further the understanding of the hydrogeologic

system present in the PAPA. The purpose of this study is to fill those data gaps. The following are study

objectives:

Develop potentiometric surface maps for identified hydrostratigraphic units (HSU) using data

from existing wells and from study wells and piezometers installed for this study.

Determine gain-loss characteristics of the New Fork River.

Describe interconnection between the New Fork River and portions of the Green River and the

groundwater system by evaluating stream stage and groundwater elevation data, and water

quality data.

Determine hydraulic properties for each HSU by conducting aquifer tests in study wells.

Generate representative groundwater hydrographs for each HSU.

Characterize flow and water quality characteristics of Mesa Spring and Antelope Spring.1

Investigate the hydraulic connection between each HSU by evaluating lithology, groundwater

chemistry, and head data.

Organize existing (e.g., SCCD groundwater data) and study-developed groundwater data into a

geodatabase.

Revise the hydrogeologic conceptual model to describe the current understanding of the

groundwater flow system with regard to recharge, groundwater flow, groundwater/surface

water interconnection, and water quality.

1.3 Report Organization

This report is organized to document investigative and monitoring work that was completed to fill the

hydrogeologic data gaps identified in AMEC (2009a) and to present the findings with respect to meeting

the objectives outlined above. Following this introductory section, the report includes seven subsequent

sections:

Section 2 – Hydrogeologic Data Gaps Investigation

Section 3 – Surface Water Flow Characteristics

Section 4 – Groundwater Occurrence and Flow

Section 5 – Water Quality

Section 6 – Surface Water – Groundwater Interconnection

Section 7 – Revised Hydrogeologic Conceptual Model

Section 8 – References Cited

1 Section 4.3 of the POS (page 33, AMEC 2009a) includes characterization of Paradise Springs. Please refer to Section 2.6,below, for a description of groundwater seeps in the vicinity of Paradise Road.





Supporting tables and figures are included in separate sections at the end of this report. Appendices A

through M contain additional supporting data and information. Several appendices contain detailed

technical memoranda or reports on several topics including aquifer testing, geologic modeling, water

balance calculations, and data validation.





2.0 HYDROGEOLOGIC DATA GAPS INVESTIGATION

This section describes results of the hydrogeologic data gaps investigation. AMEC completed the study

in general accordance methods described in the POS (AMEC 2009a). Fieldwork for groundwater and

surface water studies was initiated in October 2009 and concluded in June 2011. The following

subsections describe tasks completed as part of the data gaps investigation.

2.1 Geodatabase Development

The SCCD collected groundwater data between approximately 2001 and 2010 on behalf of the

Operators to fulfill requirements contained in BLM’s 2000 ROD (BLM 2000). Data are stored

electronically in an MS-Access database maintained by SCCD. As part of the Interim Plan (AMEC 2008),

AMEC converted the SCCD database into an ArcGIS geodatabase. Prior to the conversion, AMEC

submitted a database schema to BLM-Pinedale Field Office on March 17, 2009, which BLM approved on

April 3, 2009 via email.

The main components of the geodatabase are feature datasets, feature classes and tables. Featuredatasets contain vector spatial layers, also called feature classes, which are related by theme (Wells and

BLM Shapefiles) and must have the same spatial reference (coordinate system and projection). Tables

are not contained within feature datasets but instead exist at-large within the geodatabase. Tables are

however, related to specific feature classes by a common field. For example, the Wells feature dataset

includes a point feature class called All_Wells, which is related to all the tables within the geodatabase by

the Well ID field. Some examples of tables that are joined/related by the Well ID field are Water Well

Analytical Data, Water Well Field Data, and Water Well Water Levels.

The PAPA geodatabase includes all available PAPA groundwater data from SCCD, BLM, and Operators

through 2010. However, SCCD’s field and analytical groundwater data contained in the geodatabase

could not be verified or validated by AMEC; quality control during the conversion procedure waslimited to checking 10 percent of the converted data against data in the latest available SCCD database.

The geodatabase also includes all groundwater and surface water data collected for the various studies

defined by the Interim Plan (AMEC 2008). Key data categories in the database include:

Water well permit information, including ownership, location, depth and a summary table cross-

referencing permit numbers and SCCD well IDs.

Well locations determined using survey grade GPS equipment (AMEC 2009c) and non-survey

(e.g., recreational) grade GPS units (SCCD).

Well construction information, including type and size of casing, screened or perforatedintervals, status and total depth (refer to AMEC 2009d).

Results from the Credible/Suitable Well Determination (AMEC 2009d) including wells passing

critical selection criteria, wells suitable for aquifer test locations, wells suitable for individual data

objectives, wells suitable for water quality wells and wells suitable for all criteria.

Lithologic descriptions recorded on driller’s well logs and logs for study wells installed for this

investigation.





Static water level measurements from monitored wells.

Water quality sampling results, including field measurements and laboratory analytical results for

general chemistry parameters and petroleum hydrocarbon compounds.

Data collected from implementing the Sampling and Analysis Plan (SAP) for evaluating potential

sources of low level petroleum hydrocarbon compound (LLPHC) detections (AMEC 2009b and2010) including but not limited to: isotope data, dissolved methane, other light hydrocarbons

through C13 and BTEX, explosive gas concentration data (e.g. lower explosive limit [LEL] data

for combustible gases), field measurements of gas flow, carbon monoxide, oxygen, and hydrogen

sulfide. Results from the LLPHC SAP and their analysis will be in the forthcoming LLPHC

report. The report will include tabulated results and a discussion of results specific to the

evaluation of low level hydrocarbon sources.

With the exception of one location already under Wyoming Department of Environmental

Quality (WY-DEQ) oversight (Warbonnet 7-15; WY-DEQ Voluntary Remediation Program Site

Number 2100, 10/15/2007), initial LLPHC data indicate there are no exceedances of state

and/or federal drinking water quality standards.

Field data were managed and incorporated into the geodatabase as follows:

Field data were recorded with indelible ink on either standard AMEC field forms (well sampling

sheets, surface water measurement/discharge sheets, aquifer testing/flow sheets, etc.) or in a

project notebook. Recorded data were then inspected for anomalous values and to confirm that

procedures outlined in AMEC (2009a) were used to collect/measure each data point.

After initial verification, field data were entered into Microsoft Excel spreadsheets. A

secondary review of the data tables was then performed to ensure data entry accuracy.

Data tables were then formatted and uploaded into the geodatabase. AMEC’s database managercompleted a 100 percent QA/QC review of uploaded data relative to the spreadsheets to

confirm accuracy.

Field sheets and notes were digitally scanned and saved in project folders on AMEC’s file server

in Missoula, Montana. Paper copies of field forms and field books are stored at the AMEC office

in Missoula, Montana.

Analytical data were incorporated into the geodatabase according to the following process:

After field sample collection, chain-of-custody (COC) forms were completed with individual

sample names, collection dates and times, sampler information, and requested analytes and

analytical methods for the laboratory. Samples were shipped in sealed coolers with signed COCforms to Energy Laboratories, Inc. in Billings, Montana. Analytical results were reported to

AMEC in both complete laboratory reports and in Electronic Data Deliverables (EDDs) Each

contained receipt forms documenting sample conditions upon arrival at the laboratory.

AMEC validated analytical data using methods outlined in EPA’s National Functional Guidelines

(EPA 2010). The QA/QC process is outlined below:





COC forms and laboratory reports were checked to verify that samples were analyzed for the

requested parameters and within specified holding times (i.e., time between sample collection

and laboratory analysis). Samples that did not satisfy holding time and/or preservation

requirements were noted or flagged according to data qualifiers listed in AMEC (2009a).

Laboratory sample receipt forms were reviewed to determine if sample coolers were receivedwith an appropriate internal temperature (<6° C for most analytes). Samples that were received

above the recommended temperature were noted or flagged.

When samples are analyzed for total and dissolved metals, the dissolved metals concentrations

should be equal to or less than the total metals concentrations. Samples that exhibited

dissolved metal concentrations greater than corresponding total values, and not within the

precision of the analysis as tested by Relative Percent Difference (high concentration results) or

absolute difference (low concentration results) were noted or flagged.

Percent recoveries calculated for laboratory control samples and matrix spikes were reviewed

to verify that they were within acceptable limits described in AMEC (2009a). If recoveries were

outside limits, the results were noted or flagged.Relative percent difference (RPD) values were calculated for field and laboratory duplicate

samples and evaluated to determine if they were below the acceptable limits described in AMEC

(2009a). If RPD values were greater than the specified limit (35% for field duplicates, 20% for lab

duplicates), the results were noted or flagged.

When parameters were detected above the laboratory reporting limit (i.e. practical quantitation

limit) in blank samples, the associated natural sample results were noted or flagged. AMEC

(2009a) specifies that natural sample results less than five times the concentrations detected in

associated blanks should be qualified as estimated or as non-detect at the reported

concentrations in the blank, if the detection in the blank was greater than the detection in the

natural sample.

All data were then reviewed for transcription errors, reporting limit discrepancies, data

omissions, and suspect or anomalous values. This included evaluating and reviewing laboratory

data against previously collected or known data and contacting the laboratory regarding errors

or anomalies.

All flagged (qualified) results and validation procedures were noted and recorded on data

validation summary sheets and saved project files stored in AMEC’s Missoula, Montana office.

Where applicable, data flags were added to a separate column in EDDs and reviewed to ensure

accuracy prior to formatting for database upload.

Once verified and validated, AMEC’s database manager uploaded all formatted EDDs into thegeodatabase. A QA/QC review of 100% of the data was performed to ensure accuracy during

the electronic data upload.

Laboratory reports, EDDs, and validated EDDs were saved along with the data validation

summaries on the file server in AMEC’s Missoula, Montana office.





2.2 Surface Water Flow Study

Surface water monitoring stations included in the PAPA project are listed in Table 1 and shown on

Figure 2. River stage is being monitored by the U.S. Geological Survey (USGS) at the following five

stations on a continuous basis:

New Fork River (USGS 09205000): lower end of river approximately 3 miles upstream of confluence with Green River.

Pine Creek (USGS 09196500): upstream from Fremont Lake.

Pine Creek (USGS 09197000): downstream from Fremont Lake.

Green River (USGS 09188500): at Warren Bridge near Daniel, upstream of PAPA.

Green River (USGS 09209400): near La Barge, downstream of PAPA.

In addition, the USGS historically measured stage and/or flow at other stations on the New Fork River,

Green River, Duck Creek, Pine Creek, Pole Creek, Fall Creek, Boulder Creek, and East Fork River

(Table 1). These stations have been terminated by the USGS with respect to monitoring flow. Meanmonthly flows for the period of record for all USGS stations in the PAPA region are included in Table

2. Mean annual discharge values for four of the active USGS stations (Pine Creek above Freemont Lake;

lower New Fork River; Green River above PAPA; and Green River below PAPA) for the period 1990-

2010 are presented in Table 3.

As required by the 2000 PAPA ROD, SCCD has been measuring flows on streams and rivers in the

PAPA since 2000. Stations monitored by SCCD include: NF-4, NF-19, NF-30, NF-40, NF-50, NF-60, NF-

70, and NF-80 (Figure 2). Results of SCCD flow monitoring are included in annual monitoring reports

that are posted on the website ―www.sublettecountycd.com‖.

AMEC measured flows synoptically at several stations over a 2-day period on November 5-6, 2009 alongthe New Fork River in the PAPA, including the primary tributary streams. The purpose of this event was

to measure flow at numerous stations along the New Fork River and its major tributaries in and near

the PAPA within a short time period and when there is minimal influence from evapotranspiration and

irrigation withdrawals. This allows for a broad analysis of gaining and losing reaches of the river during

base flow conditions. Surface water stations included in the synoptic event are listed in Table 1. The

AMEC field crew began measuring flows at the uppermost station on the New Fork River (NFA-100) on

the first day, ending at station NF-50. The second day started again at NF-50 and continued downstream

to NFA-400. Flow for November 6, 2009 at the lowermost station on the New Fork River (NFA-500)

was obtained from USGS records.

2.3 Surface Water Elevations Survey

AMEC surveyed elevations of selected surface water monitoring stations in the PAPA. Surveyed

monitoring point and surface water elevations are included in (Table 4). Surface water elevations

measured in the New Fork River in April 2009 at the upstream (north) end (NF-80) and downstream

(southwest) end (NF-19) of the PAPA were 7133 and 6814 feet above mean sea level (amsl),

respectively. Therefore, the river drops 319 feet over a river length of approximately 30 miles (gradient

= 0.002 ft/ft).





Table 4 lists additional surface water monitoring sites surveyed for this project at locations where

study wells and piezometers are in close proximity to streams and rivers. Surface water elevations

measured at these locations can be compared to nearby measured groundwater levels to help evaluate

flow between surface water and groundwater.

2.4 River Stage

River/stream stage is currently measured by the USGS on a continuous basis at the five stations listed in

Section 2.1: one station on lower New Fork River; two stations on Pine Creek; and two stations on

the Green River. The stage measurements are converted to flow by the USGS based on rating curves

developed for each station. The period of record for these stations, as well as other surface water

stations in and near the PAPA that were historically monitored by the USGS, are included in Table 1.

AMEC installed pressure transducers at two New Fork River sites in late July 2009 and recorded river

stage data continuously until early November 2009. The two sites are NF-50 (just downstream of East

Fork River confluence) and NF-19 (1.5 miles upstream of NFA-500 near confluence of Green River)

(Figure 2). Hydrographs were constructed using pressure data from these transducers.

2.5 Surface Water Quality Characterization

Quality of surface water in the PAPA has been characterized by analysis of samples collected at selected

surface water stations in the PAPA. For the data gaps analysis, surface water quality data are used to

evaluate surface water – groundwater interconnection. Surface water samples were collected on

November 4, 2009 from four stations on the New Fork River (NFA-100, NFA-300, NFA-400, and NFA-

500) and submitted for laboratory analysis (Table 1 and Figure 2). Field parameters including flow,

temperature, pH, electrical conductivity (EC), dissolved oxygen (DO), and oxidation-reduction potential

(ORP) were measured in these four samples. The samples were also analyzed by a laboratory for pH,

EC, total dissolved solids (TDS), total suspended solids (TSS), alkalinity, chloride, sulfate, fluoride,calcium, magnesium, potassium, sodium, and sodium adsorption ratio (SAR) (Table 5).

The SCCD has been collecting surface water samples from NF-stations (Table 1 and Figure 2) in the

PAPA since 2004. The SCCD submits the samples for laboratory analysis of the following parameters:

TDS, TSS, alkalinity, bicarbonate, carbonate, hardness, calcium, sodium, magnesium, chloride, sulfate,

nitrate+nitrite, phosphorus, benzene/toluene/ethylbenzene/xylenes (BTEX), gasoline range organics

(GRO), and diesel range organics (DRO). Results of SCCD water quality monitoring are included in its

annual monitoring reports that are posted on the website ―www.sublettecountycd.com‖.

2.6 Characterization of Springs

Mesa and Antelope springs (Figure 2) were monitored by AMEC for flow and quality characteristics in

July and November 2009. Both springs are specifically mapped and labeled on the 1:24,000 USGS

topographic maps covering the PAPA study area. Water samples from the springs were analyzed in the

field for temperature, pH, EC, DO, and ORP; and submitted for laboratory analysis of pH, EC, TDS, TSS,

alkalinity, chloride, sulfate, fluoride, calcium, magnesium, potassium, sodium, and SAR.





Paradise Road in the center of the PAPA is constructed on a topographic bench approximately 10 to 20

feet above the New Fork River floodplain (Figure 2). An irrigation ditch (Paradise Ditch) follows a

topographic contour and is located north of and roughly parallel to Paradise Road. Water is sourced

from the New Fork River. Based on review of 2006 aerial imagery on file with the Sublette County

Planning and Zoning Department, the ditch supplies water for flood- and sprinkler-irrigated agriculture

in an area proximal to the ditch, generally between Paradise Road and the ditch. In accessing the NewFork River floodplain from Paradise Road, apparent groundwater seeps are observable along the bench

slope. A color distinction representing a change in vegetation on the bench slope is also noticeable on

Sublette County aerial imagery; however, unique springs are not labeled on USGS topographic maps of

this area. It is possible that water in excess of agricultural crop demand infiltrates the subsurface and

discharges as seeps along the topographic bench below Paradise Road. The topographic bench and

floodplain are largely private land in the area where groundwater seeps are suspected, and AMEC did

not complete a detailed survey during this investigation for the presence of individual springs issuing

water that could be characterized for flow and quality.

2.7 Piezometer Installation

Thirteen piezometers were installed at five locations along the New Fork and Green rivers in or near

the PAPA (Figures 3 and 4). An AMEC field geologist provided field oversight for piezometer

installation May 11-14, 2010.

The piezometer borings were completed with a track-mounted direct-push Geoprobe® rig operated by

Enviroprobe, Inc., which utilized a 4-ft-long macro-core sampler and 3-inch-diameter acetate liners to

allow for lithologic observation and soil collection. Boring and piezometer completion logs are included

in Appendix A. Each piezometer was completed in unconsolidated alluvial deposits of clay, silt, sand,

and/or gravel. Average depth of the piezometers is 15 feet below ground surface (bgs) within a range of

10 to 20 feet bgs (Table 6).

Each piezometer was completed with 2-inch diameter Schedule-40 PVC casing and factory-slotted

0.020-inch-opening screen. The exception was piezometer X-1-P1, which has 1-inch diameter Schedule

40 PVC casing and screen. Average screen length is 10 feet, which was placed at the bottom of the

piezometer in the saturated zone (Table 6). A diagram of typical piezometer completion is included in

Appendix B.

Following installation, all piezometers were developed by hand-bailing. A 3-foot-long, 1.5-inch-diameter

PVC bailer was used to surge the well and remove water. Development water was spread-out on the

nearby ground surface.

2.8 Study Well Installation

A total of 30 study wells were completed in the PAPA in 2009 and 2010 (Figures 3 and 4). White

Mountain Drilling of Pinedale, Wyoming began well installation in October 2009. Thomas Drilling of

Afton, Wyoming installed wells completed in 2010. Air-rotary, mud-rotary, and air-hammer drilling

methods were used to complete the study wells, with potable water, foam, and/or mud used during the

drilling process to facilitate removal of cuttings and maintain an open hole for casing installation. Waste





drill water and cuttings were disposed off-site for selected sites where required by BLM after laboratory

analysis of representative samples.

Study well locations shown on Figures 3 and 4 targeted the following general areas in the PAPA: along

New Fork River valley bottom; selected drill pad sites along the Pinedale Anticline; Sand Springs Draw

area; and other areas scattered within the PAPA. Twelve study wells were installed at five drill padsalong the north-south-trending Anticline (Ultra Sherlock Federal 15-8; QEP Mesa 15-16; Ultra

Warbonnet 7-15D; Shell Antelope 11-10D; and Shell Jensen 11-11). One of the drill pads is located on

state-managed land; one drill pad is on private land; and the remaining three drill pads are on BLM-

managed land. Of the remaining 18 study wells, four are on private land; 10 are on BLM-managed land;

and the remaining four study wells are located along state and county road right-of-ways.

A key objective of the hydrogeologic data gaps study was to determine whether or not there was both a

shallow and regional Wasatch hydrostratigraphic unit. As discussed further in Section 7.5.1, there was

no hydrogeologic evidence found to support the separation of the Wasatch formation into two separate

HSUs. Consequently for the remainder of this report, the Wasatch Formation is considered one

hydrostratigraphic unit (HSU), and is comprised of bedrock topographically higher and lower than theGreen River and New Fork River valleys within the PAPA (Figure 5). The Wasatch HSU is saturated

below the water table within the heterogeneous lithologic units of siltstone, sandstone, and shale. Refer

to Section 7.5.1 for a detailed description of the Wasatch HSU. Wells completed in bedrock near the

New Fork River are commonly artesian. The Wasatch Formation is underlain by the Fort Union

Formation. No industrial water supply wells within the PAPA penetrate the Fort Union Formation; the

deepest industrial water supply wells are separated from the Fort Union Formation by about 3,000

vertical feet based on geologic information in Scott and Sutherland (2009).

Study well identification (ID) numbers starting with an ―X‖ are for locations along river or stream valley

bottoms; the remaining well ID numbers start with a ―T‖. The following is a list of the 30 study wells

grouped by associated HSU:

Mesa Gravel (2 wells): T-2a-G & T-2b-G.

Alluvium HSU (6 wells): T-8-A; X-1-A; X-2-A; X-3-A; X-4-A; & X-5-A.

Wasatch HSU (22 wells): T-1-SW; T-1-RW; T-2-SW; T-2-RW; T-3-SW; T-3-RW; T-4-SW; T-4-

RW-a; T-4-RW-b; T-5-RW; T-6-SW; T-6-RW; T-7-SW; T-7-RW; T-8-SW; T-9-RW; X-1-SW;

X-2-SW; X-3-SW; X-4-SW; X-4-RW; & X-5-SW.

For the four major study well completion zones, study well casing depths are in the following ranges:

Mesa Gravel (2 wells): 15 to 18 feet bgs.

Alluvium (6 wells): 15 to 38 feet bgs.

Wasatch (22 wells): 150 to 780 feet bgs.





Most PAPA industrial, domestic and stock water supply wells are completed in the Wasatch Formation.

A few domestic and/or stock wells are completed in or partially open to alluvium associated with the

New Fork River. Based on available information, maximum depths for domestic, stock, and industrial

wells in the PAPA are approximately 320 feet, 600 feet, and 1,210 feet, respectively. Average depths of

the three well types are approximately 116 feet, 195 feet, and 644 feet, respectively. Based on the fact

that the two study wells installed in the Mesa Gravel (T-2a-G and T-2b-G) have been dry, this lithologicunit was eliminated from further consideration as a HSU for the PAPA study.

Nested study well pairs are located at the following sites: T-1 (both in Wasatch HSU); T-2 (both in

Wasatch HSU); T-3 (both in Wasatch HSU); T-4 (both in Wasatch HSU); T-6 (both in Wasatch HSU);

T-7 (both in Wasatch HSU); T-8 (Alluvium and Wasatch HSU); X-1, X-2, X-4, and X-5 (Alluvium and

Wasatch HSU).

A summary of study well completion information is presented in Table 6, and typical well completion

diagrams are included in Appendix B. Study well lithologic logs and as-built logs are in Appendix C

and Appendix D, respectively. Study wells were drilled using air rotary, mud rotary, and air hammer

drill rigs. Casing for wells that extended to total depth consisted of either 4-inch diameter PVC (gravel,alluvial, and most SW-Wasatch wells) or 5-inch diameter steel (RW-Wasatch wells). An exception was

well T-7-RW, which was completed with 6-inch diameter steel casing. Four study wells are artesian (T-

8-SW; X-4-SW; X-4-RW; and X-5-SW); three of these wells are located along the New Fork River, and

one well is adjacent to the East Fork River (Figures 3 and 4). Three of the wells were flowing (X-4-SW,

X-4-RW, and X-5-SW) and, therefore, were fitted with shut-in valves at the surface to prevent flowing

conditions. Study wells completed at the Warbonnet 7-15D drill pad (T-3-SW and T-3-RW) and

Antelope 11-10D drill pad (T-4-RW-a and T-4-RW-b) had measureable lower explosive limit (LEL)

vapors during drilling and sampling activities. The nature and occurrence of these vapors in study wells

will be discussed in the forthcoming LLPHC report.

Most of the SW-Wasatch, gravel, and alluvial study wells were installed using 4-inch diameter Schedule-

80 PVC casing (threaded-and-coupled) and 0.020-inch-opening factory-slotted PVC screen. The deeper

wells that were installed with 5-inch diameter black steel casing (welded) included stainless-steel factory

wire-wrap screen (0.020-inch opening) sections.

Following well installation, all study wells were developed using either the surge-and-bail method, air-lift

method, and/or pumping method. After the first round of well development was completed in 2010, a

second round of development occurred in June 2011 for those wells where insufficient development

occurred in 2010. Table 7 is a summary of groundwater volumes removed during study well

development and aquifer testing that occurred in 2010 and 2011.

For the surge-and-bail method, a decontaminated 4-ft-long, 3-inch-diameter stainless steel bailer on a

Teflon-coated steel cable was used to surge the well and remove water. For the air-lift method, the drill

rig compressor was used to surge and blow water out of the well. The pumping method involved placing

a submersible pump in the well just above the screen interval and removing water while creating

drawdown. In most cases, the development water was periodically monitored for temperature, pH, EC,

DO, ORP, and turbidity. The bailed and pumped water was first placed into an open-top container, and





then sprinkled on the nearby ground. The air-lifted water was allowed to flow away from the well on

the ground surface.

For the 23 wells developed again in June 2011, a submersible pump was set in each well with water

pumped for a period while a portion of the discharge was directed back down the well to rinse the

inside of the casing. Approximately five casing volumes of water were pumped and removed from eachwell in this manner. This well development procedure was conducted prior to collection of water

samples in June 2011 for laboratory analysis.

2.9 Well Survey and Depth to Water Measurements

2.9.1 Survey of Well and Piezometer Locations

WLC surveyed the location and elevation of study wells and piezometers between September 21 and

25, 2010 using the North American Vertical Datum of 1988 (NAVD88). Well locations and measuring

point elevations were surveyed at 52 locations (30 study wells, 13 piezometers, and nine river

locations). All survey information (location coordinates; ground surface elevation; and top of casing

elevation) for the study wells and piezometers is presented in Table 8. Depth to water was measured

in each study well and piezometer in September 2010 and June 2011; these measurements and

corresponding groundwater elevations are included in Table 8.

2.9.2 Transducer Instrumentation

In November 2010, AMEC installed 21 Solinst Leveloggers® (water pressure transducers) in study wells

to measure long-term groundwater elevations in the PAPA. Two Leveloggers were earlier installed in

July 2010 at site X-1. Of the 21 Leveloggers installed in November 2010, three did not record pressure

data due to malfunctions of the instruments (T-3-SW; T-4-RW; and T-7-RW); therefore, only manual

water level measurements are reported for these wells. Leveloggers were attached to J-plugs and PVC

well caps using eye-bolts and suspended below the potentiometric water surface using a non-stretchKevlar® cord. Deployment depths for Leveloggers were determined based on water level data measured

in September 2010. Table 9 summarizes transducer deployment in these 23 study wells.

Barometric pressure sensors (Barologgers®) were installed in wells X-1-A (northern region) and T-3-

SW (southern region) and were used to compensate for barometric pressure changes measured in the

submerged Leveloggers throughout the PAPA. Prior to deployment, each Levelogger and Barologger

was programmed to log data every 6 hours to evaluate daily fluctuations in groundwater elevations and

barometric pressure throughout the PAPA.

The static water level in each well was measured manually when the transducers were deployed (Table

9) and again when they were downloaded to allow electronic pressure data to be converted togroundwater elevations. Some wells also had water levels measured between deployment and data

downloading. Water level data were downloaded from all Leveloggers and Barologgers in June 2011.

Groundwater elevations for each well are determined by subtracting the measured depth to

groundwater from the surveyed elevation of the measuring point.





2.10 Groundwater Quality Sampling

Groundwater samples were collected from all study wells, except for dry wells T-2-SW, T-2a-G, and T-

2b-G, and submitted for laboratory analysis in June 2011. Piezometers were not sampled. Groundwater

samples were collected after completion of well development procedures as described in Section 2.8.

HydraSleeve™ no-purge (passive), single-use, grab sampling devices were used to collect a representative

groundwater samples from the study wells in June 2011. This sampling device allows the collection of a

whole water sample from a user-defined interval (i.e., mid-point of screen interval) with no drawdown and

minimum agitation. The PAPA study wells were completed with relatively short screen intervals (10 to 45

feet thick) in alluvium or Wasatch Formation sandstone units. The sampling device contains a self-sealing

check valve, which excludes water from the part of the water column not targeted for sample collection.

Once the sampling device is full, a one-way valve collapses, preventing the mixing of fluids during recovery

of the HydraSleeve™ deployed in the wells.

The assembly, deployment, retrieval, and discharge of the HydraSleeves™ followed procedures described in

the ―Sampling and Analysis Plan for Evaluating Potential Sources of Low-Level Petroleum HydrocarbonCompound Detections‖ (AMEC 2010). For each study well, the HydraSleeve™, or series of

HydraSleeves™ due to sampling volume requirements, were placed into the well to mid-depth of the

screen interval (see Table 6 for well screen intervals). Procedures used for decontamination, sample

handling and shipping, and quality assurance/quality control are described in the Sampling and Analysis Plan

(AMEC 2010).

Table 10 lists parameters analyzed by the laboratory (Energy Laboratories; Billings, Montana) for each

groundwater sample collected from study wells in June 2011. These parameters are in the following

general groups:

Inorganic constituents;

Purgeable hydrocarbons;

Extractable hydrocarbons; and

Benzene, toluene, ethylbenzene and xylenes (BTEX).

The purgeable and extractable hydrocarbon data and BTEX data are not presented in this report, but

are included in the forthcoming LLPHC report, which describes results of sampling and analyzing the

study wells and selected industrial water supply wells for a wide range of compounds. This

hydrogeologic data gaps report focuses on results of inorganic analyses for groundwater and surface

water samples, along with characterization of the physical hydrogeologic environment.

2.11 Aquifer Testing

In December 2010 and June 2011, AMEC performed aquifer tests at 12 study wells in the PAPA. The

purpose of this testing is to characterize the hydraulic properties of alluvium along the New Fork River

and sandstone units in the Wasatch Formation. The first set of aquifer tests was completed at four study

wells in December 2010, and the second set of tests was completed on eight wells between June 5 and

15, 2011.





Table 6 is a summary of well construction details that includes the 12 wells subject to aquifer testing:

T-1-SW, T-1-RW, T-3-RW, T-4-SW, T-4-RW-b, T-5-RW, T-8-SW, T-9-RW, X-2-A, X-2-SW, X-4-SW,

and X-4-RW. All of these wells, except for alluvial well X-2-A, are completed to varying depths in the

Wasatch HSU. Appendix E is a Technical Report of Aquifer Testing prepared by AMEC that provides

details of the aquifer testing setup and results.

Pressure transducers were installed in the pumping well and any nearby observations wells, if present.

Datalogger for the transducers were programmed to collect measurements every second for the first 17

minutes of the pumping and recovery period, followed by measurements every 10 seconds for 3 hours,

and then at 1-minute intervals for the remainder of the test.

Constant-discharge pumping tests were performed at all tested study wells, except for a constant-

discharge shut-in test at X-4-RW due to artesian flowing conditions. Tests were run for periods ranging

from 1.2 to 18 hours, at pumping rates ranging from 6.1 to 53 gallons per minute (gal/min). To

determine the appropriate pumping rate, a short-duration yield test was performed in each well prior to

the constant discharge test. Flow rates were measured and recorded periodically during each test usinga flow-totalizing meter.

2.12 Groundwater Consumption

Groundwater in the PAPA region is pumped for agricultural, domestic, and industrial uses. According to

the Wyoming State Engineer’s Office (SEO 2010) groundwater well database, there are approximately

nine irrigation wells, 145 stock wells, 1,076 domestic/other wells, and 366 industrial water supply wells

within the water balance region, which includes the town of Pinedale (Appendix F).

As described in Appendix F, the well categories described above have the following groundwater

consumption rates within the PAPA:

Irrigation wells = 595 acre-feet per year (ac-ft/yr)

Stock wells = 88 ac-ft/yr

Domestic/other wells = 22 ac-ft/yr (based on consumption rate of 10% for water withdrawn;

see Section 7.8.1.6 and Appendix F)

Industrial wells = 590 ac-ft/yr (based on average of 20% industrial wells actively in use; see

Section 7.8.1.6 and Appendix F)

Total estimated consumptive groundwater volume pumped annually from irrigation, stock,

domestic/other, and industrial water supply wells in the PAPA water balance region is approximately

1,300 ac-ft/yr.





2.13 Permit Requirements for Project

Several permits were required prior to completing study wells, especially those located on government-

administered land. Table 11 includes a summary of well permitting requirements. Wells located on

private land also required landowner permission. Specific permits required for some study wells include:

Right-of-way permit from BLM for study well sites located on BLM-managed land (not including

existing gas drill pads).

Sundry permit from BLM for study well sites located on existing gas drill pads that are on BLM-

managed land.

Wildlife exception permit from BLM for study wells proposed on BLM-managed land where

certain wildlife restrictions were imposed.

Wyoming Oil and Gas Conservation Commission (WOGCC) permit for study wells located on

existing gas drill pads.

Wyoming State Engineer’s Office (SEO) permit for all study wells with casing larger than 4inches in diameter.

Wyoming State Lands permit for study wells located on state-managed land.

Wyoming Department of Environmental Quality (DEQ) permit-by-rule applies to study wells

used to characterize subsurface conditions at sites where pollution is not known to exist.





3.0 SURFACE WATER FLOW CHARACTERISTICS

This section describes results of the surface water flow assessment for streams and rivers in the PAPA.

Surface water monitoring stations are shown on Figure 2.

3.1 Surface Water Hydrographs

As described in Section 2.2, river stage is currently measured on a continuous basis by the USGS at

five stations: one station on lower New Fork River; two stations on Pine Creek; and two stations on the

Green River. A hydrograph for flow at the New Fork River station (USGS 09205000; NFA-500), which

is based on mean daily measurements for the period of record (1954-2010), is included in Appendix G.

Hydrographs of flow are also included in Appendix G for several historic USGS gaging stations at

Green River (USGS 09191000), East Fork River (USGS 09204500), Boulder Creek (USGS 09202000),

Pole Creek (USGS 09198500), and Pine Creek (USGS 09198000). All of these gaging stations are shown

on Figure 2.

The hydrograph for the lower New Fork River station (NFA-500, 09205000) shows that flow ratesincrease rapidly beginning in May from approximately 200 to 400 cubic feet per second (ft 3/sec) to an

average peak flow of over 3,000 ft3/sec. The baseflow period typically extends from about August

through April, with the peak flow period occurring in May, June, and July. The hydrograph Green River

station 0919100, located approximately 15 miles upstream of confluence with New Fork River, shows a

similar pattern; however, the peak flow period is slightly longer than the New Fork River. Baseflow at

the Green River station is approximately 200 to 300 ft 3/sec, with an average peak flow of about 2,300

ft3/sec.

The other stream flow hydrographs in Appendix G for tributaries to the New Fork River (East Fork

River, Boulder Creek, Pole Creek, and Pine Creek) all have similar flow patterns with a peak flow period

in May and June (600 to 1,300 ft3/sec), and a relatively rapid decline to baseflows that extend from aboutAugust through April. The following are average baseflows for the tributary streams:

East Fork River = 40-50 ft3/sec;

Boulder Creek = 15-20 ft3/sec;

Pole Creek = 15-20 ft3/sec; and

Pine Creek = 25-30 ft3/sec.

Hydrographs constructed using pressure data from the two transducers installed by AMEC at New Fork

River stations NF-50 (downstream of East Fork River confluence) and NF-19 (1.5 miles upstream of

NFA-500 near confluence of Green River; Figure 2) are included in Appendix G. These transducers

were operated from July to November 2009. The NF-50 hydrograph shows that the river declined

approximately 1.2 feet from late July to early September, after which the water levels remained

relatively steady until early November. At the NF-19 station, the river stage declined approximately 2

feet from late July to early September. Both hydrographs also show diurnal fluctuations in stage of about

0.1 foot.





3.2 Synoptic Flow Results

Figure 6 shows results of the November 2009 synoptic flow event, extending along the New Fork

River from station NFA-100 near the town of Pinedale to station NFA-500 just upstream of the river’s

confluence with the Green River. The measurement stations are broadly located throughout the PAPA

to provide a general indication of gains and losses along the extent of the New Fork River during the

baseflow period. Flow measured at the upstream station (NFA-100) and downstream station (NFA-500)

was approximately 22 and 354 ft3/sec, respectively in early November 2009. Note that the flow

measurements reported in this section are considered ±5 percent based on cobbles in most channel

bottoms.

As shown on Figure 6, flow along the New Fork River, after subtracting measured flows from the

primary tributary streams, gains from groundwater discharge throughout the PAPA study area, with the

exception of reach NF-30 to NFA-400 near the lower part of the river. The flow measurement at NF-

30, however, has some uncertainty due to site conditions at the time of measurement (i.e., high winds

during measurement affected the measuring tape and consequently may have affected stream cross-

sectional area determinations). Therefore, the calculated flow loss of 32 ft3

/sec between stations NF-30to NFA-400 may not represent actual conditions (i.e. flow of 355.8 ft3/sec at NF-30 may be too high and,

therefore, flow loss could be less or nonexistent in this reach of the river).

The following is a summary of calculated flow gains/losses between measured stations going downstream

on the New Fork River after subtracting the tributary flows (Figure 6):

NFA-100 to NF-04 = +2.3 ft3/sec (subtracted Duck Creek flow)

NF-04 to NF-70 = +53 ft3/sec (subtracted Pine Creek and Pole Creek flows)

NF-70 to NFA-300 = <1 ft3/sec gain

NFA-300 to NF-60 = +19 ft3/sec (subtracted Boulder Creek flow)

NF-60 to NF-50 = <1 ft3/sec gain (subtracted East Fork River flow)

NF-50 to NF-40 = +16 ft3/sec

NF-40 to NF-30 = +58 ft3/sec

NF-30 to NFA-400 = -32 ft3/sec (may not accurately represent flow conditions due to

uncertainty in measurement at NF-30)

NFA-400 to NFA-500 = +30 ft3/sec (flow at NFA-500 obtained from USGS data)

Total gain in baseflow along the New Fork River measured in early November 2009 was approximately147 ft3/sec, which can be attributed to discharge of groundwater into the river channel. No water was

likely being diverted from the river for irrigation purposes in November. Also refer to Section 7.7 and

Appendix F for additional water balance information about groundwater discharge to rivers and

streams in the PAPA.





4.0 GROUNDWATER OCCURRENCE AND FLOW

This section describes the occurrence and flow characteristics of groundwater in the PAPA region. A

discussion of hydrostratigraphic units (HSUs) in the PAPA includes depth to groundwater and

characterization of hydraulic properties. Hydrogeologic cross-sections and potentiometric maps are

used to show groundwater levels and direction of flow. Groundwater recharge and discharge arediscussed at the end of this section.

Section 7 (Hydrogeologic Conceptual Model) includes further discussion of groundwater flow and

water balance. In addition, a three-dimensional numerical groundwater flow model is being completed

by AMEC as part of the PAPA project. A forthcoming report documenting the modeling effort will

provide additional information regarding groundwater flow in the PAPA.

4.1 Depth to Water

Table 8 lists depth to water measured in each study well and piezometer in September 2010 and June

2011 and groundwater elevations calculated from these measurements. As described in Section 2.9.2,AMEC installed pressure transducers (Leveloggers) in two study wells in July 2010 and in 21 additional

study wells in November 2010 (Table 9). Pressure measurements from the dataloggers for each

transducer were downloaded in June 2011. Of the 23 Leveloggers installed, three did not record

pressure data (T-3-SW; T-4-RW-b; and T-7-RW); therefore, only manual water level measurements are

reported for these wells. Groundwater hydrographs for study wells were prepared using groundwater

elevation data (from transducers and manual measurements) and are included in Appendix I. A

discussion of interpretation of hydrographs for the Alluvium HSU and Wasatch HSU follows.

As discussed below, daily or diurnal fluctuations are evident in hydrographs for some study wells located

near the New Fork River. Some wells completed in alluvium and shallow bedrock show water levels that

respond coincident with changes in stream or river flow, suggesting there is hydraulic communicationbetween these lithologic units and surface water.

Alluvial HSU Wells

Alluvial groundwater is influenced by surface water and by discharge of bedrock groundwater into

alluvium. Groundwater levels in alluvial study wells generally fluctuate about 2 feet during the period of

record, with the exception of X-3-A which fluctuated approximately 9 feet. Data recorded at X-1-A

from July 2010 to June 2011 indicate significant short-term fluctuation events with lowest levels

occurring in August and September when stream flows are low and evapotranspiration is high. The

groundwater level in X-1-A increased approximately 1 foot during March and April 2011.

Groundwater in well X-3-A initially declined approximately 6 feet from November 2010 to April 2011,

followed by an increase of about 10 feet through June 2011. These water level changes are likely

associated with seasonal water in the nearby Paradise Ditch and possibly from surface water in a nearby

gravel quarry.

Water levels measured in wells X-4-A and X-5-A, located along the lower New Fork River, generally

fluctuated about 2 feet during the period of record (November 2010 to June 2011), with water levels in





both wells indicating similar minor rising trends from November 2010 to April 2011. Water levels in

these two wells then declined approximately 1 foot in April-May 2011, with a final increase of 1 to 2 feet

in late-May/early-June 2011. Groundwater levels in well T-8-A, which is located near the East Fork River,

fluctuated about 1 foot, but there was no discernable trend nor correlation to changes in river stage.

Wasatch HSU Wells

Water levels remained relatively steady during the period of record (November 2010 to June 2011) for

Wasatch HSU wells T-1-SW, T-4-SW, T-4-RW-b, T-5-RW, T-6-RW, T-7-SW, T-7-RW, T-8-SW, T-8-

RW, and T-9-RW. Groundwater levels measured in well T-1-RW exhibit a gradual increasing trend

during the period of record of about 10 feet. This well is located at the northern end of the PAPA study

area on the Sherlock Federal 15-8 gas drill pad. The observed water level increase of 10 feet could be

related to recovery from previous pumping of one or more nearby industrial water supply wells,

although pumping schedules for surrounding wells are not available.

The hydrograph for well T-2-RW exhibits highly variable water levels for the period of record within a

range of about 25 feet. This fluctuation is assumed to be the result of pumping from a nearby industrialwater supply well, which is perforated within the same HSU. The hydrograph for well T-3-RW, which

includes two periods when water levels were not recorded, exhibits some fluctuations over a general

declining trend for the period of record.

An anomalous water level trend occurred in T-3-SW where field-measured groundwater levels declined

more than 30 feet during the period November 2010 to June 2011. Well T-3-SW is located on the

Warbonnet 7-15D gas drill pad in the southern region of the PAPA. This observation in well T-3-SW

may be related to an error in either water level measurement or data transcription. Data recording

pressure transducers are deployed in wells T-3-SW and T-3-RW, and further insight on long-term

trends in water levels will be available in the future.

Four of the ―X‖-SW wells are also completed in the Wasatch HSU. Groundwater in well X-1-SW had a

fluctuation of approximately 4 feet, with a decline occurring in July and August 2010. Groundwater in X-

3-SW shows a gradual decline of about 1 foot over the period of record. The water level in X-4-SW

remained steady until a declining trend beginning in April 2011, with an increasing spike in May. The X-5-

SW water level remained relatively steady during the period of record.

4.2 Hydraulic Properties

As described in Section 2.11, AMEC performed aquifer tests in 12 study wells in the PAPA in

December 2010 and June 2011. Constant-discharge pumping tests were performed on all tested study

wells, except for a constant-discharge shut-in test at X-4-RW due to artesian flowing conditions. Testsextended for periods ranging from 1.2 to 18 hours, at pumping rates ranging from 6.1 to 53 gal/min.

Pressure transducers were installed in the pumping well and any nearby observations wells, if present.

Appendix E provides details of the aquifer testing setup and results.

Semi-log plots of time-drawdown data along with pumping rates from each test are presented in Appendix

E. Aquifer property estimates derived from the analysis of both drawdown and recovery data are

summarized in Table 12. Aquifer property estimates derived from the analysis of recovery data in pumping





wells are more representative of aquifer conditions than the results of drawdown analyses because

drawdown data can be influenced by well efficiency and the degree of hydraulic communication between the

well casing and the surrounding HSU.

Results of aquifer testing show that hydraulic conductivity of the various lithologic units screened is

highly variable. Hydraulic conductivity (K) and transmissivity (T) determined from recovery data for the12 aquifer tests shows the following results (Table 12):

Alluvium HSU (1 well tested): K = 446 feet per day (ft/day); T = 11,144 ft2/day

Wasatch HSU (11 wells tested): K = 0.02 – 9.47 ft/day; T = 1.6 – 264 ft2/day

Four of the tested study well locations (T-1-SW/T-1-RW; T-3-SW/T-3-RW; T-4-SW/T-4-RW-b; X-4-

SW/X-4-RW) have paired wells completed to different depths in Wasatch bedrock. Two other well

pairs (T-8-A/T-8-SW and X-2-A/X-2-SW) have paired study wells where one well is completed in

alluvium and the other in underlying Wasatch bedrock.

Drawdown responses were not observed in any of the observation study wells during the six pumping

tests described above for the well pairs. The lack of drawdown response in the observation wells during

the pumping tests, with one exception noted below, indicates limited hydraulic communication between

the individual lithologic units in the tested locations.

The one observation well that exhibited a drawdown response during a pumping test was industrial

supply well AN11-10D during the test of well T-4-RW-b. This observation well exhibited 19.75 feet of

drawdown during the pumping test. Well AN11-10D (located approximately 200 feet north-northwest

of T-4-RW-b) is perforated from 470 to 660 feet bgs, across several water-bearing sandstone units in

the Wasatch HSU. Study well T-4-RW-b is screened at a depth (637 to 656 feet bgs) that corresponds

to the lower end of the perforated interval in AN11-10D and is likely screened in part of a sandstoneunit common to both wells.

4.3 Hydrogeologic Cross-Sections

Figure 7 is a northwest to southeast hydrogeologic cross-section across the entire PAPA and Figure 8

is a map showing the location of the cross-section. Additional hydrogeologic cross-sections in other

specific areas of the PAPA are included in Appendix J. The general lithologic units of gravel (primarily

located on the Mesa), alluvium (primarily located along streams and rivers), shale/siltstone, and

sandstone are based on drill logs for each well shown on the cross-sections.

The northwest-southeast cross-section in Figure 7 shows study wells and water supply wellsintercepted by the section. The potentiometric surface for the Wasatch HSU slopes toward the New

Fork River. For three of the study well pairs completed in bedrock shown on Figure 7 (T-1-SW/T-1-

RW; T-3-SW/T-3-RW; and T-4-SW/T-4-RW-b), the vertical groundwater gradient is downward. This

downward vertical gradient is indicative of a groundwater recharge area.

Hydrogeologic cross-sections in Appendix J show alluvium along the New Fork River with the

following approximate thicknesses: 20 feet at X-1 site; 30 feet at X-2 site; 50 feet at X-3 site; 40 feet at





X-4 site; and 50 feet at X-5 site. The sandstone and shale/siltstone lithologic units that comprise the

Wasatch HSU form numerous layers and lenses throughout the intervals intercepted by study wells and

water supply wells. Well screens for the Wasatch HSU study wells are generally positioned to intercept

one sandstone interval within a screened thickness of 20 to 45 feet. These discrete screen intervals are

intended to characterize the sandstone units which are the primary water-producing units in the

Wasatch Formation.

4.4 Groundwater Flow

This section discusses horizontal and vertical groundwater flow in the PAPA. Figures 3 and 4 show

locations of study wells and piezometers completed for the PAPA project. Surveyed well elevations and

measured groundwater elevations are included in Table 8.

4.4.1 Horizontal Flow

Groundwater in the PAPA study area generally flows west and south from the Wind River Mountains

and foothills toward the New Fork River (locally) and the Green River (regionally) within the GreenRiver Basin. Some of this water moves along deep groundwater flow pathways in the Wasatch and Fort

Union Formations; whereas, other groundwater moves in shallower flow paths and discharges to springs

and rivers (e.g., New Fork River and Green River). Groundwater generally moves horizontally through

the various lithologic units (i.e., sandstone, siltstone, and shale) within the Wasatch HSU, with greater

flow occurring in the higher permeability sandstone units. In places, groundwater exists in perched

zones above layers and lenses of shale/siltstone in the Wasatch HSU.

Figure 9 is a potentiometric surface map for alluvium based on groundwater elevation data obtained in

September 2010. Shallow groundwater flows southwest in alluvium along streams and channels that

extend from the mountains to the New Fork River. Then groundwater flows south-southwest in

alluvium along the New Fork River and then the Green River below their confluence. Along the westside of the PAPA study area, shallow groundwater flows south in alluvium along the Green River to its

confluence with the New Fork River. The average hydraulic gradient of groundwater in alluvium along

the New Fork River in the PAPA is approximately 0.0014 ft/ft.

Figure 10 is a potentiometric surface map for the Wasatch HSU based on September 2010

groundwater elevation data. Groundwater in the Wasatch HSU in the northern part of the PAPA flows

southward to the New Fork River. A groundwater divide is present south of the New Fork River in the

central portion of the PAPA. Groundwater north of this divide flows to the north to the New Fork

River. South of this hydraulic divide, groundwater flows west-southwest toward the Green River and

lower end of the New Fork River. The average hydraulic gradient of groundwater in the Wasatch HSU

is approximately 0.007 ft/ft.

Mesa and Antelope Spring, located in the northwest and southeast portions of the PAPA study area,

respectively, are at elevations of 7180 and 7220 feet amsl (Figure 10). The Mesa Spring may receive

recharge from the Mesa; whereas, Antelope Spring may receive water recharging from higher elevation

areas to the east, west or north. Apparent groundwater seeps located along the topographic bench

north and above the New Fork River floodplain in the center of the PAPA are likely supported on a

seasonal basis from excess water irrigated from nearby Paradise Ditch.





4.4.2 Vertical Flow

Groundwater in the shallow portions of the Wasatch HSU over much of the PAPA migrates vertically

down to the deeper regional part of the Wasatch HSU. In areas along the rivers that are losing water to

the subsurface, groundwater moves down from alluvium into the underlying Wasatch HSU. In areas of

groundwater discharge, such as along gaining river reaches, groundwater in the underlying Wasatch HSU

is moving up into alluvium and discharging to the alluvial-surface water system. Vertical flow also occurs

across the various inter-layered units within the Wasatch HSU, with potential for preferential

movement along joints or fractures, if present.

Groundwater level or head data from paired study wells screened in different sandstone units allow for

the evaluation of vertical components of groundwater flow. Figure 9 shows vertical gradients calculated

between alluvial wells paired with Wasatach bedrock wells. Vertical gradients for shallow and deeper

Wasatch bedrock well pairs are shown on Figure 10. Groundwater level hydrographs in Appendix I

show water level changes over the period of record (generally November 2010 to June 2011) for the

various study well pairs. Hydrogeologic cross-sections in Appendix J and Figure 7 also show

groundwater vertical gradients for study well pairs.

Groundwater flow is upward between the Wasatch HSU and overlying Alluvium HSU along the lower

reach of the New Fork River (X-4 and X-5 sites) and the East Fork River (T-8 site; Figure 9). Upward

hydraulic gradients at these three sites ranges from 6 to 14 percent. The Wasatch HSU wells at these

three sites are artesian, indicating that, although groundwater discharges from the bedrock system to

the alluvial system, lower permeability shale/siltstone layers between sandstone layers and overlying

alluvium inhibit flow from bedrock to alluvium.

Vertical gradients in alluvial and Wasatch well pairs in the upper reach of the New Fork River (X-1, X-2

and X-3) change seasonally (Figure 9). Water elevations measured at the three sites in September 2010

and June 2011 show that vertical gradients range from 0.1 to 1.6 percent. Based on hydrographs at theX-1 and X-2 sites (Appendix I), the vertical gradients are upward most of the time.

The hydrograph for wells X-1-A and X-1-SW (Appendix I) indicates that groundwater levels in

bedrock are usually about a foot higher than in the overlying alluvium, except for brief periods when

vertical gradients became neutral or reversed.

The hydrograph for wells X-3-A and X-3-SW (Appendix I) indicates that vertical gradients between

alluvium and bedrock were upward between November 2010 and May 2011. Beginning in April 2011,

groundwater elevations in the alluvium began to increase in response to spring runoff and water in the

nearby Paradise Ditch which led to a reversal of vertical gradient (downward) in May and June 2011.

Figure 10 shows vertical gradients at paired Wasatch bedrock well sites in the PAPA. All well pairs

completed along the primary trend of the Pinedale Anticline (T-1, T-3, T-4 and T-7 sites) have

downward vertical gradients ranging from 2 to 37 percent. These data indicate that these study well

sites are in areas of groundwater recharge.





The two study well pairs located near the lower New Fork River (X-4 and T-6 sites) show upward

vertical gradients ranging from 6 to 23 percent. These data suggest that the lower New Fork River is an

area of groundwater discharge for the Wasatch HSU.

4.5 Groundwater Recharge and Discharge

This section describes and quantifies the components for groundwater recharge and discharge in the

PAPA study area. Additional information is included in the water balance section (Section 7.8 and

Appendix F).

Most recharge occurs along the east side of the PAPA study area on the front of the Wind River

Mountains. Water flowing off the mountains recharges shallow alluvial systems along tributary streams

draining the mountains, which in turn recharges the underlying Wasatch bedrock flow system. Stream

loss from reaches of the New Fork and Green rivers in and near the PAPA also recharge groundwater.

Irrigation ditch loss is another appreciable source of groundwater recharge as is recharge from irrigated

lands. Direct precipitation and runoff within the PAPA also recharge groundwater. Due to the

topographic positions, the Mesa, Ross Ridge, and Blue Rim receive more recharge than lower elevationportions of the PAPA (refer to Section 7.8).

Groundwater discharges to the hydrologic system at the PAPA primarily as baseflow to streams. Other

points of discharge include evapotranspiration (ET) from wetlands and phreatic plants in riparian zones;

groundwater underflow out of the PAPA; and pumping from wells (smallest component of discharge).

For this report, underflow is defined as groundwater entering or exiting the water balance region.

Discussions of the entire hydrologic water balance and groundwater balance are presented in Section

7.8.





Results of surface water quality samples obtained by SCCD in the PAPA can be found by accessing the

website www.sublettecountycd.com. Surface water quality sample results obtained by the USGS in the

PAPA are located in the website ―http://waterdata/USGS/gov/wy/nwis/sw‖.

5.2 Springs

Results of field parameters for the two springs (Mesa and Antelope springs; Figure 2) measured by

AMEC in July and November 2009 are included in Table 13. Temperature measured in Mesa Spring on

these dates was 9.3 and 10.5 °C; whereas, temperature measured in Antelope Spring was colder at 6.5

and 7.7 °C, respectively. Values for EC measured in Mesa Spring was 740 and 798 µmhos/cm; while EC

in Antelope Spring was lower (122 and 138 µmhos/cm). Oxidation-reduction potential was also higher

at Mesa Spring (104 mV) than at Antelope Spring (44 and 75 mV).

Results of laboratory analysis of Mesa and Antelope springs samples are included in Table 15. Values of

pH from both springs ranged from 7.5 to 8.7 su. Similar to EC, concentrations of TDS in water from

Mesa Spring (437 and 454 mg/L) are higher than Antelope Spring (98 and 102 mg/L). All otherconstituents analyzed in Mesa Spring samples have higher concentrations than in the Antelope Spring

samples. SAR was 10.1 and 12.3 for Mesa Spring, and 2.6 and 3.5 for Antelope Spring.

The Piper diagram on Figure 12 and Stiff plots on Figure 13 include data for the Mesa Spring and

Antelope Spring samples. These diagrams show that Mesa Spring is a sodium-carbonate-bicarbonate type

water, and Antelope Spring is a calcium-carbonate-bicarbonate-type water. Quality of Mesa Spring water

is notably different than other surface water samples collected in the PAPA, with higher concentrations

of alkalinity, chloride, sulfate, and sodium. Antelope Spring is similar to New Fork River samples, except

that concentrations of sodium and SAR are higher, and concentrations of calcium and magnesium are

lower in the Antelope Spring samples.

5.3 Groundwater

AMEC collected groundwater samples from 27 study wells in June 2011, and submitted them for

laboratory analysis. Study wells T-2a-G, T-2b-G and T-2-SW did not contain groundwater. In addition,

temperature, pH, EC, DO, and ORP were measured in the field for each groundwater sample.

Table 16 summarizes groundwater field parameter data and Table 17 summarizes laboratory results

for inorganic constituents. Groundwater quality data presented in Tables 16 and 17 do not include

samples collected by SCCD; these data can be accessed at ―www.sublettecountycd.com‖.

5.3.1 Alluvial HSU

Field parameters measured in groundwater samples from the six alluvial study wells (T-8-A; X-1-A; X-2-

A; X-3-A; X-4-A; and X-5-A) exhibit the following ranges (Table 16):

temperature = 7 to 13 °C;

EC = 210 to 1,539 µmhos/cm;





pH = 6.0 to 8.1 su;

DO = 0.8 to 7.5 mg/L; and

ORP = 17 to 106 mV.

Groundwater samples from alluvial wells generally contain higher concentrations of calcium andmagnesium relative to bedrock groundwater. Concentrations of TDS in alluvial groundwater samples

range from 84 to 489 mg/L (Table 17). Values for SAR are low relative to bedrock groundwater,

ranging from 0.2 to 3.6. Common ions for groundwater samples collected from study wells completed in

alluvium are presented graphically as a Piper diagram on Figure 14, and as Stiff plots on Figure 15.

With the exception of one sample, all alluvial groundwater samples are calcium-carbonate-bicarbonate

type; the sample from well X-4a-A is a sodium-carbonate-bicarbonate-type water. None of the

groundwater samples from Alluvial HSU study wells exceed Wyoming DEQ standards for pH, TDS,

chloride, sulfate, fluoride, and SAR (Table 17).

5.3.2 Wasatch HSU

Field parameters measured for 21 Wasatch HSU study wells show the following ranges (Table 16):

temperature = 8 to 16 °C;

EC = 422 to 5,772 µmhos/cm;

pH = 7.9 to 10.5 su;

DO = 0.4 to 4.7 mg/L; and

ORP = -22 to -147 mV.

Concentrations of inorganic constituents are presented in Table 17. Values of TDS for all WasatchHSU wells are in the range of 185 to 767 mg/L, with three results greater than 1,400 mg/L (wells T-4-

SW, T-6-SW, and T-7-SW). Values for SAR are relatively high (6 to 42) compared to alluvial

groundwater.

For common ions (Table 17), groundwater samples from the Wasatch HSU study wells show that four

wells (T-3-RW, T-4-SW, T-6-SW, and T-7-SW) had relatively high concentrations of sodium, chloride,

and sulfate.

Common ions for groundwater samples collected from study wells completed in the Wasatch HSU are

presented graphically as a Piper diagram on Figure 16, and as Stiff plots on Figure 17. Groundwater

from 13 of the 21 Wasatch HSU study wells are a sodium-carbonate-bicarbonate type. Six other studywells (T-1-SW; T-4-SW; T-7-SW; T-8-SW; T-9-RW; and X-3-SW) are characterized as sodium-sulfate

type water. Some groundwater samples from the 21 Wasatch HSU study wells exceed Wyoming DEQ

standards for pH (14 wells exceed 9.0 pH), TDS (5 wells), chloride (3 wells), sulfate (4 wells), fluoride (6

wells), and SAR (21 wells) (Table 17).





5.4 Water Quality Summary

Based on the information presented above, the following summarizes water quality for surface water,

springs, and groundwater samples collected for this investigation:

Surface water in the New Fork River is a calcium-carbonate-bicarbonate type, with theupstream reach of the river having the highest concentrations of common ions. The river water

is likely being ―diluted‖ with higher quality water downstream as several primary tributary

channels (e.g., Pine Creek, Pole Creek, Boulder Creek, and East Fork River) join the New Fork

River within the PAPA. Values of EC and TDS for the New Fork River range from

approximately 150 to 400 µmhos/cm, and 111 to 179 mg/L, respectively. Values of SAR for New

Fork River samples range from 0.23 to 0.35.

Water discharging from the Mesa Spring has different quality characteristics than water from

Antelope Spring. Mesa Spring water is a sodium-carbonate-bicarbonate type water with an EC of

740 to 800 µmhos/cm and a temperature of 9.3 to 10.5 °C. Antelope Spring water is a calcium-

carbonate-bicarbonate type water with an EC of 120 to 140 µmhos/cm and a temperature of 6.5

to 7.7 °C. Values for SAR are 10.1 and 12.3 for Mesa Spring, and 2.6 and 3.5 for AntelopeSpring.

Groundwater samples from the six study wells completed in the Alluvium HSU have the

following characteristics (based on laboratory results): EC = 150 to 800 µmhos/cm; TDS = 80 to

490 mg/L; pH = 6.7 to 7.4 su; and SAR = 0.22 to 3.6. Groundwater samples from the 21

Wasatch HSU study wells have the following: EC = 330 to 3,000 µmhos/cm; TDS = 180 to

1,900 mg/L; pH = 7.9 to 9.5 su; and SAR = 6 to 42.

Several water types are represented by groundwater in the PAPA study area:

o With the exception of one sample, Alluvial HSU groundwater (six study wells) is

calcium-carbonate-bicarbonate type, similar to New Fork River water; water from wellX-4-A is a sodium-carbonate-bicarbonate type.

o Wasatch HSU groundwater shows that four wells (T-3-RW, T-4-SW, T-6-SW, and T-7-

SW) have relatively high ion concentrations of sodium, chloride, and sulfate (sodium-

carbonate-bicarbonate-type and sodium-sulfate-type water).

None of the groundwater samples from Alluvial HSU study wells exceed Wyoming DEQ water

quality standards for pH, TDS, chloride, sulfate, fluoride, and SAR. Some groundwater samples

from the 21 Wasatch HSU study wells exceed water quality standards for pH (14 wells exceed

9.0 pH), TDS (5 wells), chloride (3 wells), sulfate (4 wells), fluoride (6 wells), and SAR (21 wells).

5.5 Quality Assurance and Quality Control

Quality assurance and quality control (QA/QC) procedures used for the PAPA data gaps study were

developed in the project Plan of Study (AMEC 2009a). A key component of the QA/QC process is

validation of field and laboratory data. The objective of data validation is to identify any unreliable or

invalid field and laboratory measurements, and qualify data for interpretive use. Data validation was

performed according to guidelines specified by EPA (2010). Procedures and results of data validation for

the PAPA data gaps study are described in Appendix K .





The following statements summarize results of data validation relative to precision, accuracy,

representativeness, completeness, and comparability of the data obtained in 2009-2011 for the

Hydrogeologic Data Gaps Investigation of the PAPA:

Precision – Tests of laboratory precision successfully met all QC thresholds, with all laboratory

duplicates within control limits.

Accuracy – Accuracy of laboratory analysis was evaluated by reviewing laboratory control

standards (LCS) and matrix spike sample results. All LCS recoveries were within control limits.

Natural samples associated with matrix spike results outside of control limits were flagged (M%) in

the database (Table 17: wells T-8-A; T-8-SW; T-9-RW; X-3-A; X-3-SW; X-4-A; X-4-SW; and X-4-

RW for chloride and sulfate).

Representativeness – Acceptance for representativeness is based on results of blank samples and

review of the sampling design and sample collection techniques. Magnesium was detected in one

laboratory blank at a level less than five times the natural concentration.

Completeness – The threshold of 90% completeness indicated in the Plan of Study (AMEC 2009a)

was met.

Comparability - Standard procedures identified in the Plan of Study (AMEC 2009a) were followed

for field sampling and laboratory analyses. Standard methods including data review procedures

specified in the National Functional Guidelines (EPA 2010) were followed by the laboratory, which

allows comparison to other datasets obtained by similar methods.

All laboratory data qualified with M% in Table 17, as described above, include the ―J‖ qualifier which

indicates the value is considered estimated.





6.0 SURFACE WATER - GROUNDWATER INTERCONNECTION

This section describes the interconnection of surface water and groundwater in the PAPA based on

information presented in Sections 3, 4 and 5. The analysis focuses on three types of evidence: (1)

water elevations or head for surface water and groundwater where study wells are near the New Fork

River, Green River, and tributary streams; (2) surface water gains and losses based on stream flow dataand water balance calculations; and (3) water quality of surface water extending from upstream to

downstream reaches, and comparison of surface water quality with groundwater quality.

6.1 Water Levels and Heads

The potentiometric surface for groundwater in the Wasatch HSU (Figure 10) shows that groundwater

flows south from the northern end of the PAPA to the lower New Fork River, and a portion of the

study area just south of the river also shows groundwater flowing north-northwest to the New Fork

River, indicating that groundwater in a large portion of the Wasatch Formation within the PAPA

discharges to the alluvial system and New Fork River. The hydrogeologic cross-section in Figure 7 also

shows the water table sloping toward the New Fork River, with upward vertical gradients in theWasatch HSU. Vertical hydraulic gradients shown on Figures 9 and 10 indicate upward gradients along

the lower reach of New Fork River between bedrock and alluvium (study well sites X-4, X-5, and T-8)

and within the Wasatch HSU (study well sites X-4 and T-6). Hydrogeologic cross-sections in Appendix

J also show horizontal and vertical groundwater flow directions at selected locations in the PAPA.

A list of study well and piezometer sites with surveyed elevations that are located in close proximity to

rivers and streams in the PAPA is presented below. These data indicate that groundwater flow is toward

the river or stream at most of the well locations, except for the Boulder Creek piezometer site (X-3-

P1) where a gradient away from the creek is evident. In addition, two sites where study wells are

located close to a river (X-5 near New Fork River, and T-8 near East Fork River), indicate a flat

horizontal gradient, with flow roughly parallel to the river. Most of the study wells and piezometers onthe following list exhibit upward vertical hydraulic gradients, except for the X-3 and T-7 well sites. As

described above and shown on Figure 9, well pairs at the X-1, X-2, and X-3 sites show both upwards

and downward gradients, depending on the time of measurement.

The horizontal and vertical water level and head data described above and shown on the list below

indicate that groundwater is moving to the lower New Fork River in the PAPA, supporting the

conclusion that it is the major point of discharge for alluvial and bedrock groundwater systems in the

area.





Well or

Piezometer

No.

Elevation of

Groundwater

Surface (feet)

(Sept. 2010)

Nearby River or Stream

Elevation of

Stream or River

near Wells

(feet)

Horizontal

Hydraulic

Gradient

Vertical

Hydraulic

Gradient

X-1-A 7174.8

Upper New Fork River 7172.6 Toward river Upward

X-1-SW 7175.2

X-1-P1 7176.5

X-1-P2 7177.9

X-1-P3 7178.4

X-2-A 7108.7New Fork River

and Pine Creek 7106.4

Toward river and

creek UpwardX-2-SW 7110.1

X-2-P1 7110.2

X-3-A 6983.8

New Fork River 6958.9 Toward river Downward

X-3-SW 6979.1

X-3-P2 6958.8X-3-P3 6962.8

X-3-P4 6962.5

X-3-P1 6961.4 Boulder Creek 6961.9 Away from creek Unknown

X-4-A 6882.7

New Fork River 6884.6 Toward river UpwardX-4-SW artesian

X-4-RW artesian

X-4b-A 6884.9

X-5-A 6806.7New Fork River 6806.7 Flat gradient Upward

X-5-SW artesian

X-6-P1 6815.2

Green River 6814.1 Toward river UnknownX-6-P2 6814.8

X-6-P3 6815.3

X-6-P4 6816.3

T-8-A 6919.3East Fork River 6919.4 Flat gradient Upward

T-8-SW artesian

T-6-SW 6858.2New Fork River 6850 (approx.) Toward river Upward

T-6-RW 6874.4

T-7-SW 7197.0 Green River 7072.0 Toward river DownwardT-7-RW 7126.1





6.2 Surface Water Gains and Losses

Synoptic flow data from November 2009 in the PAPA (Section 3.2) indicate that the New Fork River

gained approximately 147 ft3/sec of flow from the upstream end to the lower downstream end of the

study area that can be attributed to groundwater discharge to the river (Figure 6). At the time of the

synoptic event, total flow in the New Fork River at farthest downstream station NFA-500 was 354

ft3/sec. Therefore, approximately 42 percent of this surface water flow is attributed to groundwater

discharge during baseflow conditions in the river.

Additionally, water balance calculations presented in Section 7.8 and Appendix F show that

groundwater discharge to the New Fork River in the PAPA totals about 201,200 ac-ft/yr (equivalent to

an average annual flux of 278 ft3/sec). This is approximately 20,000 ac-ft/yr less than the total amount of

groundwater flow or flux calculated to enter the PAPA study area. Based on these flows, about 90

percent of groundwater flux into the PAPA eventually discharges to surface water in the study area.

6.3 Water Quality

The key field parameters of water temperature, pH, and EC measured in the New Fork River during the

November 5-6, 2009 synoptic event are plotted by river distance on Figure 11. These data show that

temperature and pH gradually increase downstream in the New Fork River, except for a decline in

temperature and pH near where the East Fork River joins the main river. Values for EC are highest at

the upper end of the New Fork River, declining downstream to near the East Fork River confluence,

then increasing slightly to the lower end of the New Fork River. This decrease in EC going downstream

in the New Fork River is likely due to the addition of high quality (low EC) surface water from tributary

streams.

Comparison of surface water quality in the New Fork River with groundwater quality data for study

wells in the PAPA are best observed using the Piper and Stiff diagrams. The Piper and Stiff diagrams for

surface water quality (Figures 12 and 13) and for alluvial groundwater quality (Figures 14 and 15)

show similar quality characteristics (calcium-bicarbonate-type water). Piper and Stiff diagrams for

groundwater in Wasatch HSU wells (Figures 16 and 17) indicate a different water type (primarily

sodium-bicarbonate; and some sodium-sulfate and sodium-chloride).

The following chart shows a comparison of selected general water quality parameters between surface

water, alluvial groundwater, and Wasatch Formation groundwater for samples collected by AMEC in

2009 (surface water) and 2011 (groundwater). The surface water samples were collected from the

New Fork River, and groundwater samples were collected from study wells. These results show that,

with the exception of alkalinity, Wasatch Formation groundwater has the highest concentrations of

parameters listed in the chart. Groundwater in alluvium generally has concentrations of constituentsthat are between the quality of surface water and Wasatch Formation groundwater, but more similar to

surface water. The upper end values of each concentration range clearly show differences between the

three groups of water quality types (surface water, alluvial groundwater, and bedrock groundwater).





Parameter

General Range in Water Quality Concentrations

Surface Water Alluvial

Groundwater

Wasatch Formation

Groundwater

Electrical Conductivity (μmhos/cm) 190 – 300 200 – 1,500 400 – 5,800Total Dissolved Solids (mg/L) 110 – 180 80 – 500 200 – 1,900

Sulfate (mg/L) 7 – 11 10 – 120 2 – 900

Chloride (mg/L) 1 – 2 2 – 20 2 – 420

Alkalinity (mg/L) 85 – 150 60 – 320 40 - 300

Sodium Adsorption Ratio (SAR) 0.23 – 0.35 0.22 – 3.6 6 – 42

Note: μmhos/cm = micromhos per centimeter; mg/L = milligrams per liter. Surface water samples were collected from

New Fork River by AMEC in 2009, and groundwater samples were collected from study wells by AMEC in 2011.

The water quality information summarized above generally supports the conceptual model of Wasatch

Formation groundwater mixing with higher quality alluvial groundwater, which then mixes with highest

quality surface water. The chemistry of groundwater in alluvium is most similar to surface water quality,indicating a likely direct interconnection. The overall quality of surface water observed in the New Fork

River likely is a mixture of groundwater (alluvium and Wasatch Formation bedrock) and surface water

from tributary streams, with the majority of influence on water quality coming from surface water in

tributary streams and alluvial groundwater inflow.





7.0 HYDROGEOLOGIC CONCEPTUAL MODEL

This section presents the current conceptual model for the groundwater flow system within the PAPA.

The conceptual model described below is a refinement of the model described in Geomatrix (2008).

Data collected as part of this hydrogeologic data gaps investigation between 2009 and 2011, as described

in previous chapters of this report and other available information, were compiled and synthesized todevelop a conceptual model that describes the current understanding of physical and chemical

characteristics of the flow system in the PAPA. In developing the conceptual model, AMEC incorporated

relevant geologic, hydrogeologic, hydrologic, and meteorological information. The conceptual model

describes the groundwater and surface water balance and incorporates geologic features,

hydrostratigraphy, and groundwater recharge/discharge relationships as they are currently understood.

The conceptual model described herein forms the basis for the Project’s numerical groundwater flow

model. The numerical model will, in turn, be used in development of the Final Plan.

The conceptual model described below does not include elements related to contaminant fate and

transport. Potential contaminant sources, transport pathways, and receptors will be addressed in a

forthcoming report presenting methods and results of numerical modeling.

7.1 Physiography of Study Area

The PAPA is located in a broad northwest to southeast oriented valley between the Wind River and

Wyoming mountain ranges. The area is characterized by a semi-arid landscape, with numerous

ephemeral drainages dissecting ridges and buttes. Topographic elevations range from approximately

6850 feet above mean sea level (amsl) where the New Fork River exits the PAPA, to over 7700 feet on

top of the ―Mesa‖ in the north-central portion of the PAPA. The New Fork River and Green River are

the major drainages and, in the northern half of the PAPA, generally serve as the northern, eastern and

western boundaries. Sagebrush communities dominate the PAPA with shrub-steppe vegetation (BLM

2008a). Riparian vegetation and wetlands occupy floodplains of the New Fork and Green rivers.

7.2 Geologic Setting

The PAPA is situated in the Upper Green River Basin between the southwest-thrusted Wind River

Mountain uplift and the east-thrusted Wyoming thrust belt. The Pinedale Anticline is a thrust-rooted

detachment structure that Law and Johnson (1989) suggest formed in response to southwest-directed

compression associated with the Wind River uplift. The double-plunging anticline is about 35 miles long

and 6 miles wide whose axis generally parallels the Wind River Mountains (Figure 18). Both sides of

the anticline are bound by thrust faults of the Laramide Orogeny; the Pinedale Thrust Fault to the west

and Wind River Thrust Fault to the east (Figure 19) (Govert 2011; Law 1984).

Although Govert (2011) reports that normal faults are associated with the anticline crest, these faults do

not appear to be expressed through the thousands of feet of Tertiary-age rock overlying the anticline

(Figures 18 and 19). Faults identified by Chapin et al. (2009) in the PAPA are shown on Figure 20;

these faults are located primarily in the Cretaceous-age formations beneath the Tertiary-age Wasatch

Formation and Fort Union Formation (Figure 21). There is a greater density of faulting beneath the

south end of the PAPA compared to the north end (Figure 20).





7.2.1 Geology of Natural Gas Resources

Targets for natural gas exploration and production are within the Pinedale Anticline, a conventional

geologic structural trap. The anticline is a tight (low-permeability) gas reservoir that requires hydraulic

fracture stimulation for sustained economic production rates (Law and Spencer 2009). The gas-

producing interval at the PAPA is collectively known as the Lance Pool, which includes the upper

Cretaceous-age Mesa Verde and Lance formations (Figures 18, 19 and 21). Govert (2011) describes

these fluvially-deposited formations as medium to very fine grained cemented sandstone channels

interbedded with overbank mudstone-siltstone and splay sandstone. The uppermost gas-bearing units of

economic significance are located approximately 8,000 to 12,000 feet or more below ground surface

(Figure21).

Govert (2011) proposes a conceptual model whereby the Pinedale Anticline serves as a means to focus

upward migrating gas, but the low permeability and porosity of the Lance and Mesa Verde formations

slow the vertical migration. Although migration is slow, gas travels through the overlying Tertiary-age

formations (Wasatch and Fort Union) driven by buoyant forces without the requirement for faults to

move the gas upward (Govert 2011); however, there is an apparent concentration of faults and fracturesin the anticline area that likely enhance migration of gas to the upper formations (Chapin et al. 2009)

(Figures 20 and 21).

7.2.2 Near-Surface Geology

Near-surface geology within and adjacent to the PAPA consists of the Tertiary-age Wasatch Formation

(sedimentary rock), unconsolidated glacial outwash along the mountain fronts, terrace gravels on the

upland Mesa topographic feature, and alluvium (sand, silt, gravel) along surface water courses. The

Wyoming State Geological Society’s (WSGS) bedrock map of the Pinedale area (Figure 22; WSGS

2009) identifies the principal geologic unit in the PAPA as the New Fork Tongue of the Wasatch

Formation (hereafter referred to as the Wasatch Formation). The Wasatch Formation generally

underlies the entire PAPA and consists of fluvial sediment deposited up-paleogradient of an internally-

drained Eocene-age lake (Clarey et al. 2010). The Wasatch Formation is generally described by Clarey

et al. (2010) as dull red and green mudstone, brown sandstone, and thin limestone beds. Discontinuous,

lenticular arkosic sandstone beds represent river channel (fluvial) deposits, with sandy shale and siltstone

representing overbank and floodplain deposits. Martin and Shaughnessy (1969) further describe the

arkosic sandstones as medium to very coarse grained, angular to subangular, and poorly sorted with

mica, pyrite and numerous granitic grains; claystones are green to gray-green and, in part, mottled

maroon to red-brown.

Individual lithologic units in the Wasatch Formation generally are horizontal or sub-horizontal, but are

typically not described as being continuous over large areas. Underlying the Wasatch Formation is theTertiary-age Fort Union Formation (Figure 21) which consists of brown to gray sandstone, gray to

black shale, and thin coal beds (Clarey et al. 2010). The warm and humid Fort Union paleoenvironment

sustained organic – rich swamps that resulted in multiple coal beds in the Fort Union Formation (Clarey

et al. 2010). Thickness of the Wasatch and Fort Union formations in the PAPA is about 4,000 feet for

each of the two units (Martin 1996; Scott and Sutherland 2009).





Overlying the Wasatch Formation on the Mesa are coarse alluvial glacial outwash gravels (e.g., mapped

as terrace gravels by WSGS (2009)) of Quaternary-age that originated from glaciation in the Wind River

Range (Figure 23). Based on Geomatrix (2008), these terrace gravels are approximately 10 to 35 feet

thick. Logs from study wells T-2a-G and T-2b-G (refer to wells logs in Appendix C and cross-sections

for T-2 in Appendix J) indicate a terrace gravel thickness of 14 to 16 feet.

Recent alluvial deposits of unconsolidated sand, gravel, and some silt/clay occur in the valley bottoms of

the Green River, New Fork River, East Fork River, and their tributaries. Alluvial deposits in the PAPA

are typically less than 100 feet thick; the maximum depth of alluvial material recorded on well drillers ’

logs is from a well located west of study wells X-1 where the sandy gravel was observed to 120 feet bgs

(well AD035, Table 2 of Appendix H). Study wells situated in the New Fork River and East Fork River

valleys encountered alluvium thickness ranging from 14 feet (well T-8-A, East Fork River) to 37.5 feet

(X-3-A) (refer to cross-sections for X-3 in Appendix J, and well logs in Appendix C).

7.2.3 Geologic Model

AMEC developed a three-dimensional (3D) litho-stratigraphic geologic model of the upperapproximately 1,000 feet of geologic material in the PAPA to:

Improve the geologic understanding of the area;

Provide a tool for visualization; and,

Serve as the geologic framework for a numerical groundwater flow model.

Lithologic data available from 243 wells were modeled using CTech Mining Visualization System (MVS)

software (CTech 2010). Appendix H documents development of the geologic model.

The geologic model domain extends to the Wind River Mountains on the east and to a point below theconfluence of the New Fork River with the Green River. The model covers an area of 1,418 square

miles. Based on inspection of well driller’s logs, review of geologic literature for the PAPA, and

observations made during study well drilling, we identified four lithologic categories for the geologic

model including:

Gravel/fill – includes the surficial gravel found on top of the Mesa and ―fill‖ material. For the

purposes of the geologic model, ―fill‖ are those surficial geologic materials representing the high

elevation (e.g., Wind River Range) areas of the model domain (e.g., areas ―filled-in‖ to honor the

USGS 10-meter digital elevation model (DEM) and allow aerial imagery to be draped over the

model domain).

Unconsolidated material – includes unconsolidated material reported on driller’s logs and

alluvial material present in river/steam valleys.

Shale/siltstone – includes the variety of fine-grained rock units encountered while drilling; part

of the Wasatch Formation.

Sandstone – part of the Wasatch Formation.





A variable-spaced finite-difference grid was designed for the model that includes finer grid spacing along

the axis of the Pinedale Anticline and the central portion of the PAPA along the New Fork River. A

geologic hierarchy consisting of 68 layers was generated; lithologic surface contacts were correlated and

geologic surfaces interpolated across the site using MVS 3D kriging algorithms. The USGS DEM data

represent ground surface. The result of this work is a 3D volumetric geologic model representing

gravel/fill, unconsolidated, sandstone, and shale/siltstone contacts from the database. This volumetricmodel was used as the geologic framework for the Project’s numerical model and to produce a

conceptual block model. Vertical slice planes in Appendix H present visualizations of 10 geologic

cross-sections throughout the PAPA.

Although developed using sophisticated geostatistical methods, the geologic model reduced the

complexity of the geologic system. In regions of the model with high data density (e.g., anticline axis,

along the New Fork River), pinch-outs and lateral extents of layers were determined by interpreting

driller’s logs for the presence or absence of the particular lithology. Lithologies from the logs were

interpolated into regions of scarce data density (few or absent wells) using the MVS 3D kriging

algorithms. At some locations, artificial geologic descriptions were introduced into the model within

regions where data density was low in accordance with the understanding of the depositionalenvironment. Attributes of the artificial points were determined based on the average thickness and

depths of the working model layers. By adding artificial points, the kriging algorithms were forced to

produce reasonable layer arrangements and thicknesses in data-scarce regions of the model. Because

every fourth artificial point is identical, more variability and less repetition exist in the model in regions

where data density is high, and less variability and more repetition exist where data density is low. Due

to the absence of data regarding structural features and faulting in the modeled area, these were not

considered when creating the geologic model.

In summary, the model synthesized the complex geology of the upper approximately 1,000 feet of

geologic materials in and around the PAPA to 68 distinct layers. Siltstone/shale and sandstone units are

represented to extend laterally over many miles. In areas of greater data density (e.g., above the

Pinedale Anticline and along the New Fork River), the model shows greater variability in the lateral and

vertical extent of units; whereas at areas near the model boundaries, the paucity of data forced the

model to extend units from data points to model edges.

As part of this work, the percentages of four lithologies represented in three dimensions by the model

were statistically evaluated (Appendix H). Based on model cross-sections, 66 points were selected to

be evenly distributed at 5-mile intervals, with vertical measurements for each lithology (average vertical

section length was 988 feet). Findings include the following (input rationale and result details are

provided in Appendix H):

Lithologic CategoryNumber of

OccurrencesTotal Percentage Mean Thickness (feet)

Gravel/Fill 16 4.7 56.5

Unconsolidated 22 0.8 7.4

Siltstone/Shale 1,189 59.9 33.0

Sandstone 1,219 34.6 18.4





From the chart shown above, approximately equal numbers of siltstone/shale and sandstone lithologic

units are modeled. About one-third of the lithologies represented by the model are sandstone with a

mean thickness of approximately 18 feet, and two-thirds are siltstone/shale with a mean thickness of 33

feet. About five percent of the modeled area is represented by gravel/fill and unconsolidated materials,

and less than one percent is comprised of unconsolidated lithologies that include river/stream valley

alluvium.

The geologic model is a reasonable representation of subsurface geology in consideration of the scale of

the model and given the available lithologic data set for the upper approximately 1,000 feet of geologic

material in the PAPA. The geologic model provides an appropriate 3D geologic framework for the

Project’s numerical groundwater flow model based on hydrogeologic data limitations and scale of the

309-square-mile PAPA.

7.3 Climate

Climate throughout the PAPA varies as a function of elevation, latitude, and orographic effects.

Precipitation in the mountains northeast (Wind River Mountains) and west (Wyoming Range) of Pinedale is significantly greater than in the lower portions of Sublette County which includes the PAPA.

Temperatures in Pinedale measured for the period of record (1948-2010) range from average monthly

maximum values of 26.4 ˚F (January) to 77.0 ˚F (August), and average monthly minimum values of from -

1.0 ˚F (January) to 41.4 ˚F (July) (Table 18). Average annual maximum and minimum temperatures are

51.7 ˚F and 20.1 ˚F, respectively (Table 18).

7.3.1 Precipitation

For the 30-year period from 1971-2000, and for the period of record from 1948-2010, average annual

precipitation at Pinedale was 11.4 inches and 10.9 inches, respectively (Table 18 and Figure 24)

(Western Regional Climate Center (WRCC) 2011). Highest monthly precipitation occurs during theperiod of May through September (in the form of rain), and the driest months are November through

March (Table 18). Mean annual snowfall at the Pinedale station is 62 inches (Table 18). Based on

available SNOTEL data for mountain ranges in the vicinity of Pinedale (Elkhart Park station at elevation

9,400 feet and New Fork Lake station at elevation 8,340 feet), average annual precipitation ranges from

20 and 30 inches (rain and snow water equivalent) at these locations (Natural Resources Conservation

Service (NRCS) 2011).

7.3.2 Evapotranspiration

Total evapotranspiration includes water intercepted by vegetation, water freely evaporating from open

water surfaces, water evaporating from soil, and plant root uptake. Mean evaporation potentials forWyoming calculated from pan evaporation data range from 36.2 to 59.0 inches (WRCC 2011). At the

Green River station, mean annual pan evaporation measured for the period 1915-2005 is 50.3 inches

(Table 18). Evaporation generally occurs from May through October. Even at the lower end of the

range, average annual evaporation potential is over three times higher than the mean annual

precipitation at Pinedale.





7.4 Hydrology

Surface water resources in the PAPA are located in the northern portion of the Greater Green River

Basin, and consist of rivers and streams that flow from the west side of the Wind River Mountains.

These drainages ultimately flow southward to the Colorado River. A few small springs also are present

in the project area. Irrigation canals and ditches that divert surface water from rivers and streams are

present in the major valley bottoms.

There are two different classes of rivers and streams based on flow, known as perennial and ephemeral

or intermittent. Perennial rivers and streams flow year-round and are the direct result of flow in

mountainous areas due to groundwater discharge, snowmelt, and/or rainfall runoff. Ephemeral rivers or

streams flow occasionally in response to snowmelt and/or rainfall events. Intermittent streams have

reaches of perennial flow mixed with reaches of ephemeral flow. Ephemeral and intermittent streams

typically are smaller in size and have less energy, originating on less-steep topography or in plains areas.

Perennial rivers within and adjacent to the PAPA (Figure 2) include:

Green River located near the western PAPA boundary, primarily in the north.

New Fork River located adjacent to the eastern PAPA boundary in the north, and bisecting the

middle of the PAPA from approximately east to west.

East Fork River, a tributary to the New Fork River, which enters the PAPA from the east near

the town of Boulder.

Headwaters for these rivers are located to the north and east of the PAPA in the Wind River Range.

The confluence of the East Fork and New Fork Rivers is within the PAPA, near the east-central PAPA

boundary. The New Fork River joins the Green River approximately 6 miles west of the west-central

PAPA boundary. The Green River continues flowing southward through Fontenelle Reservoir andFlaming Gorge Reservoir, and ultimately discharges to the Colorado River in Utah.

Several perennial streams join the New Fork River east and north of the PAPA, including Duck Creek,

Pine Creek, Pole Creek, and Boulder Creek (Figure 2). Numerous ephemeral and intermittent

drainages are present in the PAPA. No lakes are present within the PAPA; however, several large lakes

occur east and northeast of the PAPA, including Freemont Lake and Boulder Lake along the western

front of the Wind River Range. Several small water storage reservoirs are present within the PAPA

where ephemeral drainages are dammed. Irrigation ditches inside the PAPA divert water from and are

generally parallel to the Green and New Fork rivers. A few springs occur within the PAPA, including

Mesa Spring and Antelope Spring (Figure 2), both of which flow at relatively low rates. Groundwater

seeps, likely resulting from excess irrigation, appear to be present in areas along the topographic benchbelow Paradise Road on the north side of the New Fork River.

Numerous irrigation ditches were located in the PAPA and digitized using topographic maps (Figure 2)

and satellite imagery (see Table F in Appendix F for a list of major irrigation ditches). Data from the

―Upper Green Normal‖ surface water model was used to determine the annual volume of water

diverted from stream reaches. The surface water model was developed by AECOM (2009) to look at

surface water resources in the Green River basin and uses historical gage and diversion data from 1971





to 2009 to calculate a surface water mass balance. Based on information available from AECOM (2009)

and the length of ditches within the model domain (167.4 miles), total average annual ditch flow in the

PAPA is approximately 48,591 acre-feet (ac-ft).

Rivers and streams in the Green River Basin show wide fluctuations in annual and seasonal flow. A major

portion of the annual stream flow is comprised of snowmelt runoff occurring during the months of Aprilthrough July. Most of the snow accumulates in the higher mountain areas.

Table 2 lists mean monthly discharge data reported by the USGS (2011) for stream gaging stations on

the New Fork River and Green River, including tributaries to the New Fork River (Pine Creek, Boulder

Creek, and East Fork River). Only four stations on Pine Creek, lower New Fork River, and Green River

(Table 2) are still being monitored by the USGS. Lowest monthly flows in the New Fork River

generally occur during the period of December through March, and highest flows occur in June,

followed by July and May. Low mean monthly flows (January) for the upper and lower New Fork River

stations are 23 and 200 cubic feet per second (ft 3/sec), respectively. High mean monthly flows (June) for

the same two New Fork River stations are 203 and 2,900 ft3/sec, respectively. Low mean monthly flows

in the Green River near Daniel (upstream) and La Barge (downstream) are 109 and 453 ft3/sec,respectively; whereas high mean monthly flows at these Green River stations are 1,760 and 5,420 ft3/sec,

respectively.

Table 3 shows mean annual discharge data for the period 1990-2010 reported by the USGS (2011) for

four gaging stations that are still being monitored. Mean annual flows at these stations have the

following ranges: Pine Creek above Fremont Lake = 116 to 245 ft3/sec; New Fork River near Big Piney

= 357 to 1,002 ft3/sec; Green River at Warren Bridge = 280 to 709 ft3/sec; and Green River near La

Barge = 728 to 2,349 ft3/sec. During this period (1990-2010), highest annual flows occurred in 1997.

Mean monthly discharge data for the three New Fork River gaging stations (near Pinedale, near Boulder,

and near Big Piney) indicate a consistent increase in flow from upstream to downstream (Table 2).

Results of a synoptic flow study conducted by AMEC along the New Fork River on November 5-6, 2009

are presented in Section 3.2. Total gain in flow along the New Fork River through the PAPA measured

in early November 2009, after subtracting flow from tributary streams, was approximately 147 ft3/sec,

which can be attributed to discharge of groundwater into the river channel (Figure 6). Most of the gain

in New Fork River flow occurs in the center of the PAPA between the mouth of the East Fork River and

the Highway 351 bridge over the New Fork River. A study by Martin (1996) also identified the upper

Green River and its tributaries to be gaining streams.

Complex geology of the Green River Basin influences water quality characteristics of the rivers and

streams. Surface water that originates in the bedrock core of the mountains generally is clear and low in

dissolved solids; whereas, surface water that originates in or flows over the plains in softer sedimentary

rocks typically has higher dissolved and suspended solids. Man-made causes of surface water quality

deterioration include irrigation return flow, livestock grazing, municipal sewage effluent, and industrial

discharge. Several stream segments in the Green River Basin are listed as impaired or threatened in

Wyoming’s Water Quality Assessment and Impaired Waters List (2010 Integrated 305(b) and 303(d)

Report). No rivers or streams in the PAPA area, however, are on the impaired list. Specific surface

water quality data collected in the PAPA are described in Section 5, above.





7.5 Hydrogeology

From a regional perspective, hydrogeologic units in the Green River Basin can be grouped on the basis

of the four geologic eras – Cenozoic, Mesozoic, Paleozoic, and Precambrian (Clarey et al. 2010). For

the PAPA, the primary hydrogeologic units encountered in the project area are in the Cenozoic era

(Quaternary- and Tertiary-age). The Quaternary-age hydrogeologic units consist mostly of

unconsolidated deposits (clay, silt, sand, gravel, and cobbles): alluvial, landslide, eolian, lacustrine, glacial,

and terrace deposits. Many of these unconsolidated deposits are less than 50 feet thick, but can be over

100 feet thick in some areas. Saturated coarser-grained zones of these deposits yield groundwater to

wells typically in an unconfined condition.

Tertiary-age hydrogeologic units are divided into upper and lower units by Clarey et al. (2010). Tertiary

sedimentary rocks contain most of the shallow bedrock aquifers used in the Green River Basin. The

Wasatch and Fort Union Formations are the two primary formations that yield groundwater to wells in

the PAPA (Figures 18, 19, and 21). As described in Section 7.2, these combined formations are

approximately 7,000 to 8,000 feet thick in the PAPA and consist primarily of discontinuous interbedded

intervals sandstone, siltstone, mudstone, and shale, with most groundwater wells screened in theuppermost sandstone units of the Wasatch Formation. Low permeability units of shale and mudstone-

siltstone can behave as confining units or aquitards that can hinder vertical groundwater flow between

sandstone units.

7.5.1 Hydrostratigraphic Units

A hydrostratigraphic unit (HSU) is a geologic unit or formation, or a group of formations, in which there

are similar hydrologic characteristics (e.g., porosity, permeability) allowing for grouping (Fetter 2001).

Groundwater intercepted by industrial, stock, domestic and study wells/piezometers within the PAPA

occurs in two principal hydrostratigraphic units (HSUs): Alluvium and Wasatch Formation bedrock

(Figure 5). The Alluvium HSU is located in the valleys of the principal watercourses in the PAPA.

Based on information evaluated for this report, the Wasatch Formation in the PAPA was not divided

into shallow and regional HSUs as mentioned in the POS (AMEC 2009a). Specific information evaluated

during this study as described in this report includes groundwater levels and flow, hydraulic properties,

and water quality for study wells completed at different depths in the Wasatch Formation. These

hydrogeologic and geochemical data collected from the Wasatch Formation study wells did not show

any significant differences that would support separation into two HSUs. One option considered was to

separate the Wasatch HSU based on topographic position relative to elevations of the primary river

valley bottoms; however, topographic position was not a sufficient reason to separate the Wasatch

Formation into unique HSUs.

The relatively thin gravel veneer on the Mesa mapped as Holocene to Pleistocene-age terrace deposits(WSGS 2009) may be saturated in some locations and may supply water to contact springs such as Mesa

Spring (refer to Figure 25). However, during this investigation, direct evidence of saturated gravels

was not observed and defining a hydrostratigraphic unit for Mesa gravel is not considered in this report.

The Tertiary-age Fort Union Formation, which underlies the Wasatch Formation (Figure 21), is below

the zone of interest for groundwater characterization for this study. However, injection wells for

produced water have been installed in the PAPA into the Fort Union Formation, so a general





description is provided here. As stated in Section 7.2.2, the Fort Union Formation is lithologically

similar to the Wasatch Formation and consists of brown to gray sandstone, gray to black shale, and thin

coal beds (Clarey et al. 2010). According to Clarey et al. (2010), the Wasatch and Fort Union

Formations can be considered as one large regional hydrostratigraphic unit, with groundwater flow

moving from recharge areas along the basin margins (e.g., Wind River Mountains) down through the

Wasatch Formation and into the underlying Fort Union Formation. Groundwater in the Fort UnionFormation moves laterally along a deeper regional flow path toward the center of the Green River

Valley where the flow path turns upward to the Green River; whereas, groundwater in the Wasatch

Formation has shorter and shallower flow paths (Clarey et al. 2010). From a regional conceptual

perspective, vertical groundwater flow between the Fort Union Formation and Wasatch Formation in

the PAPA generally would be downward; however, this deeper groundwater flow concept has not been

evaluated in this study.

7.5.1.1 Alluvium HSU

Groundwater in the Alluvium HSU is unconfined and occurs in sand and gravel deposits adjacent to the

principal watercourses in the PAPA. This HSU is hydraulically connected to the underlying WasatchFormation, as well as to subjacent streams and rivers. Based on study well logs (Appendix C), it is

generally no more than about 50 feet thick. The WSGS (2009) maps Quaternary-age alluvium as being

up to 3 miles wide along the New Fork River (Figure 23). Of the 293 wells in the project’s

geodatabase (note records for 50 wells do not include lithologic information), six study wells (X-1-A, X-

2-A, X-3-A, T-8-A, X-4-A and X-5-A) and six domestic wells are completed in the Alluvium HSU (refer

to Section 7.5.1.4, below). One aquifer test was conducted in a well completed in the Alluvium HSU

(well X-2-A, Appendix E) with a resultant hydraulic conductivity of approximately 446 feet/day based

on recovery data (Table 12).

7.5.1.2 Wasatch HSU

Lithology of the Wasatch HSU consists of laterally and vertically discontinuous porous sandstone beds

interbedded with less permeable shale, mudstone, and siltstone units. This HSU is characterized as a

heterogeneous or compound system as the water-bearing sandstone beds have not been documented as

being continuous over large areas (Figure 7). Due to hydraulic conductivity contrasts between fine-

grained units and sandstone, the discontinuous nature of individual sandstone beds, and hydraulic

potentials commonly rising above the top of the saturated zone, the Wasatch HSU in the PAPA likely

ranges from an unconfined to semi-confined or leaky-confined aquifer.

In some places, groundwater may be perched. For example, a stock well (AS008) is located within 1

mile northwest of study well T-2-SW. Both of these wells are completed to the same depth elevation

and have evidence of perched water. Well T-2-SW is currently dry, but there was a strong indicationduring drilling of a saturated zone near the bottom of the well. In contrast, well AS008 is an active

stock well with a total depth approximately 200 feet above both the New Fork River level and the

water level in nearby deeper study well T-2-RW. Although some areas of perched groundwater exist in

the PAPA, the hydrogeologic data gaps study was not designed to describe specific areas nor the spatial

extent of perched groundwater in the Wasatch Formation.





Industrial water supply wells that support natural gas exploration and development activities are

completed in the Wasatch HSU (Figure 7). Industrial wells are typically completed to depths of less

than 1,000 feet and are screened across multiple water-bearing sandstone units with reported yields

typically in the range of 150 gal/min (SEO 2009). As most domestic wells in the PAPA are located on

private property in the valleys of the principal surface water features, most of these wells also tap the

Wasatch HSU; some wells are completed in alluvium. Domestic wells completed in the Wasatch HSUtypically average about 120 feet in depth (see Section 7.5.1.4 and chart below).

AMEC conducted aquifer tests in 11 Wasatch HSU wells screened in discrete sandstone units

(Appendix E). Estimated horizontal hydraulic conductivity values for saturated Wasatch Formation

sediments range from <0.1 to 9.5 feet/day using the recovery test data, with an average hydraulic

conductivity of 2.6 feet/day. No spatial pattern (horizontal and vertical) within the Wasatch Formation

can be discerned for the hydraulic conductivity data, indicating the sandstone units have variable

permeabilities throughout the formation within the PAPA study area.

7.5.1.3 Summary of Water Wells by Hydrostratigraphic Unit

Table 20 is an inventory of 293 water wells contained in the project’s geodatabase with geographic

coordinates within the PAPA; lithologic data are available for 243 wells. The chart below identifies wells

according to hydrostratigraphic unit. Wells completed in the Alluvial HSU were determined based on

lithologic descriptions used for the Geologic Model (see Section 7.2.3 and Table 2 in Appendix H).

The number of wells completed in the Wasatch HSU was determined by creating a surface using

elevations for the New Fork River and Green River based on the USGS DEM.

Well Type* Total Number

of Wells

Hydrostratigraphic Unit (HSU)

Alluvial Wasatch

Total

Number

Average Depth

(feet)

Total

Number

Average Depth

(feet)

Domestic 81 6 77 75 118

Stock 26 0 -- 26 196

Industrial 156 0 -- 156 645

Study 30 4** 40 24 362

* Well type designated by SCCD with exception of the Interim Plan Study wells.

** Two additional study wells (T-2a-G and T-2b-G) are completed in unsaturated gravel on the Mesa.

In the PAPA, about 7 percent of domestic wells are completed in alluvium and 83 percent are completed

in the Wasatch HSU with an average depth of 118 feet. Stock wells are all completed in the WasatchHSU, with average depths of about 200 feet. All industrial wells are completed in the Wasatch HSU

with an average depth of about 650 feet. Study wells installed for this Data Gaps Investigation are

completed in each HSU (alluvium and Wasatch Formation) to characterize groundwater in these units

that are used for beneficial purposes.





7.5.2 Groundwater Flow

Groundwater in the study area generally flows west and south from the mountains and foothills toward

the Green River below the mouth of the New Fork River and into the center of the Green River Basin.

Some of this water moves along deep groundwater flow paths in the Wasatch and Fort Union

Formations; whereas, other groundwater moves in shallower flow paths and discharges to springs and

rivers (e.g., New Fork River and Green River). Figures 9 and 10 present groundwater flow maps for

groundwater in alluvium and the Wasatch Formation, respectively, based on groundwater elevation data

obtained during September 2010.

Groundwater in shallow parts of the Wasatch HSU over much of the PAPA migrates vertically down to

the underlying deeper or regional portion of the Wasatch HSU. In places, groundwater may exist in

perched saturated zones above low permeability shale/siltstone. Vertical migration of groundwater in

some shallow areas of the Wasatch HSU occurs initially as unsaturated flow. Perched groundwater in

the Wasatch HSU may discharge to the surface in some locations along the slopes and bases of

topographic features in the form of springs and seeps.

Groundwater in the Wasatch HSU flows through the aquifer preferentially in the higher permeability

sandstone units. Although not described in the geologic literature reviewed for this study, bedding

planes and joints/fractures in Wasatch Formation sandstone, shale/siltstone, and mudstone units are

likely preferential pathways for groundwater flow. Vertical flow in response to differences in hydraulic

head potential also occurs across the various inter-layered units, with the potential for preferential

movement along joints/fractures, where present.

7.5.2.1 Direction

Groundwater flow in alluvium is generally down-valley and ultimately discharges to surface water as

baseflow. Figure 9 is a contour map of water table elevations within the alluvial system in the PAPA.

Based on data collected and reviewed for this study, surface water in the New Fork and Green rivers

generally gains flow from shallow groundwater hosted in alluvium. The direction of flow in alluvium is

generally parallel to streamflow adjacent to stream channels, but towards the river at the margins of the

alluvium.

Figure 10 is a potentiometric map for the Wasatch bedrock system and includes arrows indicating

major groundwater flow paths. In the northern portion of the PAPA, groundwater flows into the PAPA

southwesterly from the Pine Creek and New Fork River valleys. Beneath the Mesa, groundwater flow is

generally southward toward the New Fork River where it eventually discharges to the river in the area

below the mouth of the East Fork River. Just south of the New Fork River in the center of the PAPA, a

small groundwater divide splits groundwater flow northerly to the New Fork River and westerly towardthe confluence of the New Fork and Green rivers. South of this area in the vicinity and south of

Highway 351, the groundwater flow direction is primarily west-southwest.





7.5.2.2 Groundwater Gradients and Average Velocity

Horizontal Gradients

Figure 9 is a potentiometric surface map for groundwater in alluvium. Where groundwater elevationcontours are closer together, horizontal hydraulic gradients are higher; where contours are farther

apart, gradients are smaller. Horizontal gradients in the Alluvial HSU range between 0.14 percent alongthe New Fork River corridor south of the Mesa, to 0.38 percent near the town of Pinedale.Groundwater elevations and gradients in alluvium are influenced by interaction with surface water.Variability in horizontal gradients for the Alluvial HSU reflects changes in land surface topography andsubsequent surface water stage. As the New Fork River valley flattens away from the Wind RiverMountain Range, horizontal gradients decrease.

Figure 10 is a potentiometric surface map for groundwater in the Wasatch HSU. The horizontalhydraulic gradient in the Wasatch Formation ranges from about 0.09 percent on the Mesa to 1.3percent south of the town of Pinedale. Areas in the Wasatch HSU with higher gradients are interpretedto be a reflection of recharge and lower transmissivity, whereas areas with lower gradients areinterpreted to be areas with higher overall transmissivity.

Vertical Gradients

Comparison of groundwater elevations in study well pairs (alluvium and Wasatch bedrock wells)

indicates upward vertical hydraulic gradients at well pairs located along the lower New Fork River (X-4

and X-5 sites) and East Fork River (T-8 site) (Figure 9). The upward vertical hydraulic gradients for

groundwater at these three sites ranges from 6 to 14 percent between bedrock and alluvium. The

Wasatch wells at these three sites also are artesian.

The alluvium and Wasatch well pairs at X-1 and X-2 (upper New Fork River area) show both downward

(in September 2010) and upward (in June 2011) vertical gradients over the period of record (Figure 9).

The vertical gradients measured at these two well sites are low, with downward vertical hydraulicgradients of 0.1 and 0.3 percent in September 2010, and upward gradients of 1.2 to 1.6 percent in June

2011. Appendix I includes hydrographs for the X-1 wells, indicating that the vertical gradient is slightly

upward for a majority of the period of record (July 2010 to June 2011).

Vertical gradients at the study well X-3 site between alluvium and bedrock started as an upward

gradient for the period of record, but then changed in May 2011 to a downward gradient (see

hydrograph in Appendix I). Groundwater in alluvial well X-3-A may be influenced by the Paradise

Ditch and/or by a large nearby pond in a gravel quarry; each source could also seasonally influence the

vertical gradient.

For sites with Wasatch bedrock study well pairs (completed to different depths), four sites havedownward vertical gradients for groundwater flow (T-1, T-3, T-4, and T-7 sites), and two sites (X-4 and

T-6) have upward vertical gradients (Figure 10). Both the X-4 and T-6 study well sites are located near

the lower end of the New Fork River where upward vertical gradients also occur between the Wasatch

bedrock and alluvial study well pairs (Figure 9). Vertical hydraulic gradients between paired Wasatch

bedrock study wells range from 2 to 37 percent.





Vertical groundwater gradients help identify discharge and recharge areas for the groundwater system.

Based on gradients measured during this investigation, the lower New Fork River valley (X-4 and X-5

study well sites) is a principal discharge area for groundwater in both the Alluvial and Wasatch HSUs

(i.e., upward vertical gradients). In the upper part of the New Fork River, groundwater hydrographs

from site X-1 (Appendix I) also shows that there is generally an upward gradient from the Wasatch

HSU to the Alluvial HSU, although the gradient does reverse at times. Areas of recharge to theWasatch HSU (i.e. downward vertical gradients) are apparent at the north end of the PAPA (study well

sites T-1 and T-7 on the Mesa), in the Warbonnet area (site T-3), and in the Antelope area (site T-4).

Average Groundwater Velocity

Average linear groundwater velocity in alluvium and in Wasatch Formation sandstone units wasestimated using the equation (Fetter 2001):

Where: V x = average linear velocity

Kh = horizontal hydraulic conductivity

dh/dl = average hydraulic gradient

ne = effective porosity

The equation above assumes groundwater flow in saturated homogenous, isotropic materials over

relatively short distances. The equation does not take into account dispersion that occurs due to

groundwater traveling through different pores at varying rates and because actual flow paths for

groundwater vary in length. In addition, the equation does not take into account flow velocities in the

vadose zone which are affected by the degree of saturation and hysteresis.

The chart below presents a range of estimated horizontal linear velocities for alluvium and for saturated

sandstone in the Wasatch HSU. The range of hydraulic conductivity values is based on aquifer testing

results (Table 12 and Appendix E), and the range of horizontal gradients is described in Section

7.5.2.2. The range of effective porosity values for alluvium and sandstone was taken from Yu et al.

(1993).

Based on estimated average groundwater velocities shown above, the rate of groundwater movement in

alluvium is much greater than in Wasatch Formation sandstone. Using the range of groundwater

velocity estimates for Wasatch Formation sandstone above, groundwater (in a unique sandstone unit)

beneath a typical 1-acre natural gas well pad would take at least 5 years to travel the width of the pad.This characteristic of groundwater movement with respect to contaminant transport is discussed

further in the forthcoming PAPA numerical groundwater flow model report.





Hydro-stratigraphicUnit (HSU)

VelocityRange

HydraulicConductivity(Kh, ft/day)

EffectivePorosity

(ne)

HydraulicGradient

(dh/dl, ft/ft)

Velocity(ft/day)

Velocity(ft/year)

Alluvium

Low 446a 0.4 0.0034 3.8 1,390

Mid 446a 0.28 0.0034 5.4 1,970

High 446a 0.13 0.0034 11.7 4,270

Wasatch*

Low 0.019b 0.41 0.00065 0.00003 0.011

Mid 2.15c 0.27 0.0018 0.014 5

High 9.47d 0.12 0.0014 0.11 40

Note: Location of calculated gradient corresponds to location of hydraulic conductivity measurement.

* Estimate for saturated sandstone units within the Wasatch HSU.

a Aquifer test for alluvium performed only at study well X-2-A (Appendix E)

b Aquifer test performed at study well T-5-RW (Appendix E)

c Aquifer test performed at study well T-1-SW (Appendix E)

d Aquifer test performed at study well T-4-RW-b (Appendix E)

Vertical and lateral discontinuities in sandstone units will have an effect on average linear groundwater

velocities. Although calculated groundwater gradients are based on the interpreted potentiometric

surface and take into account lateral and vertical lithologic discontinuities, other components of the

velocity equation do not. The equation above describes average horizontal velocities. Based on pad-

scale cross-sections (Appendix J) and the geologic model (Appendix H), lateral lithologic

discontinuities can exist at a scale of less than 1,000 feet and vertical lithologic discontinuities can exist

on a scale 5 feet or less. Because siltstone/shale units have lower hydraulic conductivity relative tosandstone, water in discontinuous sandstone units will be retarded and, at a basin scale, groundwater

will move slower than the values calculated in the chart above. Although there is a lack of information

regarding jointing/fracturing of the Wasatch Formation, groundwater flow will exploit these potential

higher conductivity features and result in faster groundwater velocities than estimated. Detailed

discussions of groundwater velocities in the modeled three-dimensional PAPA flow system and

simulations of flow paths will be included in the forthcoming PAPA numerical groundwater flow model

report (refer to Section 1.0).

7.5.2.3 Seasonal Variability

The period of record for groundwater elevation measurements was generally the 7-month spanbetween November 2010 and June 2011. Groundwater level hydrographs for the study wells contained

in Appendix I show that for the period of record, groundwater elevations fluctuated approximately

two feet in alluvial wells. Alluvial well X-1-A adjacent to the upper New Fork River exhibited a rising

water level from March through April 2011, possibly in response to the beginning of spring recharge

from the upper New Fork River. Well X-3-A exhibited the most dramatic change in groundwater

elevation, with a maximum change of about 9 feet. The water level increase occurred in May-June 2011

likely in response to the 2011 activation of the nearby Paradise Ditch. Alluvial well T-8-A located near





the East Fork River did not exhibit any significant water level change in Spring 2011 in response to rising

river flows.

Water levels in wells completed in the Wasatch HSU did not exhibit any discernable trends over the

period of record for this investigation. However, well T-2-RW on the Mesa exhibited a maximum

fluctuation of approximately 26 feet in January-February 2011, possibly in response to drawdown effectsfrom pumping in a nearby industrial water well(s). Between mid-November 2010 and early June 2011,

water levels in T-2-RW declined about 14 feet (Appendix I). Groundwater in four wells completed in

the Wasatch HSU (T-2-SW, T-3-SW, T-4-SW, and T-7-SW) showed minimal variation in groundwater

elevations between November 2010 and June 2011.

7.6 Water Quality

Recharge areas in the Upper Green River Basin are typically characterized by low concentrations of

dissolved solids, sodium, and chloride. Sulfate concentrations generally increase along groundwater flow

paths, with total dissolved solids (TDS) reaching concentrations greater than 1,500 milligrams per liter

(mg/L) (Clarey et al. 2010). Sodium-carbonate-bicarbonate becomes the dominant groundwater typeincreasing with depth and distance from recharge areas as ion exchange reactions remove calcium and

magnesium from groundwater and replace them with sodium from formation materials.

New Fork River water is a calcium-bicarbonate type water, with upstream reaches exhibiting the highest

concentrations of common ions. At downstream New Fork River reaches, river water is likely being

―diluted‖ with water showing less ionic strength from several primary tributary channels (e.g., Pine

Creek, Pole Creek, Boulder Creek, and East Fork River).

Two springs characterized for this study (Mesa Spring and Antelope Spring) have different water types.

Mesa Spring is a sodium-bicarbonate-type water; whereas Antelope Spring is a calcium-bicarbonate-type

water. As both springs are believed to be contact-type springs, water infiltrating through Mesa gravelbecomes enriched in sodium and influences Mesa Spring water. Both springs show water quality types

different than Wasatch Formation groundwater.

Groundwater from study wells completed in alluvium is a calcium-bicarbonate-type (similar to New Fork

River samples); whereas, Wasatch Formation groundwater typically is a sodium-bicarbonate or sodium-

sulfate-type water.

7.7 Groundwater – Surface Water Interconnection

The interconnection of groundwater and surface water in the PAPA is assessed below based on three

lines of evidence:

Water elevations or head for surface water and groundwater where study wells are near the

New Fork River, Green River, and tributary streams;

Surface water gains and losses based on stream flow data and water balance calculations; and

Water quality of surface water extending from upstream to downstream reaches, and

comparison of surface water quality with groundwater quality.





Potentiometric maps, hydrogeologic cross-sections, and river elevations demonstrate that groundwater

discharges to the New Fork River in the central portion of the PAPA. Upward groundwater gradients

and artesian groundwater conditions in Wasatch Formation wells along this portion of the New Fork

River also indicate that groundwater in the Wasatch HSU over the northern half of the PAPA flows to

the lower New Fork River and discharges to alluvium and the river in the valley bottom. Groundwater

in the Wasatch HSU in an area just south of the New Fork River flows north and also discharges to theriver-alluvial system (Figure 10).

Results from the synoptic flow study also provide evidence of gains in New Fork River flow attributable

to groundwater input. During base flow conditions in early November 2009, the New Fork River

gained approximately 147 ft3/sec of flow from the upper end to the lower part of the channel in the

PAPA after subtracting flows from tributary stream channels. Of the total flow in the New Fork River,

this amounts to approximately 42 percent attributed to groundwater discharge during baseflow

conditions in the river. Based on groundwater balance calculations presented in Section 7.2 below,

about 90 percent of groundwater flux (underflow) into the PAPA eventually discharges to surface water

in the study area.

Water quality relationships between groundwater and surface water are the third line of evidence used

to evaluate interconnectivity. Surface water and alluvial groundwater show similar quality characteristics

(calcium-bicarbonate-type water). The overall quality of surface water observed in the New Fork River

appears to be a mixture of groundwater (alluvium and Wasatch bedrock) and surface water from

tributary streams. However, the flux of groundwater from bedrock to surface water, as evidenced by

the relatively low hydraulic conductivity of the Wasatch Formation (Section 7.5.2.2), is low compared

to water volumes from alluvial groundwater and surface water from tributary streams.

7.8 Water Balance

AMEC developed a water balance for the entire hydrologic system (atmospheric water, surface water,and groundwater) to characterize components of water inflow and outflow. A separate groundwater

balance is also described in this section, which includes only components of flow entering and exiting the

saturated subsurface; these flow components will be used as the basis for the project’s numerical model

flux boundaries. Although each water balance (entire hydrologic system and groundwater) is addressed

individually, both are generally represented by the following equation:

Inflow = Outflow ± Change in Storage

Supporting data and calculations for each water balance component are contained in Appendix F.

7.8.1 Hydrologic System Water Balance

The water balance area was determined based on significant hydrogeologic boundaries that are

transferable to the numerical groundwater flow model being developed for the PAPA Project. Figure

26 shows the region for the PAPA project water balance (547 square miles), which is larger than the

PAPA study area (309 square miles). In general, the water balance region is bounded on the north and

east by the foothills of the Wind River Mountain Range, on the west by the Green River, on the

southwest by Alkali Creek, and on the southeast by the Big Sandy River. These boundaries and internal





stresses form the components of the PAPA project water balance. Specific components of the water

balance equation for the hydrologic study area include the following, with inflow components on the left

side, and outflow components on the right side of the equation:

P + Ron+ U in = Roff + U out + G pump + ET ± S

Where:

P = precipitation

Ron = surface water run-on

U in = groundwater underflow into region

Roff = surface water run-off U out = groundwater underflow out of region

G pump = groundwater pumped for consumptive use

ET = evapotranspiration

S = any positive or negative change in storage.

The term ―underflow‖ refers to groundwater that flows both into and out of the water balance region.Because no large lakes exist within the water balance region, meaningful changes in storage occur only

within the groundwater system. Changes in groundwater storage are caused by seasonal changes in

water table elevations. The water balance below assumes a steady-state condition where inflow equals

outflow and there is no change in storage. The steady-state water balance is represented by the

following equation:

P + Ron+ U in = Roff + U out + G pump + ET

Each component of the water balance was based on available data from the period of record. Figure 27

presents the water balance graphically and the subsections below describe the estimation for values of

each water balance component.

7.8.1.1 Precipitation

Average annual precipitation across the model region ranges from 8 to 14 inches per year (in/yr) based

on 1971-2000 annual averages (PRISM Group 2008). Precipitation in the mountains along the east side of

the water balance region and in the north-central portion of the PAPA study area (i.e., Mesa) is

significantly greater than that of the lower elevation portions of the water balance region (Figure 24).

During an average water year, approximately 375,000 ac-ft/yr of precipitation falls within the water

balance region (PRISM Group 2008).

7.8.1.2 Surface Water Run-On

Surface water run-on is water that is transmitted via overland flow to streams/rivers that flow into the

water balance region. Four major rivers flow within or at the boundary of the water balance region:

Green River; New Fork River; East Fork River; and, Big Sandy River. Average annual flow per unit area

(square foot) for each catchment or drainage was calculated using historic USGS gaging data. These data

were then multiplied by the catchment area upgradient of the water balance region for each stream or

river. The resulting flow is assumed to be the amount of surface water run-on entering the water





balance region. For streams that are boundaries to the water balance region, the run-on value was

reduced by 50 percent because it was assumed half of the flow in the stream comes from outside of the

water balance region. Historic flow records suggest that the average annual run-on volume into the

water balance region is approximately 227,400 ac-ft/yr (Appendix F).

7.8.1.3 Groundwater Underflow Into Region

A significant amount of water enters the water balance region as groundwater underflow from the north

and east. Underflow into the region was calculated using Darcy’s Law:

Q = KIA

Where:

Q = flux

K = hydraulic conductivity

I = hydraulic gradient

A = cross-sectional area

Underflow rates were estimated using the range of hydraulic conductivity values measured within the

PAPA for the hydrostratigraphic units (Appendix E). Average hydraulic gradients were estimated for

each boundary based on the potentiometric surface for the Wasatch Formation (Figure 28). The cross-

sectional area was based on the width of the boundary and the saturated thickness. The saturated

thickness was calculated as the water table elevation subtracted by the base elevation of the Wasatch

Formation, which was extrapolated from a geologic cross-section (Scott and Sutherland, 2009). The base

of the Wasatch Formation for the up-gradient and down-gradient boundaries is 3,000 feet and 4,600

feet, respectively.

Groundwater underflow is anticipated through three dominant lithologic materials: alluvium, glacialoutwash, and Wasatch Formation (bedrock). Underflow from the Fort Union Formation was not

considered in the water balance because the study only incorporates the upper portion of the Wasatch

Formation. The underflow boundary was divided into components using the thickness and length of the

saturated HSU. Hydraulic conductivity ranges for each lithology were applied to the cross-sectional area

for each lithologic unit. Using minimum and maximum hydraulic conductivity values, underflow into the

water balance region ranges from 95,040 to 345,690 ac-ft/yr, with an average of approximately 220,400

ac-ft/yr (Appendix F).

7.8.1.4 Surface Water Run-off

Surface water run-off is transmitted via overland flow to streams/rivers that exit the water balanceregion. Historic flow data from USGS gaging stations along the Green River, New Fork River, East Fork

River, and Big Sandy River allowed for estimation of surface water runoff. Average annual flow per unit

area (square foot) for each catchment or drainage was calculated using historic USGS gaging data. These

data were then multiplied by the catchment area within the water balance region for each stream or

river. The resulting flow is assumed to be the amount of surface water run-off leaving the water balance

region. Historic records suggest that average annual run-off within the water balance region is

approximately 454,200 ac-ft/yr (Appendix F).





7.8.1.5 Groundwater Underflow Out of Region

A moderate amount of water exits the water balance region as groundwater underflow to the south.

Underflow was calculated using Darcy’s Law as described previously for the calculation of underflow

into the water balance region. For the down-gradient boundary, saturated thickness was determined

from an elevation of 3000 feet (base of Wasatch Formation) to the water table. Using minimum and

maximum hydraulic conductivity values for each HSU (alluvium = 79 to 446 feet/day; Wasatch

Formation = 0.01 to 6.5 feet/day), groundwater underflow out of the water balance region ranges from

4,400 to 34,400 ac-ft/yr, with an average of approximately 19,400 ac-ft/yr (Appendix F).

7.8.1.6 Groundwater Pumped for Consumptive Use

Pumped groundwater makes up a minor component of the water balance for the PAPA study area.Groundwater in the water balance region is pumped for agricultural, domestic and industrial uses.According to the Wyoming State Engineer’s Office (2010) groundwater well database, there areapproximately nine irrigation wells, 145 stock wells, 1,076 domestic/other wells, and 366 industrialwater supply wells within the water balance region.

Estimates of consumptive groundwater use for the irrigation and stock wells are based on data from

Ahern et al. (1981), which were reproduced by Clarey et al. (2010). According to these data sources,

average annual groundwater volumes used in the Green River Basin for individual irrigation and stock

wells are 66 and 0.6 ac-ft/yr, respectively. Multiplying these rates by the nine irrigation wells and 145

stock wells, results in volumes of 595 and 88 ac-ft/yr, respectively, for these agricultural wells.

Wells coded as domestic/other are assumed to supply a standard household population (2.47 persons;

U.S. Census Bureau 2010) at an average per capita use rate of 75 gallons per day (gal/day) (USGS 2006),

resulting in 222 ac-ft/yr for the 1,076 domestic/other wells within the water balance region, which

includes the town of Pinedale (Figure 26). Since an average of 10 percent of domestic water is

consumptive and the remaining 90 percent becomes return flow, the domestic/other consumptive use isestimated at 22 ac-ft/yr.

Of the 366 industrial water supply wells, records were available for 238 wells. Based on the available

well data, an average of 20 percent of the industrial supply wells are actively in use, and of those, the

average amount of water consumed per well is 7 ac-ft/yr (based on consumptive use data from QEP,

Shell, and Ultra for 2008-2010 as reported annually to BLM). Recorded data totaled 415 ac-ft/yr,

assuming 20 percent of the remaining 128 wells are pumped at 7 ac-ft/yr. This results in an additional

175 ac-ft/yr, or a total estimated pumping rate for all industrial water supply wells of 590 ac-ft/yr.

Total estimated consumptive groundwater volume pumped annually from irrigation, stock,

domestic/other, and industrial water supply wells in the PAPA water balance region is approximately1,300 ac-ft/yr (Appendix F).

7.8.1.7 Evapotranspiration

Total evapotranspiration (ET) from the water balance region includes water intercepted by vegetation,

plant root uptake, water freely evaporating from ponded surfaces, and water evaporating from soil.





Actual ET is difficult to measure (Dingman 1994); however, long-term average water loss via ET can be

estimated by using ET to balance the water balance equation:

ET = P + Ron+ U in - Roff - U out - G pump

Using average precipitation, run-on, underflow in, run-off, underflow out, and groundwater pumpedvalues, the above equation becomes:

ET = 375,000 + 227,400 + 220,400 - 454,200 - 19,400 - 1,300 ac-ft/yr

Thus, average annual loss due to ET in the PAPA water balance region is approximately 347,900 ac-ft/yr.

7.8.2 Steady-State Groundwater Balance

A steady-state groundwater balance was developed for the PAPA water balance region (Figure 26)

using a set of hydrogeologic inputs for a period when the system receives minimal stress, to provide a

basis for simulating steady-state flow conditions in the numerical groundwater model. November waschosen because it is representative of average baseflow conditions (i.e., after irrigation season and major

run-off period). Using this period also allows use of synoptic flow data from November 2009 (Table 14

and Figure 6).

The steady-state groundwater balance can be expressed with the following equation based on significant

sources of groundwater recharge and discharge:

RN+ RI +RD+U in = BF + U out + G pump + ET G

Where:

RN = natural rechargeRI = irrigation application recharge

RD = irrigation ditch loss recharge

U in = groundwater underflow into region

BF = groundwater discharge to rivers and streams (base flow)

U out = groundwater underflow out of region

G pump = groundwater pumped for consumptive use

ET = evapotranspiration directly from saturated zone.

Table 21 presents estimated flow rates for each component of the groundwater balance. The following

subsections describe how estimates were developed using data collected historically and during this

investigation. Differences between total inflow and outflow can be attributed to estimated valuesdiffering from actual values or change in groundwater storage related to changes in water table

elevations. Supporting data and calculations for the groundwater balance are included in Appendix F.

7.8.2.1 Recharge

Measuring natural recharge is difficult. Previous studies by Martin (1996) and Hammerlick and Arneson

(1998) have attempted to map estimated recharge across the region (Figures 29 and 30). These studies





indicate that the primary recharge to Tertiary-age aquifers occurs along the basin margins where the

formations are exposed at land surface and precipitation is greatest. The mapped recharge rates across

the water balance region were used to calculate the range of volumes of natural recharge. Natural

recharge values for the water balance region range from 7,600 to 12,600 ac-ft/yr, with an average of

about 10,000 ac-ft/yr.

Figures 25 and 31 show potential recharge areas for Mesa Spring and Antelope Spring, respectively,

based on areas with elevations 5 feet or more above the spring elevations. The recharge area proximal

to Mesa Spring is on the north Mesa area, and the recharge area in the vicinity of Antelope Spring is in

the southern portion of the PAPA.

In addition to natural recharge, some artificial recharge is expected to occur in areas of irrigation.

Martin (1996) estimated a recharge rate ranging from 2.0 to 2.5 in/yr in an irrigated region around

Farson-Eden, Wyoming, southeast of the PAPA study area. This range was applied to areas of irrigated

land (35,172 acres) within the PAPA water balance region, resulting in an irrigation recharge rate ranging

from 5,900 to 7,300 ac-ft/yr, with an average of approximately 6,600 ac-ft/yr (Appendix F).

7.8.2.2 Groundwater Underflow into Region

Groundwater underflow into the water balance region was estimated as described in the entire water

balance section above (Section 7.7.1.3). Based on available data, underflow into the PAPA region

ranges from 95,090 to 345,690 ac-ft/yr, with an average of approximately 220,400 ac-ft/yr (Appendix

F).

7.8.2.3 Ditch Loss

Irrigation ditches were located and digitized using topographic maps and satellite imagery. Data from the

―Upper Green Normal‖ surface water model (AECOM 2009) were used to determine the annualvolume of water diverted from rivers into the respective ditches. Diversion data from each river

segment were compiled and applied to each ditch in the segment. Based on ditch length, a percent of

diverted water was applied to each ditch. Based on diversion information and length of ditches within

the water balance region (167 miles), total annual ditch flow in the region is estimated at approximately

48,600 ac-ft/yr.

Total ditch loss estimates were evaluated based on a review of the literature. Seven ditch loss

investigations were reviewed within western North America, including studies in Montana, Texas,

California, Oklahoma, Wyoming, and Alberta (PBS&J 2008; Montana Department of Natural Resources

and Conservation (DNRC) 2003; Leigh & Fipps 2002; Quinn et al. 1989; Nofziger 1979; Nelson

Engineering 2004; Iqbal et al. 2002). Four of these studies allowed for estimation of seepage loss in acre-ft/yr per mile of ditch; two studies allowed for estimation of seepage as a percent of total flow per mile

of ditch; and one study allowed for estimation of seepage as a volume per ditch area per day ( Table

22). Seepage rates from each study were applied to lengths and/or areas of ditches in the water balance

region, resulting in estimated ditch loss volumes within the study area (Table 22).

The average seepage rate from the Iqbal et al. (2002) study (0.07 cubic feet per square foot per day

(ft3/ft2/day)) was applied to the average 137-day irrigation season for the Green River Basin as





documented in AECOM (2009). Since the total ditch loss estimate from the PBS&J (2008) study yielded

a value greater than the estimated total annual flow in the ditches (48,600 ac-ft/yr), this estimate was

eliminated from the range of feasible values. Minimum, maximum and average losses for total ditch

length based on loss estimates from these six studies results in ditch loss estimates ranging from

approximately 1,300 to 43,100 ac-ft/yr, with an average estimate of 16,100 ac-ft/yr (Appendix F).

7.8.2.4 Groundwater Discharge to Rivers and Streams (Base Flow)

Streams and rivers in the water balance region likely have gaining and losing reaches. Where streams

flow from high elevations with significant precipitation across alluvial fans or terrace deposits, surface

water loss may occur as it infiltrates into the coarse-grained unconsolidated deposits. However, in the

valley floor along the major rivers, surface water gain is expected where local and regional groundwater

system discharge to the water bodies. Base flows (or net gains) for seven streams and rivers were

estimated, including: Green River, New Fork River, East Fork River, Big Sandy River; Pine Creek, Pole

Creek, and Boulder Creek. Synoptic flow measurements were conducted along the New Fork River and

its tributaries on November 5-6, 2009 (Table 14 and Figure 6). Flow data for streams and rivers that

were not part of the synoptic survey were obtained from the National Water Information System(USGS 2011). If available, flow data from November 5-6, 2009 were used for streams not gaged as part

of the synoptic study; otherwise the average November flow rate was used.

For each stream, discharge data from the upstream location, along with any tributary flow, was

subtracted from the downstream location. The difference in discharge was then divided by the

catchment area between gaging stations minus any tributary catchment area, resulting in a base flow per

catchment area ratio for each stream. This ratio was then multiplied by the catchment area within the

water balance region for each stream to obtain the estimated base flow (Table 23). Boulder Creek has

a net loss across the model region, likely losing water released from Boulder Lake into the glacial and

alluvial fan deposits that underlie the creek. Estimated base flow contribution to streams and rivers

within the model domain ranges from 160,981 to 241,472 ac-ft/yr, with an average of approximately201,200 ac-ft/yr (Appendix F).

7.8.2.5 Groundwater Underflow out of Region

Groundwater underflow out of the water balance region was estimated as described Section 7.8.1.3.

Using minimum and maximum hydraulic conductivity values for the HSUs, underflow out of the PAPA

region ranges from 4,400 to 34,400 ac-ft/yr, with an average of approximately 19,400 ac-ft/yr

(Appendix F).

7.8.2.6 Groundwater Pumped for Consumptive Use

Pumped groundwater makes up a minor component of the groundwater balance as described above

(Section 7.8.1.6), with an average annual consumptive use of approximately 1,300 ac-ft/yr, comprised

of the following: irrigation = 595 ac-ft/yr; stock use = 88 ac-ft/yr; domestic/other = 22 ac-ft/yr; and

industrial supply = 590 ac-ft/yr (Appendix F).





7.8.2.7 Evapotranspiration from Groundwater

Evapotranspiration from groundwater was estimated by applying mean potential ET to the area covered

by wetlands within the model region. Wyoming’s mean annual potential ET in the Sublette County area

ranges from about 43 to 48 centimeters (17 to 19 inches; Marston 1990). Based on this information, a

range of potential ET values (15 to 20 inches) was applied to the area of wetlands, which was derived

from Wyoming’s wetland geodatabase (U.S. Fish and Wildlife Service 2009). A range of wetland areas

(33,089 to 35,425 acres) was assessed by including and removing ponds and river areas.

Evapotranspiration directly from groundwater accounts for between 41,361 and 59,040 ac-ft/yr, with an

average of approximately 50,200 ac-ft/yr.

7.8.3 Summary – Groundwater Balance

Table 21 lists eight key components of the steady-state groundwater balance for the region

encompassing the PAPA (Figures 26 and 27). The average total inflow and total outflow are within 7

percent of each other, with the difference being a result of an inherent range of error associated with

the estimates (Appendix F).

There are several important observations from the groundwater balance:

The two greatest inflow and outflow components of the water balance are:

o Underflow In (groundwater entering the model, 87 percent of inflow), and

o Discharge to Rivers (groundwater discharging to rivers, 74 percent of outflow).

Total estimated volume of groundwater discharging to rivers is 91 percent of the total volume

of groundwater entering the water balance region.

The volume of groundwater exiting the water balance region as underflow, is about 9 percent of

the volume of groundwater entering the region.

In the water balance region, groundwater recharge by precipitation and by infiltration of

irrigation water is approximately the same as groundwater recharge via irrigation ditch losses,

indicating that irrigation ditch loss is a significant component of groundwater recharge in the

PAPA.

Of the estimated 375,000 ac-ft/yr of precipitation falling within the water balance region, about 3

percent recharges the groundwater system; the remaining precipitation is subject to runoff and

evapotranspiration.

Groundwater outflow by evapotranspiration is estimated to exceed the combined amount

removed from the system by pumping and groundwater underflow. The estimated evapotranspiration outflow is greater than the volume added to the groundwater

system by precipitation, irrigation recharge, and ditch loss.

The smallest component of the groundwater balance is pumping from wells, resulting in less

than one-half percent of total outflow.

Groundwater recharge by precipitation is more than seven times that withdrawn by

consumptive uses (pumping).





7.9 Conceptual Model

Our current understanding of the hydrogeologic system at the PAPA is based on findings from this

Hydrogeologic Data Gaps Investigation and review of existing hydrogeologic data and literature. The

hydrogeologic conceptual model was developed by synthesizing available precipitation, geology,

hydrology, hydrogeology, and water use data for the PAPA. This conceptual model, in turn, forms the

basis for the numerical flow model.

The hydrogeologic conceptual model is shown on Figure 32, viewed to the northeast up the New Fork

River, from the western border of the PAPA. Shown on the model diagram are components of the

hydrologic and groundwater balances, topography and geology, surface water features, and typical wells.

Beneath the vast majority of the PAPA is the Tertiary-age Wasatch Formation, consisting primarily of

fluvially-deposited sandstones, representing channel deposits, and shale/siltstone representing overbank

deposits. About one-third of the Wasatch Formation in the study area consists of sandstones, with an

average thickness of about 18 feet. About two-thirds of the Wasatch Formation consists of

siltstone/shale with an average thickness of 33 feet. Sandstone and siltstone/shale are interbedded,laterally discontinuous on a scale of 1,000 feet, and vertical discontinuity can be on the order of 5 feet.

Two other lithologic units are located in the PAPA, including alluvial deposits of sand and gravel present

in stream valleys with depths typically less than 100 feet, and a veneer of terrace gravel over the Mesa.

Wasatch Formation sandstones, alluvium along the surface water courses, and glacial deposits draining

the Wind River Mountains are the major conduits for groundwater flow. Two hydrostratigraphic units

are defined for the PAPA, including an Alluvial HSU in the valleys of the principal rivers/streams; and the

Wasatch HSU (bedrock).

Groundwater in the PAPA generally flows west and south from the mountains and foothills toward the

Green River below the mouth of the New Fork River and into the center of the Green River Basin.Groundwater in the shallow portion of the Wasatch Formation over much of the PAPA migrates

vertically down to the underlying deeper Wasatch Formation In places, groundwater in sandstones of

the shallow portion of the Wasatch HSU is perched. Groundwater in the saturated Wasatch HSU also

preferentially flows through higher permeability sandstone units. Although not observed during the

completion of this investigation, groundwater will flow preferentially along bedding planes and

joints/fractures.

The lower New Fork River in the center of the PAPA is the major point of discharge for both the

Wasatch HSU and Alluvial HSU groundwater systems. South of this zone, groundwater flow paths are

west-southwest toward the center of the Green River Basin. Vertical groundwater gradients measured

in clustered wells of different depths support both the downward movement of groundwater in theWasatch HSU and vertically upward groundwater movement along the New Fork River below the

confluence of the East Fork River.

The Alluvial HSU is connected to the Wasatch HSU, receiving and transmitting water down valley and

into the New Fork River in the central PAPA. Vertical gradients in alluvium in the upper New Fork River

valley vary seasonally, but are upward most of the year. Artesian groundwater conditions in the central





portion of the PAPA cause Wasatch HSU groundwater to discharge into alluvium and the New Fork

River.

Estimated groundwater velocity in alluvium is 30 times greater than groundwater movement in Wasatch

Formation sandstones. Given hydraulic property data based on aquifer tests in 12 study wells and

literature values for effective porosity, it may take groundwater 100 days to travel in alluvium the samedistance that it would take 10 years in a sandstone unit of the Wasatch Formation.

Groundwater enters and exits the PAPA study area in various ways. Figure 32 shows eight

groundwater balance components, four each for inflow and outflow. Most groundwater entering the

region is mountain front recharge that enters the area as underflow, while most groundwater leaving the

region occurs as groundwater discharge to the New Fork River. Only about 3 percent of precipitation

that falls within the PAPA recharges the groundwater system. Other recharge components are

infiltration of irrigation water and leakage from irrigation ditches. Groundwater is removed from the

system by evapotranspiration from wetlands and riparian phreatophytes. Only a relatively small amount

of groundwater (less than one-half percent of total outflow and seven times less than precipitation

recharge) is consumed by pumping (stock wells, domestic wells, industrial wells).

The hydrogeologic conceptual model above describes groundwater occurrence, movement, and balance

for the PAPA. It will support the companion investigation into the sources of low-level petroleum

hydrocarbon compounds (LLPHC) detected in some groundwater samples, and be the basis for the

project’s numerical groundwater model. Finally, this hydrogeologic conceptual model will be used to

support BDE and Operator decisions regarding the appropriate design of a long-term water resources

monitoring program for the PAPA.





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