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RESPONSE ACTION CONTRACT

United States Environmental Protection Agency Region 6

Contract No. 68-W6-0036

Technical Activities Work Plan

Remedial Investigation / Feasibility Study Griggs and Walnut Ground Water Plume

Superfund Site Las Cruces, New Mexico

Response Action Contract No. 68-W6-0036

EPA Work Assignment No. 961-RICO-06HZ

September 2005

In Association With:Science Applications International Corporation Geo-Marine, Inc.

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GRIGGS AND WALNUT GROUND WATER PLUME SITE RI/FS TECHNICAL ACTIVITIES WORK PLAN

GWP_TWP_VER2.0_2005-0919_TEXT.DOC SEPTEMBER 2005

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005809

Technical Activities Work Plan

Remedial Investigation/Feasibility Study Griggs and Walnut Ground Water Plume Superfund Site

Las Cruces, Doña Ana County, New Mexico EPA ID NM0002271286

Response Action Contract No. 68-W6-0036 EPA Work Assignment No. 961-RICO-06HZ

CH2M HILL Project No. 164462 DCN 05-7825

Prepared for: U.S. Environmental Protection Agency

Prepared by: CH2M HILL, INC

September 2005

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GWP_TWP_VER2.0_2005-0919_TEXT.DOC I SEPTEMBER 2005

Contents

List of Acronyms .................................................................................................................................iii

Preface ................................................................................................................................................... v

Section 1 Introduction.......................................................................................................................1-1

Section 2 Site Background and Setting............................................................................................2-1 2.1 Site Description and Background...........................................................................................2-1

2.1.1 Site Investigation History..........................................................................................2-1 2.1.2 Site Environmental Setting........................................................................................2-3

2.2 Source, Nature, and Extent of Contamination........................................................................2-7 2.2.1 Sources of Contamination .........................................................................................2-7 2.2.2 Nature and Extent of Contamination.........................................................................2-8

Section 3 Conceptual Site Model......................................................................................................3-1

Section 4 Data Quality Objectives....................................................................................................4-1 4.1 State the Problem....................................................................................................................4-1 4.2 Identify the Decision ..............................................................................................................4-3 4.3 Identify Inputs to the Decision ...............................................................................................4-4 4.4 Define the Investigation Boundaries ......................................................................................4-5 4.5 Develop a Decision Rule........................................................................................................4-5 4.6 Specify Limits of Decision Errors..........................................................................................4-6 4.7 Optimize Sampling Design ....................................................................................................4-7

Section 5 Site Characterization Tasks .............................................................................................5-1 5.1 Private Well Search and Site Reconnaissance........................................................................5-2 5.2 Field Investigation..................................................................................................................5-2

5.2.1 Site-Specific Plans.....................................................................................................5-3 5.2.2 Access Agreements ...................................................................................................5-3 5.2.3 Private Water Supply Well and Monitor Well Search ..............................................5-3 5.2.4 Sampling Effort Mobilization/Demobilization..........................................................5-3 5.2.5 Drilling/Well Installation ..........................................................................................5-4 5.2.6 Soil Vapor Survey .....................................................................................................5-5 5.2.7 Ground Water Sampling............................................................................................5-6 5.2.8 Surveying of Sample Locations ................................................................................5-7 5.2.9 Management of Investigation-Derived Waste...........................................................5-8

5.3 Data Evaluation ......................................................................................................................5-8 5.3.1 Data Validation .........................................................................................................5-8 5.3.2 Data Reduction, Tabulation, and Evaluation.............................................................5-8 5.3.3 Data Evaluation Technical Memorandum.................................................................5-8

5.4 Human Health Risk Assessment ............................................................................................5-9 5.4.1 Data to be Considered in the Human Health Risk Assessment.................................5-9 5.4.2 Chemicals of Potential Concern Selection Process ...................................................5-9 5.4.3 Potential Receptors..................................................................................................5-10 5.4.4 Exposure Scenarios to be Quantified in the Human Health Risk Assessment ........5-11 5.4.5 Toxicity Assessment................................................................................................5-11

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GWP_TWP_VER2.0_2005-0919_TEXT.DOC II SEPTEMBER 2005

5.4.6 Cleanup Goal Development ....................................................................................5-11 5.4.7 Human Health Risk Assessment Deliverables ........................................................5-11

5.5 Ecological Risk Assessment.................................................................................................5-12 5.6 Ground Water Modeling ......................................................................................................5-13 5.7 Remedial Investigation Report .............................................................................................5-13 5.8 Project Schedule ...................................................................................................................5-14

Section 6 Feasibility Study Tasks.....................................................................................................6-1 6.1 Compilation of Applicable or Relevant and Appropriate Requirements................................6-1 6.2 Development of Remedial Action Objectives........................................................................6-2

6.2.1 Development of General Response Actions..............................................................6-2 6.3 Identification and Screening of Remedial Technologies........................................................6-2 6.4 Development and Screening of Remedial Alternatives..........................................................6-3 6.5 Evaluation of Remedial Alternatives......................................................................................6-3 6.6 Feasibility Study Report.........................................................................................................6-4

Section 7 References ..........................................................................................................................7-1 List of Tables Table 4-1 Data Quality Objectives Table 5-1 Activities to be Performed for Completion of the RI/FS Table 6-1 Preliminary Screening of Remedial Technologies List of Figures Figure 1-1 Site Map Figure 2-1 Source Investigation Sample Locations Figure 2-2 Horizontal Distribution of PCE in Soil Vapor Figure 2-3 Horizontal Distribution of PCE at the Water Table (January 2004) Figure 2-4 Vertical Distribution of PCE in Ground Water Hydrogeophysical Cross-Section B-B’

(January 2004) Figure 3-1 Conceptual Model of PCE Release and Subsurface Contamination Figure 5-1 Locations of New RI Monitor Wells Figure 5-2 Location of Planned Shallow Soil Vapor Sampling and New Soil Vapor Monitor

Point Figure 5-3 Overview of RI/FS Project Schedule

List of Appendices

Appendix A Modeling Proposal

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GWP_TWP_VER2.0_2005-0919_TEXT.DOC III SEPTEMBER 2005

List of Acronyms

° Degree µg/L Micrograms per Liter ARARs Applicable or Relevant and Appropriate Requirements bgs below ground surface BHHRA Baseline Human Health Risk Assessment CERCLA Comprehensive Environmental Response, Compensation, and Liability Act CLC City of Las Cruces CLP Contract Laboratory Program COPCs Chemicals of Potential Concern DACTD Doña Ana County Transportation Department 1,2-DCA 1,2-Dichloroethane cis-1,2-DCE cis-1,2-Dichloroethene DNAPL Dense non-aqueous phase liquid DQOs Data Quality Objectives ELCR excess lifetime cancer risk EPA US Environmental Protection Agency F Fahrenheit FSP Field Sampling Plan GC Gas Chromatograph GWP Griggs and Walnut Ground Water Plume Superfund Site HEAST Health Effects Assessment Summary Tables HHRA Human Health Risk Assessment HI Hazard Index HRS Hazard Ranking System HSP Health and Safety Plan IDW Investigation-Derived Waste IH-25 Interstate Highway-25 IRIS Integrated Risk Information System MCL Maximum Contaminant Limit MNA Monitored Natural Attenuation MSL Mean Sea Level MSSL Media-Specific Screening Level NCEA National Center for Environmental Assessment NCP National Contingency Plan NMED New Mexico Environment Department NPL National Priorities List PAL Police Athletic League PCBs Polychlorinated biphenyls PCE tetrachlorothene, or perchloroethene PPRTV Provisional Peer-Reviewed Toxicity Values QAPP Quality Assurance Project Plan RAGS Risk Assessment Guidance for Superfund RI/FS Remedial Investigation/Feasibility Study SAP Sampling and Analysis Plan SMP Site Management Plan SVE Soil Vapor Extraction

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GWP_TWP_VER2.0_2005-0919_TEXT.DOC IV SEPTEMBER 2005

SVMP Soil Vapor Monitoring Point SVOCs Semi-Volatile Organic Compounds TAL Target Analyte List TAWP Technical Activities Work Plan TCE Trichloroethene TCL Target Compound List TDS Total Dissolved Solids UCL upper confidence limit USGS United States Geological Survey VOCs Volatile Organic Compounds

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GWP_TWP_VER2.0_2005-0919_TEXT.DOC V SEPTEMBER 2005

Preface

This Technical Activities Work Plan (TAWP) was prepared for the US Environmental Protection

Agency (EPA) Region 6 for the purpose of setting forth the technical activities to be conducted to

complete the Remedial Investigation/ Feasibility Study (RI/FS) for the Griggs and Walnut Ground

Water Plume (GWP) Site located in Las Cruces, Doña Ana County, New Mexico (EPA ID

NM0002271286). This TAWP was prepared under the Response Action Contract No. 68-W6-0036

and EPA Work Assignment Number 961-RICO-06HZ.

The RI/FS will use data gathered to-date by the New Mexico Environment Department (NMED) and

EPA during initial site investigation activities and the Source Investigation described by the

Identification of PCE Release Areas Report dated November 2003 (EPA, 2003). On April 20, 2005,

a Settlement Agreement between EPA and the City of Las Cruces (CLC) and Dona Ana County was

signed. To facilitate implementation of this agreement, EPA, NMED, the City of Las Cruces, and

Dona Ana County have formed a Technical Work Group, a forum for each stakeholder to share

information and provide input related to individual stakeholder needs. Based on investigations

conducted to-date, a list of data needs to complete the RI/FS were identified, and the priorities for

each were reviewed by the Technical Work Group. This TAWP incorporates the RI/FS data needs

identified and agreed upon by the Technical Work Group during a meeting held on July 21, 2005.

The summary of data needs and priorities agreed by the Technical Work Group is included here as

Table P-1. This summary forms the basis for the activities described in this work plan.

The activities described herein represent the Technical Work Group’s current understanding of the

activities necessary to complete the RI/FS, although more data might be needed based on field

findings or additional information obtained during the course of the investigation that would support

the need for further evaluation.

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GWP_TWP_VER2.0_2005-0919_TEXT.DOC VI SEPTEMBER 2005


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GWP_TAWP_VER2.0_TABLEP-1_RIFS-DATANEEDS_2005-0729_PRIORITIES.DOC PAGE 1 OF 8 SEPTEMBER 2005

Table P-1 Technical WorkGroup Confirmation of the Priorities for the Data Needs for Completion of the RI/FS Griggs and Walnut Ground Water Plume Site Las Cruces, New Mexico

Item Purpose Description of Data Need Rationale Priority Rationale for Assigning Priority

Ground Water ~ Well Installation

1. Finalize Definition of Nature & Extent

Support Long-Term Monitoring

New Monitor Well GWMW-11: Install nested well south of the DACTD Maintenance Yard. Three wells would be completed in a single borehole at the water table and at depths of approximately 300 and 530 feet below ground surface (bgs) to tap into the hydrogeologic units that, aside from the water table, seem to demonstrate the greatest mobility and degree of contamination.

To verify the extent of the GWP site plume in relation to detections of PCE observed to the south (in shallow soil vapor near Comet Cleaners, and in ground water samples from CLC Well No. 24 and irrigation well LRG-1457).

Priority I A level I priority was selected for this location because it is considered essential for evaluating the relation or lack of relation between the GWP PCE contamination and the PCE contamination observed to the south in shallow soil vapor and in ground water in CLC Well 24/LRG-1457.


Evaluate Remedial Alternatives


New Monitor Well GWMW-12: Install nested wells near Walnut Street along the southern boundary of the CLC Parks. Three wells would be installed in a single borehole to depths of approximately 275, 315, and 435 feet bgs, to tap into the hydrogeologic units that, aside from the water table, seem to demonstrate the greatest mobility and degree of contamination.

To quantify PCE concentrations in the center of the plume, for use in evaluating remedial alternatives, and to further support conclusions regarding source areas in this vicinity.

Priority I ! II A level I priority was selected for this location because it is considered essential to understanding the stratification of PCE concentrations in the center of the plume, for the evaluation of remedial alternatives (ie. so that targeted pumping could be evaluated) and would also help support conclusions regarding source areas in this vicinity.

3. Finalize Definition of Nature & Extent Support Long-Term Monitoring

New Monitor Well GWMW-13: Install a single water table monitor well west of Solano Drive and north of Griggs Avenue between monitor wells GWMW03 and GWMW07.

To verify the lack of relation between the GWP site plume and the low concentrations of PCE detected in GWMW07. Because PCE was not detected in deeper intervals at GWMW07 during the most recent sampling event in January 2004, deeper wells are not needed for this location.

Priority I ! III A level I priority was selected because this well location is considered essential for evaluating the relation or lack of relation between the GWP PCE contamination and the very low level PCE contamination observed sometimes in wells to the southwest.



New Monitor Well GWMW-14: Install a single water table monitor well west of Solano Drive and north of Spruce Avenue between CLC Well No. 10 and monitor well GWMW06.

To verify the extent of the plume in this area (PCE is present in GWMW06, but not yet in CLC Well No. 10). PCE has been detected at very low levels in deeper intervals at GWMW06, but the concentrations are below 1 ppb, and the ports at this depth at GWMW06 can be considered to represent the leading edge of contamination in this area for use in monitoring potential migration toward CLC Well No. 10.

Priority III (II) A level III priority was selected for this well location because regular sampling of CLC 10 would eliminate the need for this new well. If regular sampling of CLC 10 does not occur, this increases to a level II priority.

5. Finalize Definition of Nature & Extent Support Long-Term Monitoring

New Monitor Well GWMW-15: Install nested well east of Interstate Highway 25 and north of Lohman Avenue. These three wells would be installed in a single borehole to depths of approximately 280, 460, and 600 feet bgs, to tap into the hydrogeologic units that, aside from the water table, seem to demonstrate the greatest mobility and degree of contamination.

To verify the extent of the plume east of affected municipal supply wells CLC Well No. 19 and CLC Well No. 21 and evaluate the effectiveness of capture depending on the remedial alternative selected.

Priority II ! I A level II priority was assigned to this location because it is not essential to the evaluation of risk, and empirical evidence exists to suggest the extent of contamination does not go much further east, if at all. This well would serve to further define the downgradient edge of the plume, and would also be used to evaluate the effectiveness of implemented remedial alternatives by monitoring the downgradient migration of the plume. It could be installed at a later date (e.g. during the design phase).

Data need 3 is now considered Priority III, due to low concentrations in this area (below the MCL). Technical WorkGroup agreed it is not necessary at this time to confirm the lack of a relationship between GWMW07 and the rest of the plume. Data need is retained, however, for future consideration as needed.

Based on Technical WorkGroup discussion, data need 2 is now considered Priority II. This well will be installed if deemed necessary following evaluation of data collected through other data needs and ground water modeling effort.

Data need 1 is confirmed as Priority I. This well will be installed.

Data need 4 is confirmed as Priority III. NMED has collected a sample from CLC Well No. 10 as part of 3 year DWB sampling event. Data need is retained for future consideration as needed

Data need 5 is raised from Priority II to Priority I. This well will be installed, in particular to support the ground water modeling effort.

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DATA NEEDS FOR COMPLETION OF THE RI/FS GRIGGS AND WALNUT GROUND WATER PLUME, LAS CRUCES, NEW MEXICO


Item Purpose Need Rationale Priority Priority Rationale

Ground Water ~ Sampling




Monitor Well Sampling: One comprehensive round of ground water sampling for all new and existing wells. This sampling event would include water level collection and ground water sampling of the up to eleven newly installed conventional monitor wells, the seventeen existing conventional monitor wells, and the eight existing multi-level monitor wells (52 sample ports), for a total of up to 81 sampling locations. The proposed analytical parameters include:

• VOCs at all new and existing locations (up to 81 locations).

• TPH in all multi-level well ports (52 locations).

• Natural attenuation parameters at a subset of wells (12 sample locations are proposed).

• General water chemistry: TDS and total hardness (up to 36 locations)

The proposed natural attenuation parameters to be collected include dissolved oxygen, nitrate, ferrous iron, dissolved manganese, sulfate, sulfide, total organic carbon, carbon dioxide, dissolved gasses (methane, ethane, and ethene), total alkalinity, and chloride.

To finalize the nature and extent of contamination at the site. The final definition of the nature and extent of contamination will be used along with the existing data set to finalize the scope of the contamination to be remediated, and to support the evaluations of risk and remedial alternatives for the GWP site

Priority I (VOCs)

Priority III (TPH)

Priority III (MNA)

Priority II (TDS and hardness)

A level I priority was selection for collection of VOC data from new and existing wells because this data is considered essential in confirming the current nature and extent of contamination for evaluating remedial alternatives.

A level III priority was selected for collection of TPH data from the multi-level monitoring wells because this data is considered useful in evaluating the presence of other contaminants present within and in the vicinity of the plume, but not essential to the evaluation of PCE contamination.

A level III priority was selected for collection of MNA data because this data is considered useful in evaluating the presence of natural attenuation processes; however previous data suggests it is not likely that MNA will be effective at this site, so collection of further data is not necessarily essential. Also, due to the impact of the plume on CLC water supply wells, an “active” remedial action such as pump-and-treat is more likely to be required versus a “passive” remedial action such as MNA. Such data would be used to provide a more thorough evaluation of MNA as a possible alternative.

A level II priority was selected for the collection of TDS and total hardness because this data is important to the evaluation of alternatives, but not essential

Data need 6 is confirmed at Priority levels shown above. Technical WorkGroup agreed that a current round of ground water sampling is required at all wells to supplement/confirm existing data set.

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Item No.

Purpose Need Rationale Priority Priority Rationale

Ground Water ~ Municipal and Private Water Well Sampling

7. Assess Risk to Human Health

Finalize Definition of Nature & Extent

Search the New Mexico Office of the State Engineer’s database for the presence of additional private wells not previously identified. If any additional private wells are identified, a site survey and interview with the well owner would determine the use of the well and construction details if available.

To determine if there are any private wells not previously identified that are located in the known boundary of the plume for supporting the Human Health Risk Assessment (HHRA).

Priority I A level I priority was selected because this information is considered essential for completion of the HHRA – all potential exposure points must be confirmed.




Sample all CLC water supply wells located in and just outside of the plume boundary (CLC10, CLC18, CLC19, CLC21, CLC27 and CLC wells being blended in Upper Griggs Reservoir). Also sample all new (identified in Item No. 7 above) and existing private wells (LRG3191 and LRG1457)

To determine current concentrations of PCE in support of the HHRA evaluation and for use in finalizing the nature and extent of contamination and in evaluating remedial alternatives.

Priority I A level I priority was selected because this data is considered essential for completion of the HHRA – current data is necessary to confirm the level of risk.

Data need 7 is confirmed as Priority I.


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Item No.


Subsurface Soil Samples

9. Evaluate Remedial Alternatives

Collection of two soil cores from the newly installed wells for use in determining the fraction of organic carbon in soil present in the aquifer.

To support the ground water modeling effort and evaluation of remedial alternatives in support of the FS.

Priority III A level III priority was selected for this data because although useful this data is not considered essential. Sufficient literature values exist such that a reasonable approximation of the fraction of organic carbon might be ascertained.

Data need 9 is confirmed as Priority III. However, because ground water monitoring wells are being drilled to address other data needs, this data need can be addressed without significant additional effort.

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Item No.


Soil Vapor ~ Monitor Point Installation



New Soil Vapor Monitor Point SVMP08. Install a soil vapor monitor point near the intersection of Hadley Avenue and Walnut Street. The soil vapor monitor point would be installed at 20 feet intervals, starting at 20 feet bgs down to the water table.

Priority I ! II A level I priority was selected because this location is considered essential in defining the relation between soil vapor contamination and contamination in ground water and for use in evaluating remedial alternatives.



New Soil Vapor Monitor Point SVMP16. Install a soil vapor monitor point at the DACTD Maintenance Yard between monitor well GWMW01 and CLC Well 18. The soil vapor monitor point would be installed at 20 feet intervals, starting at 20 feet bgs down to the water table.

Priority I A level I priority was selected because this location is considered essential in defining the relation between soil vapor contamination and contamination in ground water and for use in evaluating remedial alternatives.



New Soil Vapor Monitor Point SVMP17. Install a soil vapor monitor point along Walnut Street north of Griggs. The soil vapor monitor point would be installed at 20 feet intervals, starting at 20 feet bgs down to the water table.

To finalize the vertical definition of the nature and extent of soil vapor contamination specifically associated with the GWP site. The final definition of the nature and extent of contamination will be used along with the existing data set to finalize the scope of the contamination to be remediated, and to support the evaluations of remedial alternatives for the GWP site. Specifically, the data will be used to evaluate the relation between soil vapor contamination and contamination in ground water in the previously defined source areas.

Priority I ! II A level I priority was selected because this location is considered essential in defining the relation between soil vapor contamination and contamination in ground water and for use in evaluating remedial alternatives.

The installation of one additional SVMP to finalize the vertical definition of the nature and extent of soil vapor contamination extending to the water table is confirmed as Priority 1. However, at this time, only one SVMP will be installed. SVMP16 is selected because it is near a ground water monitoring well that can be used for comparison, and because it is located in a high concentration area of the plume. Installation of other SVMPs may be considered following evaluation of new data.

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Item No.


Soil Vapor ~ Sampling



Sampling of the three new and two existing soil vapor monitor points. Sample for chlorinated VOCs.


Priority I A level I priority was selected because this data is considered essential in defining the relation between soil vapor contamination and contamination in ground water and for use in evaluating remedial alternatives



Assess Risk to Human Health

Shallow subsurface soil vapor sampling at approximately 40 locations. The samples would be collected at 5 and 10 feet bgs at residences located northeast of the intersection of Hadley Avenue and Walnut Streets.

Additional shallow subsurface soil vapor sampling would be conducted around buildings associated with the Meerscheidt Recreational Center and Police Athletic League Boxing Facility. Approximately 10 locations would be probed and samples collected at 5 and 10 ft bgs.

To address soil vapor data needs related to the HHRA and specifically indoor vapor intrusion.

Priority I A level I priority was selected because this data is considered essential for completion of the HHRA

Data need 14 is confirmed as Priority I. First priority for this data need is to conduct shallow soil vapor monitoring in residential area. The recreational areas may also be addressed depending on the amount of additional effort determined to be required.


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Item No.


Soil Vapor ~ Geotechnical Sampling


Collection of two surface soil cores for analysis of geotechnical parameters. Geotechnical parameters to include porosity, soil classification, moisture content and density. These would be collected in the residential area yards.

For use in indoor air vapor intrusion modeling. Priority II A level II priority was selected because this data is important but not essential for completion of the HHRA. Sufficient literature values exist such that a reasonable approximation of these parameters could be assumed.

Data need 15 is confirmed as Priority II. Soil cores will be collected during shallow vapor soil sampling in residential yards.

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GWP_TWP_VER2.0_2005-0919_TEXT.DOC 1-1 SEPTEMBER 2005

Section 1 Introduction

The Remedial Investigation/Feasibility Study (RI/FS) is a process by which the nature and extent of

risks posed by a hazardous waste site are quantified and potential remedial options are evaluated

sufficient to support an informed risk management decision regarding remedial action for the site.

This RI/FS Technical Activities Work Plan (TAWP) has been prepared to describe the tasks to be

conducted to complete the RI/FS for the Griggs and Walnut Ground Water Plume (GWP) Superfund

site in Las Cruces, Doña Ana County, New Mexico. Specific details regarding how the field

activities are to be conducted are presented in site-specific plans presented under separate cover (as

described below). The overall project schedule is described in Section 5.

The GWP site is a ground water plume contaminated with perchloroethylene (PCE, also known as

tetrachloroethene). PCE, a volatile organic compound (VOC), is a solvent that has been used in the

United States since the 1930's for dry cleaning and parts-cleaning operations. The site is located in

the vicinity of the intersection of East Griggs Avenue and North Walnut Street in Las Cruces, Doña

Ana County, New Mexico. Figure 1-1 shows the location of the site within the City of Las Cruces

(CLC). Routine compliance sampling conducted by the New Mexico Environment Department

(NMED) Drinking Water Bureau first identified PCE in municipal supply Wells No. 21 and No. 27 in

August 1993. The concentration of PCE in both wells was below the US Environmental Protection

Agency (EPA) maximum contaminant limit (MCL) of 5 micrograms per liter (µg/L). PCE was first

detected above the EPA MCL by the NMED Drinking Water Bureau in Well No. 18 in January 1995.

NMED provided the first regulatory response at the GWP site. The NMED’s response activities

included conducting the preliminary site assessment and site inspection activities. The NMED

identified several potential sources of the PCE. As a result, the NMED installed ground water

monitor wells and tested soil vapor at the Doña Ana County Transportation Department (DACTD)

maintenance facility. In addition, the CLC and NMED have monitored the quality of the ground water

in the drinking water supply system to ensure continued compliance with drinking water standards.

The site was added to the Superfund National Priorities List (NPL) in June 2001. At that time, the

EPA initiated a Source Investigation as a preliminary step in the RI/FS process. The results and

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conclusions from the Source Investigation are provided in the report entitled “Identification of PCE

Release Areas” (referred to as the IDRA report in this TAWP) (EPA, 2003).

The Source Investigation was conducted from April 2002 through February 2003 to identify the areas

where PCE was released at the site. The Source Investigation was conducted at EPA’s direction with

the goal of identifying specific source areas and to collect data to be used to support the RI/FS for the

site. The investigation included the collection of over 600 soil vapor samples, the installation of 7

soil vapor monitoring points (SVMPs), the installation of 8 multi-level ground water wells, and the

collection of over 200 ground water samples from new and existing monitor wells. From the observed

extent of PCE in soil vapor and ground water, the EPA determined that PCE releases occurred at

three principal locations at the GWP site. The IDRA report concluded that the PCE was released at

the surface to the soil and soil vapor and migrated down to ground water over time. The three

locations where PCE releases occurred, as identified in the IDRA report, included:

• The historical operations at the former National Guard Armory currently owned by the CLC;

• The historical operations at the former Crawford Municipal Airport currently owned by the

CLC; and,

• The historical and/or current operations at the DACTD maintenance facility (EPA, 2003).

Figure 1-1 shows the locations of the three principal source areas identified in the IDRA report.

The purpose of this RI/FS is to finalize the nature and extent of contamination, collect sufficient data

to perform the Baseline Human Health Risk Assessment (BHHRA), and to evaluate remedial

alternatives for the site. Based on the results of the Source Investigation, several data needs were

identified for completion of the RI/FS. These data needs were reviewed and confirmed during the

Technical Work Group Meeting conducted on July 21, 2005. The following data needs were

confirmed for implementation under the RI/FS at this time:

• Installation of one multi-level well east of Interstate 25.

• Installation of one multi-level well between the DACTD maintenance facility and Comet

Cleaners.

• Collection of shallow soil vapor samples in the neighborhood northeast of the intersection of

Hadley and Walnut Avenue, at the Meerscheidt Recreation Center, and at the Police Athletic

League (PAL) Boxing Facility.

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• Installation of one SVMP at the DACDT maintenance facility near monitor well GWMW01.

• Perform a records search of new and existing private wells in the vicinity of the site.

• Perform one round of ground water sampling (monitor wells, private wells, and CLC wells).

This TAWP provides an overview of the RI/FS objectives and the activities to be performed. The site-

specific plans which describe how each task activity is to be conducted are the Sampling and Analysis

Plan (SAP), the Site Management Plan (SMP), and the Health and Safety Plan (HSP). The SAP is

composed of the Field Sampling Plan (FSP) and the Quality Assurance Project Plan (QAPP); these

plans detail the sampling and analysis procedures to be followed by the field and laboratory

personnel, respectively, as well as the data management procedures to be followed throughout the

sampling and analysis activities. The SMP describes handling of site access, security, contingency

procedures, management responsibilities, and investigation-derived waste (IDW); procedures

specified in the SMP will ensure contaminants are not released offsite as a result of RI/FS activities.

The HSP describes CH2M HILL-specific employee training requirements, protective equipment

requirements, medical surveillance requirements, standard health and safety operating procedures,

and contingencies applicable to performance of the RI/FS activities. These site-specific plans are

provided under separate cover and are referenced as appropriate throughout the TAWP.

Provided in Section 2 of this TAWP is a brief description of the site background and environmental

setting. Section 3 describes the current view of the site conceptual model, used as a basis for

outlining RI/FS activities. Data Quality Objectives (DQOs) for use in defining the level of

investigation and depth of evaluation for the RI/FS are described in Section 4. Section 5 outlines the

site characterization tasks defined to supplement the existing database of information available from

historic sampling and analytical activities conducted for the site. Section 6 outlines the tasks defined

to complete a feasibility study for the site. References are listed in Section 7.

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005829


Section 2 Site Background and Setting

A summary of the available data on the physical and historical characteristics of the GWP site has

been compiled from the previous investigative record. This section provides a description of this

information as well as a summary of the nature and extent of contamination documented to-date.

2.1 Site Description and Background The GWP site is a ground water plume contaminated by PCE. The plume is centered near the

intersection of Griggs Avenue and Walnut Street in Las Cruces, Doña Ana County, New Mexico as

shown in Figure 1-1. The geographic coordinates at this location are approximately 32°18' 56.0"

north latitude and 106°45' 36.0" west longitude. Four municipal drinking water supply wells within

the site are affected (EPA, 2000b). The well with the highest concentrations is Well No. 18 (out of

service since 1996). Samples from this well have consistently demonstrated concentrations of PCE

above the MCL. This well is located at the DACTD maintenance facility, near the intersection of

Griggs Avenue and Walnut Street. The other affected wells within the GWP site are Well Nos. 19,

21, and 27. Well No. 27 has also demonstrated concentrations of PCE above the MCL, and has been

out of service since 2001. Well No. 19 has demonstrated concentrations typically below the MCL;

this well was taken out of service in July 2005 due to mechanical problems. Well No. 21

demonstrates concentrations around the MCL (slightly below or slightly above); this well is in service

and managed by the CLC under a blending program approved by NMED. A fifth well, CLC Well

No. 24 located south of the site, has demonstrated low concentration detections of PCE since June

2001. PCE contamination at this well is not considered related to the GWP site (municipal supply

wells in between this CLC Well No. 24 and the site are not affected). A brief description of the site

investigative history and environmental setting is provided in the following paragraphs.

2.1.1 Site Investigation History

Since PCE contamination was discovered at the site, several investigations have been conducted by

NMED and EPA to evaluate the extent of the PCE plume and to identify potential sources. These

investigations included the installation of monitor wells throughout the area (including 8 deep multi-

level wells) and sampling of ground water and soil vapor in the vicinity. The results of these

005830



investigations are provided in EPA’s Hazard Ranking System (HRS) documentation (EPA, 2000b)

and in EPA’s IDRA Report (EPA, 2003). A summary of the results and conclusions of the EPA

Source Investigation conducted from April 2002 through February 2003is provided in the following

paragraphs.

Two-hundred and forty soil vapor borings and 7 SVMPs were completed during the Source

Investigation. At each location, soil vapor samples were collected from multiple depths and analyzed

for selected chlorinated VOCs at an onsite mobile laboratory. Of the compounds analyzed, only PCE

and Trichloroethene (TCE) were detected in the soil vapor. Soil vapor samples were collected at

depths ranging between 5 and 50 feet below ground surface (bgs) in each boring. PCE was detected at

one or more depths in 193 of the 240 soil vapor borings completed (i.e. in 80 percent of the borings).

PCE concentrations detected in the soil vapor borings ranged from 0.05 µg/L to 25.30 µg/L.

Soil vapor samples were also collected at depths ranging from 12 to 115 feet bgs from the 7 SVMPs.

PCE was detected at 6 of the 7 SVMP locations. The range of PCE concentrations detected was 0.06

(B) to 6.83 µg/L. The “B” lab qualifier indicates that the analytical result was greater than the method

detection limit (MDL) but less than the practical quantitation limits (PQL). PCE was the only

chlorinated VOC detected in samples collected from the SVMP locations.

Eight multi-level monitor wells were installed during the Source Investigation. In December 2002,

ground water samples were collected from the eight multi-level monitor wells and the 15 existing

monitor wells. In the upper water table portion of the aquifer, PCE was detected at concentrations

ranging from 0.69 to 38 µg/L. In the middle portion of the aquifer, PCE was detected at

concentrations ranging from 2.6 to 15 µg/L. In the lower portion of the aquifer, PCE was detected at

concentrations ranging from 0.31 to 53 µg/L.

In January 2004, an additional round of ground water monitoring was conducted. This ground water

sampling event was conducted to provide a comprehensive set of analytical results for use in

monitoring changes in the plume based on previous investigation data collected by EPA and NMED,

and to support future activities at the site. The event included collection of samples for analysis of the

full suite of organic and inorganic constituents typically evaluated through the Contract Laboratory

Program (CLP). The samples collected from the multi-level monitor wells were analyzed for Target

Compound List (TCL) VOCs, TCL semi-volatile organic compounds (SVOCs), TCL pesticides and

005831



polychlorinated biphenyls (PCBs), Target Analyte List (TAL) metals, and mercury. Samples

collected from water table monitoring wells were analyzed for TCL VOCs only

(due to the limited sample volume available from these wells).

Based on the results from this sampling event, it was concluded that the PCE plume at the GWP site

appeared to be fairly stable in size relative to data collected at the site since July 2000. The plume did

not appear to be significantly increasing or decreasing in size, and the extent of the plume was well

defined horizontally in most areas. Two areas where the plume was found to be not completely

defined horizontally was northwest of monitor well GWMW06 and east of Interstate Highway-25

(IH-25).

For a description of the other organic and inorganic constituents detected, refer to the January 2004

sampling event technical memorandum (CH2M HILL, 2004).

Figure 2-1 shows the soil vapor and ground water sampling locations from the Source Investigation.

2.1.2 Site Environmental Setting

This section describes the physical characteristics of the site.

2.1.2.1 Land Use

Land use around the site is mixed. Just north of CLC Well No. 18 and extending west to North

Solano Drive and east to past Walnut Street, a large portion of the area is used for public parks.

Residential neighborhoods are present west of North Solano Drive, east of Walnut Street, north of

Hadley Avenue, and south of Griggs Avenue. The rest of the area along Hadley Avenue and Griggs

Avenue between Solano Drive and just east of Walnut Street is light industrial/commercial, including

the CLC Fleet maintenance facility and the DACTD maintenance facility. Other commercial and light

industrial properties can be found along the major roadways in the vicinity of the site, including

Lohman Avenue, North Solano Drive, and Spruce Avenue.

2.1.2.2 Topography

Las Cruces is situated in the central portion of Doña Ana County, New Mexico. The site is located on

the United States Geological Survey (USGS) 7.5 Minute Topographic Quadrangle “Las Cruces”. The

elevation at the site varies from a maximum of about 4,080 feet above mean sea level (MSL) to 3,930

005832



feet MSL (USGS, 1978). Surficial topographic features at the eastern end of affected ground water

(between north of Hadley Avenue and south of Griggs Avenue, just west of IH-25) include two high

areas with an arroyo valley extending west-east in between. This arroyo is located along the south

side and parallel to Hadley Avenue; the southern high area approximately parallels Griggs Avenue. A

second arroyo is present south of Griggs Avenue, extending slightly southwest towards Lohman

Avenue and west of Walnut Street. The land surface in the area flattens and slopes down toward the

western edge of the affected ground water (the ground surface continues to slope downward toward

the Rio Grande, about 3.5 miles to the west). In this area, surface drainage is from east to west.

2.1.2.3 Climate

Surface water in the Las Cruces area is very limited. The climate in the area is arid. In the Mesilla

Valley, where Las Cruces is located, temperatures reach 90 degrees (º) Fahrenheit (F) or greater an

average of 101 days a year. In January, the coolest month, the average daily maximum temperature is

57º F and the average daily minimum temperature is 25º F. Precipitation amounts in the valley range

between 8.0 and 9.0 inches per year, with most precipitation being in the form of rain. Most rain is

limited to brief, intense thunderstorms that occur between July and September. Potential evaporation

and transpiration greatly exceeds rainfall. Potential evaporation rates measured in an evaporation pan

average about 97 inches per year. Potential evaporation and transpiration rates limit the amount of

surface water available in the area. This also limits the amount of recharge the aquifer receives from

rainfall (King, et al., 1971).

2.1.2.4 Regional Geology

Las Cruces is located in the Mexican Highlands section of the Basin and Range physiographic

province. In general, the physiography of the area consists of uplifted fault-block mountain ranges

and intermontane basins. The intermontane basins are structurally depressed areas that have been

displaced downward with respect to the mountains. The mountain ranges and intermontane basins

generally have a north-south trend. Other mountain types in the area include broad domal uplifts and

erosional remnants of igneous intrusive bodies. The major physiographic features in the Las Cruces

area are the entrenched Rio Grande and two intermontane basins, the Jornada del Muerto and the

Mesilla Bolson. The CLC is located in the Mesilla Valley (located within the Mesilla Bolson) east of

the Rio Grande. The Jornada del Muerto is located north and east of Las Cruces (King, et al., 1971).

The regional geology is comprised of Quaternary-aged flood plain alluvium and the Miocene to

Middle Pleistocene Santa Fe Group. The flood plain alluvium was deposited by the Rio Grande. It

005833



generally consists of a thick basal sand and gravel channel unit overlain by finer-grained flood plain

deposits. The unit is generally about 4 miles wide and 80 feet thick. The Santa Fe Group is a rock

stratigraphic unit composed of sequences of unconsolidated to moderately consolidated sedimentary

deposits and volcanic deposits consisting of basalts and minor ash-fall deposits. These deposits have

partially filled the intermontane basins along the Rio Grande depression from the San Luis Valley of

Colorado to the lower El Paso Valley of Texas and Chihuahua, Mexico. The Santa Fe Group occurs

at thicknesses up to 4,000 feet (Frentzel, et. al, 1990).

2.1.2.5 Regional Hydrogeology

The regional hydrogeology is largely controlled by the geologic structures present in the area.

Ground water basins are situated in the intermontane basins between the uplifted fault-block

mountain ranges. The major ground water basins in the Las Cruces area are the Mesilla Ground

Water Basin and the Jornada del Muerto Ground Water Basin. Las Cruces is located within the

Mesilla Ground Water Basin, and the Jornada del Muerto Basin is further to the north and east. The

two basins are separated by a subsurface high in the less permeable bedrock (King, et al., 1971).

The Rio Grande flood plain alluvium and the Santa Fe Group are the two major ground water

reservoirs in the area. In the Mesilla Ground Water Basin, these two ground water reservoirs form a

complex aquifer system. Ground water recharge is primarily from the Rio Grande into the flood plain

alluvium. The ground water then migrates downward through the shallow alluvium to the upper

Santa Fe Group through a series of interconnected gravel, sand, and clay lenses. Vertical flow within

the system is restricted by thin, interbedded clay lenses in the lower part of the flood plain alluvium

and the upper portion of the Santa Fe Group. This vertical heterogeneity results in the horizontal

permeability generally exceeding the vertical permeability by several orders of magnitude. Ground

water occurs under unconfined conditions within the flood plain alluvium and under unconfined to

semi-confined conditions within the Santa Fe Group. Ground water flow within the Mesilla Ground

Water Basin is generally to the southeast (King, et al., 1971).

The Mesilla Ground Water Basin aquifer has excellent recharge, transmission, and storage capacity.

These characteristics make the aquifer system capable of producing large quantities of high quality

water for agricultural, municipal, and industrial uses. The CLC Municipal Water System is a blended

system supplying water from 30 wells to approximately 67,900 people. The well field is located on

the east side of the Rio Grande within inter-tonguing sand and gravel layers in the Santa Fe Group.

005834



No single well supplies more than 40% of the total water within the system, and the system produces

on average approximately 8 million gallons per day (EPA, 2000b).

2.1.2.6 Site Hydrogeology

In the vicinity of the GWP site, ground water occurs under unconfined conditions in unconsolidated

to semi-consolidated fine to coarse sands with some gravel, silt, and clay. The aquifer is primarily

within the Santa Fe Group. Ground water flow is typically towards the east, away from the Rio

Grande and towards the City’s well field. Ground water flow direction at the site is influenced by the

recharge zone at the Rio Grande and the pumping in the City’s well field. The depth-to-water at the

site is approximately 187 feet bgs (as measured at the DACTD maintenance facility) (CH2M HILL,

2004).

At the GWP site, the aquifer can be subdivided into two general hydrologic zones. Both zones can be

correlated across the area of the site. The upper hydrologic zone is composed of one hydrogeologic

unit (designated Unit 1), while the lower hydrologic zone is composed of two hydrogeologic units

(Units 2 and 3). A brief description of each unit is provided below (all bgs depths are relative to an

approximate surface elevation of 4,100 feet MSL):

• Unit 1 (235 to 340 feet bgs): The unit is composed of the lower portions of the Rio Grande

Alluvium and the upper portion of the Santa Fe Group. The top of the unit is composed of the

basal gravel and coarse sand unit of the Rio Grande Alluvium (where present). Fine sand with

varying percentages of silt and clay compose the lower portion of this unit.

• Unit 2 (340 to 383 feet bgs): This unit is composed primarily of silt and clay. The center of the

unit contains a bed of fine sand with silt and clay.

• Unit 3 (383 to >800 feet bgs): This unit is composed primarily of fine to coarse sand. The unit

contains thin beds of finer grained materials, especially along the western portions of the study

area. The unit also contains some gravel layers in the lower portions. The bottom of the unit was

not attained in boreholes drilled during the Source Investigation.

The hydrogeologic boundaries were developed based on observed water levels and geophysical

changes observed with depth.

005835



Based on the distribution of water levels at the water table, ground water flow is generally from the

northwest to the southeast along the western portion of the plume. The ground water flow direction at

the water table is consistent with ground water flowing towards the CLC production wells in the

vicinity of the GWP site. Ground water levels obtained from multi-level monitor wells indicate that a

downward vertical gradient exists at the site.

2.2 Source, Nature, and Extent of Contamination

Site investigation activities were conducted by the NMED Superfund Oversight Section between

1997 and 2000 to identify the source and extent of the PCE contaminated ground water plume.

Likewise, EPA initiated a source investigation during 2002 with the goal of identifying specific areas

where PCE might have been released to the environment and to collect data on the nature and extent

of contamination. Several source areas were identified as a result of this investigation. A summary

of findings regarding the source, nature, and extent of contamination is provided in the following

paragraphs. A more detailed description of the findings of the Source Investigation work is available

in the IDRA Report (EPA, 2003).

2.2.1 Sources of Contamination

In 2002, EPA initiated an investigation to evaluate the presence of potential sources of PCE

associated with the GWP site. A source investigation was performed that included the collection of

over 600 soil vapor samples, the installation of 7 SVMPs, the installation of 8 multi-level ground

water monitor wells, and the collection of over 200 ground water samples from new and existing

monitor wells. Based on the observed extent of PCE in soil vapor and ground water, EPA determined

that three principal locations in the area of investigation demonstrated releases of PCE at the surface

to the soil that migrated down to ground water over time:

• The historical operations at the former National Guard Armory currently owned by the CLC.

• The historical operations at the former Crawford Municipal Airport currently owned by the

CLC.

• The historical and/or current operations at the DACTD maintenance facility (EPA, 2003).

005836



2.2.2 Nature and Extent of Contamination

The current understanding of the nature and extent of contamination at the GWP site is described in

the IDRA Report (EPA, 2003) and the January Ground Water Sampling Report (CH2M HILL,

2004). A summary of the nature and extent of contamination is provided in the following paragraphs.

The extent of PCE detected in soil vapor during the Source Investigation is illustrated on Figure 2-2.

Although the concentrations of PCE in soil vapor are low and widespread, higher relative

concentrations of PCE in shallow soil vapor are observed in the vicinity of the North Solano

Drive/East Hadley Avenue intersection (at sample location SVMP03), in the vicinity of the East

Hadley Avenue/North Walnut Street intersection (at sample location PA077), and northwest/northeast

of the East Griggs Avenue/North Walnut Street intersection (at sample locations SVMP01, DA028,

R8005, and R2017) which corresponds to the identified PCE release areas. The migration of PCE

contamination to soil and ground water most likely came from low volume spills of PCE over time at

locations corresponding in general to the three areas of higher relative PCE concentrations in soil

vapor shown in Figures 2-2. It is not likely, based on the concentrations observed, that a source of

PCE liquid is still present in the shallow surface or subsurface soil, although some residual may be

present. Concentrations of PCE in the soil vapor decrease outside of the primary area of

contamination thus indicating that the detections of PCE observed to the south (near CLC Well No.

24) and southwest (near multi-level ground water monitor well GWMW07) are unrelated to the GWP

site.

The ground water plume at the GWP site appears to be fairly stable in size, based on the current

known extent of the site boundaries and data collected at the site since July 2000 (CH2M HILL,

2004). The plume does not appear to be significantly increasing or decreasing in size, and the extent

of the plume is well defined horizontally in most areas as shown in Figure 2-3. Two areas where the

plume is not completely defined horizontally are northwest of monitor well GWMW06 and east of

IH-25. The northwest portion of the plume may be migrating towards CLC Well No. 10; there is

currently no monitor well upgradient (northwest) of GWMW06 to verify this. While there are also

currently no monitor wells east of IH-25, and it is acknowledged that the horizontal extent is not

completely defined to the east, the plume is likely limited in extent in that area due to the capture

provided by CLC Wells 19 and 21. At depth, the PCE plume is defined by concentrations below the

MCL except in the area around multi-level monitor well GWMW01, located near CLC Well No. 18.

In general, the PCE concentrations are decreasing or remaining stable within the plume; however, the

005837



PCE concentration has increased to above the MCL in one well, at GWMW06 port 1, in the northwest

area of the plume (the concentration increased from 3.6 µg/L in December 2002 to 10 µg/L in

January 2004).

The highest PCE concentrations in ground water at the GWP site occur at the water table in the area

near CLC Well 18 (see Figure 2-3) at multi-level monitor well GWMW01 (at the DACTD

maintenance facility, one of the PCE release areas identified in the IDRA report). A second PCE

release area identified in the IDRA report is located nearby (the intersection of East Hadley Avenue

and North Walnut Street, located within the former municipal airport). The portion of the PCE plume

where concentrations exceed the MCL extends outward from this area towards the west (to monitor

well MW-SF3), north (to between monitor wells GWMW01 and GWMW08), and east (to monitor

wells MW-SF10 and GWMW10). Ground water concentrations are lower near the third PCE release

area (former National Guard Armory at the corner of Solano and Hadley), as defined by the

concentrations at monitor wells MW-SF8 and GWMW06.

Horizontally, the portion of the PCE plume above the MCL appears mostly within the area between

CLC Well Nos. 18, 19, 21, and 27 particularly in the deeper zones. Vertically, PCE concentrations

above the MCL appear to have been pulled down from the water table into deeper portions of the

aquifer by pumping associated with the municipal supply wells. Figure 2-4 shows that CLC Well 18

has had the greatest overall influence on the PCE migration into deeper portions of the aquifer.

However, PCE contamination is also migrating towards the east in the upper portion of the lower

ground water zone. This is evident based on the PCE concentrations at monitor well GWMW09. The

most likely cause for this migration is the influence of pumping at CLC Well Nos. 19 and 21.

Concentrations of PCE in ground water decrease outside of the primary plume boundary thus

indicating that the detections of PCE observed to the south (near City Well No. 24) and southwest

(near multi-level ground water monitoring well GWMW07) are unrelated to the GWP site.

005838




005839


Section 3 Conceptual Site Model

Data gathered from initial field investigations and the Source Investigation completed in 2003, was

used to develop a conceptual understanding of the site in terms of sources and potential migration

pathways. This conceptual model is used to evaluate potential risks to human health and the

environment, to assist in identifying locations where additional sampling is necessary, and ultimately

to assist in the identification of possible remedial technologies. This understanding is necessary to

enable appropriate design of the RI/FS in the planning stage.

During the Source Investigation, PCE source areas were identified at the following locations:

• The former National Guard Armory currently owned by the CLC.

• The former Crawford Municipal Airport currently owned by the CLC.

• The DACTD maintenance facility.

At these locations, historic operations involving the use of PCE have resulted in the release of PCE to

the surface soil which subsequently migrated into the unsaturated zone through leaching/infiltration

and volatilization into the soil vapor. Current soil vapor and ground water data suggests that no dense

non-aqueous phase liquid (DNAPL) exists in the unsaturated zone and aquifer, respectively. PCE

contamination in the ground water is therefore likely a result of the partitioning of PCE from the soil

vapor to the ground water. Once dissolved in the ground water, PCE migrates horizontally in the

direction of ground water flow. Ground water flow at the site is generally eastward in the direction of

the CLC municipal supply wells. Vertically, pumping from the CLC municipal wells has pulled PCE

contaminated ground water downward into deeper portions of the aquifer. Figure 3-1 shows a

generalized depiction of the conceptual model for the site.

The migration pathways for contamination originating from the identified source area include surface

soil, subsurface soil, soil vapor, and ground water. The identification of potential receptors along

these migration pathways, and the risk to these potential receptors, is a function of the RI/FS process.

CLC municipal supply Well Nos. 18, 19, 21, and 27 are impacted by PCE and serve as the only

primary identified link to possible receptors at the site. CLC Well Nos. 18 and 27 are shut down due

005840



to the presence of elevated levels of PCE and are not anticipated to be returned to service. CLC Well

No. 19 was shut down in July 2005 due to well failure. Only CLC Well No 21 currently remains as a

potential link of PCE contaminated ground water associated with the GWP site to possible receptors.

The CLC currently blends water from CLC Well No. 21 with non-PCE impacted water from several

other CLC wells prior to entering the water distribution system. While ground water potentially

affected with low levels of PCE may be found in the water distribution system, concentrations that

may reach water users are documented below the drinking water MCL.

Private water supply wells that exist within the footprint of the PCE plume may also provide a link to

potential receptors. A search of private water supply wells was conducted during the Source

Investigation (EPA, 2003). Three private wells were identified in the vicinity of the plume and two

contained low levels of PCE in the ground water. However, these wells are cross-gradient to the

direction of ground water flow and to the plume, and therefore PCE detects in these private wells are

not likely associated with the site. An additional search for private supply wells in the plume

footprint is identified in Section 5 to address this link to potential receptors.

To address the concern that drinking water from the CLC municipal water distribution system may

pose an inhalation risk to human receptors, through the use of the water in showers or evaporative

coolers, the potential for risk to human receptors through exposure to volatilized PCE in indoor air

was evaluated. A calculation was performed to determine the concentration of PCE that would have

to be present in the water supply to present an indoor air risk to human receptors using the Integrated

Human Exposure Model (Foster and Chrostowski, 1987). The assumed exposure scenario was for a

person taking a shower using PCE-contaminated water (a more direct exposure than through the use

of an evaporative cooler). The calculation shows that the PCE concentration in the shower water

would have to be 7,140 µg/L to pose a 1 x 10-6 carcinogenic risk to human receptors through

inhalation. This concentration is over 100 times greater than the highest PCE concentration

historically detected in monitor wells at the site (53.0 µg/L at monitor well MW-SF3), and

concentrations of PCE in ground water in the distribution system are significantly lower than that

(less than 5 µg/L). Therefore, it is highly unlikely that exposure to PCE in indoor air resulting from a

shower or the use of evaporative coolers fed with water contaminated with PCE below the MCL (5

µg/L), would pose a risk to human receptors that isn’t already addressed by the pathway of direct

ingestion or direct contact with the affected water.

005841



A review of shallow soil vapor data collected during the Source Investigation and subsequent vapor

intrusion screening based on the Source Investigation shallow soil vapor results, indicated that PCE

concentrations in the shallow soil vapor in the residential neighborhood northeast of the intersection

of Hadley Avenue and Walnut Street may pose a link to potential receptors. Additional shallow soil

vapor sampling is described in Section 5 to further evaluate this link to potential residential receptors

in this neighborhood.

005842




005843


Section 4 Data Quality Objectives

To identify and describe the type and quality of the data needed to support future decisions regarding

remedial actions at the GWP site, general DQOs have been identified. These DQOs are qualitative

and/or quantitative statements that provide a basis for the identification of the RI/FS activities to be

performed, and ensure that data collected during the RI/FS will be of sufficient and adequate quality

for their intended use. EPA guidance on the DQO process has been utilized in developing these

initial DQOs (EPA, 2000a). The DQO process outlined in the guidance is a seven-step process

which provides a systematic approach for defining the criteria to be met in the data collection effort.

The DQOs developed using this process are presented in Table 4-1, and discussion of the DQO

process as applied to this site is provided in the following paragraphs.

4.1 State the Problem The purpose of this first step in the DQO process is to develop an understanding of the broad context

of the problem being addressed by the investigation, and to define the issue(s) to be resolved by

completing the investigation.

An important consideration in defining the problem is identifying the involved groups who can

provide input to the planning stages of the RI/FS. For this site, these agencies are:

• EPA Region 6 Superfund Division (lead Agency).

• NMED Superfund Oversight Section (technical support).

• NMED Drinking Water Bureau.

• DACTD.

• CLC Utilities Division.

Each of these groups is familiar with the site, can provide both technical and regulatory input to the

process, and have a stake in the outcome. The community is also a key stakeholder, and the

involvement of citizens into the process is an integral part of the Superfund program. Community

005844



involvement is addressed through EPA’s development of a separate Community Involvement Plan

and assignment of an EPA Community Involvement Coordinator.

Based on the descriptions provided in Sections 2 and 3, including input provided by EPA, NMED,

DACTD, and CLC, what is known about the site is as follows: (1) there is one known contaminant

specifically associated with the GWP site (PCE); (2) soil vapor and ground water within the

investigation area are known to be affected by the presence of the contaminant PCE (in gaseous and

dissolved phases, respectively) at certain sampled locations; (3) dissolved PCE is detected in ground

water in monitor wells screened at and below the water table and in CLC Wells 18, 19, 21, and 27; (4)

concentrations of PCE in the ground water at some locations exceed the MCL of 5 µg/L; (5) PCE has

been found in shallow soil vapor above the plume, confirming that at one time there was a surface

source of PCE; and (6) potential receptors exist (consisting of users of the drinking water supply

system supplied by the ground water and possible homeowners in the residential neighborhood

northeast of the intersection of Hadley Avenue and Walnut Street).

What is known specific to the contaminant is as follows: (1) PCE was first commercially produced in

the US in 1925, and was widely used in dry-cleaning beginning in the 1930s; (2) historically, the

typical uses of PCE have been in dry cleaning, textile processing, and metal degreasing; and (3)

degradation products of PCE are TCE, cis-1,2-dichloroethene (cis-1,2-DCE), 1,2-dichloroethane (1,2-

DCA), vinyl chloride, ethene, ethane, and methane, and these degradation products are not typically

detected in ground water at the GWP site, although low concentrations of 1,2-DCA, at MW-1 (at the

DACTD facility), and TCE, in MW-SF10, have been detected

The following problem statements were determined by the RI/FS Technical Work Group to represent

that which must be evaluated for completion of the RI/FS:

1. The magnitude and extent of PCE in ground water sufficient to perform an evaluation of risk

and an evaluation of remedial alternatives.

• The extent of the plume in relation to detections of PCE observed to the south (in

shallow soil vapor near Comet cleaners, and in ground water samples from CLC Well

No. 24 and private irrigation well LRG1457).

• The extent of the plume east of affected CLC Wells 19 and 21.

• Recent concentrations of PCE in municipal supply wells within the plume boundary

and in the immediate vicinity (CLC Well No. 10).

005845



2. The relation between soil vapor contamination and contamination in the ground water in the

identified source area at DACTD Maintenance facility and whether the soil vapor is acting as

a continual source of ground water contamination.

3. The impact of PCE in shallow soil vapor to indoor air quality in the residential neighborhood

northeast of the intersection of Hadley Avenue and Walnut Street, at the Meerscheidt

Recreational Center, and at the PAL boxing facility.

4. Information regarding chemical and physical properties of the aquifer sufficient to support

evaluation of fate and transport of the PCE contamination and remedial alternatives.

5. Presence of additional private wells in the vicinity of the plume and not identified during the

source investigation field activities that may serve as potential exposure routes.

4.2 Identify the Decision The purpose of this step in the DQO process is to define the decision statement which combines the

key question(s) the investigation will attempt to resolve with the alternative actions that may be taken.

For the GWP site, the principal RI-related investigation questions associated with each problem

statement identified in Section 4.1 are as follows:

Problem Statement 1:

• Is the extent of the Griggs and Walnut sufficiently defined south of the DACTD yard, north

of Comet Cleaners?

• Where is the downgradient edge of the plume in relation to CLC Wells 19 and 21?

• What are the current concentrations of PCE in municipal supply wells within the plume

boundary and in the immediate vicinity (CLC Well No. 10)?


• What is the relation between soil vapor and ground water in the identified source area at the

DACTD maintenance facility and is the soil vapor in this area acting as a continuing source?


• Does shallow soil vapor in the residential neighborhood northeast of the intersection of

Hadley Avenue and Walnut Street, at the Meerscheidt Recreational Center, and at the PAL

boxing facility pose an unacceptable risk to human health through indoor vapor intrusion?

005846




• What physical and chemical information is needed to support an evaluation of fate and

transport of the PCE contamination in the ground water and an evaluation of remedial

alternatives?


• Are additional private wells present in the vicinity of the plume that were not identified

during the source investigation field activities and which may serve as potential exposure

routes?

Actions that could result from the resolution of the principal investigation questions are:

• Recommendation that no response action is required based on the lack of unacceptable risk to

potential receptors.

• Recommendation that some response action is required based on the unacceptable risk posed

to potential receptors.

• Identification and evaluation of potential response actions.

The ultimate outcome would be that the actions taken help achieve the goal of protecting human

health and the environment. The overall decision statement based on the principal investigation

questions and the possible actions is:

Determine whether or not the nature and extent of contamination and confirmed sources or secondary

sources of the PCE contamination in soil vapor, and ground water warrant response actions to protect

human health and the environment, and evaluate potential response action alternatives appropriate for

the site under the requirements of the National Contingency Plan (NCP).

4.3 Identify Inputs to the Decision The purpose of this step in the DQO process is to identify what information is required to support the

decision to be made, and specify which inputs require collection of additional data in the RI. These

inputs are outlined in Table 4-1.

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4.4 Define the Investigation Boundaries The investigation area for the RI corresponds to the vertical (approximately 600 feet bgs) and

horizontal (see Figure 2-3) extent of the GWP PCE ground water plume and surrounding areas where

water wells could be adversely affected by the contamination or its degradation products.

4.5 Develop a Decision Rule The purpose of this step in the DQO process is to develop a logical “if..then” statement that defines

conditions that would cause the decision makers to choose among alternative actions. Three decision

rules have been developed for the primary activities (monitor well installation and shallow soil vapor

sampling) discussed in this work plan.

Monitor Well Installation

If PCE concentrations in any of the newly installed monitor wells exceeds the MCL of 5 µg/L, then

the technical work group will need to determine if additional well installations are required or if

sufficient ground water sampling data exists to proceed with evaluating remedial alternatives. If PCE

concentrations in the ground water do not exceed the MCL of 5 µg/L, then additional well

installations are not required.

Shallow Soil Vapor (Residential Neighborhood)

If the 95 percent upper confidence limit (95 % UCL) of PCE concentrations in the shallow soil vapor

adjacent to residences just northeast of the corner of Hadley and Walnut exceed the screening level of

120 ppbv for impact to indoor air, then additional characterization such as indoor air sampling may be

required. If PCE concentrations in the shallow soil vapor do not exceed the screening level, then

additional sampling is not required.

Shallow Soil Vapor (Residential Neighborhood)

If the PCE concentration in the shallow soil vapor in any single result is higher than the screening

level of 120 ppbv then further evaluation of the potential vapor intrusion pathway may be needed.

If all shallow soil vapor PCE concentration fall below the screening level then the vapor intrusion

pathway will be concluded to be incomplete, and no further investigation is required.

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4.6 Specify Limits of Decision Errors The purpose of this step in the DQO process is to specify quantitative performance criteria for the

decision rule expressed as probability limits on potential errors in decision making. It should be

noted that this step in the DQO process does not necessarily involve a formal statistical statement,

depending on the nature of the decisions being addressed.

Monitor Well Installations

The baseline assumption in identifying decision errors is that the PCE concentration in the ground

water at each selected monitor well locations exceeds the MCL. The decision errors associated with

this sampling event therefore are: 1) erroneously deciding that the PCE concentration in the ground

water does not exceed the MCL (false negative, or Type I error); 2) erroneously deciding that the

PCE concentration in the ground water exceeds the MCL (false positive or Type II error). While the

false negative error is considered more significant, because the ground water plume will have been

determined to be bounded in these areas when in actuality the plume may extend further, thus

potentially impacting additional receptors, both types of errors will be controlled by conservatively

evaluating the sampling results. Each individual PCE ground water result will be compared with the

PCE MCL of 5 µg/L.

Residential Shallow Soil Vapor Sampling

The baseline assumption in identifying decision errors is that a potential vapor intrusion pathway is

present. The decision errors associated with this sampling event therefore are: 1) erroneously

deciding that a vapor intrusion pathway is absent (false negative, or Type I error); 2) erroneously

deciding that a vapor intrusion pathway is present (false positive or Type II error). The false negative

error is considered more significant, because it is less protective of human health. Therefore, a more

stringent probability of the false negative error of 10% is assigned (i.e. an alpha of 0.9). The

probability of a false positive error is assigned at 20% (i.e. a beta of 0.8).

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Meerscheidt Recreation Center and PAL Boxing Facility Shallow Soil Vapor Sampling

The baseline assumption in identifying decision errors is that a potential vapor intrusion pathway is

present. The decision errors associated with this sampling event therefore are: 1) erroneously

deciding that a vapor intrusion pathway is absent (false negative, or Type I error); 2) erroneously

deciding that a vapor intrusion pathway is present (false positive or Type II error). While the false

negative error is considered more significant, because it is less protective of human health, both types

of errors will be controlled by conservatively evaluating the sampling results. Each individual result

will be compared with a soil vapor screening level of 120ppbv. If all results for the building fall

below the screening level, the vapor intrusion pathway will be concluded to be incomplete, and will

not require further evaluation. If any single result is higher than the screening level, further

evaluation of the potential vapor intrusion pathway may be needed.

4.7 Optimize Sampling Design The purpose of this step in the DQO process is to identify a resource-effective sampling and analysis

design for generating data that are expected to satisfy the DQOs. Information and sampling data to be

collected in this TAWP addresses specific data gaps identified after the evaluation of data collected

during previous site investigations and which are considered essential for completion of an evaluation

of risk and remedial alternatives at the site. Details of the sampling and analysis design will be

included in the SAP.

Monitor Well Installation

The sampling design for the placement of the two multi-level ground water monitor wells were

selected by EPA and agreed upon by the technical work group. The locations were selected based on

site knowledge to address known data gaps in the existing site data. The two new monitor wells will

address Problem Statements No. 1 and 2 as defined in Section 4.1. Additional monitor wells may be

required based on the decision statement for the monitor well installation provided in Section 4.5.

During well installation soil cores of the aquifer soil matrix will be collected to address problem

statement No. 6.

Soil Vapor Monitor Point Installation

The sampling design for placement of the additional SVMP was selected by EPA agreed upon by the

technical work group. The location was selected to correspond with an identified PCE source area

and the existence of a multi-level Flute monitor well so that the relation between soil vapor and

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ground water can be properly evaluated. The new SVMP will address problem statement No. 3 as

defined in Section 4.1.

Residential Shallow Soil Vapor Sampling (Northeast of the corner of Hadley Avenue and

Walnut Street)

The sampling design to identify a vapor pathway in the 5-house area (total of 10 soil vapor sampling

locations) is intended to be able to see a minimum detectable relative difference of 2-fold between the

screening level in soil vapor (120 ppbv), and the average concentration in soil vapor. Therefore, the

design will have sufficient power to "see" a vapor intrusion risk no greater than 2E-05, a risk level

that falls well within EPA's risk reduction goals (i.e. between 1E-04 and 1E-06). Collecting these

shallow soil vapor samples will partially address problem statements No. 4 as defined in Section 4.1.

Additional sampling may be required based on the decision statement provided in Section 4.5.

During well installation, a soil core will be collected to address problem statement No. 5.

Meerscheidt Recreation Center and PAL Boxing Facility Shallow Soil Vapor Sampling

The sampling design is intended to provide spatial coverage to detect potential soil vapor

concentrations underneath an individual building. Therefore, the samples have been placed

judgmentally, to be in proximity to the building foundation, and to provide representative coverage of

the building footprint. Collecting these shallow soil vapor samples will partially address problem

statements No. 4 as defined in Section 4.1. Additional sampling may be required based on the

decision statement provided in Section 4.5.

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Section 5 Site Characterization Tasks

This section describes the tasks to be conducted to complete the RI for this site, i.e. the site

characterization portion of the RI/FS. The activities described have been structured to complement

existing data available for the site from previous investigations conducted by the NMED and EPA.

Primary tasks to be conducted as part of this RI/FS including task responsibility (shown in brackets)

are provided as follows:

• Installation of two new multi-level monitoring wells. [EPA]

• Collection of two soil cores from the newly installed monitor wells for determining fraction

of organic carbon in the aquifer soil matrix. [EPA]

• Review the New Mexico Office of the State Engineer’s database for the presence of

additional private wells. [EPA]

• Perform ground water sampling of all new and existing monitoring wells, private wells and

CLC municipal wells within the vicinity of the site. [EPA/NMED/CLC]

• Install one new SVMP. [EPA]

• Perform soil vapor sampling of the new SVMP and two existing SVMPs. [EPA]

• Conduct shallow subsurface soil vapor sampling around the residences located northeast of

the intersection of Hadley Avenue and Walnut Street, the Meerscheidt recreational Center,

and the PAL Boxing Facility. [EPA]

• Collect two subsurface soil cores around the residences located northeast of the intersection

of Hadley Avenue and Walnut Street for analysis of geotechnical parameters used in

modeling vapor intrusion. [EPA]

• Develop a ground water model for evaluation of remedial alternatives. [CLC/DAC]

• Perform an evaluation of risk to human receptors. [EPA]

• Perform an evaluation of potential remedial alternatives. [EPA]

These tasks will be conducted in accordance with EPA’s Guidance for Conducting Remedial

Investigations and Feasibility Studies Under CERCLA (EPA, 1988). The following paragraphs

address the site characterization-related activities. Section 6 describes the work to be conducted

under the Feasibility Study portion of the RI/FS.

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5.1 Private Well Search and Site Reconnaissance

This task will be performed to locate any new or existing private well not previously identified within

the vicinity of the GWP site and addresses DQO Problem Statement No. 5 in Section 4.1. The New

Mexico Office of State Engineer’s database will be searched for the presence of additional private

wells. If additional private wells are identified, a site survey will be conducted to verify the well’s

existence. In addition, the well’s owner will be interviewed to determine the use of the well and well

construction details if available. The private well information gathered during this task will be

utilized to assess potential exposure pathways for use in the completing the Human Health Risk

Assessment (HHRA) in Section 5.4.

This task also includes conducting a site reconnaissance prior to commencement of field activities.

The site reconnaissance will include the following activities:

• Identification and field marking of new monitor well and SVMP locations.

• Identification of residences where shallow soil vapor sampling will be conducted and

assisting EPA in identifying the property owner and obtaining the required access

agreements.

• Location of utility right-of-ways.

5.2 Field Investigation This section describes in general the field investigation tasks to be conducted to meet the DQOs

defined in Section 4. Monitor well, and SVMP locations to be installed and areas where shallow soil

vapor sampling will be performed are illustrated on Figure 5-1 (monitor wells) and Figure 5-2

(SVMP and shallow soil vapor sampling). Locations are approximate and will be finalized in the

field based on logistical considerations. Soil vapor and ground water samples will be analyzed

primarily for PCE and/or VOCs; however, some monitored natural attenuation (MNA) and general

water chemistry parameters will also be analyzed in the ground water for evaluation of remedial

alternatives. In addition, some geotechnical soil samples will also be collected to aid in the

evaluation of potential indoor air vapor intrusion and remedial alternatives. Table 5-1 lists each

proposed field activity and the rationale for each location relative to defining the nature and extent of

contamination and supporting an assessment of risk to human receptors and evaluation of remedial

alternatives.

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5.2.1 Site-Specific Plans

Site-specific plans that define in detail the procedures to be followed through performance of the field

investigation are provided under separate cover. These site-specific plans are: the SAP, which is

composed of the FSP and QAPP; the SMP; and the HSP. Sample collection and data management

procedures are defined in the FSP; analytical methods and quality assurance/quality control

procedures are defined in the QAPP. Access, security, contingency procedures, management

responsibilities, and IDW management procedures are described in the SMP. The HSP defines CH2M

HILL-specific employee training, required personal protective equipment, medical surveillance

requirements, and standard operating procedures applicable to the field investigation tasks to be

performed.

During mobilization, these plans will be revised as necessary to take into account site-specific details

not yet identified that may affect field procedures.

5.2.2 Access Agreements

This task includes providing support to EPA in identifying and obtaining access agreements to

complete the RI sampling effort. This work will be done prior to any field investigation work.

5.2.3 Private Water Supply Well and Monitor Well Search

Private water supply wells, both existing and abandoned will be researched (as described in Section

5.1) and located so that their locations may be surveyed as part of the civil survey activities. In

addition, this activity will include measurement of the total depth and depth to ground water in each

existing well, and determination of the viability of each private well for sampling of ground water.

Details regarding this activity are provided in the FSP.

5.2.4 Sampling Effort Mobilization/Demobilization

In preparation for performance of field investigation tasks, mobilization activities will be performed.

These activities will include identification of field support equipment and necessary facilities for

performance of the field investigation tasks, procurement of all equipment and supplies, set up and

maintenance of a property inventory control system, and shipment of equipment to the site. Also

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included in this task is procurement of subcontractors, filing of property access documentation

(obtained in the task described in Section 5.2.2) and distribution of access documentation to the field

team, and identification and delineation of a sampling equipment staging area and an IDW staging

area. This task will include setup of a sample team headquarters facility, whether an onsite trailer or

an offsite location. Such a facility will be necessary for phone, computer, and electrical connections

during performance of the field investigation.

At the completion of performance of the field investigation tasks, demobilization activities will be

performed. These activities will include restoration of the site to a standard determined by its prior

condition, removal of any temporary facilities placed onsite during performance of the field

investigation, preparation of a description and access procedures for any facilities remaining onsite

(such as monitor wells), performance of an equipment inventory and disposition of all remaining

materials and equipment procured for the investigation.

Details regarding mobilization and demobilization procedures are defined in the FSP.

5.2.5 Drilling/Well Installation

Two multi-level nested wells will be installed under this task as identified in Table 5-1. This activity,

in conjunction with other activities described in this TAWP, addresses DQO Problem Statement No.

1 in Section 4.1. Figure 5-1 shows the location of the two new monitor wells (GWMW11 and

GWMW15). Actual field locations will depend on the ability to obtain access, general site conditions

at each location, and the proximity of utilities. The installation of the additional well locations

(GWMW12, GWMW13, and GWMW14) identified in Table 5-1 and shown in Figure 5-1 have been

deferred indefinitely or until such time as deemed necessary.

Monitor well GWMW11 will be installed south of the DACTD Maintenance Yard to verify the extent

of the GWP Plume in relation to detections of PCE observed to the south (in the shallow soil vapor

near Comet Cleaners and in ground water samples collected from CLC Well No. 24 and LRG-1457).

Monitor well GWMW11 will consist of three nested wells completed in a single borehole at the water

table and at depths of approximately 300 and 530 feet bgs. Monitor well GWMW015 will be

installed east of IH-25 and north of Lohman Avenue to verify the extent of the plume east of affected

municipal supply wells CLC Well 19 and Well 21 and to evaluate the effectiveness of capture

depending on the remedial alternative selected. Monitor well GWMW15 will consist of three nested

005855



wells completed in a single borehole at depths of approximately 280, 460, and 600 feet bgs. The

exact screened interval for each nested well will be determined based on geophysical logging of each

borehole.

After installation and well development, a ground water sample will be collected from each nested

well and submitted to a subcontract laboratory for quick turnaround analysis of PCE only to obtain a

preliminary understanding of PCE concentrations in the new monitor well. The sample results will be

used to determine the necessity to potentially step-out to another location in order to define the

horizontal extent of contamination. This flexibility allows for better use of resources while in the

field.

In addition to the ground water samples collected after each well has been installed and developed,

one soil core will be collected from below the water table in each borehole during drilling for a

determination of the fraction of organic carbon in the aquifer matrix. This data will be used to support

the ground water modeling effort and in evaluation of remedial alternatives, in particular to address

DQO Problem Statement No. 4 in Section 4.1. Although the necessity of this information is not

deemed critical, the data can be obtained readily during drilling and without significant additional

effort.

Details regarding drilling and well installation procedures are defined in the FSP.

5.2.6 Soil Vapor Survey

Shallow soil vapor sampling and the installation of one SVMP as identified in Table 5-1 will be

performed under this task. This work will address DQO Problem Statement No. 2 and No. 3 in

Section 4.1. Shallow soil vapor sampling will be conducted in three locations as described below:

• Residences located in the neighborhood northeast of the intersection of Hadley Avenue and

Walnut Street.

• Around the Meerscheidt Recreational Center.

• Around the PAL Boxing Facility.

Figure 5-2 shows the locations proposed for shallow soil vapor sampling in relation to existing soil

vapor data. The shallow soil vapor sampling data will be used to assess the potential for soil vapor

005856



intrusion to pose an unacceptable risk to humans either living or using buildings/residences in the

identified locations.

The shallow soil vapor sampling will be conducted using field sampling techniques that will allow

collection of soil vapor samples close to building and residential foundations. Shallow soil vapor

samples will be analyzed for VOCs. It is anticipated that the shallow soil vapor analysis will be

performed using a portable field gas chromatograph (GC). Approximately 80 to 120 soil vapor

samples will be collected from 40 to 60 locations at depth intervals of 5 and 10 feet bgs. Each soil

vapor sample will be analyzed using a portable GC to allow for quick decisions to be made in the

field as to the location of additional sample points.

Two shallow subsurface soil cores will also be collected in the residential neighborhood during the

shallow soil vapor sampling. The soil cores will analyzed for geotechnical parameters which will be

used in modeling concentrations of PCE in indoor air as a result of vapor intrusions. The shallow soil

cores will be sent to a geotechnical laboratory for analysis of porosity, soil classification, moisture

content, and density.

In addition to the shallow soil vapor sampling, one SVMP (see Figure 5-2) will be installed at the

DACTD Maintenance facility. This SVMP will be installed to evaluate the relation between soil

vapor contamination and contamination in the ground water in the previously identified source area

located at the DACTD Maintenance facility and for use in evaluating remedial alternatives. The

SVMP will be installed at 20-foot intervals starting 20 feet bgs to the water table. Soil vapor samples

will be collected from the newly installed SVMP and two existing SVMPs (SVMP01 and SVMP03)

at intervals of 20 feet to the water table for analysis of VOCs.

Details regarding the soil vapor survey, drilling, and SVMP installation procedures are defined in the

FSP.

5.2.7 Ground Water Sampling

This activity includes ground water sampling of all new and existing monitor wells, new and existing

private wells, and select CLC water supply wells within and in the immediate vicinity of the plume as

identified in Table 5-1. This activity will address, in conjunction with other activities described in

this TAWP, DQO Problem Statement No. 1 in Section 4.1.

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One round of ground water sampling will be performed for all new and existing wells. This sampling

event would include water level collection and ground water sampling of the up to six newly installed

conventional monitor wells, the seventeen existing conventional monitor wells, and the eight existing

multi-level monitor wells (52 sample ports), for a total of up to 75 sampling locations. The new and

existing conventional monitor wells would be sampled with a pump and the existing multi-level

monitor wells would be sampled using existing dedicated equipment. The proposed analytical

parameters include:


• Natural attenuation parameters at a subset of wells (12 sample locations).

• Total dissolved solids (TDS) and total hardness (up to 31 locations).

All ground water samples for VOC analysis, approximately 75 plus quality assurance/quality control

(QA/QC) samples, will be sent to an EPA CLP laboratory. The MNA parameters to be analyzed for

includes: dissolved oxygen, nitrate, ferrous iron, dissolved manganese, sulfate, sulfide, total organic

carbon, carbon dioxide, dissolved gasses (methane, ethane, and ethene). The dissolved gas samples

will be sent to a specialty subcontract laboratory for analysis. The remaining MNA samples with the

exception of ferrous iron and dissolved manganese will be sent to EPA’s Houston Laboratory for

analysis. Ferrous iron and dissolved manganese will be analyzed in the field. In addition, a subset of

up to 31 wells will be sampled and analyzed for TDS and total hardness. These samples will also be

sent to EPA’s Houston Laboratory for analysis.

In addition to performing ground water sampling on all new and existing site monitor wells, newly

identified private supply wells will also be samples for VOCs. Likewise, CLC water supply wells

No. 10, 18, 19, 21, 24, and 27 will also be sampled for VOCs.

Details regarding sample collection procedures and selected analyses are defined in the FSP.

Analytical method procedures and quality assurance/quality control procedures are defined in the

QAPP.

5.2.8 Surveying of Sample Locations

All new shallow soil vapor sampling, monitor well and SVMP locations will be surveyed for northing

and easting using the New Mexico State Plane coordinate system. Well casing elevations will be

005858



surveyed for elevation to the nearest 0.01 foot using the National Geodetic Vertical Datum (NAD 83).

The point on the well casing used for surveying will be permanently etched or notched into the

northernmost point on the rim of the casing.

Details regarding the surveying of sample locations are included in the FSP.

5.2.9 Management of Investigation-Derived Waste

This task includes management, characterization and disposition of IDW associated with performance

of the field investigation. Procedures will be conducted in accordance with EPA’s Guide to

Management of Investigation-Derived Wastes (EPA, 1992a). Detailed procedures regarding

management of IDW are provided in the SMP.

5.3 Data Evaluation The data evaluation task is included for the organization and evaluation of all new and existing data

gathered for the site. Activities include validation of laboratory analytical data, and data reduction,

tabulation, and evaluation.

5.3.1 Data Validation

This task includes validation of the laboratory analytical results, and an evaluation of the usability of

the data. Details regarding data validation are presented in the QAPP.

5.3.2 Data Reduction, Tabulation, and Evaluation

Upon validation of the laboratory analytical results, these results will be incorporated into the existing

site database. Evaluation of the data in terms of nature and extent of contamination and contaminant

fate and transport will be performed. This evaluation will support preparation of the RI Report

described in Section 5.6.

5.3.3 Data Evaluation Technical Memorandum

Once data validation, reduction, tabulation, and evaluation are complete, a draft technical

memorandum will be submitted to the Technical Work Group detailing the results of the data

evaluation. Once comments are received for the draft technical memorandum, a final technical

005859



memorandum will be prepared that incorporates the comments and submitted to the Technical Work

Group.

5.4 Human Health Risk Assessment A HHRA will be performed to assess whether site-related chemicals pose a potential current or future

risk to human health in the absence of remedial action. Included in the HHRA will be an

identification of chemicals of potential concern (COPCs), assessment of potential exposure pathways,

assessment of contaminant toxicity, and risk characterization. This characterization will provide a

basis for determining whether remedial action is necessary at the site, identify which exposure

pathways may warrant remediation, and provide justification for performance of remedial actions.

5.4.1 Data to be Considered in the Human Health Risk Assessment

All soil vapor data that is available will be used in the HHRA. If indoor air samples are collected

(based on results of the soil vapor sampling), the indoor air data will be used in the HHRA instead of

the soil vapor data. Ground water data collected within the last two years (2003 through 2005) will

be used in the HHRA.

5.4.2 Chemicals of Potential Concern Selection Process

The COPCs will be identified for soil vapor (if used), indoor air (if used), and ground water by a

three-step screening process that evaluates 1) frequency of detection, 2) background concentrations

(for evaluation of indoor air only), and 3) risk-based screening levels.

5.4.2.1 Step 1: Frequency of Detection Evaluation

The frequency at which each chemical was detected will be evaluated. Those constituents detected at

a frequency of five percent or less in soil vapor, indoor air, or ground water will be eliminated from

the HHRA. Those constituents detected at a frequency greater than five percent will be carried to

Step 2 of the COPC screening process.

5.4.2.2 Step 2: Comparison to Background Levels (Indoor Air Only)

For each analyte carried to Step 2, the detected concentrations in indoor air samples, if collected, will

be compared to background concentrations measured in outdoor (ambient) air samples to determine if

005860



indoor air concentrations resemble outdoor air concentrations. If indoor and outdoor air

concentrations are similar, it may not be possible to determine if measured indoor air concentrations

are due to vapor intrusion. Chemicals detected in indoor air samples at maximum concentrations

equal to or less than maximum background samples will be eliminated as COPCs. However,

chemicals detected in indoor samples at maximum concentrations greater than background levels will

be carried to Step 3 of the COPC selection process.

5.4.2.3 Step 3: Comparison to Screening Levels

For each analyte carried to Step 3, the 95 % UCL on the mean concentration will be compared to the

human health risk-based screening levels identified below:

• Soil Vapor – EPA draft generic screening levels for deep soil vapor concentrations for indoor

air vapor intrusion, based on a residential scenario, a target excess lifetime cancer risk

(ELCR) of 1x10-5 , and a non-cancer hazard index (HI) of 1 (EPA, 2002).

• Indoor Air – EPA draft generic screening levels for indoor air concentrations, based on a

residential scenario, a target ELCR of 1x10-5 , and a non-cancer HI of 1 (EPA, 2002). The

chemicals, if any, detected at concentrations exceeding the screening levels will be identified

and compared with survey information on indoor chemical storage and use. It will be noted

in the risk characterization if chemicals detected in indoor air above screening levels are also

used or stored in the building sampled.

• Ground Water – The federal or state MCL, if one is available. For those chemicals without

MCLs, the EPA Region 6 Media-Specific Screening Level (MSSL) for tap water based on a

residential scenario, a target ELCR of 1x10-6 and a non-cancer HI of 1.

In addition, the sample quantitation limits will be compared to screening levels for analytes that were

non-detected in all samples from a specific environmental medium.

5.4.3 Potential Receptors

Child and adult residents, as well as industrial/commercial workers, were identified as current and

future realistic receptors in the vicinity of the site. These receptors will be evaluated for significant

exposure pathways in the HHRA. The future land uses and activities are assumed to be the same as

present.

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5.4.4 Exposure Scenarios to be Quantified in the Human Health Risk Assessment

Various potential exposure scenarios will be quantified in the HHRA. The specific exposure points,

receptors, and intakes to be quantified will be based on results of the COPC screening and the

locations of the exceedances. After the field investigation activities described in Section 5.2 have

been conducted and the data have been validated, the COPC screening identified in Section 5.4.2 will

be performed. Subsequently, a discussion will be held with EPA to identify the specific exposure

points, receptors, and intakes to be quantified.

5.4.5 Toxicity Assessment

The following hierarchy of sources will be used to obtain toxicity data for COPCs at the site:

• Integrated Risk Information System (IRIS)

• Provisional Peer-Reviewed Toxicity Values (PPRTVs)

• National Center for Environmental Assessment (NCEA)

• Health Effects Assessment Summary Tables (HEAST)

For those constituents (if any) with missing toxicity values, toxicity values for proxy chemicals will

be used if available. Constituents with no appropriate proxy toxicity values will be evaluated

qualitatively in the HHRA.

5.4.6 Cleanup Goal Development

Cleanup goals will be developed for soil vapor, ground water, or indoor air if the total risk for a

receptor exceeds 1x10-5 or a HI of 1. The cleanup goals will be developed for those COPCs with an

individual ELCR exceeding 1x10-5 or HI of 1, based on these target risk levels. The same exposure

factor values used in the exposure assessment will be used to calculate cleanup goals.

5.4.7 Human Health Risk Assessment Deliverables

Three deliverables are anticipated for the HHRA:

1. Interim deliverable

2. Draft HHRA

3. Final HHRA

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Interim Deliverable

An interim deliverable, consisting of draft Risk Assessment Guidance for Superfund (RAGS) Part D

Tables 1 through 6, will be provided to the Technical Work Group for review and comment prior to

calculating estimated risks.

Draft HHRA

After receipt of comments on the interim deliverable, a draft version of the HHRA document will be

prepared and submitted to the Technical Work Group for comment. An abbreviated technical

memorandum format, rather than a typical, lengthy report format, will be used to present the HHRA.

The technical memorandum will present the four main steps of the HHRA process:

• 1 - Identification of COPCs

• 2 - Exposure assessment

• 3 - Toxicity assessment

• 4 - Risk Characterization (including uncertainties)

The technical memorandum will clearly state the assumptions used in identifying the potential

exposure scenarios, receptors, and exposure factors. The RAGS Part D tables will be provided as an

attachment to the technical memorandum.

Final HHRA

After receipt of comments on the draft HHRA, a final version of the HHRA document will be

prepared and submitted to the Technical Work Group.

5.5 Ecological Risk Assessment

In accordance with EPA guidance, a Tier 1 Ecological Checklist will be prepared to characterize the

ecological setting and to determine the existence of potentially complete and significant ecological

exposure pathways. Since the impacted environmental medium at the GWP Site is ground water, and

since ground water does not release to surface water near the site, it is expected that no complete or

significant exposure pathways to ecological receptors will be identified, and ecological concerns will

be eliminated from further (Tier 2 or 3) ecological assessment.

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5.6 Ground Water Modeling

This task includes the preparation of a site-specific ground water flow and contaminant transport

model using the MODFLOW and MT3D codes. The model will serve as a tool for assessing the zone

of capture related to existing CLC water supply wells and to assess pumping rates from these wells to

determine the most effective removal of PCE contamination from within the site boundary. The CLC

has assumed primary responsibility for the modeling task with review by the Technical Work Group;

the CLC’s detailed description of the scope of work for the ground water modeling is provided in

Appendix A to this Work Plan.

5.7 Remedial Investigation Report A RI report will be prepared to document the information collected during the site characterization

and relevant data from previous sampling events. The data collected will be summarized and

evaluated to provide an assessment of key organic and/or inorganic contaminants attributable to the

site and the nature, extent, and degree of contamination by those key contaminants. The evaluation

will include preparation of cross-sections. Interpretation of the fate and transport of site contaminants

will be included. Supporting data, information, and calculations will be included as appendices. In

addition, the report will include the human health and ecological risk assessment. The report will be

structured to include the following:

• Site description and background.

• Description of site characterization tasks, including field investigation activities and

description and rationale behind any deviations from the work plan or site-specific plans.

• Description of site characterization in terms of geographical and environmental setting, based

on literature sources and available site-specific data, including the final site conceptual

model.

• Description of nature and extent of contamination.

• Description of applicable and site-specific fate and transport mechanisms and migration

pathways, based on the final site conceptual model.

• Description of the risk assessment.

• Summary and conclusions.

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A draft report will be prepared for review by the Technical Work Group. Upon receipt of comments,

a final report which incorporates these comments will be prepared and submitted.

5.8 Project Schedule

The overall project schedule to complete the field investigation, conduct the FS, and prepare the RI

and FS reports is included as Figure 5-3. Refinements to the schedule are likely and will be

communicated by the project manager to the project team via project instruction updates.

005865


Section 6 Feasibility Study Tasks

This section describes the tasks to be conducted to address the FS portion of the RI/FS. Tasks to be

conducted include compilation of Applicable or Relevant and Appropriate Requirements (ARARs),

definition of remedial action objectives, establishment of general response actions, identification and

screening of remedial technologies, description and detailed analysis of potential remedial

alternatives, performing a remedial alternatives evaluation, and preparation of a Feasibility Study

Report. These tasks will be performed in accordance with EPA’s Guidance for Conducting Remedial

Investigations and Feasibility Studies under CERCLA (EPA, 1988).

6.1 Compilation of Applicable or Relevant and Appropriate

Requirements Remedial actions selected for a site must comply with all ARARs of federal laws and more stringent

state environmental laws. Under the Comprehensive Environmental Response, Compensation, and

Liability Act (CERCLA), a requirement may be either “applicable” or “relevant and appropriate” to a

specific removal action, but not both. Definitions are as follows:

Applicable Requirements are defined as those clean-up standards, standards of control, and other

substantive environmental requirements, criteria, or limitations promulgated under federal or state

environmental or facility-siting laws that specifically address a hazardous substance, pollutant,

contaminant response action, or location at a CERCLA site.

Relevant and Appropriate Requirements are those requirements that, while not specifically

applicable to a hazardous substance, pollutant, contaminant, response action, location, or other

circumstance at a CERCLA site, address problems or situations sufficiently similar to those

encountered at a CERCLA site that their use is well-suited to the site.

Under this task, ARARs will be identified and compiled for the GWP site, and utilized in the

evaluation of remedial actions.

005866



6.2 Development of Remedial Action Objectives Based on the information collected and described for the site, site-specific remedial action objectives

will be developed. These remedial action objectives will be designed to ensure protection of human

health and the environment. Each objective will include a definition of the contaminant and media of

concern, the migration pathways and exposure routes, receptors, and preliminary remediation goals.

The preliminary remediation goals will define acceptable contaminant levels or a range of levels for

each exposure route.

6.2.1 Development of General Response Actions

This task will include the development of general response actions for each media of concern in terms

of treatment, excavation, pumping, etc., that would satisfy the remedial action objectives. The

response actions will account for the level of protectiveness identified by the remedial action

objectives and the chemical and physical characteristics of the site.

6.3 Identification and Screening of Remedial Technologies Available remedial technologies will be identified and screened based on the remedial action

objectives and the general response actions described for the site. Table 6-1 includes a preliminary

screening of potential remedial alternatives effective in removing VOCs from ground water. Only

those technologies applicable to the contaminants of concern, their physical matrix, and the exposure

pathways will be considered, and not all of these technologies will pass the screening process.

Representative process options will be selected to undergo remedial alternative development; this

selection will be based on the technology’s ability to effectively address the contamination at the site

and the technology’s implementability and potential cost.

The preferred presumptive remedy for treatment of VOCs in the vadose zone is soil vapor extraction

(SVE). EPA’s User’s Guide to the VOCs in Soils Presumptive Remedy (EPA, 1996a) and Site

Characterization and Technology Selection for CERCLA Sites with Volatile Organic Compounds in

Soils (EPA, 1993) will be used as a basis for the identification and review of technologies for soils

alternatives, as supplemented by other technologies described in literature. The presumptive remedy

will be utilized for the development and screening of alternatives portion of the feasibility study.

005867



The preferred remedial alternatives for treatment of contaminated ground water include no action,

MNA, and ground water extraction and treatment. EPA’s Considerations in Ground Water

Remediation at Superfund Sites (EPA, 1992b) and Presumptive Response Strategy and Ex-Situ

Treatment Technologies for Contaminated Ground Water at CERCLA Sites (EPA, 1996b) will be

used as a basis for the identification and review of ex-situ treatment technologies for ground water

alternatives, as supplemented by other technologies described in literature.

Data collected during the site characterization described in Section 5 will be used to evaluate the

applicability of the various technologies. Treatability study activities and/or aquifer testing may be

recommended to EPA during performance of this task if they are determined to be necessary for the

evaluation of remedial technologies.

6.4 Development and Screening of Remedial Alternatives Potential remedial alternatives will be developed based on the identification and screening of

remedial technologies and the site characterization. These media-specific or site-wide alternatives,

based on potential technologies or combination of technologies identified in the technology screening

process, will be defined with respect to size and configuration of the representative process options,

time for remediation, spatial requirements, disposal options, required permits, imposed limitations,

and other factors necessary for evaluation of the alternatives. These alternatives will be preliminarily

screened for effectiveness, implementability, and cost.

Following completion of these tasks, a draft Technical Memorandum will be prepared and submitted

to the Technical Work Group for review. This Technical Memorandum will detail the compilation of

ARARs, the remedial action objectives, the general response actions, identification and screening of

applicable remedial technologies, and the development and screening of remedial alternatives. After

incorporation of comments, a final Technical Memorandum will be prepared and submitted.

6.5 Evaluation of Remedial Alternatives The selected alternatives that are selected based on the preliminary screening will undergo a remedial

alternatives evaluation. This evaluation will include a description of each media-specific or site-wide

alternative that outlines the remediation strategy and identifies associated ARARs and a profile of

each alternative in terms of each of the evaluation criteria. The evaluation will be presented in tabular

form. After analysis of individual alternatives, all alternatives will be compared and contrasted to one

005868



another with respect to each evaluation criteria. A draft Technical Memorandum presenting the

evaluation of each alternative will be prepared and submitted to the Technical Work Group for

review. After incorporation of comments, a final Technical Memorandum will be prepared and

submitted.

6.6 Feasibility Study Report A feasibility study report will be prepared to document the identification, screening, and evaluation of

remedial alternatives for the GWP site. This report will include a description of the remedial action

objectives and general response actions, a presentation of ARARs, a description of the technologies

screened and the results of that screening process, a description of the identified remedial alternatives,

and a description of the detailed evaluation of those alternatives.

A draft report will be prepared and submitted to the Technical Work Group for review. Upon receipt

of comments, a final report which incorporates these comments will be prepared and submitted.

005869


Section 7 References

CH2M HILL, 2001. Work Assignment Work Plan, Remedial Investigation/Feasibility Study, Griggs

and Walnut Ground Water Plume Site. Remedial Action Contract Work Assignment 061-

RICO-06HZ. April 3, 2001.

CH2M HILL, 2002a. Field Sampling Plan, Remedial Investigation/Feasibility Study, Griggs and

Walnut Ground Water Plume Site. Remedial Action Contract Work Assignment 061-RICO-

06HZ. Version 1.1. February 2002.

CH2M HILL, 2002b. Quality Assurance Project Plan, Remedial Investigation/Feasibility Study,

Griggs and Walnut Ground Water Plume Site. Remedial Action Contract Work Assignment

061-RICO-06HZ. Version 1.1. February 2002.

CH2M HILL, 2002c. Site Management Plan, Remedial Investigation/Feasibility Study, Griggs and



CH2M HILL, 2002d. Health and Safety Plan, Remedial Investigation/Feasibility Study, Griggs and



CH2M HILL, 2004. January 2004 Ground Water Sampling Report. Remedial Action Contract Work

Assignment 961-RICO-06HZ. Version 1.1. June 2004.

Foster, S.A., and P. C. Chrostowski. “Inhalation Exposures to Volatile Organic Contaminants in the

Shower.” APCA. June 1987.

Frentzel, Peter F., et. al, 1990. Geohydrology and Simulation of Ground-Water Flow in the Messila

Basin, Doña Ana County, New Mexico, and El Paso, Texas. U S Geological Survey Open-

File Report 88-305. January 1, 1990.

King, W. E., et. al, 1971. Hydrogeologic Report 1, Geology and Ground-Water Resources of Central

and Western Doña Ana County, New Mexico. New Mexico State Bureau of Mines and

Mineral Resources, New Mexico Institute of Mining Technology. 1971.

US Environmental Protection Agency (EPA), 1988. Guidance for Conducting Remedial

Investigations and Feasibility Studies Under CERCLA. Interim Final. EPA/540/G-89/004.

OSWER Directive 9355.3-01. October 1988.

005870



US Environmental Protection Agency (EPA), 1992a. Guide to Management of Investigation-Derived

Wastes. Fact Sheet. OSWER Directive 9345.3-03FS. January 1992.

US Environmental Protection Agency (EPA), 1992b. Considerations in Ground-Water Remediation

at Superfund Sites and RCRA Facilities - Update. OSWER Directive 9283.1-06. May 1992.

US Environmental Protection Agency (EPA), 1993. Presumptive Remedies: Site Characterization

and Technology Selection for CERCLA Sites with Volatile Organic Compounds in Soils.

OSWER Directive 9355.0-48FS. September 1993.

US Environmental Protection Agency (EPA), 1996a. User’s Guide to the VOCs in Soils Presumptive

Remedy. OSWER Directive 9355.0-63FS. July 1996.

US Environmental Protection Agency (EPA), 1996b. Presumptive Response Strategy and Ex Situ

Treatment Technologies for Contaminated Ground Water at CERCLA Sites, Final Guidance.

OSWER Directive 9283.1-12. October 1996.

US Environmental Protection Agency (EPA), 2000a. Data Quality Objectives Process for Hazardous

Waste Site Investigations, EPA QA/G-4HW, Final. EPA/600/R-00/007. January 2000.

US Environmental Protection Agency (EPA), 2000b. HRS Documentation Record, Griggs and

Walnut Ground Water Plume Site, Las Cruces, Doña Ana County, New Mexico, CERCLIS

ID. No. NM0002271286. Prepared for EPA by Roy F. Weston. November, 2000.

US Environmental Protection Agency (EPA), 2001. Statement of Work for Remedial

Investigation/Feasibility Study (Griggs and Walnut Ave Ground Water Plume, Las Cruces,

New Mexico). Remedial Action Contract Work Assignment 029-RI-CO-06HZ. January 18,

2001.

US Environmental Protection Agency (EPA), 2002. Draft Guidance for Evaluating the Vapor

Intrusion to Indoor Air Pathway from Groundwater and Soils. 2002.

US Environmental Protection Agency (EPA), 2003. Identification of PCE Release Areas (Griggs and

Walnut Ave Ground Water Plume, Las Cruces, New Mexico). Remedial Action Contract

Work Assignment 961-RI-CO-06HZ. November 2003.

United States Geological Survey (USGS), 1978. Topographic Map. UTM 13 334177E 3576538N,

Las Cruces Quad. 1978.

005871

Tables

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005873

GWP_TWP_VER2.0_TABLE4-1_2005-0919.DOC PAGE 1 OF 2 SEPTEMBER 2005

Table 4-1 Data Quality Objectives Griggs and Walnut Avenue Groundwater Plume Superfund Site Las Cruces, New Mexico Media of Interest Data Quality Objective RI/FS Activity Analytes

Shallow soil vapor ( 0 to 10 feet bgs)

Determine the impact of PCE in shallow soil vapor to indoor air quality in the residential neighborhood northeast of the intersection of Hadley Avenue and Walnut Street, at the Meerscheidt Recreational Center, and at the PAL boxing facility.

• Collect shallow soil vapor measurements next to existing structures in three areas: at the residential neighborhood northeast of the intersection of Hadley Avenue and Walnut Street; at the Meerscheidt Recreational Center; and at the Police Athletic League Boxing facility

• Collect two shallow subsurface soil cores adequate to support modeling of soil vapor intrusion.

• Collect data adequate to perform an evaluation of risk, using existing data as appropriate to reduce RI data collection.

• Volatile Organics • Physical soil

parameters1

Subsurface soil vapor (10 to approximately 200 feet bgs)

In the source area at the DACTD maintenance Facility, identify the relation between PCE contamination in the soil vapor and ground water and confirm is PCE in the soil vapor is acting as a continuing source to the ground water.

• Install one soil vapor monitoring point down to the water table in the identified source area located in the DACTD maintenance facility

• Sample subsurface soil vapor for volatile organics.

• Volatile Organics

Ground water (below water table - below approximately 200 feet bgs)

Confirm magnitude and extent of PCE in ground water sufficient to perform an evaluation of risk and to make risk-based decision regarding necessary response actions.

• Collect adequate ground water data from monitor wells, CLC municipal supply wells and private supply wells to perform an evaluation of risks and remedial alternatives.

• Install two new nested monitor wells to further define the extent of contamination sufficient to perform an evaluation of remedial alternatives

• Volatile Organics

005874


Table 4-1 Data Quality Objectives Griggs and Walnut Avenue Groundwater Plume Superfund Site Las Cruces, New Mexico Media of Interest Data Quality Objective RI/FS Activity Analytes

Ground water and subsurface soil (below water table - below approximately 200 feet bgs)

Characterize local aquifer properties (physical and chemical) and flow conditions sufficient to support evaluation of fate and transport of the PCE contamination and remedial alternatives.

• Computer modeling to evaluate ground water flow conditions, contaminant fate and transport, and to evaluate potential remedial action alternatives.

• Collect two soil cores from the aquifer matrix for use in ground water modeling and evaluation of remedial alternatives

• Collect natural attenuation and other general water chemistry parameters for use in evaluating remedial alternatives

• MNA parameters3 • General water

chemistry parameters2

• Fraction of Organic Carbon

Ground water (below water table - below approximately 200 feet bgs)

Evaluate the presence of additional private wells in the vicinity of the plume and not identified during the source investigation field activities that may serve as potential exposure routes.

• Perform a records search of existing private supply wells in the vicinity of the plume for use in evaluating potential receptors and exposure pathways.

• NA

Notes: 1. Physical soil parameters include porosity, soil classification, moisture content, and density. 2. Water quality parameters include total dissolved solids, and total hardness. 3. MNA parameters include dissolved oxygen, nitrate, ferrous iron, dissolved manganese, sulfate sulfide, total organic carbon, carbon dioxide,

dissolved gasses (methane, ethane, ethene), total alkalinity, and chloride.

005875


Table 5-1 Activities to Performed for Completion of the RI/FS Griggs and Walnut Ground Water Plume Site Las Cruces, New Mexico

Item Purpose Description of Data Need Rationale Activities to be Completed/Deferred

Ground Water ~ Well Installation



New Monitor Well GWMW-11: Install nested well south of the DACTD Maintenance Yard. Three wells would be completed in a single borehole at the water table and at depths of approximately 300 and 530 feet below ground surface (bgs) to tap into the hydrogeologic units that, aside from the water table, seem to demonstrate the greatest mobility and degree of contamination.

To confirm the southern edge of the plume in this area, in particular to verify the extent of the GWP site plume in relation to detections of PCE observed to the south (in shallow soil vapor near Comet Cleaners, and in ground water samples from CLC Well No. 24 and irrigation well LRG-1457).

This monitor well will be installed during the planned 2005 RI field activities



New Monitor Well GWMW-15: Install nested well east of Interstate Highway 25 and north of Lohman Avenue. These three wells would be installed in a single borehole to depths of approximately 280, 460, and 600 feet bgs, to tap into the hydrogeologic units that, aside from the water table, seem to demonstrate the greatest mobility and degree of contamination.

To verify the extent of the plume east of affected municipal supply wells CLC Well No. 19 and CLC Well No. 21 and evaluate the effectiveness of capture depending on the remedial alternative selected.

This monitor well will be installed during the planned 2005 RI field activities

005876



Item Purpose Need Rationale Activities to be Completed/Deferred

Ground Water ~ Sampling




Monitor Well Sampling: One round of ground water sampling for all new and existing wells. This sampling event would include water level collection and ground water sampling of the up to eleven newly installed conventional monitor wells, the seventeen existing conventional monitor wells, and the eight existing multi-level monitor wells (52 sample ports), for a total of up to 81 sampling locations. The proposed analytical parameters include:


• Natural attenuation parameters at a subset of wells (12 sample locations are proposed).

• General water chemistry: TDS and total hardness (up to 36 locations)

The proposed natural attenuation parameters to be collected include dissolved oxygen, nitrate, ferrous iron, dissolved manganese, sulfate, sulfide, total organic carbon, carbon dioxide, dissolved gasses (methane, ethane, and ethene), total alkalinity, and chloride.

To finalize the nature and extent of contamination at the site. The final definition of the nature and extent of contamination will be used along with the existing data set to finalize the scope of the contamination to be remediated, and to support the evaluations of risk and remedial alternatives for the GWP site

One round of ground water sampling for VOCs and MNA and general water chemistry parameters will be performed during the planned 2005 RI field activities

005877



Item No.

Purpose Need Rationale Activities to be Completed/Deferred

Ground Water ~ Municipal and Private Water Well Sampling



Search the New Mexico Office of the State Engineer’s database for the presence of additional private wells not previously identified. If any additional private wells are identified, a site survey and interview with the well owner would determine the use of the well and construction details if available.

To determine if there are any private wells not previously identified that are located in the known boundary of the plume for supporting the Human Health Risk Assessment (HHRA).

A search of the New Mexico Office of the State Engineer’s database for the presence of additional private wells not previously identified will be performed during the planned 2005 RI field activities




Sample all CLC water supply wells located in and just outside of the plume boundary (CLC10, CLC18, CLC19, CLC21, CLC27 and CLC wells being blended in Upper Griggs Reservoir). Also sample all new (identified in Item No. 7 above) and existing private wells (LRG3191 and LRG1457)

To determine current concentrations of PCE in support of the HHRA evaluation and for use in finalizing the nature and extent of contamination and in evaluating remedial alternatives.

Collection of VOC samples from CLC Well No. 10, 18, 19, 21, 27, and all CLC wells being blended in the Upper Griggs Reservoir will be performed during the planned 2005 RI field activities

005878



Item No.


Subsurface Soil Samples

6. Evaluate Remedial Alternatives

Collection of two soil cores from the newly installed wells for use in determining the fraction of organic carbon in soil present in the aquifer.

To support the ground water modeling effort and evaluation of remedial alternatives in support of the FS.

One soil core from each of the newly installed monitor wells will be collected during the planned 2005 RI field activities. Although this data was not deemed critical, the soil cores could be collected with little additional effort during well drilling.

005879



Item No.


Soil Vapor ~ Monitor Point Installation



New Soil Vapor Monitor Point SVMP16. Install a soil vapor monitor point at the DACTD Maintenance Yard between monitor well GWMW01 and CLC Well 18. The soil vapor monitor point would be installed at 20 feet intervals, starting at 20 feet bgs down to the water table.


SVMP16 will be installed during the planned 2005 RI field activities. This location currently has a nearby monitor well GWMW01 available for use in evaluating the relation between soil vapor contamination and contamination in ground water

005880



Item No.


Soil Vapor ~ Sampling



Sampling of the three new and two existing soil vapor monitor points. Sample for chlorinated VOCs.


Soil vapor sampling will be performed during the planned 2005 RI field activities because this data is considered essential in defining the relation between soil vapor contamination and contamination in ground water and for use in evaluating remedial alternatives. However, only one (SVMP16) of the three proposed SVMPs will be installed.



Assess Risk to Human Health

Shallow subsurface soil vapor sampling at approximately 5 residential properties. The samples would be collected at 5 and 10 feet bgs at residences located northeast of the intersection of Hadley Avenue and Walnut Streets.

Additional shallow subsurface soil vapor sampling would be conducted around buildings associated with the Meerscheidt Recreational Center and Police Athletic League Boxing Facility. Approximately 10 locations would be probed and samples collected at 5 and 10 ft bgs.

To address soil vapor data needs related to the HHRA and specifically indoor vapor intrusion.

Shallow soil vapor sampling will be performed during the planned 2005 RI field activities because this data is considered essential for completion of the HHRA

005881



Item No.


Soil Vapor ~ Geotechnical Sampling


Collection of two surface soil cores for analysis of geotechnical parameters. Geotechnical parameters to include porosity, soil classification, moisture content and density. These would be collected in the residential area properties.

For use in indoor air vapor intrusion modeling.

Two surface soil cores will be collected during the planned 2005 RI field activities because this data is considered essential for completion of the HHRA

005882

ACTIVITIES TO PERFORMED FOR COMPLETION OF THE RI/FS GRIGGS AND WALNUT GROUND WATER PLUME SUPERFUND SITE



005883


Table 6-1 Preliminary Screening of Remedial Technologies – Ground Water Griggs and Walnut Ground Water Plume Site Las Cruces, New Mexico

Item Technology Associated Data Needs Reference

Ground Water

1. Air stripping (Ex Situ GW Remediation Technology)

• Packed tower − Ambient temperature − Higher temperature

• Aeration methods − Ambient temperature − Higher temperature

• Cascade falls

Air stripping uses volatilization to transfer contaminants from ground water to air. In general, water is contacted with an air stream to volatilize dissolved contaminants into the air stream. Stripping of a specific chemical depends on the equilibrium vapor pressure of that chemical as expressed by its Henry's law constant. Air stripping is most effective for contaminants with a dimensionless (molar volume) Henry's law constant greater than 0.01 (or 2.4 × 10 atm-m /gmol at 25 C). Removal efficiencies greater than 99 percent are difficult to achieve for certain compounds. In general, other treatment technologies will be required for such chemicals when ground-water concentrations are high (e.g., above 10,000 ppm or 1 percent). The following information is required to select the properly configured tower and packing for a specific application:

− Range of feedwater flow rates − Range of water and air temperatures − Whether the tower will operate continuously or intermittently − Tower feed and discharge systems (gravity feed or type and

location of pumps) − Height restrictions on the tower − Influent contaminant identification and concentrations − Mineral content and pH − Requirements for effluent water contaminant concentrations − Restrictions on air discharge from the tower

“Presumptive response strategy and ex-situ treatment technologies for contaminated ground water at CERCLA sites” EPA 540/R-96/023 PB96-963508 October 1996

http://www.epa.gov/superfund/resources/gwguide/gwfinal.pdf

Federal Remediation Technologies Roundtable (FRTR). The Remediation Technologies Screening Matrix. 4.45 Air Stripping

http://www.frtr.gov/matrix2/section4/4-46.html

2. Granular activated carbon (GAC) (Ex Situ GW Remediation Technology)

Activated carbon removes contaminants from ground water by adsorption. The adsorption process takes place in three steps: (1) contaminant migration to the external sorbent surface; (2) diffusion into the sorbent pore structure; and (3) adsorption onto the sorbent surface. The principal form of activated carbon used for ground-water treatment is granular activated carbon (GAC). GAC is an excellent sorbent due to its large surface area, which generally ranges from 500 to 2,000 m /g.

GAC is applicable to a wide variety of contaminants including: halogenated volatile and semivolatileorganics, nonhalogenated volatile and semivolatile organics, PCBs, pesticides, dioxins/furans, most



005884










Ground Water

Granular activated carbon (GAC), Cont.,

organiccorrosives, metals, radioactive materials, inorganic cyanides, and certain oxidizers.

The major design variables for liquid phase carbon applications are empty bed contact time (EBCT), usage rate, and system configuration. Particle size and hydraulic loading are often chosen to minimize pressure drop and reduce or eliminate backwashing. System configuration and EBCT have an impact on carbon usage rate.

Federal Remediation Technologies Roundtable (FRTR). The Remediation Technologies Screening Matrix. 4.46 Granulated Activated Carbon (GAC)


3. Chemical/UV Oxidation (Ex Situ GW Remediation Technology)

• Chemical oxidation alone − Ozone − Hydrogen peroxide − Chlorine compounds − Potassium

permanganate • Chemical with UV

oxidation − Ozone − Hydrogen peroxide

• UV oxidation alone (photolysis)

• Unspecified oxidation methods

Chemical oxidation uses chemical oxidizing agents to destroy toxic organic chemicals and cyanide compounds (CN) in ground water. Commonly used oxidizing agents include: ozone, hydrogen peroxide, hypochlorites, chlorine, and chlorine dioxide. Ozone and hydrogen peroxide are generally preferred for removing organics and CN from ground water because chlorine-based oxidants can produce toxic byproducts (e.g., HCl, chlorinated organics). Ultraviolet light (UV) is often used in conjunction with ozone and/or hydrogen peroxide to promote faster and more complete destruction of organic compounds (reaction rates may be increased by factors of 100 to 1,000).

Design and operational parameters include contact or retention time, influent water turbidity, metals and contaminant concentrations, existence of free radical scavengers, oxidizer influent dosages, pH, temperature, UV lamp intensity, and performance characteristics of catalysts.



Federal Remediation Technologies Roundtable (FRTR). The Remediation Technologies Screening Matrix. 4.44 Advanced Oxidation Processes


005885










Ground Water

4. Monitored Natural Attenuation (In Situ GW Remediation)

“Monitored Natural Attenuation”, refers to the reliance on natural attenuation processes (within the context of a carefully controlled and monitored site cleanup approach) to achieve site-specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. Natural attenuation processes may reduce the potential risk posed by site contaminants in three ways:

1. Transformation of contaminant(s) to a less toxic form through destructive processes such as biodegradation or abiotic transformations;

2. Reduction of contaminant concentrations whereby potential exposure levels may be reduced; and

3. Reduction of contaminant mobility and bioavailability through sorption onto the soil or rock matrix.

The evaluation of natural attenuation is often not straightforward and will require expertise in several technical areas including microbiology/bioremediation, hydrogeology, and geochemistry. When available, information to be obtained during data review includes:

• Soil and ground water quality data: − Three-dimensional distribution of residual-, free-, and

dissolved-phase contaminants. The distribution of residual- and free-phase contaminants will be used to define the dissolved-phase plume source area.

− Historical water quality data showing variations in contaminant concentrations through time.

− Chemical and physical characteristics of the contaminants. − Geochemical data to assess the potential for biodegradation of

the contaminants. • Location of potential receptors:

− Ground water wells. − Surface water discharge points.

Sites where the contaminant plumes are no longer increasing in extent, or are shrinking, would be the most appropriate candidates for MNA remedies.

“Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites” OSWER Directive 9200.4-17P April 1999

http://www.epa.gov/swerust1/directiv/d9200417.pdf

Federal Remediation Technologies Roundtable (FRTR). The Remediation Technologies Screening Matrix. 4.30 Natural Attenuation


005886






Table 6-1 Screening of Remedial Technologies – Soil Vapor Griggs and Walnut Ground Water Plume Site Las Cruces, New Mexico


Soil Vapor

5. Soil Vapor Extraction (In Situ Soil Remediation Technology)

Data requirements include the depth and areal extent of contamination, the concentration of the contaminants, depth to water table, and soil type and properties (e.g., structure, texture, permeability, and moisture content). Pilot studies should be performed to provide design information, including extraction well, radius of influence, gas flow rates, optimal applied vacuum, and contaminant mass removal rates.

Federal Remediation Technologies Roundtable (FRTR). The Remediation Technologies Screening Matrix. 4.8 Soil Vapor Extraction


6. Dual-Phase Extraction (DPE), (SVE) Enhancement Technologies

(In Situ Soil Remediation Technology)

• Drop-tube entrainment extraction.

• Well-screen entrainment extraction.

• Downhole-pump extraction.

DPE involves concurrent extraction of groundwater and soil vapors from a common borehole. DPE enables venting of soil vapors through previously saturated and semisaturated (capillary fringe) soils by lowering the groundwater table at the point of vapor extraction. High vacuums typically associated with DPE systems enhance both soil vapor and groundwater recovery rates. Water extraction rate increases of up to tenfold over conventional downhole pump systems have been reported. DPE is applicable to sites with the following characteristics:

• VOC contamination • Soil, groundwater, and free-product contaminant phases • Low to moderate hydraulic conductivity soils DPE is most effectively implemented in areas with saturated soils exhibiting moderate to low hydraulic conductivity (silty sands, silts, and clayey silts). Lower permeability soils enable formation of deeper water table cones of depression, exposing more saturated soils and residual contamination to extraction system vapor flow.

“Analysis of Selected Enhancements for Soil Vapor Extraction” EPA-542-R-97-007 September 1997

http://www.epa.gov/tio/download/remed/sveenhmt.pdf

7. Directional Drilling, (SVE) Enhancement Technologies (In Situ Soil Remediation Technology)

Directional drilling technologies allow SVE to be conducted in areas not easily accessed by vertical drilling techniques. Directional drilling, along the geometry of the contaminated zone, may increase the zone of influence of a single extraction or injection well. Directional drilling also enhances SVE by reducing air short-circuiting within the borehole in vertical well systems.



005887








Table 6-1 Screening of Remedial Technologies – Soil Vapor Griggs and Walnut Ground Water Plume Site Las Cruces, New Mexico


Soil Vapor

8. Thermal Treatment (In Situ Soil Remediation Technology) Electrical Resistance Heating Radio Frequency/ Electromagnetic Heating Hot Air Injection Steam Injection Conductive Heating

Thermal enhancements for SVE may involve a number of different technologies aimed at transferring heat to the subsurface to (1) increase the vapor pressure of VOCs or semivolatile organic compounds (SVOC) to enhance their removal via SVE or (2) dry soil to increase air permeability. Thermal enhancement technologies include hot air or steam injection, electrical resistance (ER) heating, radio-frequency heating (RFH), and thermal conduction heating.

Data requirements include the depth and areal extent of contamination, the concentration of the contaminants, depth to water table, and soil type and properties (e.g., structure, texture, permeability, and moisture content).



Federal Remediation Technologies Roundtable (FRTR). The Remediation Technologies Screening Matrix. 4.10 Thermal Treatment


005888





PRELIMINARY SCREENING OF REMEDIAL TECHNOLOGIES GRIGGS AND WALNUT GROUND WATER PLUME SUPERFUND SITE



005889

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005890




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City of Las Cruces (CLC) Municipal Water Supply Wells:affected by perchloroethylene (PCE)not affected by perchloroethylene (PCE)(screen depths of these wells range from 281 to 1,050 feet bgs.)

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Estimated Extent of PCE Detections

0 1,000 2,000500 FeetImage Data: USGS DOQQ, Resolution: 1 meter Map Projection: New Mexico Central State Plane, NAD83Date Flown: 1996-98

PCE Release Areas

005892

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Figure 1-1

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East Hadley Avenue

Spruce Avenue

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LEGEND

Manhole Covers

600 0 600 1200 1800 Feet

Figure 2-6

Source Investigation Sample Locations

Griggs & Walnut Ground Water Plume Site


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Image Data: USGS DOQQ, Resolution: 1 meter Map Projection: New Mexico Central State Plane, NAD83Date Flown: 1996-98

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2-1


VERSION 2.0



005895

005896

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PCE Concentration

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FIGURE 2-2 Horizontal Distribution of PCE in Soil Vapor Griggs and Walnut Ground Water Plume Site Las Cruces, New Mexico

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at the W at er Table (January 2004)Griggs & W alnut Ground W ater Plume Site

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Low Resistivity Units(Clays and Silts)Resistivity < 20 ohm/m

LEGEND

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1

Water Table (line is dashed where the location is inferred)

Inferred Lithologic Contact

Inferred Contact Between the Rio Grande Alluvium and the Santa Fe Group Lithostratigraphic Units

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Figure 9Vertical Distribution of PCE in Ground Water,

Hydrogeophysical Cross-Section B-B'January 2004

Griggs and Walnut Ground Water Plume SiteLas Cruces, New Mexico

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VERSION 2.0



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Estimated Extent of PCE Detections

0 1,000 2,000500 FeetImage Data: USGS DOQQ, Resolution: 1 meter Map Projection: New Mexico Central State Plane, NAD83Date Flown: 1996-98

PCE Release Areas

005904

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Figure 1

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Location of New Monitor Wells to be Installed during the RI

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Figure 5-1 Location of New RI Monitor Wells Griggs & Walnut Plume Site Las Cruces, New Mexico

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Area of PCE Detections

Margaret

Note: At this time, per the conclusions of the Technical WorkGroup, only GWMW11 and GWMW15 will be installed. The other locations are retained for future consideration as needed.

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Location of Proposed New Monitor Wells to be Deferred


VERSION 2.0



005905

Shallow Soil Vapor Sampling for Use inEvaluating Risk (Left to Right: PAL,Meerscheidt Rec Center, Residents)

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Depth (ft)204060

PCE (ppbv)111 B194263

Depth (ft)2040

PCE (ppbv)73 B123 B

Depth (ft)30486890115

PCE (ppbv)575771848939984

Depth (ft)20406080100

PCE (ppbv)1685047319191135

Depth (ft)1235557595115

PCE (ppbv)NDNDNDNDNDND

Depth (ft)40607592

PCE (ppbv)ND10 BNDND

South Solano Drive

East Lohman Avenue

Walnut Street

Griggs Avenue

Griggs & Walnut Ground Water Plume Site

N



Soil Vapor PCE Concentration Map

Legend

1 - 10 ppbv11 - 100 ppbv101 - 1000 ppbv>1000 ppbv

PCE Values for Soil Vapor Locations

PLOT_DATE: 7/6/2005

0 750 1,500375Feet

FILENAME: J:\Griggs_Walnut\Pres\MXD\PCE_pres.mxd

Area of Proposed Additional ShallowSoil Vapor Sampling to Assess VaporIntrusion Risk

Location of Proposed New Soil VaporMonitoring PointsLocation of Existing Soil VaporMonitoring Points

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Notes1.) The maximum detected soil vaporconcentrations per location are shownirregardless of depth. Most soil vaporlocations were sampled at multipledepth intervals.2.) Data Qualifier "B" - Value is belowthe lower calibration limit

005906

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Figure 5-2 Location of Planned Shallow Soil Vapor Sampling and New Soil Vapor Monitor Point

Margaret

Note: At this time, per the conclusions of hte Technical WorkGroup, only SVMP16 will be installed. The other locations are retained for future consideration as needed.


VERSION 2.0



005907

ActID Description Orig

DurRemDur

EarlyStart

EarlyFinish % Resource Budgeted

Cost MAY2005

JUN2006

JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT

1000 Prepare for Technical Workgroup Meeting 35 35 01JUN05 21JUL05 0 01010 Prepare Community Meeting Posters 30 30 08JUN05 * 21JUL05 0 01020 RI/FS Technical Workgroup Meeting 0 0 21JUL05 * 0 01030 Community Meeting 0 0 21JUL05 * 0 01040 Prepare RI/FSTechnical Work Plan 40 40 27JUL05 20SEP05 * 0 01100 Prepare RI/FS Sampling and Analysis Plan 25 25 31AUG05 04OCT05 0 01110 Prepare RI/FS Site Management Plan 25 25 31AUG05 04OCT05 0 01120 Prepare Procurement Documents 40 40 12AUG05 06OCT05 0 01130 Procure RI/FS Subcontractors 20 20 23SEP05 20OCT05 0 01140 Perform RI/FS Field Work 47 47 17OCT05 20DEC05 0 01150 Analysis and Validation of Results 30 30 07DEC05 17JAN06 0 01160 Prepare Human Health Risk Assessment 40 40 04JAN06 28FEB06 0 01170 Prepare RI Report 40 40 04JAN06 28FEB06 0 01180 CLC and County Complete GW Modeling Effort 181 181 20JUN05 * 28FEB06 0 01190 Prepare Feasibility Study Report 40 40 06FEB06 31MAR06 * 0 01200 EPA Completes the Proposed Plan 60 60 03APR06 23JUN06 0 01210 EPA Completes the Record of Decision 60 60 26JUN06 18SEP06 0 0

Start date 23MAY05Finish date 18SEP06Data date 23MAY05Run date 19SEP05Page number 1A

© Primavera Systems, Inc.

Figure 5-3Overview of RIFS Project Schedule

Griggs and Walnut Plume Surperfund SiteLas Cruces, New Mexico

Early barProgress barCritical barSummary barStart milestone pointFinish milestone point

005908


VERSION 2.0



005909

Appendix A Modeling Proposal

005910


VERSION 2.0



005911

Revision of June 9, 2005

Dan Santantonio, Ph.D. Interim Regulatory and Environmental Services Administrator Utilities Department City of Las Cruces P. O. Box 20000 Las Cruces, New Mexico 88004-9002 Re: ground-water modeling, Griggs and Walnut Superfund Site Dear Dan: This letter will provide our proposed workplan, schedule, and estimated costs for the ground-water modeling related the Griggs and Walnut site, as outlined in the March 31, 2005 letter from Samuel Coleman of EPA to Mr. Haines (Doña Ana County) and Mr. Moore. This revision reflects comments by EPA in the document review dated May 25, 2005.

We propose to work closely with Daniel B. Stephens & Associates (DBS&A) in all phases of the project, as will be more fully described below, and this workplan includes the time and costs proposed to Shomaker & Associates by DBS&A in a letter of May 2, 2005. We understand that all of the work related to modeling is to be carried under a contract between John Shomaker & Associates, Inc. (JSAI) and the City of Las Cruces, with DBS&A and other consultants as subcontractors. Workplan

The objectives of the modeling are primarily (1) to provide a tool for assessment of the zone of capture related to existing City of Las Cruces supply wells, and (2) to assess pumping rates from these and other wells to determine the most effective removal of PCE contamination from within the plume boundary. Although identification of potential sources of contamination other than those currently identified is not a primary objective, it may be that the model will be applied for that purpose. The model will be developed and tested in parallel with continued work by others on the RI/FS, and will reflect additional data as it becomes available from the RI/FS and continued monitoring. We propose to prepare a site-specific ground-water flow and contaminant-transport model, using the MODFLOW and MT3D codes, starting with the Weeden-Maddock model, the most recent publicly available version of the modeling begun by the

JOHN SHOMAKER & ASSOCIATES, INC. WATER-RESOURCE AND ENVIRONMENTAL CONSULTANTS 2703 BROADBENT PARKWAY NE, SUITE B ALBUQUERQUE, NEW MEXICO 87107 (505) 345-3407, FAX (505) 345-9920

005912

Dr. Dan Santantonio 2 May 9, 2005

U.S. Geological Survey1 and continued by the University of Arizona Department of Hydrology and Water Resources.2 The Weeden-Maddock model is regional in scale, extending from Caballo Reservoir to El Paso, and with grid dimensions of about 0.5 mile by 0.5 mile in Las Cruces. It is strictly a regional flow model, and has no solute-transport component. The site-specific model would represent, at a minimum, the area between the bedrock high along the eastern side of the inner Rio Grande valley and the Rio Grande, and would extend north and south for a sufficient distance to encompass the influences on ground-water flow in the vicinity of the Griggs and Walnut plume. The model would represent the aquifer system in finer detail than the existing models, and be calibrated to reflect known flows (pumping and recharge rates), water- levels and water- level change over time, as well as concentrations of the contaminants of interest. The elements of the proposed workplan, with principal responsibility indicated for each, are as listed below. The workplan includes provision for EPA and NMED review at specific stages, as indicated.

It is expected that close communication with EPA’s designated technical contact will be maintained throughout the project, to facilitate active integration of the modeling with the RI data collection and FS evaluation of remediation alternatives. The project budget contemplates approximately 1.5 days per month, separate from technical work on the modeling, for an initial scoping meeting and regular telephone and email communi-cation with agency staff or contractors. A.1 Initial scoping meeting to establish project objectives, milestones, deliverables, and

schedule, to include anticipated dates for meetings and peer review of deliverables. (JSAI and DBS&A).

A.2. Assemble mapping and input files for existing modeling, and supporting literature (JSAI and DBS&A).

B.1 Determine the primary historical sources of ground-water contamination that should be incorporated in the model, and develop source input parameters to apply. Develop the conceptual model. This task includes evaluation of data from existing publications, as well as all data from the ongoing investigations by EPA3 and from other resources as they are identified. All sources of contamination already identified by EPA will be considered. Other sources of information as to contamination are as yet unknown, but will be sought and evaluated (DBS&A).

1 Frenzel, P.F., and Kaehler, C.A., 1990, Geohydrology and simulation of groundwater flow in the Mesilla

Basin, Doña Ana County, New Mexico, and El Paso County, Texas, U.S. Geological Survey, Open File Report 88-305.

2 Weeden, A.C., and Maddock, T., 1999, Simulation of groundwater flow in the Rincon Valley area and Mesilla Basin, New Mexico and Texas, U. of Ariz. Research Laboratory for Riparian Studies and Dep’t. of Hydrology and Water Resources.

3 EPA, November 2003, Identification of PCE release areas in the vicinity of the Griggs and Walnut ground water plume: U.S. Environmental Protection Agency, Region 6.

CH2M HILL, June 2004, Results of the January 2004 ground water sampling event, Griggs & Walnut ground water plume Superfund site: CH2M HILL, consultant’s report to EPA.

EPA, July 2004, Presentation to City of Las Cruces and Doña Ana County.

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B.2 Submit the conceptual model for EPA and NMED review. C. Prepare a contaminant-transport package for the existing Weeden-Maddock model

(JSAI). D. Operate the Weeden-Maddock model with the contaminant-transport package to

evaluate the general validity of the existing model’s predictions as to the distribution of contamination, and therefore whether it will serve as a satisfactory basis for the site-specific model. Advective transport (particle tracking) will be applied in the Weeden-Maddock model to evaluate general ground-water flow directions and solute-transport timing. This will show whether the hydraulic properties and fthe flows represented in the Weeden-Maddock model are approximately correct, and thus will serve as a useful starting point, or are seriously in error. In any case, more rigorous solute transport modeling will be conducted using the site-specific model, with much finer discretization, developed during the project (JSAI and DBS&A).

E.1 Prepare a site-specific model, with a finer model grid, both horizontally and vertically, and with appropriate modifications in aquifer properties (JSAI and DBS&A). DBS&A will assist with identification of solute transport conceptual models, determination of appropriate aquifer and solute-transport parameters, and selection of appropriate grid dimensions for solute-transport simulation. We anticipate that the model will incorporate conservative solute transport calcula-tions, but a final determination will be made during development of the transport model.

E.2 Submit proposed model grid dimensions, input parameters for aquifer characteristics, and source areas for EPA and NMED review.

F.1 Calibrate the site-specific model (JSAI and DBS&A). The model will be a multii-layer (3-D), transient simulation. Calibration will take the form of adjustment of model parameters so that the model’s predictions adequately match historical and current hydraulic-heads, ground-water flow directions, and streamflow depletion estimates. Available data for calibration of solute transport is less certain, although basic items such as interpreted plume extent (both horizontal and vertical) will be taken into account. Adequacy of the solute transport model will be determined based on the ability to simulate, in a fairly general manner, the extent of the plume. The model is not intended to provide a detailed simulation of historical solute concentrations in each part of the aquifer, but to meet the primary objective of evaluating future remediation scenarios. DBS&A will assist in evaluation of the adequacy of both the ground-water flow and solute-transport calibrations. The calibration process may lead to an understanding of the sources and strengths of contamination that is different from the pattern as presently recognized.

F.2 Submit calibration results for EPA and NMED review. G.1 Establish plume-capture predictive scenarios, including scenarios calling for

operation of existing City of Las Cruces wells to control plume movement, and to allow for treatment of contaminated water for use or discharge. Predictive scenarios have not been determined yet, but we expect that one or more scenarios would evaluate new wells, and possibly injection of treated water. Certainly one

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scenario would contemplate using existing City wells alone to contain the plume (JSAI and DBS&A).

G.2 Submit proposed plume-capture scenarios for EPA and NMED review. H.1 Operate the calibrated model to evaluate the effectiveness of various plume-capture

scenarios (JSAI). An electronic copy of the model will be furnished to EPA to facilitate the agency’s incorporation of plume-capture scenarios into the evaluation of remedial alternatives.

H.2 Submit predictive scenarios for EPA and NMED review, and determine appropriate adjustments in pumping scenarios in consultation with agencies.

I.1 Prepare a draft report (JSAI); submit to client, EPA, and NMED for review. I.2 Prepare final report. Schedule The schedule outlined below is in terms of months from notice-to-proceed. If notice is received by June 21, 2005, and if agency review and extensive model revisions do not delay the project, the draft report would be completed by March 17, 2006. Clearly the schedule will be strongly influenced by the responsiveness of reviewing agencies.

Workplan element

Description Elapsed time (months from

notice-to-proceed to completion date)

A assemble mapping and input files 1 B determine historical sources of contamination 1

C prepare contaminant-transport package for Weeden-Maddock model 2

D operate Weeden-Maddock model 2.5 E prepare site-specific model 4 F calibrate site-specific model 6 G establish plume-capture scenarios 6

H operate the calibrated model to evaluate plume-capture scenarios

7

I prepare report 9 Cost Summary The work enumerated above would be carried out on a time-and-materials basis. Shomaker & Associates’ fees will be invoiced at our standard hourly rates as reflected in our January 2005 Schedule of Consulting Fees, less the 10-percent discount we offer to the City of Las Cruces. DBS&A fees and expenses are estimated as shown below. The estimated project costs, not including New Mexico Gross Receipts Tax, are as follows: John Shomaker & Associates, Inc. $78,451.00 Daniel B. Stephens & Associates, Inc. 36,240.00 $114,691.00

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We look forward to working with you on this project, and we would be ready to begin the project in mid-June 2005 if that meets the City’s requirements. Please let me know if there are questions, or if any further information would be helpful. Sincerely, JOHN SHOMAKER & ASSOCIATES, INC. John W. Shomaker

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