United States
Environmental Protection
Agency
Off ice of
Emergency and
Remedial Response
EPA/ROD/R09-93/088
March 1993
£EPA Superfund
Record of Decision:
San Gabriel Valley Area 1
(Operable Unit 2), CA
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50272-101
REPORT DOCUMENTATION 11. REPORT NO. 2. 3. Reclplenf. Ac:c88.lon No.
PAGE EPA/ROD/R09-93/088
4. Thle and Subth18 5. Report Date
SUPERFUND RECORD OF DECISION 03/31/93
San Gabriel Valley Area 1 (Operable Unit 2), CA 6.
Third Remedial Action
7. Author(.) 8. Performing Organization R.pt. No.
9. Performing Org.nlzatlon Name .nd Addr... 10 ProJ.ct Ta.klWork Unh No.
11. Contract(C) or Grant(G) No.
(C)
(G)
12. Sponsoring Organization Narne and Add,... 13. Type of Report & Period Cov.red
U.S. Environmental Protection Agency
401 M Street, S.W. 800/800
Washington, D.C. 20460 14.
15. Supplementary Note.
PB94-964524
16. Abstract (Llmh: 200 word.)
The San Gabriel Valley Area 1 (Operable Unit 2) site is part of a larger area of ground
water contamination located near the San Bernadino Border, in Los Angeles County,
California. This site is situated to the south of the Pomona Freeway and to the west
of the San Gabriel Freeway, and consists of low lying hills. Much of the OU is
utilized for flood control, and the Whittier Narrows Flood Control Dam serves as a
boundary between the adjacent San Gabriel and Central Basins. Two major rivers located
within the OU boundaries are the San Gabriel and Rio Hondo Rivers. Land use in the
area is mixed residential, commercial, recreational, and light industrial. The nearest
residential areas are South El Monte and South San Gabriel to the north and Montebello
and pico Rivera to the south. Currently, ground water from onsite production wells is
used for domestic, industrial, and agricultural purposes. In 1984, EPA investigations
detected VOC contamination and determined it was a direct result of past manufacturing,
cleaning, and degreasing operations in the area, in both ground water and surface water
in the San Gabriel Basin. Since impacted ground water must flow through the Whittier
Narrows before exiting the San Gabriel Basin, EPA designated the Whittier Narrows area
as one of six OUs for this site. 1988 and 1989 RODs addressed contamination at the
Richwood and Suburban OUs, respectively. This ROD focuses on evaluation of ground
(See Attached Page)
17. Document Analyala e. Dacrlptora
Record of Decision - San Gabriel Valley Area 1 (Operable Unit 2), CA
Third Remedial Action
Contaminated Medium: None
Key Contaminants: None
b. Identlfl.rsIOpen-Ended Term8
c. COSATI Field/Group
18. Avallabllhy Statement 19. Sacurhy Class (ThIs Report) 21. No. of Pages
None 44
20. Sacurhy Claes (Thl. Page) 22. Price
None
(See ANSI-Z39.18)
SNlnstructlons on RIVlrB6
OPTIONAL FORM 272 (4-77)
(Form.rly NTI5-35)
Department of Comm.rce
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EPA/ROD/R09-93/088
San Gabriel Valley Area 1 (Operable Unit 2), CA
Third Remedial Action
Abstract (Continued)
water contamination potentially flowing from within the San Gabriel (Areas 1-4) Superfund
site into the Whittier Narrows Area, and subsequently into the Central Basin, as OU2.
Future RODs will address the remaining three OUs, which all are located upgradient of this
site, and include the Baldwin Park OU, Puente Valley OU, and South El Monte OU. Based on
monitoring data and risk assessments conducted as part of the RI/FS, EPA has determined
that the risk level of the contaminants in the OU falls well within EPA's acceptable risk
range; therefore there are no contaminants of concern affecting this site.
The selected remedial action for this site is no action, with ground water monitoring.
Site investigations have confirmed that contaminants within OU2 currently pose no risk to
human health and the environment. The estimated present worth cost for this remedial
action is $5,200,000.
PERFORMANCE STANDARDS OR GOALS:
Not applicable.
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.RECORD OF DECISION
"MONITORING ONLY" (NO ACTION) ALTERNATIVE SELECTION
DECLARATION
SI-TE NAME AND LOCATION
Whittier Narrows Operable Unit
San Gabriel Valley Superfund Site, Areas 1 through 4
Los Angeles County, California
STATEMENT OF BASIS AND PURPOSE
This decision document represents the selection of the "Monitoring
Only" Alternative for the Whittier Narrows Operable Unit in Los
Angeles County, California, one of six operable units for the San
Gabriel Valley Superfund Site, Areas 1 through 4. This decision
was made in accordance with the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980 (CERCLA), as
amended by the Superfund Amendments and Reauthorization Act of 1986
(SARA), and the National Contingency Plan (NCP). This decision is
based on the Administrative Record File for this operable unit.
The State of California concurs with this.decision.
DESCRIPTION'OF THE "MONITORING ONLY" (NO ACTION) ALTERNATIVE
The "Monitoring Only" Alternative selected for the Whittier Narrows
Operable Unit will include the installation of up to nine
additional multiport or cluster groundwater monitoring wells plus
approximately eight single point wells. The installation of these
additional wells will enhance the existing groundwater monitoring
network at the operable unit. Sampling and analysis of groundwater
from the new monitoring wells will be conducted quarterly for one
year, then adjusted upon review of validated analytical results and
seasonal fluctuations. The current sampling and analysis schedule
will be followed for the existing groundwater monitoring network
(and will also be adjusted pursuant to validated analytical results
and seasonal fluctuations as necessary). In addition to the
installation of new monitoring wells, well logging and depth-
specific sampling will be performed at approximately ten production
wells located within the Whittier Narrows area. Additional well
logging and depth specific sampling may be required depending on
the results of the depth specific sampling of the initial ten
wells. New groundwater monitoring wells will be installed using
a phased approach. The "A" priority multiport wells and the single
point wells will be installed as a first phase, most of which are
located along the northern boundary of the operable unit. The "B"
priority multiport wells, if needed, will be installed as a second
phase, after monitoring results are evaluated from the "A" priority
multiport wells, the single depth wells and local water level
measurements:
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DECLARATION
Based on the currently available data, no remedial action is
necessary to ensure protection of human health and the environment.
Because future groundwater conditions within the operable unit may
change as groundwater flows through the area, the groundwater will
continue tb be monitored and results evaluated, in an annual
summary report, to verify continued protection of human health and
the environment. A five-year review will be performed for the
Whittier Narrows Operable Unit, at which time more information on
factors affecting the groundwater quality within the operable unit
will be available, and EPA's decision will be revisited. The five-
year period to be used for the review will start when field work
(installation of monitoring wells) commences.
John^Wise, Acting Regional Administrator
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1.0
RECORD 01' DECISION
''KOHrlORDIG ONLY" (BO AC'.rIOB) ALTERDTrvB SELBCTION
DBCISION SUHHARY
OPERABLE UNIT NAME. LOCATION. AND DESCRIPTION
1.1
OPERABLE UNIT NAME
Whittier Narrows Operable Unit
San Gabriel Valley Superfund site, Areas 1 through 4
Los Angeles County, California
1.2
OPERABLE UNIT LOCATION
The Whittier Narrows Operable Unit (OU) is located in Southern
.-- ." - California in eastern Los Angeles County near the San
Bernardino County border as shown in Figure 1. The OU area is
situated primarily to the south of State Route 60 (the Pomona
Freeway) and mostly to the west of Interstate Route 605 (the
San Gabriel River Freeway). The OU is bisected by Rosemead
Boulevard. The nearest residential areas are South El Monte
and South San Gabriel to the north and Montebello and Pico
Rivera to the south.
. .
1.3
OPERABLE UNIT DESCRIPTION
The San Gabriel Valley Superfund Site, Areas 1-4, consists of
large areas of groundwater contamination from many sources.
The groundwater is contaminated mainly with various volatile
organic compounds, such as trichloroethene (TCE) and
tetrachloroethene (PCE) that have been used in manufacturing
processes and in cleaning and deqreasing operations.
The OU consists of the area between the 1-1/2-mile-wide gap in
the low lying hills, that serves as the boundary between the
.San Gabriel Basin and the Central Basin. This area
constitutes the southernmost portion of the San Gabriel Valley
Superfund site, Areas 1 through 4, to the Pomona Freeway (see
Figure 2). The OU is bordered on the west and northwest by
the Montebello Hills and on the east and southeast by the
Puente Hills. .
The San Gabriel River and Rio Hondo River are two major rivers
located within the OU boundaries. Much of the OU is used for
flood control, with compatible secondary uses such as golf
courses, equestrian areas, camp grounds, and recreational
parks. The Whittier Narrows Flood Control Dam is the
designated boundary between the San Gabriel Basin and Central
Basin (see Figure 2). Other land use in the OU consists of
residential, commercial, or light industrial. Most of the
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RAYMOND
BASIN
u
SAN GABRIEL BASIN
UPPER SAf>
WHITTIER NARROWS
LOS
ANGELES
QROUNDWATER
RECHARGE AREAS -
NOT TO SCALE
CENTRAL
BASIN
WEST COAST
BASIN *.
MONTEBELLO
FOREBAY AREA
L-_ _%£< ^ _ _c_ _ _~L:
ORANGE COUNTY
GROUNDWATER
ALLUVIUM AND ASSOCIATED OCPOSlTS
OF RECENT OR PLEISTOCENE ACE
SEDIMENTARY ROCKS OF MARINE ORIGIN,
MAINLY TERTIARY WITH SOME CRETACEOUS
m ....... fc "'U CRYSTALLINE AND METAMORPHIC ROCKS,
I j _. » J JURASSIC OR OLDER; SOME TERTIARY ROCKS
FIGURE 1
LOCATION MAP
WHITTIER NARROWS OPERABLE UNIT
FEASIBILITY STUDY
(SOURCE: CDWR, 1966)
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U)
\T^ E;
. ARpR
S SI*E
V GROU
XWHITTIER NARROWS OPERABLE UNIT
AND SURROUNDING AREA ,-"^ " "
OPERABLE UNIT FEASIBILITY
STUDY REPORT /i
new- Y ,>^\:J » i*;--
^-l:.^' -r B'nStfr-t)
WHITTIER NARROWS
•i$f i ri
L/kO69126.tV01
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area that is not restricted to flood control or recreation is
fully developed (these areas are limited to the extreme
northeast portion of the OU.
Groundwater, from 14 production wells, is currently used for
domestic, industrial, and agricultural purposes.
1.3.1 Geolocry
Whittier Narrows was formed by erosion, faulting, and
subsequent filling with alluvium of a gap between the
Montebello Hills to the west and the Puente Hills to the
east.
The San Gabriel Mountains form the northern boundary of
the San Gabriel Basin and range from 900 feet at the base
to over 10,000 feet above mean sea level (msl) in
elevation. The San Gabriel Mountains are comprised
primarily of Cretaceous and older rocks including quartz
diorite, granite, gneiss, schist, and associated dikes
and inclusions. The Repetto, Merced, Puente, Montebello,
and San Jose Hills bound the basin along the southwest
and southeast. These hills are composed of primarily
Tertiary marine sedimentary rocks consisting of
sandstone, siltstone, and shale locally interbedded with
conglomerate and cut by volcanic dikes.
The San Gabriel Basin is a broad piedmont plain with an
average slope of about 65 feet per mile. Ground surface
elevations range front about 900 feet above msl in the
north to about 200 feet above msl at Whittier Narrows
Dam. The basin contains alluvium and assorted deposits
of Recent and Pleistocene age. The San Gabriel Mountains
and, to a lesser extent, the flanking low hills are the
sources of the basin-fill sediments, which reach a
maximum depth of approximately 4,000 feet in the
southwestern portion of the basin.
Sedimentary rocks of the Quaternary and Tertiary age
occur in the northeastern portion of the Central Basin
(the area referred to as the Montebello Forebay) . These
rocks are categorized as either alluvium, sediments of
the Upper and Lower Pleistocene age, or sediments of the
Tertiary age. The alluvium is primarily unconsolidated
gravel, sand, and silt deposited by streams. Alluvium
generally occurs from the ground surface to about 100 to
200 feet below ground surface (bgs). The sediments
underlying the alluvium consist of the Lakewood and San
Pedro Formations and are of the Upper and Lower
Pleistocene Age. The Lakewood Formation is generally
comprised of gravel, sand, silt, and clay, and occurs
from about 100 feet bgs to 250 feet bgs. The San Pedro
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--- .--
Formation is composed of stratified sand with some beds
of fine gravel, silty sand, and silt. The San Pedro
Formation occurs from about 200 feet bgs to about 900
feet bgs. Sediments in the San Pedro Formation are
offset more by faults than in the Lakewood Formation
sedimen"ts. Except for the geologic faults, which offset
these formations, the stratigraphy within the OU is
generally ~lat lying.
Tertiary rocks in the Whittier Narrows are divided into
the P ico and Repetto Formations, older sediments and
volcanic rocks, and other undifferentiated rocks. The
Pico Formation is composed of sand, silt, and clay of .
marine origin, interbedded with gravels. Layers of
gravel and sand range in thickness from 20 to 100 feet
and are interbedded with micaceous siltstone and clay.
The Repetto Formation is generally composed of siltstone
with layers of sandstone and conglomerate. The older
sedimentary rocks include the Puente Formation, which
contains mostly siltstone and shale, with lesser amounts
of sandstone and conglomerate. The Topanga Formation
also occurs in the Central Basin area and consists of
shale, sandstone, and conglomerate. Volcanic rocks
include calcic andesite flows, tuffs, and volcanic
breccias. The volcan~c rocks are interbedded wi th
se~inientary rocks of the Topanga Formation in some areas.
Compared to the rest of the San Gabriel Basin, the
geology of the Whittier Narrows is relatively well
characterized to depths of at least 400 feet because of
the density of well logs. oil wells to the west and
water wells to the east are particularly abundant in the
vicinity of the Whittier Narrows Dam, and water wells are
somewhat abundant a1ong"the San Gabriel River and Rio
Hondo River below the dam. At greater depths,." the
geology is generalized and well logs must be examined
individually for local details. Several very thick
(several hundred feet) clay and gravel layers occur
. locally at depths greater than 400 to 500 feet bgs, based
on data from a limited number of very deep wells.
1.3.2 Hvdroqeoloqy
The San Gabriel Basin aquifer consists of the alluvial
sediments deposited in the San Gabriel Basin. Over 300
production wells pump over 200,000 acre-feet per year of
groundwater from the San Gabriel Basin.
In the Central Basin, the aquifers of the Lakewood and
San Pedro Formations are in places separated by low-
permeability materials. In stratigraphic order, these
aquifers are: the Gaspur-Ballona, Exposition-Artesian,
5
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Gardena-Gage, Hollydale, Jefferson. Lynwood, Silverado,
and Sunnyside. The lateral and vertical extent of clay,
silt, and sandy-clay layers is poorly defined. In some
areas, individual aquifers in the Lakewood arid San Pedro
Formations are not separated by low-permeability
materials and may directly overlie each other. However,
between the Silverado and Sunnyside aquifers of the San
Pedro Formation, a layer of low-permeability materials
exists that is laterally continuous over much of the
Whittier Narrows area and the northeastern portion of the
Central Basin.
Aquifers in the Whittier Narrows occur in the alluvium in
addition to the Lakewood and San Pedro Formations. The
formations older than the San Pedro Formation typically
have very few production wells.
Available well logs indicate that Whittier Narrows and
the adjacent part of the Montebello Forebay have the same
general characteristics of the San Gabriel aquifer (i.e.,
discontinuous inter finger ing lenses of alluvial deposits)
with typical yields of 500 gallons per minute or greater.
Zones producing groundwater to wells in Whittier Narrows
are generally composed of sand and gravel. These zones
may be laterally continuous with aquifers of the Lakewood
and San Pedro Formations in the Central Basin. These
aquifers are generally flat-lying, except for the area
adjacent to the Rio Hondo and Pico fault systems.
The geologic materials in the Whittier Narrows vary from
clay to gravel over short distances, and the hydraulic
conductivity is expected to vary by several orders of
magnitude within the vertical interval that a well may
penetrate. Hydraulic conductivity values estimated from
aquifer tests in the Whittier Narrows range from near one
feet per day to over 1,000 feet per day.
In the San Gabriel Basin, estimates of specific yield
based on well logs, range from 3 percent near the
peripheral areas of the basin to 24 percent in the
central portion of the basin. Values of specific yield
are greater near the mountains and in the center of the
basin where the clay content of the alluvium is small.
This analysis indicates that the specific yield within
the Whittier Narrows ranges from 10 to 20 percent.
Groundwater pumping in Whittier Narrows for potable water
uses occurs at the City of Whittier and Suburban Water
Systems well fields. These wells have produced an
average of 16,000 acre-feet per year of groundwater from
1977 to 1990.
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2.0
OPERABLE UNIT HISTORY AND ENFORCEMENT ACTIVITIES
The u.S. Environmental Protection Agency (EPA) identified the San
Gabriel Valley as a Superfund site due to the detection of a
variety of:'volatile organic contaminants in' the groundwater and
surface waters in'the San Gabr~el Basin and the risk or potential
risk to people consuming the water. EPA listed this site as the
San Gabriel Valley Superfund Site, Areas 1 through 4, on the
National Priorities List in 1984.
Since impacted groundwater from sources within the San' Gabriel
Valley Superfund Site, Areas 1 through 4, must first flow through
the Whittier Narrows before exiting the San Gabriel Basin, EPA
identified the Whittier Narrows as an operable unit to address
groundwater contamination potentially flowing into the Central
Basin. EPA evaluated .groundwater quality data within the OU to
de..termine what risks are posed by groundwater conditions within the
OU to determine if it is necessary to limit or control the
migration of impacted groundwater through the Whittier Narrows.
Whi ttier Narrows is one of six OUs (see page 8) that EPA has
designated for investigation in the San Gabriel Valley.
EPA is pursuing overall remediation of the San Gabriel Valley
Superfund Site, Areas 1 through 4, at, two levels: 1) via a
Superfund ~~operative Agreement with the-Los Angeles Regional Water
Quality Control Board (LARWQCB). The LARWQCB is the lead agency for
investigations and 'remediation of soil and shallow groundwater at
individual facilities (source investigations) throughout the San
Gabriel Basin, and 2) EPA-lead investigations and remediation of
deeper, regional groundwater contamination potentially originating
from multiple facilities. These two elements are being implemented
concurrently within the San Gabriel Basin.
To date,. Qver 300 General Notice letters have been issued, by EPA,
to potentially responsible parties throughout the San Gabriel
Valley. special Notice letters will be issued for the Baldwin Park
and Puente Valley OUs in 1993.
EPA had previously prepared a Feasibility Study for Whi ttier
Narrows in 1989 which evaluated various remedial alternatives,
based on computer modeling predictions of increasing contamination
levels in Whittier Narrows. Subsequent groundwater monitoring did
not support these modeling predictions. Based on the groundwater
monitoring data and the hydrogeologic complexity of the area, EPA
has decided that it will no longer rely on. computer modeling for
predicting future contamination levels in this OU. (See EPA
response to general comment #11 in Responsiveness summary)
7
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3.0 HIGHLIGHTS OF COMMUNITY PARTICIPATION
The Feasibility Study Report and Proposed Plan for the Whittier
Narrows Operable Unit were released to the public in September
1992. These two documents were made available to the public in
both the administrative record file and an information repository
maintained at the EPA Docket Room in Region 9 and at the Whittier
Central Public Library. The notice of availability for these two
documents was published in the Los Angeles Times on September 15,
1992. A public comment period was held from September 16, 1992
through November 16, 1992. In addition, a public meeting was held
on September 23, 1992. At this meeting, representatives from the
U.S. Environmental Protection Agency, Region 9 answered questions
about the OU and the "monitoring only" alternative under
consideration. Following the meeting, written comments were
received from state and local agencies only, not private citizens.
A response to the comments received during this period is included
in_ the Responsiveness Summary, which is part of this Record of
Decision. This decision document presents the "monitoring only"
alternative selected for the Whittier Narrows Operable Unit, in Los
Angeles County, California, chosen in accordance with CERCLA, as
amended by SARA, and the NCP. The decision for this OU is based on
the administrative record.
4.0 SCOPE AND ROLE OF THE OPERABLE UNIT
The term "Operable Unit" is used to define a discrete action that
is an incremental step toward a comprehensive site remedy.
Operable Units may address certain geographical areas, specific
site problems, initial phases of a remedy, or a set of actions over
time.
This operable unit was identified, in accordance with the NCP, to
address groundwater contamination in the Whittier Narrows area and
potentially flowing from the San Gabriel Valley Superfund Site,
Areas l through 4, through Whittier Narrows, and into the Central
Basin. Source identification and control investigations are
currently being performed by the State of California and are not a
part of this Record of Decision.
The objective of this OU is to evaluate groundwater quality data
within the Whittier Narrows Operable Unit to determine what risks,
if any, are posed by groundwater conditions and, if necessary,
limit or control the migration of impacted groundwater through
Whittier Narrows.
As with many Superfund sites, the investigation at the San Gabriel
Valley Superfund Site, Areas 1 through 4, is complex. As a result,
EPA has organized the groundwater investigation into six distinct
operable units to date: Whittier Narrows OU, Richwood OU, Suburban
OU, Baldwin Park OU, Puente Valley OU, and South El Monte OU. The
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Suburban OU is adjacent to the Whittier Narrows OU, while the
remaining OUs are hydraulically upgradient of Whittier Narrows.
Records of Decision were signed for the Richwood and Suburban OUs
in 1988 and 1989, respectively. The Suburban OU Record of Decision
is currently being amended to reflect current groundwater
conditions of low-level contamination in Whittier Narrows. A
Record of Decision for the Baldwin Park OU is scheduled to be
signed by EPA in 1993.
5.0 SUMMARY OF OPERABLE UNIT CHARACTERISTICS
Table 1 lists the chemicals of potential concern, identified for
the groundwater within the Whittier Narrows OU. Groundwater within
the Whittier Narrows OU appears to be impacted mainly from sources
located hydraulically upgradient from the OU. The LARWQCB however,
has identified some potential sources within the Whittier Narrows
OU and is currently investigating them. Potential routes of human
exposure include the use of groundwater for domestic, industrial,
and agricultural purposes, and volatilization through soil.
Potential routes of environmental exposure include groundwater from
production wells used for irrigation and other nondrinking water
purposes.
6.0 SUMMARY OF RISKS
The information presented in this section is a summary of the
Screening Baseline Risk Assessment performed for the Whittier
Narrows OU and can be found, in its entirety, in the Public Review
Draft. Whittier Narrows Operable Unit Feasibility Study. San
Gabriel Basin, Los Angeles County California located at the
information repositories at EPA Region 9 and the Whittier Central
Public Library.
6.1 HUMAN HEALTH RISKS
The media of concern for this OU is groundwater. Table 2
lists the contaminants of potential concern along with the
mean, maximum, and minimum concentrations detected in
groundwater samples obtained at the wellhead for production
wells screened over multiple intervals and from discrete
intervals in the aquifer from two multiport monitoring wells
and four single point monitoring wells.
Exposure to contaminants in groundwater could occur through
the use of groundwater for domestic purposes. In residences,
people can be exposed to contaminants from ingestion of water
used for drinking and cooking. They can also be exposed
through dermal absorption of contaminants, primarily during
bathing and showering, and inhalation of volatile organic
compounds (VOCs) released from the water into the household
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Table 1
CheD1icals of Potential Concern in Groundwater
Whittier Narrows Operable Unit.
-
Chemical Name
Chloroform
1,1- Dichloroethane
1,1- Dichloroethene
cis-1,2- Dichloroethene
Ethylbenzene
Styrene
T etrachloroethene
Toluene
1,1,1- Trichloroethane
Trichloroethene ..
-- -
- - - . Xylene
10
.;\
. .
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Table 2
Chemicals of Potential Concern in Groundwater
Mean, Maximum, and Minimum Concentrations Detected
- Whittier Narrows Operable Unit
Chemical Name
Chloroform
1, 1-Dichloroethane
1, 1-Dichloroethene
cis-1,2-
Dichloroethene
Ethylbenzene
Styrene
Tetrachloroethene.
Toluene
1,1,1-
Trichloroethane
Trichloroethene
Xylene
# Detected/
# Sampled*
1/49
14/51
11/56
23/29
4/49
2/37
43/67
4/49
5/53
37/63
2/49
Concentration (ug/1)
Arithmetic
Mean*
0.4
0.4
0.4
2.5
0.9
0.5
1.1
0.9
0.5
1.4
1.4
Maximum
Detected
0.3
0.6
1.0
6.1
20.0
0.6
7.0
2.8
2.2
7.0
22.0
Minimum
Detected
0.3
0.2
0.2
0.5
0.3
0.5
0.3
0.3
0.2
0.2
4.0
Drinking
Water
Standard
100
5
6
6
680
100
5
1,000
200
5
1,750
' Duplicate/split samples were averaged before summary statistics were calculated.
" The arithmetic mean was calculated using actual detected values and 1/2 the
detection limit for those sampling events where the chemical was not detected.
11
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air d~ring showering, bathing, cooking, or by use of household
appliances such as dishwashers. Exposure to contaminants in
groundwater could also occur through use of groundwater for
industrial purposes. Workers could be exposed through dermal
absorption of contaminants or inhalation of VOCs.
Residents and workers could also be exposed to contaminants in
groundwater through transport of VOCs from groundwater through
soil and into ambient air or into the foundation of a
building.
Additionally, groundwater from two production wells within the
OU is used to fill three manmade lakes in the Whittier Narrows
Recreation Area. Individuals may be exposed to contaminants
in the surface water through inhalation of VOCs or through
ingestion of fish. Because swimming is not allowed in these
lakes, ingestion of lake water by individuals was not
._- .-.-considered. .
Based on potential exposure frequency, duration, and estimated
intake exposures, residents exposed to contaminated
groundwater used for domestic purposes are expected to be the
maximally exposed population.
The estimated size of the exposedp.opulation in the Whittier
NarrotfS-OU is 99,400, based. on the number of individuals
. provided drinking water from production wells located within
the OU. .
Table 3 presents the intake assumptions used to estimate the
average and reasonable maximum exposure to chemicals in
groundwater used for domestic purposes.
6.2
TOXICITY ASSESSMENT
Toxic response depends on the dose or concentration of the
substance. Toxicity values are a quantitative expression of
the dose-response relationship for a chemical. Toxicity
values take the form of reference doses (RfDs) for
noncarcinogenic effects and cancer slope factors (CSFs) for
carcinogenic effects. Both RfDs and CSFs are specific to the
exposure route.
RfDs have been developed by the EPA for indicating the
potential for adverse health effects from exposure to
chemicals exhibiting noncarcinogenic effects. RfDs, which are
usually expressed in units of milligrams per kilogram per day
(mg/kg-day), are estimates of lifetime daily exposure levels
that should not pose an adverse health effect for humans,
including sensitive individuals. Estimated intakes of
chemicals from environmental media (e. g., the amount of
chemical ingested from contaminated drinking water) can be
12
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compared to the Rf D. Rf Ds are derived from human
epidemiological studies or animal studies to which uncertainty
factors have been applied (e.g., to account for the use of
animal data to predict effects on humans). These uncertainty
factors help ensure that RfDs will riot underestimate the
potential for adverse noncarcinogenic effects to occur.
The dose-response relationship for carcinogens is expressed as
a CSF. Generally, the slope factor is a plausible upper-bound
estimate of a response per unit intake of a chemical over a
lifetime. The approach used to estimate the slope factor from
animal studies or human data assumes a dose-response
relationship with no threshold (i.e., even the smallest
exposure may produce a carcinogenic response). There is
uncertainty and conservatism built into the risk extrapolation
approach (where results of animal and human studies are
applied to the human population). Cancer risks estimated by
this method produce an estimate that provides a rough but
plausible upper limit of risk (i.e., it is not likely that the
true risk would be much more than the estimated risk, but it
could be considerably lower).
Table 4 presents the RfDs and CSFs for the contaminants of
potential concern.
6.3 RISK-CHARACTERIZATION •
* • ^
Excess lifetime cancer risks are determined by multiplying the
intake level with the CSF. These risks are probabilities that
are generally expressed in scientific notation (e.g., IxlO"6).
An excess lifetime cancer risk of IxlO"6 indicates that, as a
plausible upper bound, an individual has a one in a million
chance of developing cancer as a result of a site-related
exposure to a carcinogen over a 70-year lifetime under the
specific exposure conditions of a site. EPA's acceptable risk
range is 10~4 to 10~6, meaning 1 in 10,000 to 1 in 1,000,000
chance of excess cancer.
Potential concern for noncarcinogenic effects of a single
contaminant in a single medium is expressed as a hazard
quotient (HQ) (or the ratio of the estimated intake derived
from the contaminant concentration in a given medium to the
contaminant's RfD). By adding the HQs for all contaminants
within a medium or across all media to which a given
population may reasonably be exposed, the Hazard Index (HI)
can be generated. The HI provides a useful reference point
for gauging the potential significance of multiple contaminant
exposures within a single medium or across media.
A summary of estimated risks for residential exposure to
groundwater from the Whittier Narrows OU is presented in Table
5 for noncarcinogenic effects and Table 6 for carcinogenic
13
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Table 3
Intake Assumptions Used In Future-Use Scenarios
.. Whittier Narrows Operable Unit
Intake Value (Adult)
Reasonable
Parameter Average Maximum
Ingestion Rate. 2 liter/day 2 liter/day
Body Weight 70 kg 70 kg
Exposure Frequency 350 days/year 350 days/year
Exposure Duration 9 years 30 years -.
Years in Lifetime 70 years 70 years
. .
. The dose from inhalation of VOCs is assumed to be equivalent to the dose from
ingestion of 2 liters/day.
. -..
14
-------
TihU«
DoM-RapooM VuUbla for Ckokab of Cooun
WUtthrNuTawiOpfnbUUuit
Cboaiul
Chloroform
l.t'Dichloroctninc
LI-DIchloroctbenc
ci»- 1 .2-Dichloroeih.ne
Einylbciucne
Slyrene
Tdnchlonxlh.rtt
TolutM
I.l.l-Trichloraillitn.
TrichlorocUum
XyleM
Srdfink Toricity '• ,
(mf^i/dir)
CfWulEffvl
Ljv«r
Ljv«r
Liv.r
Blood
Livtr, Kidney
Blood/Li v.r
Liv.r
CHI. l>«. Now, U«tr. Kldnty
Uvir
-
Liv.r. MOM, Taiott. CNS, Ftuuilclly
Onl
UD
0.01
O.I
0.0009
0.01
O.I
0.]
0.01
0.1
0.09
0.006
2.0
Sourtt
BUS
HEAST
EPA
HBAST
BUS
DUS
DIU
out
HEAST
ECAO
BUS
Ukiladoi
RfD
-
O.I
-
-
0.)
-
-
o.«
0.1
-
0.09
Soon*
DUS
HEAST
urn
ous
QUS
DU1
nu
HEAST
HEAST
OUS
HEAST •
Cuxinogmic rottnty •'•
(miWW
Tatar 9ti
Liv.r, KidMy
Mamnury, Uvtr
Kidney, Adnnil
-
-
Lunf, Bronchi, Uuk.mii
Uvir. Ltuktmlt
^
-
Lunf, Llv«r
-
Oral
Sop.
Factor
0.0061
-
-
-
•^. •
0.0)
0.051
-
-
O.'OII
-
Wdthlor
Efidaca*
Bl
C
C
O
0
B7
tl
0
D
B2
D
Soma
DUS
DUS
EPA
OUS
DUS
HEAST
HEA1T
DUS
OUS
HEAST
OUS
InKalflfjoQ
Soot
Factor
0.011
-
-
-
-
0.002
0.002
-
-
0.017
-
Wafhlof
Cridmct'
B2
C
C
D
O
B2
n
D
D
B2
D
Soarct
DUS
HEAST
EPA
PUS
' IRIS
HEAST
HEAST
out
DUS
HEAST
OUS
Hour.
HE AST • Hulih EffMU Autumnl Summiry Ttblti.
DtlS - InUf raud Riik InlbmuUoa Syium.
EPA • 1 , 1-DichloroclhCM it iviliuud tccordioj to t nud!fi«d-R(D tppro^d: Group C circlnof.ru which ixhibll wuk nUialt of utvino|iaiciljr in co Croopi: A It Humia Clrcli»t4o; B jl Prohibit Humu Ctrtioofto (Bl -limiUd tvidtnct of ctn!ao|cnkiiy la humicu. BJ-MilTKUM lt with budcqutu or lick of ividtnct in hunuiu): C it
Pouibli humia Cixinofin; D ii Not CUnifUblt it lo Humia Ctreinotiaiciljr.
-------
Table 5
Estimated Noncancer Hazard Quotients from !
Domestic Use of Groundwater*
Whittier Narrows Operable Unit
Chemical
Chloroform
1, 1-Dichloroelhane
1, 1-Dichloroelhene
cis-l ,2-Dichloroethene
Ethylbenzene
Styrene
Tetrachloroethene
Toluene
1,1,1-Trichloroethane
Trichloroethene
Xylene
//Detected/
^Sampled
1/49
14/51
11/56
23/29
4/49
2/37
43/67
4/49
5/53
37/63
2/49
Concentration (/tg/1)
*
Arithmetic
Mean
0.4
0.4
0.4
2.5
0,9
0.5
1.1
0.9
0.5
1.4
1.4
95 Percent
UCLk
0.4
0.4
0.5
3.2
1.3
0.5
1.3
1.2
0.6
1.8
2.3
Total Hazard Index
Average Exposure
Ingestion
0.001
0.0001
0.01
0.007
0.0002
0.00007
0.003
0.0001
0.0002
0.006
0.00002
0.03
Inhalation
0.001
0.0001
0.01
0.007
0.00008
0.00007
0.003
0.00004
0.00005
0.006
0.0004
0.03
Reasonable Maximum
Exposure • .
Ingestion
0.001
0.0001
0.02
0.009
0.0004
0.00007
0.004
0.0002
0.0002
0.008
0.00003
0.04
Inhalation
0.001
0.0001
0.02
0.009
0.0001
0.00007
0.004
0.00005
0.00005
0.008
0.0007
0.04
' Exposure assumptions used are shown in Table 3. .
b 95 Percent Upper Confidence Limit.
-------
Table 6
Estimated Excess Lifetime Cancer Risk from '
Domestic Use of Groundwater*
YVhittier Narrows Operable Unit
Chemical
Chloroform
1,1-Dichloroethane
1 , 1 -Dichloroelhene
cis-l,2-Dichloroethene
Eihylbcnz<;ne
Styrene
Telrachloroethene
Toluene
1,1,1 -Trichloroelhane
Trichloroelhene
Xylene
^Detected/
^Sampled
1/49
14/51
11/56
23/29
4/49
2/37
43/67
4/49
5/53
37/63
2/49
Concentration (jig/1)
Arithmetic
Mean
0.4
0.4
0.4
2.5
0.9
0.5
1.1
0.9
0.5
1.4
1.4
95
Percent
UCL>
0.4
0.4
0.5
3.2
1.3
0.5
1.3
1.2
0.6
1.8
2.3
Total Cancer Risk
' . Average Exposure
Ingestion
9x 10-'
*«
--
--
--
5 x 10'
2 x 10'r
--
-- •
5 x 10*
«
3 x 10'7
Inhalation
1 x 1
-------
risk.
For average ingestion and inhalation exposures from the
domestic use of tap water, the sum of the noncancer HQs is
0.Q3 for each route. The HI, based on an average exposure
scenario, is.0.06. For the reasonable maximum exposure (RME)
to groundwater from the domestic use of .tap water, the sum of
the noncancer HQs is 0.04 for each route. The overall
noncancer HI from RME to groundwater in the Whittier Narrows
is 0.09, well below the level of concern for potential
noncancer health effects. When the HI exceeds 1 (i.e., intake
exceeds RfD), there is a potential for health concern.
The estimated excess lifetime cancer risks for average
ingestion and inhalation exposures to tap water are 3x10-7 and
2xlO-7 , respectively. The total estimated excess lifetime
cancer risk for average residential exposure through domestic
--- _--use of groundwater is 5X10-7. The estimate lifetime cancer
risk for RME from tap water are 1x10-6 for ingestion exposures
and 8X10-7 for inhalation exposures. The total estimated
excess lifetime cancer risk for the residential RME through
domestic use of groundwater is 2X10-6 which is at the lower
end of EPA's acceptable risk "target range" of 10-4 - 10-6.
~:-.._~.~ ]:,
uncertainties
uncertainties associated with this screening are due to
uncertainties in the risk assessment process in general
(i.e., the toxicological data base), specific
uncertainties in characterizing the site, and
uncertainties associated with describing exposures.
EPA's risk assessment is conservative in nature and
attempts to account for concentrations by typically
overestimatinq rather than underestimating risks in order
to ensure adequate protection of public health.
Therefore, actual risks are likely to be lower (if they
exist at all) than estimated risks. This screening risk
assessment is subject to uncertainty from a variety of
sources including:
.
.
Sampling and Analysis
Fate and transport .
Exposure estimation
Toxicological data
.
.
Uncertainty associated with sampling and analysis include
the inherent variability (standard error) in the
analysis , representativeness of the samples, sampling
errors, and heterogeneity of the sample matrix.
This
screening
risk
assessment
makes
simplifying
18
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assumptions about the environmental fate and transport of
the site contaminants, specifically, that no contaminant
loss or transformation occurred. The assessment also
assumes that the chemical concentrations detected in
groundwater remain constant during the assessed exposure
duration. The choice of data to represent exposure point
concentrations is an additional source of potential
error.
In addition, the screening risk assessment focuses only
on VOCs detected in groundwater in the Whittier Narrows
OU. Other chemicals present in the groundwater, such as
inorganics, may present an additional health risk not
addressed in the assessment.
The estimation of exposure requires numerous assumptions
to describe potential exposure situations. There are a
number of uncertainties regarding the likelihood of
exposure, frequency of contact with contaminated media,
the concentration of contaminants at exposure points, and
the time period exposure. Assumptions used in this risk
assessment tend to simplify and approximate actual site
conditions.
The toxicological data base is also a source of
Uncertainty. These uncertainties include, extrapolation
from high to low doses and from animals to humans;
species, gender, age, and strain differences in uptake,
metabolism, organ distribution, and target site
susceptibility; and human population variability with
respect to diet, environment, activity patterns, and
cultural factors.
6.3.2 Summary of Risks
Eleven VOCs were detected in groundwater from production
and monitoring wells located within the Whittier Narrows
OU. Human populations potentially exposed to VOCs
present in the groundwater include individuals using the
groundwater for domestic, industrial, and recreational
purposes. The exposure scenario evaluated assumes a
resident would come in contact with groundwater through
domestic use of tap water. Based on potential for
exposure frequency, duration, and estimated intake,
residents exposed to contaminated groundwater used for
domestic purposes are expected to be the maximally
exposed population.
The groundwater exposure scenario was evaluated by
estimating the noncarcinogenic and carcinogenic risks
associated with it. The noncarcinogenic exposure levels
do not exceed the corresponding RfDs for individual
19
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contaminants of potential concern. The sum of the
noncancer HQs for the contaminants of potential concern
is 0.06 for the average exposure scenario and 0.08 for
the RME scenario, both below the level of concern for
noncancer health effects. The estimated excess lifetime
cancer risk for residential domestic use of groundwater
is 5xlO~7 for the average exposure scenario and 2xlO~6
for the RME scenario. In general, EPA uses 10~6 to 10"4
as its "target range" within which EPA strives to manage
risks as part of a Superfund cleanup. Estimated excess
lifetime cancer risks for residential domestic use of
groundwater fall below this range for the average
exposure scenario and at the lower end of the target
range for the RME scenario.
6.4 ENVIRONMENTAL RISKS
Six VOCs were detected in groundwater from production wells in
the Whittier Narrows Nature Center and Rose Hills Memorial
Park. Groundwater from these production wells is currently
being used for irrigation and other nondrinking water
purposes. Potential environmental receptors include vegetation
and wildlife exposed to groundwater in these areas. The
detected VOCs will be removed from water primarily by
volatilization to the atmosphere. These VOCs are not expected
to significantly bioconcentrate in aquatic organisms or adsorb
to sediment. A comparison of concentrations detected in these
production wells to the corresponding chemical-specific acute
and chronic National Ambient Water Quality Criteria (AWQC)
shows that the AWQC are considerably higher (greater than 400
times) than the detected concentrations.
National Ambient Water Quality Criteria (AWQC) are published
by EPA under the Clean Water Act. If not exceeded, the
appropriate AWQC should protect most aquatic life and its uses
(Federal Register, Vol. 45, No. 231, November 28, 1980). The
freshwater AWQC for acute effects is 11,600 ug/1 for toluene.
There is no freshwater AWQC for acute effects for 1,1-DCA. The
freshwater AWQC for chronic effects is 20,000 ug/1 for 1,2-DCA
and 840 ug/1 for PCE. There is no chronic AWQC for
1,1-DCA, 1,1-DCE, TCE, or toluene. The acute and chronic
chemical-specific AWQC are considerably higher than the
concentrations detected in production wells in Rose Hills
Memorial Park in 1991 (maximum of 3 ug/1) and in the Whittier
Narrows Nature Center in 1987-1988 (less than 1 ug/1).
20
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7.0
DESCRIPTION OF THE "MONITORING ONLY" (NO ACTION)
ALTERNATIVE
As a general policy, EPA uses the results of the risk assessment to
establish .the need or basis for taking a' remedial action and
compares a "no action" alternative to several remedial (action)
alternatives. For this OU, the risk assessment established there
are currently no unaccepable risks present, therefore, no remedial
action and no comparison of remedial alternatives is necessary at
this time. .
Although the risk assessment has demonstrated that current risk at
the OU is well within EPA's acceptable risk range, EPA recognizes
that there is some degree of uncertainty as to the future
conditions at the OU. Therefore, EPA will continue the currently
operating groundwater monitoring network and supplement this
monitoring program with the instal~ation of up to nine additional
multiport or cluster - groundwater monitoring wells, plus
approximately eight single point wells, to gather groundwater data
where currently none exists. The new wells will be sampled for
inorganic and organic compounds. Design and construction of the
new monitoring wells will be consistent with current and potential
future remedial action goals of the basinwide Superfund project.
The approximate locations of the poten~~~l additional monitoring
wells are shown, in Figure 3. New well locations were selected to
fill data gaps in Whittier Narrows, to evaluate groundwater quality
entering Whittier Narrows, to evaluate local groundwater levels and
flow directions, and to serve as early warning wells for some
drinking water wells. Each new well will be a multiport well (if
more than three or four zones will be sampled, a cluster well (if
less than three or four zones are sampled), or a single depth well.
Figure 3 shows the approxiInate locations of the new wells. The
multiport wells have been designated as "A" priority and "B"
priority wells. The "A" wells, and the si,ngle point wells (at the
"B" priority locations) will be installed as a first phase in order
to fill data gaps downgradient of potential contaminant sources and
to establish some localized groundwater flow gradients. The "B"
wells, if needed, will be installed the following year, pending the
resul ts of local water level measurements and monitoring results of
the "A" wells and single point wells. The well logging and depth
specific sampling will be conducted concurrently (if technically
feasible) with the installation of the '''A'' priority wells and
single point wells.
In addition to the new monitoring wells, EPA will provide well
logging and depth-specific sampling of approximately ten existing
wells in the OU area. The locations of these wells are also shown
in Figure 3.
Validated monitoring data. will be shared with all interested
pat:ties. In addition, EPA will prepare an annual report summarizing
21
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the monitoring data collected from the expanded monitoring network.
This report will also be made available to all interested parties.
Should future conditions change to where an unacceptable risk is
present within the OU (i.e., a risk greater than 10~4, or if
operating" drinking water wells are threatened or impacted by
groundwater contamination from the San Gabriel Valley) then EPA is
prepared to take the appropriate response(s). Such response (s) may
include an accelerated feasibility study to determine an
appropriate remedial action and/or the need to install additional
monitoring wells, or, if response time is critical, a removal
action. CERCLA Section 104 authorizes removal responses whenever
any hazardous substance is released or there is a substantial
threat of such a release into the environment of any pollutant or
contaminant which may present an imminent and substantial danger to
the public health or welfare. In addition to requirements of CERCLA
and the NCP, EPA removal actions will be guided by, Superfund
Removal Procedures - Action Memorandum Guidance. dated
December,1990, and Interim Final Guidance on Numeric Removal Action
Levels at Contaminated Drinking Water Sites, OSWER Directive
9360.1-10, dated October 6, 1987. Also, removal action levels for
some chemicals have been revised in a (Draft) Final Guidance on
Numeric Removal Action Levels at Contaminated Drinking Water Sites.
that EPA is currently evaluating. This "Final" guidance will
replace the 1987 guidance once the evaluation has been completed.
If groundwater' data in the Whittier Narrows OU show an unacceptable
risk or a" trend towards an unacceptable risk, EPA will begin to
evaluate the appropriate location(s) for extraction and treatment
systems. For operating drinking water wells in the San Gabriel
Valley or the Central Basin that are unable to meet federal or
state drinking water standards due to San Gabriel Valley
contamination, EPA may determine that well head treatment or an
alternative drinking water supply is necessary. Depending upon
contamination levels, EPA may use its removal authority for
drinking water wells threatened or impacted by San Gabriel Valley
contamination because of the much quicker response time compared to
EPA's remedial authority.
The type of treatment will depend upon the contaminants present and
the pumping rates of the wells. However, based on treatment
systems in operation in the San Gabriel Valley and Central Basin,
liquid-phase Granular Activated Carbon (GAG) or air stripping may
be used. Air stripping systems may require off-gas treatment to
meet air quality standards. All treatment systems will be designed
to meet applicable or relevant and appropriate requirements
(ARARs).
Water reuse or disposal from new extraction systems will be
evaluated, and will largely depend upon extraction rates and the
location of the extraction system relative to the point(s) of use.
22
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The total present worth cost associated with the implementation and
operation and maintenance of phases A and B of the expanded
monitoring network, plus the cost of monitoring the existing,
network is approximately $ 5,200,000. This cost assumes a phased
installation approach with incremental costs discounted 5 percent
to the base year. Well installation is scheduled to begin in
fiscal year (FY) 93. The period to be used for the five-year
review will start when monitoring well installation begins.
23
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RECORD OF DECISION
"MONITORING ONLY11 (NO ACTION) ALTERNATIVE SELECTION
RESPONSIVENESS SUMMARY
Whittier Narrows Operable Unit
San.Gabriel Valley superfund Site/ Areas 1 through 4
Los Angeles County/ California
A. OVERVIEW
At the time of the public comment period, the US Environmental
Protection Agency (EPA) had identified a preferred alternative for
the Whittier Narrows Operable Unit, Los Angeles County, California.
EPA's recommended alternative ("monitoring only") addresses- the
need to expand the existing groundwater monitoring network at
Whittier Narrows to enhance the continued monitoring of groundwater
quality within the operable unit area. The preferred "monitoring
only" alternative, as specified in the Record of Decision, involves
the installation of additional multiport or cluster monitoring
wells and single point wells within the operable unit area, as well
as, additional depth-specific sampling and well logging of existing
production wells. EPA recommended the Whittier Narrows Operable
Unit for a five year review.
Additional monitoring work will also be performed by local agencies
of the San Gabriel and Central Basins. EPA is working with these
agencies to. coordinate field activities, and. to share and evaluate
monitoring-'data.
Judging from the comments received during the public meeting and
the public comment .period, concerned state and local agencies
strongly agreed with the need for an expanded monitoring network at
Whittier Narrows. Of major concern to these agencies was the
number and location of new monitoring wells proposed to be
installed and the proposed time frame recommended for their
installation. Many agencies expressed a desire to be more involved
in the design and implementation of the new monitoring network. In
addition, the agencies recommended that a contingency plan for
groundwater treatment be part of any Record of Decision. The
California Department of Toxic Substances Control (DTSC) expressed
the concern that EPA did not have sufficient data to characterize
the risk or to conclude that no remedial action was needed at this
time. DTSC was also concerned that the proposed monitoring system
may not provide early detection of contamination entering the OU
because of the large distances between the wells. DTSC recommended
that all field work be completed within a two year time frame. EPA
also received one comment letter (from a state agency) after the
close of the comment period. Since the letter was received after
the
close of the comment period, EPA is not required to respond in the
responsiveness summary. However, the main comment expressed in the
letter was a general agreement with the comments contained in the
comment letter submitted by the California Department of Toxic
Substances Control.
No written comments were received from private citizens during
-------
the public comment period. Oral comments received from private
citizens attending the public meeting concerned drinking water
quality at'the tap (i.e., color, turbidity, etc.) and were not
considered significant to the low-level volatile organic compound
groundwater contamination at this operable unit. These citizens
were referred to their local water purveyor.'
These sections follow:
.
Background on community Involvement.
.
Summary of Comments Received During PUblic Comment Period
and EPA Responses.
B.
BACKGROUND ON COMMUNITY INVOLVEMENT.
EPA identified the San Gabriel Valley as a Superfund site due to
the detection of a variety of organic contaminants in the
groundwater and surface waters in the San Gabriel Basin. The EPA
listed this srte as the San Gabriel Valley Superfund Site, Areas 1
through 4, on the National Priorities List in 1984. Because of the
large size and complexity of the San Gabriel Basin, EPA has
organized the groundwater investigation into six distinct Operable
Units (aU): Whittier Narrows OU, Richwood au, Suburban au, Baldwin
Park au, Puente Valley OU, and the Sout~ El Monte OU.
Contaminate"d groundwater from sources within the San Gabriel Valley
Superfund Site, Areas 1 through 4, must first flow through the
Whittier Narrows before exiting the San Gabriel Basin. EPA
identified the Whittier Narrows as an operable unit to evaluate
groundwater quality data within the OU to determine what risks are
posed by groundwater conditions within the OU and, if necessary,
limit or control the migration of impacted groundwater through the
Whittier Narrows.
EPA is pursuing overall remediation of the San Gabriel Valley
Superfund, site, Areas 1 through 4, at two levels: 1) in
cooperation with the Los Angeles Regional Water Quality Control
Board (LARWQCB), LARWQCB-lead investigations and remediation of
soil and shallow groundwater at individual facilities (source
investigations), and 2) EPA-lead investigation and remediation of
deeper, regional groundwater contamination potentially originating
from mUltiple facilities. These two elements are being implemented
concurrently within the San Gabriel Basin.
To date, over 300 General Notice letters have been issued, by EPA,
to potentially responsible parties throughout the San Gabriel
Valley. special Notice letters will be issued for the Baldwin Park
and Puente Valley OUs in 1993.
EPA had previously prepared a Feasibility Study for Whittier
Narrows in 1989, which evaluated various remedial alternatives,
based on computer modeling predictions of increasing contamination
2
-------
levels in Whittier Narrows. Subsequent groundwater monitoring did
not support these modeling predictions. Based on the groundwater
monitoring data and the hydrogeologic complexity of the area, EPA
had decided that is will no longer rely' on computer modeling for
predicting future contamination levels in this OU. (See EPA
response tc'~'general comment #11.) .
The Feasibility study Report and Proposed Plan for the Whittier
Narrows Operable Unit were released to the public in September
1992. These two documents were made available to the public in the
administrative record file at an information repository maintained
at the EPA Docket Room in Region 9 and at the Whittier Central
Public Library. The notice of availability for these two documents
was published in the Los Angeles Times on September 15, 1992.
This notice briefly described the proposed alternative and
announced the public comment period and the upcoming public
meeting. The notice also announced locations where the Whittier
N~~~QWS Operable Unit Feasibility Study (OUFS) report could be
reviewed. The OUFS report was located in the Whittier Central
Public Library and the EPA Region IX office in San Francisco.
EPA also prepared a 7-page fact sheet describing the Whittier
Narrows OUFS report and EPA's recommended alternative. Copies of
the fact sheet were mailed on September 14, 1992 to the general
mailing list for the San Gabriel Vall~y. Superfund site. This
general mail.ipg'list consisted, at the time, of approximately 1,955
names, inciuding elected officials, Potentially Responsible Parties
(PRPs), media representatives, and repres~ntatives of various
cities and water districts in the Central and San Gabriel Basins.
A public comment period was held from September 16, 1992 through
November 16, 1992. In addition, a public meeting was held on
September 23, 1992. At this meeting, representatives from the u.S.
Environmental Protection Agency, Region 9 answered questions about
the au and the "monitoring only" alternative under consideration.
A response to the comments received during this period is included
in this document, which is part of this Record of Decision. The
Record of Decision presents the "monitoring only" (no action)
alternative selected for the Whittier Narrows Operable unit, in Los
Angeles County, California, chosen in accordance with CERCLA, as
amended by SARA, and the NCP. The decision for this OU is based on
the administrative record.
3
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C.
SUMMARY OF COMMENTS RECEIVED DURING PUBLIC COMMENT PERIOD
Comments received during the Whittier Narrows Operable unit public
comment period for the Feasibility Study Report and Proposed Plan
are summar.ized briefly below. The comment'period was held from
September 16 to November 16, 1992. The comments are divided into
two categories: General Comments are those comments that pertain
to the general proj ect approach and were common to most of the
agencies submitting comments, unless otherwise stated; and Specific
Comments are comments that pertain to specific technical issues of
the Feasibility study or Proposed Plan.
GENERAL COMMENTS
1.
Most of the local agencies located in the San Gabriel and
Central Basins stated that EPA should continue to solicit
input from them regarding remedial acti vi ties in the
Whittier Narrows area. Many agencies suggested that EPA
designate one local agency to take the lead for
developing the design and implementation of new
monitoring wells. Many of these agencies also
recommended a second public meeting, to be located in the
Central Basin, to provide private citizens and local
agencies, within the Central Basin, a better forum for
~.~essing their comments and,"concerns.
EPA Response EPA considers one public meeting
,sufficient. Should the need arise, there will be other
opportunities for public input as described in EPA's
response to comment #2 below. Also, EPA is willing to
meet with interested parties to discuss the proposed
expanded monitoring network, and to meet and, discuss
monitoring results and potential modifications to the
monitoring network. EPA will retain the lead for the
design and installation of new monitoring wells and for
any remedial actions as part of the Whittier Narrows
Operable unit.
2.
Many of the agencies submitting comments recommended that
a contingency plan be included in the Proposed Plan for
the Whittier Narrows Operable Unit, since no remedial
actions have been identified. '
EPA Response - Based on the results of the continuing
groundwater monitoring effort and :the risk assessment for
the Whittier Narrows Operable unit, EPA has determined
that no remedial action is necessary at this time for the
continued protection of human health and the environment.
EPA rec6gnizes however, that there is some degree of
uncertainty as to the current condition in the au. In
the event that future groundwater monitoring results
within the operable unit change to where an unacceptable
4
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risk' (e.g. greater than 10-4) is present within the
operable unit, EPA is prepared to take the appropriate
response (s) . Potential response actions (such as an
accelerated feasibility study, additional monitoring well
installation, drinking water well-head treatment, or use
af EPA's removal authority) are described in the Record
of Decision for the Whittier Narrows Operable Unit. EPA
has met with the state and local agencies and has agreed
to continued discussions of trigger criteria and
potential contingency actions, outside of the framework
of the Record of Decision. However, the conunenters
should recognize that developing trigger criteria and
contingency actions will be very difficult because of
lack of information regarding where contamination sources
originated and where contamination may be found, the
specific contaminations that may be found, where
extraction systems will be located, what extraction rates
should be, and what to do with the treated groundwater.
EPA believes that there are too many uncertainties to
developing a contingency plan with any measureable degree
of accuracy. Before any remedial or non-time critical
removal actions are undertaken by EPA, there will be a
minimum of 30 days allowed for the general public to
comment on EPA's proposed actions.
3.
Water generated from Whittie:r;' Narrows project-related
activities (i.e., spinner logging,' groundwater sampling,
etc.) should be put to the maximum beneficial use
possible.
4.
EPA Response - EPA concurs and will do so whenever it is
practicable. It should be noted that water from spinner
logging, if disposed of on the ground will recharge the
aquifer to a certain degree as the water percolates
through the ground into the aquifer.
Many of the agencies submitting comments stated that the
cost of assistance from local agencies or the costs
associated with treatment plants required on production
wells because of contamination from the San Gabriel
Valley should be reimbursable from the Superfund.
EPA Response - Unless there i.s a formal cooperati ve
Agreement between EPA and another agency, assistance
(including well-head treatment) provided by local
agencies is typically not reimbursed from Superfund. EPA
does however appreciate the cooperative efforts of the
local agencies, and may be able to provide guidance in
future to the local agencies on how to recover costs from
PRPs.
5.
Many of .the agencies submitting comments noted that
treatment of groundwater should consider both Federal and
State of California requirements and regulations.
5
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EPA Response - Any removal actions taken by EPA involving
treatment of groundwater, will comply with Federal,
state, and local applicable or relevant and appropriate
requirements (ARARs) to the extent practicable. Any
remedial actions involving treatment of groundwater will
comply with ARARs unless a formal waiver is deemed
necessary and justified by EPA. It should be noted
however, groundwater treatment was not formally evaluated
in the OUFS and Proposed Plan because groundwater
conditions and EPA's risk assessment do not indicate any
significant risks to human health or the environment.
6. The Proposed Plan does not provide sufficient security
that a remedial action will be undertaken in the Whittier
Narrows Operable Unit when warranted.
EPA Response - Although a remedial action is not
warranted at this time, EPA remains committed to take the
appropriate remedial or removal action, if and when
necessary. EPA intends to exercise its removal authority
if appropriate, if a situation arises that does not
permit the time required to adequately implement the
remedial action process. The removal action process is
described in the Record of Decision for the Whittier
Narrows Operable Unit and in the National Contingency
Plan (NCP). All EPA monitoring data from the Whittier
Narrows monitoring network will be made available to all
Interested parties. In addition, EPA is willing to meet
with interested parties to discuss groundwater quality
data and potential contingency measures. EPA believes
its remedial and removal authorities under CERCLA and the
NCP, combined with its commitment to share monitoring
data and to meet with interested parties, is sufficient
security that remedial action will be taken if warranted.
7. Many agencies commented that the technical basis for the
phased installation of the proposed new monitoring wells
has not been adequately described.
EPA Response - EPA feels it is not prudent to install
all the monitoring wells at this time, because installing
all of the proposed new monitoring wells right away may
lead to well locations that are not ideal. This approach
may lead to an inefficient monitoring network and may
lead to the placement of previously unneeded additional
wells, thereby increasing monitoring costs. On the other
hand, a phased installation approach allows for the
optimum placement of any succeeding wells once the
priority wells have been installed and analytical results
from these wells have been assessed. EPA has in
cooperation with state and local agencies, prioritized
the installation of the multiport wells as "A" and "B".
The "A" wells plus approximately eight single point wells
will be installed first. The "B" wells will be installed
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8.
after water level measurements have been taken
monitoring from the "A" wells has been evaluated.
anticipates both phases of the new wells will
installed in approximately a 2 year period.
Many' agencies commented that the approach described in
the proposed plan does not offer a 5-year early warning
system, as stated, but perhaps as little as 2-years.
and
EPA
be
9.
EPA Response - EPA believes there is at least a 5 year
warning period for groundwater contamination entering
Whi ttier Narrows from areas north of Highway 60. Of
course contamination already within Whittier Narrows
could reduce contamination travel time to the Central
Basin. The monitoring network, however, should be able
to detect this contamination and provide sufficient early
warning to take appropriate actions. The travel time
estimates are based on approximate continuous groundwater
flow times. Conservative groundwater flows were used in
these approximations. Furthermore, 'given EPA's removal
authority and its commitment to accelerate its remedial
process, EPA is confident that even a two year warning
will be sufficient to respond.
Many local agencies commented that a data gap is present
in the western segment of'the..Whittier Narrows that was
~~~'. c,onsidered in the proposed new monitoring network.
BPA Response - EPA has been meeting with and will
continue to meet with interested parties (e.g. ,state and
local agencies) to refine monitoring well locations. The
"final" monitoring well locations and prioritization of
the placement of the wells (shown in figure 3 of the ROD)
. were chosen by BPA and were based on comments received by
EPA. Actual field conditions and future monitoring
results however, may cause some monitoring wells to be
relocated from the locations depicted on figure 3 of the
ROD.
10.
Several local agencies stated that it is their
preliminary opinion that the source of contamination
(present above state, and federal maximum contaminant
levels) found in one well loca~ed in Pico Rivera is the
San Gabriel Valley.
EPA Response - The source of this contamination is not
clear. There are' potential source areas wi thin the
Central Basin which need to be evaluated. EPA is
currently working with a local agency to' investigate
potential sources in the pico Rivera area. Placement of
new monitoring wells, as part of the Whittier Narrows
Operable Unit Proposed Plan, may also assist in
evaluating the source of this contamination.
7
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11. Several agencies commented that the Feasibility Study for
the Whittier Narrows Operable Unit makes no attempt to
-forecast future groundwater conditions within the
Narrows. The study assumes that concentrations of
contaminants remain constant and, therefore, the health
risks remain constant. The technical basis for assuming
constant contamination concentrations in the future is
not adequately described. Past EPA analyses have
forecast rising contaminant levels in the Narrows.
EPA Response - Current monitoring results collected by
EPA have shown that contaminant levels within the
Whittier Narrows area have not risen according to past
predictions. Instead of an increase in contaminant
levels, there appears to be a decrease in contaminant
levels. Changing groundwater conditions may be affected
by many complex factors, including retardation and
natural attenuation of contamination, as well as
upgradient remedial activities and the elimination of
sources. EPA used groundwater modeling (computer
modeling) in an attempt to predict future groundwater
chemical contaminations. In order to be protective of
public health, very conservative assumptions were used in
the model (e.g. the highest chemical concentrations found
In groundwater were used, and chemicals would move at
the same rate as groundwater) , and did not take into
consideration such factors as natural attenuation,
retardation, and the ongoing elimination of contamination
sources. In addition, other factors affecting chemical
movement in groundwater such as hydraulic conductivity
and hydraulic gradients were areally averaged
(simplified) to take into account variations in those
parameters. However, local (as opposed to the larger
areal) variations in these parameters could affect
groundwater flow and therefore contaminant movement.
Because it now appears the assumptions used in the model
were too conservative, EPA expects from now on to rely on
field data for indicating trends in contaminant levels
rather than using modeling to predict contamination
levels in the Whittier Narrows. Plus, the complexity of
groundwater conditions there makes it unlikely that
modeling can be used to accurately predict future
groundwater chemical concentrations.
12. Many agencies commented that, in accordance with the
Montebello Forebay protection strategy, the installation
of well head treatment systems is essential for
protection of the drinking water within the Central
Basin.
EPA Response - Generally, EPA agrees that for production
wells that cannot meet drinking water standards, well
head treatment may be appropriate. EPA will evaluate any
such problems which appear to be caused by contamination
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. .-.- .~..-
from the San Gabriel Superfund sites and determine, in
consultation with state and local authorities, what, if
any, action is warranted. .
SPECIFIC COMMENTS
1.
The California Department of Toxic Substances Control
(DTSC) commented that a screening risk assessment is
inappropriate at the level of an OUFS. Such a risk
assessment should be thorough and quantitative, per U.S.
EPA guidance. DTSC also questioned the existence of a
Remedial Investigation Report.
EPA Response - The EPA refers the-DTSC to OSWER Directive
9355.0-30. contained within this document is the
following: "Early and interim action RODs do not require
a completed baseline risk assessment, although enough
information must be available to demonstrate the
potential for risk and the need to take action. Data
sufficient to support the interim action decision can be
extracted from the ongoing RIfFS for the site and set out
in a focused feasibility. study or other appropriate
dQcUltlent that includes a short analysis of a limited
number of alternatives (55 Fed. Reg. at 8704)." Because
the Whittier Narrows ROD is for an interim action, the
criteria for a screening risk assessment has thus been
satisfied. A basinwide Remedial Investigation Report is
available at the Whittier Central Public Library and in
the EPA Region IX information repository.
2.
The DTSC commented that this OUFS addresses only volatile
contaminants in groundwater. If other organic chemicals
were sought, these data are absent and not mentioned.
Inorganic contaminants are surely present at this site at
levels above background. Therefore, it seems highly
probable that potential health risks are underestimated
in the documents reviewed. At the very least, estimates
of risk are made greatly more uncertain by the exclusion
of these classes of chemicals,. but such uncertainty is
not reflected in Table 6-9 of the Feasibility Study
Report.
EPA Response - All organic chemicals that were positively
detected in at least one sample were included as
contaminants of potential concern (COPCs). Admittedly,
inorganics were not the focus of the RIfFS or the risk
assessment. The risk assessment acknowledges that
inorganics present in the groundwater may present
additional risk (p. 6-31). EPA cannot respond to the
statement that II inorganic contaminants are surely present
at this site above background," since, as far as we know,
background levels have not been established for this
9
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area. New monitoring wells installed as part of the
Whittier Narrows monitoring network will be sampled for
inorganics.
3. The DTSC commented that for exposure pathways, residents
could be exposed to contaminants of potential concern via
volatilization from underground sources, but this pathway
is apparently dismissed. Given that groundwater is the
only contaminated media, please construct a matrix of
possible exposure routes, as shown in U.S. EPA risk
guidance, Exhibit 6-7.
EPA Response - We disagree that the universe of possible
exposure pathways should be quantitatively evaluated in
a screening baseline risk assessment. Dominant pathways
of exposure were addressed in the interim risk
assessment. Because dominant pathways did not show a
significant risk, it is extremely unlikely that
additional pathways, such as volatilization from
underground sources, would pose a significant risk.
4. The DTSC commented that on Page 6-10, Table 6-24 of the
Feasibility Study Report, they do not understand the
meaning of the "P" data qualifier, which is stated to be
used for data for which both the "J" and "U" data
qualifier apply. According to U.S. EPA guidance
documents on data validation and risk assessment, the "J"
and "U" categories are mutually exclusive. If an analyte
is not detected, its concentration cannot be estimated.
EPA Response - "U" and "J" categories are not mutually
exclusive. A "UJ" qualifier indicates an estimated
quantitation limit. The compound was analyzed for, but
not considered non-detected. Because of analytical
problems, the quantitation limit is approximated
(estimated). The "P" qualifier means that both the "J"
and "U" qualifiers apply.
5. The DTSC commented on Page 6-18 of the Feasibility Study
Report, for Tables 6-4 and 6-7, the 95 percent upper
confidence limit (UCL) on the mean concentration is
incorrectly referred to as an "upper 95th percentile."
These terms are not synonymous. The 95th percentile
values for chemical concentrations would be considerably
higher than the 95 percent UCLs, which are the values
correctly shown on the tables. Please correct the use of
these terms.
EPA Response - We acknowledge this error. However, it
does not affect the outcome of the risk assessment.
6. The DTSC commented on Page 6-4 and 6-76 of the
Feasibility Study Report, Frequency of Detection - Based
on Table 6-2, we tallied the ratio of the number of tiroes
10
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a chemical was detected to the number of samples analyzed
for that chemical. Data qualified with a IIJII" "L", or
~P" were scored as detections. These data, especially'
the denominators, disagree with the ratios shown in
Tables 6-5 and 6-7. Since these denominators are used in
the calculation of the 95 percent UCLs on mean chemical
concentrations (mean.:!: s.d. /nl/2), these discrepancies
should be resolved.
EPA Response - Monitoring Wells EPAMW011, EPAMW012,
X11TMA01, and X11TMAG1 did not contain detectable levels
of VOCs. As the risk assessment states (p. 6-18), these
wells have not been included in the evaluation of '
groundwater exposures. This likely explains the
inconsistency wi th respect to the denominators.
Regarding the numerator, the inclusion of the "P"
qualifier as a detection is not appropriate (see above).
7.
The DTSC commented on the Dermal Exposure portion of the
Feasibility study Report. Risks from dermal exposures to
volatile organic chemicals in domestic water can be
greater than portrayed in this section. DTSC believes
risks due to dermal exposure to volatiles in domestic
wat~r. should be quantified.' ,"The. most recent guidance
from U. S. EPA on the subj ect of dermal exposure to
volatiles is "Relevant Contribution of Dermal Exposure to
Total Absorbed Dose," which is Chapter 9 in Interim
Guidance for Dermal Exposure Assessment. The
contribution of the dermal pathway for, ethylbenzene,
tetrachloroethene, and trichloroethene in domestic water
is estimated to be between 2 and 20 percent of total
exposure via ingestion, inhalation, and dermal exposure.
Therefore, addition of the dermal route might be expected
to increase estimates of risk by less than a factor of
two. This is strikingly different from statements in the
OUFS which dismisses risks from the dermal route as being
several orders of magnitude less than those from
ingestion and inhalation.
EPA Response - The risk assessment did not discount the
dermal route based on the risks 'being "several orders of
magnitude less than those from ingestion and inhalation"
as is implied in the comment. Rather (p. 6-22), the
"screening assessment does not quantitatively estimate
dermal absorption from household water use because of the
uncertainty associated with making a quantitative
estimate of such an exposure." The risk assessment does
state that the absorbed dose through dermal exposure
could be several orders of magnitude less than through
ingestion of tap water. We also acknowledge that the
exposure could be 2 to 20 percent of the ingestion dose.
Even if one were to assume these latter estimates
provided by the reviewer, the conclusions of the interim
risk assessment would not be affected.
11
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10.
8.
The Water Replenishment District (WRD) of Southern
California commented that the Feasibility study Report
fails in its water quality assessment of impacts to the
Montebello Forebay of the Central Basin by neglecting to
account for existing TCE and PCE contamination already
existing in the Central Basin. The screening baseline
risk assessment provided in Section 6 of the report does
not take into account potential health impacts to
Montebello Forebay consumers which are already receiving
a background or baseline level of PCE contamination in
drinking water supplies. Therefore, an assessment should
be made of potential health impacts and water quality
treatment requirements for Montebello Forebay wells
receiving the incremental contamination from Whittier
Narrows.
EPA Response - We found the risks to be insignificant in
the Whittier Narrows. The risks would still be
insignificant when added to the Montebello Forebay of the
Central Basin. Not knowing the background or baseline
level of PCE contamination in drinking water supplies at
the Montebello Forebay let us assume two different
scenarios. The first scenario assumes that no other
sources of contamination besides Whittier Narrows would
be responsible for contamination in the Central Basin.
In this case, the concehtrations present in the
MQn~ebello Forebay would be predicted to be similar to
concentrations in Whittier Narrows (barring the presence
of an isolated spot of contamination that has already
moved through Whittier Narrows) and no additic;mal risk is
predicted. For the second scenario, let us assume that
the contamination is rather high in the Montebello
Forebay (close to 1 in 10,000 excess cancer risk) due'to
other sources. In this case, the incremental risk from
Whittier Narrows (assuming no dilution) would still be
insignificant relative to the preexisting risk and no
additional water quality treatment requirements would be
necessary. '
9.
The WRD commented that the proposed revised Record of
Decision for the Bortollo (Suburban) Well Field Operable
Unit should be developed in conjunction with the Record
of Decision for the Whittier Narrows Operable Unit.
EPA Response - The monitoring of groundwater quality
within the Whittier Narrows will take into account the
groundwater affecting the Suburban Operable Unit. After
the Records of Decision for both the Suburban and
Whittier Narrows Operable Units are signed, EPA will
manage these operable units together as one area.
Suburban wells will also be part of the Whittier Narrows
monitoring network.
The WRD commented that
even
though the average blended
12
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water quality for subsurface flow coming through the
Whittier Narrows into the Central Basin meets drinking
water standards for trace ,organic compounds, water
flowing through the Narrows at specific depths is in
excess of standards for both ,TCE and PCE. The
?easibility Study Report should address potential
remedial action at specific depth intervals for both TCE
and PCE. Depth-specific production and treatment would
be very effective in significantly reducing the mass
transport of these industrial solvents of concern into
the Central Basin.
. .
EPA Response - The residents of Whittier Narrows and the
Central Basin are exposed to groundwater that is blended
from multiple aquifer zones o.r intervals. Discrete
intervals of production wells are not points of exposure
for residents. At such low concentrations (barely above
MCLs) , it would be premature and it would not be cost
effective to initiate remedial activities for these
discrete intervals. However, depth specific production
and treatment may be appropriate if future data show
increased contamination levels, and EPA will certainly
evaluate this method if a remedial action is warranted.
11.
The City of Pico Rivera. requested that 'the City be
incl~ded in the FeasibilitX.'st\,ldy. for the Whittier
Narrows Operable Unit so that its wells may serve as an
early warning system for the Central Basin.
EPA Response - Selected wells in the City of Pico Rivera
(see figure 3 of the Record of Decision) will be included
in EPA' s expanded monitoring network for the Whittier
Narrows Operable Unit to determine the extent that
contaminants from the San Gabriel Basin are impacting the
Central Basin. EPA believes that the monitoring wells
currently in place and the proposed new wells to be
placed north of the whittier Narrows Dam are better
suited as early warning wells for the Central Basin.
*12. The California State Water Resources Control Board
(SWRCB) requested clarification on, (a) how' hydraulic
conductivity was estimated from specific gravity tests,
(b) how aquifer tests were used to determine hydraulic
conductivity.
EPA Response - (a) - For specific capacity test data
that included information on the duration of pumping, the
transmissiVity was estimated using the Cooper - Jacob
approximation (1946). This methodology assumes that the
drawdown is small compared to the initial saturated
thickness (additional assumptions are listed in Cooper
and Jacob (1946) and Bear (1979). For specific capacity
test data that did not include information on the
duration of pumping, the transmissivity was estimated
13
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from the Theim equation (Bear, 1979). Hydraulic
conductivity was estimated from the values of
transmissivity by dividing the transmissivity by the
length of the well in the saturated alluvium. As
.mentioned in the OUFS, additional discussion of this
•methodology is presented in the San Gabriel Supplemental
Sampling Program Report (EPA, 1986)
(b) - Some of the aquifer test data were from tests
analyzed by the California Department of Water Resources
(CDWR, 1966) in their Bulletin 104-2. CDWR used the
methods of Theis (1935) and Chow (1952). Aquifer test
data from the monitoring wells installed by EPA in
Whittier Narrows were evaluated using the Cooper-Jacob
approximation (1946). These analyses assume that the
well penetrates an aquifer that is homogeneous,
isotropic, and of infinite horizontal extent. Additional
assumptions are discussed in Bear (1979).
13. The SWRCB also commented that the equation used for
calculating groundwater velocity on page A-2 of the
Whittier Narrows OUFS, yields only an average velocity.
EPA Response - We agree with the comment made that the
equation V=Ki/ne yields only an average velocity. The
velocity calculated with this equation would represent
.the average velocity over the volume of the aquifer that
the parameters were measured in. For example, if the
gradient "i", hydraulic conductivity "K", and porosity
"ne" were estimated at two wells, the velocity would
represent average velocity between the two wells.
However, because hydrogeologic properties and groundwater
discharge/recharge may vary between the two wells, the
actual velocity at any point in space between the two
wells may vary from the estimated average velocity.
In Whittier Narrows, hydrogeologic data from wells (i.e.,
individual, discrete points in space) are the only
available data for estimating the groundwater velocity.
It is thus necessary to utilize estimates of "average
velocity" based on data from wells, even though the
velocity may vary between the wells. Because another
draft of the OUFS report will not be produced, we will
unfortunately not be able to add more text to further
clarify this point. The average velocity estimated could
be used to estimate the average velocity for transport of
a contaminant if the contaminant travelled at the same
velocity as the groundwater.
14
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*References
Bear, J.
HYdraulics of Groundwater.
MCGraw-Hill, New York.
1979.
California Department of Water Resources. Planned Utilization of
Ground Water Basins. San Gabriel ValleY. ADDendix A: GeohYdroloqy.
Bulletin 104-2. 1966.
Chow, V. T. On the Determination of Transmissivity and Storage
Coefficients from Pumping Test Data. Transactions American
GeoDhysical Union. 33:397-404. 1952.
Cooper, H. H., Jr. and C. E. Jacob. A Generalized Graphical Method
for Evaluating Formation Constants and Summarizing Well Field
History. Transactions American Geophysical Union. 27: 526-534.
1946
EPt\;- see United States Environmental Protection Agency.
Theis, C. V. The ~elationship Between the Lowering of the
Piezometric Surface and Rate and Duration of Discharge of a Well
Using Groundwater Storage. Transactions American Geophvsical
Union. 16: 519-524. 1935.
United States Environmental Protection Agency, Draft San Gabriel
Supplement~l Samplinq Proqram ReDort. Volume 2. Prepared by CH2M
Hill, May -19.;. 1986.
15
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MAILING LIST FOR WHITTIER NARROWS OUFS
Jim Goodrich
Main San Gabriel Basin Water
425 East Huntington Drive
Monrovia, CA 91016
Quality Authority
Tim Jochem
Upper San Gabriel Valley
11410 E. Valley Blvd.
El Monte, CA 91731
Municipal Water District
Tim Hampton
Metropolitan Water
1111 Sunset Blvd.
P.O. Box 54153
Los Angeles, CA 90054-0153
District of Southern California
Mike Sorensen
California Department of Toxic Substances Control
P.O. Box 806
400 P Street, 4th Floor
Sacramento, CA 95812-0806
Jon Bishop
California Regional Water
101 Centre Plaza Drive
Monterey Park, CA 91754
Quality Control Board, Los Angeles
John Maulding
Main San Gabriel Basin Watermaster
425 E. Huntington Drive, suite 200
Monrovia, CA 91016
Ken Harris
State Water Resources
901 P Street
Sacramento, CA 95814
Control Board
~ob Stalling
San Gabriel Valley Municipal
549 E. Sierra Madre Ave.
P.O. Box 1299
Azusa, CA 91702
Water District
Richard Atwater
General Manager
Central Basin Municipal
7439 East Florence Ave.
Downey, CA -90240-3699
Water District
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jeff Helsley
District Engineer
central and West Basin Water Replenishment District
1261 East 166th Street
Cerritos, CA 90701
John Norman
General Manager
Central and West Basin Water Replenishment District
1261 East 166th Street
Cerritos, CA 90701
Robert Wagner
Chairperson
Southeast Water Coalition
12700 Norwalk Blvd.
Norwalk, CA 90651-1030
Mike Stover
Assistant City Manager
City of Lakewood
5050 Clark Ave.
Lakewood, CA 90712
Thomas M. Regan
Bookman - Edmonston Engineering, Inc.
100 North Bravo Blvd., Suite 600
Glendale, CA 91203- 2699
Fran McPoland
c/o Rep. Esteban Torres
U.S. House of Representatives
1740 Longworth House Office Bldg.
Washington, D.C. 20515
Richard Powers
City Manager
Norwalk City Hall
12700 Norwalk Blvd.
Norwalk, CA 90650
Engineer
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PROPOSEO UON I TOR I NG
PLAN - WHITTIER NARROWS
. RECORD or DECISION
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