preliminary conceptual site model report · 9001 lander avenue hilmar, california hilmar cheese...

Preliminary Conceptual Site

Model ReportHilmar Cheese Company

Hilmar, California

October 1, 2008

(Revised)

Prepared for:

Prepared by:

Mr.

9001 Lander Avenue

Hilmar, California

Hilmar Cheese Company

Burton Fleischer, Environmental Director

4231 Pacific Street, Suite 1

Rocklin, California 95677

J A C O B S O N J A M E S

& a s s o c i a t e s , i n c

HILMAR

PRELIMINARY CONCEPTUAL SITE MODEL REPORT Hilmar Cheese Company - October 1, 2008

ii

TABLE OF CONTENTS PAGE

LIST OF FIGURES ...................................................................................................................................................... iv LIST OF TABLES ........................................................................................................................................................ iv LIST OF APPENDICES ................................................................................................................................................ v LIST OF ACRONYMS AND ABBREVIATIONS ............................................................................................................ vi

1.0 INTRODUCTION ................................................................................................................ 1‐1

2.0 BACKGROUND .................................................................................................................. 2‐1 2.1 SITE LOCATION AND LAYOUT ............................................................................................... 2‐1 2.2 OPERATIONS ..................................................................................................................... 2‐1 2.3 LAND USE ........................................................................................................................ 2‐4

3.0 ENVIRONMENTAL SETTING .............................................................................................. 3‐1 3.1 REGIONAL SETTING ............................................................................................................ 3‐1 3.2 WATER RESOURCES ........................................................................................................... 3‐3 3.3 SITE SETTING .................................................................................................................... 3‐8 3.3.1 SITE LITHOLOGIES AND HYDROGEOLOGIC UNITS ............................................................... 3‐8 3.3.2 HYDROGEOLOGIC CONDITIONS AND GROUNDWATER FLOW PATTERNS ............................. 3‐11

3.4 AMBIENT WATER QUALITY .............................................................................................. 3‐15 3.4.1 UPPER AQUIFER AMBIENT WATER QUALITY CONDITIONS .............................................. 3‐15 3.4.2 LOWER AQUIFER AMBIENT WATER QUALITY CONDITIONS .............................................. 3‐16

3.5 ENVIRONMENTAL SETTING DATA GAPS SUMMARY .............................................................. 3‐16

4.0 POTENTIAL SOURCES, MEDIA AND CONSTITUENTS OF CONCERN ................................... 4‐1 4.1 POTENTIAL SOURCES .......................................................................................................... 4‐1 4.1.1 POTENTIAL ONSITE SOURCE AREAS ................................................................................ 4‐1 4.1.2 POTENTIAL OFFSITE SOURCE AREAS ............................................................................... 4‐2

4.2 MEDIA AND POTENTIAL CONSTITUENTS OF CONCERN ............................................................ 4‐2 4.2.1 MEDIA OF CONCERN ................................................................................................... 4‐2 4.2.2 POTENTIAL CONSTITUENTS OF CONCERN ........................................................................ 4‐2

4.3 POTENTIAL SOURCES, MEDIA AND CONSTITUENTS OF CONCERN DATA GAPS SUMMARY .............. 4‐4

5.0 MIGRATION PATHWAYS, CONTAMINANT FATE AND TRANSPORT .................................. 5‐1 5.1 EXTENT OF THE TOTAL DISSOLVED SOLIDS PLUME .................................................................. 5‐1 5.2 PLUME STABILITY .............................................................................................................. 5‐5 5.3 GEOCHEMICAL CONCEPTUAL MODEL ................................................................................... 5‐6 5.4 MIGRATION PATHWAYS, CONTAMINANT FATE AND TRANSPORT DATA GAPS SUMMARY .............. 5‐7


iii

6.0 POTENTIAL RECEPTORS AND WATER QUALITY RESOURCES ............................................ 6‐1 6.1 POTENTIAL RECEPTORS TO GROUNDWATER EXPOSURES .......................................................... 6‐1 6.2 POTENTIAL RECEPTORS TO SURFACE WATER EXPOSURES ......................................................... 6‐1 6.3 POTENTIAL RECEPTORS AND WATER RESOURCES DATA GAPS................................................... 6‐1

7.0 PRELIMINARY CSM SUMMARY ........................................................................................ 7‐1 7.1 ENVIRONMENTAL SETTING .................................................................................................. 7‐1 7.2 POTENTIAL ONSITE AND OFFSITE SOURCES ............................................................................ 7‐1 7.3 MEDIA AND POTENTIAL CONSTITUENTS OF CONCERN ............................................................. 7‐1 7.4 MIGRATIONS PATHWAYS/CONTAMINANT FATE AND TRANSPORT ............................................. 7‐3 7.5 POTENTIAL RECEPTORS ....................................................................................................... 7‐3

8.0 DATA GAPS SUMMARY .................................................................................................... 8‐1 8.1 ENVIRONMENTAL SETTING DATA GAPS SUMMARY ................................................................. 8‐1 8.2 POTENTIAL SOURCES, MEDIA AND PCOC DATA GAPS SUMMARY ............................................. 8‐2 8.3 MIGRATION PATHWAYS, CONTAMINANT FATE AND TRANSPORT DATA GAPS SUMMARY .............. 8‐2 8.4 POTENTIAL RECEPTORS AND WATER RESOURCES DATA GAPS................................................... 8‐3

9.0 REFERENCES ..................................................................................................................... 9‐1


iv

LIST OF TABLES

Table 2.1 Treated Wastewater Analytical Summary

Table 4.1 Statistical Summary of Groundwater Analytical Results for the Upper Aquifer (A‐ and B‐Zones)

Table 4.2 Statistical Summary of Groundwater Analytical Results for the Lower Aquifer (C‐ and D‐Zones)

LIST OF FIGURES

Figure 1.1 Site Location Map

Figure 2.1 Site Plan and Cross Section Transects

Figure 2.2 Wastewater and Primary Land Use Timeline

Figure 2.3 Land Use Classifications

Figure 3.1 Physiographic Setting

Figure 3.2 Map of Geologic Units

Figure 3.3 Measured Groundwater Elevations in Intermediate Depth Monitoring Wells – Spring 2005

Figure 3.4 San Joaquin Valley Groundwater Basin

Figure 3.5 Regional Well Locations

Figure 3.6 Supply Well Locations

Figure 3.7 Well Construction Details for Private Wells

Figure 3.8 Geological Cross Section A‐A’

Figure 3.9 Geological Cross Section B‐B’

Figure 3.10 Groundwater Elevation Versus Time (MW‐12 and MW‐19)

Figure 3.11 Groundwater Elevation Versus Time (MW‐22 and MW‐23)

Figure 3.12 Potentiometric Surface Map– Fall (November 2007)

Figure 3.13 Potentiometric Surface Map – Winter (February 2008)

Figure 3.14 Potentiometric Surface Map – Spring (May 2008)

Figure 3.15 Potentiometric Surface Map – Summer (August 2008)

Figure 4.1 Potential Sources and Land Use

Figure 5.1 TDS Detected in Groundwater ‐ Upper A‐Zone


v

LIST OF FIGURES Figure 5.2 TDS Detected in Grab Groundwater ‐ Lower A‐Zone

Figure 5.3 TDS Detected in Grab Groundwater ‐ B‐Zone

Figure 5.4 TDS Detected in Grab Groundwater ‐ C‐Zone

Figure 5.5 TDS Detected in Grab Groundwater ‐ D‐Zone

Figure 5.6 Vertical Extent of TDS in Cross Section A‐A’

Figure 5.7 Vertical Extent of TDS in Cross Section B‐B’

Figure 5.8 Geochemical Model

Figure 6.1 Supply Well Findings

Figure 7.1 Preliminary Conceptual Site Model Schematic

LIST OF APPENDICES

Appendix A Time Versus Concentration Graphs for TDS and Chloride


vi

LIST OF ACRONYMS

AGR Agricultural Supply

CRWQCB Central Valley Regional Water Quality Control Board

CSM Conceptual Site Model

DWR Department of Water Resources

Fm Formation

ft‐bgs Feet below ground surface

ft msl Feet above mean sea level

GAMA California Groundwater Ambient Monitoring and Assessment

HCC Hilmar Cheese Company

IND Industrial Service Supply

K Potassium

mg/L Milligrams per liter

mgd Million gallons per day

MUN Municipal and Domestic Supply

Na Sodium

PCOC Potential Constituents of Concern

PRO Industrial Process Supply

RO Reverse osmosis

Site Hilmar Cheese Company Facility and Associated Primary Lands

TDS Total Dissolved Solids

USGS United States Geological Survey

UTL Upper Tolerance Level

WDR Waste discharge Requirement


1-1

1.0 INTRODUCTION

This Preliminary Conceptual Site Model (CSM) Report has been prepared for the Hilmar Cheese Company

(HCC) facility and associated Primary Lands (the Site) located north of the town of Hilmar in Merced County,

California as shown on Figure 1.1. The objectives of this report are: (1) to present the current preliminary

CSM based on the data collected pursuant to Cleanup and Abatement Order No. R5‐2004‐0722 (the Order)

under the direction of the Central Valley Regional Water Quality Control Board (CVRWQCB); and, (2)

present the identified data gaps for the CSM. The CSM presented herein, to be refined through future data

collection efforts, has been developed to include descriptions of the environmental setting, potential

sources, media and constituents of concern, migration pathways/contaminant fate and transport and

potential receptors.

FIGURE 1.1 SITE LOCATION MAP


2-1

FIGURE 2.1 SITE PLAN AND CROSS SECTION TRANSECTS

2.0 BACKGROUND

This section identifies the Site location and operational history and land use.

2.1 SITE LOCATION AND LAYOUT

The Site is located at 9001 Lander Avenue in Hilmar, Merced County, California. The facility was constructed

in 1985 and currently comprises approximately 73 acres, including the HCC processing plant and associated

buildings. The Site is comprised of the facility and the adjacent Primary Lands as shown on Figure 2.1.

2.2 OPERATIONS

Beginning in 1985, facility wastewater was discharged to a holding/percolation pond (B&C, 2004a).

Application of waste water to the Primary Lands began in 1989. The Primary Lands currently receive only

treated wastewater from the HCC facility, which is regulated under Waste Discharge Requirements (WDR)

Order No. 97‐206. Highly treated

wastewaters have been applied to

nearby Secondary Lands since 2001,

also in accordance with WDR Order

No. 97‐206.

The wastewater from the HCC

facility discharged to Primary Lands

is characterized as an organic rich,

reduced nitrogen, dissolved solids

laden byproduct of the HCC

processing operation. Table 2.1

provides a summary of the

wastewater characteristics from

2001 to 2008.


2-2

TABLE 2.1 TREATED WASTEWATER ANALYTICAL SUMMARY

1,2

Compound Units 2001 2002 2003 2004 2005 2006 2007 2008 8‐yr

Average Alkalinity, bicarbonate (as CaCO3) mg/L 388 332 389 227 1231 1500 1448 1455 871.25

Ammonia as Nitrogen mg/L 37 23 29 25 54 62 107 76 51.63

BOD mg/L 5334 3879 4289 4086 178 645 519 205 2391.88

Calcium mg/L 120 134 126 70 120 96 89 57 101.50

Chloride mg/L 486 197 241 320 388 288 290 300 313.75

COD mg/L 9360 6728 6518 6968 623 2086 1572 896 4343.88

EC umhos/cm 3916 2495 2768 2720 3420 3506 3561 3610 3249.50

Iron mg/L 1 2.5 2.6 1.1 16.83 11.61 3.3 2.4 5.17

Magnesium mg/L 25 19 15 14 12.09 15 14 17 16.39

Nitrate‐nitrogen mg/L 82 101 94 40 1.3 4 1 3 40.79

pH unit less 6.5 6.7 6.7 5.7 7.9 8.1 8 8 7.20

Phosphorus, total mg/L 88 73 78 89 16 64 48 51 63.38

Potassium mg/L 253 164 223 358 188 169 165 179 212.38

Sodium mg/L 679 346 384 304 499 618 586 673 511.13

Total dissolved solids mg/L 6333 4596 4885 4836 2074 2248 2100 2217 3661.13

Sulfate mg/L 51 30 22 25 78 32 39 39 39.50

Sulfide mg/L 0.29 0.18 0.13 0.13 9.36 4.2 2.7 2.05 2.38

TKN mg/L 189 119 136 146 93 207 218 121 153.63 Notes:

mg/L = miligrams per liter

umhos/cm = micromhos per centimeter 1‐ Treated wastewater applied to Primary Lands. 2 ‐ Brown and Caldwell, 2004a. HCC, Monthly Water Quality Monitoring Reports. January ‐ December, 2005.

KennedyJenks, 2008.

The quality and volume of wastewater application to the Primary Lands has varied over time, as have the

size and arrangement of the Primary Lands. Figure 2.2 provides a timeline depicting the changes to the

wastewater quality and volumes, and the changes to the Primary Lands, based on information provided in

project‐related documents (B&C, 2004a; B&C, 2004b; B&C, 2005; KJ, 2008). As shown on Figure 2.2,

wastewater was initially applied to Primary Lands beginning in 1989. Since 1997, various modifications in

the wastewater treatment process have been implemented resulting in improvements to the quality of the

wastewaters applied to the Primary Lands. As shown in Figure 2.2, total dissolved solid (TDS)

concentrations have been reduced from approximately 6,330 mg/L in 2001 to the current range of 2,000 to

2,005 mg/L. Beginning in 2001, highly treated wastewater treated by reverse osmosis (RO) was used for

irrigation of crops at off‐Site areas referred to as the Secondary Lands.


2-3

FIGURE 2.2 WASTEWATER AND PRIMARY LAND USE TIMELINE


2-4

2.3 LAND USE

As shown on Figure 2.3, and as documented in the Phase II report (JJ&A, 2008a), the land use in the vicinity

of the Site is predominantly agricultural. The indicated land use shown within the Site boundaries on Figure

2.3 includes agricultural, urban, the HCC plant and water, which includes the RO permeate and stormwater

retention ponds.

FIGURE 2.3 LAND USE CLASSIFICATION


3-1

3.0 ENVIRONMENTAL SETTING

The environmental setting discussed in this section includes the regional setting, hydrogeology,

groundwater resources and ambient groundwater conditions.

3.1 REGIONAL SETTING

The Site is located in the northern portion of the San Joaquin Valley at an elevation of approximately 90 feet

above mean sea level. The San Joaquin Valley gradually slopes westward from the Sierra Nevada Mountain

Range to the San Joaquin River. As shown on Figure 3.1, the Site is located on a low alluvial plain

approximately 4 miles north of the Merced River and 8 miles east of the San Joaquin River.

The Site is situated on the floor of the San Joaquin Valley in an area underlain predominantly by

unconsolidated fluvial and lacustrine deposits. As shown on Figure 3.2, the Site is located in an area

mapped by the United States Geological Survey (Burrow, et al, 2004) as the Modesto Formation (Fm). The

Modesto Fm consists of alluvial sediments including unconfined to semi‐confined groundwater in the

vicinity of the Site (Burrow, et al, 2004). The primary source of present‐day recharge to the Modesto Fm in

the vicinity of the Site is irrigation water (Burrow, et al, 2004). Irrigation practices combined with extensive

groundwater extraction in the area results in a significant downward vertical gradient in the region (Burrow,

et al, 2004) and in the vicinity of the Site as measured in Site specific well pairs as discussed in Section 3.3.2.

FIGURE 3.1 PHYSIOGRAPHIC SETTING


3-2

FIGURE 3.2 MAP OF GEOLOGIC UNITS

The aquifer system present in the Modesto Fm is separated from the deeper aquifer system of the Turlock

Lake Fm. by the Corcoran Clay. The Corcoran Clay is a fine‐grained lacustrine deposit in the upper portion of

the Turlock Lake Formation estimated to be up to 50‐feet thick in the vicinity of the Site. The Corcoran Clay,

also known locally as the “Blue Clay”, is laterally extensive and reported to significantly impede the vertical

movement of groundwater. The Corcoran Clay has been observed beneath the Site at depths of 110 to 160

feet below ground surface (ft‐bgs) (JJ&A, 2008a). Figure 3.2 indicates the estimated lateral extent of the

Corcoran Clay in the region. The Corcoran Clay is the defining hydrogeologic feature at the Site separating

the aquifer systems into the Upper Aquifer (above the Corcoran Clay) and the Lower Aquifer (below the

Corcoran Clay).


3-3

Regionally, groundwater flows west and southwest in the deeper aquifers as shown on Figure 3.3; although

extensive groundwater extraction results in a gradient reversal to the east as noted on the figure. A west to

southwest regional groundwater gradient is also reported for the shallow aquifer systems (Burrow, et al,

2004).

3.2 WATER RESOURCES

The Site is located in the San Joaquin Valley Groundwater Basin, Turlock Sub‐Basin as shown on Figure 3.4.

The Turlock Sub‐Basin is bounded to the north, west and south by the Tuolumne, San Joaquin and Merced

Rivers, respectively. The beneficial uses of the groundwater within the Turlock Sub‐Basin and underlying

the Site are identified in the Water Quality Control Plan (the “Basin Plan”, [CVRWQCB, 2007]) as follows:

Municipal and Domestic Supply (MUN) – Water supply for community, military, or individual use;

Agricultural Supply (AGR) ‐ Uses of water for farming, horticulture, or ranching including, but not

limited to, irrigation (including leaching of salts), stock watering, or support of vegetation for range

grazing;

FIGURE 3.3 MEASURED GROUNDWATER ELEVATIONS IN INTERMEDIATE DEPTH MONITORING WELLS ‐ SPRING 2005


3-4

FIGURE 3.4 SAN JOAQUIN VALLEY GROUNDWATER BASIN

Industrial Service Supply (IND) ‐ Uses of water for industrial activities that do not depend primarily

on water quality including, but not limited to, mining, cooling water supply, hydraulic conveyance,

gravel washing, fire protection, or oil well re‐pressurization; and

Industrial Process Supply (PRO) ‐ Uses of water for industrial activities that depend primarily on

water quality.

Groundwater use is considered heavy in the vicinity of the Site for domestic, irrigation and industrial process

supplies (Burrow, et al, 2004). Figure 3.5 depicts the locations and density of supply wells in the region

based on well logs filed with the Department of Water Resources (DWR). This figure also identifies the wells

used in the California Groundwater Ambient Monitoring and Assessment (GAMA) program, implemented

by the United States Geological Survey (USGS) in cooperation with the California State Water Resources

Control Board (Landon, M.K., and Belitz, Kenneth, 2008). Data collected through this program may be

useful in evaluating ambient conditions in the Lower Aquifer is discussed in Section 3.4.2.


3-5

FIGURE 3.5 REGIONAL WELL LOCATIONS

Figure 3.6 identifies the locations of supply wells at and in the immediate vicinity of the Site, based on DWR

records, prior Site work (B&C, 2005) and field reconnaissance by JJ&A (JJ&A, 2008c,d). Figure 3.7 provides

the well construction details for the supply wells identified on Figure 3.6. As shown on Figure 3.7, supply

wells have been installed to extract groundwater from the Upper Aquifer (above the Corcoran Clay) and the

Lower Aquifer (below the Corcoran Clay). Several of the supply wells have been constructed such that their

screened intervals and/or their filter packs connect the discreet aquifer systems across the Corcoran Clay.

These wells present potential pathways for groundwater to migrate between discreet aquifers, as identified

on Figure 3.7.

As shown on Figure 3.2, there are no natural surface water bodies such as creeks, streams, rivers or lakes

located proximal to the Site. Based on this, there are no surface water bodies affected by the Site discharge

as further discussed in Section 4.0.


3-6

FIGURE 3.6 SUPPLY WELL LOCATIONS


3-7

FIGURE 3.7 WELL CONSTRUCTION DETAILS FOR PRIVATE WELLS


3-8

3.3 SITE SETTING

The following sections present the Site‐specific data collected and the resultant interpretations.

3.3.1 SITE LITHOLOGIES AND HYDROGEOLOGIC UNITS

The subsurface is comprised of several defined lithological units as illustrated in the two cross sections

prepared for the northeast‐southwest transect (cross section A‐A’) and the east‐west transect (cross section

B‐B’) provided as Figures 3.8 and 3.9 (see Figure 2.1 for transect locations). The units have been divided

based on the various lithologies encountered, their respective lateral continuity and groundwater

occurrence. The eight (8) lithological units defined for the Site are, in order of increasing depth below

grade: (1) Vadose zone; (2) A‐Zone; (3) A‐Aquitard; (4) B‐Zone; (5) B‐Aquitard; (6) C‐Zone; (7) C‐Aquitard;

and, (8) D‐Zone. The B‐Aquitard is a laterally continuous clay unit encountered at an approximate depth

range of 110 to 160 ft‐bgs in the vicinity of the Site. This unit varies from ~ 25‐ft up to 50‐ft thick across the

Site and appears to dip slightly to the south and west. This unit correlates with, and is interpreted to be

analogous to, the Corcoran Clay. The units beneath the Site appear to correlate with the Modesto and

Turlock Lake Formations, noted in studies of the USGS (Burrow, et al, 2004) and the California DWR (DWR,

2003).


3-9

FIGURE 3.8 GEOLOGICAL CROSS SECTION A‐A' (1) (Data Source: JJ&A, 2008a)

(1) Supply well log information shown for information purposes only; not used in definition of lithologic units.


3-10

FIGURE 3.9 GEOLOGICAL CROSS SECTION B‐B' (1) (Data Source: JJ&A, 2008a)

(1) Supply well log information shown for information purposes only; not used in definition of lithologic units.


3-11

The A‐ and B‐Zones comprise the Upper Aquifer over the Corcoran Clay. The C‐ and D‐Zones comprise the

Lower Aquifer to the maximum depth of 250 ft‐bgs explored through the Phase II work.

3.3.2 HYDROGEOLOGIC CONDITIONS AND GROUNDWATER FLOW PATTERNS

A review of water level data

from drill logs and routine

groundwater level

monitoring events indicates

groundwater in the upper

25 feet exists under

unconfined (i.e., water

table) conditions.

Semi‐confined conditions

exist in the lower A‐Zone

due to discontinuous lenses

of relatively fine‐grained

lithologies that locally

restrict upward flow of

groundwater.

Monitoring well pairs installed in the Upper A‐Zone and Lower A‐Zone, (MW‐12 and MW‐19) and in the B‐

Zone and C‐Zone, (MW‐22 and MW‐23) primarily exhibit down‐ward vertical gradients as shown on Figures

3.10 and 3.11,

respectively;

although there was

frequently an

upward gradient at

the MW‐12 and

MW‐19 location

prior to 2003. The

presence of

downward gradients

is consistent with

the regional data

discussed in Section

3.1.

FIGURE 3.10 GROUNDWATER ELEVATION VERSUS TIME (MW‐12 AND MW‐19) (Data from monthly HCC monitoring events)

FIGURE 3.11 GROUNDWATER ELEVATION VERSUS TIME (MW‐22 AND MW‐23) (Data collected from pressure transducers installed as part of the extended water elevation study in progress)


3-12

Lateral groundwater flow in the Upper Aquifer A‐Zone in the immediate vicinity of the Site is affected by the

surface application of treated wastewater on‐Site and irrigation practices on adjacent properties. The

lateral groundwater flow direction and gradient for November 2007, February, May and August 2008 are

presented as Figures 3.12 through 3.15. These figures are intended to represent typical fall, winter, spring

and summer conditions in the vicinity of the Site. A review of these figures indicate that groundwater

mounding is consistently noted in the area south of the RO permeate and stormwater retention ponds (i.e.,

MW‐1 area), extending into the Primary Lands to the west. Groundwater flow directions are generally to

the west and southwest; however, there may be localized groundwater mounding that results in localized

gradient reversals (e.g., northerly flow directions occasionally noted in the northeast corner of the facility as

shown on Figure 3.12).

An extended water level survey is in progress to better understand local land use on shallow groundwater

flow. The survey is planned to collect water level measurements during three 30‐day periods representing

summer, fall and winter. The summer data was collected in July through August 2008 and the fall and

winter events are currently planned for October 2008 and February 2009.

FIGURE 3.12 POTENTIOMETRIC SURFACE MAP– FALL (NOVEMBER 2007)


3-13

FIGURE 3.13 POTENTIOMETRIC SURFACE MAP – WINTER (FEBRUARY 2008)

FIGURE 3.14 POTENTIOMETRIC SURFACE MAP – SPRING (MAY 2008)


3-14

Site‐specific aquifer testing has not been conducted to define aquifer parameters for the Upper or Lower

Aquifer beneath the Site. This data is necessary to support estimates of ground flow rates and well yields.

Additionally, laboratory physical and geochemical testing data are needed to quantify aquifer parameters

relevant to determining the homogeneity of the aquifers and/or aquitards, grain size distributions for design

of extraction wells and estimates of fate and transport rates for specific constituents.

FIGURE 3.15 POTENTIOMETRIC SURFACE MAP – SUMMER (AUGUST 2008)


3-15

3.4 AMBIENT WATER QUALITY

The groundwater quality in the vicinity of the Site has been degraded over time by agricultural land use.

The potential constituents of concern (PCOCs) for the Site are essentially the same, or very similar, to those

associated with the agricultural land use and resultant regional water quality degradation. An

understanding of the ambient water quality is therefore necessary to discern HCC groundwater impact from

the regional, non‐HCC groundwater impact.

Ambient conditions are best described by a range of values, which are subject to seasonal and spatial

variations. As such, there is not a single value that can accurately represent an ambient concentration level

for a particular PCOC. The 95% Upper Tolerance Limit (UTL) has been proposed by JJ&A as a means of

evaluating a well result to discern the HCC Site impact, if present, from regional conditions.

3.4.1 UPPER AQUIFER AMBIENT WATER QUALITY CONDITIONS

The 95% UTL was calculated for TDS within the Upper Aquifer (JJ&A, 2008b). A 95% UTL was calculated for

the shallow portion of the Upper Aquifer (i.e., the upper 25 feet of the A‐Zone) and the Upper Aquifer

Supply Well Zone1. The 95% UTL for TDS in the upper A‐Zone and the Upper Aquifer Supply Well Zone was

determined to be 930 mg/L and 760 mg/L, respectively.

Chloride ions do not significantly enter into oxidation/reduction reactions, do not generally form solute

complexes, are not adsorbed on mineral surfaces and are not particularly affected by bio‐chemical reactions

(JJ&A, 2008d). Based on this, chloride may be used as a conservative tracer for HCC groundwater. It is

noted that chloride is also present in groundwater as a result of non‐HCC sources (e.g., dairy operations).

The 95% UTL was calculated for chloride in the upper A‐Zone and the Upper Aquifer Supply Zone and

determined to be 110 mg/L and 54 mg/L, respectively (JJ&A, 2008d).

The data set used to calculate the 95% UTL for TDS and chloride for the Upper A‐Zone (25 foot zone) was

primarily comprised of grab groundwater samples. The data set used to calculate the 95% UTL for TDS and

chloride for the Upper Aquifer Supply Well Zone was limited to existing supply wells.

Monitoring wells for ongoing sample collection and refinement of the ambient data set are appropriate to

confirm ambient levels for the Upper Aquifer for TDS, chloride and other Site PCOCs. The data set and

statistical methodology to represent ambient conditions will continue to be refined through future data

collection and evaluation.

1 The Upper Aquifer Supply Well Zone is defined as the lower portion of the A-Zone and the B-Zone and represents the Upper Aquifer interval that supplies groundwater to local users for domestic, agricultural and industrial purposes.


3-16

3.4.2 LOWER AQUIFER AMBIENT WATER QUALITY CONDITIONS

Ambient conditions have not been determined for the Lower Aquifer underlying the Corcoran Clay. This

represents a data gap in the current CSM. Existing GAMA and supply wells may be suitably constructed

and/or located for use in this effort and will be evaluated as possible ambient data sources for the Lower

Aquifer.

3.5 ENVIRONMENTAL SETTING DATA GAPS SUMMARY

Data gaps relative to the Site environmental setting are summarized as follows.

Geology and Hydrogeology

Site specific hydraulic parameters for the Upper Aquifer have not been established. The Upper

Aquifer contains the majority of the observed impact and is the appropriate aquifer to collect data

for plume migration estimates.

The physical and geochemical parameters for the unconsolidated lithologies in the Upper Aquifer,

Corcoran Clay and Lower Aquifer systems have not been adequately characterized to estimate

PCOC fate and transport.

Characterization of the magnitude and extent of shallow groundwater mounding at the Site; data

relevant to this data gap is being collected through the extended water level survey in progress.

Ambient Water Quality

Upper Aquifer

- Refine data sets and statistical methodologies for calculation of ambient TDS and chloride

levels in the Upper Aquifer.

- Collect and analyze data from ambient sample locations for other Site PCOCs to determine

ambient levels.

Lower Aquifer

- Evaluate potential use of existing groundwater supply and GAMA well locations to estimate

ambient PCOC levels.


4-1

4.0 POTENTIAL SOURCES, MEDIA AND CONSTITUENTS OF CONCERN

Potential sources, media and constituents of concern are discussed in this section.

4.1 POTENTIAL SOURCES

Historical and ongoing agricultural operations have created multiple potential source areas on and in the

vicinity of the Site. Potential on‐Site and off‐Site sources are discussed below.

4.1.1 POTENTIAL ONSITE SOURCE AREAS

The wastewater holding/percolation ponds used for wastewater management prior to the application of

wastewaters to the Primary Lands in 1989 are a potential source area of concern. The location of these

former structures is unknown. The identified Primary Lands (historic and current) represent the primary on‐

Site source area. The current and historical Primary Land layout is indicated on Figure 4.1.

FIGURE 4.1 POTENTIAL SOURCES AND LAND USE


4-2

Wastewater application to the Primary Lands began in 1989 with an average of 0.050 million gallons per day

(mgd). After a peak in 1999 (0.863 mgd), approximately half of the wastewater was diverted through the

RO treatment system resulting in highly treated water discharged via irrigation to Secondary Lands, in

accordance with WDR Order 97‐206.

4.1.2 POTENTIAL OFFSITE SOURCE AREAS

The potential off‐Site sources include dairy/livestock/poultry operations (i.e., waste management related to

confined animal feeding operations), and irrigated row crops and orchards as shown on Figure 4.1. The

identified off‐Site locations represent potential sources of similar PCOCs to groundwater (i.e., non‐HCC

potential sources of impact to off‐Site supply wells and regional water quality).

The potential for discharges (historic and current) from the subject off‐Site source areas to degrade

groundwater quality represent a data gap.

4.2 MEDIA AND POTENTIAL CONSTITUENTS OF CONCERN

The following sections present the potentially affected media and PCOCs.

4.2.1 MEDIA OF CONCERN

Impacted media include soil and groundwater. The soil beneath the Primary Lands is a media of concern as

the wastewater application has likely resulted in elevated concentrations of select PCOCs in soil. In

addition, the attenuation capacity of the soil has been reduced to varying degrees and it no longer has the

ability to effectively remove select PCOCs from the wastewater as it percolates through. The result of this

loss of attenuation capacity is that PCOCs are migrating into and impacting the groundwater. Groundwater

is a media of concern as PCOCs are present in the groundwater system.

4.2.2 POTENTIAL CONSTITUENTS OF CONCERN

Groundwater data has been collected through several investigation events pursuant to the Order. A

statistical summary of the groundwater data collected through the most recent Site investigation event is

provided in Tables 4.1 and 4.2 for the Upper Aquifer and Lower Aquifer, respectively. These tables identify

the current analytical suite of groundwater parameters and include the PCOCs for the Site groundwater.


4-3

TABLE 4.1 STATISTICAL SUMMARY OF GROUNDWATER ANALYTICAL RESULTS FOR THE UPPER AQUIFER (A AND B‐ZONES)

Compound Units Total Number of Samples

Analyzed ‡ Frequency of Detections

Minimum Detection

Maximum Detection

Bicarbonate Alkalinity mg/L 47 97.87% 25 930

Carbonate Alkalinity mg/L 47 14.89% 4.6 100

Hydroxide Alkalinity mg/L 47 2.13% 3.4 3.4

Total Alkalinity mg/L 47 100.00% 25 930

Chloride mg/L 47 100.00% 8 340

Dissolved Arsenic* mg/L 47 68.09% 0.0021 0.06

Dissolved Calcium mg/L 47 100.00% 11 300

Dissolved Iron mg/L 47 27.66% 0.055 8

Dissolved Magnesium mg/L 47 100.00% 2.1 92

Dissolved Manganese mg/L 45 86.67% 0.012 4

Dissolved Potassium mg/L 47 97.87% 2.1 210

Dissolved Sodium mg/L 47 100.00% 11 620

Nitrate‐Nitrogen mg/L 47 95.74% 1.4 110

Total Dissolved Solids mg/L 47 100.00% 260 2400

Sulfate mg/L 47 100.00% 6.2 190

Total Kjeldahl Nitrogen mg/L 47 82.98% 1.8 44

* Arsenic may not be a HCC PCOC. It is noted that elevated concentrations of arsenic may occur naturally in ambient groundwater.

‡ Monitoring wells excluded except MW‐21 and MW‐22.

mg/L = milligrams per liter.


4-4

TABLE 4.2 STATISTICAL SUMMARY OF GROUNDWATER ANALYTICAL RESULTS FOR THE LOWER AQUIFER (C AND D‐ZONES)

Compound Units Total Number of Samples

Analyzed ‡ Frequency of Detections

Minimum Detection

Maximum Detection

Bicarbonate Alkalinity mg/L 13 92.31% 52 170

Carbonate Alkalinity mg/L 13 53.85% 3.2 220

Hydroxide Alkalinity mg/L 13 7.69% 52 52

Total Alkalinity mg/L 13 100.00% 80 380

Chloride mg/L 13 100.00% 88 530

Dissolved Arsenic* mg/L 13 100.00% 0.01 0.15

Dissolved Calcium mg/L 13 100.00% 2.7 81

Dissolved Iron mg/L 13 15.38% 0.064 0.081

Dissolved Magnesium mg/L 13 100.00% 0.83 30

Dissolved Manganese mg/L 12 91.67% 0.045 0.5

Dissolved Potassium mg/L 13 100.00% 3.4 150

Dissolved Sodium mg/L 13 100.00% 81 270

Nitrate‐Nitrogen mg/L 12 16.67% 0.27 0.47

Total Dissolved Solids mg/L 13 100.00% 290 1200

Sulfate mg/L 13 69.23% 4.5 130

Total Kjeldahl Nitrogen mg/L 13 53.85% 1.2 5.3

* Arsenic may not be a HCC PCOC. It is noted that elevated concentrations of arsenic may occur naturally in ambient groundwater.

‡ Monitoring wells excluded except MW‐23.

mg/L = milligrams per liter

4.3 POTENTIAL SOURCES, MEDIA AND CONSTITUENTS OF CONCERN DATA GAPS SUMMARY

Data gaps relevant to potential sources, media and constituents of concern are summarized as follows:

Potential Source Areas

Location of former holding/percolation pond.

Potential for historic and current discharge from off‐Site properties to degrade groundwater quality

with PCOCs similar to HCC’s.

Media

Magnitude of PCOCs in soils underlying the Primary Lands and their potential to contribute PCOCs

to groundwater.


4-5

PCOCs

Comparisons of PCOCs detected in groundwater to ambient levels is necessary to determine which

are HCC COCs.

Ambient levels have only been determined for TDS and chloride in the shallow A‐Zone and the

Upper Aquifer Supply Zone. These ambient levels need to be further refined.

Additional ambient levels need to be established for other PCOCs.

Ambient levels for all PCOCs need to be determined for the aquifer system beneath the Corcoran

Clay


5-1

5.0 MIGRATION PATHWAYS, CONTAMINANT FATE AND TRANSPORT

The following sections discuss the known, or suspected, migration routes and pathways and the fate and

transport PCOCs at the Site.

5.1 EXTENT OF THE TOTAL DISSOLVED SOLIDS PLUME

Total dissolved solids (TDS) is a comprehensive measurement of dissolved ionic species in water. This

measurement is useful in evaluating the magnitude and extent of impact in groundwater due to HCC

operations. The lateral extent of HCC related TDS impact, defined to date, for the Upper A‐Zone, Lower A‐

Zone and B‐Zone (all of which are above the Corcoran Clay); and the C‐Zone and D‐Zone (which are below

the Corcoran Clay) are provided in Figures 5.1 through 5.5. Figures 5.6 and 5.7 provide cross‐sectional

representations of the vertical extent of TDS along the A‐A’ and B‐B’ transects shown on Figure 2.1.

A review of the subject figures indicate that the impact to groundwater quality by TDS is concentrated

within in the A‐Zone. Lower TDS concentrations are encountered in the underlying saturated zones. The

locations of elevated TDS detections (i.e., > 1,000 mg/L) in deeper saturated zones do not always show a

clear correlation with samples collected at shallower depths at the same location. It is unclear if these

elevated detections below the Corcoran Clay (e.g., Figure 5.5 [HP‐05@228’] and Figure 5.4 [HP‐03@190’])

are solely the result of preferential migration through improperly constructed supply wells or also a result of

natural plume dispersion and diffusion through the Corcoran Clay.


5-2

FIGURE 5.1 TDS DETECTED IN GROUNDWATER ‐ UPPER A‐ZONE(Data Source: JJ&A, 2008a)

FIGURE 5.2 TDS DETECTED IN GROUNDWATER ‐ LOWER A‐ZONE(Data Source: JJ&A, 2008a)


5-3

FIGURE 5.3 TDS DETECTED IN GROUNDWATER ‐ B‐ZONE(Data Source: JJ&A, 2008a)

FIGURE 5.4 TDS DETECTED IN GROUNDWATER ‐ C‐ZONE(Data Source: JJ&A, 2008a)


5-4

FIGURE 5.5 TDS DETECTED IN GROUNDWATER ‐ D‐ZONE(Data Source: JJ&A, 2008a)

FIGURE 5.6 VERTICAL EXTENT OF TDS IN CROSS SECTION A‐A'(Data Source: JJ&A, 2008a)


5-5

5.2 PLUME STABILITY

Time versus concentration graphs for TDS and chloride data collected from the Site monitoring wells are

provided in Appendix A. These graphs depict the trends for the 18 monitoring wells installed in the upper A‐

Zone (MW‐1 through MW‐17, MW‐20) and the 2 monitoring wells installed in the lower A‐Zone (MW‐18 ,

MW‐19). The wells locations are shown on Figure 2.1.

A review of these graphs indicates that wells installed in and around the Primary Lands exhibit an increasing

trend of TDS concentrations over time. However, the wells installed in the lower A‐Zone, MW‐18 and MW‐

19, indicate stable to decreasing concentrations of TDS and chloride.

The trend of TDS concentrations over time indicate that the plume has not reached steady‐state conditions

in and around the Primary Lands. The predicted point of plume steady‐state (i.e., the point at which the

plume is stable and no longer expanding) cannot be ascertained at this time as current data are not

sufficient to perform predictive modeling. Additional physical and geochemical properties data for the

aquifer media, along with aquifer hydraulic parameters is required to allow for projections of plume

dynamics over time.

FIGURE 5.7 VERTICAL EXTENT OF TDS IN CROSS SECTION B‐B'(Data Source: JJ&A, 2008a)


5-6

5.3 GEOCHEMICAL CONCEPTUAL MODEL

For primarily non‐reactive compounds, such as chloride, groundwater velocity can provide a reasonable

means of estimating a contaminant migration rate. However, for reactive compounds, such as the majority

of HCC PCOCs, migration rates are significantly affected by the physical and chemical properties of the

specific PCOCs. Significant factors that can affect PCOC migration rates include (Deutsch, 1997; Suthersan

and Payne, 2005);

Solubility of the PCOC;

Partitioning onto soil organic matter;

Exchange onto soil inorganic matter;

Groundwater geochemistry (most importantly pH and oxidation‐reduction potential);

Reaction chemistry of a specific PCOC;

Capacity to form mixed and pure solid precipitates (particularly metals); and,

Availability of other chemical species necessary for precipitation.

The significant reaction chemistry for HCC wastewater PCOCs include decomposition, chemical reduction,

nitrification, and ion exchange.

A geochemical model is proposed to evaluate the fate and transport of PCOCs for the Site. The geochemical

model includes “zones” representing the state of the affected wastewater as it interacts with the existing

conditions in the sub‐surface. The geochemical zones defined for the Site consists of: (1) a core zone where

the attenuating capacity of the media has been significantly diminished and impacts to groundwater

generally reflect the geochemistry of the waters being applied; (2) an attenuation zone where the

attenuation capacity for the media is diminished but available and the migration of reactive PCOCs is

limited; and, (3) the attenuated zone where the concentrations of PCOCs have decreased to within ambient

levels. The components of the geochemical model as applied to the Site are described as follows and as

illustrated in Figure 5.8.

Core Zone – Although native soils originally had the ability to attenuate PCOCs from the HCC

wastewater applied to the Primary Lands, it appears that their attenuating capacity has been

significantly diminished in the soils beneath the Primary Lands and potentially in the saturated A‐

Zone beneath the Primary Lands and adjacent areas. The net result is a core zone of A‐Zone

groundwater characterized by elevated TDS concentrations, co‐existing reduced and oxidized

nitrogen species, and elevated potassium (K) concentrations resulting in high K/Sodium (Na) ratios.

Attenuation Zone – Down‐gradient of the core zone, an attenuation zone exist that contains a

decrease in dissolved ionic species concentrations as the PCOCs are attenuated based on their


5-7

respective physical and geochemical properties and the attenuation capacity of the aquifer.

Potassium concentrations in this zone attenuate rapidly resulting in much lower K/Na rations. HCC

related impacts are still discernable within this area via a weight‐of‐evidence approach that includes

comparison of TDS to calculated 95% UTLs as shown on the vertical TDS extent plume figures

provided as Figures 5.6 and 5.7.

Attenuated Zone – The attenuated zone exists downgradient of the attenuation zone and is

typically represented by concentrations of PCOCs in groundwater consistent with ambient

conditions. The aquifer solids in this zone retain significant attenuation capacity.

It is important to note that the relatively simple geochemical model proposed does not take into account

the land use in the vicinity of the Site. Other agricultural activities introduce constituents into the

groundwater that are similar in nature to the HCC PCOCs. As such, an understanding of current ambient

conditions, and the specific affect other land uses have on groundwater quality, is necessary to develop a

mechanism for discerning the transition between the attenuation zone and the attenuated zone.

5.4 MIGRATION PATHWAYS, CONTAMINANT FATE AND TRANSPORT DATA GAPS SUMMARY

The data gaps identified relevant to migration pathways and fate and transport are discussed below.

The lateral and vertical extent of HCC related TDS impact in the Upper and Lower Aquifers has not

been definitively established and represents a data gap. Additionally, the absence of monitoring

wells in the lower A‐Zone and C/D‐Zones to confirm the boundaries of impact represents a data

gap.

FIGURE 5.8 GEOCHEMICAL MODEL


5-8

The mechanism for the migration of PCOCs to the Lower Aquifer (below the Corcoran Clay) is a data

gap; the elevated detections of TDS may be the result of preferential migration through improperly

constructed wells with or without some additive component from plume dispersion and diffusion

through the Corcoran Clay.

The data necessary to predict rates of plume migration and the point of steady‐state with source

areas has not been collected.

Discernment of HCC impacts to water quality versus impacts from off‐Site sources and/or current

ambient conditions.

Determination of the geochemical and physical characteristics for the core, attenuation and

attenuated zones by analytical testing of soils and groundwater to determine their respective

attenuating capacities.

Chemical composition of off‐Site sources and their potential to degrade groundwater quality with

PCOCs similar to HCC’s.


6-1

6.0 POTENTIAL RECEPTORS AND WATER QUALITY RESOURCES

6.1 POTENTIAL RECEPTORS TO GROUNDWATER EXPOSURES

The Upper and Lower Aquifers have designated beneficial uses and provide water supplies for domestic,

agricultural and industrial purposes. Supply wells in the vicinity of the Site were sampled in 2005 and 2008

to determine if HCC operations were a source of impact to the supply wells. Based on a weight of evidence

approach, the data indicated that HCC is:

a significant source of impact for 6 supply wells;

a primary contributor of impact to 11 supply wells;

a secondary contributor of impact for 5 supply wells; and,

not a source of impact for the remaining 8 supply wells sampled.

Additionally, a specific source could not be discerned from regional conditions for 11 supply wells (JJ&A,

2008d). Figure 6.1 identifies the locations of the supply wells and their designation relative to the source of

impact.

6.2 POTENTIAL RECEPTORS TO SURFACE WATER EXPOSURES

Groundwater impacted by HCC operations does not discharge to natural surface water bodies, including

creeks, streams, rivers or lakes.

6.3 POTENTIAL RECEPTORS AND WATER RESOURCES DATA GAPS

The following data gaps were defined in the 2008 Supply Well Evaluation Technical Report (JJ&A, 2008d) to

confirm the findings.

Discern and/or quantify impact due to regional sources versus HCC related impact;

Determine the migration pathway for detected impact at DW‐53;

Determine the potential source of elevated chloride concentration reported at DW‐97;

Determine the source of observed impact at IN‐04/IN‐04A;

Determine the source of groundwater (i.e., well construction) at IW‐20 and IW‐21; and,

Determine source of groundwater characterized in the area surrounding DW‐74.


6-2

FIGURE 6.1 SUPPLY WELL FINDINGS (Data Source: JJ&A, 2008a)


7-1

7.0 PRELIMINARY CSM SUMMARY

Based on the information presented herein, Figure 7.1 provides a schematic of the preliminary CSM which is

summarized as follows.

7.1 ENVIRONMENTAL SETTING

The Site is located in an area of heavy groundwater use. The aquifers beneath the Site are comprised of

alluvial deposits providing reliable groundwater yields. The aquifers beneath the Site include an Upper

Aquifer and a Lower Aquifer separated by the Corcoran Clay which impedes the vertical movement of

groundwater and dissolved PCOCs.

The Upper Aquifer water bearing units are unconfined to semi‐confined; the Lower Aquifer is confined.

Regional groundwater flow is west to southwest towards the San Joaquin River. Local groundwater flow is

affected by surface water discharges on the Site, and by irrigation on adjacent properties, resulting in

localized groundwater mounding. The vertical gradient is generally downward, the result of groundwater

extraction combined with irrigation. Irrigation is the predominant means of groundwater recharge in the

area. There are no natural creeks, streams, rivers or lake surface water bodies in the vicinity of the Site.

7.2 POTENTIAL ONSITE AND OFFSITE SOURCES

Site operations began in 1985, including the discharge of wastewaters to a holding/percolation pond. The

application of wastewaters to the Primary Lands began in 1989. The former holding/percolation pond and

Primary Lands represent the primary sources of concern on the Site.

Long term agricultural land use in the vicinity of the Site has resulted in documented regional degradation of

the groundwater quality. Additionally, land uses adjacent to the Site (e.g., dairies and other agricultural

operations) represent potential off‐Site sources of impact to groundwater.

7.3 MEDIA AND POTENTIAL CONSTITUENTS OF CONCERN

The media of concern at the Site include the soil underlying the Primary Lands and groundwater within the

Upper and Lower Aquifers. The potential PCOCs are primarily dissolved ions sourced from the HCC

wastewater discharged to Primary Lands. The potential PCOCs include naturally occurring compounds

which are similar to those associated with off‐Site operations and the degraded regional water.


7-2

Figure 7.1 Preliminary Conceptual Site Model Schematic


7-3

7.4 MIGRATIONS PATHWAYS/CONTAMINANT FATE AND TRANSPORT

The attenuating capacity of the vadose and shallow A‐Zone media beneath the Site appears to have been

significantly diminished such that groundwater reflects impact from the wastewater, both in terms of

general geochemistry and elevated PCOC concentrations. This area is referred to as the Core Zone.

Current data indicate that attenuation of PCOCs is occurring in groundwater laterally off‐Site and vertically

below the A‐Zone; within the area defined as the attenuation zone. Beyond the attenuation zone, the

PCOCs have decreased to concentrations consistent with the range of ambient conditions. The source of

PCOCs present in the attenuated zone cannot be discerned from off‐Site sources or regional impacts.

The groundwater plume within the A‐Zone has not reached steady‐state conditions and the core and

attenuating zones may continue to expand. The migration of PCOCs from the Upper Aquifer to the Lower

Aquifer is attenuated by the aquifer media and impeded by the Corcoran Clay. The presence of improperly

constructed supply wells in the vicinity of the Site represent potential preferential migration pathways for

groundwater from the Upper Aquifer to the Lower Aquifer.

7.5 POTENTIAL RECEPTORS

The groundwater beneath the Site has designated beneficial uses and potential receptors include domestic,

agricultural and industrial users of groundwater supply wells located in the vicinity of the Site. A supply well

sampling and evaluation program was performed in 2005 and 2008 to identify wells affected by HCC. Steps

have been taken by HCC to provide alternative water supplies as appropriate. Additional data collection has

also been proposed to resolve data gaps regarding well impacts.

The impacted groundwater does not discharge to natural creek, stream, river or lake surface waters.


8-1

8.0 DATA GAPS SUMMARY

A Data Gaps Work Plan will be prepared to address the data gaps identified herein, following CVRWQCB

review and comment on this Preliminary CSM Report. The Data Gaps Work Plan will present the rationale

and approach to fill the data gaps. A final CSM Report will be prepared and submitted when the data gaps

have been resolved.

The data gaps identified in this Preliminary CSM Report and to be addressed through the Data Gaps Work

Plan are summarized below.

8.1 ENVIRONMENTAL SETTING DATA GAPS SUMMARY

Geology and Hydrogeology

Site specific hydraulic parameters for the Upper Aquifer have not been established. The Upper

Aquifer contains the majority of the observed impact and is the appropriate aquifer to collect data

for plume migration estimates.

The physical and geochemical parameters for the unconsolidated lithologies in the Upper Aquifer,

Corcoran Clay and Lower Aquifer systems have not been adequately characterized to estimate

PCOC fate and transport.

Characterization of the magnitude extent of shallow groundwater mounding at the Site; data

relevant to this data gap is being collected through the extended water level survey in progress.

Ambient Water Quality

Upper Aquifer

- Refine data sets and statistical methodologies for calculation of ambient TDS and chloride

levels in the Upper Aquifer.

- Collect and analyze data from ambient sample locations for other Site PCOCs to determine

ambient levels.

Lower Aquifer

- Evaluate potential use of existing groundwater supply and GAMA well locations to estimate

ambient PCOC levels.


8-2

8.2 POTENTIAL SOURCES, MEDIA AND PCOC DATA GAPS SUMMARY

Potential Source Areas

Location of former holding/percolation pond.

Potential for discharge from off‐Site properties (historic and current) to degrade groundwater

quality with PCOCs similar to HCC’s.

Media

Magnitude of PCOCs in soils underlying the Primary Lands and their potential to contribute PCOCs

to groundwater.

PCOCs

Comparisons of PCOCs detected in groundwater to ambient levels is necessary to determine which

are HCC COCs.

Ambient levels have only been determined for TDS and chloride in the shallow A‐Zone and the

Upper Aquifer Supply Zone. These ambient levels need to be further refined.

Additional ambient levels need to be established for other PCOCs.

Ambient levels for all PCOCs need to be determined for the aquifer system beneath the Corcoran

Clay

8.3 MIGRATION PATHWAYS, CONTAMINANT FATE AND TRANSPORT DATA GAPS SUMMARY

The lateral and vertical extent of HCC related TDS impact in the Upper and Lower Aquifers has not

been definitively established. Additionally, the absence of monitoring wells in the lower A‐Zone

and C/D‐Zones to confirm the boundaries of impact represents a data gap.

The mechanism for the migration of PCOCs to the Lower Aquifer (below the Corcoran Clay) is a data

gap; the elevated detections of TDS may be the result of preferential migration through improperly

constructed wells or without some additive component from plume dispersion and diffusion

through the Corcoran Clay.

The data necessary to predict rates of plume migration and the point of steady‐state with source

areas has not been collected.

Discernment of HCC impacts to water quality versus ambient conditions.


8-3

Determination of the geochemical and physical characteristics for the core, attenuation and

attenuated zones by analytical testing of soils and groundwater to determine their respective

attenuating capacities.

Chemical composition of off‐Site sources and their potential to degrade groundwater quality with

PCOCs similar to HCC’s.

8.4 POTENTIAL RECEPTORS AND WATER RESOURCES DATA GAPS

Discern and/or quantify impact due to regional sources versus HCC related impact;

Determine the migration pathway for detected impact at DW‐53;

Determine the potential source of elevated chloride concentration reported at DW‐97;

Determine the source of observed impact at IN‐04/IN‐04A;

Determine the source of groundwater (i.e., well construction) at IW‐20 and IW‐21; and,

Determine source of groundwater characterized in the area surrounding DW‐74.


9-1

9.0 REFERENCES

Brown and Caldwell (B&C), 2004a. Report of Waste Discharge, Hilmar Cheese Company, Merced County. August, 2004.

B&C, 2004b. Groundwater Characterization Report, Hilmar Cheese Company, Merced County. September, 2004.

B&C, 2005. Water Supply Well Sampling Technical Report. July 11, 2005.

Burrow, K.R., Shelton, J.L., Hevesi, J.A., and Weissmann, G.S., 2004. Hydrogeologic Characterization of the Modesto Area, San Joaquin Valley, California: U.S. Geological Survey Scientific Investigations Report 2004‐5232, pp. 54.

California Department of Water Resources (DWR), 2003. California’s Groundwater, Bulletin 118 – Update 2003. October, 2003

California Regional Water Quality Control Board ‐ Central Valley Region, 2007. The Water Quality Control Plan (Basin Plan) for the California Regional Water Quality Control Board, Central Valley Region, Fourth Edition. Revised October 2007.

Deutsch, W.J., 1997. Groundwater Geochemistry Fundamentals and Applications to Contamination, Lewis Publishers, pp 221.

Jacobson James & Associates, Inc. (JJ&A), 2008a. Phase II Investigation Data Deliverable and Summary Report, Hilmar Cheese Company, Hilmar, California. June 23, 2008.

JJ&A, 2008b. Technical Memorandum, Determination of Ambient TDS Conditions for the Upper Aquifer, Hilmar Cheese Company, Hilmar, California. June 23, 2008.

JJ&A, 2008c. 2008 Area Supply Well Sampling Data Deliverable, Hilmar Cheese Company, Hilmar, Merced County. July 1, 2008.

JJ&A, 2008d. Supply Well Evaluation Technical Report, Hilmar Cheese Company, Hilmar, California. August 15, 2008.

KennedyJenks Consultants (KJ), 2008. Report of Waste Discharge, Hilmar Cheese Company, Merced County. June 2, 2008.

Landon, M.K., and Belitz, Kenneth, 2008. Ground‐Water Quality Data in the Central Eastside San Joaquin Basin 2006: Results from the California GAMA Program (Prepared in Cooperation with the California State Water Resources Control Board); U.S. Geological Survey Data Series 325, 88p.

Suthersan, S.S. and P.C. Payne, 2005. In Situ Remediation Engineering, CRC Press, pp 511.

Turlock Groundwater Basin, Groundwater Management Plan, TID, March 2008


APPENDIX A

Time Versus Concentration Graphs for TDS and Chloride

TDS AND CHLORIDE VERSUS TIME(MW‐01)

Hilmar Cheese CompanyHilmar, California

500

600

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mg/L)

ids (m

g/L)

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licationto Areas A and

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clay‐lined

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Discontinue

dapplication to Area B.

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TDS Concentrations Chloride Concentrations



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mg/L)

ids (m

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Discontinue

dapplication to Area B.

TileDrain covering Are A is

plugged.

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licationto Areas A and

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/L)

ids (m

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.

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.

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g/L)

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lication to Areas F and

G began.

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.

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Apr‐99

Oct‐99

Apr‐00

Oct‐00

Apr‐01

Oct‐01

Apr‐02

Oct‐02

Apr‐03

Oct‐03

Apr‐04

Oct‐04

Apr‐05

Oct‐05

Apr‐06

Oct‐06

Apr‐07

Oct‐07

Apr‐08

Chloride

(mg

Total D

issolved

Soli




800

1000

1200

2000

2500

3000

3500

g/L)

ids (m

g/L)

App

lication to

Area H began.

Tile Drain

covering

Area

H is plugged

.

Discontinue

d application to Area B.

Discontinue

d application

to 6 acres of A

rea H.

Beginn

ing of discharge of R

O

Perm

eate to

clay‐lined

RO Pon

ds

0

200

400

600

0

500

1000

1500

Oct‐90

Apr‐91

Oct‐91

Apr‐92

Oct‐92

Apr‐93

Oct‐93

Apr‐94

Oct‐94

Apr‐95

Oct‐95

Apr‐96

Oct‐96

Apr‐97

Oct‐97

Apr‐98

Oct‐98

Apr‐99

Oct‐99

Apr‐00

Oct‐00

Apr‐01

Oct‐01

Apr‐02

Oct‐02

Apr‐03

Oct‐03

Apr‐04

Oct‐04

Apr‐05

Oct‐05

Apr‐06

Oct‐06

Apr‐07

Oct‐07

Apr‐08

Chloride

(m

Total D

issolved

Soli




300

350

400

450

500

2000

2500

3000

mg/L)

ids (m

g/L)

Tile Drain covering AreaA is plugged

.

App

lication to Area C began.

App

lication to Area D began.

0

50

100

150

200

250

0

500

1000

1500

Nov‐94

May‐95

Nov‐95

May‐96

Nov‐96

May‐97

Nov‐97

May‐98

Nov‐98

May‐99

Nov‐99

May‐00

Nov‐00

May‐01

Nov‐01

May‐02

Nov‐02

May‐03

Nov‐03

May‐04

Nov‐04

May‐05

Nov‐05

May‐06

Nov‐06

May‐07

Nov‐07

May‐08

Chloride

( m

Total D

issolved

Soli




250

300

350

400

450

1500

2000

2500

g/L)

ids (m

g/L)

App

licationto Area C began.

0

50

100

150

200

0

500

1000

Nov‐94

May‐95

Nov‐95

May‐96

Nov‐96

May‐97

Nov‐97

May‐98

Nov‐98

May‐99

Nov‐99

May‐00

Nov‐00

May‐01

Nov‐01

May‐02

Nov‐02

May‐03

Nov‐03

May‐04

Nov‐04

May‐05

Nov‐05

May‐06

Nov‐06

May‐07

Nov‐07

May‐08

Chloride

(mg

Total D

issolved

Soli




250

300

350

400

1500

2000

2500

mg/L)

ids (m

g/L)

App

lication to Area E began.

0

50

100

150

200

0

500

1000

Nov‐94

May‐95

Nov‐95

May‐96

Nov‐96

May‐97

Nov‐97

May‐98

Nov‐98

May‐99

Nov‐99

May‐00

Nov‐00

May‐01

Nov‐01

May‐02

Nov‐02

May‐03

Nov‐03

May‐04

Nov‐04

May‐05

Nov‐05

May‐06

Nov‐06

May‐07

Nov‐07

May‐08

Chloride

( m

Total D

issolved

Soli


App

lication to Secon

dary Lands began.



150

200

250

800

1000

1200

mg/L)

ids (m

g/L)

App

lication to Area Hbegan.

Tile Drain covering Area H is

plugged.

Discontinue

d application

to 6 acres of A

rea H.

0

50

100

0

200

400

600

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

(m

Total D

issolved

Soli




100

120

140

160

180

800

1000

1200

1400

mg/L)

ids (m

g/L)

App

lication to Secon

dary Lands began.

0

20

40

60

80

0

200

400

600

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

( m

Total D

issolved

Soli




500

600

700

800

900

2000

2500

3000

3500

g/L)ids (m

g/L)

App

lication to Area H began.

ile Drain covering Area H is plugged.

0

100

200

300

400

0

500

1000

1500

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

(mg

Total D

issolved

Soli


A Ti



150

200

250

1000

1200

1400

1600

mg/L)

ids (m

g/L) App

lication to Secon

dary Lands

began.

0

50

100

0

200

400

600

800

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

( m

Total D

issolved

Soli




500

600

700

800

2000

2500

3000

3500

mg/L)

ids (m

g/L)

App

lication to Secon

dary Lands began.

0

100

200

300

400

0

500

1000

1500

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

( m

Total D

issolved

Soli




100

120

140

160

800

1000

1200

1400

mg/L)

ids (m

g/L)

App

lication to Secon

dary Lands began.

0

20

40

60

80

0

200

400

600

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

( m

Total D

issolved

Soli




100

120

140

160

180

800

1000

1200

g/L)

ids (m

g/L)

App

lication to Secon

dary Lands began.

0

20

40

60

80

0

200

400

600

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

(mg

Total D

issolved

Soli




25

30

35

40

45

600

700

800

900

1000

g/L)

ids (m

g/L)

0

5

10

15

20

0

100

200

300

400

500

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

(mg

Total D

issolved

Soli


App

lication to Area H began.

Tile Drain covering Area H is plugged

.

Discontinue

d application to 6 acres of

Area H.



80

100

120

140

600

700

800

900

1000

mg/L)

ids (m

g/L)

0

20

40

60

0

100

200

300

400

500

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

( m

Total D

issolved

Soli


App

lication to Secon

dary Lands

began.



30

35

40

45

50

800

1000

1200

g/L)

ids (m

g/L)

plication to Secon

dary Lands began.

0

5

10

15

20

25

0

200

400

600

Feb‐98

Aug

‐98

Feb‐99

Aug

‐99

Feb‐00

Aug

‐00

Feb‐01

Aug

‐01

Feb‐02

Aug

‐02

Feb‐03

Aug

‐03

Feb‐04

Aug

‐04

Feb‐05

Aug

‐05

Feb‐06

Aug

‐06

Feb‐07

Aug

‐07

Feb‐08

Chloride

(m

Total D

issolved

Soli


App

Preliminary Conceptual Site Model Report Hilmar Cheese Company, Hilmar, California

October 1, 2008 (Revised)

Prepared By:

4231 Pacific Street, Suite 1

Rocklin, California 95677

916.660.9994

preliminary conceptual site model report · 9001 lander avenue hilmar, california hilmar cheese...

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