United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response •
E PA/ROD/R07-89/022
November 1988
Superfund
Record of Decision
Todtz, Lawrence Farm, IA
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50272-tOt
" REPORT DOCUMENT A TJON 11. REJIOAT NO. 1 2.
PAGE EPA/ROD/R07-89/022 .
~ A8c1pi8nC'. ill H II II an No..
4. ".. end SubII88
SUPERFUND RECORD OF DECISION
Todtz, Lawrence Farm, IA
~irst Remedial Action - Final
s. RItIart 0et8
11/04/88
I.
,. AuItor(.1
I. PwfotmioIQ OrveniD1Ion ~ No.
.
8. ~.."'...~""'end~
10. ProjedfT ull/Woril Unit No.
.
11. Contnct(C) 011 Gnnt(G) No..
(C)
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U.S. Environmental Protection
401 M Street, S.W.
Washington, D.C. 20460
(0)
1~ Typ8 of A8part. P8Itod Co--
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Agency
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15. ,. u' v*It8y""-
11. AII8bc1 (UInt: 200--1
The 2.7-acre Dupont Impoundment of the Todtz Farm site is part at the 12-acre parcel of
land known as the Todtz Farm Landfill, which is located on a 120-acre farm 1.25 miles
west of Camanche, Iowa. Originally a sand and gravel mine, the landfill received
municipal waste from 1969 to 1975. In 1971, Dupont constructed the impoundment in the
~9rthwest corner of the landfill and dispos~d of an estimated 4,300 .tons of wet end
~llophane process wastes from 1971 until its closure in 1975. Impoundment wastes are
,eriodically in direct contact with the ground water beneath the site, which flows
southeasterly toward the Mississippi River. Domestic wells and the municipal water
supply wells for Camanche located downgradient of the site may be affected by
contamination from the site. In addition, several ponds and lakes in the vicinity are
potential receptors for contaminated runoff and recharge. The primary contaminants of
concern affecting the ground water are VOCs including toluene and benzene, and metals
including arsenic, lead, and chromium. .
The selected remedial action for this site includes installation of a soil cover "over
the Dupont Impoundment: implementation of institutional controls including deed and land
use restrictions: provision of an alternate water supply for an
(See Attached Sheet)
17. o--tAlWyei8.. Dn~~
Record of Decision - Todtz, Lawrence Farm, IA
First Remedial Action - Final
Contaminated Media: gw
Key Contaminants: VOCs (benzene, toluene), metals (arsenic, lead, chromium)
b. Id8nlltleniOpen.Ended Tenne
c. coo.. n FIeidIGroup
"y!!!~1Ity s...m.ne
11. Security a... ("OIl. AetIortI
None
20. Security a- (T11I8 PlIO-I
1'Jt"lnp-
21. No.. 01 P.ge.
22. Price
(See A~Z38.I')
See m.fNCfI- 0""'-
OPnONALFOAM2n(~~
(Fonnerty NTlS,35) " .
0epInnen1 of Co_ce"
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~ GPO
1983 0 - 381-526 (8393)
OPTIONAL FORM 272 BACK I
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EPA/ROD/R07-89/022
Todtz, Lawrence Farm, IA
First Remedial Action - Final
\6.
Abstract (continued)
affected residence by relocating an existing well; and groundwater monitoring. SPA has
determined that further remedial actions will be immediately implemented if ground water
trigger levels provided in the ROD are met or exceeded. If ground water monitoring
indicates that contaminant levels exceed the less stringent chemical-specific action
levels provided in the ROD, ground water pumping and treatment will be implemented; if
the more stringent action levels are exceeded, a treatability study of the impoundment
waste will be conducted and either a permanent treatment remedy of the impoundment
material or a cap and slurry wall containment system will be implemented. The estimated
present worth cost for this remedial action is $1,030,000. O&M cost was not provided.
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-~
.
RECORD OF DECISION DECLARATION
SITE NAME AND LOCATION
DuPont Impoundment of the Todtz Farm Site
Camanche, Iowa
STATEMENT OF BASIS AHQ PURPOSE
This decision document presents the selected remedial action
for the DuPont Impoundment of the Todtz Farm site in Camanche,
Iowa. This final plan has been developed in accordance with
CERCLA as amended by SARA, and, to the extent practicable, the
National Contingency Plan. The decision is based on the
administrative record for .this site. The attached index
identifies. the. items which comprise the administrative record
upon which the selection of the remedial action is based.
DESCRIPTION OF THE SELECTED REMEDY
This remedial action represents the final action for the
DuPont Impoundment of the Todtz Farm Site. The selected remedy
includes the following major components:
- A 2-foot soil cover over the DuPont Impoundment;
- Access restrictions which include deed limitations and -
site fencing;
- Site maintenance which includes mowing the grass and
repairing the fence;
- A ground water monitoring system which includes
implementation of further remedial actions if certain
chemical specific action levels are exceeded;
- Replacement of the Bark residence drinking water well in
the deeper bedrock aquifer.
DECLARATION
The selected remedy is protective of human health and the
environment, attains Federal and State requirements that are
applicable or relevant and appropriate to this remedial action, .
and is cost-effective. ~is yemedy utilizes permanent solutions
and alternative treatment technologies to the maximu~ extent.
practicable for this site. However, because implementation of
treatment at this time was determined not to be cost-effective
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2
based on the relative overall risk to public health and the"
environment, this remedy does not satisfy the statutory
preference for treatment as a principal element of the remedy.
However, if the exceedance of certain chemical specific action
levels (as detected in the qround water monitorinq system) are
exceeded in the future, there will be provisions to implement
treatment it it is teasible at that time.
This remedy will result in hazardous substances remaininq
onsite above health based levels, that will be covered by a
2-toot soil cover. Since these hazardous substances will remain
onsite, a review will be conducted within five years after
commencement of remedial action to ensure that the remedy
continues to provide adequate protection of human health and the
environment.
/J-4-1f~
Date
/J'J1-- / ~~
v Morris Kay ,
Reqional Administrator
Region VII
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RECORD OF DECISION
FOR
THE DUPONT IMPOUNDMENT
OF
THE TODTZ FARM SITE
CAMANCHE, IOWA
Prepared by:
U.S. ENVIRONMENTAL PROTECTION AGENCY
October, 1988
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TABLE OF CONTENTS
1.0 INTRODUCTION
1.1 BACKGROUND
1.2 HYDROGEOLOGIC SETTING
1.3 PREVIOUS STUDIES
1.4 COMMUNITY RELATIONS HISTORY
1.5 ROLE AND SCOPE OF REMEDIAL ACTION
1.6 ENFORCEMENT ACTIVITIES
1.71 SITE CHARACTERISTICS
1.72 SUMMARY OF SITE RISKS
1.8 DOCUMENTATION OF SIGNIFICANT CHANGES
2.0 ALTERNATIVES EVALUATED
2.1 NO ACTION
2.2 SOIL COVER
2.2A ALTERNATIVE 2 WITH TREATABILITY STUDY
2.3 GEOMEMBRANE MULTILAYER CAP
2.3A ALTERNATIVE 3 WITH TREATABILITY STUDY
2.4 GEOMEMBRANE - CLAY MULTILAYER CAP WITH BENTONITE
SLURRY WALL
3.0 SUMMARY OF THE COMPARATIVE ANALYSIS OF THE ALTERNATIVES
3.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
3.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS
3.3 REDUCTION OF TOXICITY, MOBILITY OR VOLUME
3.4 SHORT-TERM EFFECTIVENESS
3.5 LONG-TERM EFFECTIVENESS AND PERMANENCE
3.6 IMPLEMENTABILITY
3.7 COST
3.8 COMMUNITY ACCEPTANCE
3.9 STATE ACCEPTANCE
4.0 THE SELECTED ALTERNATIVE
4.1 SOIL COVER
4.2 ACCESS RESTRICTIONS
4.3 MAINTENANCE
4.4 GROUND WATER MONITORING
4.5 HEALTH AND SAFETY
4.6 TIME SCHEDULE
5.0 STATUTORY DETERMINATIONS
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FIGURE NO.
1-3
1-4
7-1a
7-1b
7-10
7-1d
7-1e
7-1f
2-1
4-1
TOPOGRAPHIC SURVEY AREAS
SITE SAMPLING LOCATION MAP
DISTRIBUTION OF ORGANIC CONSTITUENTS IN TEST
PIT SOILS
DISTRIBUTION OF INORGANIC CONSTITUENTS IN TEST
PIT SOILS
DISTRIBUTION OF ORGANIC CONSTITUENTS IN TEST
PIT WATER
DISTRIBUTION OF INORGANIC CONSTITUENTS IN TEST
PIT WATER
DISTRIBUTION OF ORGANIC CONSTITUENTS IN GROUND
WATER, SURFACE WATER
DISTRIBUTION OF INORGANIC CONSTITUENTS IN GROUND
WATER
MONITORING WELL LOCATIONS
SOIL COVER
'PAGE NO.
1a
2a
4a
4b
40
4d
4e
4f
Sa
17a
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TABLE NO.
7-2a
7-2b
7-2c
2-la
2-lb
3-2
PAGE NO.
POSSIBLE HUMAN EXPOSURE SETTINGS
POSSIBLE ENVIRONMENTAL EXPOSURE SETTINGS
SUMMARY OF CONTAMINANT CONCENTRATIONS
IMPLEMENT ALT 4 OR TREATMENT REMEDY
IMPLEMENT GROUND WATER REMEDIATION
.ARARS IDENTIFIED
4g
4h
Sa
lOa
lOb
l2a
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1.0 INTRODUCTION
1.1 BACKGROUND
The 2.7 acre DuPont Impoundment is located within tte
12-acre parcel of land known as the Todtz Farm Landfill
located on the 120 acre Todtz family farm, 1-1/4 miles west of
Camanche, Iowa. Camanche is located on the Mississippi river
about 2 miles south of Clinton, Iowa.
Between 1959 and 1969, sand and gravel were mined from
the 12-acre parcel of land. The mined area was used as a
landfill for disposal of municipal refuse from 1969 to 1975. The
DuPont Impoundment was constructed in the northwest corner of the
Todtz Farm Landfill sometime in 1971. An estimated 4300 tons of
wet end cellophane process wastes from DuPont's Clinton, Iowa
plant were disposed of in the impoundment between 1971 and its
closure in 1975.
1.2 HYDROGEOLOGIC SETTING
A sand and gravel terrace associated with glacial outwash
activity forms the natural uppermost aquifer around the site.
Ground water in the uppermost water bearing unit flows generally
in a southeasterly direction toward the Mississippi River.
Domestic wells are located downgradient of the site and are
potential receptors for contaminated ground water. It is
possible that the municipal. water supply wells of Camanche may
also"may be impacted. "
In the vicinity of the landfill, the sand and gravel
unit is underlain by a thick sequence of low permeability clays
and silts with occasional lenses of silty to clayey fine sands.
These low permeability soils directly overlie dolomite bedrock
that also serves as a source of drinking water to local
residents. The low permeability soils appear to behave as an
aquitard preventing hydraulic connection between the two water
bearing units.
Surface water bodies in the vicinity of the site which
are potential receptors for contaminated run-off and/or recharge
are the north and south ponds, Murphy's Lake and Bandixen Lake.
Secondary potential receptors include other downgradient lakes
and the federally owned and managed Upper Mississippi River Fish
and Wildlife refuge located less than one mile from the site.
(Refer to Figure 1.3)
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,........,.... ".",
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-2-
1.3 PREVIOUS STUDIES
The Todtz Farm Landfill was identified as a potential
uncontrolled hazardous waste site in 1979. A preliminary site
inspection was conducted by EPA's Field Investigation Team (FIT)
Contractor in 1980. The site was given a Hazard Ranking. System
(HRS) score of 52.11 in March 1985, and added to the National
priorities List (NPL) in June 1986.
FIT returned to the site in August 1985 to take
additional surface water, sediment, and residential drinking
water samples.
In September 1986, EPA's REM II contractor installed six
ground water monitoring wells around the landfill and near the
DuPont Impoundment and collected additional surface water,
sediment, soil and residential well samples. The monitoring
wells were sampled five times through August 1987 by REM II.
Ground water samples taken from the monitoring wells installed in
the downgradient impoundment berm (monitoring wells MW~3, MW-4,
and MW-5 as shown on Figure 1.4) have shown the presence of
levels as high as 3600 ug/l for carbon disulfide, .400 ug/l for
lead, 8,800 ug/l for toluene, 97,000 ug/l for tetrahydrofuran,
1,000 ug/l for 4-methyl phenol, 1.10 ug/l for mercury, 160 ug/l
for arsenic, and 209 ug/l for benzene. Except for arsenic and
benzene, these compounds are among ~hose reported by DuPont as
being used at the Clinton cellophane plant and were disposed in
the DuPont Impoundmertt.
1.4 COMMUNITY RELATIONS HISTORY
The local community has not recently expressed concern
regarding remediati6ns of the Lawrence Todtz Farm site.
A 21-day public comment period was held from August 20
through September 10, 1988. In that time period, no public
comments from the local community were received and there were no
requests for a public meeting. A comment letter was received
from DuPont's consultant. A phone call was also received from
the Bark residence. These comments are addressed in the
Responsiveness Summary.
All community relations activities have been in conformance
with the requirements of Sections 113 and 117, CERCLA, and the
National Contingency Plan (NCP) in 40 CFR 300.
1.5 ROLE AND SCOPE OF REMEDIAL ACTION
Based on investigations conducted onsite prior to 1988, 'it
was evident that there was a release or a threat of release of
hazardous substances from the DuPont Impoundment. EPA had also
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SOURCE; FIT REPORT, AUGUST, 1885, REVISIONS 8ASEO ON
SITE VISIT YAY, 'Iue.
NOTE: LOCATION OF ROADS AND SURFACE WATER FEATURE
APPROXIMATED BY FIELD PERSONNEL
~ GEOTECHNICAL BORING
o MONITORING WELLS
RW RESIDENTIAL WELL
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SURFACE WATER AND SEDIMENT
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DUPONT LANDFILL
GROUNDWATER CONTAMINATION SITE
CAMANCHE. IOWA
/IC.A Woodward-Clyde Cons\:
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-3-
sent CERCLA 104/RCRA 3007 information request letters to
companies who reportedly had sent wastes to the municipal,
landfill. Responses to these letters did not indicate that
hazardous substances had been disposed in the municipal landfill.
It seemed likely that the source of contamination for the
Lawrence Todtz Farm site was the DuPont Impoundment and that the
remedial alternative selected for the impoundment would pe a
sufficient final remedy for the entire site.
1.6 ENFORCEMENT ACTIVITIES
During the REM II site investigation, EPA began
negotiations with E.I. DuPont de Nemours and Co. for DuPont to
conduct a Remedial Investigation/Feasibility Study (RI/FS) for
the site. DuPont agreed to conduct a RI/FS focused on their
impoundment. On April 5, 1988, a CERCLA 104/122 Consent Order was
signed by both EPA and DuPont, finalizing the agreement for
DuPont to conduct the RI/FS.
Dupont conducted the RI/FS pursuant to the "DuPont
Impoundment Operable Unit RI/FS Work Plan" dated February 12,
1988. This workplan, prepared by DuPont's consultant CH2M Hill,
was approved by EPA and included as an attachment to the CERCLA
104/122 Consent Order. The purpose of the RI/FS was to fully
characterize the DuPont Impoundment, determine the extent of
contamination, evaluate the risk to downgradient receptors, and
evaluate appropriate remedial alternatives for the DuPont
Impoundment.
. .
1~71 SITE CHARACTERISTICS
The RI was conducted during the spring of 1988 and consisted
of the following tasks: a source area characterization study to
evaluate physical and chemical characteristics of the
impoundment; a hydrogeologic investigation to define site
stratigraphy, ground water flow paths and contaminant migration
pathways; and an environmental sampling task to define the nature
and extent of contaminants of concern in ground water and surface
water.
The upper ground water aquifer at the site generally flows
in a southeast direction with the majority of the ground water
recharge occurring upgradient of the site. The impoundment
wastes are periodically in direct contact with the ground water.
The bedrock aquifer is separated from the upper aquifer by a
thick sequence of low permeable clays and silts that appear to
behave as an aquitard. Although the Todtz and Bandixen residence
wells are completed in bedrock, ground water quality in the
bedrock aquifer has not been fully investigated at this time:
--
~~. .""--CC --...- ---=-~_.,-- .-C' .
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-4-
As part of the source area characterization, soil and
water samples were taken from test pits excavated within the
impoundment. Figures 7-1a and 7-1b indicate levels of organic
and inorganic substances detected in the test pit soils.
Comparing the test pit samples (TP-01, TP-02, and TP-03) with the
background location (FB-04), the levels of organics and
inorganics in the impoundment soils exceed background.
concentrations. Figures 7-1c and 7-1d indicate levels of organic
and inorganic substances detected in the test pit water.
Comparing test pit water samples (TW-01, TW-02, and TW-03) to th~
background ground water sample (DP-01), it was concluded that
ground water in the impoundme~lt exceeds background concentrations
of organic and inorganic constituents.
As indicated on Figures 7-1e and 7-1f, analysis of ground
water samples confirms the presence of elevated levels of organic
and inorganic constituents significantly.above background in the
monitoring wells (MW-03, MW-04, and MW-OS) located downgradient
of the DuPoot Impoundment in the impoundment berm, as was
concluded by the REM II Investigation. Above background
concentrations of several inorganic constituents were detected in
other downgradient wells (DP-OS, DP-02, PZ-02 and the Bark
residence well). Arsenic was also detected in the ground water
sample from PZ-03 in concentrations above background. Also, EPA
split samples for DP-OS, DP-02 and PZ-02 detected results of
tetrahydrofuran of 7 ug/l, 2 ug/l M and 1 ug/l M respectively.
(The "M" code designates that the compound was detected, but th~
levels are below the EPA contract detection limits. Therefore, .
the quantification is an estimate). The tetrahydrofuran found in
the split sample analysis was not confirmed during a subsequent
sampling event.
1.72 SUMMARY OF SITE RISKS
The Endangerment Assessment (EA) is included in the RI
report and. presents an evaluation of the existing and potential
future impacts of contamination at the DuPont Impoundment on
human health and the environment. One of the major objectives of
the assessment was to assist in identification of the principal
routes of human and environmental exposure to site contaminants
in order to focus the FS on remedial alternatives that would most
effectively prevent or preclude adverse impacts.
Several potential human and environmental exposure
settings that could be impacted by the contaminants of concern
were evaluated on a qualitative basis Ly the EA (Refer to Tables
7-2a and 7-2b). Those exposure settings that had a low
probability of occurrence were not evaluated on a quantitative
basis.
One of the more likely scenarios would be a setting in which
children trespassing on the site to play might be exposed by
direct contact with or inadvertent ingestion o~ contaminated
-------
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" LEGEND
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. . ,6 MONITORING WELL INSTALLED IY erA
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I I =~==-=. "'t".
-------
.' .
-------
-4g-
Table 7-la
POSSIBLE HUMAN EXPOSURE SETTINGS
Medium
Settino
Air
Surface soils and
impoundment wastes
Surface water
Grour.dvater from
surficiai or
bedrock acuifers
Agricultural
products
Inhalation of vapors or
contaminated dusts re-
leased from contaminated
areas of the site
Ingestion of contaminated
soils or wastes during
recreational, residential
or occupational
activities onsite
Ingestion cf contaminated
fish fron the Murphy and
Bandixen Lakes
Dermal absorption of
contaminants while
swimming in the Murphy and
Bandixen Lakes
Ingestion of contaminated
groundwater from surfi-
ciai aquifers
Inhalation of volatile
organic contaminants
released during showers
or other household uses
of groundwater
Dermal contact with con-
taminants during showers,
baths, or other household
use of groundwater
Ingestion of dairy pro-
ducts or beef from cattle
grazing onsite or drink-
ing from north and south
ponds
Popu 1 a t i on -a t - ?. i s k
Nearby residents
Children playing/
riding bikes;
adults working/
gardening;
construction
workers
Recreational
fishermer. and their
families
Local families
Families with
private wells
downgradient of
site, or onsite
assuming future
development
Same as above
Same as above
Consumers of meat and
dairy products
317766/59
-------
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Table 7-.:lb
PCSSI2LF E~:\OIFONl-1E~7t\:. E:cr.s, c'.;cks,
other aquati:
feeders
-------
-5-
surface and impoundment soils. This scenario was, therefore,
evaluated on a quantitative basis. possible future exposures
were also evaluated on a quantitative basis for a scenario in
which the site was assumed to be developed for residential use.
In this scenario, both soil ingestion and ground water use were
evaluated for adults and young infants. All of the exposure
settings assumed long-term exposures to existing levels of con-
taminants, which provides conservative assessments, since some
degradation of contaminants may occur. over time.
To evaluate the potential adverse effects of exposure to
surface and impoundment soils at the concentrations of
contaminants present, the hazard index (HI) was calculated. The
HI, which is calculated by the summation of the DI/RfD (daily
intake/reference dose) ratio for each chemical present, is
intended to provide a measure of possible effects of exposure to
several toxic chemicals. The daily intake (DI) or estimated do~e
is calculated based on soil ingestion. The reference dose (RfD)
is defined as an estimate of a daily exposure to the human
population that is unlikely to result in appreciable risk of
deleterious effects during a ,lifetime. An HI of one or greater
indicates the possibility of adverse health effects. For all of
the contaminants detected in the surface and impoundment soils,
the HIs were calculated to be below one.
To evaluate the health risks associated with consumption'
of contaminated drinking water, it was assumed that ground water
from monitoring wells MW-3, MW-4, and MW-5 would be ingested.
These wells were chosen because they contain elevated .
concentrations of contaminants associated with the DuPont
.Impoundment. The concentrations of contaminants in the wells
were evaluated on the basis of hazard index, increased lifetime
cancer risk, and comparison with EPA National Primary Drinking
Water Standards established for the protection of human' health.
The ground water assessment concluded that the Hazard Index
exceeded one for both mean and maximum concentrations of
contaminants detected in the .three monitoring wells. The
contaminant concentrations also exceeded a number of MCLs and
MCLGs (refer to Table 7-2c). Lifetime cancer risk, based on
exposure to concentrations of benzene and arsenic in the three
wells, was' also greatly increased.
The following conclusions have been reached based on the
. exposure scenarios evaluated in the EA.
1. Risks to human health or the environment associated with
direct contact and ingestion of surface soils or surface
downgradient to the impoundment appear to be
below those used by EPA in determining whether human
. health or the environment are protected.
2. There would be an unacceptable risk to human health or
the environment through ingestion of ground water within
impoundment and at the impoundment berm.
-------
. .
-Sa-
TaOle 7. 2c
~Y OF CX>ITIWIIINN'lf c:DCENTRATlQooIS IN -'03. _.O~. _.OS.
CDIIIPAaI$O.l TO CRIPeI"': "ATER S'TAI<)AaCS CR QJIOELINfS
M'H'-
VALuE
M£OI-
VALuE
Not. T I C)ouI. L PR I IfoAR Y
CRINKiNC ~ATfR ST~AROS
811CL IIICLC
MAJ\'-
VALuE
Mf-
VALuE
...............-....--.-......-.-...-.-.--......-.-..-[[[
CIte-Ie ~s
contenllal,Qft Cug/I)
............-.-..........................-...........-.-.-................................................
ACt TOolE 1 2000 U3.' 2 1
IENZEHE 0.1 20. ".1 2 1
- CAAIOoI 0 I SI.A. , I DE 2 .no 1056.6 360
tn«\. 8fP«EHE 2 3.) 2. , 2 1
tIC1WI'\. ENE 0«.011 DE 2 noo 126.4 2 1
ME'TW'f\. ('n-fYL I.ETCJooIE 2 15 5 5 2 1
.'.E'n-fYLPMEpoOL 14 7 1000 109 3 2?
fIt1EpoOL 14.7 185 40.2 '4.7 1
TmA04\.OItOE'nofVL EHE 2 1 2 0 2 I
TETR ArfYCQOFIA - 2 .5500 2~8J0.I 2600
TOLUEHE 1 1400 110.0 1 I
1CYLEHES (TOT"L) 2 S3 2 2 2 1
5
610
o
.~O
. .
[[[
'toOIc-,e ~S
.-........- ...- ..... -... ....................... ......................... .... ...-... ... ..... -......... .................................
.aSENIC 5 1600 3'9 0 89 SO ~O
..aIUM as 1900 620 0 585 '000
IUYLL IUM 0.151 ,. 2 6 0151
~IUM 2 '55 60 7.9 1.155 '0 5
O«08IUM (Tot. I) 0 .05 360 121 5 150 50 120
L(40 2.5 400 6J 1 7 1 50 10
-------
-6-
3. Risks to human health or the environment through
ingestion or direct contact with ground water from the
shallow aquifer at or near the southern or southeastern
boundaries of the Todtz Landfill site perimeter,
which is several hundred feet downgradient from the
DuPont Impoundment, appear to be below those used by EPA
in determining whether human health or the environment
are protected. Concentrations of 60 ug/l and 80 ug/l
of arsenic have been detected at PZ-03 on the eastern
boundary of the landfill. These concentrations exceed
the Maximum Contaminant Level of 50 ug/l. However, risks
to human health or the environment in this portion of the
landfill would appear to be acceptable because the
aquifer would not be considered a viable drinking water
supply at this location.
The findings of the RI and the EA indicate that the DuPont
Impoundment is the source of contamination for the Lawrence Todtz
Farm site. "The focus of the FS was on the development of cost-
effective remedial actions for controlling potential release of
waste constituents from the impoundment.
1.8 DOCUMENTATION OF
SIGNIFICANT CHANGES
There are no significant changes between the Record of
Decision and the Proposed Plan. A few non-significant changes
have been made throughout the Record of Decision to clarify
various aspects of site conditions and the selected remedy.
-------
-7-
2.0 ALTERNATIVES EVALUATED
Remedial alternatives were screened based on effectiveness,
implementability, and relative capital, operations, and
maintenance costs. Excavation of the impoundment wastes. and
disposal at a RCRA landfill or treatment onsite using
incineration, stabilization or in-situ treatment technologies
were eliminated since they were not cost-effective based on the
relatively low risk to the public health and the environment and
the large capital cost.
The EPA has evaluated four basic alternatives and two
variations for remediation of the DuPont Impoundment of the Todtz
Farm Landfill Site. These alternatives are 1) no action, 2)
soil cover, 3) geomembrane multilayer cap, and 4) geomembrane-
clay multilayer cap with bentonite slurry wall. Alternatives 2TS
and 3TS have also been developed as variations of Alternatives 2
and 3 which would allow for permanent treatment remedies to be
considered as further remedial actions. Alternatives 2, 3, and 4
would also include ground water monitoring (with contingency
triggers for further remedial actions if certain action levels
are exceeded), institutional controls, fencing, and deed
restrictions. Installation of a new well in the deeper aquifer
for the Bark residence would be included as part of Alternatives
2, 3, 4, 2TS'and 3TS. A description of the alternatives is
provided below.
.2.1 ALTERNATIVE 1 - NO ACTION
The no action alternative would allow site conditions
to remain as they currently exist. Evaluation of the no action
alternative is required by the National Contingency Plan (NCP)
and also provides a baseline of comparison for the other
alternatives.
2.2 ALTERNATIVE 2 - SOIL COVER
The major component of Alternative 2 is a 2-foot soil
cover which consists of an la-inch thick soil layer overlain by a
6-inch layer of topsoil and vegetation over the DuPont
Impoundment. site fencing, ground water monitoring, cover
maintenance, and deed restrictions would also be incorporated.
Installation of a drinking water well for the Bark residence in
the deeper aquifer is also included in this alternative.
T~e cover would prevent erosion and subsequent direct
contact with the contaminated materials or contaminant transport
by wind or surface water run-off and would also reduce the volume
of. surface water currently infiltrating into the impoundment by
as much as 10% per year.
-------
. -8-
The installation of a new well in the deeper.aquifer for the
Bark residence is necessary because the residence well is -located
in the shallow aquifer and would be the immediate receptor of any
ground water contamination from the DuPont Impoundment that would
migrate beyond the landfill. The Bark well has already detected
concentrations above background for sodium and arsenic which may
indicate that ground water quality is being impacted by the site.
The ground water monitoring system is depicted in Figure
2-1. If the ground water monitoring system at any" time
detects the exceedance of any specified chemical specific action
levels, the exceedance would first be verified through
statistical analysis and additional sampling. If the exceedance
is verified, a cap and slurry wall containment system would then
be installed.
If these action levels are exceeded and the slurry wall
containment system is constructed, another set of action levels
would immediately be in effect in the event of failure of the
containment system. In this case, if any of these action levels
would be exceeded (which will be verified by statistical analysis
and additional sampling), ground water remediation would
immediately be incorporated.
2.2A ALTERNATIVE 2TS - ALTERNATIVE 2 WITH TREATABILITY STUDY
In order to incorporate the preference for permanent
treatment remedies, EPA has developed a.version of Alternative 2
that will allow for treatment as a further remedial action if any
of the chemical specific action levels are exceeded and if
treatment would be determined to be feasible at tha~ time.
". Chemical specific action levels as specified in Table
2-1a and b have been established to trigger further remedial
actions prior to any adverse effects on human health and the
environment. The first set of specified chemical action levels
are as listed on Table 2-1a. If any of these action levels are
exceeded (which will be verified by statistical analysis and
additional sampling), a treatability study of the impoundment
waste will immediately be conducted. If the cost of the
treatment remedy is comparable to the cost of the slurry wall,
either Alternative 4 (cap and slurry wall) or a permanent
treatment remedy of the impoundment material will be selected by
EPA. .
If a second set of action levels, as listed in Table 2-
1b, are exceeded (which will be verified by statistical analysis
and additional sampling), ground water remediation would
immediately be incorporated.
-------
.
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FIGURE 2-.1
~OORNITORING WELL LOCCAnONS
~LTERNATIVE, :2.T.5
TO IMtIOUNCUENT "I/F5
DTZ FA"U LANDFILL SITE
-------
-9-
2.3 'ALTERNATIVE 3 - GEOMEMBRANE MULTILAYER CAP
This multilayer cap would consist of a geomembrane,
gravel drainage layer, geotextile and a soil cover. The other
components, including fence, deed restrictions,' cap maintenance
and the contingent slurry wall would be the same for Alternative
3 as Alternative 2. Like Alternative 2, this alternative would
prevent erosion and direct contact with contaminated soils, and
wind or surface run-off. This alternative would also virtually
eliminate surface water infiltration into the impoundment.
2.3A ALTERNATIVE 3TS - ALTERNATIVE 3 WITH TREATABILITY STUDY
Alternative 3TS has the same components as Alternative 3.
However, Alternative 3TS, like Alternative 2TS, has been
developed to allow the consideration of treatment as a further
remedial action if the chemical specific action levels, as listed
in Table 2-1a, are exceeded.
2.4 ALTERNATIVE 4 - GEOMEMBRANE-CLAY MULTILAYER CAP WITH
BENTONITE SLURRY WALL
Alternative 4 would include'construction of a soil-
bentonite slurry wall in the native soil surrounding the
impoundment in addition to the other components as described in
Alternative 3. A collection system (trench) would also be
installed within the perimeter of the slurry wall to collect
enough ground water to maintain gradient control. This ground
water would be. hauled to a publicly owned treatment works (POTW)
for treatment. This alternative would prevent surface water
infiltration through the impoundme~t and prevent migration of
contaminated ground water from the impoundment.
-------
, Notes:
-lOa-
TABLE 2-1a
IMPLEMENT ALTERNATIVE 4 OR TREATMENT REMEDY
COMPOUND
ORGANICS:
Carbon disulfide
Tetrahydrofuran
INORGANICS:
Arsenic
Chromium (VI)
1.
Action level
HEALTH BASED STANDARD
(UG/L)
3500
700
50
50
ACTION LEVELl
(UG/T,)
500/25~2
100/50
125/503
100/502
= Concentration to go to treatability study
prior to implementing Alternative 4 or a
treatment based alternative at comparable
cost.
2.
The binary values apply to monitoring wells DP05/and
perimeter monitoring wells respectively.
3.
The binary values apply to monitoring wells FS-03, " FS-02/and
MW-2, FS-Ol. .
-------
-lOb-
TABLE 2-1b
IMPLEMENT GROUND WATER REMEDIATION
COMPOUND
HEALTH BASED STANDARD
(UG/L)
ACTION LEVELl
(UGj.L:
ORGANICS:
Carbon disulfide
Tetrahydrofuran
3500
700
3500/17~02
70'0/350
INORGANICS:
Arsenic
Chromium (VI)
50
50
. 25~/753
50
Notes:
~ i.
Action level requiring ground water extraction and treatment
to Maximum contaminant Level.
2.
The binary values apply to monitoring wells DP05/and
perimeter monitoring wells respectively.
The binary values apply to monitoring wells FS-03, FS-02/and
MW-2, FS-Ol.
3 .
4.. Landfill perimeter wells only.
-------
-11-
3.0 SUMMARY OF THE COMPARATIVE ANALYSIS OF THE ALTERNATIVES
The alternatives described in section 2~0 were
evaluated using evaluation criteria presented in EPA Directive
9355.3-02, "Draft Guidance on Preparing Superfund Decision
Documents: The Proposed Plan and Record of Decision." These
criteria relate directly to factors mandated by Section 121 of
CERCLA and as amended by the Superfund Amendments and
Reauthorization Act (SARA) of 1986 and considerations which
measure the overall feasibility and acceptability of the remedy.
These evaluations are summarized below.
3.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
Protection of human health and the environment is the
central mandate of CERCLA, as amended by SARA. Protection is
achieved by. minimizing risks and taking action to ensure that
there will be no future unacceptable risks to human health and
the environment through any pathway. Each remedial alternative
will have different long-term and short-term effects on the
protection of human health and the environment.
Alternative 1, which would allow site conditions to remain
unchanged, would not be protective of human health and the
environment. Under thts alternative, there would be continued
contaminant migration from onsite wastes to ground water and an
unacceptable threat to human health through potential ingestion
of ground water contained within the impoundment or at the
impoundment perimeter.
Alternatives 2, 2TS, 3, 3TS, and 4 would all be protective
of human health and the environment. Alternat~ve 4 would be more
.protective than Alternatives 2, iTS, 3, and 3TS since it would
essentially eliminate contaminant migration to ground water.
However, at this time, there is no confirmed evidence of ground
water contamination by hazardous substances downgradient of the
site, with the possible exception of arsenic at PZ-03. Since
Alternative 4 would be less dependent on ground water monitoring,
it is considered more reliable in the protection of human health
and the environment. A substantial difference in protection of
human health and the environment between Alternatives 2 and 3 and
Alternatives 2TS and 3TS is not anticipated because the o~site
surface water recharge component to the ground water'underneath
the impoundment is thought to be minimal.
3.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS
section 121 (d) of CERCLA, as amended by SARA, requires'
that remedial actions comply with applicable or relevant and
appropriate requirements (ARARs) under Federal and State
-------
-12-
environmental laws. All of the alternatives considered, with the
exception of the no action alternative, meet or exceed ARARs
identified for the site at the landfill boundary. Refer to Table
3.2 which provides a list of the appropriate ARARs for the site.
The trigger levels for monitoring wells installed in the
causeway between the Todtz Landfill site and Murphy's Lake have
been established at values above Maximum Contaminant Levels
(MCL). The ground water between this zone is not considered a
viable water supply, since it is in a mined-out gravel pit area
between two hydraulically connected surface water bodies on the
boundary of the municipal landfill. Therefore, the MCLs would
not be considered applicable, relevant or appropriate.
3.3, REDUCTION OF TOXICITY, MOBILITY OR VOLUME
This evaluation criteria relates to the performance of a
technology or remedial alternative in terms of eliminating or
controlling risks posed by the toxicity, mobility, or volume of
hazardous substances.
None of the six alternatives include treatment of the
contauinated source material of the impoundment as a component to
reduce toxicity, mobility, or volume of hazardous substances.
Treatment of the source material was considered during the
initial phase of the feasibility study, was determined not to be
cost-effective based on the relative low overall risk to public
health and environment, and, therefore, was eliminated during the
screening process. Treatment of a certain amount of ground
wate~, collected to maintain gradient control would take place in
Alternative 4. This is, "therefore, the only alternative which
would use treatment to reduce toxicity and volume of contaminants
at this time. However, Alternatives 2TS and 3TS would allow
treatment of the source material if any of the specified chemical
action levels are exceeded, if the treatment alternative was
cost-effective.
since the contaminated source material would not initially
be treated or removed for Alternatives 2, 2TS, 3, 3TS, and 4, the
toxicity and volume of the source would not be reduced. However,
Alternatives 2, 2TS, 3, 3TS, and 4 would all be effective in
reducing mobility of contaminated soils because capping would
prevent erosion and reduce mobility by wind and surface water
transport. Alternatives 3, 3TS, and 4 would, in addition,
eliminate surface water migration into the ground water.
However, since the waste will remain in contact with the ground
water for Alternatives 2, 2TS, 3, and 3TS andonsite surface
water recharge is relatively small, Alternatives 2 and 2TS would
be virtually as effective as Alternatives 3 and 3TS in reducing
the mobility of the contaminants via surface water recharge to
ground water.
-------
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-------
-13-
Alternative 4 is the only alternative which would not only
reduce the toxicity and volume of the contaminated ground water,
but would also eliminate the mobility of contaminated ground
water outside of the site. However, Alternatives 2, 2TS, 3, and
3TS would contain the necessary contingency triggers to implement
further remedial actions if any of the predetermined chemical
action levels are exceeded in the future.
3.4 SHORT-TERM EFFECTIVENESS
Short-term effectiveness addresses how well an alternative
is expected to perform, the time to achieve performance and the
potential adverse impacts of its implementation.
Adverse impacts to nearby residents and construction workers
involved in impoundment remedial actions will not be significant
for any of the alternatives if the mitigative actions and health
and safety precautions outlined in the feasibility study are
taken. The relatively minor impacts from noise, dust, and
vehicular traffic that do occur during construction are greatest
due to the truck traffic to and from the site. The truck traffic
would be about:
- 1,000 truckloads for Alternatives 2 and 2TS
- 1,400 truckloads for Alternatives 3 and 3TS
- 1,800 truckloads for Alternative 4
The time required between signature of the Record of
Decision (ROD) and completion of remedial actions is not
. significantly different between. alternatives. The estimated
times range from 10 to 12 months for Alternatives 2° and 2TS, 12
to 14 months for Alternatives 3 and 3TS, and 13 to 15 months for
Alternative 4.
3.5 LONG-TERM EFFECTIVENESS AND PERMANENCE
Long-term effectiveness and permanence address the long-
term protection and reliability an alternative affords.
All of the alternatives, except Alternative 1, are nearly
. equal in their effectiveness in preventing erosion of the
contaminated source material given proper construction and
maintenance. They also rely equally on deed restriction and the
IDNR state registry to prevent future development of the site.
Alternatives 2, 2TS, 3, 3TS, and 4 would. all provide
protection to human health and the environment by minimizing
contact with contaminated ground water within the impoundment
-------
-14-
and, through monitoring, possible future contact with
contaminants potentially released from the impoundment. The
differences in effectiveness of the alternatives result from the
varying levels of reliance on ground water monitoring and
implementation of contingency plans to achieve protection.
Alternatives 2 and 2TS would reduce contaminant loa~'ings to
ground water by a maximum of 10 percent and would not
substantially alter contaminant migration when compared to the no
action alternative. The RI results detected elevated levels of
some inorganic constituents, indicating t~at the ground water may
have already been impacted by the site. Therefore, ground water
monitoring of Alternatives 2 and 2TS is necessary to detect the
predetermined chemical specific action levels in order to provide
the time necessary to implement further remedial actions.
Alternatives 3 and 3TS further reduces contaminant loading
to the ground water by essentially eliminating infiltration of
water through the impoundment waste. Because 25 to 50 percent of
the waste would remain in periodic contact with the water table,
it is anticipated that the contaminant loading to ground water
could remain substantial. However, since the onsite surface
water component of ground water recharge is believed to be a
minimal amount of the ground water volume, the reduction of .
contaminant loading by Alternatives 3 and 3TS would probably not
be much different than Alternatives 2 and 2TS. Therefore,
Alternatives 3 and 3TS are similar to Alternatives 2 and 2TS in.
the reliance on monitoring and the contingency for implementation
of further remedial actions.
Alternative 4 reli~s least on ground water monitoring since
the potential for future contaminant levels to exceed health risk
levels in offsite residential wells would be less. The slurry
wall and cap containment would be effective in minimizing future
contaminant contributions to the ground water given proper
maintenance. The contaminants that would remain outside the
containment structure would diminish over time as a result of
dispersion, adsorption, 'biodegradation, or volatilization.
Ground water monitoring would still be implemented to monitor the
migration of residual contamination.
3.6 IMPLEMENTABILITY
Implementability addresses how easy or difficult, feasible
or infeasible, an alternative would be to carry out from design
through construction, operation and maintenance.
The various components of Alternatives 2, 2TS, 3, 3TS, and 4
are proven technologies and materials necessary to implement them
should 'be readily available. Implementation of these
alternatives will require detailed design and competent
supervision.
-------
-15-
Implementation time ranges from 10 to 12 months for
Alternatives 2 and 2TS, 12 to 14 months for Alternatives 3 and
3TS, and 13 to 15 months for Alternative 4.
3.7 COST
CERCLA requires that EPA select the most cost-effective (not
merely the lowest cost) alternative that protects human health
and the environment and meets other requirements of the law.
Treatment alternatives were eliminated during the screening
process since they were not cost-effective. The no action
alternative, which would involve no cost, was considered in order
to meet requirements of the law.
Total capital costs are estimated at $520,000, 880,000 and
2,300,000 respectively for Alternatives 2, 3, and 4. Present
worth operation and maintenance costs (at 5%) are estimated at
$510,000, 560,000, and 520,000 for Alternatives 2, 3, and 4
respectively. The total present worth costs are, therefore,
estimated at $1,030,000 for Alternative 2, $1,440,000 for
Alternative 3, and $2,820,000 for Alternative 4. These costs
were taken directly from the FS Report and are presented for
comparative purpose. Costs for Alternatives 2TS and 3TS are
assumed to be the same as Alternatives 2 and 3, respectively.
Final costs will be developed during design.
Alternative 2TS is' the most cost-effective alternative since
it is t~e least costly alternative that is protective of human
health and the environment and 'meets other requirements of the
,l~.
3.8 COMMUNITY ACCEPTANCE
This evaluation criteria addresses the degree to which
members of the local community support the remedial alternatives
being evaluated.
The local community has not recently expressed concern over
remediation of the Todtz Farm site. There were no written
comments received from the community during the 21-day public
comment period which began on August 20 and ended on
, September 10, 1988.
3.9 STATE ACCEPTANCE
The state acceptance criteria addresses the concern and
degree of support that the state government has expressed
regarding the remedial alternatives being evaluated.
-------
-16-
This is an EPA enforcement-lead site. The state has
participated in the review of all of the RI/FS documents and in
negotiations with DuPont.
In a letter to EPA dated September 10, 1988, the State
indicated a preference for Alternative 4 rather than Alternative
2TS. Subsequently, the EPA and the state discussed the ~ata,
information, technical considerations and legal constraints
involved. The State issued their concurrence on the selected
remedy in a letter dated October 20, 1988.
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-17-
4.0 THE SELECTED ALTERNATIVE
Based on the information available to evaluate the remedial
options against the required nine criteria, EPA"has concluded
that Alternative 2TS is the preferred remedy (Figure 4-1).
The major components of Alternative 2TS are a 2-foot soil
cover, ground water monitoring, site fencing and deed
restrict~ons. The soil cover will provide protection of human
health and the environment against direct contact with the waste.
If the monitoring system detects exceedance of the predetermined
chemical action levels, either a cap and slurry wall containment
system or treatment remedy will be implemented. The monitoring
system and contingency plans would protect human health and the
environment by providing adequate protection against contact with
contaminants in the ground water. Installation of a new well in
the deeper aquifer for the Bark residence will provide additional
protection of human health because the present Bark well would
probably be the immediate receptor of releases of contaminants
from the site.
The preferred remedy satisfies the remedy selection
requirements under CERCLA, as amended, and the National
Contingency Plan (NCP). The pr~ferred remedy at the site is
protective of human health and the environment,. satisfies all
identified applicable or relevant and appropriate environmental
requirements, and is the most cost-effective. The advantages of
this alternative outweigh those offered by the other
alternatives.
In order to initiate construction of the preferred
alternative, detailed design plans and specifications will need
to be prepared. Implementation of the plans and specifications
will need to be conducted by qualified field personnel.
Following is a summary of the components that will be
implemented.
4.1 SOIL COVER
Clearing, grubbing and preliminary grading would be the
first phases of construction. A geotextile layer would then be
placed to provide a distinct boundary between the potentially
contaminated soil and the cover materials and to lessen the
possibility of their mixing in the future.
An lS-inch thick soil layer would then be placed over the
geotextile layer, followed by a 6-inch layer of topsoil (Figure
4-1). The cover will prevent erosion and subsequent direct
contact with the contaminated materials or contaminant transport
by wind or surface run-off. The vegetation and slope of the'
cover will reduce the volume of surface water currently
infiltrating into the impoundment by as much as 10 percent.
-------
. I" 1"'JIIIIl' 1 '91'
I . ",. .
I
GRASS
I
......
. '-.I
PI
I
WASTE
FIGURE 4-1
ALTERNATIVE 2
SOIL COVER nl/fS
(HWONT IM"OllNOMENT
"'-l Sllf.
lOUT I f AIIM t A.-
-
-------
-18-
4.2 ACCESS RESTRICTIONS
A restrictive covenant will be placed on the deed for the
property on which the DuPont Impoundment is located. Deed
limitations would prevent future development of the area without
further remedial action or consideration of impacts to public
health and the environment. The site is being placed on'the Iowa
State' registry of hazardous waste sites. This action will
include a notice on the deed preventing sale of the property or
change in land use without approval by the State.
A site fence will also be installed a minimum of 10-feet
outside of the perimeter of the impoundment to limit access by
human or animal traffic to the contaminated source. The fence
will include a locking gate to allow entry for regular
maintenance, such as mowing or cover repair.
4.3 MAINTENANCE
Site maintenance will consist. of mowing the grass and
repairing the fence. The soil cover will require routine
inspection semiannually for the first 5 years and annually
thereafter. Maintenance would consist of repairing damage caused
by erosion, freeze-thaw, and settlement. It is estimated that
500 cu yards of. soil (10 percent of cover, i-foot thick) will
need to be replaced every 5 years to fill depressions and replace
soil lost by erosion~ The .actual amount of settlement and
erosion occurring will depend on the properties of the materials
dis~osed in the impoundment and the finished surface slopes.
4.4 GROUND WATER MONITORING
Ground water monitoring will .consist of monitoring ,wells
upgradient and downgradient of the site to be sampled and tested
routinely. The ground water monitoring wells included in the
plan are as indicated on Figure 2-1. Bedrock monitoring wells
have been included to document the water quality in the bedrock
aquifer. Monitoring is considered an integral part of this
alternative because detection of contaminants at concentrations
above target leve~s at or within the landfill will call for
immediate implementation of further remedial actions as discussed
further in section 4.5. The target levels are as stated in
Tables 2-la and,2-lb.
All of the shallow wells would be sampled semiannually for
the first 5 years, and on an annual basis thereafter. The deep
wells would be sampled semiannually until four consecutive
samples show no traces of contamination, and once every 5 years
thereafter.
-
-------
-19-
Ground water well samples will be tested for volatile
organic compounds (including tetrahydrofuran), sulfates, .
sulfides, chloride, iron, manganese, phenols, pH, conductivity,
total organic carbon, total organic halogen, sodium, arsenic,
lead, chromium. EPA plans to periodically conduct an independent
analysis of all semi-volatile organic and inorganic compounds.
The ground water monitoring program will include the
following components to detect changes in ground water quality
over time and to verify the exceedance of target contaminant
action levels through statistical analysis.
a.
If contamination is found within 50% of action levels at
any of the perimeter wells or DP-05, quarterly sampling
at the well will be done for 1 year with 4 replicates of
each sample. .
A treatability study will be conducted and either a
treatment remedy (if feasible) or Alternative 4 will be
implemented if in 2 successive sampling episodes, the
mean of any of the concentrations of compounds listed in
Table 2-1a (using the 4 replicates) is significantly
greater than the indicated action level at the 0.05
significance level using the Student's t-test.
b.
c.
Construction of a ground water collection system and
treatment of ground water to MCLs if, in 2 successive
sampling episodes, the mean of any of the concentration
of compounds listed in Table 2-1b (using the 4
replicates) is significantly greater than the indicated
action level of 0.05 significance level using the
Student's t-test. . .
4.5 FURTHER REMEDIAL ACTIONS
EPA has determined that further remedial actions will be
immediately implemented in the event that certain trigger levels
as shown in Tables 2-1a and 2-1b are met or exceeded (which will
be verified by statistical analysis).
If any of the first set of trigger levels as shown in Table 2-1a
are met or exceeded (which will be verified by statistical
analysis), a treatability study will immediately be conducted.
The treatability study will include an evaluation of the most
appropriate technologies that will be available at that time and
their comparative costs. suitable pilot tests and/or bench scale
studies will be conducted as needed. At the conclusion of the
treatability study, EPA will decide whether the remedial action
will consist of treatment of the impoundment waste or
encapsulation by a slurry wall. If the second set of trigger
levels shown in Table 2-1b are met or exceeded (which will b~
statistically verified), remedial action including pumping and
treatment of groundwater will immediately be implemented.
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-20-
The trigger levels, as indicated' on Tables 2-1a and 2-1b
have been established to protect human health and the' .
environment. It should be noted that for carbon disulfide and
tetrahydrofuran, the two contaminants that are the main
fingerprint constituents of DuPont's cellophane 'waste, action
levels that will trigger treatment or encapsulation of the DuPont
Impoundment have been established at less than 10 percent of the
drinking water equivalent level (DWEL) at the landfill boundary
(i.e., 50 ug/l for tetrahydrofuran which has a DWEL of 700 ug/l).
For the implementation of ground water extraction and treatment,
the action levels of, these two compounds have been set at half of
the DWEL at the landfill boundary (i.e., 350 ug/l for
tetrahydrofuran which has a DWEL of 700 ug/l).
For Chromium VI the action levels have been set at the MCL
at the landfill boundary for both sets of trigger levels.
Arsenic, unlike tetrahydrofuran and carbon disulfide, is
found at elevated concentrations in both the DuPont Impoundment
and the municipal landfill as well as some lesser concentrations
upgradient and offsite. Arsenic is not a known constituent of
the DuPont cellophane process. However, a high concentration of
arsenic was found in the DuPont Impoundment.
In the area of PZ-03, where monitoring wells FS-02 and FS-03
will be installed, trig~er levels of arsenic higher than the MCL
of 50 ug/l can be allow~ because the ground water at this.
location cannot potentially be used as a drinking water source.
. The major component of ground water flow in the area of
PZ-03 would be towards Murphy's Lake. The surface water
, concentration of arsenic detected in Murphy's Lake is 1 ug/l.
That is substantially less than the U. S. EPA Ambient Water
Quality criteria of 48 ug/l for the more toxic form of arsenic
which has been developed for the protection of aquatic life.
If the concentration of arsenic of 125 ug/l in monitoring
wells FS-02 and FS-03 is met or exceeded (which will be
statistically verified), a treatability study will immediately be
conducted. The treatability study will include an evaluation of
the most appropriate technologies that will be available at that
time and their comparative costs. suitable pilot tests and/or
bench scale studies as needed will be conducted. At the
conclusion of the treatability study, EPA will decide whether
the remedial action will consist of treatment of the impoundment
waste or encapsulation of the impoundment by a slurry wall.
If the second trigger level of' 250 ug/l of arsenic at FS-02
and FS-03 is met or exceeded (which will be statistically
verified), a ground water extraction and treatment system will be
implemented. The resulting cleanup level will be the MCL of 50
uq/l. '
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-21-
In regard to the trigger levels set for arsenic in FS-Ol and
MW-02, it should be noted that ground water flow from the DuPont
Impoundment would be expected to flow primarily in the
southeasterly direction toward FS-01. However, the onsite
monitoring wells located downgradient of the impoundment and
between the impoundment and FS-Ol have detected relatively low
levels of arsenic as compared to the levels found in the.
impoundment, PZ-03 and Bark's well, the immediate downgradient
receptor. EPA has established that monitoring will be conducted
and treatment or encapsulation of the impoundment will be
implemented if the MCL of 50 ug/l of arsenic is met or exceeded
in FS-01 and MW-2. An additional trigger of 75 ug/l of arsenic
at FS-01 and MW-02 has been established for implementation of
ground water extraction and treatment. If triggered, ground
water extraction and treatment will continue until the MCL of 50
ug/l for arsenic is achieved and maintained at the site boundary.
The only known receptor located directly downgradient of the
site is the. Bark's drinking well, which is presently screened in
the upper sand and gravel aquifer. For an extra measure of
safety, this well will be decommissioned and a new drinking water
well will be installed in the deeper bedrock aquifer, below the
clay aquitard. EPA anticipates that an onsite trigger level of
75 ug/l would not result in contamination of usable ground water
at levels exceeding the MCL of .arsenic of 50 ug/l due to the
natural ground water attenuation and the influence of the
remedial pumping and treatment which would be triggered by a
level of 75 ug/l.
4.6 HEALTH AND SAFETY
A health and safety plan, similar to the one successfully
utilized during the RI/FS activities will be prepared and
.followed during the. remedial action.
It is anticipated that Level D protection will be necessary
for clearing, grubbing, preliminary site grading, and placement
of the geotextile and that minimal protection will be necessary
for placement of the soil cover.
4.7 TIME SCHEDULE
It is estimated that the entire action will take
approximately 10 to 12 months from the beginning of the onsite
mobilization.
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-22-
5.0 STATUTORY DETERMINATION
Based upon available information, the selected remedy
satisfies the remedy selection requirements under CERCLA, as
amended, and the National Contingency Plan. The selected remedy
at the site is protective of public health and the environment,
satisfied all applicable or relevant and appropriate.
environmental requirements and is cost-effective.
The 2-foot soil cover would provide adequate protection of
human health and the environment against direct contact with the
waste. If the ground water monitoring system indicates
exceedance of predetermined chemical specific action levels,
either a cap and slurry wall or treatment remedy will be
installed. The monitoring system and contingency plans would
also provide adequate protection of human health and the
environment against contact~with contaminants in ground water.
It should be noted that the concentrations of arsenic from
the ground water samples taken at PZ-03 were 80 ug/l and 60 ug/l
during the two remedial investig~tion sampling ~vents, which
exceed the Maximum contaminant Level (MCL) of 50 ug/l. The MCL
was established for the protection of human health. However, the
MCL is applicable only if the ground water is a public drinking
water supply and would be considered relevant and appropriate
only if the ground water could be used for human consumption. In
this case, the ground water at PZ-03 would not be considered a
viable water supply and, therefore, the.MCL is not applicable or
relevant and appropriate. The trigger levels for the monitoring
wells to be install~d adjacent to PZ-03 have been established
above the MCL because of the same rationale. However, MCL is the
cleanup level established in the event ground water remediation
is triggered.
The estimated total present worth cost of the selected
remedy is $1,030,000 which includes the cost of soil cover
construction and maintenance and ground water monitoring. The
remedy is the most cost-effective of those that were evaluated.
In evaluation of treatment alternatives, it was determined
that these alternatives are not cost-effective based on the
relatively low overall risk of the site to public health and the
environment. The selected alternative also provides for
treatment in the future if the predetermined chemical action
levels are exceeded and tre~tment would be comparable in cost to
the cap and slurry wall.
Based on the cost-effectiveness, the consideration of
treatment to the maximum extent practicable, and satisfaction of
the remaining nine criteria, the selected remedy provides the
best combination of attribut~s of all of the remedies available
for the site.
-------
-23-
The Agency has determined that 'a five-year review will need
to be conducted onsite since contamination will remain above
health based criteria.
-------
RESPONSIVENESS SUMMARY
Record of Decision for
The DuPont Impoundment 0;
The Todtz Farm Site in
Camanche, Iowa
This Responsiveness Summary presents the responses of the
Environmental Protection Agency (EPA) to public comments received
regarding the Proposed Plan and the Remedial Investigation/
Feasibility'Study (RI/FS) report for the DuPont Impoundment of
the Todtz Farm site in Camanche, Iowa. This document addresses
the comments received by EPA during the public comment period
conducted as part of the remedy selection process. The public
comment period ended on September 10, 1988.
The only. comment received from the local community was in
reg~rd to replacement of a local resident's drinking water well.
A comment letter was a~so received from the Iowa Department of
Natural Resources (IDNR). All of the remaining comments, which
were in regard to the Proposed Plan, were submitted on behalf of
DuPont by their consultant, CH2M Hill.
Comment: The comment or wanted clarification as to whether the
local resident's drinking water well would automically be
replaced as part of the-remedial alternative or whether
_replacement of the well would be contingent on exceedance of
chemical specific action levels. The preference is to have the
well replaced as soon as possible.
Response: Although analyses of samples from the resident's well
has not detected the presence of any compounds which exceed EPA
Primary National Drinking Water Standards (established for
protection of human health), analyses has detected exceedance of
some of the Secondary Drinking Water Standards (sodium and
manganese) which indicate taste and odor characteristics.' Also,
the well would be the immediate receptor of any contamination
migrating from the site.
In response to the comment, the resident's drinking water
well is to be replaced as part of the remedial action and is not
a contingency. Since the remedial action will probably not take
place until next year, EPA will discuss the possibilty of
replacing the local resident's well as soon as possible with'
DuPont. .
-'
-------
2
Comment from the Iowa Department of Natural Resources (IDNR):
In a letter to EPA dated September 10, 1988, IDNR indicated
that Alternative 4 was preferable (among the alternatives'
considered in the FS) because it would not allow further
contaminant migration from the DuPont Impoundment. IDNR further
said that it did not support Alternative 2TS, because it would
allow contaminant concentrations to increase to a level in excess
of the MCL at or beyond the site bowldary. .
At a meeting between EPA and IDNR on October 18, 1988, EPA
explained how the offsite ground water would be protected by the
monitoring program, trigger levels and further contingent
remedial actions. Since tetrahydrofuran and carbon disulfide
triggers would be set at a fraction of the DWE~, the discussion
focused primarily on the arsenic contamination at PZ-03 which
exceeds .the MCL of 50 ug/l. The ground water at PZ-03 would not
be a potential drinking water source and the MCL would not be
considered applicable, relevant or appropriate. EPA further
explained that the trigger levels would provide adequate.
protection of human health and the environment and that an
appropriate remedial response wou~d be implemented if and when
the staged trigger levels were met or exceeded. Further, it was
pointed out that any agreement with a private party to perform
the remedy as contemplated in the.ROD would be incorporated in a
judicial Consent Decree as required by SARA.
In a letter to EPA dated October 20, 1988, IDNR concurred
that the selected alternative would be. an appropriate remedial
response for the site.
. The remaining comments are in regard to the Proposed Plan.
The section, page, and paragraphs referred to below are in
reference to those in the Proposed Plan.
Comment:
p. 2, section 1.3, 1st paragraph, last sentence
The City of Camanche water supply wells are not located
downgradient of the Todtz Farm Landfill site and are not likely
to be affected by any contaminants leaving the site. Further, it
is our understanding that the two water supply wells completed in
the alluvial aquifer are no longer in use due to nitrate
contamination from other sources.
Response: According to the Iowa Department of Natural Resources
(IDNR), the City of Camanche has three municipal water wells
completed in the alluvial aquifer and one deep well completed in
the Jordon aquifer. At this time, the City is using the deep
well exclusively because of nitrate problems in the alluvial
wells. However, the alluvial wells are maintained for use should
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3
the need arise. since these wells lie in the general
downgradient direction of ground water flow, they may possibly be
impacted sometime in the future.
Comment:
p. 2, section 1.3, 3rd paragraph
The North and South Ponds are located onsite, ar,e in direct
contact with municipal refuse, and do not support a thriving
aquatic community. '
The Mississippi wildlife Refuge is so far removed from the
site and 50 unlikely to be affected by the Todtz Farm Landfill
site that its mention as a potential receptor of site
contaminants is, in our opinion, inappropriate and should be
deleted.
Response: The Proposed Plan does not state that the onsite ponds
support a thriving aquatic community.
The Upper Mississippi Fish and Wildlife Refuge is a
potential secondary receptor. Since the HRS scoring system
assigns values to critical habitat within one mile of a Superfund
site, this area meets that criterion. Also, the CERCLA Consent
104/122 Order, signed. by both EPA and DuPont acknowledges the
Refuge as a potential secondary receptor. However, EPA agrees
that the Refuge is far removed from the site and not likely to be
affected.
Comment: p.3, Section 1.4, 1st full sentence
It should be mentioned that the site was listed based on
trace levels of phthalate detec~ed in nearby residential wells,
and that the results of the analyses were questionable because
they were also found in blanks.
Phthalate compounds are ubiquitous in the environment and
are a common constituent of municipal landfill leachate.
It should also be mentioned that the FIT investigation
concluded that there was. no evidence of any release having
occurred from the DuPont Impoundment. However, EPA continued
with additional phases of remedial investigation.
Response: The HRS site scoring for the NPL did include a release
of phthalates at a nearby resident's drinking water well and in
one of the onsite ponds. These samples were collected and
analyzed in August of 1980 according to quality control and
quality assurance procedures that ~ere in effect at that time.
Apparently, no blanks were analyzed.
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4
During the October 1985 FIT site Investigation, phthalates
were detected in several surface water locations. However, the
residential well used in the HRS scoring was not resampled due to
access problems. In June of 1986, a qualification check
conducted of the October 1985 samples indicated that since
phthalates were also detected at certain concentrations in the
blanks, the data were suspect.
EPA acknowledges that phthalate compounds are considered
ubiquitous in the environment and may be a constituent of
municipal landfill leachate. However, they were also reported by
DuPont as being part of the feed stock and waste products
associated with the manufacturing of cellophane and, therefore,
are likely to have originated from the DuPont Impoundment.
since the phthalate data from the FIT Site Investigation was
inconclusive and it had not been resolved whether there was a
release or threat of release, EPA concluded that further
investigation was required. Duri~g the REM II investigation,
tetrahydrofuran and carbon disulfide were detected in elevated
concentrations in MW-3, MW-4, and MW-5. These compounds were
known to be used in DuPont's cellophane manufacturing process.
They became the main contaminants of concern.
Comment:
p. 3, 2nd full paragraph, last sentence
DuPont did not use lead, arsenic, benzene, or mercury in its
manufacturing process nor did it report the use of -these
compounds to EPA. ..
.,' . . ~ '.. .
'. .". .. \ . . .. ~.,'... ... . . -, '.." ,"
, .. -.". ". '-..,. " ". ".' #, ",- .,.~. ,-:..- '.
.," '-.
. -, . ." :..,' . '!
Response: In a response to a CERCLA 104 letter dated August 25,
.1986, DuPont acknowledged the use of lead acetate and mercury in
their laboratory and maintenance but not necessarily in the
cellophane manufacturing process. These constituents were found
in the DuPont Impoundment which was reportedly used only by
DuPont.
It is true that in the same
the use of arsenic or benzene in
however, these constituents also
Impoundment during the RI.
letter, DuPont did not report
the cellophane process to EPA,
were found in the DuPont
Comment:
p.3, section 1.5
The first two sentences of this paragraph are false. First,
the REM II data do not show a release of hazardous substances
from the DuPont Impoundment. Samples collected from wells placed
in the impoundment berm showed the presence of hazardous .
substances. The berm is part of the impoundment and hence part
of the containment structure. The REM II data do not show a
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5
release of hazardous substances beyond the berm of the DuPont
Impoundment. The REM II data do not indicate the presence of any
hazardous substances in the municipal landfill 'either. Secondly,
the scope of the REM II investigation was insufficient to make
the blanket statement that "a significant release of hazardous
substances from the municipal landfill was not observed." The.
REM II contractor placed only one monitoring well at the
periphery of the municipal landfill. Examination of the REM II
ground water data clearly show that this well (MW-2) is
downgradient of only a small portion of the municipal landfill.
Therefore, EPA has no basis in fact for making this statement.
Response: EPA acknowledges that it would be more correct to say,
"Based on investigations conducted prior to 1988, it was evident
that there was a release or threat of release of hazardous
substances from the DuPont Impoundment." The presence of
hazardous constituents in the berm wells indicates that the
constituents have migrated at least as far as the outside
periphery of the berm.
EPA considers the second sentence of page 5, section 1.5 of
the Proposed Plan to be a correct statement, but acknowledges
additional work was needed.that was conducted in the RIjFS.
Gomment:
p.3, Section 1.5, last sentence
What contamination is EPA referring to? The REM II data,
collected prior to 1988, do not show hazardous substances having
been released from the DuPont Impoundment, therefore, it is not
clear what contamination EPA is referring to. The REM II data
showed some elevated concentrations of sodium in a residential
.well downgradient of the Todtz Farm Landfill. Is this the
contamination EPA is referring to? .If so, there is no conclusive
evidence that the DuPont Impoundment is the source of this
elevated sodium. In fact, the municipal landfill is as likely a
source of the elevated sodium as the DuPont Impoundment.
Why is EPA discussing "the remedial alternative selected for
the impoundment" at this point in reference to the REM II work
when the REM II contractor did not perform a feasibility study.
Any discussion of remedial action should be in reference to the
feasibility study performed by DuPont's contractor.
Response: EPA believes that the DuPont Impoundment is a
potential source of contamination for the Todtz Farm Landfill.
This fact is evidenced based on the levels of contaminants
observed in MW-3, MW-4 and MW-5. These wells are located on the
outside periphery of the berm and indicate that hazardous
constituents are migrating into and at least as far as the back
edge of the berm.
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6
The contamination referred to is tetrahydrofuran and carbon
disulfide which are fingerprint constituents of the cellophane
manufacturing process.
EPA acknowledges that discussion of remedial alternatives
for the impoundment is more appropriate in reference to the RI/FS
as opposed to the REM II investigation alone. On the basis of
the RI/FS, EPA believes that the selected remedy will suffice for
the entire Todtz Landfill site. '
Comment:
p.4, section 1.6 1st paragraph
The objective of the RI/FS was to determine the physical and
chemical characteristics of the DuPont Impoundment, determine
whether a release of DuPont related constituents had occurred
beyond the confines of the DuPont Impoundment and, if a release
had occurred, evaluate the extent of the released constituents
and determine if released constituents presented a risk to human
health or the environment.
Response: EPA believes that the objective of the RI/FS stated
above is consistent with that stated in the Proposed Plan.
Comment:
p. 4, section 1.7.1, 1st paragraph
The first sentence should be changed to read. . . . ; and
environmental sampling task to determine whether DuPont related,
constituents had migrated from the impoundment to surrounding
surface water bodies and grpund water.
, The impoundment wastes are periodically in contact, with
ground water.
Samples from the Todtz and Bandixen residential wells,
completed in bedrock, provide some indication of local bedrock
aquifer qround water qu~lity.
Response: EPA acknowledges that the statement as provided above
is that presented in the DuPont RI/FS report. However, the
DuPont-related constituents contain the contaminants of concern
so there is no need for revision of the sentence.
EPA stands by the statement as given. Figure 3-12, 3-13,
3-14, and 3-15 in the DuPont RI report do not illustrate an
instance when at least a portion of the waste material is not in
direct.contact with the qround water.
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7
EPA acknowledges that samples from the Todtz and Bandixen
residential wells do provide some indication of local bedrock
aquifer ground water quality. However, ground water quality in
the bedrock has not been specifically investigated at this time.
. Comment:
p.4, section 1.71, 2nd paragraph
EPA should mention that only one background soil sample was
collected and that this one sample may not reflect true
background conditions. .
Response: EPA acknowledges that only one background soil sample
was collected. However, the information obtained from this
single sample is more useful than a strict comparison to
literature values in estimating background concentrations.
Comment:
p. 4, Section 1.71, 3rd paragraph
The use of the word"significantly" is inappropriate.
PZ-01should be changed to PZ-02.
The above background concentrations of inorganic
constituents in DP-02, DP-OS, and PZ-02 and the Bark well could
very well be from the municipal landfill.
Response: EPA believes that order of magnitude differences are
significant.
EPA acknowledges that PZ-01 is incorrectly identified and
that the well referred to should be PZ-02.
The statement does not assert that the inorganic
constituents originated from the DuPont Impoundment.
states that they were also observed in these wells.
It simply
Comment:
p. 4-5, section 1.71, last paragraph
DuPont feels that this paragraph is biased against DuPont by
not presenting the complete facts relative to this matter.
EPA fails to mention that ~etrahydrofuran was not detected
in the three rounds of sampling the same wells by DuPont's
contractor including the first round, for which EPA split
samples. EPA also fails to mention that independent review of
EPA's data package showed that the EPA contract laboratory did
not meet the criteria for identification of tetrahydrofuran. .
Therefore, the EPA data are suspect.
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8
In our opinion there is no conclusive evidence of DuPont
related constituents being present in monitoring wells DP-02,
DP-OS, PZ-02 and the Bark residential well. .
Again, based on the findings of the DuPont RI, it i$ not
clear exactly what contamination EPA is referring to.
Response: EPA acknowledges that the tetrahydrofuran (THF) found
in the split sample analysis was not confirmed during a
subsequent sampling event and that two of the values were below
the contract detection limit (M-coded) and are, therefore,
estimates. EPA also acknowledges that DuPont's laboratory
reviewed the data and questions whether the contract laboratory
met identification criteria. However, EPA Region VII laboratory
re-reviewed the data and believes that the THF was present in the
samples. The commenter also did not mention that the detection
limit utilized by DuPont's laboratory was higher than that used
by EPA (10 ug/l versus S ug/l) during the sampling event in which
EPA identified the presence of THF in DP-02, DP-OS, and PZ-02.
EPA does not refer to contamination of any kind in this
paragraph.
Comment:
p. 6, last paragraph, 1st sentence
Dupont cannot agree with this statement.
clear to what contamination EPA is referring.
. findings of the RI conclude the following:
First " it is not
Secondly, the'
. .
While there is evidence that ground water degradation has
occurred downgradient of the DuPont Impoundment, degradation
,cannot be conclusively tied to the DuPont Impoundment
because of the intervening presence of municipal refuse
between the DuPont Impoundment and downgradient sampling
points. There is also no conclusive evidence that the upper
sand and gravel aquifer has been contaminated by DuPont-
related constituents beyond the perimeter of the DuPont
Impoundment with the exception of arsenic which is present
in low concentrations in piezometer PZ-03.
Potential human environmental exposures resulting from
direct contact or ingestion of surface water downgradient of
the impoundment do not exceed criteria u~ed by EPA in
evaluating whether humap health or the environment are
protected with the exception of arsenic. Concentrations of
arsenic in onsite surface water bodies exceed the Ambient
Water Quality criteria for the Protection of Human Health at
a 1 x 10- . protection level but do not exceed the MCL.
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9
Exposures to human health or the environment through
ingestion or direct contact with ground water from the
shallow aquifer at or near the Todtz Farm Landfill perimeter
are also below the criteria used by EPA in evaluating whether
human health or the environment are protected with the'
exception of arsenic which exceed the MCL at PZ-03.
None of these statements imply or conclude that the DuPont
Impoundment is the source of any "contamination" at the Todtz
Farm site with the possible exception of arsenic in PZ-03.
Response: EPA believes that the DuPont Impoundment' is the source
of the tetrahydrofuran (THF) observed in the EPA split samples
and at least one of the sources of the elevated arsenic level in
PZ-03. EPA also believes that the DuPont Impoundment is
contributing to the elevated sodium levels observed in wells
downgradient of the landfill. The RIfFS does not appear to
identify any contaminants of concern migrating from the Todtz
Landfill site that are not present in significant concentrations
in the DuPont Impoundment. Tetrahydrofuran and carbon disulfide
found at high 'concentrations in the DuPont Impoundment appear to
be in the process of migrating and remain sources of
contamination at the Todtz Farm Landfill Site as a whole.
Comment:
p.7, section 2.0, 1st paragraph
The second sentence should be changed to read: "Excavation
of the impoundment wastes and disposal at a RCRA landfill or
treatment onsite using incineration."
Response: EPA acknowledges that this statement, as presented
above, is consistent with statements made in the DuPont RIfFS
report. However, the statement does not acknowledge that other
technologies were also screened out. The sentence in the
Proposed Plan should be restated as follows: "Excavation of the
impoundment wastes and disposal at a RCRA landfill or treatment
onsite using inceration, stabilization, or in-situ treatment
technologies were eliminated since they were not cost-effective
based on the relatively low risk to public health and the
environment and the large capital cost."
Comment:
p. 8, 1st paragraph
All references to the DuPont Impoundment'i~ this paragraph
should be changed to the Todtz Farm Landfill.
Response: EPA believes that this comment is correct and would
consent to changing references to the Todtz Farm Landfill. .
However, EPA notes that sodium and arsenic detected in the Bark's
well are in .uch higher concentrations in the DuPont Impoundment.
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10
Comment:
p.S, 2nd paragraph
This statement is not quite true. If an exceedance of a
trigger compound is detected, steps will be taken to verify this
exceedance through statistical analysis and additional sampling.
If the exceedance is verified, then DuPont will undertake
treatability studies to determine whether a treatment based
remedial action is appropriate. If the treatment based option is
determined to be appropriate and is comparable in cost to
Alternative 4, the treatment based remedial action will be
implemented.
Response: EPA acknowledges that a statistically based analysis
will be performed to verify if the action levels have been
exceeded. It should also be noted that there is a difference
between Alternative 2, which is described in the RI/FS report and
section 2.2 ~f the Proposed Plan, and Alternative 2TS, which is
described in Sectiion 2.2A. Alternative 2TS is similar to
Alternative 2 except that Alternative 2TS calls for a treatment
study and implementation of a treatment remedy if action levels
are exceeded and if treatment is determined to be cost-effective
at that time.
Comment:
p. 10, Table 2-1b
Chromium (Total) should be changed to Chromium (VI).
Response:
EPA acknowledges the change.
Comment:
p. 13, Se~tion 3.2, 2nd paragraph
Change the word berm to causeway. Confusion may result
because the word berm is used consistently in reference to the
berm encapsulating the DuPont Impoundment.
Response: EPA acknowledges that the use of the word berm may be
confusing and agrees that causeway is an appropriate description.
However, EPA further wants to point out that the berm does not
encapsulate the impoundment but surrounds.
Comment:
p.14, section 3.4, 1st paragraph
Short-term effectiveness addresses the effect of an
alternative during construction and implementation.
Response: EPA agrees that short-term effectiveness does address
,
the effect of an alternative during construction and
implementation. However, it also defines the period of time
needed to achieve protection of human health and the environment
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11
during implementation of a remedy and until cleanup goals are
reached. This definition is consistent with that provided in the
Proposed Plan.
Comment:
p. 15, 2nd paragraph, 2nd sentence
The sentence should be modified to reflect that the
municipal landfill may also be affecting ground water quality.
Response: EPA acknowledges that the municipal landfill may also
be affecting ground water quality.
Comment: p. 18, Section 4.0, 2nd paragraph
The paragraph should be clarified that deed restrictions
will be placed. on the Todtz property and that the DuPont
Impoundment will be fenced as part of the remedial action, not
the entire Todtz Farm Landfill.
Response: EPA agrees with the_comment.
made in section 4.2.
This clarificatiion is
Comment:
p.20, 3rd paragraph
Ground water samples will be' analyzed for all of the
.compounds listed EXCEPT lead, barium, beryllium, and mercury. To
the best of our knowledge, DuPont agreed ~o add arsenic, sodium
and chromium to the iist of analytes, but at no time agreed to add
lead, barium, beryllium, or mercury. EPA should delete these
compounds from the list. .
Response: EPA acknowledges that DuPont did not agree to analyze
for lead, barium, beryllium or mercury. However, EPA intends to
include these metals in the list of analytes.
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