REMEDIATION SYSTEM EVALUATION
MODESTO GROUNDWATER CONTAMINATION SUPERFUND SITE
MODESTO, CALIFORNIA
Report of the Remediation System Evaluation,
Site Visit Conducted at the Modesto Groundwater Contamination Superfund Site
July 19, 2001
Final Report Submitted to Region 9
December 10, 2001
I
3J
\
LU
-------
NOTICE
Work described herein was performed by GeoTrans, Inc. (GeoTrans) and the United States Army Corps
of Engineers (USAGE) 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-02-008o) may be downloaded from EPA's Technology Innovation Office
website at www.epa.gov/tio or www.cluin.org/rse.
-------
EXECUTIVE SUMMARY
The Modesto Ground-water Contamination Site is located in a commercial area on McHenry Avenue south
of West Fairmont Avenue in the City of Modesto, Stanislaus County, California. The remedy at the site
addresses tetrachloroethylene (PCE) contamination primarily from Halford's Cleaners, located at 941
McHenry Avenue. Contamination originally was discovered in municipal water supply Well 11 in 1984.
The well was shut down until 1991 when granular activated carbon units were added to treat the water.
However, in 1995 uranium concentrations above the maximum contaminant levels (due to naturally
occurring uranium) were detected in the extracted water, and the well was shut down. An interim remedy
consisting of a soil vapor extraction (SVE) system was installed and operated in 1991 to address the PCE
contamination, but shortly after operation, it was determined that the remedy required expansion. An
expanded remedy consisting of an SVE system and a pump-and-treat system and was installed in August
2000 but experienced difficulty operating without excessive operator attention. New contractors began
work on the system in June 2001, and on the day of the RSE they had completed start up adjustments, and
the system was operating continuously.
The SVE system consists of a single vapor extraction well with no currently used monitoring points, and
the pump-and-treat system consists of a single groundwater extraction well. Fifteen groundwater
monitoring wells are sampled quarterly for volatile organic compounds including PCE.
The RSE team found the site managers and the new contractor committed to system optimization.
Recommendations made by the RSE team to improve system effectiveness include the following:
The subsurface performance of the SVE system should be monitored by installing monitoring
points at multiple locations and depths. Such monitoring would help quantify the flow of air
through the subsurface, determine capture of the SVE system, and evaluate the progress toward
remediation of the unsaturated zone.
The responsibility of analyzing monitoring and performance data should be delegated to a
particular party. Such analysis is currently not included in the scope of work for the contractors,
and without clarification of this responsibility and perhaps appropriate modifications to the scope
of work, regularly collected data may not be analyzed leaving the site managers questioning the
performance and progress of the remedy.
A capture zone analysis should be conducted to ensure that the appropriate portions of the
contaminant plume are contained by the groundwater extraction system. A preliminary analysis
was conducted previously, but subsequent data suggest variations in the site water levels and
potentiometric surface that were not originally considered. Development of a simple but
appropriately calibrated groundwater flow model or modification of the previous groundwater flow
model would be useful in evaluating capture and in determining the appropriate final remedy for
the site.
PCE concentrations to the southeast and southwest had extended beyond the outermost monitoring
wells as of November 2000. In addition, in August 1999 the concentration in the deeper aquifer
had increased by an order of magnitude suggesting downward migration of the contamination.
Continued migration may be occurring in these directions, and additional monitoring wells
-------
downgradient of this portion of the plume may be necessary to accurately delineate the plume if
concentrations in the present monitoring wells in these areas do not decrease.
These recommendations might require approximately $48,000 in capital costs and might increase annual
costs by approximately $30,000 per year.
Recommendations to reduce life-cycle costs include the following:
The groundwater treatment plant removes PCE and uranium and discharges the treated water to the
local sanitary sewer for a monthly POTW charge of approximately $1,500. If alternate discharge
locations are available and could be utilized, then the POTW charge, as well as other costs, could
be eliminated. The RSE report highlights two potential alternatives.
If treated water is discharged to the local storm sewer, the POTW charges and possibly
costs associated with liquid phase carbon treatment could be eliminated. This alternative
may cost $20,000 to implement but would likely save $20,500 per year.
If treated water is reinjected into the subsurface, the POTW charges, and possibly the
costs of the liquid phase carbon and the ion exchange treatment could all be eliminated.
This alternative may cost $150,000 to implement but would likely save $31,000 per year.
The equalization tank at the front of the groundwater treatment train does not facilitate operation
and requires the use of an additional transfer pump. In addition, the automatic backwash filtration
system requires substantial maintenance. The filter system should be simplified and the
equalization tank and transfer pump should be removed. Initial costs of $10,000 may be incurred
for implementing these changes, but a cost savings of approximately $6,000 per year due to a
reduction in electricity would result. If the equalization tank must be left in place a smaller
transfer pump should be installed to reduce the usage of electricity.
Because the uranium concentrations in the extracted groundwater are only slightly higher than the
maximum contaminant level of 20 pCi/L, the RSE team recommends regularly evaluating the
influent uranium concentrations to determine the necessity of continuing uranium removal via ion
exchange. Elimination of the ion exchange units may save approximately $20,000 per year.
Implementing the recommendations to reduce costs would require initial investments, but savings from
operations and maintenance could offset these initial investments and the costs associated with
recommendations for enhanced system effectiveness and technical improvement.
Recommendations for technical improvement and for gaining site closeout are also discussed. Many of the
recommendations geared toward technical improvement include modifications to improve safety, prevent
damage, and facilitate operation of the systems, and some of the recommendations reflect suggestions made
by the system operator. The recommendations concerning site close out include encouraging the site
managers to proceed with the final remedy screening and sampling for parameters that affect subsurface
degradation of PCE. Both of these recommendations are geared toward developing a site exit strategy.
A summary of recommendations, including estimated costs and/or savings associated with those
recommendations is presented in Section 7.0 of the report.
-------
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 pump-
and-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: 617-918-8417
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)
Rob Greenwald
GeoTrans, Inc.
2 Paragon Way
Freehold, NJ 07728
(732) 409-0344
Fax: (732) 409-3020
rgreenwald@geotransinc.com
Army Corp of Engineers:
Hazardous, Toxic, and Radioactive
Waste Center of Expertise
(USAGE 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
in
-------
The project team is grateful for the help provided by the following EPA Project Liaisons.
Regionl Darryl Luce and Larry Brill
Region 2 Diana Curt
Region 3 Kathy Davies
Region 4 Kay Wischkaemper
Region 5 Dion Novak
Region 6 Vincent Malott
Region 7 Mary Peterson
Region 8 Armando Saenz and Richard Muza
Region 9 Herb Levine
Region 10 Bernie Zavala
They were vital in selecting the Fund-lead P&T systems to be evaluated and facilitating communication
between the project team and the Remedial Project Managers (RPM's).
IV
-------
TABLE OF CONTENTS
EXECUTIVE SUMMARY i
PREFACE iii
TABLE OF CONTENTS v
1.0 INTRODUCTION 1
1.1 PURPOSE 1
1.2 TEAM COMPOSITION 2
1.3 DOCUMENTS REVIEWED 2
1.4 PERSONS CONTACTED 3
1.5 SITE LOCATION, HISTORY, AND CHARACTERISTICS 3
1.5.1 LOCATION AND HISTORY 3
1.5.2 POTENTIAL SOURCES 4
1.5.3 HYDROGEOLOGIC SETTING 4
1.5.4 DESCRIPTION OF GROUND WATER PLUME 5
2.0 SYSTEM DESCRIPTION 6
2.1 SYSTEM OVERVIEW 6
2.2 EXTRACTION SYSTEMS 6
2.3 TREATMENT SYSTEM 6
2.4 MONITORING SYSTEM 7
3.0 SYSTEM OBJECTIVES, PERFORMANCE AND CLOSURE CRITERIA 8
3.1 CURRENT SYSTEM OBJECTIVES AND CLOSURE CRITERIA 8
3.2 TREATMENT PLANT OPERATION GOALS 8
3.3 ACTION LEVELS 8
4.0 FINDINGS AND OBSERVATIONS FROM THE RSE SITE VISIT 9
4.1 FINDINGS 9
4.2 SUBSURFACE PERFORMANCE AND RESPONSE 9
4.2.1 WATER LEVELS 9
4.2.2 CAPTURE ZONE 9
4.2.3 CONTAMINANT LEVELS 10
4.3 COMPONENT PERFORMANCE 10
4.3.1 GROUNDWATEREXTRACTION AND TREATMENT SYSTEMS 10
4.3.1.1 EXTRACTION WELL 10
4.3.1.2 EQUALIZATION TANK 10
4.3.1.3 FILTRATION UNIT 10
4.3.1.4 TRAY AERATOR 11
4.3.1.5 LIQUID PHASE GAC UNITS 11
4.3.1.6 VAPORPHASE GAC UNIT 11
4.3.1.7 lONEXCHANGE 11
4.3.1.8 CONTROLS 11
4.3.2 SVE SYSTEM 12
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 COSTS 13
4.4.3 LABOR 13
4.4.4 CHEMICAL ANALYSIS 13
4.5 RECURRING PROBLEMS OR ISSUES 13
4.6 REGULATORY COMPLIANCE 14
4.7 TREATMENT PROCESS EXCURSIONS AND UPSETS, ACCIDENTAL CONTAMINANT/REAGENT
RELEASES 14
4.8 SAFETY RECORD 14
5.0 EFFECTIVENESS OF THE SYSTEM TO PROTECT HUMAN HEALTH AND THE ENVIRONMENT . 15
5.1 GROUND WATER 15
5.2 SURFACE WATER 15
5.3 AIR 15
5.4 SOILS 16
5.5 WETLANDS AND SEDIMENTS 16
6.0 RECOMMENDATIONS 17
6.1 RECOMMENDED STUDIES TO ENSURE EFFECTIVENESS 17
6.1.1 MONITOR SUBSURFACE PERFORMANCE OF THE SVE SYSTEM 17
6.1.2 ASSIGN RESPONSIBILITY FOR EVALUATING MONITORING AND PERFORMANCE DATA 17
6.1.3 ANALYZE CAPTUREZONE 17
6.1.4 DELINEATE PLUME VERTICALLY AND TO THE SOUTHEAST AND SOUTHWEST 18
6.2 RECOMMENDED CHANGES TO REDUCE COSTS 18
6.2.1 INVESTIGATE ALTERNATE DISCHARGE OPTIONS 18
6.2.2 ELIMINATE EQUALIZATION TANK, SIMPLIFY FILTRATION SYSTEM AND REMOVE
TRANSFER PUMP 19
6.2.3 REGULARLY EVALUATE THE NEED FOR THE ION EXCHANGE UNITS 20
6.3 MODIFICATIONS INTENDED FOR TECHNICAL IMPROVEMENT 20
6.3.1 RELOCATE VACUUM BREAKER TO HIGH POINT AFTER THE SECOND ION EXCHANGE
UNIT 20
6.3.2 INSTALL VALVING TO ALLOW FOR BACKWASHING OF GAC AND ION EXCHANGE UNITS
21
6.3.3 ADD PERFORMANCE OF EXTRACTION WELL TO THE MONITORING PROGRAM 21
6.3.4 MODIFY SVE SYSTEM TO ADDRESS HIGH DISCHARGE TEMPERATURE 21
6.3.5 REGULARLY EVALUATE NECESSITY OF VAPOR PHASE CARBON UNIT FOR THE
GROUNDWATER TREATMENT SYSTEM 21
6.3.6 APPLY PROPER CONVERSIONS TO PCE CONCENTRATIONS DETERMINED BY PID
MEASUREMENTS 22
6.3.7 IMPROVE ACCURACY OF FLOW MEASUREMENT FOR SVE SYSTEM 22
6.3.8 ADJUST MEMBRANE SURROUNDING THE BAKER TANK 22
6.3.9 IMPROVE DRAINAGE TO THE SECONDARY CONTAINMENT SUMP 22
6.3.10 ADD FANS FOR THE CONTROL PANEL 22
6.3.11 RELOCATE VAPOR PHASE GAC UNIT FOR GROUNDWATER TREATMENT SYSTEM ... 22
6.3.12 ADD AN ADDITIONAL PHONE LINE FOR DATA ACQUISITION 23
6.4 MODIFICATIONS INTENDED TO GAIN SITE CLOSE-OUT 23
6.4.1 PURSUE FINAL REMEDY SCREENING 23
6.4.2 ADD DISSOLVED OXYGEN AND REDOX POTENTIAL TO THE SAMPLING PROGRAM ... 23
6.5 SUGGESTED APPROACH TO IMPLEMENTATION OF RECOMMENDATIONS 24
7.0 SUMMARY 25
VI
-------
List of Tables
Table 7-1. Cost summary table
List of Figures
Figure 1-1 Site layout showing well locations and the PCE plume as determined from November 2000
sampling
vn
-------
1.0 INTRODUCTION
1.1 PURPOSE
In the OSWER Directive No. 9200.0-33, Transmittal of Final FYOO - 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 (USAGE), using a process called a Remediation System Evaluation (RSE),
which was developed by USAGE. 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 Modesto Ground-water Contamination 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 Remedial Project
Manager for the site and the Superfund Reform Initiative Project Liaison for that Region. 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, USAGE, Kansas City District
Dave Becker, Hydrogeologist, USAGE HTRW CX
Peter Rich, Civil and Environmental Engineer, GeoTrans, Inc.
Doug Sutton, Water Resources Engineer, GeoTrans, Inc.
1.3
DOCUMENTS REVIEWED
Author
US EPA
Ecology & Environment,
Inc.
Ecology & Environment,
Inc.
Ecology & Environment,
Inc.
Ecology & Environment,
Inc.
USAGE, Sacramento
Ecology & Environment,
Inc.
Ecology & Environment,
Inc.
USAGE, Sacramento
Ecology & Environment,
Inc.
Ecology & Environment,
Inc.
City of Modesto
Date
9/26/1997
2/9/1998
4/17/1998
8/14/1998
8/17/1998
2000
11/17/2000
1 1/27/2000
1/18/2001
April 2001
4/5/2001
6/11/2001
Title/Description
Interim Record of Decision, Modesto Groundwater
Contamination Superfund Site
Memorandum: Soil Vapor Extraction/Pilot Study Report
Memorandum: Modesto Groundwater Flow and
Contaminant Transport Model
Contract Documents, Modesto Groundwater
Contamination Site, Groundwater Treatment and Soil
Vapor Extraction Systems
Modesto Groundwater Contamination Site, Final Design,
Interim Remedial Action Draft Interim Design
Bid Schedule- Modesto Superfund Site O&M
Groundwater Treatment System Operation and
Maintenance
Soil Vapor Extraction System Operation and
Maintenance
Statement of Work
Modesto Groundwater Contamination Site Interim
Remedial Action Report
Modesto Monitoring Report- April 2000, August 2000,
November 2000
Conditional and Revocable Groundwater Discharge
Permit
-------
1.4 PERSONS CONTACTED
The following individuals were present for the site visit:
Chris Goodrich, Field Service Supervisor, Montgomery Watson
Vilay Lee, Associate Engineer, Montgomery Watson
Doug MacKenzie, Project Engineer, USAGE, Sacramento District
David Seter, Remedial Project Manager, EPA Region 9
1.5 SITE LOCATION, HISTORY, AND CHARACTERISTICS
1.5.1 LOCATION AND HISTORY
The Modesto Groundwater Contamination Site is located on McHenry Avenue south of West Fairmont Avenue
in the City of Modesto, Stanislaus County, California. The remedy at the site addresses tetrachloroethylene
(PCE) contamination stemming from Halford's Cleaners, located at 941 McHenry Avenue. Halford's
Cleaners is bordered directly to the north by the Elk's Lodge, to west by a parking lot, to the south by an auto
repair shop, and to the east by McHenry Avenue. In general, the surrounding area to the north and west is
residential and to the south and east is light commercial. Figure 1-1 shows a layout of the site and the
surrounding area.
The following items provide a brief history of the site and remedy up to the time of the RSE visit.
PCE contamination was originally discovered in Municipal Well 11 in September 1984 and the well
was deactivated. The Modesto Groundwater Contamination Site was defined to include Well 11 and
the potential sources of contamination. Within a few weeks of the discovery of the PCE contamination
of Well 11, Halford's Cleaners was identified as a potential source due to its proximity to the well
(1,300 ft) and the use of PCE in dry cleaning.
In April 1985, the Stanislaus County Department of Environmental Resources conducted a
groundwater investigation in the immediate vicinity of Halford's Cleaners. Results indicated a PCE
concentration of 84.6 ppb in the groundwater sample collected from the Elk Lodge well (just north of
Halford's Cleaners) and a PCE concentration of 176,000 ppb in soil samples taken near a dry cleaning
machine owned by Halford's Cleaners.
Continuous monitoring for PCE revealed no detectable levels at Well 11. The well was restarted but
was shut down again in 1989 when PCE was detected again. The well then was equipped with
granular activated carbon units in 1991 and resumed operation.
Following several studies to determine the source of the PCE, the EPA issued an order in 1990 to
Halford's Cleaners for treatment of the contaminated soil at the Halford site and the removal action
commenced with operation of a SVE system in February 1991.
Shortly after operation of that remedy began, EPA determined that remedy needed to be expanded and
began a subsequent remedial investigation in 1991.
-------
In October 1995 the City of Modesto detected uranium concentrations in water extracted by Well 11
that exceeded the maximum contaminant level (MCL) of 20 pico Curies per liter (pCi/L). Well
operation was discontinued, and the well has remained non-operational.
In September 26, 1997 an interim Record of Decision (ROD) specified groundwater extraction and
treatment by air stripping, discharge of treated groundwater, soil vapor extraction, and institutional
controls.
By August 2000 the pump-and-treat and SVE systems were constructed, and a 12-week O&M period
ran from mid-August to early November.
The U.S. Army Corps of Engineers (USAGE) now oversees the site and has contracted anew operator
who began work in June 2001. The systems had just begun steady-state operation on the day of the
RSE visit on July 19,2001.
1.5.2 POTENTIAL SOURCES
In 1985 a dry cleaning machine at Halford's Cleaners was found to have leaks. In addition, this unit also
discharged PCE into the private sanitary sewer line that connected the cleaners to the main sewer line. Thus,
PCE entered the subsurface both through a leak in the machine above ground and also through a leak in the
sewer line. The machine has since been replaced and PCE is no longer discharged to the sewer. Soil samples
collected in 1985 revealed PCE concentrations in soil as high as 176,000 ppb within three feet of the surface.
Later sampling conducted in July 1990 revealed soil concentrations of 21,000 ppb within five feet of the
surface. Sampling conducted in 1995 revealed lower soil concentrations but groundwater PCE concentrations
as high as 74,000 ug/L. This highest PCE concentration was found in MW-8, and groundwater PCE
concentrations of 17,300 ug/L and 2,706 ug/L were also found in MW-5 and MW-3, respectively. These three
concentrations are all higher than 1% of the solubility for PCE suggesting the presence of freephase PCE in
the form of a dense non-aqueous phase liquid (DNAPL). Please refer to Figure 1-1 for the location of these
monitoring wells.
1.5.3 HYDROGEOLOGIC SETTING
In the Modesto area groundwater occurs in both an upper semi-confined unit and a lower confined unit that
are separated by the Corcoran Clay. The edge of this clay layer, however, is near the Modesto Groundwater
Contamination Site; therefore, these two aquifer systems may be interconnected in the vicinity of the site-related
contamination. Sediments beneath the site are discontinuous layers or lenses of sands, silts, and clays that are
usually less than 10 feet thick. Fine-grained sediments dominate to the south of the site and coarser grained
material dominates to the north. Onsite drilling revealed a fine-grained layer from approximately 95 feet below
ground surface (bgs) to 145 feet bgs. Observation of subsurface material obtained from soil borings do not
concur with previous observations of the Corcoran Clay. The layer does appear to provide at least a partial
barrier to site-related contamination.
The regional water-level gradient is approximately 5 x 10"4 feet/foot, and groundwater levels and flow directions
are significantly affected by regional pumping. When Well 11 and other municipal wells were operating,
groundwater elevations were 20 feet above mean sea level (MSL) or 70 feet bgs, and flow at the site was
directed toward Well 11. Recent measurements (without the influence of regional pumping) yielded water
-------
levels of approximately 50 feet MSL or 40 feet bgs and suggested ground-water flow to the south or southwest
away from Well 11.
A 1997 pump test suggests a hydraulic conductivity ranging from approximately 50 ft/day to 100 ft/day and
a storage coefficient of 0.007, which suggests the formation is semi-confined. A hydraulic connection across
the fine-grained layer between 95 feet bgs and 145 feet bgs was evident from the pumping test. The non-
pumping gradient supports upward flow thereby potentially limiting contamination of the groundwater beneath
this layer.
1.5.4 DESCRIPTION OF GROUND WATER PLUME
The highest concentrations of PCE center around Halford's Cleaners and diminish in all directions as the
distance from the cleaners increases. PCE concentrations in the monitoring wells adjacent to the site and above
95 feet bgs (MW-3, MW-5, and MW-8) range from 2,200 ppb to 5,500 ppb. Over time, and in the absence
of pumping from Well 11, the plume has spread to the south. Approximately 300 feet to the south of the site
(MW-4) the November-2000 PCE concentration was 810 ppb and approximately 600 feet south of the site
(MW-6) the November-2000 PCE concentration was 270 ppb. PCE concentrations in monitoring wells to the
north (upgradient in the absence of pumping from Well 11) are 20 ppb or lower and are likely residuals from
periods when Well 11 was operating. PCE contamination has extended below the fine-grained layer that
extends from 95 to 145 feet bgs as revealed by samples taken from MW-9. The concentrations, however, are
two orders of magnitude lower than those in MW-8 which is adjacent to MW-9 but over 50 feet above it. A
plume map is provided in Figure 1-1.
-------
2.0 SYSTEM DESCRIPTION
2.1 SYSTEM OVERVIEW
The interim remedy for the Modesto Groundwater Contamination Site specified in the 1997 interim ROD
includes the following items:
groundwater extraction from one well located on site; above ground treatment (air stripping, carbon
adsorption, and ion exchange treatment), and discharge to city sewer;
soil vapor extraction, above-ground treatment (carbon adsorption), and discharge to the atmosphere;
and
institutional controls that include signs and fencing.
Although a number of test periods for both the pump-and-treat and SVE systems were conducted during 2000,
continuous operation of this system did not begin until July 2001 under oversight by USAGE and their new
operations contractor.
2.2 EXTRACTION SYSTEMS
The groundwater extraction system consists of one extraction well, EW-1, installed in June 2000. It is screened
from 65 feet bgs to 95 feet bgs and is designed to pump at 50 gpm. A flush mounted concrete vault has been
constructed over the well to prevent damage. The vault also includes a manual winch to facilitate pump
maintenance.
The soil vapor extraction system consists of one vapor extraction well, SV-1, installed in May 2000. It
replaced the original SVE well from 1991, which was damaged during the excavation of the piping trench in
2000. The new SVE well is screened from 18 to 38 ft bgs, and soil vapor is extracted from the well at 160
standard cubic feet per minute (scfm).
2.3 TREATMENT SYSTEM
The groundwater treatment system was designed to operate at 50 gpm with influent PCE concentrations of
4,500 ppb and effluent PCE concentrations of 0.5 ppb, which translates to removing 2.7 pounds of PCE per
day. Maximum design effluent concentrations for uranium and toluene are 20 pCi/L and 150 ppb, respectively.
The system consists of the following elements:
equalization tank
-------
filters
anti-scaling system (non-toxic)
tray aerator (air stripper)
one vapor phase granular activated carbon (GAC)
two liquid phase GAC
two ion exchange units
The entire system, with the exception of one liquid phase GAC unit, is housed in an 8.5' x 8.5' x 40' metal
storage container.
The soil vapor treatment system was designed to operate at 160 scfm and remove up to 100 pounds per day
of PCE with treated off-gas concentrations of less than 15 ppm total organics. It consists of the following
elements:
knock-out drum
air filter
discharge silencers
vapor phase GAC
The system housed in an 8.5' x 8.5' x 12.5' treatment unit with the exception of the vapor phase GAC
unit, which is adjacent to the treatment unit.
2.4 MONITORING SYSTEM
On a quarterly basis, the operations contractors measure water levels and sample for volatile organic
compounds from fifteen monitoring wells. All but one of the wells screen above the fine-grained layer from
95 feet bgs to 145 feet bgs. Between November 2000 and August 2001 aquifer samples were not collected and
water levels were not measured due to a switch in operations oversight and contractors. There is no subsurface
monitoring program for the SVE system.
Monitoring of the process water includes monthly sampling of the influent and effluent and quarterly sampling
of two additional points. Monitoring of the soil vapor treatment system includes sampling and analysis for
VOCs five times per quarter. All aquifer and process samples, both air and water, are sent to an offsite
laboratory for analysis.
-------
3.0 SYSTEM OBJECTIVES, PERFORMANCE AND CLOSURE
CRITERIA
3.1 CURRENT SYSTEM OBJECTIVES AND CLOSURE CRITERIA
The current system is an interim remedy until further information can be gathered to determine the appropriate
final remedy. The interim ROD signed on September 26, 1997 states the following goals:
eliminate and contain the highest contaminant levels at the source [source control];
prevent exposure to contaminated ground-water, above acceptable risk levels, to human health and the
environment;
minimize the impact of interim cleanup measures to the community;
collect data to determine if federal and state requirements can be met throughout the aquifer; and
to delineate more clearly the downgradient edges of the plume and to prevent its further migration.
The duration of the interim remedy has not been determined, but it is expected to be at least one year.
3.2 TREATMENT PLANT OPERATION GOALS
The treatment plant goals are consistent with the discharge permit issued by the City of Modesto. The
permitted discharge limits include 0.5 ppb for PCE, 150 ppb for toluene, and 20 pCi/L for each isotope of
uranium (U 234, U 238, or U 235). Treated air discharged to the atmosphere must meet the requirements of
San Joaquin Valley Unified Air Pollution Control District Rule 2201, which states that Best Available Control
Technology must be used if groundwater or soil vapor treatment systems that emit more than 2 pounds of
contaminants per day.
3.3 ACTION LEVELS
The discharge limits stated above are the action levels for the site. Cleanup standards for the site are yet to be
determined. Data from the interim remedy will be used to determine cleanup standards for the final remedy.
-------
4.0 FINDINGS AND OBSERVATIONS FROM THE RSE SITE VISIT
4.1 FINDINGS
The RSE team visited the site within weeks of the new operations contractor commencing work on the
pump-and-treat and SVE systems. The RSE team found the oversight managers and the contractors
committed to optimizing the system for consistent and reliable operation. 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 obviously have the benefit of the operational data unavailable to the
original designers.
4.2 SUBSURFACE PERFORMANCE AND RESPONSE
4.2.1 WATER LEVELS
Water-level data collected prior to 1997 indicate a hydraulic head gradient of approximately 0.0005 that
directs flow south, and the 1997 groundwater modeling study of the site assumes such a gradient.
Quarterly measurements of water levels conducted in 2000 from the fifteen monitoring wells also indicate
that groundwater generally flows south, but this more recent data suggests more complicated flow patterns
with a hydraulic head gradient of closer to 0.001 and flow directions ranging from southeast to southwest.
Water levels are approximately 30 feet higher than they were during operation of Well 11.
4.2.2 CAPTURE ZONE
The capture zone of the groundwater extraction well was analyzed in the 1997 modeling study of the site.
The study assumed a hydraulic conductivity ranging from approximately 37 to 300 ft/day, a hydraulic
gradient ranging from 0.00057 to 0.00065, approximately 50 feet of saturated thickness for the
contaminated zone, and pumping at 50 gpm. The resulting capture zone has a width of approximately
1,800 feet (900 feet cross gradient on each side of the extraction well) and a downgradient stagnation point
over 600 feet from the extraction well. An overlay of this capture zone and the December 1997 simulated
PCE plume map from the same study suggest capture of the most contaminated portions of the plume.
Only a small portion of the plume with concentrations up to 50 ppb extended downgradient beyond the
simulated capture zone. No capture zone analysis has been conducted with water level and concentration
data since 1997, and water level data from 2000 may suggest a higher and variable hydraulic gradient,
which could result in a smaller capture zone.
-------
4.2.3 CONTAMINANT LEVELS
Although a capture zone analysis has not been performed since the modeling study conducted in 1997, a
comparison of the plume maps from 1997 and April 2000 suggests no appreciable horizontal spreading of
the PCE plume or increases in the sampled concentrations of the shallow monitoring wells. Rather, the PCE
concentrations in the monitoring wells near the source area decreased, suggesting limited dilution of the
source area. The PCE concentrations in the deeper well (MW-9), however, did increase by an order of
magnitude between April and August 1999. It should be noted that before August 2000 the SVE and
pump-and-treat systems were not operational. PCE sampling results from November 2000, after a three
month test period of the SVE and pump-and-treat systems, are similar to those obtained in April 2000 with
the exception that PCE concentrations in the monitoring wells near the source area were higher (more
comparable to those obtained in 1997). Thus, it appears that the plume area has not increased appreciably
over a three year period even in the absence of pumping. The magnitude of PCE concentrations in the
deeper monitoring wells, however, have increased significantly.
The groundwater treatment system is designed for influent concentrations up to 4,500 ppb PCE. Actual
influent PCE concentrations measured during the 12-week trial period in the Fall of 2000 ranged from 30
ppb to 12,000 ppb. The influent concentrations for uranium were 23.5 pCi/L for U 234, 19.1 pCi/L for U
238, and less than 15 pCi/L for U 235. PCE concentrations in the extracted groundwater was
approximately 3,000 ppb at the time of the RSE visit. In June 2001, the PCE concentration in the air
extracted from the SVE system was 522 ppm by volume as determined by laboratory analysis of collected
air samples.
4.3 COMPONENT PERFORMANCE
4.3.1 GROUNDWATER EXTRACTION AND TREATMENT SYSTEMS
4.3.1.1 EXTRACTION WELL
The extraction well operates at 48 gpm. The pump is 2 horsepower, and the well is screened from 65 to 95
feet bgs. During the initial operation of the well, sand and silt were drawn from the extraction well into the
treatment plant.
4.3.1.2 EQUALIZATION TANK
The 550 gallon equalization tank provides for eleven minutes of storage at the design pump rate of 50 gpm
and is equipped with high level alarms which can shut down the system to reduce the threat of overflowing.
A metering pump injects scaling agent into the equalization tank to prevent fouling of the other process
components. A 7.5 horsepower transfer pump sends the water from the bottom of the equalization tank
through a filter system and the rest of the treatment process train.
4.3.1.3 FILTRATION UNIT
Water from the equalization tank flows through an automatic backwash filtering system before entering the
tray aerator. The filter system consists of 10 micron filters, associated plumbing, and a clarifying tank.
10
-------
The system automatically backwashes at a pressure differential of 10 pounds per square inch (psi).
Backwashed water is sent through a clarifier and then to the equalization tank. The system cycled 10 times
in two days during initial operation in June 2001 and has required substantial maintenance.
4.3.1.4 TRAY AERATOR
The tray aerator (air stripper) consists of three trays and is designed for 99.99% VOC removal efficiency
when provided with approximately 900 cfm of air. A 7.5 horsepower blower provides this required air
flow. The transfer pump that sends water from the tray aerator through the carbon is the rate-limiting step
of the groundwater extraction and treatment system.
4.3.1.5 LIQUID PHASE GAC UNITS
The liquid phase GAC units contain approximately 1,000 Ibs of GAC. They were replaced in October of
2000 because the units were not rated at the pressure specified in the design. The pressure drop across the
GAC unit is monitored, and the system automatically shuts down if the pressure reaches a predetermined
limit. The system was shutting down frequently due to a "water hammer" effect caused by high pressures
when the transfer pump from the air stripper activated. The new operators remedied this by placing a five-
second delay in the logic that allows the pressure to abate so the system does not shut down.
4.3.1.6 VAPOR PHASE GAC UNIT
The vapor phase GAC unit contains approximately 2,000 Ibs of GAC and has not been replaced since it
was installed in 2000. According to design influent concentrations, the vapor phase GAC was projected to
last 12 weeks assuming continuous operation. At the current flow rates chemical loading to this unit is less
than 2 pounds per day. With this loading rate the unit could last up to 30 weeks without requiring
replacement.
4.3.1.7 ION EXCHANGE UNITS
Two ion exchange units are placed in series after the liquid phase GAC unit. The resin has not been
replaced to date, but based on current influent concentrations, the manufacturer projected that the resin
should be changed out after approximately 300 days. The lead vessel has fouled and requires replacement.
The vacuum relief valve is currently placed prior to this system. As a result, when the system shuts down,
water is siphoned from these units to the discharge point producing a strong vacuum within the units
possibly contributing to unnecessary compression of the resin. More importantly, this vacuum could
implode these units.
4.3.1.8 CONTROLS
The system has auto dial-out capability when an alarm condition exists and allows remote restart and
shutdown. Also, the anti-scaling system does not shut down automatically in the event of an automatic
plant shutdown and will continue to pump at approximately one gallon per day until it is manually shut off.
This is not a problem as it will not harm downstream units or the tank containing this agent. The cost of
this system and its chemicals are minimal.
11
-------
4.3.2 SVE SYSTEM
The SVE system consists of an extraction well, a 7.5 horsepower blower operating at approximately 160
scfin, a knock out drum to lower the humidity, filters to remove particulates, and a vapor phase GAC unit.
The knock out drum has a capacity of 50 gallons and was modified to include a sump that drains the drum
to the equalization tank of the groundwater treatment system. The vapor phase GAC unit contains
approximately 2,000 Ibs of GAC and was replaced after eleven days of continuous operation. Frequent
replacement of the carbon in this unit may be required during the initial operation periods until the PCE
concentration in the soil vapor decreases. At the time of the RSE visit, discharge from the blower was
200 F, which is above normal operating conditions. Flow rates through the SVE system are currently
measured with a hot-wire anemometer because the pitot tube originally installed in the 3-inch line was
designed for 2-inch lines.
4.4 COMPONENTS OR PROCESSES THAT ACCOUNT FOR MAJORITY OF
MONTHLY COSTS
Costs associated with the operation and maintenance of the pump-and-treat and SVE systems can only be
approximated because the systems had only operated for three weeks under the current contract. These
costs are provided in the following list and are estimated based on the proposal from the original operator
and the bid schedule for the current operator. Quantities for electricity, carbon, and ion exchange resin are
estimates based on engineering judgment and may be significantly different during actual operations
O&M labor, management, and reporting $20,000
Response to autodialer calls and alarms $ 1,000
Optimization $1,250
Reimbursable parts $1,700
Chemical analysis $3,500
Chemicals (anti-scaling agent) $200
Electricity $5,000
Ion exchange replacement $1,700
GAC replacement (liquid and vapor phase) $2,900
POTWfees $1,500
$37,750
4.4.1 UTILITIES
Operation of the pumps and blowers for the pump-and-treat and SVE systems require approximately 60 to
70 kilowatts which translates to approximately $5,000. City water and natural gas are not used at site.
The average monthly cost for discharging plant effluent to the POTW is approximately $1,500.
12
-------
4.4.2 NON-UTILITY CONSUMABLES AND DISPOSAL COSTS
Approximately two drums of anti-scaling agent are used each year at a cost of approximately $1,200 per
drum. The initial bid schedule filed by the current contractors suggests approximately $32,500 per year for
eight replacements of a vapor phase carbon unit (equivalent to the six replacements over nine months as
specified in the bid schedule) and $2,500 per year for replacement of a liquid phase carbon unit. At an
estimated annual cost of $35,000 per year, this translates to approximate monthly costs of $2,900 for GAC
replacement. The bid schedule indicates one change out of the ion exchange units is expected per year at an
approximate cost of $22,000 per year.
4.4.3 LABOR
The bid schedule, prior to negotiation, allocated approximately $20,000 per month for the nine months of
operation and maintenance occurring after an initial three-month period of startup. These costs presumably
include the costs of management and reporting but do not include up to $10,000 over nine months for
responding to autodialer calls and meetings.
4.4.4 CHEMICAL ANALYSIS
According to the scope of work, after the initial three-month startup period, quarterly monitoring
requirements include the following sampling:
5 samples of vapor from the SVE system analyzed for VOCs;
10 samples of the process water (including influent and effluent) analyzed for VOCs;
7 samples of the process water (including influent and effluent) analyzed for total uranium; and
15 groundwater samples analyzed for VOCs.
At costs of approximately $300 per sample for the vapor samples and an average of $200 per sample for
the groundwater samples (uranium or VOCs), this program translates to quarterly sampling costs of
approximately $8,000 or monthly costs of $2,700. Field blanks and other required additional samples
would likely increase these costs to $3,500 per month.
4.5 RECURRING PROBLEMS OR ISSUES
A number of technical problems regarding the initial design have delayed steady-state operation of the
system. The following list itemizes a few of these issues or problems highlighted by the current operators
during the RSE visit:
high temperatures in the metal storage containers housing the SVE and groundwater treatment
systems;
difficulty in sampling vapor phase GAC due to the lack of room within the storage containers;
13
-------
continuous cycling of the automatic backwash filters;
fouling of the lead ion exchange unit; and
siphoning of water from the ion exchange vessels to the system discharge when the system is shut
down.
4.6 REGULATORY COMPLIANCE
The groundwater treatment system has had a number of problems that have delayed operation including
PCE effluent concentrations exceeding the limit of 0.5 ug/L specified in the discharge permit. According to
sampling events in late June and July 2001, the treatment system has met the required discharge criteria.
4.7 TREATMENT PROCESS EXCURSIONS AND UPSETS, ACCIDENTAL
CONTAMINANT/REAGENT RELEASES
Since steady-state operation of the plant in July 2001, there have been no treatment process excursions or
accidental releases of contaminants or reagents.
4.8 SAFETY RECORD
There have been no reported accidents on site.
14
-------
5.0 EFFECTIVENESS OF THE SYSTEM TO PROTECT HUMAN
HEALTH AND THE ENVIRONMENT
5.1 GROUND WATER
The groundwater underlying Modesto is no longer used for drinking water due to uranium concentrations
exceeding the maximum contaminant levels (MCLs). However, according to State Water Resources
Control Board Resolution No. 88-63, "Sources of Drinking Water Policy", with some exceptions, all
groundwater and surface water are considered suitable, or potentially suitable, for municipal or domestic
water supply. Thus, groundwater underlying the Modesto site may be considered a potential source of
drinking water in the future. Also, given the prominence of agriculture in the areas surrounding Modesto,
the possibility exists that groundwater could be used for agricultural purposes in the future.
The municipal water supply is now provided from the Stanislaus River located approximately 5 miles from
the site. Thus, groundwater currently does not represent a direct avenue of exposure to site-related
contamination.
5.2 SURFACE WATER
The Stanislaus River is approximately 5 miles upgradient to the north of the site, and the Tuolumne River
is approximately 3 miles downgradient to the south of the site. Dry Creek passes within a mile of the site
to the southeast and empties into the Tuolumne River. The November 2000 groundwater sampling does
suggest transport of PCE from the site toward both the Tuolumne River and Dry Creek suggesting, that
without adequate capture of the plume, impacted groundwater could eventually reach these two surface
water bodies. In November 2000 MW-13, located approximately 1,000 feet south-southwest of the site,
had a PCE concentration of 10 ppb, and MW-12, located approximately 600 feet to the east-southeast of
the site, had a PCE concentration of 51 ppb.
5.3 AIR
The SVE system is installed to remove PCE and other VOCs from the unsaturated zone; however, the
capture zone of this system is currently unknown due to an insufficient number of monitoring points. The
emissions from the pump-and-treat and SVE systems represent the most significant avenue of site-related
contamination to the air. However, vapor phase carbon units on both systems keep emissions from the
systems well below a pound of PCE per day.
15
-------
5.4 SOILS
Subsurface soils at the site are impacted by PCE and other VOCs, and these soils are addressed by the
SVE system. Asphalt over these soils prevents direct exposure of the public to these impacted subsurface
soils.
5.5 WETLANDS AND SEDIMENTS
Wetlands and sediments are not impacted by site-related contamination. If the contaminant plume were to
reach the Dry Creek or the Tuolumne River such exposure of the related soils to PCE would be expected.
16
-------
6.0 RECOMMENDATIONS
6.1 RECOMMENDED STUDIES TO ENSURE EFFECTIVENESS
6.1.1 MONITOR SUBSURFACE PERFORMANCE OF THE SVE SYSTEM
The soil vapor extraction system requires monitoring points to properly evaluate its capture zone and
progress toward remediation. Monitoring from approximately four locations with multiple depths should
suffice. According to the project team, two monitoring locations with multiple sampling depths are already
installed at the site, but sampling them is not part of the operations scope of work. The condition of these
existing monitoring wells should be evaluated, and if they are functional they should be included in the
proposed monitoring program for the SVE system. Regardless of the condition of the existing wells,
additional points are also required. They can be installed using direct-push techniques and should include
short screens placed at three depths above the water table (e.g., 15, 25, and 35 feet) and in at least two new
locations. Monitoring these points for VOCs and measuring them for vacuums will help evaluate the
throughput of air for remediation, progress toward cleanup, and location of significant vadose zone
sources. Installation of the new monitoring points should cost approximately $18,000. Sampling for
VOCs from twelve sampling points (four locations with three depths each) should be added to the quarterly
aquifer monitoring events and should translate to additional labor costs of approximately $12,000 per year
and additional analytical costs of approximately $8,000 per year.
6.1.2 ASSIGN RESPONSIBILITY FOR EVALUATING MONITORING AND PERFORMANCE DATA
The aquifer sampling program under the current contractor is scheduled to begin in August 2001. Before
the program is underway the responsibility of data analysis should be properly delegated. Data analysis
could be conducted by the EPA Remedial Project Manager, EPA technical support staff, the USAGE
project manager, or the contractor. All of these parties are capable of evaluating the aquifer data and
providing adequate data analysis, and all parties should review the data independently. However, one of
those parties should take on the primary responsibility of evaluating and analyzing the data to continually
evaluate capture of site-related contaminants and remediation progress as well as provide a knowledge base
from which an optimal final remedy can be determined. It should be noted that in the scope of work for the
contractor, groundwater sampling and reporting of the results is required the scope of work does not
require data analysis, evaluation of plume capture, or evaluation of remedy progress. Thus, without a
modification to this scope, adequate data analysis likely will not be performed by the contractor.
6.1.3 ANALYZE CAPTURE ZONE
The capture zone was analyzed in 1997 with the use of a groundwater model calibrated with steady-state
and transient water level measurements. Since this original capture zone analysis additional water level and
water quality data have been collected showing potential variations in groundwater flow and limited
migration of the site-related contaminants. A relatively simplistic groundwater model should be developed
and calibrated with historical water level data and continuously updated with new water level data. A
capture zone analysis should be conducted based on recent plume maps and model simulations. Such an
17
-------
analysis may show less capture than was originally determined in 1997 suggesting the possible need for
additional pumping if pump-and-treat is selected as the final remedy. The recommended capture zone
analysis should illustrate which portions of the plume are captured and the approximate concentrations of
those portions that are not captured. Development of the model may result in an initial cost of $30,000.
Regular updating and calibration of the model as well as simulations for determining capture and
experimenting with final remedy scenarios may cost $10,000 per year.
6.1.4 DELINEATE PLUME VERTICALLY AND TO THE SOUTHEAST AND SOUTHWEST
Aquifer sampling in and since August 1999 indicate PCE concentrations over 50 ppb in MW-9 which
screens an interval beneath the fine-grained layer that is located between 95 and 145 feet bgs. If
concentrations in this well continue to rise or do not decrease after a year of quarterly sampling additional
monitoring may be required at depths of more than 145 feet bgs. If contamination is considered extensive,
a remediation strategy may be required at these depths. Additional pumping at these depths is not
advisable as it may assist in downward migration of the contamination. In-well stripping may be more
appropriate.
The November 2000 aquifer sampling also indicates that the plume has extended beyond MW-13 to the
south-southwest and beyond MW-12 to east-southeast. Concentrations at these two wells in November
2000 were 10 ppb and 51 ppb, respectively. Given that these are the outermost monitoring wells for the
site and they have detectable concentrations of PCE, they cannot be used to adequately determine the
outermost extent of the plume. If concentrations in these wells increase or remain the same after a year of
quarterly sampling, additional monitoring wells may need to be placed beyond these monitoring wells to
help delineate the PCE plume, as these portions of the plume are likely beyond the capture zone and likely
will continue to migrate downgradient.
An additional well would require a capital cost of approximately $14,000. This figure would include the
costs of a work plan, the design, contracting, and installation. As mentioned above, the need for such wells
should be evaluated by evaluating monitoring data from existing wells over a year of continuous system
operation. An increase of approximately $1,500 per well per year would be expected if such wells were
added to the current sampling program.
6.2 RECOMMENDED CHANGES TO REDUCE COSTS
6.2.1 INVESTIGATE ALTERNATE DISCHARGE OPTIONS
A substantial portion of the remedy costs are associated with discharging to the local sanitary sewer. The
POTW charges on average $1,500 per month to accept the treated water with undetectable concentrations
of PCE and uranium concentrations of less than 20 pCi/L. A number of alternative discharge options
should be considered in an effort to reduce life-cycle costs, especially with potential future increases in
extraction rates for the final remedy. The following list provides a few alternatives and the advantages and
disadvantages of each one.
18
-------
Discharge to the local storm sewer:
Advantages:
Discharging the treated water to the local storm sewer in place of the sanitary sewer (POTW)
would eliminate the POTW charges of approximately $1,500 per month. In addition, this alternate
discharge location may allow the relaxation of the PCE discharge requirements from 0.5 ug/L to
the maximum contaminant level (MCL) of 5 ug/L. A relaxed standard would allow removal of the
polishing step with liquid phase carbon and could save an additional $2,500 per year.
Disadvantages:
This option would require additional permitting and acceptance by the City of Modesto. Applying
for the permit including negotiations, toxicity testing, and piping to the sewer may cost $20,000.
Cost Summary:
This option may cost $20,000 up front to obtain the permit, but an estimated annual potential
savings of approximately $20,500 per year could be expected suggesting payoff and potential
savings in approximately one year.
Reinjection to the subsurface:
Advantages:
Reinjecting treated water would eliminate the POTW charges of approximately $1,500 per month.
In addition, this alternate discharge location may allow the relaxation of the PCE discharge
requirements from 0.5 ug/L to the maximum contaminant level (MCL) of 5 ug/L. A relaxed
standard would allow removal of the polishing step with liquid phase carbon and could save an
additional $2,500 per year. Furthermore, because this option involves returning the treated water to
the subsurface that has a background uranium concentration equal to that of the treated water the
ion exchange units used for uranium treatment could likely be removed at a cost savings of
approximately $1,700 per month.
Disadvantages:
This discharge option would require additional permitting and acceptance of the permit application
by the State of California. Furthermore, it would require the construction of a reinjection system
capable of reinjecting the water to the subsurface 400 to 500 feet down gradient from the
extraction well. Designing, permitting, obtaining easements for, and constructing the system may
result in capital costs of approximately $150,000. Continued maintenance of the system would
likely require approximately $10,000 per year.
Cost Summary:
This option includes a significant capital cost of approximately $150,000 for design and
installation. An estimated annual potential savings of approximately $31,000 could be expected
suggesting payoff and savings after approximately 5 years. The savings could be more substantial
if pumping rates are increased for the final site remedy.
6.2.2 ELIMINATE EQUALIZATION TANK, SIMPLIFY FILTRATION SYSTEM AND REMOVE
TRANSFER PUMP
Influent to the treatment plant currently enters an equalization tank before passing through the treatment
process train. The presence of this tank provides no added benefit to the system (well purge water can be
19
-------
added to the system through the SVE knockout drum and scale inhibitor can be added in line) and requires
additional transfer pumps to move water through the treatment process train. In addition, the automatic
backwash filtering system currently installed between the equalization tank and the tray aerator is overly
complicated and requires frequent maintenance.
The 2 horsepower submersible pump in the extraction well is sufficient to transfer the water from the well
through a simple filtering system to the top of the tray aerator. Thus, the 7.5 horsepower transfer pump
located between the equalization tank and the current filtration system could be eliminated if the
equalization tank is removed and the filtration unit is simplified. The simplified filtering system should
consist of inline bag filters, with 10 or 25 micron pores, arranged in parallel and located prior to the air
stripper. In addition, it should have a differential pressure switch interlocked with the well pump and a
bypass or parallel unit to allow bag filter changes without system downtime. If necessary, a second filter
could be added after the tray aerator to further limit pressure buildup in the downstream units.
Removal of the equalization tank and the 7.5 horsepower pump in addition to purchasing and installing two
bag filter units in parallel would cost approximately $10,000. This change, however, would result in a cost
savings of approximately $500 per month ($6,000 per year) assuming electricity costs of $0.10/kilowatt-
hour and would greatly reduce the amount of maintenance required by the current automatic backwash
filtering system.
It should be noted that if extraction of DNAPL is a concern, the equalization tank may be required to act as
a phase separator. However, because the tank drains from the bottom, a baffle would be needed in the tank
to prevent transfer of DNAPL to the tray aerator. While aquifer concentrations do suggest DNAPL in the
subsurface, influent concentrations do not indicate the DNAPL is being transferred from the well to the
treatment system. If the equalization tank is left in place and the filtration system is simplified, a smaller
transfer pump could be used to reduce electricity costs.
6.2.3 REGULARLY EVALUATE THE NEED FOR THE ION EXCHANGE UNITS
With continued pumping, the influent uranium concentrations may drop over time, and if this influent
concentration drops consistently below 20 pCi/L, treatment for uranium would no longer be required.
Given that replacement of the ion exchange resin costs approximately $1,700 per month (over $20,000 per
year) significant cost savings could be realized if these units are eliminated. Thus, influent uranium
concentrations should be evaluated regularly to determine if the discharge criteria can be met without
treatment.
6.3 MODIFICATIONS INTENDED FOR TECHNICAL IMPROVEMENT
6.3.1 RELOCATE VACUUM BREAKER TO HIGH POINT AFTER THE SECOND ION EXCHANGE
UNIT
When the groundwater treatment system shuts down, water from the ion exchange units is siphoned to the
discharge point creating a strong vacuum within the ion exchange units. Such a vacuum could damage the
units and could result in injury to operations personnel if the units collapse. A vacuum breaker is currently
located prior to the ion exchange units, and if this breaker is relocated to the high point after the last ion
20
-------
exchange unit, the potential for such vacuums would be eliminated. Due to the potential of injury and
serious damage, this recommendation should be implemented immediately. Implementing this
recommendation should require a maximum of $2,000 for labor and any necessary materials.
6.3.2 INSTALL VALVING TO ALLOW FOR BACKWASHING OF GAC AND ION EXCHANGE
UNITS
Valving should be added to the system to allow removal and backwashing of individual GAC and ion
exchange units. The backwash effluent should be directed inline prior to the recommended bag filters that
precede the tray aerator. The purchase and installation of the appropriate valves would costs
approximately $7,000.
6.3.3 ADD PERFORMANCE OF EXTRACTION WELL TO THE MONITORING PROGRAM
The effectiveness of the extraction system rests solely on a single well and pump. As such, the
performance of this well and the pump should be monitored frequently to determine if fouling is becoming
an issue. The specific capacity of the well and the production of sand and silt should be noted regularly.
Measuring the water level in the extraction well monthly and noting the flow rate will provide the specific
capacity. If the water level is decreasing, the specific capacity is decreasing, and well maintenance likely is
necessary. It should be noted that monitoring the extraction rate alone may not be sufficient as fouling may
occur with a decrease in the water levels and no substantial decrease in the extraction rate. The water level
and flow rate in the extraction well should be noted as soon as possible to provide a baseline level for the
specific capacity. If the specific capacity drops to less than 70% of that baseline, well maintenance is
necessary. More information about well maintenance can be found in USAGE Engineering Pamphlet
EP 1110-1-27 at
Determining the specific capacity each month and assessing the need for maintenance may cost an
additional $1,000 per year. As a contingency for well maintenance, an additional $1,000 per year should
be budgeted.
6.3.4 MODIFY SVE SYSTEM TO ADDRESS HIGH DISCHARGE TEMPERATURE
At the time of the RSE, the SVE system was operating at 160 scfm and 68 inches of water suction, which
is at the high end of the pressure/low flow curve for the installed DR 858. The operating temperature of
200 F is within the max of the 140 C limit for the blower but above the design level for the CPVC pipe. If
the temperature cannot be reduced by removing inline restrictions such as a throttling valve or plugged
filters, the discharge pipe prior to the increase in diameter should be converted to galvanized steel with a
protective screen around it. The blower is probably too large for the one extraction point, but since the
system could be altered and may not have a long life span, operating with a slightly open dilution valve to
keep adequate flow through the blower is the best option.
6.3.5 REGULARLY EVALUATE NECESSITY OF VAPOR PHASE CARBON UNIT FOR THE
GROUNDWATER TREATMENT SYSTEM
An extraction rate of 48 gpm and an influent PCE concentration of 3,000 ug/L translates to a daily loading
of approximately 1.8 pounds of PCE per day that is stripped by the tray aerator. Because this loading and
the subsequent loading of the tray aerator offgas is less than 2 pounds per day, according to San Joaquin
21
-------
Valley Unified Air Pollution Control District Rule 2201, treatment of this offgas is not required. Thus, the
vapor phase carbon unit could be removed from the groundwater treatment system. The RSE team does
not recommend removing this carbon unit until a final remedy is selected and it is verified that the daily
loading will consistently remain below 2 pounds per day. Additionally, many sites do maintain vapor
treatment even when it is not required by permit to transfer contaminants to another media.
It should also be noted that the vapor phase carbon unit for the groundwater treatment system likely does
not require a preheater to improve its overall cost effectiveness. Although such a heater would improve the
efficiency, the associated costs savings in carbon replacement likely would fail to offset the capital costs of
installing the heater and the increase in costs for the electricity.
6.3.6 APPLY PROPER CONVERSIONS TO PCE CONCENTRATIONS DETERMINED BY PID
MEASUREMENTS
A MiniRae Plus Classic PID calibrated with isobutylene is used to determine PCE concentrations
associated with the air stripper offgas and extracted and treated soil vapor. Because isobutylene is used
for calibration, the readings on the PID should be properly adjusted for PCE concentrations. According to
the RAE Systems website readings from a PID calibrated with a 100 ppm
isobutylene standard should be multiplied by a factor of 0.59 to obtain PCE concentrations.
6.3.7 IMPROVE ACCURACY OF FLOW MEASUREMENT FOR SVE SYSTEM
The flow rate for the SVE system is inaccurate due to an incorrectly sized pitot tube. The pitot tube
originally installed into the 3-inch piping is meant for 2-inch piping. A properly sized pitot tube should be
installed. This could be accomplished for under $1,000.
6.3.8 ADJUST MEMBRANE SURROUNDING THE BAKER TANK
The membrane surrounding the Baker tank is compromised at the tank drain. The membrane should be
draped over the berm frame for the entire tank circumference.
6.3.9 IMPROVE DRAINAGE TO THE SECONDARY CONTAINMENT SUMP
The RSE team concurs with the operators recommendation to add better drainage to the secondary
containment sump.
6.3.10 ADD FANS FOR THE CONTROL PANEL
The RSE team concurs with the operators recommendation to add fans to the control panel to reduce
temperatures.
6.3.11 RELOCATE VAPOR PHASE GAC UNIT FOR GROUNDWATER TREATMENT SYSTEM
The RSE team concurs with the operators recommendation to relocate the vapor phase GAC unit for the
groundwater treatment system to the outside of the metal storage container in an attempt to provide more
room for maneuvering around the system.
22
-------
6.3.12 ADD AN ADDITIONAL PHONE LINE FOR DATA ACQUISITION
The RSE team concurs with the operators recommendation to add a phone line to allow concurrent phone
communication and data acquisition.
6.4 MODIFICATIONS INTENDED TO GAIN SITE CLOSE-OUT
6.4.1 PURSUE FINAL REMEDY SCREENING
The RSE team encourages the site managers to pursue a final remedy screening. This is important in
developing an exit strategy. The use of a groundwater flow model (Section 6.1.3) would be helpful in
determining what part of the concentrated plume would need to be captured to prevent substantial growth
of the plume. It is likely that portions of the plume above 100 ug/L would need to be contained. If
additional pumping is required for adequate capture, aspects of the groundwater treatment system may
require adjustment. For example, increased extraction rates will increase discharge costs paid to the
POTW thereby making alternate discharge locations (see Recommendation 6.2.1) more attractive.
The final remedy should also seriously consider the possibility of a continuing source of contamination in
the subsurface including PCE in the unsaturated soil and free product PCE below the water table.
Depending on results from the monitoring suggested in recommendation 6.1.1, the SVE system may require
expansion in order to fully address the PCE in the unsaturated zone. Remediating DNAPL, however, is
beyond the capability of the SVE and pump-and-treat systems. If continued operation of the current
remedy and monitoring suggest the presence of DNAPL, aggressive source removal strategies should be
weighed against a containment remedy. Due to the stratified geologic cross section, air sparging will likely
have a low likelihood of success and may even impact effectiveness by spreading PCE vapors through the
unsaturated zone beyond the influence of the SVE system. In addition, utilities and active businesses may
limit application of thermal or other in situ remedies. Dual phase extraction (reducing the water level
through pumping and extracting vapor from the same location) may be preferable if the source area beneath
the water table can be delineated and exposed by groundwater extraction.
In-well stripping may prove cost-effective for control of plume migration near the source area as VOCs
could be removed from the subsurface without the added requirements of carbon polishing or uranium
treatment via the ion exchange units. Consideration of this and other alternate technologies or strategies
should be considered, and a comparison of a containment remedy to aggressive source removal should
include analysis of life-cycle costs.
6.4.2 ADD DISSOLVED OXYGEN AND REDOX POTENTIAL TO THE SAMPLING PROGRAM
PCE is known to undergo reductive dechlorination in reduced environments, and measurements of
oxidation-reduction potential (ORP) and dissolved oxygen (DO) will help determine the potential for
reductive dechlorination. These measurements could easily be made during quarterly monitoring events for
one year with field test kits and reported for minimal additional costs (less than $1,000). If these ORP and
DO measurements indicate a potential for dechlorination of these compounds then measurement of
additional parameters such as sulfate, nitrate, and dissolved iron in future sampling events may be
beneficial. On the other hand, if the ORP and DO measurements indicate minimal potential for
23
-------
dechlorination then dispersion will be the only likely natural mechanism for reducing concentrations, and
such results should be included in final remedy screening for the site.
6.5 SUGGESTED APPROACH TO IMPLEMENTATION OF
RECOMMENDATIONS
Relocating the vacuum breaker (Recommendation 6.3.1) should occur immediately due to the possibility
for damage and injury. All other recommendations can be implemented immediately and concurrently as
there are few dependencies between the recommendations. Recommendation 6.2.1 (considering alternate
discharge locations), however, should only proceed with investigation and evaluation of potential alternate
discharge locations until further information is gathered about the remedy performance. As data is
gathered during a year of continuous operation a more informed decision about the final remedy and the
most appropriate discharge location can be made.
24
-------
7.0 SUMMARY
In general, the RSE team found a well-operated treatment system. 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, reduce future operations and
maintenance costs, improve technical operation, and gain site close out. The recommendations to enhance
effectiveness include monitoring the subsurface performance of the SVE system, analyzing the capture
zone, further delineating the plume, and delegating responsibility for evaluation of aquifer and process
monitoring. Recommendations to reduce costs include investigating alternate discharge options, eliminating
the equalization tank and the associated transfer pump, and regularly evaluating the necessity of the ion
exchange units and the groundwater treatment system vapor phase carbon unit. The RSE team identified a
number of possibilities for technical improvement such as relocation of a vacuum breaker to prevent
damage to the ion exchange units and replacement of the current filter system with bag filters that are easier
to maintain. In addition, the RSE team concurs with a number of optimization recommendations provided
by the operator. Finally, recommendations regarding site closure include proceeding with the final remedy
screening and sampling of parameters that would affect degradation of site-related compounds in the
subsurface. The table below itemizes all of the recommendations as well as the cost (or cost savings) and
reason for each one.
25
-------
Table 7-1. Cost Summary Table
Recommendation
6.1.1 Monitor subsurface
performance of SVE system
6.1.2 Assign Responsibility for
Evaluating Monitoring and
Performance Data
6.1.3 Analyze capture zone
6.1.4 Delineate plume (if
necessary)
6.2.1 Consider alternate discharge
locations
1. Discharge to storm sewer
or
2. Reinject to subsurface
6.2.2 Remove equalization tank,
simplify filtration system, and
remove transfer pump
6.2.3 Regularly evaluate need for
ion exchange units
6.3.1 Relocate vacuum breaker
6.3.2 Install valving for
backwashing carbon and ion
exchange units
6.3.3 Monitor extraction well
performance
6.3.4 Modify SVE system to
address high operating
temperatures
Reason
Effectiveness
Effectiveness
Effectiveness
Effectiveness
Cost
Reduction
Cost
Reduction
Cost
Reduction
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Estimated Change in
Capital
Costs
$18,000
$0
$30,000
$0
$20,000
or
$150,000
$10,000
$0
$2,000
$7,000
$0
$0
Annual
Costs
$20,000
$0
$10,000
$0
($20,500)
or
($31,000)
($6,000)
($20,000)
$0
$0
$2,000
$0
Lifecycle
Costs *
$118,000t
$0
$330,000
$0
($595,000)
or
($780,000)
($170,000)
($600,000)
$2,000
$7,000
$60,000
$0
Lifecycle
Costs **
$109,000t
$0
$191,000
$0
($310,000)
or
($350,000)
($87,000)
($322,000)
$2,000
$7,000
($32,000)
$0
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
f assumes only 5 years of operation rather than 30 years of operation
Note: Costs are "not quantified" for recommendations initiated and begun by operations contractor.
26
-------
Recommendation
6.3.5 Regularly evaluate need for
vapor phase carbon
6.3.6 Properly convert PID
readings to PCE concentrations
6.3.7 Improve accuracy of SVE
flow
6.3.8 Adjust membrane around
Baker tank
6.3.9 Improve drainage to
secondary sump
6. 3. 10 Add fans to the control panel
6.3.1 IRelocate vapor phase carbon
for the groundwater treatment
system
6.3.12 Add phone line for data
acquisition
6. 4.1 Initiate screening of final
remedy
6.4.2 Measure DO and ORP in
monitoring wells
Reason
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Technical
Improvement
Gain site
close-out
Gain site
close-out
Estimated Change in
Capital
Costs
$0
$0
<$1,000
$0
Not
quantified
Not
quantified
Not
quantified
Not
quantified
$0
<$1,000
Annual
Costs
$0
$0
$0
$0
Not
quantified
Not
quantified
Not
quantified
Not
quantified
$0
$0
Lifecycle
Costs *
$0
$0
<$1,000
$0
Not
quantified
Not
quantified
Not
quantified
Not
quantified
$0
$0
Lifecycle
Costs **
$0
$0
<$1,000
$0
Not
quantified
Not
quantified
Not
quantified
Not
quantified
$0
$0
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
f assumes only 5 years of operation rather than 30 years of operation
Note: Costs are "not quantified" for recommendations initiated and begun by operations contractor.
27
-------
FIGURES
-------
FIGURE 1-1. SITE LAYOUT SHOWING THE WELLS AND THE PCE PLUME AS DETERMINED BY THE NOVEMBER 2000
SAMPLING RESULTS.
*
ฎ
0.6
ซMW-15
* 0.2
-N-
MW-1 4
0.5
~Tป
ซ-
\
i
i
i
i
i
i
i
JO
/
/
A
/
/
/
;
/
/
/
i
;
/
/
/
/
^
/ GRISl,
-t __^
7
i
cc
r>
o
o
cr
UJ
LjJ
C3
f
s
^'''
\
\
^
^>
^
>
<
CO
3
CJ
Z3
O
O
/'
X
/
/
^^^
VOID
ฎ
L ^^^^ MW-1
ฎMW-2 1 ^
20 1 ELKS 1 ~~-.
H LODGE L
x*** T MW 5~H -^
''' T_ 53^?- -T-
-r ' ,
,'" ovLTS C ^-
bV-1 C --
/ MW-9^b4_EW-1 v
1 SV-2T \
i MW-8/ |\|71 MW-3
\ 3900 /T-1 ^00 [
\ REPAIR-/ .
\ SHOP
V- -WOO ->
MW-4
5/0
AVENUE
^''''
MW-6 X
^70 xx'"
x'x MW-10/^N --
vx /f7ฎ .-''
,x--' GROVE AVENUE _X^'
^ 1 K
/ xx''
^
X
X
X
X
X
X
X
X
1
0
/ "
a:
LU
LU
O
1 I
THE
PARTS
HOUSE
^AUTO
)EALERSH
-GOLDEN
STATE
AUTO^
EAST FAIRMONT AVENUE
J
^- HALFORD'S"~-X
-^ CLEANERS \
\
p !
i
,"7 /
/
X
X
X
\ X
X
/"HINTZE AVENUE SMV^712
,--'
X
HELEN AVENUE
LEGEND
ซ GROUNDWATER MONITORING WELL
O GROUNDWATER EXTRACTION WELL
T VAPOR EXTRACTION WELL
VADOSE ZONE MONITORING WELL
270 ROE CONCENTRATION (ug/L)
PCE CONCENTRATION ISOPLETH
(DASHED WHERE INFERRED)
FRANCIS AVENUE
0 200
^^-^-
400
SCALE IN FEET
(Figure compiled from Figure 3 of the Modesto Groundwater Contamination Site, November 2000 Monitoring Report,
Ecology and Environment, April 5, 2001).
-------
Solid Waste and
Emergency Response
(5102G)
542-R-02-0080
October 2002
vwwv.clu-in.org/rse
www.epa.gov/tio
U.S. EPA National Service Center
for Environmental Publications
P.O. Box 42419
Cincinnati, OH 45242-2419
------- |