REMEDIATION SYSTEM EVALUATION

SELMA PRESSURE TREATING SUPERFUND SITE

SELMA, CALIFORNIA

Report of the Remediation System Evaluation,

Site Visit Conducted at the Selma Pressure Treating Superfund Site

November 7-8, 2001

Final Report Submitted to Region 9

January 31, 2002

 
NOTICE

Work described herein was performed by GeoTrans, Inc. (GeoTrans) and the United States Army Corps

of Engineers (USACE) for the U.S. Environmental Protection Agency (U.S. EPA). Work conducted by

GeoTrans, including preparation of this report, was performed under Dynamac Contract No. 68-C-99-

256, Subcontract No. 91517. Mention of trade names or commercial products does not constitute

endorsement or recommendation for use.

This document (EPA 542-R-02-008u) may be downloaded from EPA’s Technology Innovation Office

website at www.epa.gov/tio or www.cluin.org/rse. 
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EXECUTIVE SUMMARY

The Selma Pressure Treating site is located 15 miles south of Fresno, adjacent to the city limits of Selma,

California and has subsurface contamination from a former wood treating facility. The site occupies

approximately 40 acres, including the 14-acre former wood treating and storage facility and a 26-acre

neighboring vineyard. Zoned for heavy use, the site is located in a transition zone between agricultural,

residential, and industrial areas. Drippings from the former wood treating processes have led to both soil

and groundwater contamination beneath the former facilities. The primary contaminant of concern is

chromium, predominantly found as hexavalent chromium, its more mobile state. Remedial investigations of

the contamination began in 1984, and by 1991 soil cleanup activities had started. Approximately 18,000

cubic yards of contaminated soil have been addressed, and an additional contaminated soil will be

addressed in the future. 

A pump and treat system began operation in September 1998 to address the chromium contamination in

groundwater. The system consists of seven extraction wells, a treatment plant that removes chromium

through a co-precipitation process, and discharge of treated water to onsite percolation ponds. 

A Remediation System Evaluation (RSE) was conducted on the system in November 2001. A RSE

involves a team of expert hydrogeologists and engineers, independent of the site, conducting a third-party

review of site operations. The evaluation includes reviewing site documents, visiting the site for up to 1.5

days, and compiling a report that includes recommendations to improve the system. 

The RSE team found the site managers and contractor committed to system optimization and cost-effective

operation. Recommendations made by the RSE team to improve system effectiveness include the

following:

• An analysis of the capture zone provided by the extraction system should be conducted to

determine if site-related groundwater contamination is adequately contained. This analysis should

consist of the following three items:

< The plume boundaries, both horizontal and vertical, should be clearly delineated and

plotted for each sampling event. From these plume maps, target capture zones should be

determined. Trend analyses of chromium concentrations in each sampled well on an

annual basis would also give an indication of the progress of the remedy.

< The water level measurements that are collected during each sampling event should be

used to develop potentiometric surface maps. From these maps groundwater flow

directions and estimated capture zones may be determined and compared to the target

capture zones drawn from the plume maps. Analyses of the historical and future

potentiometric surface maps will provide site hydrogeologists with better insight into

groundwater flow beneath the site

< The groundwater flow model used to analyze the capture zone during system design should

be updated and recalibrated using historical water level measurements. In addition,

improved estimates of natural recharge and recharge from the percolation ponds should be

determined and used in modeling efforts. Once the model has been recalibrated, it should
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be used for particle tracking to provide estimates of the extraction system capture zone in

both vertical and horizontal directions. 

• The groundwater flow model can also be used to optimize the extraction system by relocating wells

or adjusting pumping rates. When the optimized extraction system is selected and implemented,

water level measurements from the regularly scheduled sampling events should be used to

recalibrate and update the groundwater flow model. Eventually, the groundwater flow model

should be able to reproduce water levels measured during the various pumping scenarios

implemented at the site.

• A contingency plan should be developed in case contaminant concentrations above MCLs are

detected in nearby residential wells.

These recommendations might require approximately $39,000 in capital costs and might increase annual

costs by approximately $7,000 per year.

The only recommendation to reduce life-cycle cost is to delist the sludge generated from the groundwater

treatment plant. The sludge from the plant is currently listed as hazardous waste from a wood treating

facility thereby requiring it to be disposed of as hazardous waste. The sludge is generated from

groundwater treatment, passes TCLP testing, and should be delisted so that it can be disposed of as

nonhazardous waste. Implementing this recommendation to reduce costs may result in savings during

operations and maintenance and could offset initial investments and costs associated with recommendations

for enhanced system effectiveness and technical improvement.

Finally, the RSE team provides additional recommendations regarding site close out, including developing

an exit strategy and addressing the remaining soil contamination.

A summary of recommendations, including estimated costs and/or savings associated with those

recommendations is presented in Section 7.0 of the report.
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PREFACE

This report was prepared as part of a project conducted by the United States Environmental Protection

Agency (USEPA) Technology Innovation Office (TIO) and Office of Emergency and Remedial Response

(OERR). The objective of this project is to conduct Remediation System Evaluations (RSEs) of pumpand-treat systems at Superfund sites that are “Fund-lead” (i.e., financed by USEPA). RSEs are to be

conducted for up to two systems in each EPA Region with the exception of Regions 4 and 5, which already

had similar evaluations in a pilot project.

The following organizations are implementing this project.

Organization Key Contact Contact Information

USEPA Technology Innovation

Office

(USEPA TIO)

Kathy Yager 11 Technology Drive (ECA/OEME)

North Chelmsford, MA 01863

phone: 617-918-8362

fax: 617-918-8427

yager.kathleen@epa.gov

USEPA Office of Emergency and

Remedial Response 

(OERR)

Paul Nadeau 1200 Pennsylvania Avenue, NW

Washington, DC 20460

Mail Code 5201G

phone: 703-603-8794

fax: 703-603-9112

nadeau.paul@epa.gov

GeoTrans, Inc. 

(Contractor to USEPA TIO)

Doug Sutton GeoTrans, Inc.

2 Paragon Way

Freehold, NJ 07728

(732) 409-0344 

Fax: (732) 409-3020

dsutton@geotransinc.com

Army Corp of Engineers:

Hazardous, Toxic, and Radioactive

Waste Center of Expertise

(USACE HTRW CX)

Dave Becker 12565 W. Center Road

Omaha, NE 68144-3869

(402) 697-2655

Fax: (402) 691-2673

dave.j.becker@nwd02.usace.army.mil
iv

The project team is grateful for the help provided by the following EPA Project Liaisons.

Region 1 

Region 2

Region 3

Region 4

Region 5

Darryl Luce and Larry Brill

Diana Cutt

Kathy Davies

Kay Wischkaemper

Dion Novak

Region 6

Region 7

Region 8

Region 9

Region 10

Vincent Malott

Mary Peterson 

Armando Saenz and Richard Muza

Herb Levine

Bernie Zavala

They were vital in selecting the Fund-lead pump and treat systems to be evaluated and facilitating

communication between the project team and the Remedial Project Managers (RPM’s).
v

TABLE OF CONTENTS

EXECUTIVE SUMMARY............................................................. . i

PREFACE .............................................................................. iii

TABLE OF CONTENTS ................................................................... v

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

1.1 PURPOSE ........................................................................ 1

1.2 TEAM COMPOSITION ............................................................... 1

1.3 DOCUMENTS REVIEWED ............................................................. 2

1.4 PERSONS CONTACTED ...................................... 2

1.5 SITE LOCATION, HISTORY, AND CHARACTERISTICS ........................................ 3

1.5.1 LOCATION ................................................................ 3

1.5.2 POTENTIAL SOURCES ........................................................ 3

1.5.3 HYDROGEOLOGIC SETTING .................................................... 3

1.5.4 DESCRIPTION OF GROUND WATER PLUME ........................................ 4

2.0 SYSTEM DESCRIPTION .............................................................. 5

2.1 SYSTEM OVERVIEW ................................................................ 5

2.2 EXTRACTION SYSTEM .............................................................. 5

2.3 TREATMENT SYSTEM ............................................................... 5

2.4 MONITORING PROGRAM ............................................................. 6

3.0 SYSTEM OBJECTIVES, PERFORMANCE AND CLOSURE CRITERIA ........................ 7

3.1 CURRENT SYSTEM OBJECTIVES AND CLOSURE CRITERIA .................................... 7

3.2 TREATMENT PLANT OPERATION GOALS ................................................. 7

4.0 FINDINGS AND OBSERVATIONS FROM THE RSE SITE VISIT .............................. 8

4.1 FINDINGS ........................................................................ 8

4.2 SUBSURFACE PERFORMANCE AND RESPONSE ............................................. 8

4.2.1 WATER LEVELS ............................................................ 8

4.2.2 CAPTURE ZONES ........................................................... 8

4.2.3 CONTAMINANT LEVELS ...................................................... 9

4.3 COMPONENT PERFORMANCE ........................................................ 10

4.3.1 WELL PUMPS AND TRANSDUCERS ............................................. 10

4.3.2 EQUALIZATION TANK ....................................................... 10

4.3.3 REACTOR ................................................................ 10

4.3.4 FLASH MIX AND FLOCCULATION TANKS ......................................... 11

4.3.5 CLARIFIER ............................................................... 11

4.3.6 SOLIDS HOLDING TANK/FILTER PRESS .......................................... 11

4.3.7 FILTER FEED TANK ........................................................ 11

4.3.8 MULTIMEDIA FILTERS ...................................................... 11

4.3.9 EFFLUENT TANK (FINAL PH ADJUSTMENT) ....................................... 11

4.3.10 SYSTEM CONTROLS ........................................................ 11

4.4 COMPONENTS OR PROCESSES THAT ACCOUNT FOR MAJORITY OF MONTHLY COSTS .............. 12

4.4.1 UTILITIES ............................................................... 12

4.4.2 NON-UTILITY CONSUMABLES AND DISPOSAL COS ................................. 12

4.4.3 LABOR .................................................................. 13

4.4.4 CHEMICAL ANALYSIS ....................................................... 13
vi

4.5 RECURRING PROBLEMS OR ISSUES .................................................... 13

4.6 REGULATORY COMPLIANCE ......................................................... 13

4.7 TREATMENT PROCESS EXCURSIONS AND UPSETS, ACCIDENTAL CONTAMINANT/REAGENT RELEASES . 13

4.8 SAFETY RECORD ................................................................. 13

5.0 EFFECTIVENESS OF THE SYSTEM TO PROTECT HUMAN HEALTH AND THE ENVIRONMENT . 14

5.1 GROUND WATER ................................................................. 14

5.2 SURFACE WATER ................................................................. 14

5.3 AIR ........................................................................... 14

5.4 SOILS .......................................................................... 14

5.5 WETLANDS AND SEDIMENTS ........................................................ 14

6.0 RECOMMENDATIONS .............................................................. 15

6.1 RECOMMENDED STUDIES TO ENSURE EFFECTIVENESS ..................................... 15

6.1.1 REGULARLY ANALYZE DATA AND CAPTURE ZONES AND REPORT RESULTS .............. 15

6.1.1.1 UPDATE CONTAMINANT PLUME MAPS AND ANALYZE TRENDS IN CONCENTRATIONS ....... 15

6.1.1.2 ANALYZE WATER LEVEL MEASUREMENTS AND DEVELOP POTENTIOMETRIC SURFACE MAPS . 16

6.1.1.3 RECALIBRATE THE GROUNDWATER FLOW MODEL AND USE SIMULATIONS FOR CAPTURE ZONE

ANALYSES ............................................................... 16

6.1.2 USE MODEL SIMULATIONS TO OPTIMIZE LOCATIONS FOR NEW EXTRACTION WELLS ....... 18

6.1.3 DEVELOP A CONTINGENCY PLAN FOR EXCEEDENCES IN LOCAL GROUNDWATER WELLS .... 18

6.2 RECOMMENDED CHANGES TO REDUCE COSTS ........................................... 18

6.2.1 DISPOSE OF SLUDGE AS NON-HAZARDOUS WASTE ................................. 18

6.3 MODIFICATIONS INTENDED FOR TECHNICAL IMPROVEMENT ................................ 19

6.3.1 REPAIR LEAKS IN THE PLANT ................................................. 19

6.4 MODIFICATIONS INTENDED TO GAIN SITE CLOSE-OUT ..................................... 19

6.4.1 DEVELOP AND EXIT STRATEGY ............................................... 19

6.4.2 ADDRESS ONSITE SOIL CONTAMINATION ........................................ 19

7.0 SUMMARY ....................................................................... 20

List of Tables

Table 7-1. Cost summary table

List of Figures

Figure 1-1. Site layout showing the extent of contamination and locations of the monitoring, extraction, and

residential wells

Figure 4-1. Site layout showing the approximate locations of extraction wells in the proposed extraction

system

Figure 6-1. Model simulation from the original capture zone analysis suggesting capture of the plume in the

absence of recharge from the percolation ponds

Figure 6-2. Model simulation from the original capture zone analysis suggesting capture of the plume in the

presence of recharge from the percolation ponds
1

1.0 INTRODUCTION

1.1 PURPOSE

In the OSWER Directive No. 9200.0-33, Transmittal of Final FY00 - FY01 Superfund Reforms Strategy,

dated July 7,2000, the Office of Solid Waste and Emergency Response outlined a commitment to optimize

Fund-lead pump-and-treat systems. To fulfill this commitment, the US Environmental Protection Agency

(USEPA) Technology Innovation Office (TIO) and Office of Emergency and Remedial Response (OERR),

through a nationwide project, is assisting the ten EPA Regions in evaluating their Fund-lead operating

pump-and-treat systems. This nationwide project is a continuation of a demonstration project in which the

Fund-lead pump-and-treat systems in Regions 4 and 5 were screened and two sites from each of the two

Regions were evaluated. It is also part of a larger effort by TIO to provide USEPA Regions with various

means for optimization, including screening tools for identifying sites likely to benefit from optimization

and computer modeling optimization tools for pump and treat systems.

This nationwide project identifies all Fund-lead pump-and-treat systems in EPA Regions 1 through 3 and 6

through 10, collects and reports baseline cost and performance data, and evaluates up to two sites per

Region. The site evaluations are conducted by EPA-TIO contractors, GeoTrans, Inc. and the United States

Army Corps of Engineers (USACE), using a process called a Remediation System Evaluation (RSE),

which was developed by USACE. The RSE process is meant to evaluate performance and effectiveness (as

required under the NCP, i.e., and “five-year" review), identify cost savings through changes in operation

and technology, assure clear and realistic remediation goals and an exit strategy, and verify adequate

maintenance of Government owned equipment. 

The Selma Pressure Treating Superfund Site was chosen based on initial screening of the pump-and-treat

systems managed by USEPA Region 9 as well as discussions with the EPA Remedal Project Manager for

the site and the Superfund Reform Initiative Project Liaison for that Region. This site has high operation

costs relative to the cost of an RSE and a long projected operating life. This report provides a brief

background on the site and current operations, a summary of the observations made during a site visit, and

recommendations for changes and additional studies. The cost impacts of the recommendations are also

discussed.

A report on the overall results from the RSEs conducted for this system and other Fund-lead P&T systems

throughout the nation will also be prepared and will identify lessons learned and typical costs savings.

1.2 TEAM COMPOSITION

The team conducting the RSE consisted of the following individuals:

Frank Bales, Chemical Engineer, USACE, Kansas City District

Todd Hagemeyer, Hydrogeologist, GeoTrans, Inc.

Peter Rich, Civil and Environmental Engineer, GeoTrans, Inc.

Doug Sutton, Water Resources Engineer, GeoTrans, Inc.
2

1.3 DOCUMENTS REVIEWED

Author Date Title

US EPA September 1988 Record of Decision

US EPA October 1993 Record of Decision Explanation of

Significant Differences

US EPA April 1997 Record of Decision Explaination of

Significant Differences

US EPA January 22, 1998 1-page excerpt from Request for Proposal

#116

IT Corp. February 1999-July 2001 Groundwater Monitoring Reports

IT Corp. May 1999 Operations and Maintenance Manual

IT Corp. January 1999 Remedial Action Design Drawings

IT Corp. October 2000 Draft Final Report, Selma Pressure Treating

Superfund Site

IT Corp. March 2001 Report for Monitor Well Sampling

Geomatrix Consultants, Inc April 17, 2001 Focused Feasibility Study Report, Final

Document, Selma Pressure Treating

Superfund Site

Geomatrix Consultants, Inc July 2001 First Five Year Review

IT Corp. August 2001 APCL Analytical Report

US EPA September 2001 Memorandum for First Five Year Review

IT Corp. October 2001 Monitoring Well Data

1.4 PERSONS CONTACTED

The following individuals were present for the site visit:

Wally Shaheen, Project Manager, U.S. Army Corps of Engineers, Rapid Response Program

Cleet Carlton, Project Geologist, IT Corp.

Mike Toepfer, Plant Operator, IT Corp.

Larry Hudson, Project Manager, IT Corp. Project Manager

Chris Sherman, Hazardous Substances Engineer, California Dept. of Toxic Substances Control

Tom Kremer, Remedial Project Manager, US EPA Region 9
3

1.5 SITE LOCATION, HISTORY, AND CHARACTERISTICS

1.5.1 LOCATION

The Selma Pressure Treating site is located 15 miles south of Fresno, adjacent to the city limits of Selma,

California and addresses subsurface contamination from a former wood treating facility. The site occupies

approximately 40 acres, including the 14-acre former wood treating and storage facility and a 26-acre

neighboring vineyard. Zoned for heavy use, the site is located in a transition zone between agricultural,

residential, and industrial areas. A business named Upright Scaffolding and a small transmission repair

shop both border the site to the north and residences border the site to the east. Highway 99 cuts through

the center of the site as shown in Figure 1-1, residences lie to the east of the site, and vineyards and other

farm area border the site to the south and west.

1.5.2 POTENTIAL SOURCES

Wood treating operations began at the site in 1936. The treating process originally involved the use of

pentachlorophenol (PCP) and oil, but the associated treating facility was replaced by a pressure treating

facility that used chemicals including fluor-chromium-arsenate-phenol, chromated copper arsenate, PCP,

copper-8-quinolinolate, LST concentrate, Woodtox 140 RTU, and Heavy Oil Penta 5% solution. The

operating area and wood storage area were paved with asphalt in 1982; the asphalt remains in place. 

Wood treating activities were suspended in 1994, and all structures from the site were removed with the

exception of the concrete drip pad and other concrete foundations in the stormwater runoff area. Drippings

from the former treatment processes have led to both soil and groundwater contamination beneath the

former facilities. The primary contaminant of concern is chromium, predominantly found as hexavalent

chromium, its more mobile state.

Remedial investigations of the contamination began in 1984, and by 1991 soil cleanup activities had

started. Approximately 13,000 cubic yards of soil were excavated, fixed, placed in an onsite impoundment

area, and capped. Additionally, further investigations led to excavation of an additional 5,000 cubic yards

of contaminated soil. This soil is currently stockpiled onsite under temporary cover for eventual disposal.

Approximately 21,000 cubic yards of soil, affected by the contaminants of concern at levels above cleanup

standards, remain at depths of up to five feet below ground surface. In addition, 30,000 cubic yards of soil

that exceeds cleanup standards have been estimated to lie as much as 25 feet below grade. Remedial

alternatives for these areas of concern are under consideration. Until these areas are remediated, they may

act as continuing sources of groundwater contamination.

1.5.3 HYDROGEOLOGIC SETTING

The site is located in the Central Valley of California, which is filled primarily with fluvial deposits. The

ground surface is approximately 300 feet above mean sea level (MSL) and is essentially flat. Sand, silt,

and clay in the form of discontinuous lenses result in significant heterogeneity at the site and preferential

pathways for the transport of contamination. The water table is approximately 30 feet below ground

surface (bgs) and is relatively flat. A gradient of 0.0015 feet per foot directs groundwater to the southwest. 

As summarized in the October 2000 Draft Final Report, for modeling purposes, hydraulic conductivities at

the site were estimated to range from 1 foot per day (for areas with silt and clay) to 100 feet per day for

(areas with sand). The actual range, however, is likely much broader.
4

Recharge to the site is estimated at approximately 10 inches per year of infiltration. Additional recharge is

also provided by the discharge of treated water to the onsite percolation ponds and by the infiltration of

stormwater from the neighboring Upright Scaffolding facility. Dudley Pond is the nearest surface water

body to the site, and it is located approximately 1.5 miles to the west. 

1.5.4 DESCRIPTION OF GROUND WATER PLUME

The groundwater plume, as illustrated in Figure 1-1, stretches from the former wood treating area to

approximately 2,500 feet downgradient to the southwest and is approximately 1,000 feet wide. The plume

extends approximately 50 feet below the water table, but due geologic heterogeneity (preferential

pathways), the distribution is uneven. At approximately 1,600 feet downgradient from the source area, the

plume splits into two separate, but parallel plumes as if an area of low hydraulic conductivity exists

between them. Based on the July 2001 sampling event, the highest concentrations of chromium within the

plume were found in monitoring well R23-I (6280 ug/L total chromium and 6020 ug/L hexavalent

chromium). 

In general, chromium concentrations in groundwater are highest near the former wood treating facility in

the areas around EW-1 (and EW-1a), R23, and R23I. The highest chromium concentration in R23 (total

depth of 40 feet below ground surface) was observed during the first sampling event in February 1999. 

Since then, the concentration has consistently decreased, despite the measured fluctuations in the water

table elevation. On the other hand, chromium concentrations in R23I (adjacent to, but beneath R23) have

increased. 

Although soil contamination at depth could serve as a source of dissolved groundwater contamination due

to rising water levels, this cannot be easily confirmed with the present data because limited groundwater

data exists prior to February 1999 and limited soil data exists for chromium. Another, more likely,

scenario for transport of chromium from the soil to the groundwater is percolation of water from the

surface through the chromium-contaminated vadose zone to the saturated zone.
5

2.0 SYSTEM DESCRIPTION

2.1 SYSTEM OVERVIEW

The original ROD signed in 1988 required that groundwater be extracted from 25 wells at 50 feet deep at a

cumulative rate of 1,040 gallons per minute (gpm); however, an Explanation of Significant Differences

(ESD) signed in 1993 reduced the required pumping to 250 gpm from 7 wells up to 70 feet deep with the

ability to expand the capacity of the plant. A second ESD signed in 1997 allowed discharge of the treated

effluent to percolation ponds to recharge water to the aquifer. The current system, which began operation

on September 29, 1998, meets the specifications of the 1993 and 1997 ESDs

2.2 EXTRACTION SYSTEM

The extraction system originally included 8 wells. However, one well (EW-3B) has been shut down due to

a low yield and very low contaminant concentrations. In addition, wells EW-1 and EW-2 (originally placed

to protect residential wells to the east) were replaced in February 2000 with EW-1a and EW-2a, which are

both shallow wells positioned for improved recovery of contamination. Analysis by the site team suggest

that moving these extraction wells does not pose added risk to the residential wells originally protected by

them. The well locations (both the original wells and the new locations) are presented in Figure 1-1. The

pumping rates and screened intervals for all of extraction wells are provided in a table in Section 4.3.1 of

this report..

2.3 TREATMENT SYSTEM

The treatment system is located inside of a prefabricated building on a concrete pad and utilizes the

UNIPURE Process Technology. The process consists of an equalization tank, mixing tank/reactor, flash

mixer, clarifier, filter feed tank, multi-media filter, pH adjustment, and discharge to one of two recharge

basins. Solids from the clarifier are held in sludge thickening tanks and then run through a filter press. 

The system operates at a rate of 220 gpm including both extracted water and water recycled through the

treatment system. The anticipated design influent (as listed in a 1-page excerpt from the 1998 request for

proposal) and the actual influent obtained from sampling in August 2001 are in the following table for

comparison. The data suggests that the influent concentrations for chromium are within the design criteria

but that the concentrations of some other constituents of the influent are not within the design criteria. The

system effluent has consistently met effluent discharge criteria. 

Contaminant Design Influent Concentration Actual Influent Concentrations Aug. 2001

Arsenic <10 ug/L <5 ug/L

Hexavalent Chromium 50-1,100 ug/L 406 ug/L

Total Chromium 50-1,100 ug/L 448 ug/L

Copper <50 ug/L 24.1 ug/L

Alkalinity as CaCO3 150-250 mg/L 390 mg/L
Contaminant Design Influent Concentration Actual Influent Concentrations Aug. 2001

6

Chloride 45-60 mg/L 91 mg/L

Nitrate as Nitrogen 8-10 mg/L 13.2 mg/L

Sulfate as SO4 60-90 mg/L 98 mg/L

Phosphorous <0.3 mg/L 0.02 mg/L

Calcium 60-120 mg/L 105 mg/L

Iron <20 mg/L 0.394 mg/L

Magnesium 10-40 mg/L 27.8 mg/L

Manganese <1 ug/L not reported

Potassium 3-10 mg/L 5.97 mg/L

Sodium 30-100 mg/L 122 mg/L

pH 6.5-7.5 7.35

Total Suspended Solids <10 mg/L <10 mg/L

Total Dissolved Solids <500 mg/L 827 mg/L

2.4 MONITORING PROGRAM

Groundwater monitoring reports are submitted every four months and include results from sampling for

chromium and arsenic in 29 monitoring wells and 10 residential wells. Additionally, R-23S is sampled for

dioxins, furans, and PCBs annually. These samples are sent offsite for analysis. Hach test kits are used to

sample the chromium concentrations in the extraction wells on a regular basis. The results from the Hach

test kits have proven reliable based on comparison with analytical results. 

Water levels are also collected during sampling events, but potentiometric surface maps are not generated

from these measurements in the sampling reports.

Influent and effluent is sampled monthly and analyzed offsite for chromium, arsenic, and the other

constituents listed in the table in Section 2.3 of this report. In addition, a continuous sampler is used to

analyze chromium in the effluent and notify the operator if standards are exceeded.
7

3.0 SYSTEM OBJECTIVES, PERFORMANCE AND CLOSURE 

CRITERIA

3.1 CURRENT SYSTEM OBJECTIVES AND CLOSURE CRITERIA

The current system is operating based on the 1988 ROD and two subsequent ESDs in 1993 and 1997. The

objective of the pump and treat system is to extract contaminated groundwater, treat it to MCLs and return

it to the aquifer via infiltration. Neither the ROD nor ESDs explicitly state whether the objective is to

restore the aquifer to MCLs or to contain the plume. As stated in the first Five-Year Review, an ESD is

required to clearly define the objective of the existing pump and treat system.

3.2 TREATMENT PLANT OPERATION GOALS

The effluent or discharge goals are stated in the ROD and ESDs. The following table includes the current

effluent discharge standards for some of the constituents of the extracted water.

Contaminant Concentration

Arsenic <50 ug/l

Hexavalent Chromium not detected

Total Chromium <50 mg/l

pH 6.5-7.5

Total Suspended Solids <20 mg/l

Total Dissolved Solids <1,200 mg/l

* the “not detected” criteria for hexavalent chromium is self-imposed by the plant operators and is regularly

achieved given a detection level of 50 ug/L. The actual discharge criteria is more lenient.
8

4.0 FINDINGS AND OBSERVATIONS FROM THE RSE SITE VISIT

4.1 FINDINGS

The RSE team found an extremely well maintained and functional facility. The system is not only well

maintained but is staffed by a conscientious and competent operator and team of managers. The

observations and recommendations given below are not intended to imply a deficiency in the work of the

designers, operators or site managers but are offered as constructive suggestions in the best interest of the

EPA and the public. These recommendations have the benefit of several years of operating data

unavailable to designers or site managers.

4.2 SUBSURFACE PERFORMANCE AND RESPONSE

4.2.1 WATER LEVELS

Although water levels are collected three times per year, they are not used to generate potentiometric

surface maps. Therefore, detailed analysis of these water levels is difficult within the scope of an RSE. In

general, water level measurements support the flow of groundwater to the southwest. There is little

evidence of a vertical gradient as measured by water levels in piezometer clusters, with the exception of

R24 and R24I, which indicate a downward gradient. However, this lack of evidence does not conclusively

show that groundwater and contamination do not travel vertically within the aquifer. Preferential pathways

may exist in areas (such as the area surrounding R24 and R24I) that transport groundwater and

contamination vertically. Mounding from infiltration from the percolation ponds is difficult to discern but

may be indicated by a relatively high water level in R22. 

4.2.2 CAPTURE ZONES

Due to the high degree of heterogeneity at the site and the various influences on groundwater flow

(percolation ponds, extraction wells, residential wells, etc.) a capture zone analysis with water level

measurements alone would likely be inconclusive. Although there are a number of piezometers at the site

screened at various elevations, there may be an insufficient number to adequately resolve groundwater flow

for the purpose of analyzing a capture zone. Nevertheless, potentiometric surface maps based on the water

level measurements would likely be useful in understanding groundwater flow underlying the site during

various times of the year. For example, water levels and the potentiometric surface maps could provide

additional information as to the effects of recharge on groundwater flow. For a more thorough capture

zone analysis, groundwater flow modeling and particle tracking are likely necessary.

Capture zones at the site are not analyzed on a regular basis; however, a capture zone analysis was

conducted as part of the design of the extraction system and is included in the October 2000 Draft Final

Report. A 3-layer model generated with the parameters mentioned in section 1.5.3 of this report as well as

other information indicated capture of the plume by the seven extraction wells. Flow fields from the

groundwater flow model were used to track particles between the percolation ponds and the extraction

wells. Analysis by the model suggests that, despite recharging treated extracted water through the

percolation ponds, the plume is captured. In fact, the analysis suggests that flushing of the aquifer in the
9

area of the plume is increased such that time to remediation could be accelerated because less water is

pulled from the surrounding cleaner portions of the aquifer. This may, in fact, be the case as

concentrations in EW-7 have decreased since installation and remained clean ever since, which suggests

that upgradient wells may have decreased or eliminated the transport of chromium toward that well. 

However, the particle tracking analysis does not appear to track particles in the various model layers,

leaving open to question, the degree of capture vertically. Also, the model was only calibrated with one

round of water level measurements, the accuracy of the model and its predictions could be called into

question if variations in recharge and water levels are significant.

4.2.3 CONTAMINANT LEVELS

With a few exceptions near the source area, contaminant levels in piezometers across the site have

remained relatively constant with some fluctuation but no consistent increase or decrease. Three of the

exceptions are summarized in the following table.

Well Depth to Bottom of Well 

(feet below ground surface)

February 1999 hexavalent

chromium concentration 

(ug/L)

July 2001 hexavalent

chromium concentration 

(ug/L)

R23 ~40 30,400 1,780

R23I ~60 414 6,020

R25 ~40 1,450 180

As shown in Figure 1-1, R23 and R23I are adjacent to each other and are near former extraction well 

EW-1 and current extraction well EW-1a. Both extraction wells are screened between 45 and 60 feet below

ground surface. The decrease of chromium in R23 and R23I may result from pumping water from EW-1

or EW-1a, treating it, and discharging the treated water through the percolation ponds. A possible

explanation follows: 

In extracting groundwater, EW-1 and/or EW-1a pull water from surrounding horizontal and vertical areas. 

A capture zone analysis conducted as part of the system design (later discussed in Section 6.1.1.3 and

depicted in Figure 6-2) indicates that treated water from the percolation ponds was likely captured by EW1. Because EW-1a is located closer to the ponds than the former EW-1, EW-1a also likely captures treated

water from the percolation ponds. As this treated water migrates from the shallow zone below the

percolation ponds toward EW-1 or EW-1a, it may serve to dilute the water sampled in R23, a relatively

shallow monitoring well. However, because R23I is deeper than R23, the treated water from the

percolation ponds may not reach it. Rather, contaminated water from other surrounding areas may pass

through R23I as it travels toward the extraction well resulting in an increase in chromium concentrations in

R23I.

Due to the proximity of EW-2 and EW-2a to R25, the decrease in concentrations in R25 may be attributed

to the extraction of groundwater from EW-2 prior to February 2000 and EW-2a after February 2000.

Contaminant levels in the influent (and each of the extraction wells) have remained relatively constant over

time (with the exception of a small increase due to the new locations of EW-1 and EW-2 to EW-1a and

EW-2a). The influent concentration in August 2001 was 448 ug/L total chromium, which corresponds to a

chromium mass loading to the treatment plant of approximately 1 pound per day.
10

4.3 COMPONENT PERFORMANCE

4.3.1 WELL PUMPS AND TRANSDUCERS

The maximum extraction rate for the system is currently around 200 gpm.. The flow through the plant is 220

gpm including all recycle streams. The well names, screened intervals, chromium concentrations, and flow

rates are provided in the following table.

Well Screen Interval 

(feet below surface)

Chromium

Concentration (ug/l)

Flowrate (gpm)

EW-1a (new location) 45-60 2800 25

EW-2a (new location) 35-45 470 20

EW-3A 45-100 250 35

EW-3B (shutdown) 105-125 10 0

EW-4 60-95 330 50

EW-5 121-136 190 25

EW-6 47-87 140 25

EW-7 55-85 10 14

Total 194

The site managers are planning to possibly shutdown EW-7 and relocate some of the other extraction wells to

improve contaminant recovery. The proposed well relocations are depicted in Figure 4-1. Monitoring from

EW-7 will likely continue to confirm shutdown of the well is appropriate.

4.3.2 EQUALIZATION TANK

The equalization tank is designed to blend contaminated groundwater and recycle streams to produce a

homogeneous feed to the plant. Centrifugal pumps driven by variable speed drives maintain a selected setpoint

in the equalization tank.

4.3.3 REACTOR

Both pH adjustment and chemical oxidation-reduction reactions occur in this vessel. As part of the UNIPURE

Process Technology, chromium is reduced and iron is oxidized for later co-precipitation in the clarifier.

Ferrous Chloride is added to provide the necessary concentration of Fe+2 for the desired reaction. Sodium

hydroxide is then added to control pH and air is sparged to rapidly oxidize the iron to Fe+3 and reduce the

chromium from Cr+6 to Cr+3. The reaction vessel is well mixed via baffles and injection of air. The iron

precipitates out of the solution with the chromium. The chromium is occluded in the iron solids due to its close

association with the iron prior to its precipitation. 

Chromium not removed by occlusion is removed by adsorption to the ferric iron solids. From the reactor, the

process water is transferred to the flash tank.
11

4.3.4 FLASH MIX AND FLOCCULATION TANKS

The flash mix and flocculation tanks are located immediately prior to the clarifier. An anionic polymer is added

to the process water with a high speed mixer so that the iron solids produced in the reactor can be coagulated

in the flocculation tank. The flocculation tank allows a five minute retention time with a slow speed mixer to

form larger solids (floc) that settle more easily in the clarifier.

4.3.5 CLARIFIER

The clarifier contains lamella plates which enhance collection of the iron solids. The solids settle and fall to

the bottom of the clarifier. Air operated diaphragm pumps are utilized to both recycle the solids to the reactor

as well as transfer solids to the sludge holding tanks. The process water flows over the top of the clarifier weir

into the filter feed tank. The clarifier plates are cleaned once per month.

4.3.6 SOLIDS HOLDING TANK/FILTER PRESS

The sludge holding tanks are used to hold and thicken clarifier solids (approximately 4 cubic yards of

dewatered filter cake are generated per week) until they are processed through the filter press for dewatering.

These tanks have conical bottoms to allow easy removal of the solid contents. Solids from the filter press are

disposed of as a hazardous waste, due to F-032 and F-035 designations, despite easily passing TCLP testing.

Filter press filtrate and decant water from the sludge holding tanks are recycled to the equalization tank.

4.3.7 FILTER FEED TANK

The filter feed tank is used to hold clarified process water that will be treated via the multimedia filters to

remove remaining solids prior to discharge.

4.3.8 MULTIMEDIA FILTERS

The multimedia filters are backwashed whenever the pressure drop exceeds 18 psi or within 72 hours,

whichever occurs first. The standard operation has been to backwash two or three times per day for

approximately one and a half minutes each time. Backwash water is discharged to the sludge holding tanks.

4.3.9 EFFLUENT TANK (FINAL PH ADJUSTMENT)

The effluent tank contains a mixer and allows the addition of sulfuric acid for final pH adjustment. The tank

is emptied to the recharge basins via variable speed driven pumps. The effluent flow is measured and also

contains an inline, continuous hexavalent chromium analyzer, 1024 Analyzer from Scientific Instruments. 

4.3.10 SYSTEM CONTROLS

The system has an autodialer and emergency stop switches for plant safety. The system operator is contacted

for any stoppage to operations which may occur for a number of reasons including alarms for power outages,

a high floor sump level, or a high chrome level in the effluent as determined by a continuous chrome analyzer.

The control system is currently not set to restart at the prior settings. The alarms sound infrequently, with

power outages the main reason for system shutdown.
12

4.4 COMPONENTS OR PROCESSES THAT ACCOUNT FOR MAJORITY OF

MONTHLY COSTS

The following table provides average monthly costs associated with the routine operation and maintenance of

the Selma Pressure Treating site. The values were obtained by averaging the monthly expenses from three

months of operation within the past year. 

Plant Operator $4,100

IT Project management and administration $2,500

Total Chemicals: 

Polymer

Ferrous chloride

Caustic

Sulfuric acid

Chromium meter chemicals

$3,350

$550

$1,225

$1,000

$425

$150

Influent/Effluent Analysis $460

Groundwater Sampling/Analysis $2,000 ($8,000 per 4 months)

Utilities (electric and telephone) $3,600

Relocate Rolloff bins on site $850

Trans and dispose filter cake $1,050

Pickup rental and gasoline $1,000

Misc Repair Parts $1,000

Storage Container $75

O&M subtotal cost $19,985

IT fee, 7% $1,400

IT Subtotal Cost $21,385

USACE fee, 11% $2,350

Average cost per month $23,735

4.4.1 UTILITIES 

The current electrical usage is as expected. The electrical bills demonstrate an average monthly costs of

approximately $3,500 per month. There are no oversized motors or equipment onsite with the exception of the

effluent discharge pumps, which, if necessary, could be used to pump effluent to an alternate discharge point.

4.4.2 NON-UTILITY CONSUMABLES AND DISPOSAL COST

Disposal of generated sludge (approximately 4 cubic yards per week) costs about $1,000 per month on average.

The sludge passes all TCLP criteria; however, it is disposed as hazardous due to F-032 and F-035 designations

as wastes from a wood treating facility. The costs for chemicals used in the plant are reasonable considering
13

plant operations. The system operator and engineer have reduced chemical consumption; however, to further

reduce chemical additions could lead to increased chromium concentrations in the effluent.

4.4.3 LABOR 

The plant is maintained by a single full time operator, 40 hours per week. The site is also supported by a

project manager and geologist.

4.4.4 CHEMICAL ANALYSIS

The analyses performed for routine monitoring utilize a Hach kit for chromium, which has proven cost-effective

and accurate. Samples from the monitoring wells, the residential wells, and the influent and effluent are

analyzed offsite.

4.5 RECURRING PROBLEMS OR ISSUES

There have been no major recurring problems with operating the plant. During the RSE, a feed pump was

leaking and required repair. In an isolated incident, the treatment plant was burglarized. Items, including site

binders and reports, were stolen. A security system has since been installed at the plant.

4.6 REGULATORY COMPLIANCE

The system has maintain an efficient operation while attaining all discharge requirements.

4.7 TREATMENT PROCESS EXCURSIONS AND UPSETS, ACCIDENTAL

CONTAMINANT/REAGENT RELEASES

No process excursions and upsets were noted. The ferrous chloride tank emptied due to corrosion of fittings,

but the spilled liquid was contained by the berm. The corrosion has been addressed and no other leaks have

occurred. 

4.8 SAFETY RECORD

No safety issues were identified.
14

5.0 EFFECTIVENESS OF THE SYSTEM TO PROTECT HUMAN

HEALTH AND THE ENVIRONMENT

5.1 GROUND WATER

Residential and irrigation wells (irrigation wells are rarely used) are located down and cross gradient of the

plume and could become impacted if groundwater is not adequately contained. The capture zones have not

been analyzed since design of the original extraction system, and it is questionable if the original capture zone

adequately addressed vertical capture of the plume. In addition, recharge from the percolation ponds may

reduce the capacity of the extraction system to capture the plume. The closest municipal well is located

approximately 0.25 miles upgradient and is screened in a deeper aquifer than that impacted by site-related

contamination.

5.2 SURFACE WATER

Dudley Pond is the nearest surface water body to the site, and it is located approximately 1.5 miles to the west.

Impacts to this water body are not expected.

5.3 AIR

No air emissions are notable from this plant.

5.4 SOILS

A separate Record of Decision is currently being developed regarding site soils remaining. Contamination at

depth and at the surface remains. The remedy from this new ROD is anticipated to be implemented in fiscal

year 2003.

5.5 WETLANDS AND SEDIMENTS

No wetlands or sediments are at risk to site-related contamination.
15

6.0 RECOMMENDATIONS

Cost estimates provided have levels of certainty comparable to those done for CERCLA Feasibility

Studies (-30/+50%), and these cost estimates have been prepared in a manner consistent with EPA

540-R-00-002, A Guide to Developing and Documenting Cost Estimates During the Feasibility Study, July

2000.

6.1 RECOMMENDED STUDIES TO ENSURE EFFECTIVENESS

6.1.1 REGULARLY ANALYZE DATA AND CAPTURE ZONES AND REPORT RESULTS

The capture zone of the extraction system should be analyzed to confirm containment of site-related

contamination. Such an analysis should involve the following items:

• an update of the plume boundaries,

• analysis of the measured water levels and development of potentiometric surfaces, and

• recalibration of and simulations with the site groundwater flow model.

Based on the results of the capture zone analysis, the extraction system and/or discharge system may require

modification to improve capture of the plume.

6.1.1.1 UPDATE CONTAMINANT PLUME MAPS AND ANALYZE TRENDS IN CONCENTRATIONS

The first step of conducting a capture zone analysis is to determine the portion of the plume targeted for

capture. In the case of the Selma site, it may be sufficient to capture all portions of the plume greater than the

MCL for chromium (50 ug/L). Groundwater sampling events that include sampling of approximately 40 wells

or piezometers are conducted every four months and provide updated information on the extent of the

contamination in the shallow, intermediate, and deep zones of the aquifer. Although site hydrogeologists are

working with this data, updated plume maps are not being generated. Rather, a generic plume map is

repeatedly used in the reports and no analysis is provided.

Updated plume maps should be generated for each sampling round so that trends in the plume shape can be

tracked over time. Although natural fluctuations in the concentrations may result in a plume shape that differs

for each event, a noticeable trend may become apparent. Such a trend may indicate shrinking of the plume or

migration in one direction or another. Once accurate plume maps have been developed, the target capture zone

(perhaps the 50 ug/L contours) can be determined. This target capture would then serve as the basis for

capture zone analyses conducted with water levels and groundwater flow modeling.

On an annual basis, trend analyses of the concentrations in the sampled wells and the plume maps should be

conducted. These analyses will help site managers determine the effectiveness of the remedy and the likelihood

of achieving the objectives. A description of these analyses along with the historical data should be included

in one of the groundwater sampling reports each year.
16

Creating plume maps based on historical sampling events (approximately 10 events) and analyzing trends in

chromium concentration over time should cost approximately $7,000 given that a base map already exists and

historical data is readily available in a spreadsheet. An additional $3,000 may be required for reporting the

historical data, plume maps, and trend analysis in the next groundwater sampling report. To provide site

managers with updated information in the future, plume maps should be generated for each sampling event and

provided in the associated report, and trend analyses should be conducted on an annual basis and included in

one of the regular groundwater sampling reports along with the historical groundwater quality data for the site.

These tasks may require an additional $3,000 per year.

6.1.1.2 ANALYZEWATER LEVEL MEASUREMENTS AND DEVELOP POTENTIOMETRIC SURFACE

MAPS

Water level measurements provide direct information regarding groundwater flow and are indispensable for

understanding groundwater flow at a site. Water levels at the Selma site are currently collected every four

months; however, analyses of these measurements and development of potentiometric surface maps are not

evident from reviewing the sampling reports. Water levels measured throughout the history of system operation

should be processed, analyzed, and used to develop potentiometric surfaces. Variations in pumping or recharge

should be reflected in the potentiometric surfaces and should give site hydrogeologists additional insight into

groundwater flow at the site. 

These potentiometric surfaces can also be used for a preliminary capture zone analysis. General groundwater

flow directions throughout the site can be determined from the interpreted hydraulic gradient, and flow paths

that are directed into extraction wells will help interpret the capture zone. Then, once updated plume maps and

target capture zones are obtained for the historical chromium concentrations, site hydrogeologists can overlay

the interpreted capture zones with the target capture zones to determine the degree of capture. However, as

stated in Section 4.2.2 of this report, the number of piezometers at the site may not provide adequate resolution

of the flow field for capture zone analyses without the aid of a groundwater flow model. Thus, these water

levels and potentiometric surfaces should also be used to calibrate and update the groundwater flow model.

The model, in turn, would be used to estimate the degree of capture based on principles of groundwater flow

and the available data (please refer to Section 6.1.1.3 for more information on this step.) 

A capture zone analysis should be conducted and reported on a regular basis, perhaps for each sampling event

until the variation capture is better understood. In addition, on an annual basis, hydrogeological data for the

site should be updated, analyzed, and included in one of the groundwater sampling reports, preferably the same

report that would include the analyses of groundwater concentrations recommended in Section 6.1.1.1. 

Organizing the data, producing the potentiometric surface maps for the historical data, and analyzing the data

will likely require approximately $7,000 (costs of modeling are provided in Section 6.1.13). An additional

$3,000 may be required to include the data and the analyses in the next groundwater sampling report.

Conducting similar tasks on a regular basis with newly collected data may require an additional $4,000 per

year. 

6.1.1.3 RECALIBRATE THE GROUNDWATER FLOW MODEL AND USE SIMULATIONS FOR

CAPTURE ZONE ANALYSES

The site managers already have a groundwater flow model that was used for a capture zone analysis prior to

installation of the original extraction system. This model provides an excellent framework for further capture

zone analyses and for simulations to aid in site management decisions. However, the model should be

recalibrated with water level measurements taken over the history of system operation to improve the accuracy
17

and reliability of the model. An accurate model should be able to reproduce the water levels obtained from

measurements for a variety of pumping and recharge scenarios at the site, including pumping from the old and

new locations of EW-1 and EW-2 and pumping during different seasons. The model used by the site managers

reportedly reproduced, with reasonable accuracy, the water levels from the December 1997 sampling event.

Now that additional rounds of water levels have been collected, the existing model can be made more robust.

Once accurate flow fields are obtained, particle tracking can be conducted to ensure that particles from the

contaminated cells in the model domain (as determined from updated plume maps) are captured by the

extraction system. It is important to note that reverse particle tracking, as was done in the original capture zone

analysis will not give a thorough evaluation of capture in a heterogeneous, three-dimensional model. The

reverse particle tracking method only employed the release of 8 particles per well at a single elevation and

tracked them backward to outline the capture zone. A more thorough analysis would involve the release of

particles from each cell in each layer that coincides with the target capture zone. Furthermore, the release of

particles from various elevations within a cell should be tested because the vertical component of flow at this

particular site could be significant, especially with pumping from different elevations. Particles should also

be color coded based on which wells capture them to better identify the capture zones of each well. 

On a more general note, a capture zone analysis should demonstrate that water flow through the impacted area

is captured by the extraction wells. According to the particle tracking from the existing model shown in Figure

6-1, particles in the background flow field (upgradient of the extraction wells) traveled at approximately 200

to 300 feet per year. Removing the effect of porosity, this translates to a Darcy velocity of approximately 100

feet per year. The model domain is 3,000 feet wide, and it appears from Figure 6-1 that the extraction system

capture zone is also approximately 3,000 feet wide. The thickness of the three layers varied across the domain,

but on average, it appears that a saturated thickness of 100 feet is fairly representative. Assuming that half

of the formation has a significantly lower hydraulic conductivity than the other portions, the majority of

groundwater flow of 200 to 300 feet per year may be occurring only through effectively half of the crosssectional area of the model domain and flow through other portions may be significantly less. Following this

assumption about the formation, the above Darcy velocity should be reduced by half from 100 feet per year

to 50 feet per year. Thus, groundwater flow into the model domain and to be captured by the extraction system

is approximately

3 000 100

50 7 48 1 1

, 213

.

 ft ft

 ft

year

 gal.

ft

 year

365 days

 day

1440 min.

× × × 3 × × = gpm

This simple calculation, although based on crude estimates, suggests that the extraction system extracts

approximately the same amount of groundwater as is flowing from upgradient. If the recharge provided by

the percolation ponds is included, then the width of the capture zone decreases, which is consistent with another

model simulation (depicted in Figure 6-2) conducted as part of the original capture zone analysis. The degree

to which the capture zone narrows, however, will be dependent on the amount of recharge provided by the

percolation ponds or by natural recharge. The amount of recharge from the ponds likely varies with the seasons

because more water in the ponds will evaporate in the summer than in the winter, and the amount of natural

recharge will also vary based on the seasons— potential increases may occur in the winter with the rainy season

or in the summer during irrigation. The recharge rate through the percolation ponds that was used in the

original capture zone analysis should be reviewed and the model should be used to determine how sensitive

capture is to that recharge rate. In addition, estimates of the amount of recharge should be obtained. This

could, perhaps, be accomplished by taking the discharge rate from the treatment plant and accounting for

potential evaporation. If the potential evaporation is not known, then it could be measured through simple

studies with evaporation pans. 
18

If the estimated recharge rate (either natural or through the ponds) exceeds the rate that can be captured as

determined by the model, then efforts may be required to reduce the amount of water being recharged. This

could be addressed by increasing evaporation of the discharged water through spraying, discharging treated

water to both ponds at the same time, or otherwise increasing the areal extent of the ponds.

Recalibrating the model based on historical water sampling events will likely cost approximately $5,000.

Conducting particle tracking simulations and associated capture zone analyses for various pumping and

recharge scenarios will likely cost an additional $5,000. The cost of estimating the evaporation potential and

the amount of water recharging to the aquifer from the percolation ponds should be negligible and included in

the above costs. 

6.1.2 USE MODEL SIMULATIONS TO OPTIMIZE LOCATIONS FOR NEW EXTRACTION WELLS

The site managers are considering relocating some of the extraction wells to improve capture and

simultaneously increase contaminant recovery rates. The proposed relocations are noted in Figure 4-1.

Although these locations make sense conceptually, verifying these proposed locations and screening intervals

with the model would be beneficial. 

Once the extraction wells are installed and a new pumping regime is established, water levels should be

measured, interpreted, and used to improve the model calibration. An accurate model would be able to

adequately reproduce the measured water levels for the two previous pumping scenarios (EW-1 and EW-2

original locations) and this new pumping scenario.

Running simulations to determine the optimal locations and screening intervals, in addition to recalibrating the

model to include the new pumping would cost approximately $4,000.

6.1.3 DEVELOP ACONTINGENCYPLAN FOREXCEEDENCES IN LOCAL GROUNDWATER WELLS

A contingency plan should be developed that outlines a course of action to be taken if local irrigation or

residential wells show an exceedence in site related compounds. This plan may include providing bottled water

and/or could involve adjusting the pumping rates of the various extraction wells to improve capture and

contaminant recovery in the area of the exceedence. This contingency plan should take into account the site

managers’ knowledge of the Selma area and should be documented. Development and documentation of a

contingency plan may cost $5,000. However, costs to implement the plan, if necessary, would be higher and

dependent on the extent of contamination and the availability of alternative resources.

6.2 RECOMMENDED CHANGES TO REDUCE COSTS

6.2.1 DISPOSE OF SLUDGE AS NON-HAZARDOUS WASTE

The sludge generated by the treatment plant is currently listed as hazardous waste based on F-032 and F-035

designations, which are consistent with waste generated from wood treating facilities. However, the current

facility is a groundwater treatment system and is not a wood treating facility. Therefore, the waste designation

should be changed. The sludge passes TCLP testing indicating it will not act as a source of groundwater

contamination; therefore, the waste should be disposed of as non-hazardous. Current waste transfer and

disposal costs are approximately $12,600 per year. This cost would likely be reduced by half if this

recommendation is implemented.
19

6.3 MODIFICATIONS INTENDED FOR TECHNICAL IMPROVEMENT

6.3.1 REPAIR LEAKS IN THE PLANT

A leak from a transfer pump was noted during the RSE site visit. The leak was contained and not alarming;

however, the repair should be performed.

6.4 MODIFICATIONS INTENDED TO GAIN SITE CLOSE-OUT

6.4.1 DEVELOP AND EXIT STRATEGY

The ROD states groundwater cleanup as the site objective with cleanup levels set at the more stringent of

federal and state MCLs. Developing an exit strategy based on this objective will provide a framework for

making future decisions at the site, including determining when cleanup is reached and the system can be shut

down. The site managers have already reached a point where an exit strategy would be useful. EW-7 has had

chromium concentrations below the cleanup level since operation began, and site managers are deciding

whether or not to shutdown or relocate the well. An exit strategy that specified, for example, four or eight

quarters of chromium concentrations below cleanup levels, would have given site managers criteria to help

them decide the appropriateness of shutting down or relocating the well. An exit strategy that provides a clear

framework for shutting down individual wells or the system as a whole should be developed. In addition, this

strategy should also include other steps necessary for achieving site closure, such as addressing the soil

contamination.

6.4.2 ADDRESS ONSITE SOIL CONTAMINATION

Previous investigations of soil contamination as summarized in the April 2001 Focused Feasibility Study

focused primarily on pentachlorophenol (PCP), arsenic, and dioxin/furans as the contaminants of concern.

PCP contamination as high as 92 mg/kg was found as deep as 25 feet in one 80 foot by 80 foot area of the site,

but soil contamination, in general, was predominantly located near the surface. 

Despite soil contamination with these constituents, the only contaminant of concern detected above cleanup

levels in groundwater has been chromium. Limited data are available in the ROD for chromium contamination

of the soil with concentrations exceeding 800 mg/kg near the surface. The highest chromium concentration

detected beneath the surface was 31 mg/kg at a depth of 1 to 2.5 feet.

Soil contamination, particularly near the surface should be addressed to reduce exposure. Historical data

indicates that soil has not acted as a continuing source of groundwater contamination of PCP, arsenic, or

dioxin/furan. The soil should be more thoroughly investigated for chromium contamination to determine if it

is acting as a continuing source of chromium contamination of the groundwater and a remedy should be

designed accordingly. No cost is provided for this recommendation as site managers have already begun

considering alternatives.
20

7.0 SUMMARY

In general, the RSE team found a well-operated and cost-effective pump and treat system. In addition,

decreasing chromium concentrations in two monitoring wells the highly impacted zone of the aquifer suggest

that the pump and treat system is having a positive impact on reducing the maximum concentrations measured

when system operation began. 

The observations and recommendations mentioned are not intended to imply a deficiency in the work of either

the designers or operators but are offered as constructive suggestions in the best interest of the EPA and the

public. These recommendations have the obvious benefit of the operational data unavailable to the original

designers.

Several recommendations are made to enhance system effectiveness that predominantly focus on the analyzing

the capture zone of the extraction system. The only recommendation to reduce cost includes delisting the

sludge generated from the treatment system and disposing of it as non-hazardous waste. The only

recommendation for technical improvement involves fixing a leaking pump. Finally, the recommendations

regarding site closure include developing an exit strategy and addressing remaining soil contamination.
21

Table 7-1. Cost Summary Table

Recommendation Reason

Additional

Capital

Costs 

($)

Estimated

Change in

Annual

Costs

($/yr)

Estimated Change

In Lifecycle Costs

 ($) *

6.1.1 Analyze Capture Zones

for Current Extraction System

6.1.1.1 Update contaminant

plume maps and analyze

trends in concentrations

6.1.1.2 Analyze level

measurements and develop

potentiometric surface maps

6.1.1.3 Recalibrate the

groundwater flow model

and use simulations for

capture zone analyses

Effectiveness

$10,000

$10,000

$10,000

$3,000

$4,000

$0

$58,400

$74,600

$10,000

6.1.2 Use model simulations to

optimize locations for new

extraction wells

Effectiveness $4,000 $0 $4,000

6.1.3 Develop a contingency

plan for exceedences in local

groundwater wells

Effectiveness $5,000 $0 $5,000

6.2.1 Dispose of sludge as nonhazardousReduce Cost $0 ($6,300) ($101,700)

6.3.1 Repair leaks in the plant Technical

Improvement

$200 $0 $200

6.4.1 Develop an exit strategy

for the site

Gain Closeout Not

Quantified

Not 

Quantified

Not 

Quantified

6.4.2 Address remaining soil

contamination

Gain Closeout Not

Quantified

Not

Quantified

Not

Quantified

Costs in parentheses imply cost reductions.

* assumes 30 years of operation with a discount rate of 0% (i.e., no discounting)

** assumes 30 years of operation with a discount rate of 5% and no discounting in the first year
FIGURES
EW-1

EW-1A

EW-2

EW-3A

EW-3B EW-4 EW-5

EW-2A

EW-7

plume maps provided by IT site hydrogeologist and Figure 4-1 from the Selma Pressure Treating Site, Report for Monitoring Well 

SHOWING THE MONITORING, EXTRACTION, AND RESIDENTIAL WELLS AND THE EXTENT OF CONTAMINATION IN THE

E, AND DEEP ZONES
EW-1D

CURRENT EW-3A

CURRENT EW-4

EW-5

EW-15

CURRENT EW-1A

CURRENT EW-6

plume maps provided by IT site hydrogeologist and Figure 4-1 from the Selma Pressure Treating Site, Report for Monitoring Well 

YOUT SHOWING THE APPROXIMATE LOCATIONS OF EXTRACTION WELLS IN THE PROPOSED EXTRACTION SYSTEM.
FIGURE 6-1. MODEL SIMULATION FROM THE ORIGINAL CAPTURE ZONE ANALYSIS SUGGESTING CAPTURE OF THE PLUME IN THE ABSENCE OF

RECHARGE FROM THE PERCOLATION PONDS

(Note: This figure is Figure 4.4.4-1 from the Draft Final Report, IT Corp., October 2000.)
FIGURE 6-2. MODEL SIMULATION FROM THE ORIGINAL CAPTURE ZONE ANALYSIS SUGGESTING CAPTURE OF THE PLUME IN THE PRESENCE

OF RECHARGE FROM THE PERCOLATION PONDS

(Note: This figure is Figure 4.4.4-2 from the Draft Final Report, IT Corp., October 2000.)
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