SEMS-RM DOCID # 100034743
FOURTH FIVE-YEAR REVIEW REPORT FOR
MODESTO GROUNDWATER CONTAMINATION SUPERFUND SITE
STANISLAUS COUNTY, CALIFORNIA
£
<
00
O
\
ro
z
PRO^°
o
J
PREPARED BY
U.S. Army Corps of Engineers
Seattle District
FOR
U.S. Environmental Protection Agency
Region 9
MICHAEL
Digitally signed by
MICHAEL MONTGOMERY
Approvedby: MONTGOMERY0^202309'25 Date:
18:21:39-07'00'
Michael Montgomery. Director
Region 9 Superfund and Emergency Response Division
U.S. Environmental Protection Agency, Region 9
-------
Executive Summary
This is the fourth Five-Year Review of the Modesto Groundwater Contamination Superfund Site (Site)
located in Modesto, Stanislaus County, California. The purpose of this Five-Year Review is to review
information to determine if the remedy is and will continue to be protective of human health and the
environment.
Halford's Cleaners, a dry-cleaning facility that leaked tetrachloroethylene into the soil and groundwater,
is the source of contamination at the Site. The dry-cleaning facility discharged wastewater with
tetrachloroethylene into the sanitary sewer system for approximately fifty years, releasing an unknown
quantity of tetrachloroethylene.
In 1997, United States Environmental Protection Agency (EPA) selected an interim remedy to address
source control, which consisted of soil vapor and groundwater extraction and treatment to address
tetrachloroethylene in the subsurface. The interim remedy's objectives were to eliminate and contain the
highest contaminant levels at the source, to prevent exposure to contaminated groundwater, to minimize
impact of interim cleanup measures to the community, to collect data to determine if federal and state
requirements could be met throughout the aquifer, and to delineate more clearly the downgradient edges
of the plume.
On May 21, 2021, EPA issued the Final Record of Decision selecting a groundwater remedy and a soil
gas remedy for the Site. The final groundwater remedy does not require any changes to the operations of
the existing groundwater extraction and treatment system remedy. The final groundwater remedy also
includes groundwater monitoring and, if tetrachloroethylene levels at the monitoring wells nearest the
operating municipal supply wells approach or exceed the drinking water standard, then groundwater
contingency measures may be implemented, including stopping production (pumping) at a municipal
supply well, or the use of well-head treatment, such that the water produced at the municipal supply well
contaminant concentrations would be decreased below drinking water standards.
The final soil gas remedy includes enhancing the existing interim soil vapor extraction and treatment
system by adding directional wells to improve extraction of contaminant mass in areas that are not
reached with the current system, as well as upgrading monitors and controls for system performance and
remedy progress tracking. In addition to incorporating the sub-slab depressurization system located at an
adjacent building to Halford's Cleaners, this remedy also includes indoor air contingency measures if
indoor air concentrations exceed risk-based levels. Institutional controls (e.g., deed restrictions and/or
requirements for vapor barriers or sub-slab depressurization in new buildings) would be reserved for any
other areas where potential vapor intrusion is of concern.
EPA selected the following remedial action objectives for the Site in the 2021 Final Record of Decision:
• Prevent exposure to contaminated soil, soil gas, and groundwater, above acceptable risk levels;
-------
• Restore groundwater to its beneficial uses to the extent technically practicable within a
reasonable timeframe: reduce the tetrachloroethylene concentration to less than its federal
drinking water standard within 30 years;
• Reduce soil and soil gas contaminant levels in the source area to below the cleanup levels
established in the 2021 Record of Decision;
• Prevent migration of contaminants into groundwater at concentrations that would adversely affect
the beneficial use;
• Prevent exposure from direct contact to soil that contains contaminants above health-protective
levels under current and potential future land use (through institutional controls which will
maintain the current industrial land use at the Site);
• Prevent the release of volatile organic compounds from soil gas and groundwater into indoor air
at concentrations that exceed health-protective levels; and
• Mitigate long-term contaminant plume migration to prevent potential commingling with
contaminant plumes from other sources in the area.
The final remedy incorporated the interim remedy components: the existing groundwater extraction and
treatment system and the existing soil vapor extraction system. As such, the majority of the final remedy
has been implemented; the soil vapor extraction system enhancement design was approved by EPA on
March 1, 2023, and remedial action construction is in progress and anticipated to be completed in October
2023.
The groundwater remedy has significantly reduced tetrachlorethylene concentrations in the vicinity of the
groundwater extraction wells where concentrations were highest. The treatment system has removed over
750 pounds of tetrachloroethylene since operation began. The two existing groundwater extraction wells
are controlling groundwater in the source area and part of the dissolved plume area.
The soil vapor extraction system operated on a pulsed schedule (five months off, one month on) from
December 2017 until it was shut down in June 2020. The soil vapor extraction system was not restarted
until May 2021, at which time it was operated continuously until June 2023 when it was turned off to
implement the soil vapor extraction system enhancements. Soil gas concentrations beneath Halford's and
adjacent businesses increased while the soil vapor extraction system was shut down from June 2020 to
May 2021. In October 2022, the highest soil gas concentration, 121,000 (ig/m3, during the review period
was measured while the soil vapor extraction system was operating. Indoor air concentrations at Halford's
also increased during the extended period of time when soil vapor extraction system was shut-off and
exceeded indoor air cleanup levels in May and October 2021. There is no vapor mitigation system in
Halford's Cleaners. The sub-slab de pressurization system for the building adjacent to Halford's Cleaners
was repaired and turned on in April 2023.
The remedy is not functioning as intended by the decision documents. The soil vapor extraction system is
currently shut-off to install system improvements and connect horizontal soil vapor extraction wells.
When operating, the soil vapor extraction system reduces contaminants in soil gas but there have been
indoor air exceedances at Halford's Cleaners. The groundwater treatment system continues to control the
groundwater contamination source.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
-------
Exposure assumptions from the interim remedy and the final remedy are still valid.
The Modesto Superfund Site remedy is not protective of human health and the environment because
indoor air concentrations of tetrachloroethylene have exceeded risk-based levels over the past five years,
and there is no vapor intrusion mitigation at the Halford's Cleaners. The groundwater remedy continues to
operate and remove mass. Groundwater monitoring shows that the municipal wells are not impacted. The
City of Modesto ordinance prohibits wells installation within city limits. However, to ensure
protectiveness, EPA will develop a notification plan to allow rapid response by EPA if soil gas or indoor
air concentrations approach levels of concern and complete a Focused Feasibility Study to select a
permanent indoor air mitigation system.
-------
Executive Summary ii
List of Figures vi
List of Tables vii
List of Acronyms and Abbreviations vii
1. Introduction 1
1.1. Background 3
1.2. Physical Characteristics 3
1.3. Hydrology 6
2. Remedial Actions Summary 9
2.1. Basis for Taking Action 9
2.2. Remedy Selection 9
2.3. Remedy Implementation 11
2.3.1. Soil Vapor Extraction System 11
2.3.2. Groundwater Treatment System 12
2.3.3. Institutional Controls 12
2.4. System Operations/Operation and Maintenance 13
2.4.1. Operations and Maintenance Requirements 13
2.4.2. Significant Operations and Maintenance over the Past Five Years 13
3. Progress Since the Last Five-Year Review 14
3.1. Previous Five-Year Review Protectiveness Statement and Issues 14
3.2. Work Completed at the Site During this Five-Year Review Period 14
4. Five-Year Review Process 14
4.1. Community Notification, Involvement and Site Interviews 14
4.1.1. Five-Year Review Public Notice 14
4.1.2. Site Interviews 15
4.2. Data Review 15
4.2.1. Soil Vapor Extraction System 15
4.2.2. Soil Gas 16
4.2.3. IndoorAir 21
4.2.4. Groundwater 24
4.2.5. Sustainability 29
4.3. Site Inspection 29
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
v
-------
5. Technical Assessment 29
5.1. Question A: Is the remedy functioning as intended by the decision documents?.... 29
5.2. Question B: Are the exposure assumptions, Toxicity Data, Cleanup Levels, and
Remedial Action Objectives Used at the Time of Remedy Selection Still Valid? 30
5.3. Question C: Has Any Other Information Come to Light That Could Call Into Question
the Protectiveness of the Remedy? 30
6. Issues/Recommendations 31
6.1. Other Findings 32
7. Protectiveness Statement 32
8. Next Review 32
Appendix A: List of Documents Reviewed 33
Appendix B: Site Chronology 35
Appendix C: Data Review 37
Appendix D: Applicable or Relevant and Appropriate Requirements Assessment 40
Appendix E. Toxicity Assessment 42
Appendix F: Public Notice 43
Appendix G: Interview Forms 44
Appendix H: Site Inspection Report and Photos 48
List of Figures
Figure 1. Location Map 4
Figure 2. Detailed Map 5
Figure 3. Detailed Map of Modesto Commingled Groundwater PCE Plumes 7
Figure 4. North-South Geologic Cross-Section A-A' 8
Figure 5. Soil Vapor Wells Location Map 18
Figure 6. Soil Gas Results Over Time 19
Figure 7. Soil Vapor Sample Locations along Hintze Avenue 20
Figure 8. Indoor Air and Sub slab Vapor Analytical Results for PCE 23
Figure 9. Cumulative PCE Mass Removed by the Groundwater Treatment System 24
Figure 10. Extent of PCE in A-zone 26
Figure 11. Extent of Plume in B-zone 27
Figure 12. Extent of Plume in C-zone 28
-------
List of Tables
Table 1. Five-Year Review Summary Form 2
Table 2. Groundwater Cleanup Levels from 2021 ROD 11
Table 3. Indoor Air Cleanup Levels from 2021 ROD 11
Table 4. Soil Gas Vapor Intrusion Cleanup Levels from 2021 ROD 11
Table 5. Indoor Air and Sub-slab Results (2019 through 2023) 21
Table 6. Mann Kendall Trend Analysis of PCE in Source Area Groundwater 25
Table 8. Issues and Recommendations Identified in the Five-Year Review 31
Table 7. Protectiveness Statement 32
List of Acronyms and Abbreviations
l-tg/m3
micrograms per cubic meter
l-ig/L
micrograms per liter
%
Percent
AECOM
Contractor for the Department of Toxic Substance Control
DTSC
Department of Toxic Substance Control
EPA
United States Environmental Protection Agency
NDN Sundance
NDN Sundance Joint Venture, LLC, contractors for USACE
PCE
T etrachloroethylene
TCE
Trichloroethylene
ROD
Record of Decision
Site
Modesto Groundwater Contamination Superfund Site
USACE
United States Army Corps of Engineers
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
vii
-------
1. Introduction
The purpose of a Five-Year Review is to evaluate the implementation and performance of a remedy to
determine if the remedy will continue to be protective of human health and the environment. The
methods, findings, and conclusions of reviews are documented in Five-Year Review reports. In addition,
Five-Year Review reports identify issues found during the review, if any, and document
recommendations to address them.
The U.S. Environmental Protection Agency (EPA) is preparing this five-year review pursuant to the
Comprehensive Environmental Response, Compensation, and Liability Act Section 121, 40 Code of
Federal Regulation Section 300.430(f)(4)(h) of the National Contingency Plan and EPA policy.
This is the fourth Five-Year Review for the Modesto Groundwater Contamination Superfund Site (the
Site). The triggering action for this statutory review is the completion of the previous Five-Year Review.
The Five-Year Review has been prepared because hazardous substances, pollutants, or contaminants
remain at the site above levels that allow for unlimited use and unrestricted exposure.
The Site consists of two remedies: the groundwater remedy and soil gas remedy, both of which are
evaluated in this Five-Year Review.
The Modesto Groundwater Contamination Superfund Site Five-Year Review was led by Anhtu Nguyen,
EPA Region 9 Remedial Project Manager. Participants included Cynthia Wetmore, EPA Region 9
Superfund Five-Year Review Coordinator; Cynthia Ruelas, EPA Region 9 Superfund Five-Year Review
co-coordinator; and from the U.S. Army Corps of Engineers (USACE): Jake Williams, Project Manager;
Sara Benovic, Geologist; Justin McNabb, Geologist; Katie Richwine, Physical Scientist, and James
Stellmach, Environmental Engineer. The review began on December 15, 2022.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
1
-------
Table 1. Five-Year Review Summary Form
SITE IDENTIFICATION
Site Name: Modesto Groundwater Contamination Superfund Site
EPA ID: CA981997752
Region: 9
State: CA
City/County: Modesto, Stanislaus
National Priorities List Status: Final
Multiple Operable Units? Yes
Has the site achieved construction completion? No
Lead agency: EPA
Author name: Anhtu Nguyen, Remedial Project Manager
Author affiliation: EPA
Review period: 12/15/2022 - 7/7/2023
Date of site inspection: 3/8/2023
Type of review: Statutory
Review number: 4
Triggering action date: 9/24/2018
Due date (five years after triggering action date): 9/24/2023
-------
1.1. Background
Halford's Cleaners, a dry-cleaning facility that leaked tetrachloroethylene (PCE) into the soil and
groundwater located at 941 McHenry Ave, is the source of contamination at the Modesto Groundwater
Contamination Superfund Site (the Site; Figures 1 and 2). Halford's Cleaners also discharged wastewater
with PCE into the City of Modesto's sanitary sewer system for approximately fifty years, releasing an
unknown quantity of PCE.
In 1984, the City of Modesto discovered PCE in one of their municipal wells, Municipal Well 11, during
a routine monitoring event. PCE was subsequently found at relatively high concentrations in soil, soil gas,
and groundwater near Halford's Cleaners. In addition, the sanitary sewer line leading from Halford's
Cleaners contained PCE-contaminated sediment. EPA listed the Site on the National Priorities List in
1989.
The Site boundary is defined by the extent of groundwater contamination originating from Halford's
Cleaners. Along the southern boundary of the Site, contamination commingles with a plume originating
from another site associated with the Elwood's Dry Cleaners at 441 McHenry Ave (the responsibly party
for PCE contamination) that is being addressed under a different regulatory program in relation to a fuels
release cleanup (Figure 3).
1.2. Physic icierisiics
The Site is located at 941 McHenry Avenue in the City of Modesto, approximately 80 miles southeast of
Sacramento, California in Stanislaus County (Figure 1). The population of the City of Modesto is
approximately 220,968 people as of January 2023.
The Site still operates as a drycleaning facility and is in a commercial area, approximately 1.5 miles north
of downtown on McHenry Avenue, between West Fairmont Avenue and Griswold Avenue. Land use in
the Site vicinity ranges from commercial/light industrial to residential. Nearly all the land surface above
the contaminant source area is paved or covered by buildings.
The City of Modesto is on public municipal water supply as there are no known active, private, or
commercial wells for consumptive groundwater use. The City of Modesto well permitting process
currently prohibits well installation for consumptive use. The Site is not located in or near any
environmentally sensitive areas.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
3
-------
M
*
Modesto Groundwater
Superfund Site
. -a Detai Area
(See Insert)
¦IW *
A|S(IH)1R"5
I
rW
M.V-3D5 A
MW-30A
M
H.
MW-JC3A
||MA-WA
liiWM
|ma-G4C
MAM2A 0
MAM OA
MAM 08
MW-1DC
MA-;se 1
WA-llf
H MA-JO
MA-2CS
«AV-20<
MA-17A
MA-17B
MA-17C
K
H
MA-ISA
MA-168
MA-ISC
MkV-21A|
MACES *4
MW-22A|
•JA-338 ~
MA-3S8 ¦#"
*
-«( IMW
D ED
HMD * « 1
¦Ml*
Detail Area
LEGEND
^ Groundwater Extraction Well
~ Groundwater Monitoring Well
• Damaged Groundwater Monitoring Well
Figure 1-5
Groundwater Well Locations Map
Modesto Groundwater Superfund Site
Modesto, California
February 2018
Source: USAGE, Sacramento District, 2019. Final Feasibility Study Report for the Modesto Groundwater Superfund Site.
Figure 1. Location Map
-------
rr
Season's Lodge
L
\
Dry Wei \
-z-ficsraer&i =*Txixaon Mtal
\
DP-02
Existing
SVE T'eatment
System S VE-01i -s
H^hoST" cWsa"d'
SVE-03
SVE-04
DP-05
/SVE-02
- —
DP-01
-X/
J"OSVE-IOO OOSVE-11
~L_
Half old's
Cleaners
¦y Existing
\ Groundwater
Treatment
System
.=a5S»e at'/anz
The Paris House
of Modesto
DP-06
SV-01
MW-09B C S
MW-08AG
DP-03
EH
¦01
Concrete
Pad
rrn
V—aST-——,
\
JttJtar
Dry Well
Former UST
/Excavation (1909)
v
EW-01R
4 j*ija-aon«3 &rcr©«
;mw-03a
Private Property
• pP-04
fjl j
Hf-'I
T nTTs?
1 To
4 EW-02
Legend
¦ Groundwater Extraction Well
2 Groundwater Monitoring Well
J Soil Vapor Extraction Well
Soil Vapor Monitoring Well
• Abandoned Borehole
C Abandoned Monitoring Well
-5- Abandoned Production Well
Dry Well
Misc. Drain
Sanitary Sewer Manhole
—1— Fence
Existing Utilities
—am— GWTS Conveyance Piping
-35- Main Sanitary Sewer Line
—SVE System Piping
—3S7- Sanitary Sewer Line Trunk/Stub-out
Figure 1-4, SVE System and GroundwaterTreatment System Layout
Modesto Groundwater Superfund Site
Source: USACE, Sacramento District, 2019. Final Feasibility Study Report for the Modesto Groundwater Superfund Site.
Figure 2. Detailed Map
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
5
-------
Hydrology
The Site is underlain by interbedded sands, silty sands, sandy silts, and silts with occasional clay layers
typical of the San Joaquin Valley with limited vertical and lateral extents, which results in a highly
variable subsurface geology.
There are three aquifers beneath the site, which are labeled A, B, and C from shallowest to deepest. Low
permeability aquitards separate the aquifers. Groundwater elevations have generally declined since 2018
likely due to a combination of decreased precipitation and increased regional pumping.
The A-zone aquifer is a sandy layer extending from ground surface to approximately 95 to 100 feet below
ground surface. The A-zone aquifer is unconfined, with no hydraulic barrier between the groundwater and
ground surface. The average groundwater elevations declined from around 46 feet in 2018 to around 40
feet in 2023, with flow to the southeast. The aquitard separating the A and B aquifers is approximately 80
feet thick at the north end of the Site near the contaminant source and thins out to approximately 40 feet
thick near the south end of the Site.
The B-zone aquifer is approximately 15 to 40 feet thick, thickening to the south. The B-zone occurs
beneath the A/B aquitard to depths of 155 to 165 feet below ground surface and is semi-confined. The
average groundwater elevations declined from around 45 feet in 2018 to around 39 feet in 2023, with flow
to the southeast. The B/C aquitard is comprised of similar geologic strata to the A/B aquitard and
separates the B-zone and C-zone. It is generally thinner than the A/B aquitard, with a thickness varying
from 10 to 40 feet.
The C-zone aquifer extends from the bottom of the B/C aquitard to beyond the total depth monitored for
the Modesto Site. The investigated portion of the C-zone varies throughout the Site from 45 feet to 10 feet
or less. The average groundwater elevations declined from around 45 ft in 2018 to around 39 ft in 2023,
with flow to the south-southeast.
There are reportedly as many as 26 municipal wells within a one-mile radius of the Site that continue to
affect the Site's hydraulic gradient to varying degrees. Modesto Municipal Wells 06 and 07 are the closest
wells to the downgradient plume extent located southeast and southwest, respectively. Municipal Well 06
is 234 ft deep and draws water from the bottom of the B Zone and top of the C Zone. Municipal Well 07
is 260 ft deep and draws water from the A, B, and C Zones.
-------
¦*%+ir «4*«.ee
Hallord'a PI nine Zone A
Halford's Plume : Zone 8
Elwood's Plume • Zone A
Etwocxf'« Plum* Zona B
MWV-40B
Legend
<}} Monitoring Well - Halford's Plume Zone A
X Extraction Well • Halford's Plume Zone A
Existing Monitoring Wells - Halford's Plume ; Zone A
Monrtonng Well - Halford's Plume Zone B
~ Existing Monitcnng Well - Halford's Plume Zone 8
Monitoring Well - Elwood's Plume Zone B
• Existing Monitcnng Well - Elwood's Plume : Zone A
¦ Staging Area
Halford's Plume [4Q, 2015]
PCE In Groundwater
t00-999 pg/L
I 49-99 pg/L
I l 6-48
Elwood's Plume [2013]
PCE in Groundwater
HI 2000-4600 pg/L
¦B 1000-1999 pg/L
100-999 ps/L
J 50-99 pg/L
5-49 pg/L
I Zont deftrcaticm* d»nn«d by 3iiart*1«
•jtions i-n Monitoring.
R«?RE
Figure 1
Monitoring Wells
Halford's and Elwood's Phimes
Zone A and Zone B
Modesto, CA Superfund Site
011-40001-15
FEBRUARY 2017
Source: RORE. February I. 2017. Final Well Completion Report.
Figure 3. Detailed Map of Modesto Commingled Groundwater PCE Plumes
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
7
-------
GEOLOGIC CROSS SECTION A-A'
THIRD QUARTER 2017
MODESTO GROUNDWATER
SUPERFUND SITE
MODESTO, CALIFORNIA
210-
220-
230-
240-
Deptii
feet
bg®
SYMBOL
Sand, grave, wefl graded sand, poorly graded sand, wefl girased sand wrm sin.
we'l graded sand with day, poorty graded sand with silt poorly graded sand wttti clay.
sSly sand, clayey sand
Sandy si, sandy clay, sift, lean day. silt wtoi sand, aay vtfilt sand, clay with silt
slit with ciay
n
~
~
SHtfCJay
PCE In Groundwater 5-49 jjgrt. (Inferred}
PCE In Groundwater 50 - 99 pg/L (Inferred)
PCE In Groundwater 10D - 999 ygiI. (Inferred)
¥
U
Weil casing screen
Groundwater
Duplcate Result
« Less Ttian the Detection Limit
63 PCE Concentration < pg/L)
NS Not Sampled
[MW-U3A] Well Adjacent to Cross-Section
[1 tfl] pce Concentration Adjacent to Cross-Section (|jg/L)
Not contoured. Extraction well Screened in A and
Upper B Zones
Source: US ACE, Sacramento District, 2019. Final Feasibility Study Report for the Modesto Groundwater Superfund Site.
Figure 4. North-South Geologic Cross-Section A-A'
-------
2. Remedial Actions Summary
2.1. Basis for Taking Action
In 1984, the City of Modesto found PCE above federal and state drinking water standards in Municipal
Well 11. Halford's Cleaners is located approximately 1,000 feet southeast of Municipal Well 11.
Additional investigations were carried out to trace the source and in 1985, leakage of PCE was discovered
from a dry-cleaning machine within the building that housed Halford's Cleaners. PCE was also found at
relatively high concentrations in soil, soil gas, and groundwater near Halford's Cleaners. In addition, the
sanitary sewer line leading from Halford's Cleaners contained PCE-contaminated sediment. The primary
threat posed by the PCE was the ingestion of contaminated groundwater from the contaminated municipal
well.
2.2. lection
In September 1997, EPA issued an interim Record of Decision (ROD) that selected soil vapor and
groundwater extraction treatment as the interim remedial technologies to address PCE contamination in
soil and groundwater in the source area.
The groundwater remedy included groundwater extraction, groundwater treatment by air stripping with
carbon adsorption, and discharge of treated groundwater to the City of Modesto's Publicly Operated
Treatment Works sanitary sewer system. EPA deferred selection of chemical-specific cleanup standards
for groundwater in the interim ROD until a decision regarding final groundwater remedial action was
made for the Site. The soil gas remedy included soil vapor extraction followed by carbon adsorption.
EPA also selected engineering controls of signage and fencing around the treatment area as institutional
controls. These engineering controls were to be maintained for the duration of treatment.
On May 21, 2021, EPA signed the final ROD for the Site. The final soil gas remedy is to enhance the
existing soil vapor extraction system by adding directional soil vapor extraction wells to increase
extraction of contaminant mass in areas not influenced by the current system layout. It also includes
continued operation of a sub-slab depressurization unit already in place in the building adjacent to
Halford's Cleaners. Additional improvements planned for the soil vapor extraction system as part of the
final remedy include upgraded monitors and controls to assess system performance and remedy progress.
The selected groundwater remedy makes no changes to current groundwater remedy operations for the
existing groundwater treatment system. The treatment system shall continue to operate at 50 gallons per
minute. In addition to the two existing groundwater extraction wells, the treatment system consists of a
primary liquid-phase granulated-activated carbon filter which feeds two additional activated carbon
filters. Treated water is then discharged to the City of Modesto's sewer system. Due to the naturally-
occuring uranium concentrations in the groundwater treatment system influent, the treatment system
includes ion exchange units after the activated carbon vessels to meet permit discharge requirements.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
9
-------
EPA included several contingencies in the final groundwater remedy to address specific exposure
pathways and/or low contaminant concentrations outside the primary source area of the groundwater
plume. EPA included monitored natural attenuation/long-term monitoring in the final groundwater
remedy as a contingency for dispersed areas of contamination not captured by active remediation as well
as the use of well-head treatment if the dispersed PCE plume threatens to impact a municipal supply well.
The selected remedy also includes contingency measures if PCE concentrations exceed risk-based action
levels in indoor air. If PCE (or other chemicals of concern) exceed risk-based action levels in indoor air,
contingency measures will be implemented to mitigate the human health risks following a Focused
Feasibility Study to determine which measures to implement.
EPA incorporated existing and future land use covenants as part of the final selected remedy. Additional
environmental covenants that place restrictions on land use at the Halford's Cleaners source area, on land
use and water use within and near the known Halford's PCE plume area and possibly at the Hintze
Avenue 'hot spot1' will be specified and detailed, as part of the remedial design and remedial action
phases of work.
EPA outlined the following final remedial action objectives for the Site in the 2021 ROD:
• Prevent exposure to contaminated soil, soil gas, and groundwater, above acceptable risk levels;
• Restore groundwater to its beneficial uses to the extent technically practicable within a reasonable
timeframe: reduce the PCE concentration to less than its federal and state drinking water
standards within 30 years;
• Reduce soil and soil gas contaminant levels in the source area;
• Prevent migration of contaminants into groundwater at concentrations that would adversely affect
the beneficial uses of that resource;
• Prevent exposure from direct contact to soil that contains contaminants above health-protective
levels under current and potential future land use (through institutional controls which will
maintain the current industrial land use at the Site);
• Prevent the release of volatile organic compounds from soil gas and groundwater into indoor air
at concentrations that exceed health-protective levels; and
• Mitigate long-term contaminant plume migration to prevent potential commingling with
contaminant plumes from other sources in the area.
1 The remedy includes geotechnical sampling and soil gas sampling as part of the pre-design for the proposed soil
vapor extraction enhancements. This sampling will occur near the source area, as well as near a high concentration
'hot spot' along Griswold and Hintze Avenues. This sampling may indicate additional mitigation measures that may
be needed to address possible vapor intrusion. If so, the design will also include such measures.
-------
Chemical
Cleanup Levels (|i
-------
operations followed by five months of shutdown) in an attempt to improve efficiency of contaminant
extraction and treatment. In June 2020, the system shut down and remained off until May 2021 due to a
change in contractors. The system was then operated continuously from May 202lto June 2023 when it
was shut down to expand and upgrade the soil vapor extraction system by adding horizontal extraction
wells, increasing the size of the blower and automating controls.
EPA installed and began operating a sub-slab depressurization system beneath 939 McHenry Avenue, the
building adjacent to Halford's Cleaners in 2010. The sub-slab de-pressurization system was turned off in
2016 when the building became unoccupied. The sub-slab de-pressurization system was repaired and
restarted on April 26, 2023.
2.3.2. Groundwater Treatment System
EPA completed installation of the groundwater extraction and treatment system on June 12, 2000. The
installation included two ion exchange systems to treat the naturally-occurring uranium concentrations in
groundwater. The groundwater treatment system ran from late 2000 to November 2004 with only minor
downtime for maintenance. The system was not operational between November 2004 and June 2006
because the original extraction well (EW-01) had mechanical and well integrity issues. A replacement
well (EW-01R) was constructed and brought online in August 2006. A new extraction well (EW-02) was
installed in 2012 to better capture high concentrations of dissolved PCE in groundwater downgradient of
the source area. At that time, EW-01R was shut down but remained operable. On July 22, 2014, EW-01R
was restarted and ran at an equal extraction rate as EW-02. On August 29, 2017, the flow ratio changed to
20:80 (EW-01: EW-02) to increase mass removal rates. In August 2020, California Department of Toxic
Substance Control (DTSC) decommissioned the air stripper, with EPA concurrence.
2.3.3. Institutional Controls
A Land Use Covenant was placed on Halford's Cleaners property (APN 113-006-036) on April 30, 2015,
to prohibit using the Site as a residence, hospital, school, or children's daycare center. The covenant also
requires any soil and material removed from the Site to be managed by the DTSC-approved soil
management plan. In addition, drilling for water, oil, or gas; extraction for purposes other than
remediation; and any alteration of existing drainage patterns must have EPA approval. The covenant
requires non-interference with remediation, access for oversight and work, and annual inspections with
reporting by the Site owner.
Although not included as part of the remedy, a City of Modesto ordinance prohibits wells within the City
limits served by their public water supply system for purposes other than groundwater monitoring or
remedial treatment.
Institutional controls for groundwater and soils in the form of fencing and signs have also been installed
around the treatment system for the remedies.
-------
2,4, System Operations/Operation aintenance
2.4.1. Operations and Maintenance Requirements
EPA has used various contractors for technical assistance or directly, to operate, maintain, monitor, and
report on the progress of the remedial systems since their installation. NDN Sundance is the current
contractor for all Site remedial tasks, except operation of the groundwater extraction and treatment
system.
EPA transferred responsibility for operation of the groundwater extraction and treatment system to DTSC
in 2012. DTSC has contracted with AECOM for maintenance and monitoring of the groundwater
extraction and treatment system. EPA and DTSC are in the process of transferring responsibility for
groundwater plume monitoring to DTSC, which is anticipated to occur in early 2024.
The USACE initially contracted with RORE, Inc. to perform operation and maintenance on the soil vapor
extraction system, and to collect quarterly sampling. The quarterly sampling program includes Site
sampling (groundwater, indoor air and soil vapor) and system sampling. RORE, Inc.'s contract expired in
June 20202. The USACE subsequently contracted with NDN Sundance, in February 2021, to assume the
operation, maintenance and sampling responsibilities. Sampling of the groundwater monitoring wells, soil
vapor monitoring wells, indoor air and soil vapor extraction system was conducted under the approved
Sampling and Analysis Plan for Long-Term Monitoring, Site Investigation, and Soil Vapor Extraction.
AECOM has prepared quarterly reports for operations and maintenance of the groundwater treatment
system. AECOM performs weekly Site visits for maintenance and compliance sampling of the
groundwater treatment system, including monthly and quarterly compliance monitoring samples from the
system influent and effluent as the system is operating.
2.4.2. Significant Operations and Maintenance over the Past Five Years
On April 29, 2022, NDN Sundance used a high-performance epoxy coating to seal cracks and
penetrations within the building adjacent to the Site, located at 939 McHenry Avenue, to prevent or limit
soil vapor intrusion into the building.
On December 31, 2018, the uranium effluent concentration from the groundwater treatment system
exceeded the City of Modesto's discharge requirement of 20 pCi/L. AECOM shut down the system and
notified the City of Modesto. AECOM conducted an evaluation of the resin performance in the ion
exchange unit through the end of 2019. During this time, AECOM would restart the system after making
system changes, but continued to have periodic exceedances. In January 2020, after changing the type of
resin, effluent concentrations were reduced to below the City of Modesto's discharge requirements.
2 The date was provided in USACE's Site Interview (Appendix G) and could not be independently verified. USACE recollection
is that RORE Inc. shutdown the soil vapor extraction system when contract ended. No sampling was conducted between June
2020 and May 2021.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
13
-------
3. Progress Since the Last Five-Year Review
3.1. Previa ¦. mw Protectiveness Statement and Issues
The protectiveness statement from the 2018 Five-Year Review for the Modesto Groundwater
Contamination Superfund Site stated the following:
The interim remedy at the Modesto Groundwater Superfund Site is protective of human health
and the environment. Soil vapor extraction and sub-slab vapor intrusion mitigation have reduced
indoor air PCE concentrations to be within acceptable levels within the source area, and there
are no complete receptor pathways for ingestion of impacted Site groundwater within the source
area.
The 2018 Five-Year Review did not include any issues or recommendations.
Work Complett ', | th iew Period
EPA completed the final Feasibility Study for the Site in May 2019 and signed the final ROD in May
2021, which includes enhancements to the soil gas remedy. The enhancements include adding improved
controls and real-time monitoring capabilities as well as adding two horizontal directional wells to
improve the ability to extract more contaminants. The soil vapor extraction system enhancement design
was approved by EPA on March 1, 2023. Construction of the enhancements began in March 2023 and is
anticipated to be completed by October 2023. The groundwater remedy continues with the same pump
and treat system along with monitored natural attenuation and other contingencies specific exposure
pathways as described in Section 2.2.
NDN Sundance completed the Final Soil and Soil Vapor Investigation for remedial action support in June
2022. The investigation included two investigations for soil vapor: 1) to better define potential soil vapor
well installation options (and placement of vertical and/or horizontal soil vapor extraction wells), and
potential installation of pneumatic fracturing wells and/or locations, and 2) to investigate a high
concentration 'hot spot' along Griswold and Hintze Avenues. This sampling indicated additional
mitigation measures that may be needed to address possible vapor intrusion. A comprehensive lithology
of the vadose zone was confirmed with cone penetrometer tests which correlated well with the
geotechnical soil samples by showing a wide variation in the vertical soil strata. The results from the hot-
spot investigation are discussed in Section 4.2.2.
4. Five-Year Review Process
4.1. ity Notification, Jverm >ite Interviews
4.1.1. Five-Year Review Public Notice
EPA published a public notice in the Mercury-Register, on Wednesday, January 18, 2023, stating that
there was a Five-Year Review and inviting the public to submit any comments to EPA. No public
-------
comments were received. The results of the review and the report will be made available on-line at
http://www.epa.gov/superfund/modesto and at the Superfund Records Center, 75 Hawthorne Street,
Room 3100, San Francisco, California, 94105.
4.1.2. Site Interviews
As part of the Five-Year Review process, EPA sent written interview questions to document any
perceived problems or successes with the remedy that has been implemented to date. James Stellmach, an
environmental engineer from USACE Sacramento District, and McKinley Lewis, Project Manager from
DTSC, provided responses. The results of these interviews are summarized below.
James Stellmach stated that the project is a success but with a few caveats. In his opinion, the interim
remedy did not entirely meet its goal to significantly control the source of the groundwater contamination
and the soil vapor extraction system was not able to fully alleviate the indoor air risk at the Site. The soil
vapor extraction remedy is being enhanced to include two additional horizontal soil vapor extraction wells
to address contaminant mass that has not been removed via the current system's four vertical soil vapor
extraction wells.
McKinley Lewis stated that the overall impression of the project is positive as the remediation systems
were found to be in good working condition during the Site inspection. Construction crews were observed
on-Site implementing repairs and enhancements to the soil vapor extraction system as detailed in the 2021
Final ROD. The remedy is functioning as expected per the 1997 Interim ROD and enhancements to the
soil vapor extraction system are on-schedule for implementation. DTSC reports that there is an ongoing
presence of operations and maintenance at the Site with one significant change as the air stripper
associated with the groundwater treatment system was decommissioned to optimize the system in August
2020, with EPA concurrence. In addition, many groundwater monitoring wells were recently repaired to
prepare for the transfer of groundwater plume sampling duties between EPA and DTSC. The initial
timeline for transferring the system was by the end of 2024. However, due to excellent relations and
collaboration, the timeline for transfer is now ahead of schedule and will likely take place by the end of
2023.
4. '101/1/
4.2.1. Soil Vapor Extraction System
As noted above, the soil vapor extraction system was operated in pulsed mode from December 2017 to
June 2020, when the system was turned off due to transitioning to a different contractor for treatment
system operations and support. In June 2021, after the new Contractor, NDN Sundance, restarted the soil
vapor extraction system, it operated continuously until recently when the system was shut down for
upgrades called for in the 2021 ROD. NDN Sundance is expected to restart the system in October 2023.
During operations, samples are collected in the influent, mid-GAC and effluent on a monthly basis. The
soil vapor extraction system is monitored in compliance with a discharge limit of 20 (ig/m3.
There have been several instances where the effluent PCE concentrations exceeded the discharge limits:
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
15
-------
• In March 2019 and June 2019, PCE effluent concentrations were 1,700 (ig/m3 and 200 (ig/m3,
respectively. The granulated activated carbon was replaced after June and during the next
sampling event the effluent result was non-detect.
• In May 2021, the PCE effluent concentration was 139 (ig/m3. Subsequent effluent concentrations
were non-detect for the remainder of 2021 and either non-detect or below discharge limits for all
of2022.
• In February and March 2023, PCE effluent concentrations were 22.7 (ig/m3 and 28.5 (ig/m3
respectively; however, the SVE system influent concentrations for both of those months were
below detection limits. The granulated activated carbon was replaced. As part of the replacement
process, a sample of the carbon was collected and sent it off for analysis for disposal
characterization purposes. The carbon came back as non-detect.
4.2.2. Soil Gas
Samples are collected from three soil vapor extraction wells (SVE-02, SVE-03 and SVE-04), three
additional dual-point (shallow and deep) soil vapor monitoring wells ((DP-01, DP-05, and DP-06), and
two soil vapor monitoring wells located in Halford's Cleaners (941 McHenry Avenue, OSVE-10 and
OSVE-11). While the soil vapor extraction system was operated in pulse mode (December 2017 to June
2020), soil gas samples were mostly below the soil vapor cleanup level of 670 (ig/m3 for PCE with the
exception of samples from DP-01S and DP-01D in the second quarter 2019 sampling event, at 1,000
(ig/m3 and 1,200 (ig/m3, respectively. Concentrations of PCE increased in the soil gas during the period of
non-operation (June 2020 to May 2021) and peaked in May 2021 at 11,200 (ig/m3 at DP-05 S. During the
2022 sampling, while the soil vapor extraction system operated continuously, there were limited
exceedances in the soil vapor monitoring well. Those exceedances were in DP-03S and DP-03D in the
third and fourth quarter and were a result of a change in the soil gas extraction system operations when
the flowrate from extraction well SVE-01 was decreased in April 2022.
Two of the soil gas wells sampled on a quarterly basis, OSVE-10 and OSVE-11, are located underneath
the Halford's building and both are screened at a shallow depth (approximately 5 feet below ground
surface). They are located in the western portion of the 941 McHenry Building in the area of the historical
PCE leak. PCE concentrations in these wells have increased and exceeded cleanup goals in response to
the extended shut down of the soil vapor extraction system (Figure 6). PCE concentrations in well OSVE-
10 unexpectedly spiked in October 2022 (121,000 (.ig/ni3). even though the soil vapor treatment system
was in operation, but have subsequently decreased, and as of July 2023, the soil gas concentration is
2,010 (ig/m3. PCE concentrations recently increased in OSVE-11 in July 2023 to a high for this well of
10,900 (ig/m3.
NDN Sundance completed an additional soil vapor investigation in 2022 as part of the investigation of the
Hintz Avenue hot-spot. The purpose of the investigation was to measure soil gas along Hintze Avenue
and Griswold Avenue, at an area of formerly high concentrations of PCE in groundwater. NDN Sundance
collected 16 samples from eight temporary soil vapor monitoring wells from both shallow (2 to 7 feet
below ground surface) and deep (34 to 44 feet below ground surface) intervals to evaluate current volatile
organic compound concentrations when the soil vapor extraction system was not in operation (Figure 6).
PCE concentrations exceeded the selected in-field PCE screening level of 603 (ig/m3 in two out of the
-------
eight deep soil vapor samples from soil vapor monitoring wells DP-08B (along Griswold Avenue) and
DP-09B (along Hintze Avenue) with PCE concentrations of 650 (ig/m3 and 2,240 (ig/m3, respectively. All
other PCE sample results were below 100 (ig/m3. The soil vapor monitoring results indicated that there
are soil vapor impacts from volatilization of the groundwater plume in the area near Hintze Avenue. The
impacts were limited to the deeper vadose zone just above the water table and are not currently impacting
any potential surface receptors.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
17
-------
N
15 30
Season's
LEGEND
~ Sub-Slab Sample
m Approximate Soil Vapor
Monitoring Well Location
~ Sal Vapor Monitoring Well
O Soil Vapor Extraction Well
—H- Fence
Soil Vapor Extraction System
Piping
Avenue
I I Buildings
Notes:
pg/m3
micrograms per cubic meter
500 lig/irrt Concentrations
PCE Concentration greater
670 pg/m3 PSL of 670 M0/m3
TCE Concentration greater
290 P0/m3 psL of 290 w/rn3
DP-02A
PCE: 111 |ig/m3
TCE: 0.422 J pg'm3
c-DCE: ND
DP-02B
PCE: 16.4 pg>'m3
TCE: ND
c-DCE: ND
DP-01A
PC E:-127- pgi'm3
TCE: ND
c-DCE: ND
DP-01 B
PCE: 529 pg.m3
TCE: ND
c-DCE: ND
SVE-01
PCE: 107 M9'm3
TCE: 0.997 J pg/m3
c-DCE: ND
SVE-03
PCE: 71.3ng,lm3
TCE: 0.325 pg/m3
- c-DCE: ND
SVE-04
PCE: 148 pg/m3
TCE: 0.407 |jgi'm3
c-DCE: ND
¦" -
DP-05A
PCE: 6.99 |jg/m3
TCE: ND
c-DCE: ND
DP-05B
PCE: 46.4 pg.im3
TCE: ND
c-DCE: ND
SVE-02
PCE: 1,200 figi'm3
TCE: 1.86 |ig/m3_
c-DCE
ND
NS
PCE
PSL
TCE
ds-1,2-Dichloroethe-ne
The anatyte was positively
identified; Hie quantitation is
estimated.
Not Detected
Not Sampled
Tetradi loroethene
Project Screening Level
Tri chioro ethylene
OSVE-10
PCE: 4,640 ngmS
TCE: 6.32 pgi'm3
c-DCE: 4.84 pg/m3
;-DCE: 0.468 J pg.'m3
a OSVE-11
f PCE: 365 pgi'm3
TCE: 0.841 pg'm3
c-DCE: ND ^
OSC-3
PCE: 16.90 pgi'm3
TCE:~6.05 pg'm3
if c-DCE: ND
941 McHenry Ave.
(Halford's Cleaners)
939-SS-02
_PCE: 4.42 pg.'ms 939 McHenry Ave.
TCE: 1.46 Mg/m3 '
c-dce: nd (Vacant)
941-SS-01
PC E: 7.60 pg/m3
TCE: 5.68 pgi'm3
c-DCE: ND
939-SS-01
PCE: 50.9 pg.'mS
TCE: 1.52 J pg.'m3
DCE: ND
I
DP-03A
PCE: 1,410 MQ-'rrl3
TCE: ND
c-DCE: ND
DP-03B
PCE: 1.260 M9'm3
TCE: 13.70 pg/m3
c-DCE: ND
931 McHenry Ave.
(Transmatic Transmission)
dp-06a
PCE: 128 M9''m3
TCE: 0^970 fjg,'m3
c-DCE: ND
DP-06B'
PCE: 620 |jgi'm3
TCE: 0.477 pg/m3
c-DCE: ND
-------
OSVE-IO and OSVE-11 PCE Concentrations
125000
100000
75000
o 50000
iij
u
a
25000
•OSVE-IO
~OSVE-11
4400
!.6
a^O-78.812 26ElJ^j|^
-------
iPCE- 38.2 M0/m3
•TCE- C.492 J pg/m3
DP-07 A
iPCE-^Mpg/ml
TCE-.ND '
DP-09 A
PCE- 57.6
TCE- ND
DP-09 B
[IpEpK
TCE- 4.2
D%W{B
¦ PCE?41.3 pg/m3
TCE- 0.437 J [Jg/m3
DP-14 B
PCE- ND
TCE- ND
PCE- 76.7 |jg/m3
¦ICE- ND
DP-08 B]
'PCE- 65(
TCE- M
State Of California
Location
Stanislaus County
Dual Point Soil Vapor Sampling
Location
" •*1
Sample ID = DP-15-dd/mm/yy-depth
I- Pvv
t T •¦ ¦ ¦ -
Acronyms and Notes:
pg/m3- micrograms per cubic meter
CHHSL- California Human Health Screening Levels [
J- The analyte was positively identified;
the quantitation is estimated
ND- not detected
PCE- tetrachloroethene
TCE- Tnchloroethene
Results in RED exceed the CHHSL
PCE= 603 M&'m3
TCE= 1.770 pg m3
Imagery Esri, 2016
Modesto Superfund Site
Modesto. California
Contract Number: W912PP-21-C-0007
Dual Point Soil Vapor Monitoring Well
Installation and Soil Vapor Sample
Locations
Figure 4
Figure 7. Soil Vapor Sample Locations along Hintze Avenue
-------
4.2.3.
Indoor Air
When the soil vapor extraction and treatment system was operated prior to June 2020, indoor air and sub-
slab concentrations were below the 2021 ROD indoor air cleanup levels. However, after the system shut
down, no indoor air samples were collected for nearly a year during which PCE and TCE concentrations
increased. When indoor air sampling resumed in May 2021, the indoor air concentrations exceeded indoor
air cleanup levels due to soil vapor extraction system being off. All indoor air sample exceedances in this
review period occurred at Halford's Cleaners in 2021.
The remedial action objective is to prevent the release of volatile organic compounds from soil gas and
groundwater into indoor air at concentrations that exceed health-protective levels.
The sub-slab depressurization system located at 939 McHenry Avenue was recently re-started in April
2023. There is no vapor mitigation system at 941 McHenry Avenue
Table 5. Indoor Air and Sub-slab Results (2019 through 2023)
Sample
Location
Sample Date
PCE Oig/m3)
TCE Oig/m3)
PCE Oig/m3)
TCE Oig/m3)
Indoor Air
Sub-slab
2021 ROD Standard
20
30
670
290
DTSC Indoor Risk Level3
2
3
931-IA-01
3/14/2019
0.26
0.27
931-SS-01
0.27
200
(Parts Store)
2/24/2020
ND
-
20
-
4/27/2020
0.037
0.034 U
5.7
30
5/14/2021
NS
NS
-
-
7/8/2021
ND
ND
-
-
10/13/2021
0.105
ND
-
-
1/14/2022
ND
102
NS
NS
4/28/2022
ND
0.0802
NS
NS
8/2/2022
ND
ND
NS
NS
12/19/2022
0.239 J
0.294
NS
NS
1/25/2023
0.318.T
ND
50.9
1.52 J
4/21/2023 11
0.0678
0.102
145
6.43
7/19/2023 11
0.093
0.44.T
939-IA-01
3/14/2019
0.34
0.31
939-SS-01
ND
30
(Vacant
2/24/2020
5.4
-
(Vacant
9
-
Building)
4/27/2020
NS
NS
Building)
NS
NS
5/14/2021
0.706
0.943
3,330
6.43
7/8/2021
ND
0.48
1,900
6.20
10/13/2021
0.554
0.323
284
3.28
1/14/2022
0.314
3.49
19.1
1.31
4/28/2022
ND
ND
34.2
0.385
8/2/2022
0.233 J
0.294
1279
6.48
3 DTSC's Human and Ecological Risk Office developed modified screening levels (Human Health Risk
Assessment Note Number 3) based on US EPA's Regional Screening Levels for use in the human health
risk assessment process and potentially for developing risk-based cleanup standards. As shown, for PCE
and TCE, indoor air screening level concentrations (corresponding to 1 x 10"6 excess lifetime cancer risk)
are 10 times lower than 2021 ROD standards. For TCE, the DTSC screening level shown is equal to US
EPA's Regional Screening Level. These values are being provided for comparison purposes.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
21
-------
Sample
Location
Sample Date
PCE (ji${/m3)
TCE (jig/m3)
PCE (jijj/m3)
TCE (jijj/m3)
Indoor Air
Sub-slab
2021 ROD Standard
20
30
670
290
DTSC Indoor Risk Level3
2
3
12/19/2022
0.262 J
1.06
373
3.02
1/25/2023
0.828
2.25
NS
-
4/21/2023 17
0.141 J
0.352
-
-
7/19/2023 17
0.297
0.37
930
12
939-IA-03
(Vacant
Building)
3/14/2019
0.36
0.32
939-SS-02
ND
ND
2/24/2020
5.4
-
ND
-
4/27/2020
NS
NS
ND
-
5/14/2021
0.625
2 IS
4,760
3.9
7/8/2021
ND
0.39
280
11
10/13/2021
0.379
0.333
6.19
1.6
1/14/2022
0.227
0.938
ND
0.659
4/28/2022
ND
0.0147
ND
0.102
8/2/2022
NS
NS
NS
NS
12/19/2022
0.273 J
1.16
NS
NS
1/25/2023
0.869
2.13
4.42
1.46
4/21/2023 17
0.113 J
0.298
3.63
5.39
7/19/2023 17
ND
0.356 J
51.5
1.83
941-IA-01
(Halford's
Cleaners)
3/14/2019
6.1
6.1
941-SS-01
(Halford's
Cleaners)
10
ND
2/24/2020
19
0.31
20
-
4/27/2020
2.9
0.22
0.77
-
5/14/2021
2S.I
12.8
4,160
8.3
7/8/2021
5.30
17.0
220
ND
10/13/2021
24.3
11.0
16.4
18.1
1/14/2022
1.43
5.68
19.5
8.68
4/28/2022
0.413
1.35
3.49
1.360
8/2/2022
14
11.6
449
8.63
12/19/2022
2.48
8.68
9.51
8.36
1/25/2023
1.47
7.7
16.9
6.05
4/21/2023 17
2.25
12.4
18.1
5.1
7/19/2023 17
10.5
13.1 J
352
21.3
941-IA-02
(Halford's
Cleaners)
3/14/2019
4.2
4
941-SS-03
(Halford's
Cleaners)
-
-
2/24/2020
7.7
-
-
-
4/27/2020
2.8
0.21
-
-
5/14/2021
12.0
7.50
NS
NS
7/8/2021
3.20
12.0
NS
NS
10/13/2021
2S.3
8.52
NS
NS
1/14/2022
2.29
4.82
NS
NS
4/28/2022
1.10
1.00
0.955
0.447
8/2/2022
11.5
1.0
NS
NS
12/19/2022
2.24
18.3
NS
NS
1/25/2023
1.15
6.43
NS
NS
4/21/2023 1
1.31
9.91
-
-
7/19/2023 1
12.5
11.1
-
-
1 Preliminary Data
Bold - sample result exceedances the DTSC HERO risk screening level for commercial indoor air)
Grey Highlighted - exceeds 2021 ROD cleanup values.
J - The report result is an estimate. The value is less than the minimum calibration level but greater than the estimated detection
limit. NS - not sampled; ROD - Record of Decision; ND - The analyte was not detected in the sample at the estimated detection
limit.
-------
15 30
—I I
Season's
DP-02A
PCE: 111 |ig/m3
TCE: 0.422 J yg/m3
c-DCE: ND
DP-02B
PCE: 16.4 M9'm3
TCE: ND
c-DCE: ND
LEGEND
~ Sub-Slab Sample
. Approximate Soil Vapor
Monitoring Well Location
~ Soil Vapor Monitoring Well
3 Soil Vapor Extraction Well
—H- Fence
Soil Vapor Extraction System
Piping
Avenue
I I Buildings
Notes:
pg/m3 micrograms per cubic meter
500 iig/m3 Concentrations
PCE Concentration greater
670 pg/m3 ^e PSL of 670
TCE Concentration greater
290 yg/m3 ^3n ^ PSL of 2go pg,'m3
C-DCE cis-1,2-Dichloroethene
The analyte was positively
J identified; the quantitation is
estimated.
Groundwater
Treatment
System
"frailer
~
SV-01
DP-01A
PCE>127-ng''m3
TCE: ND
c-DCE: ND
DP-01 B
PCE: 529 |jg.'m3
TCE: ND
c-DCE: ND
--.---3--'
SVE-01
PCE: 107 fjgi'm3
TCE: 0.997 J pg/nr
c-DCE: ND
SVE-03
PCE: 71.3Mg.m3
TCE: 0.325 Hg/m3
-c-DCE: ND
.
SVE-04
PCE: 148 pg/m3
TCE: 0.407 Mg>'m3
c-DCE: ND
~
DP-05A
PCE: 6.99 ygi'm3
TCE: ND
c-DCE: ND
DP-05B
PCE: 46.4 jjg m3
TCE: ND
c-DCE: ND
SVE-02
PCE: 1,200 MgVm3
TCE: 1.86 pg/m3_
ND
NS
PCE
PSL
TCE
Not Detected
Not Sampled
Tetrach loroethene
Project Screening Level
Trichl oro ethylene
OSVE-10
PCE: 4.640 |jg'm3
TCE: 6.32 pg/mS
c-DCE: 4.84.Mg|,'T>3
c-DCE: 0.468 J pg/m3
* OSVE-11
? PCE: 365 Mgi'm3
TCE: 0.841 |ig.'m3
c-DCE: ND
941 McHenry Ave
(Halford's Cleaners)
939-SS-02
_PCE: 4.42 pg/m3 gjg MCf-fenry /[ VQ.
TCE: 1.46 |jg'm3
c-DCE: ND (Vacant)
OSC-3
PCE: 16.90 pgi'm3
TCEf6.05 Mg,jm3
if c-DCE: ND'
~
94I-SS-01
PCE: 7.60 pg/m3
TCE: 5.68 pgi'm3
c-DCE: ND
939-SS-01
PCE: 50.9 {J9'm3
TCE: 1.52 J pg/m3
c-DCE: ND
DP-06A
PCE: 128 [jgi'm3
TCE: 0.970 (jg'm3
c-DCE: ND
DP-06B
PCE: 620 Mg>'m3
TCE: 0.'477 pg.'m3
c-DCE
DP-03A
PCE: 1,410 Mg.'m3
TCE: ND
c-DCE: ND
DP-03B
PCE: 1,260 pg.'m3
TCE: 13.70 pg/m3
c-DCE: ND
931 McHenry Ave.
(Transmatic Transmission)
DP-04B
NS
ND
QJ
3
C
§
b
e
CD
cj
Figure 4
Soil Vapor Well and Sub-Slab Analytical
Results for PCE:
First Quarter 2023
Modesto Groundwater Superfund Site
Modesto. California
Project Number: W12PP-21-C-Q007
May 2023
Source: NDN Sundance Joint Venture, LLC 2022. 2023 First Quarter Operation, Maintenance, and Monitoring Report for Soil Vapor Extraction System, Soil Vapor, and Groundwater.
Figure 8. Indoor Air and Sub slab Vapor Analytical Results for PCE.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
23
-------
4.2.4. Groundwater
The groundwater treatment system has operated as intended. Concentrations of PCE in the effluent have
been below discharge requirements of 0.5 (ig/L. As of June 2023, the system has treated approximately
416 million gallons of water and removed more than 757.9 pounds of PCE.
d
1
c
2
*
3000
2500
2000
1500
1000
f**v
r1
'V"> » V.n.ii'1
0 o o o o o
1 j 1 3 1 2
«i0iocp Q -» O ->
i -k i ± 4
> EW-01 Shutdown and Replaced by EW-01R
Shutdown EW-1R and Startup EW-2
* Operation of both EW-1R and EW-2
—~—1.03 « EW-01 Shutdown and Replaced by EW-01 R • • Shutdown EW-1 R and Startup EW-2 ........ Operation of both EW-1 R and EW-2
Source: AECOM, 2023, Quarterly Operations And Monitoring Report Groundwater Treatment System Second Quarter 2023
Figure 9. Cumulative PCE Mass Removed by the Groundwater Treatment System
USACE evaluated mass removal at the source component of the remedy by completing the Mann Kendall
trend analysis of key monitoring wells. The Mann Kendall trends from the current review period and PCE
concentrations from October 2022 were also compared to the trend analysis completed for the 2018 Five-
Year Review and the November 2016 PCE concentration to assess mass removal. In general, the PCE
concentration trends in key monitoring wells have been either stable or decreasing over the past five years
with no change from the prior trend analysis, indicating mass removal is continuing to occur.
The PCE concentration trend over the past five years is for MW-5A labelled 'no trend", which means the
data have no consistent pattern. The 2018 Five-Year PCE concentration trend at MW-5A was stable and
no significant change in PCE concentration has occurred between November 2016 and October 2022,
However, MW-5A is located approximately 200 feet upgradient of Halford's between soil gas wells DP-
-------
01 and OSVE-10 where soil gas concentrations have increased. Based on the proximity of well MW-5A
to the area of elevated soil gas concentrations and the inconsistent PCE concentration trends during the
current review period, the groundwater in the MW-5A area may have been influenced by the on-/off-
operation of the soil vapor extraction system.
USACE also completed Mann Kendall trend analysis for the extraction wells, but extraction well
concentration trends are influenced by changes in pumping rates, radius of influence, and other changes in
system operation, which make them unsuitable for measuring remedy progress.
Table S. Mann Kendall Trend Analysis of PCE in Source
Well II)
December 2012-
\o\ ember 20 Hi Trend
Result
(Pre\ ions l-"i\c-Yc;ir
Rc\ic\\ Period)
P( T. (onccnlmlion
\o\ ember 20l(»
(fiji/l.)
October 201"- 2022
Trend Rcsull
(( iiiTcnl l"i\c-Yc;ir
Rc\ ic\\ Period)
PC T. C oncciilmlion
October 2022
(iiii/l.l
EW-01R
Increasing
18
Decreasing
3.3
EW-02
Decreasing
61
No Trend
91.1
MW-03A
Stable
140
Stable
129
MW-05A
Stable
24
No Trend
19.6
MW-08A
Decreasing
12
Decreasing
6.5
MW-10A
Decreasing
12
Decreasing
11.4
MW-20A
Decreasing
110
Decreasing
41.6
There are several municipal supply wells in the Site vicinity; however, not all of the supply wells are
operational and the supply wells that are operational are not located within the groundwater contaminant
plume. The three closest operating supply wells, Municipal Wells -06, -07, and -12, are located within
3,000 feet of the Site and are pumped as needed to supply water to the City of Modesto (see red circles in
Figure 11). Sentinel wells located within 300-400 feet of the municipal wells are sampled to detect
increases in contaminants prior to reaching the supply wells. In addition, the City of Modesto regularly
tests the drinking water and no detections above the drinking standard occurred during the review period.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
25
-------
Legend
Groundwater Extraction Well
Groundwater Monitoring Wed
t- Municipal Drinking Water Well
Approximate PCE Concentration "A" Zone (2022)
3 5-49 pg/l
>100 pgfl.
- Approximate Groundwater Flow Direction
— Groundwater Elevation Contour (ft amsQ
Notes
() Duplicate Result
pg/l Myograms per Lfter
1 pg/l Concentrations
. PCE Concentration greater
3 WL tfwn the PSL of 5 pgt
44 94 Groundwater Elevation (ft msl)
c-DCE ce-f, 2-DkMoroethene
ft msl Feet above mean sea level
J Estimated Result
ND Not Detected
NS Not Sampled
PCE TetrachJoroethene
PSL Project Screening Level
TCE Trichkxoethene
U Nor Detected
t Not monitored, extraction well
screened in A and upper B Zones.
Plumes are approximate and include
historical data from previous reports.
Figure 6
Groundwater Potentiometric Surface
and PCE in A-Zone Groundwater:
Fourth Quarter 2022
Modesto Groundwater Superfund Site
Modesto. California
Project Number: W12PP-21-C-0007
February 2023
rMua< C*«.*
PCE: ND
MW-16A
/TCE: ND
/ c-DCE: ND
S 36.20
Source: 2022 Fourth Quarter Operation, Maintenance, And Monitoring Report For Soil Vapor Extraction System, Soil Vapor, And Groundwater, NDN Sundance Joint Venture, LLC, July
2023.
Figure 10. Extent of PCE in A-zone
-------
Legend
'o, Groundwater Extraction Well
~ Groundwater Monitoring Well
Municipal Drinking Water Wei
¦*— Approximate Groundwater Flow Direction
Groundwater Elevation Contour (ft rnsl)
— ¦ Approximate Extent of PCE Plume
Approximate PCE Concentration "B"Zone (2022)
£53 5-49 pg/L
522 50-99 pg/L
() Duplicate Result
pg/L Micrograms per Liter
1 M9/L Concentration
PCE and TCE Concentrations greater
5M«'L than the PSL of 5 pg/L
44.95 Groundwater Elevation (ft msl)
c-DCE cis-1.2-Dichloroethene
ft msl Feet above mean sea level
J Estimated Result
ND Not Detected
NS Not Sampled
PCE Tetrachloroethene
PSL Project Screening Level
TCE Trichloroethene
Plumes are approximate and include
historical data from previous reports.
Figure 7
Groundwater Potentiometric Surface.
PCE and cis-1.2-DCE in B-Zone Groundwater:
Fourth Quarter 2022
Modesto Groundwater Superfund Site
Modesto. California
Project Number: W12PP-21-C-0007
February 2023
Source: 2022 Fourth Quarter Operation, Maintenance, And Monitoring Report For Soil Vapor Extraction System, Soil Vapor, And Groundwater, NDN Sundance Joint Venture, LLC, July 2023.
Figure 11. Extent of Plume in B-zone
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
27
-------
Legend
Approximate PCE Concentration "C"
Zone 2022
5-49 pg/L
~ Groundwater Monitoring WeN
Municipal Drinking Water Well
^ Approximate Groundwater Flow Direction
Groundwater Elevation Contour (ft msl)
Notes
() Duplicate Result
pg/L Micrograms per Liter
2.8 pg L Concentration
42.76
Groundwater Elevation (ft msl)
5pg/L
PCE Concentration greater
than the PSL of 5 pg/L
c-DCE
cis-1,2-Dichloroethene
ft msl
Feet above mean sea level
ND
Not Detected
PSL
Project Screening Level
PCE
tetrachloroethene
TCE
Trie Noroethene
MW-32C
PCE: ND
TCE: ND
/i lc: Ml
c-DCE:
33.93
Figure 8
Groundwater Potentiometric Surface
and PCE in C-Zone Groundwater:
Fourth Quarter 2022
Modesto Groundwater Superfund Site
Modesto, California
Project Number: W12PP-21-C-0Q07
February 2023
A
0 300 1
1 I I
Scale in Feet
Source: 2022 Fourth Quarter Operation, Maintenance, And Monitoring Report For Soil Vapor Extraction System, Soil Vapor, And Groundwater, NDN Sundance Joint Venture, LLC, July 2023.
Figure 12. Extent of Plume in C-zone
-------
4.2.5. Sustainability
The 2019 Government Accounting Office Report notes that no additional hazards associated with climate
change were identified for the Site. While the report does not evaluate all hazards, it does assess
vulnerability to flooding, sea level rise, wildfires, and storm surge.
The San Joaquin Valley, which includes the City of Modesto, is likely to experience a greater number of
days with extreme heat as the climate changes. Recent climate modeling conducted as part of California's
Fourth Climate Change Assessment universally supports increasing temperatures across the Valley in all
scenarios investigated. The risk of electrical brownouts and/or blackouts because of heavy electrical usage
is a potential risk. However, the City of Modesto is on the public electrical grid and, if an electrical issue
were to occur, the City of Modesto would address any interruptions in power in a timely manner;
therefore, the remedy would not be impacted due to the reliance on the electric grid. Additionally, the risk
of damage to electrical transmission lines from large and unpredictable wildfires in Central and Southern
California is anticipated to increase, particularly in urban fringe areas.
S/fe Inspection
The Site inspection occurred on March 8, 2023. In attendance were Anhtu Nguyen, EPA; John Consoletti,
NDN Sundance Consulting; George Garner, NDN Sundance Consulting; Andrew Archuleta, AECOM;
McKinley Lewis, DTSC; Randall Bleichner, DTSC; and James Stellmach, USACE. The purpose of the
inspection was to assess the condition of the remedy and verify that the remedy is operating as intended
(Appendix H).
Overall, the Site remedies appeared to be functioning as expected with no major issues or security
problems observed. The group visited the groundwater extraction and treatment system, which has seen
several equipment additions and/or replacements during the review period; the soil vapor extraction and
treatment system that changed from pulsed to continuous operation in May 2021; and several
groundwater extraction wells, some of which have seen recent refurbishment in preparation for
transferring the groundwater remedy from EPA to DTSC.
5. Technical Assessment
Question A: is the remedy functioning as intende the decision
documents?
The soil gas remedy is not functioning as intended by the decision documents. The final ROD was signed
in 2021, and the enhancement of the soil gas remedy is currently in the construction phase. The soil vapor
extraction and treatment system operated in pulse-mode from December 2017 to June 2020. The system
did not operate between June 2020 and May 2021 and has not operated since June 2023 while upgrades to
the system are implemented. Indoor air concentrations at Halford's increased during the extended period
of time when soil vapor extraction system was shut-off and exceeded indoor air cleanup levels in May
and October 2021. When the system was restarted for continuous operation in June 2021, the average
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
29
-------
PCE sample results at all locations declined each quarter. Indoor air concentrations have been below the
2021 ROD indoor air cleanup levels in all samples collected since January 2022. Recently, soil gas
concentrations beneath Halford's Cleaners have increased to their highest concentrations since
approximately 2020. In October 2022, the highest PCE soil gas concentration, 121,000 (ig/m3 occurred
while the soil vapor extraction system was turned on. There is no vapor mitigation system in Halford's
Cleaners.
When the soil vapor extraction system was in operation, the soil vapor effluent exceeded soil gas cleanup
levels three times over the past five years. EPA was not aware of the exceedances until subsequent
quarterly reports were received. However, as part of the soil vapor extraction system upgrades currently
being installed, a second granulated activated carbon vessel and a real-time monitoring of the influent,
mid-point and effluent concentrations will be installed. The second granulated activated carbon vessel in
series with the first will prevent future effluent exceedances; and the real-time monitoring response will
improve notifications and response times.
The groundwater remedy is functioning as intended. The groundwater remedy continues with the same
pump and treat system as previously installed. The groundwater treatment system operated as intended,
except for a period of time between December 2018 and January 2020, when naturally-occurring uranium
concentrations from the groundwater treatment system exceeded the City of Modesto's discharge
requirement of 20 pCi/L. This system operated intermittently during that time. The PCE concentration
trends in key monitoring wells and extraction wells have been either stable or decreasing over the past
five years, indicating mass removal is occurring.
The closest operating municipal wells are not impacted by the contamination from Modesto. The City of
Modesto ordinance prohibits wells within city limits served by their public water supply system for
purposes other than groundwater monitoring or remedial treatment. The Land Use Convent on the
Halford's property is in place.
Questi ¦ mre assumptk icity C
medial Action Objects >ed at the 7 mdy
Selection Si id?
Exposure assumptions from the interim ROD are still valid. All Applicable or Relevant and Appropriate
Requirements in the 2021 ROD and toxicity values are valid and do not affect the final remedy (Appendix
D and E).
Other Infc ¦ . )uld
Caff estion the Protectiveness of mdy?
No other information has come to light that could call into question the protectiveness of the remedy.
-------
6. Issues/Recommendations
Table ?. Issues and Recommendations Identified in the Five-Year Review
Issues ;ind Recommendations 1 dentilied in (lie l i\e-Ye:ir Rexiew:
Sitewide
Issue Category: Remedy Performance
Issue: Indoor air concentrations of PCE have exceed cleanup levels. There is no
indoor air mitigation system at 941 McHenry Avenue.
Recommendation: Interim vapor mitigation system should be installed at 941
McHenry Avenue.
Affect Current
Proteetiveness
Affect Future
Proteetiveness
Party Responsible
Oversight Party
Milestone Date
Yes
Yes
EPA
EPA
10/31/2023
Issues and Recommendations Identified in (lie l"i\e-Year Rcxicw:
Sitewide
Issue Category: Remedy Performance
Issue: The remedy specifies that a Focused Feasibility Study should be completed if
indoor air exceedances occur.
Recommendation: The remedy should be re-evaluated considering a documented case of
vapor intrusion exceeding protective level and a Focus Feasibility Study should be
completed.
Affect Current
Proteetiveness
Affect Future
Proteetiveness
Party Responsible
Oversight Party
Milestone Date
No
Yes
EPA
EPA
11/30/2026
Issues and Recommendations IdeiKil'ied in (lie ri\e-Ycar Rcxicw:
Sitewide
Issue Category: Operations and Maintenance
Issue: EPA was not notified of soil gas effluent exceedances or of indoor exceedances in
a timely manner. There is no documentation of action taken by US ACE or its
subcontractor in response to exceedances.
Recommendation: A notification plan should be developed that includes notification
requirements and required remedy actions if concentrations approach
Affect Current
Proteetiveness
Affect Future
Proteetiveness
Party Responsible
Oversight Party
Milestone Date
No
No
EPA
EPA
4/30/2024
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
31
-------
Othi clings
In addition, the following are recommendations that improve performance of the remedy but do not affect
current and/or future protectiveness and were identified during the Five-Year Review:
• The Annual and Quarterly Reports were written inconsistently with different terminology, and
conflicting data between text and tables. The reports lacked interpretation of the data.
• The analytical laboratory is currently not submitting electronic data deliverable files to EPA. The
data included in an electronic data deliverable file would provide analytical data in an electronic
format and would support EPA in quickly and more efficiently evaluating whether exceedances
are present during the previous sampling event and would allow EPA to provide proper
notifications or take action in a timely manner.
7. Protectiveness Statement
Table 8. Protectiveness Statement
Protectiveness Statement(s)
Operable Unit: Protectiveness Determination:
Groundwater and Soil Gas Not Protective
Protectiveness Statement: The Modesto Superfund Site remedy is not protective of human health and the
environment because indoor air concentrations of PCE have exceeded risk-based levels over the past five years,
and there is no vapor intrusion mitigation at the Halford's Cleaners. The groundwater remedy continues to operate
and remove mass. Groundwater monitoring shows that the municipal wells are not impacted. The City of Modesto
ordinance prohibits wells installation within city limits. However, to ensure protectiveness, EPA will develop a
notification plan to allow rapid response by EPA if soil gas or indoor air concentrations approach levels of concern
and complete a Focused Feasibility Study to select a permanent indoor air mitigation system.
8. Next Review
The next Five-Year Review report for the Modesto Groundwater Contamination Superfund Site is
required five years from the completion date of this review.
-------
Appendix A: List of Documents Reviewed
AECOM. 2023. Quarterly Operations And Monitoring Report, Groundwater Treatment System, First
Quarter 2023, May
AECOM. 2023. Quarterly Operations And Monitoring Report, Groundwater Treatment System, Second
Quarter 2023, August
AECOM. 2022. Quarterly Operations And Monitoring Report, Groundwater Treatment System, Fourth
Quarter 2022, February
AECOM. 2021. Quarterly Operations And Monitoring Report, Groundwater Treatment System, First
Quarter 2021, May
AECOM. 2020. Quarterly Operations And Monitoring Report, Groundwater Treatment System , Fourth
Quarter 2020, February
AECOM. 2020. Quarterly Operations And Monitoring Report, Groundwater Treatment System, First
Quarter 2020, May
AECOM. 2020. Quarterly Operations And Monitoring Report, Groundwater Treatment System, Second
Quarter 2020, August
AECOM. 2020. Quarterly Operations And Monitoring Report, Groundwater Treatment System, Third
Quarter 2020, November
AECOM. 2019. Quarterly Operations And Monitoring Report, Groundwater Treatment System , Fourth
Quarter 2019, February
AECOM. 2019. Quarterly Operations And Monitoring Report, Groundwater Treatment System, First
Quarter 2019, May
AECOM. 2019. Quarterly Operations And Monitoring Report, Groundwater Treatment System, Second
Quarter 2019, August
AECOM. 2019. Quarterly Operations And Monitoring Report, Groundwater Treatment System, Third
Quarter 2019, November
City of Modesto. 2023. California's Fourth Climate Change Assessment. State of California website.
https://climateassessment.ca.gov/ Accessed March 6.
EPA (United States Environmental Protection Agency). 1997. Interim Record of Decision, Modesto
Groundwater Contamination Superfund Site, Modesto, California, September 26.
EPA. 2021. Record of Decision, Modesto Groundwater Contamination Superfund Site, Modesto,
California. May 21.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
33
-------
USACE (United States Army Corps of Engineers). 2019. Final Feasibility Study Report, Modesto
Groundwater Contamination Superfund Site, Modesto, California. May.
UASCE 2018 - 2020, Quarterly Operation And Monitoring Reports, multiple dates
USACE. 2022. Final Soil and Soil Vapor Investigation Technical Memorandum for the Modesto
Groundwater Contamination Superfund Site, prepared by NDN Sundance Joint Venture.
Modesto, California, June.
USACE. 2022. 2021 Annual Report for Operations, Maintenance, and Monitoring Report for the Modesto
Groundwater Contamination Superfund Site, prepared by NDN Sundance Joint Venture.
Modesto, California, June.
USACE. 2022. Preliminary 60% Remedial Design for Remedial Action Support for the Modesto
Groundwater Contamination Superfund Site, prepared by NDN Sundance Joint Venture.
Modesto, California, November.
USACE. 2023. 2022 Annual Report Operations, Maintenance, And Monitoring Report For Soil Vapor
Extraction System, Soil Vapor, And Groundwater, August
USACE. 2023. Sub-Slab System Upgrades And Groundwater Monitoring Network Improvements
Technical Memorandum, prepared by NDN Sundance Joint Venture. Modesto, California, May
United States Government Accountability Office, 2019. Superfund Sites and Climate Change.
https://www.gao.gov/products/GAO-20-73. Accessed February 9, 2023.
-------
Appendix B: Site Chronology
Event
Date
Initial discovery of contamination: Modesto Municipal Well 11 found to be contaminated
with PCE.
September 1984
Investigations of soil, groundwater, and sanitary sewer lines by Regional Water Quality
Control Board and City of Modesto confirmed Halford's Cleaners as Municipal Well 11
PCE source.
April 1985-April 1990
Modesto Site placed on the National Priorities List
March 1989
EPA issues order to Potential Responsible Parties for treatment of contaminated soil.
September 1990
Potential Responsible Parties conduct Removal Action of limited soil vapor extraction
system.
February 1991
EPA takes over investigation and cleanup activities from Potential Responsible Parties.
1991
Municipal Well 11 permanently deactivated due to presence of naturally occurring
uranium.
October 1995
Remedial Investigation completed.
December 1996
Feasibility Study completed.
March 1997
Baseline Human Health Risk Assessment completed.
July 1997
Interim Record of Decision signed.
September 1997
Soil vapor extraction and treatment system installed.
May 2000
Groundwater extraction and treatment system installed.
June 2000
Groundwater extraction and treatment system extraction well EW-01R permanently shut
off due to operational difficulties.
November 2004
Groundwater extraction and treatment system replacement extraction well EW-01R
installed.
June 2006
Supplemental Site Investigation completed.
January 2007
EPA conducts vapor intrusion investigation at the source area.
February 2008- February
2012
EPA completes vapor intrusion mitigation in two businesses at the source area.
February 2008- April 2010
First Five-Year Review submitted.
September 2008
Soil vapor extraction Optimization Report completed.
June 2008
Soil vapor extraction system expanded.
October 2008
Groundwater Remediation Optimization Report completed.
March 2010
New extraction well EW-02 installed, groundwater extraction and treatment system
optimized through operation of EW-02 and shut down of EW-01R.
June-September 2012
Groundwater extraction and treatment system operation transferred from EPA to state.
July 2012
Second Five-Year Review submitted.
September 2013
Restarted EW-01R (EW-01R and EW-02 operated at 50/50 ratio).
July 2014
Soil vapor extraction system shutdown for Soil Vapor Rebound Study.
January 2014
Soil vapor extraction system re-started after Rebound Study.
April 2014
Soil vapor extraction system blower failure. Soil vapor extraction system shutdown.
November 2015
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
35
-------
Event
Date
Human Health Risk Assessment completed.
March 2017
Soil vapor extraction system blower replaced. Soil vapor extraction system re-started.
April 2017
Adjusted EW flow rates: EW-01R approximately 10 gallons per minute; EW-02
approximately 40 gallons per minute.
August 2017
Soil vapor extraction system blower shut off (for 'pulsed' operation; planned blower for 2
months per year).
December 2017
Third Five-Year Review submitted.
September 2018
Final Feasibility Study submitted.
May 2019
EPA signs the Final Record of Decision
May 2021
2021 Annual Operations, Maintenance, and Monitoring Report is submitted.
June 2022
Final Soil and Soil Vapor Investigation Technical Memorandum submitted.
June 2022
2022 Quarter One Sampling Report submitted.
July 2022
2022 Quarter Two Sampling Report submitted.
November 2022
Final 30% Remedial Design Report submitted.
November 2022
Final 90% Remedial Design Report submitted
March 2023
Final Sub-Slab Upgrades and Groundwater Monitoring Networks Improvements is
submitted
May 2023
2023 Quarter One Sampling Report submitted
June 2023
2022 Annual Operations, Maintenance, and Monitoring Report is submitted
August 2023
-------
Appendix C: Data Review
GSI MANN-KENDALL TOOLKIT
for Constituent Trend Analysis
Evaluation Date:
Facility Name:
Conducted By:
13-Jul-23
Modesto
Katie Richwine
Job ID:
Constituent:
Concentration Units:
PCE Zone A
ug/L
Sampling Point ID:
EW-01R
EW-02
MW-03A
MW-05A
MW-08A
MW-10A
MW-20A
Sampling
Event
Sampling
Date
PCE ZONE A CONCENTRATION (ug7L)
1
18-Jul-17
10
81
120
24
3.6
13
30
2
31-Oct-17
18
38
130
24
8.6
17
100
3
14-Feb-18
18
68
110
18
8.8
26
75
4
1B-Hau-18
17
84
180
6.4
7.8
20
33
5
12-Qct-18
13
60
200
6
10-Jan-13
14
41
200
8.1
6.5
15
75
7
5-Mar-13
31
72
180
8.8
7.8
14
81
8
10-Jan-20
120
5.6
6.3
25
52
9
15-Feb-20
140
8.3
7.1
24
48
10
15-May-20
130
5.4
1.2
11
51
11
15-Feb-21
130
5.4
1.2
13
43
12
5-Mar-21
130
5.4
1.2
13
43
13
17-May-21
130
11
6.2
15
31
14
9-Jul-21
7
41
98
13
2.4
26
15
15-Oct-21
4.4
62
121
16
5.2
11.4
26.5
16
16-Jan-22
4.5
43.4
143
3.77
5.4
11.7
23
17
23-Apr-22
4.7
77
132
10.8
6.6
13
23.4
18
31-Jul-22
2.5
60.1
134
24.7
1.5
11.4
31.2
18
11-Oct-22
3.3
81.1
128
196
6.5
11.4
41.6
20
I
Coefficient of Variation:
0.73
0.28
0.21
0.55
0.52
0.32
0.47
Mann-Kendall Statistic (S>:
-44
9
-11
12
-66
-73
-101
Confidence Factor:
99.7%
68.4%
63.5%
66.0%
99.4%
99.9%
>99.9%
Concentration Trend:
Decreasing
No Trend
Stable
No Trend
Decreasing
Decreasing
Decreasing
O)
3
C
O
c
-------
Sampling Point ID:
MW-4A
MW-18A
MW-21A I I I I I
Sampling
Event
Sampling
Date
PCE ZONE A CONCENTRATION (ug/l)
1
18-Jul-17
20
2.0
0.4
2
31-Oct-17
12
0.25
3
14-Feb-18
0.25
0.25
0.25
4
18-May-18
120
2.4
5
12-Oct-18
74
2.1
6
10-Jan-19
110
1.9
7
5-Ma<-19
130
2.0
0.8
8
30-Sep-19
92
2.8
0.25
9
1-Dec-19
100
2.1
0.25
10
1-Feb-20
110
2.1
0.3
11
14-Apr-20
110
2.1
0.3
12
16-MaV-21
140
2.60
0.68
13
17—Jul—21
120
2.10
0.25
14
15-Oc(-21
93.9
2.19
0.391
15
16-Jan-22
103
2.51
0.381
16
29-Apr-22
162
2.91
0.378
17
31-Jul-22
121
2.31
0.393
18
11-Oct-22
102
2.92
0.475
19
20
Coefficient of Variation:
Mann-Kendall Statistic (S):
Confidence Factor:
Concentration Trend:
1000
=1 100 -
a 1
C
o
Z 10
S
c
U
c
o
o
0.1
-MW-4A
-MW16A
- MW-21 /V
05/16
09/17
02/19
06/20
Sampling Date
10/21
03/23
Notes:
. At least four independent sampling events per well are required for calculating the trend. for 4 to 40f-a/npfcs.
. Confidence in Trend = Confidence (in percent) that constituent concentration is increasing (S>0) or decreasing (5<0): >95% = Increasing or Decreasing;
* 90% = Probably Increasing or Probably Decreasing; < 90% and S>0 = No Trend; < 90%, S*0, and COV * 1 = No Trend; < 90% and COV < 1 = Stable.
. Methodology based on "MAROS: A Decision Support System for Optimizing Monitoring Plans", J.J. Aziz, M. Ling, H.S. Rifai, C.J. Newell, and J.R. Gonzales,
Ground f/jfcv, 41(3):355-367,2003.
Figure C 2. Mann-Kendall Analysis of the A-zone Aquifer for Monitoring wells outside of the
source area.
-------
GSI MANN-KENDALL TOOLKIT
for Constituent Trend Analysis
Stable
Sampling Sampling
Event Date
PCE B ZONE CONCENTRATION (ug/L)
—•—MW-26B
^^-MW-27B
—MW-36B
—MW-38B
——MW-40B
—MW-33B
—MW-3GB
0.49S
0.652
0.82
65
>99.9*
increasing
Increasing Increasing Decreasing
6-JUI-23
Modesto
Sara Benovic
15-Mar-18
14-Jun-1S
1 5-Sep-18
15-Nov-18
15-Jan-19
10-Jun-19
13-Dec-19
8-Apr-20
14-May-21
S-Jul-21
15-Oct-21
0.482
15-Jan-22
0.616
29-Apr-22
0.561
24-Feb-20
3-1-Jul-22
12-Oct-22
0.50
I &
59.4%
0.95
35
96.9%
0.66
26
95.7%
0.36
.36
97.3%
Figure C 3. Mann-Kendall Analysis of B-zone Aquifer Wells on the Perimeter of the Plume.
Sampling Point ID: [
1 22-Oct-17
Evaluation Date:
Facility Name:
Conducted By:
Job ID:
Constituent:
Concentration Units:
PCE B Zone
Coefficient of Variation
Mann-Kendall Statistic (S|
Confidence Factor
Concentration T rend
0.1
03/17 09/17 04/18 MS 05/19 12/19 06/20 01/21 07/21 02/22 08/22 03/23
Sampling Date
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
39
-------
Appendix D: Applicable or Relevant and
Appropriate Requirements
Assessment
Section 121(d)(2)(A) of the Comprehensive Environmental Response, Compensation, and Liability Act
specifies that Superfund remedial actions must meet any Federal standards, requirements, criteria, or
limitations that are determined to be legally applicable or relevant and appropriate requirements
(ARARs). ARARs are those standards, criteria, or limitations promulgated under Federal or State law that
specifically address a hazardous substance, pollutant, contaminant, remedial action, location, or other
circumstance at a Comprehensive Environmental Response, Compensation, and Liability Act site.
Changes (if any) in ARARs are evaluated to determine if the changes affect the protectiveness of the
remedy. EPA finalized the ROD in May 2021, and the project is still awaiting final remedy construction
to enhance the soil vapor extraction system. The chemical-specific groundwater ARAR analysis is based
on Federal drinking water standards for the Site (Table D-l).
Cleanup levels for indoor air and soil gas are toxicity-based, not ARAR-based, and will be evaluated in
the Toxicity Analysis (Appendix E).
Table D-1. Summary of Groundwater Chemical-Specific ARAR Changes
Chemical
2021
Basis for Cleanup
Level
Current Regulations (jig/L)
ARARs More or
Less Stringent
than Cleanup
Levels?
Cleanup
Levels (jig/L)
State
Federal
T etrachloroethy lene
5
Federal Drinking
Water Standard
5
5
No change
Trichloroethene
5
Federal Drinking
Water Standard
5
5
No change
There have been no revisions to laws or regulations that affect the protectiveness of the remedy. The
following action- or location-specific regulations have been identified as ARARs:
• National Historic Preservation Act: 16USC470
• Occupational Health and Safety - 8 CCR Sections 1500, 2300, and 3200 et seq.
• Clean Water Act Section 402
• SWRCB Order 2009-009-DWQ as amended by 2010- 0014-DWQ and 2012-006-DWQ.
• California Hazardous Waste Determination 22 CCR 66261.20-.24
• Hazardous Waste Control: California Health and Safety Code 25100-252550.26
• Transportation of Hazardous Waste 8 CCR Sections 1500, 2300, and 3200 et seq.D2
• LDRs 22 CCR 66268
• LLRW Disposal 42 USC 2014(c); 10 CFR 40.13; 10 CFR 40.22
• LLRW Disposal Records 10 CFR 20 and 10 CFR 61 (incorporated in 17 CCR 30471)
-------
• Waste Characterization and Disposal 27 CCR 20200(a)(2)
• Designated Waste 27 CCR 20210
• Nonhazardous Solid Waste 27 CCR 20220
• Inert Waste 27 CCR 20230
• Safe Drinking Water Act- Class V Injection Wells 40 CFR 144.12
• SWRCB Anti-Degradation Policy: SWRCB Resolution No. 68-16
• California Toxic Injection Well Control Act: CH&SC 25159.10-25159.25; 22 CCR 66260.10
• California Water Code Section 13263 Subdivision (i)
• California Toxics Rule 40 CFR Part 131
• Discharge to Publicly Owned Treatment Works 40 CFR 403.5; 40 CFR 261.4; Modesto City
Municipal Code Title 5, Chapter 6, Articles 2 and 4
• Permit to Operate and Use of BACT: SJVAPCD Reg. II; Rules 2010, 2020, and 2021 (per the SIP as
required by the CAA, 42 USC Section 7401 et seq.)
• Nuisance Prohibition: SJVAPCD Reg. IV; Rule 4102 (per the SIP as required by the CAA, 42 USC
Section 7401 et seq.)
• Fugitive Dust Emissions from Construction, Demolition, Excavation, and other Earthmoving
Activities: SJVAPCD Reg. VIII; Rules 8021, 8031, and 8041 (per the SIP as required by the CAA, 42
USC Section 7401 et seq.)
• California Civil Code 1471 (a&b); 22 CCR 67390.2-67391.1
• RCRA Hazardous Waste Determination Title 40 CFR 261.21
• Ambient Air Quality Standards (Health and Safety Code) Section 39000-44071
• Safe Drinking Act: 40 CFR 141
• 40 CFR Parts 122-125
• Discharge to Publicly Owned Treatment Works: 22 CCR 66261.4
• Porter Cologne Water Quality Control Act: 23 CCR 2550 et seq.
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
41
-------
Appendix E. Toxicity Assessment
Chemical-specific ARARs identified in the 2021 ROD for indoor air and vapor intrusion are shown in the
tables below (Table E-l and E-2). EPA selected indoor air cleanup levels for commercial buildings in the
2021 ROD. EPA adopted Regional Screening Levels as indoor air and soil gas cleanup levels. EPA's
Integrated Risk Information System updates toxicity values used by EPA in risk assessment when newer
scientific information becomes available. EPA Regional Screening Levels are less stringent in some cases
than the California Human Health Screening levels for soil gas and for indoor air PCE project screening
levels, therefore in some cases, the state levels supersede EPA Regional Screening Levels.
Table E-1. Summary of Commercial Indoor Air Toxicity Changes
Chemical
Indoor Air Cleanup
Level for
Commercial
Buildings
(Hg/m3)
Basis for Cleanup
Level
Current Commercial
RSL (ng/m3)
c = cancer
n = noncancer
RSLs More or Less Stringent
than Cleanup Levels?
T etrachloroethy lenea
20
1 x 10"5 lifetime
cancer target risk
20 (c)
No change
Trichloroetheneb
9
non-cancer hazard
quotient level of
1.0
9 (n)
No change
Motes:
R.SL = Regional Screening Level
aDTSC screening level (HHRA Note 3 June, Table 3).
bEPA Regional Screening Level calculator
Table E-2. Summary
of Commercial Soil Gas Vapor Intrusion Toxicity Changes
Chemical
Soil Gas Vapor
Intrusion Cleanup
Level for
Commercial
Buildings
(Hg/m3)
Basis for Cleanup
Level
Current Commercial
screening level (jig/m3)
c = cancer
n = noncancer
Screening Levels More or
Less Stringent than Cleanup
Levels?
T etrachloroethy lenea
670
1 x 10"5 lifetime
cancer target risk
670 (c)
No change
Trichloroetheneb
1,000
1 x 10"5 lifetime
cancer target risk
1,000 (c)
No change
Trichloroetheneb
290
non-cancer hazard
quotient level of
1.0
290 (n)
No change
Notes:
aDTSC screening level (HHRA Note 3 June, Table 3).
bEPA Vapor Intrusion screening level calculator
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
42
-------
Appendix F: Public Notice
EPA WANTS TO HEAR FROM YOU ABOUT THE
MODESTO GROUNDWATER SUPERFUND SITE CLEANUP
The U.S. Environmental Protection Agency (ER^) has started a review of
the cleanup plan for the Modesto Groundwater Superfund site. The site is in
Modesto, California. This review wil show if the deanup plan is working as EPA
intended.
Federal law requires EPA to review its cleanup plans every five years if:
- a cleanup takes more than five years to complete; or
- hazardous waste is still on-site.
EPAcfid the last review in 2018 and found the cleanup plan was working as
intended.
What is included in the review?
• An inspection of the site and technologies used for the cleanup
• A review of site data and maintenance
• A review of any new laws or requirements that could affect the cleanup
EPA would like to hear from you!
We would fike to interview community members about how you think the
site cleanup is going. If you want to learn more about the site and/or be
interviewed, please call Mr. Nguyen before May 30, 2023:
• Anhtu Nguyen, EFA Project Manager: (415) 972-3443 or n guy en anhtuigi
epa.Qov
Where can I learn more?
Visit ERAs webpage at eoa.Qov/superfung/modes to or our Superfund Record
Center (see below) for more infotmation. EPA has also set up an information
repository, closer to the site, with a copy of the site's Administrative Record
(which includes key documents and reports for the cleanup) at:
Stanislaus County Library
Main Library
15001 Street
Modesto, CA 95354
(209) 558-7800
Please call for current hours of operation
Superfund Record Center
75 Hawthorne Street, Room 3100
San Francisco. CA 94105
Phone:(415)947-8717
Please call for current hours of operation
EPA will complete the Five-Year Review report no later than September 30,
2023. When complete, EPA will post a copy on the site's webpage and send
a copy to the site information repository listed above.
Background
The Modesto Groundwater Contamnation Superfund site includes a dry-cleaning
facility that leaked tetrachloroethylene (also known as PCE) into the soil,
groundwater, and sewer system for many years. The site was added to EPA's
Superfund cleanup program in 1989 to address the contamination. EPA signed
an interim cleanup plan in 1997 and two groundwater treatment systems were
installed and have operated since 2000. In 2021. a final cleanup plan was issued.
Cleanup of the site is on-going.
CN SB #3656104
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
43
-------
Appendix G: Interview Forms
Five-Year Review Interview Record
Site:
Modesto Groundwater Contamination Superfund Site
EPA ID
No: CA981997752
Interview Questionnaire
Date: 2/24/2023
(Fill in the com
ponents below, one line per person if multiple persons are providinq responses)
Name
Organization
Title
Telephone
Email
James
Stelimach
USACE-SPK
Environmental Engineer
(916) 557-8893
iames.p.stellmach@Jusace.army.mil
(Record responses to the questions below)
1) What is your overall impression of the project?
The project has been a success, but with some caveats. The intent of the interim remedy was mostly accomplished (to
significantly control the source of groundwater contamination). But the interim remedy did not entirely meet its goals, as
contamination at greater than the MCI as progressed down gradient outside of the extraction wells' capture zone. Also, while the
soil vapor extraction component of the interim remedy did meet its goal of assisting the groundwater remedy through removing
contaminant mass in the source area vadose zone, the soil vapor extraction system was not able to impact the vadose zone
contamination enough to fully alleviate indoor air risk (which, incidentally, was not a specific goal of the IROD).
2) Is the remedy functioning as expected? How well is the remedy performing?
The groundwater interim remedy is functioning as expected and is performing adequately, but as noted above, the remedy did
not fully contain the source area groundwater contamination. The soil vapor extraction aspect of the interim remedy is functioning
as expected and performing; the intent of the soil vapor extraction in the IROD was to assist the groundwater remediation; the
soil vapor extraction did that, somewhat, but was not able to fully address contaminant mass retained in fine-grained soil in the
source area vadose zone. The soil vapor extraction will shortly be enhanced with two additional horizontal soil vapor extraction
wells in order to address contaminant mass that has not been removed via the current system's four vertical soil vapor extraction
wells.
3) A new Record of Decision has been signed in 2021. How does this affect the implementation of the remedies?
Wearing construction on the remedy based on the 2021 ROD, the project is at an important stage, at a crossroads: the
(unchanged) groundwater remedy should maintain its effectiveness, and in approximately 12-24 months, hopefully it may be
determined that the enhanced soil vapor extraction has controlled the source are vadose zone contamination in order to alleviate
the indoor air risk, in 2019, a PCE fingerprinting was done, which determined that the leading edge of the B Zone plume (i.e., at
MW-40B) is likely not caused by the Modesto Superfund (Halford's drycleaning) source, but rater from other sources. This
determination partially led to EPA's deciding that the groundwater remedy remain the status quo operation of the extraction wells
near the source area (with ongoing monitored natural attenuation), rather than including additional down-gradient extraction
wells.
4) Are there plans to increase/decrease the number of groundwater or soil vapor wells? If so, please provide details such as the
number of wells and reasoning for the changes.
The number of groundwater extraction wells is set to remain the same. One additional groundwater monitoring well is planned.
The precise location is not determined, but it will be to the west of the defined MCL PCE plume, up-gradient from MW-27B and
near and cross-gradient from Municipal well 07, The reasoning for the well is that MW-27B had bound the plume, but recent
results at that well exceed the PCE MCL, and that MWIs cross- and down-gradient from Muni 07, so it therefore no longer acts
as a sentinel well for Muni 07; the intent of the new well is to bound the west side of the B zone PCE plume, and to guard Muni
07, There may also be additional B Zone wells farther south from MW-40B, as the leading edge of the PCE plume is no longer
bound.
There are no additional soil vapor monitoring wells planned. There are two horizontal soil vapor extraction wells planned (as
described above), intended to remove addition vadose zone contaminant mass that has not been addressed by the current soil
vapor extraction system.
5) What does the groundwater monitoring data show? Are there any trends that show increasing or decreasing contaminant
levels?
-------
The shallow (A Zone) PCE trend has been mostly stable, but with some expansion to the west and south greater than the MCL in
2022. The deep (C Zone) monitoring PCE data is basically stable. The overall shape and trend of the B Zone PCE plume has
been consistent, but with some spreading to the west (e.g., at MW-27B) and increased concentrations at the leading (southerly)
extent since 2020 (e.g., MW-26B, MW-35B, MW-MW-40B and MW-38B). TCE and other PCE daughter products have only
sporadically been detected, but in Q3 2022 TCE was detected at greater than its MCL at MW-40B.
6) What does the soil gas data show? Are there any trends that show increasing or decreasing contaminant levels in indoor air or
sub-slab sampling?
Soil gas, indoor air, and sub slab data have recently not shown any consistent upward or downward trends: after extended
periods of the soil vapor extraction system having been off, PCE and TCE concentrations have generally risen, and then levels
have lowered upon periods of soil vapor extraction operation; but the extent of theses fluctuations has not been entirely
consistent, (soil vapor extraction was off from June 2020 through May 2021, and has been operated continuously since May
2021.)
7) Is there a continuous O&M presence? If so, please describe staff and activities. Ifthere is not a continuous on-Site presence,
describe staff and frequency of Site inspections and activities.
There is not a continuous on-site presence. The soil vapor extraction contractor (USACE contract for EPA) performs monthly
O&M (system inlet and outlet sampling and any needed maintenance) (a single O&M technician, I think). The groundwater
contractor (for California DTSC) also performs monthly O&M (system sampling and any needed maintenance, performed by a
single technician).
8) Have there been any significant changes in the O&M requirements, maintenance schedules, or sampling routines in the last 5
years? If so, do they affect protectiveness of the remedy? Please describe changes and impacts.
There have been no O&M changes.
9) Have there been any unexpected O&M difficulties at the Site in the last five years? If so, please give details.
There have been no unexpected O&M difficulties that I am aware of.
10) Have there been opportunities to optimize O&M or sampling efforts? Please describe changes or improved efficiency.
From 2018 through 2021, the soil vapor extraction system was operated intermittently, as contaminant mass removal became
asymptotic after several months of continuous operation (e.g., system operation for several months, followed by system shut-off
for several months). As of 2021, in an attempt to better mitigate indoor air TCE and PCE levels, it was decided to return to
continuous system operation with the soil vapor extraction O&M contractor proposing and implementing differential flow rates
from among the four soil vapor extraction wells (versus equal flow rates from each well). The changes have not significantly
increased mass removal, but the soil vapor extraction system has been more adequately alleviating the indoor air contaminant
levels. I am not aware of any changes to the groundwater extraction system O&M. The groundwater monitoring wells have been
improved recently (in 2022), with re-doing surface completions on some wells in order to maintain well integrity along with well
redevelopment in order to ensure more accurately sampling the groundwater (due to concerns regarding likely previous surface
water infiltration). The sampling efforts have not been optimized, with O&M sampling occurring quarterly and all monitoring wells
and indoor air/ambient air being sampled quarterly; the soil vapor extraction / groundwater sampling contractor is expected to
offer groundwater sampling optimization proposals in the 2022 annual report, as well as re-doing the soil vapor extraction
sampling plan as part of implementing the remedy from the 2021 ROD in early 2023.
11) Are you aware of any changes in Federal/State/County/Local laws and regulations that may impact the protectiveness of the
remedy?
The state of California switched to Human and Ecological Risk Office (HERO) Toxicity Criteria Selection for Risk Assessments,
Screening Levels, and Remediation Goals as of late 2018. The ongoing sampling plans at the site were based on the California
Human Health Screening Levels (CHHSLs). As of Q3 2022, the soil vapor extraction and groundwater sampling contractor had
not switched over to using HERO values for screening levels for the vapor sampling program. As of the Q4 2022 (which is also
the 2022 Annual Report), the contractor should be switching to HERO values, at the request of California DTSC, and will be
using the HERO screening levels in the updated QAPPP/Sampling Plan as part of the 2021 ROD remedy implementation.
12) Do you have any comments, suggestions, or recommendations regarding the project?
The soon-to-occur remedial construction is a key phase for the project, with the forthcoming approximately two years likely being
pivotal for determining the effectiveness of the remedy implementation regarding removing additional vadose zone contamination
and better mitigating indoor air contaminant levels. It is also a key period in the groundwater sampling program, as B Zone PCE
levels greater than the MCL are near the city's production well Muni 07. The contaminant plume is mostly stable in its trajectory
to the east of Muni 07, but the stability of that trajectory is not entirely certain. Further, the leading edge of the groundwater
plume is likely comingled with other PCE sources, adding further uncertainty to maintaining protectiveness of the groundwater at
Muni 07.
Additional Site-Specific Questions
[If needed]
Trip Report
Modesto Groundwater Contamination FYR 45
-------
Five-Year Review Interview Record
Site:
Modesto Groundwater Contamination Superfund Site
EPA ID No:
CA981997752
Interview Questionnaire
Date: March 27, 2023
(Fill in the components below, one line
per person if multiple persons are providing responses)
Name
Organization
Title
Telephone
Email
McKinley Lewis
Project Manager
McKinley.Lewis@dtsc.ca.gov
(Record responses to the questions below)
1) What is your overall impression of the project?
On March 8, 2023, DTSC, USEPA, respective contractors and USACE conducted a site inspection as required under CERCLA
for a Five-Year Review (FYR). At conclusion of the inspection, DTSC, overall, was left with a positive impression and outlook for
the project.
As part of the FYR requirement, a close inspection of the remediation systems (pumping system, soil vapor extraction system
and monitoring wells) was done, and, in general, the systems were found to be in good working condition. Where there were
deficits, plans for improvements were in the works. A sample of the monitoring wells previously identified as needing repairs were
inspected and showed repairs had been made and/or plans were in the works do so.
Observations seem to show a strong commitment from USEPA to the Modesto community. During the inspection, USEPA
reiterated its commitment to fulfilling the 2021 Final ROD on schedule for final turnover to the state. Construction crews were
observed onsite during the inspection to implement repairs/enhancements to the soil vapor extraction system as detailed in the
2021 Final ROD. An attentive USEPA spent time addressing questions and/or concerns from the Modesto community that
approached our group during the inspection.
DTSC is committed to protecting the human health and environment of the Modesto community. The groundwater treatment
system has operated under DTSC responsibility for more than a decade and continues to perform as designed. Monthly
groundwater discharge reports show that the water discharged into the City of Modesto sewer system complies with federal,
state and county requirements. The extraction wells of the groundwater treatment system also continue to perform as designed
and regular operation and maintenance is performed. In addition, DTSC is considering enhancements for the system and facility
that will optimize performance and result in cost savings.
2) Is the remedy functioning as expected? How well is the remedy performing?
Review of the data in past quarterly and annual groundwater monitoring reports seem to suggest that the groundwater interim
remedy is functioning as intended as measured by the 1997 Interim Record of Decision (IROD). The objective of the remedy, in
part, is source control and reduce tetrachloroethylene (PCE) concentrations in groundwater. Concentrations of PCE have
decreased or remained stable in the source area and plume since the 2018 FYR however, data also shows the efficiency of the
system to be decreasing.
Understanding the need to address deficiency of the system, USEPA developed a plan. In the 2021 Final ROD, the current
groundwater treatment system will continue; however, the soil gas contamination impact will be addressed by modifying the
current soil gas extraction system. The expected outcome of this augmentation of the remedy is to improve ability to extract
contaminant in areas not reached by the current system.
3) A new Record of Decision was signed in 2021. How does this affect the implementation of the remedies?
The 2021 Final ROD selected long-term remedial actions for remediation of PCE contamination in both the soil gas and
groundwater. The 1997 IROD had an interim cleanup measure meant to address the groundwater and soil gas contamination
through implementation of a groundwater extraction treatment system and a soil vapor extraction (SVE) treatment system. Since
then, USEPA has reevaluated those actions taken and determined that the effectiveness of the groundwater treatment system
has decreased over time, and the SVE system does not adequately address the remaining soil vapor contamination at the Site.
Under the 2021 ROD, USEPA elected to continue with the two systems because a departure to another option could complicate
cleanup efforts by bringing in cross contamination from other sources unrelated to this site; in short, there is no impact to the
current remedy by implementation of the 2021 ROD.
4) Are there plans to increase/decrease the number of groundwater monitoring wells? If so, please provide details such as the
number of wells and reasoning for the changes.
The chosen Alternative GW-2 in the Final 2021 ROD calls for status quo of current operations of the groundwater extraction
treatment system with continuation of quarterly sampling of the 51 well network, monthly sampling of the two extraction wells for
compliance, and operating the extraction wells at 50 gallons per minute for the next 30 years. The Alternative does not call for
-------
installation of additional wells; however, DTSC continues to assess performance of the treatment system and evaluate the data
collected from groundwater samples to determine whether changes to the groundwater monitoring network are needed.
5) What does the groundwater monitoring data show? Are there any trends that show increasing or decreasing contaminant
levels?
The Site has a network of 51 groundwater monitoring wells plus one independent extraction well. The wells covering three
defined hydrogeological zones A, B, and C are sampled quarterly and semi-annually for PCE, TCE, t-DCE, c-DCE, 1,1 -DCE, and
VC and the analytical results are compared against the project screening levels (PSLs) for groundwater, which are based on
USEPA Region 9 Screening Levels and California maximum concentration limits (MCLs).
Referencing the 2021 Annual Operations, Maintenance and Monitoring Report, analytical results show a mixed bag. PCE
concentrations exceeded the PSL for groundwater in all three hydrogeological zones and one analytical for TCE concentration
was observed exceeding PSL for groundwater in the B Zone; however, exceedance of the PSL for concentrations of t-DCE, c-
DCE, 1,1 -DCE, or VC were not observed. The range of concentration values were from 0.0146 to 187 microgram per liter (|jg/L)
for PCE, 0.062 to 13.60 |jg/L for TCE and non-detect to 5.45 |jg/L for the remaining compounds. California's MCL for PCE and
TCE is 5 |jg/L; MCL for t-DCE is 10 |jg/L; MCL for c-DCE and 1,1 -DCE is 6 |jg/L; and the MCL for VC is 0.5 |jg/L.
6) Is there a continuous O&M presence? If so, please describe staff and activities. If there is not a continuous on-Site presence,
describe staff and frequency of Site inspections and activities.
Yes, there is a continuous presence at the site. DTSC's contractor has assigned two staff to the site that have combined
experience of more than 20 years. At least twice a week, the two staff team visits the site to perform operation and maintenance
activities on the groundwater extraction treatment system and periodic sampling from the system. In addition, the DTSC project
manager overseeing the Site and contractor performs periodic site visits.
7) Have there been any significant changes in the O&M requirements, maintenance schedules, or sampling routines in the last 5
years? If so, do they affect protectiveness of the remedy? Please describe changes and impacts.
Yes, there have been changes. In August 2020, after receiving USEPA concurrence, DTSC decommissioned the air stripper to
optimize the groundwater treatment system and cost savings. Removal of the air stripper simplified the treatment process by
running only GAC for the water treatment eliminating the need to add a sequestrant to reduce scaling. Removal of the stripper
also negated a need for off-gas treatment and the costs associated with vapor phase carbon usage. A pump/motor from the air
stripper sump was also removed that resulted in additional saving on electricity.
8) Have there been any unexpected O&M difficulties at the Site in the last five years? If so, please give details.
An unexpected issue with the IX resin occurred in 2018 with a breakthrough after only two months of operations. At first look,
there was not a clear understanding as to what caused the breakthrough; however, optimizing the system by removing the air
stripper and performing a series of acid washes fix the issue. DTSC is looking into making a replacement of the aging system
soon.
9) Have there been opportunities to optimize O&M or sampling efforts? Please describe changes or improved efficiency.
A large percentage of the monitoring wells for the groundwater extraction treatment system were recently repaired as part of an
agreement between the two agencies ahead of the transfer for the sampling duties. Also, see the response #8 above.
10) Are you aware of any changes in Federal/State/County/Local laws and regulations that may impact the protectiveness of the
remedy?
Yes, there has been changes in state regulations that could adversely affect how protective of human health the current remedy
is viewed. In September 2018, DTSC adopted new regulations, Toxicity Criteria for Human Health Risk Assessments, Screening
Levels, and Remediation Goals, that aim at further protecting human health by ensuring human health risk assessments, risk-
based screening levels, and risk-based remediation goals for hazardous waste and hazardous substance cleanup sites in
California use the appropriate toxicity criteria. Any release of hazardous waste or hazardous constituents, the human health risk
assessment calculations, including, but not limited to, all cancer risk and non-cancer hazard screening levels and corrective
action objectives, shall use the toxicity criteria specified in California Code of Regulations, title 22, section 69021 and attain the
human health protection specified in section 69022, subdivisions (a) and (b).
11) Do you have any comments, suggestions, or recommendations regarding the project?
DTSC and USEPA recognized it is in the best interest of both agencies to continue development and fostering of good relations
that has led to a great partnership. Frequent communications have enabled us to identify potential obstacles early and address
them even sooner, which has led to efficiency, cost savings, and beating timelines on the project. At the end of the FY21/22, it
was forecasted transfer of the groundwater monitoring program to the state would take place by end of the 2024 calendar year;
however, due to excellent communication, relations, and collaboration on problem-solving the timeline been halved. Transfer is to
take place by end of 2023.
Trip Report
Modesto Groundwater Contamination FYR 47
-------
[If needed]
Appendix H: Site Inspection Report and
Photos
Trip Report
Modesto Groundwater Contamination Superfund Site - Modesto, Stanislaus
County, CA
1. INTRODUCTION
a. Date of Visit: March 08, 2023
b. Location: Modesto CA
c. Purpose: A site visit was conducted to visually inspect and document the conditions of the
remedy, the site, and the surrounding area for inclusion into the Five-Year Review Report.
d. Participants:
NAME
ORGANIZATION
James Stellmach
Tu Nguyen
John Consoletti
George Garner
Andrew Archuleta
McKinley Lewis
Randall Bleichner
USACE-SPK, Environmental Engineer
EPA, RPM
Sundance Consulting (Site Contractor), PM
Sundance Consulting, Geologist
AECOM (Groundwater Treatment Contractor), Field Manager
DTSC, PM
DTSC, Engineering Geologist
2. SUMMARY
The site visit was completed at the Modesto Groundwater Contamination Superfund Site (Site)
on March 08, 2023, as part of the Site's Five-Year Review. The participants listed attended the
site visit. The weather was partly cloudy and in the 60s. The site visit lasted from approximately
11:15 a.m. to 1:15 p.m. The Site is located in a mixed-use area of Modesto, CA. All participants
agreed that land use at and near the Site has not changed within the past five years.
3. DISCUSSION
The inspection began in the parking lot to the west of the groundwater treatment system (GWTS)
(after arriving at the Site, all inspected areas were visited via walking). The GWTS and Soil
Vapor Extraction (SVE) system are adjacent to a commercial avenue (but within a half-block of
a residential area). A roll call was performed, and Mr. Consoletti did a safety briefing regarding
safety hazards at the Site.
-------
The GWTS is enclosed within a metal shipping box which is surrounded by a secured chain-link
fence - the shipping box has padlocked doors, and the fence has padlocked gates, but with no on-
site security. The fence was in good condition. Mr. Archuleta noted that there have been no
known security concerns within the past five years.
Mr. Stellmach, Mr. Archuleta, Mr. Lewis, and Mr. Bleichner then entered the GWTS enclosure
and discussed aspects of the GWTS. Mr. Archuleta noted that all necessary documents including
the safety plans and O&M manuals are kept on-site to address any concerns any emergencies
such as a hazardous waste spill, fire, or natural disaster. Mr. Stellmach asked Mr. Archuleta to
describe any potential challenges and the overall operational history of the GWTS. Mr.
Archuleta listed improvements done within the past five years: the adding of one GAC treatment
unit (3 total units) and the removal of the air stripper; and a new SCADA system and a new flow
meter. Mr. Archuleta then mentioned other possible future improvements: cleaning of the
enclosure's sump; revisiting reinjection of treated water (versus the discharge of treated water to
the sewer system); and further automation (to possibly lessen the need for weekly O&M visits).
Mr. Archuleta explained that the elimination of the air stripper seemed to have solved the issue
of excessive scaling in the system.
After the tour of the GWTS was complete, Mr. Stellmach, Mr. Bleichner, and Mr. Garner visited
the SVE system. The SVE system is enclosed in a metal shipping container adjacent to the
GWTS, within the same secure fenced area as the GWTS. Similar to the GWTS, the SVE
enclosure also has doors that are secured with padlocks when closed. Mr. Garner noted that all
necessary documents including the safety plans and O&M manuals are kept on-site to address
any concerns any emergencies such as a hazardous waste spill, fire, or natural disaster. Mr.
Stellmach asked Mr. Garner to describe any challenges and the overall operational history of the
SVE. Mr. Garner stated that the SVE has been running continually since May 2021, except for
brief system stoppages due to power failures, and that the system has been performing as
expected with no major issues. Mr. Garner stated that the one recent notable O&M change was
that the condensate drum had 20 gallons of water in it the previous month (the first instance of
any condensate since system re-start in 2021). Mr. Garner then detailed the notable changes to
SVE operations within the past five years: the system had been "pulsed" prior to 2021 (several
months of system shut-down, followed by approximately two months of system operation), but
has run continually since May 2021; and the adjustment of the in-flow from equivalent between
the four SVE wells to be predominately from SVE-2 and SVE-3 (approximately 85% to 90%
from these wells), as those wells have exhibited far greater concentrations of contaminants than
SVE-1 and SVE-4.
The full group then toured extraction well EW-1. The well was operational and operating. The
only issue noted at EW-1 by any of the group was that there was approximately six inches of
surface water in the bottom of the well vault. The surface water infiltration does not seem to have
impacted the well's operation.
The group then toured several of the Site's groundwater monitoring wells that had recently been
improved via re-doing the surface completions (wells MW-10A, MW-29B, and MW-13A were
visited). Mr. Consoletti briefed that Sundance Consulting had been scoped to assess all
Trip Report
Modesto Groundwater Contamination FYR 49
-------
groundwater monitoring wells and to improve certain wells due to possible surface water
infiltration concerns. Mr. Consoletti stated that the work was done during 2022, and that each
improved well had the previous well box and lid removed and replaced, with the surface concrete
completion around the well lid re-done to slope away from the lid, followed by redevelopment of
each well; and he further noted that all existing groundwater monitoring wells are in good
condition. The wells that were visited are in a residential area to the south and west of the
contaminant source area. Mr. Stellmach noted that the improved wells were in good condition,
with the only notable issue being that MW-29B did have some surface water in the annular space
within the well box (approximately one inch water depth, below the well casing's cap). Mr.
Consoletti then explained that the well improvements are being documented in a memo report
that would soon be submitted.
After touring the improved wells, the group visited extraction well EW-2. The well was
operational and operating. Mr. Archuleta stated that there have been no major operational issues
with either extraction well within the past five years, and that EW-1 operates at approximately 10
gallons per minute, with EW-2 operating at approximately 40 gallons per minute.
The group then walked back to the parking lot adjacent to the GWTS and concluded the site
visit. Mr. Stellmach left the Site at 1:15 p.m.
James Stellmach
Environmental Engineer
Sacramento District
-------
No.
Photo
Caption
Fence around the groundwater
treatment system (GWTS) and
soil vapor extraction (SVE)
system enclosures.
GWTS GAC vessels inside
enclosure
Fourth Five-Year Review for Modesto Groundwater Contamination Superfund Site
51
-------
GWTS equalization tank and
sampling supplies.
-------
Trip Report
Modesto Groundwater Contamination FYR 53
-------
Groundwater extraction well
EW-1
Soil vapor extraction well SVE-
1 with valve mostly closed to
suppress in-flow
-------
Groundwater monitoring well
MW-10A, with re-done well
completion
Groundwater monitoring well
MW-29B, with re-done well
completion (~ 1" surface water
in well annulus).
Trip Report
Modesto Groundwater Contamination FYR 55
------- |