United States Office of
Environmental Protection Emergency and
Agency Remedial Response
EPA/ROD/R07-91/052
September 1991
&EPA Superfund
Record of Decision:
People's Natural Gas, IA
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50272-101
I REPORT DOCUMENTATION .'1. REPORT NO. , ~ 3. RKIpIenI'. ACC888/on No.
PAGE EPA/ROD/R07-91/052
, 11tI8 8nd SubIIII8 S. R8por1 Data
SUPERFUND RECORD OF DECISION 09/16/91
People's Natural Gas, IA
6.
First Remedial Action - Final
7.~.) s. Performing Organization Rapt. No.
II. ParformIng Org8lnlZ8llon N8nw and Adell-. 10. PtojactlT88k/Work Unit No.
11. Contr8ct(C) or Grant(G) No.
(C)
(G)
1~ SponaorIng Organization N8nw and Add- 13. Type of R8por1 & PertocI Cowred
U.S. Environmental Protection Agency 800/000
401 M Street, S.W.
Washington, D.C. 20460 14.
15. ~18ry No..
16. Abalr.a (UIri\: 2110 worda)
The 5-acre People's Natural Gas site is a former coal gasification plant in Dubuque
County, Iowa. The city of Dubuque maintains a public works garage on the eastern
portion of the site, and the Iowa Department of Transportation owns the western
portion. The site is located 300 feet west of the Mississippi River, and is within
the Mississippi River floodplain. In addition, the site overlies a silty sand unit
and an alluvial aquifer, which has been determined to be a potential source of
drinking water. Surrounding land use is primarily industrial and commercial, with
adjacent residential areas. From at least the 1930's to 1954, the site was used to
manufacture gas. By-products produced during this process included coal tar, which
was stored in an underground tank and an above-ground tank, and cyanide-bearing
woodchips, which were buried on the eastern portion of the site. From 1954 to 1964,
the site was used as a natural gas distribution, storage, and maintenance facility.
In 1986r EPA investigations identified extensive contamination of onsite soil and
ground water at the site. In 1989, the PRPs conducted a removal action that included
excavating 5,500 cubic yards of PAH-contaminated soil from the western portion of the
site, removing tanks used to store coal tar, installing a leachate collection system
to prevent contamination from leaching into the alluvial aquifer; and implementing
(See Attached Paqe)
17. Document An81y818 L De8eltptora
Record of Decision - People's Natural Gas, IA
First Remedial Action - Final
Contaminated Medium: soil, gw
Key Contaminants: VOCs (benzene, toluene, xylenes), other organics (PAHs)
b. Id8ntIfIer8IOpen-Ende Tarma
Co COBAn ReIdIGroup
18. AYaiiabIIIty s..~\ 111. Securt\y a... (1111. Report) 21. No. of P.ge.
None 86
20. S8c:urity a... (1hI8 P.ge) ~ PrIce
. N"'ne
(4-71)
(See AN5Io238.18)
See IMlrUClioM on Revef'H
(Formerly NTlS-35)
Department of Commerce
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EPA/ROD/R07-91/052
People's Natural Gas, IA
~irst Remedial Action - Final
Abstract (Continued)
institutional controls. This Record of Decision (ROD) addresses both soil and ground
water contamination, as a final remedy. The primary contaminants of concern affecting
the soil and ground water areVOCs including benzene, toluene, and xylenesi and other
organics including PARs. .
The selected remedial action for this site includes excavating and incinerating an
estimated 18,500 cubic yards of contaminated soil offsitei treating the soil and
ground water within the silty sand unit, which are contaminated with coal tar wastes
using in-situ bioremediationi pumping and onsite treatment of contaminated ground
water using air stripping followed by offsite and storm sewers discharge to a publicly
owned treatment works (POTW); ground water and air monitoring; and implementing
institutional controls such as ground water and land use restrictions, as well as site
access restrictions including fencing. A contingency for ground water treatment
includes engineering controls and an ARAR waiver if the extraction system does not
achieve cleanup levels. The estimated present worth cost for this remedial action is
$8,000,000, which includes an estimated O&M cost of $788,000 for 10 years.
PERFORMANCE STANDARDS OR GOALS: Federal and State clean-up standards for soil have
not been established at this time. Therefore, goals for soil clean-up are based on a
carcinogenic risk level of 10-~ and include 500 mg/kg for total PAHs and carcinogenic
PARs 100 mg/kg. Remediation levels for ground water are based on SDWA MCLs, and
include benzene 1 ug/l.
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RECORD OF DECISION
PEOPLES NATURAL GAS COAL GASIFICATION SITE
DUBUQUE, IOWA
Prepared by:
U. S. ENVIRONMENTAL PROTECTION AGENCY
REGION VII
KANSAS CITY, KANSAS
SEPTEMBER 1991
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DECLARATION
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Declaration for the Record of Decision
Peoples Natural Gas Coal Gasification Site
Dubuque, Iowa
Statement 2f Basis ~ Purnose
This decision document presents the selected remedial action
for the Peoples Natural Gas Coal Gasification site, in Dubuque,
Iowa. The selected remedy was chosen in accordance with the
requirements of the Comprehensive Environmental Response, Compen-
sation, and Liability Act of 1980 (CERCLA), as amended by the
Superfund Amendments and Reauthorization Act of 1986 (SARA) and
the National Oil and Hazardous Substances Pollution contingency
Plan (NCP). This decision document explains the factual and
legal basis for selecting the remedy for this site. The informa-
tion supporting this remedial action decision is contained in the
administrative record for this site.
The State of Iowa concurs with the selected remedy.
Assessment 2! the ~
Actual or threatened releases of hazardous substances from
this site, if not addressed by implementing the response action
selected in this Record of Decision (ROD), may present a
current or potential threat to public health, welfare, or the
environment.
DescriDtion Qt ~ Selected Remedv
The principal threat at this site is buried coa~ tar waste
and cyanide bearing woodchips that present a direct contact
threat to on-site workers and has contaminated the ground water.
Volatile organics and polynuclear aromatic hydrocarbons have
leached from the tars into' the ground water.
The major components of the selected remedy include the
following: .
. Excavation and off-site incineration of coal tar contami-
nated soil:
. Extraction of contaminated ground water to reduce concen-
trations to acceptable levels and treatment and discharge of
extracted ground water to the City of Dubuque sewer system:
. The in-situ treatment of certain coal tar contaminated
areas by the injection of nutrients into the aquifer to stimulate
biological degradation, and
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. Ground water monitoring to assure successful implementa-
tion of treatment systems.
Declaration g! statutory Determinations
The selected remedy is protective of human health and the
.environment, complies with federal and state requirements that
are legally applicable or relevant and appropriate to the
rem~dial action, and is cost-effective. This remedy utilizes
permanent solutions and alternative treatment technologies to the
maximum extent practicable, and it satisfies the statutory
preference for remedies that employ treatment that reduce
toxicity, mobility, or volume as their principal element.
Institutional controls will be installed at the site to insure
that the remedy provides protection of human health and the
environment. This.protection is based on health-based levels
that have been determined to be protective in conjunction with
institutional controls. Because these controls will not allow
for unlimited use and unrestricted exposure at the site, a review
will be performed no less often than every five years after
initiation of the selected remedial action.
~/L{~
'!Morri Kay
/Regional Administrator
united states Environmental
Region VII
9-16 -q/
Date
Protection Agency
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TABLE OF CONTENTS
DECISION SUMMARY
1.0 SITE BACKGROUND
1.1 SITE LOCATION AND DESCRIPTION
1.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES
1.3 REMOVAL ACTIONS
1.4 COMMUNITY RELATIONS ACTIVITIES
2.0 SCOPE OF RESPONSE ACTIVITIES
3.0 SUMMARY OF SITE CHARACTERISTICS
3.1 CONTAMINANT CHARACTERIZATION
3.2 CHARACTERIZATION OF THE NATURE AND EXTENT OF
CONTAMINATION
3.3 NATURE AND EXTENT OF CONTAMINATION
3.3.1 SURFACE AND SHALLOW SUBSURFACE RESULTS
3.3.2 DEEP SUBSURFACE RESULTS
3.3.3 GROUND WATER RESULTS
4.0 SUMMARY OF SITE RISKS
4.1 OVERVIEW OF BASELINE RISK ASSESSMENT
4.2 INDICATOR COMPOUNDS
4.3 EXPOSURE ASSESSMENT
4.4 TOXICITY ASSESSMENT
4.5 RISK CHARACTERIZATION
4.5.1 RISKS FROM NON-CARCINOGENIC COMPOUNDS
4.5.2 RISKS FROM CARCINOGENIC COMPOUNDS
4.5.3 RISKS FROM EXPOSURE TO SOILS
4.5.4 RISKS FROM EXPOSURE TO GROUND WATER
4.5.5 UNCERTAINTIES
4.5.6 CONCLUSION
4.6 REMEDIATION GOALS
5. 0 SUMMARY OF ALTERNATIVES
5.1 NO ACTION
5.2 REMOVAL ACTION WITH GROUND WATER QUALITY MONITORING
5.3 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATER
EXTRACTION AND TREATMENT . .
5.4 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATER
EXTRACTION AND TREATMENT, CAPPING OF SOURCE SOILS, AND
IN-SITU BIOREMEDIATION
5.5 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATER
EXTRACTION AND TREATMENT AND REMOVAL OF SOURCE SOILS
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6.0 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES
6.1 OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
6.2 COMPLIANCE WITH ARARS . .
6.3 LONG-TERM EFFECTIVENESS AND PERMANENCE
6.4 REDUCTION OF TOXICITY, MOBILITY, OR VOLUME
6.5 SHORT-TERM EFFECTIVENESS
6.6 IMPLEMENTABILITY
6.7 COST
6.8 STATE ACCEPTANCE
6.9 .COMMUNITY ACCEPTANCE
7.0 SELECTED REMEDY
8.0 STATUTORY DETERMINATIONS
8.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
8.2 COMPLIANCE WITH APPLICABLE RELEVANT AND APPROPRIATE
REQUIREMENTS
8.3 COST-EFFECTIVENESS
8.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE
TREATMENT TECHNOLOGIES TO THE MAXIMUM EXTENT
PRACTICABLE .
8.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT
9.0 DOCUMENTATION OF SIGNIFICANT CHANGES
APPENDIX A
RESPONSE TO PUBLIC COMMENTS ON THE. PROPOSED PLAN
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Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
LIST OF FIGURES
Location Map - Peoples Natural Gas site
Vicinity Map - Peoples Natural Gas site
site Plan - Existing Conditions, 1990
Proposed u.s. Highway 61 Alignment
Geologic Cross Section Locations
Geologic Cross Section 4 - 4'
Completed Removal Action site Plan, 1990
Location of Tar/Ammonia Tanks and Gas Plant Waste
Disposal Area
Estimated Limits ofPAH Soil Contamination
PAH Cross Section 4 - 4'
Estimated Limits of BETX Soil Contamination
Distribution of PAHs in Ground Water, February 1990
Distribution of BETX in Ground Water, November 1989
Distribution of BETX in Ground Water, January 1990
,
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Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
Table 8
Table 9
Table 10
Table 11
Table 12
Table 13
Table 14
Table 15
Table 16
Table 17
LIST OF TABLES
Summary of Maximum Contaminant Concentrations for
Disposal Area
Summary of Maximum contaminant Levels in Ground Water
Summary statistics for Analytical Data, Detected
Compounds in Soil
Summary statistics for Analytical Data, Detected
Compounds in Ground Water
Remediation Levels in Ground Water
Indicator Compounds for Risk Assessment Compounds
Calculated Incremental Lifetime Cancer Risks and Global
Hazard Indices
Carcinogenic Risks - Residential Exposure Ingestion of
Chemicals in Soil by Children
Carcinogenic Risks - Residential Exposure Ingestion of
Chemicals in Soil by Adults
Carcinogenic Risks - Residential Exposure Ingestion of
Chemicals in Soil by Municipal Garage Workers
Carcinogenic Risks - Residential Exposure Ingestion of
Chemicals in Soil by Construction Workers
Ground Water Results for Risk Assessment
Carcinogenic Exposure Calculations for Ingestion of
Chemicals in Drinking Water - Alluvial Aquifer
Carcinogenic Exposure Calculations for Ingestion of
Chemicals in Drinking Water - Water Table Wells
Noncarcinogenic Exposure Calculations for Ingestion of
Chemicals in Drinking Water - Alluvial Aquifer
Noncarcinogenic Exposure Calculations for Ingestion of
Chemicals in Drinking Water - Water Table Wells
Cost Estimate Summary for Selected Remedy
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RECORD OF DECISION
DECISION SUMMARY
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1.0
SITE BACKGROUND
1.1
SITE LOCATION AND DESCRIPTION
The Peoples Natural Gas site is located in Dubuque, Iowa, a
city of approximately 100,000 people, in eastern DUbuque County.
The address of the site is 925 Kerper Boulevard. Maps of the
vicinity and site location are shown in Figures 1-3.
The site occupies approximately 5 acres. It is bounded by
11 th Street to the north, Kerper Boulevard to the south and east,
and the Soo Line railroad track that parallels Pine Street to the
west. The southeast boundary of the site extends to within 300
feet of Dove Harbor on the Mississippi River.
The eastern portion of the site is owned and occupied by the
city of Dubuque. The City of Dubuque Street Division operates
out of the public works garage built on the site. The garage and
the surrounding land are used to store street maintenance vehi-
cles and cars for city officials. Also, the Street Division
stores snow removal chemicals (rock salt and liquid calcium
chloride) as well as sand on the City's portion of the site. The
western portion of the site is owned by the Iowa Department of
Transportation (IDOT). A highway is scheduled for construction
on this portion of the site with a projected completion date of
July 1992. The highway corridor is diagramed in relation to the
site in Figure 4.
The site is\located 300 feet west of the Mississippi River
on a broad Mississippi River flood plain. Sediments underlying
the fill material at the site generally consist of unconsolidated
silts, sands, and clays. The hydrogeologic setting of the site
consists of surficial material and an underlying clay unit (upper
confining unit)~ and an underlying thin silty sand (silty sand
unit) which is separated from an alluvial sand (alluvial aquifer)
by a thin clay unit (lower confining unit). Ground water in the
silty sand unit and the alluvial aquifer flow to the northeast
toward a high capacity well field located 1,800 feet north of the
site. Ground water in the alluvial aquifer in the vicinity of
the site is. classified as Class IIB, a potential source of drink-
ing water. The geologic features are shown in Figure ~ as a
vertical cross section through the site shown as section 4 - 4'
in Figure 5.
A well search was conducted for the area within a one-mile
radius of the Peoples site to identify wells in the vicinity that
could be affected by the site and to identify local wells that
pump large enough volumes of water to influence.ground water in
the vicinity of the site. The results of the well- search indi-
cate that there are no wells on or near the site that are used as
a source of drinking water.
1
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1.2
SITE HISTORY AND ENFORCEMENT ACTIVITIES
The Peoples site is the location of a former coal
gasification plant formerly owned and operated by the Key City
Gas Company. The manufacture of gas at the site occurred from
approximately the 1930's to 1954 and ceased with the availability
of natural gas to the community.
During operations, the plant produced as by-products coal
tar and cyanide-bearing woodchips and stored them on the site.
The coal tar was stored in one 14,000 gallon underground concrete
tank and one 7,000 gallon above ground tank. A large portion of
the coal tar was transferred to railroad cars and sold for use as
wood preservative and road treatment. The woodchips were buried
on the eastern portion of the site. The hazardous constituents
of concern associated with the coal gas process include: polycy-
clic aromatic hydrocarbons (PAHs); phenols; aromatic volatile
organic compounds, including benzene, ethylbenzene, toluene, and
xylene (BETX); and cyanide.
North Central Public Service Company acquired ownership of
Key City Gas in approximately 1954. Northern Natural Gas
Company, which later became Peoples Natural Gas (PNG), acquired
ownership of the site in approximately 1957. PNG used the site
as a natural gas distribution, storage, and maintenance facility.
The City acquired the site property in 1964. IDOT acquired the
western one-third of the site in 1985.
In November 1986 the Environmental Protection Agency (EPA)
conducted an, Expanded Site Investigation (ESI) at the site. The
ESI documented extensive soil contamination and ground water
releases of phenol, cyanide, and PAHs.
EPA proposed that the site be listed on the National Priori-
ties List in June 1988. On August 30, 1990, the Peoples site was
listed as a National Priorities List site.
On'April 19, 1989, EPA issued an Administrative Order on
Consent to Midwest Gas, a division of Iowa Public Service
Company, the successor to North Central Public Service Company;
the Iowa Department of Transportation; and the City of Dubuque.
. All three entities are parties to the Administrative Order on
Consent. The order required these parties to conduct a removal
action and a Remedial Investigation and Feasibility Study
(RIjFS). The purpose of the Remedial Investigation was to deter-
mine the source as well as the nature and extent of contamination
at the site and to collect the data necessary to determine the
proper alternatives to be evaluated ,in the Feasibility Study.
Midwest Gas contracted with Barr Engineering of Minneapolis,
Minnesota to conduct sampling at the site, which included surface
soil, ground water, sediment, and surface water samples. Midwest
Gas prepared an RIjFS Report which was reviewed by EPA. The
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final RI/FS Report was completed in May 1991. Based on the
findings of the FS, EPA prepared a Proposed Plan which described
the selected remedy for this site.
The Administrative Order also required that the parties
conduct a site Characterization and Removal Alternative study
(SC/RAS) to determine the extent of contamination of soils in the
Highway 61 corridor. Midwest Gas conducted the study and pre-
pared a SC/RAS Report which was reviewed by EPA and used to
determine the scope of removal activities in the highway corri-
dor. The final SC/RAS Report was completed in January 1990.
Based on information presented in the SC/RAS reportEPA developed
a Removal Action Decision Document (RADD) dated June 6, 1990
which presented the selected removal action for the highway
portion of the site. The RADD also presented the factual and
legal basis for the selected removal action.
1.3 REMOVAL ACTIONS
Midwest Gas is nearing completion of a removal action on the
western portion of the Peoples site within the construction
corridor for u.s. Highway 61. Figure 7 shows the extent of
excavation conducted during the removal action. The excavation
portions of the removal action were completed in July 1991 and
included excavation of contaminated soils, removal of underground
tanks used to store coal tar, installation of a leachate collec-
tion system to prevent contamination from leaching into the
alluvial aquifer, and institutional controls to prevent public
exposure to soils exceeding 100 mg/kg (milligrams per kilogram or
PPM) carcinogenic PAHs. All soils exceeding the cleanup stand-
ards, which were excavated as part of removal action, will be
incinerated off-site. Approximately 5,500 cubic yards of soils
and stabilized coal tar sludges were excavated. Cyanide bearing
woodchips were not encountered during removal activtties.
As part of the removal action, soils to a depth of 6 feet
were excavated which contained concentrations in excess of 100
mg/kg carcinogenic PAHs and 500 mg/kg total PAHs. This depth of
excavation and these cleanup levels were selected to remove the
threat of direct contact with site soils by persons working on
the ~ite or potential onsite residents. In addition, soils were
excavated below 6 feet that contained concentrations in excess of
200 mg/kg carcinogenic PAHs and 2,900 mg/kg total PAHs. This
depth of excavation and these cleanup levels were selected to
protect the ground water from future leaching of volatile organic
compounds and PAHs into the aquifers. The Agency for Toxic
Substances and Disease Registry (ATSDR) was consulted regarding
the cleanup level for soils excavated below 6 feet. As stated in
ATSDR's response to EPA " ATSDR considers a concentration of
200 mg/kg total PAHs and 2,900 mg/kg carcinogenic PAHs remaining
in the subsurface soils to be protective of human health."
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Midwest Gas prepared a Removal Action Report (RAR) in July
1991. The RAR summarizes the removal action that was completed
at the Peoples site within the Hiqhway 61 corridor. Detailed
descriptions of construction and excavation activities are in-
cluded in the RAR.
1.4
COMMUNITY RELATIONS ACTIVITIES
The RI/FS Report and the Proposed Plan for the Peoples site
were released to the public for comment. The public comment
period was from June 17, 1991 to Auqust 17, 1991. These two.
documents were made available to the public with the administra-
tive record, which is located at the information repositories
maintained at the Dubuque Public Library and at the EPA Reqion
VII office. The notice of availability for these documents was
published in the Dubuaue TelearaDh Herald on June 17, 1991. A
public meetinq was held on July 9, 1991 in Dubuque, Iowa. At
this meetinq, representatives from EPA, the State of Iowa, and
the Aqency for Toxic Substances and Disease Reqistry (ATSDR)
answered questions about problems at the site and the remedial
alternatives under consideration. A summary of comments received
at this meetinq and durinq the comment period and EPA's response
to those comments, the Responsiveness Summary, is attached hereto
as Appendix A. Community involvement activities were conducted
as a requirement of sections 113 and 117 of CERCLA.
2.0
SCOPE OF RESPONSE ACTIVITIES
The response activities described in this Decision Summary
address all contaminants known at the site. When implemented,
these actions will eliminate the need for future response actions
at the site. This ROD is intended to be the final ROD for the
site. The principal threat at this site is buried coal tar waste
and cyanide bearinq woodchips that present a direct contact
threat to on-site workers and have contaminated the qround water.
Volatile orqanics and polynuclear aromatic hydrocarbons have
leached from the tars into the qround water. .
~3.0
SUMMARY OF .SITE CHARACTERISTICS
3.i
CONTAMINANT CHARACTERIZATION
Coal tar waste contains polynuclear aromatic hydrocarbons
(PAHs) such as naphthalene and benzo(a)pyrene. Also produced
from coal tar wastes are volatile orqanic contaminants, such as
benzene, ethylbenzene, toluene, and xylene (BETX), and semi-vola-
tile contaminants, such as methylphenol, dibenzofuran, and
phenol. Cyanide can also be associated with coal tar wastes
includinq wood chips used for qas purification. .
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3.2
NATURE AND EXTENT OF CONTAMINATION
The Remedial Investigation identified the source of contami-
nation and characterized the nature and extent of contamination
at the site. The discussion of these findings is divided into
four main groups: surface and shallow subsurface results, deep
subsurface results, and ground water results. A site diagram
displaying areas of soil contamination is shown in Figure 8. The
removal action involved excavation of soil contamination in the
tar tank area. The area excavated as part of the removal action
is shown in Figure 7. Areas of contamination discussed in this
section pertain to the soils not addressed during the removal
action which are currently located on the eastern portion of the
Peoples site.
Maximum contaminant concentrations for soil and source areas
remaining at the site are summarized in Table 1. Maximum contam-
inant concentrations for ground water are summarized in Table 2.
standards for these contaminants are summarized in Table 5.
3.2.1 SURFACE AND SHALLOW SUBSURFACE RESULTS
. .
The highest concentrations of PAHs in surface and shallow
subsurface borings are at a location 4.5-6.5 feet deep northeast
of the City of Dubuque public works garage at boring #21 (SB-21)
with 4,300 mg/kg (milligrams per kilogram or parts per million) .
total PAHs and 1,800 mg/kg carcinogenic PAHs. Other areas with
significant PAH concentrations in soil are borings SB-16 and SB-
17 which are located along the northern edge of the site with
150-900 mg/kg total PAHs and 7.5-89 mg/kg carcinogenic PAHs at
4.5-6.5 feet below surface. Soil boring SB-12 contained 8,000
mg/kg total PAHs at 4.5-6.5 feet below surface and is located
approximately 50 f~et northeast of SB-21. Figure 10 displays PAH
contamination in the subsurface as a vertical cross section
through the site shown as section 4 - 4' in Figure 4.
Field screening indicated that BETX concentrations in the
surface and shallow subsurface were below 50 mg/kg with the
exception of SB-34 which gave a field screening result of 250
mg/kg at 2-4 feet below surface. Figure 11 displays BETX contam-
ination in the subsurface. Table 3 summarizes contaminants
detected in soils and source areas for each of the parameter
groups addressed during the RI/FS; i.e., volatile organics, semi-
volatile organics, and cyanide. .
3.2.2
DEEP SUBSURFACE RESULTS
The highest concentrations of contaminants in the deep
subsurface testing were in three borings northeast of the public
works garage. SB-21 resulted in concentrations of 5,400 mg/kg
total PAHs, 120 mg/kg carcinogenic PAHs at a depth of 27-29 feet.
SB-22 contained 2,700 mg/kg total PAHs, 240 mg/kg carcinogenic
5
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./
PARs at a depth of 7-9 feet.SB-12 contained 4,100 mg/kg total
PARs at a depth of 9.5-11.5 feet. Figure 9 shows the areas of
PAR contamination in the silty sand unit.
The results obtained for BETX compounds confirm the PAH
results. The highest concentrations were located at SB-22 with
560 mg/kg BETX compounds at 12-14 feet. SB-21 contained 98 mg/kg
BETX compounds at 27-29 feet.
3.2.3
GROUND WATER RESULTS
. Ground water samples were collected from 20 monitoring wells
on and offsite in four rounds of sampling. Water samples were
collected from both the silty sand and the alluvial aquifers.
The analytical results of these samples show that both aquifers
contain detectable levels of PAH and BETX ~ompounds both on and
off site. Table 4 summarizes contaminants detected in ground
water for each of the parameter groups addressed during the
RI/FS: i.e., volatile organics, semi-volatile organics, and
cyanide.. .
The highest PAR concentrations were found in water table
monitoring well W-2, adjacent to the west edge of the public
works garage with 580 ug/l (micrograms per liter or part per
billion) total PAHs and 52 ug/l carcinogenic PABs. Alluvial
aquifer monitoring well W-17 contained 43 ug/l total PARs and
silty sand aquifer P-110 monitoring well contained 18 ug/l total
PAHs. Figure 12 displays locations of PABs detected in the
ground.water.
The wells were analyzed for BETX compounds and similar
results were found. Well W-2 had a total BETX concentration of
250 ug/l, W-17 500 ug/l total BETX, and P-110 had 5.0 ug/l total
BETX. Many of the 'samples exceeded EPA primary drinking water.
standards for the BETX compound benzene. Alluvial aquifer moni-
toring well W-16, which is approximately 200 feet north of the
site, contained 360 ug/l BETX. Figures 13 and 14 display loca-
tions of BETXs in the ground water.
~esults of the RI indicate that the primary ground water
flow is to the northeast while the exact ground water flow pat-
terns will. be investigated further during the Remedial Design,
sufficient information is available from the RI to select a
proper remedy for the ground water.
4.0
SUMMARY OF SITE RISKS
4.1
OVERVIEW OF BASELINE RISK ASSESSMENT
A baseline risk assessment is an evaluation of the potential
threat to human health and the environment in the absence of any
remedial action. A base line risk assessment is done in part to
6
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help EPA determine whether remedial action is necessary at a
site. A baseline risk assessment was conducted for this site to
determine the potential effects of the contamination on human
health and the environment. .In this evaluation, both .current and
future land-use scenarios were evaluated. .
4.2
INDICATOR COMPOUNDS
Fifteen chemicals were identified in the Risk Assessment to
be of potential concern, 13 of which were PAHs. Toxicity infor-
mation was evaluated for all chemicals of concern, including
cancer potency factors and noncarcinogenic effects. Contaminants
of concern (COCs) are contaminants that have been detected at the
site, have inherent toxic or carcinogenic effects, and are likely
to pose the greatest concern with respect to the protection of
human health and the environment. The compounds selected include
the more mobile and persistent chemicals at the site, as well as
those present at the highest concentrations. These indicator
compounds are listed in Table 6. Toxicity information was evalu-
ated for all indicator chemicals, including cancer potency fac-
tors and noncarcinogenic effects. .
4.3 EXPOSURE ASSESSMENT
The exposure assessment i4entified potential pathways and
routes for contaminants of concern to reach the receptors and the
estimated contaminant concentration at the points of exposure.
Pathways by which humans could be exposed to the chemicals of
concern at the site were evaluated based on reasonable assump-
tions about current and future land uses. Calculations for site
risks are based on upper bound values for contaminants of con-
cern. The following pathways were evaluated:
. Exposure of public works garage workers on-site to
contaminated soil through dermal contact and ingestion;
. Exposure of future construction workers on-site to
contaminated soil through dermal contact and ingestion;
. Exposure of adults and children as potential on-site
residents to contaminated soil through dermal contact and
ingestion; .
. EXposure of future adult and children residents to
contaminated ground water used as a primary potable water source.
4.4 TOXICITY ASSESSMENT
Reference doses (RfDs) have been developed by EPA for
indicating the potential for adverse effects from exposure to
chemicals exhibiting noncarcinogenic effects. RfDs, which are
expressed in units of mg/kg/day (parts per million/day), are .
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estimates of daily exposure levels for humans that are likely to
have an appreciable risk of adverse health effects. Estimated
intakes of chemicals from environmental media (e.g., the amount
of a chemical ingested from contaminated drinking water) can be
compared to the RfD. The RfDs applicable at the Peoples site are
listed in Tables 15 and 16.
Cancer potency factors (CPFs) or slope factors have been
developed for estimating excess lifetime cancer risks associated
with exposure to potentially carcinogenic chemicals. CPFs, which
are also expressed in units of parts per million/day, are multi-
plied by the estimated intake of a potential carcinogen to pro-
vide an upper-bound estimate of the excess lifetime cancer risk
associated with exposure at that intake level. The CPFs applica-
ble to the Peoples site are listed in Tables 8 - 14.
4.5 RISK CHARACTERIZATION
The risk characterization quantifies present and/or poten-
tial future risk to human health that may result from exposure to
the contaminants of concern found at the site. The site-specific
risk values are estimated by incorporating information from the
toxicity and exposure assessments.
Two quantitative evaluations are made: the incremental risk
to the individual resulting from exposure to a carcinogen: or,
for noncarcinogens, a numerical index or ratio of the exposure
dose level to an acceptable reference dose. .
4.5.1
RISKS FROM NON-CARCINOGENIC COMPOUNDS
A Hazard Index (HI) was calculated for each pathway evaluat-
ed. An HI of less than 1.0 (unity) indicates that the risks
associated with that pathway are low. An HI above 1.0 indicates
that some risk of noncarcinogenic effects exist and .these risks
increase proportional to the HI value. The HI value for poten-
tial offsite residents 'using the water table aquifer as a drink-
ing water source is 3.8 (Table 16), which indicates that they are
potentially at risk. . However, the water table aquifer does not
produce a continuous and reliable source of water for potential
user~ of the aquifer, and therefore does not present a risk to
potential residents. The HI for future workers on and offsite
was determined to be less than one, indicating no significant
noncarcinogenic risks.
4.5.2 RISKS FROM CARCINOGENIC COMPOUNDS
EPA has determined that remeiial act~ons should mitigate
risk to fall within a range of 10- to 10- , which the Agency
believeg to be a generally acceptable level of risk. A risk of
1 X 10- would mean that one person in a million is in potential
danger of developing cancer from .the site contaminants. The
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carcinogenic risks were calculated for the evaluated pathways at
the site.4 The carcinogenic risk to future onsite residents is
3.7 X 10-. The risk to future offsite residents is 1.7 X 10-4.
Onsite risk to futures construction workers at the site was calcu-
lated to be 3.4 X 10- and the risk ~o future onsite workers at
the public works garage is 1.1 X 10-. Table 7 summarizes site
risks for the various pathways.
4.S.3
RISKS FROM EXPOSURE TO SOILS
Based on the pathway analysis it was also determined that
exposure to site soils results in an unacceptable risk to persons
having direct contact with these site soils. Site soils contami-
nated with carcinogenic PAHs are the principal threat at the
Peoples site due to the threat of direct exposure by public works
garage workers to these soils. The risk for residential expos~re
by ingestion of chemicals in the soil by children is 1.2 x 10-
(Table 8). The risk for residential exposure by ingestion of
chemicals in the soil by adults is 2.0 x 10-4 (Table 9) The
risk to workers at the public works garage is 1.1 x 10-~ based on
exposure by ingestion of chemicals in the soil (Table 10). The
risk for residential exposure by ingsstion of chemicals in soil
by construction workers is 3.4 x 10- (Table 11).
4.5.4
RISKS FROM EXPOSURE TO GROUND WATER
It was determined that exposure could result from ground
water in zones contaminated by chemical compounds from the site,
based on the potential ground water yield and consumption from
both the silty sand and alluvial aquifers. A listing of well
locations, compounds, and contaminant concentrations used in the
risk calculations i~ provided in Table 12. The alluvial aquifer
presents a carcinogenic risk of 1.70 x 10-4 for residential
consumption of ground water by adults (Table 13).
4.5.4
CONCLUSION
In conclusion, based on the results of the risk assessment,
EPA has determined that actual or threatened releases of hazard-
ous substances from this site, if not remediated by the selected
. remedy may present a current or potential threat to public
health, welfare, or the environment. .
4.6
REMEDIATION GOALS
No federal and state cleanup standards for the contaminants
of concern in soil have been established at this time. There-
fore, it is appropriate to determine soil cleanup levels on a
site-specific basis using the carcinogenic ris~ factors developed
in the risk assessment. At this site, the 10- risk level would
be protective if no institutional controls were in place. Using
the proper institutional controls at the site, EPA believes that
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the cleanup of soil at this site would be adequately Piotective
of human health and the environment when using the 10- risk
level.. Based on this risk level, EPA considers a cleanup level
for soil, from surface level to six feet below surface, of 500
mg/kg for total PAR contaminants and 100 mg/kg carcinogenic PAR
contaminants to be protective of human health. This cleanup
level calculated to a risk of 5.8 x 10 -4 for incidental soil
ingestion by public works garage workers, the population with the
highest potential for incidental exposure. PAR contaminants
below 6 feet are not considered by EPA to constitute a direct
contact threat to persons at the site. The purpose of clean up
of soils below 6 feet would be to protect ground water from con-
tamination from coal tar materials. The developed cleanup levels
specify a concentration in the soil that is sufficiently protec-
tive of human health and the environment when considering insti-
tutional controls required at the site.
The 40 C.F.R. 300.430 siates that preliminary remediation
goals are to be set at a 10- excess upper bound lifetime cancer
risk level as a point of departure, but may be revised to a risk
level in the acceptable range (10-~ to 10-6) based on considera-
tion of appropriate factors, including uncertainty, technica~,
and exposure factors.
Federal and state cleanup standards have been established
for ground water. EPA has established the Safe Drinking Water
Act National Primary Drinking Water Standards' Maximum
Contaminant Levels (MCLs) as cleanup criteria for drinking water
aquifers. The Iowa Administrative Code Chapter 133, effective
August 16, 1989, established action levels for contaminated
ground water in Iowa. The level to first be considered is the
EPA lifetime health advisory level (HAL), then the EPA negligible
risk level (NRL), and finally MCLs. The most stringent level is
considered to be t~e appropriate cleanup criteria for contaminat-
ed ground wa~er. These levels correspond to'a protective risk
level of 10- .
For the Peoples site, EPA believes that a cleanup level of
1 ug/l (parts per billion) benzene, the most abundant volatile
organic present in the contaminated ground water, would be pro-
tective of human health, based on the NRL. The level that EPA
believes would be protective for carcinogenic PARs such as
benzo(a)pyrene is 0.2 ug/l (parts per billion), based on the
analytical detection limit.
For carcinogenic PARs for which there are no state or feder-
al standards, the proposed cleanup levels will be established
using the detection limits for each specific compound, based on
the best available technology at the time of the signing of this
ROD. The goal for these cleanup levels is to achieve a level
protective of human health and the environment. EPA.believes
that a level established using the current best available detec-
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. tion limits will fulfill this goal. The minimum laboratory
detection limits that can be achieved under ideal conditions fo;
carcinogenic PAHs corresponds to a protective risk level of 10- .
The best level that can be measured practically during routine
laboratory 0ierating C02ditions correspond to a protective risk
level of 10-. The 10- risk level is considered appropriate for
this site based on the uncertainty factor and the technical
factors associated with the detection/quantification limits for
contaminants.
The levels discussed in this section have been reviewed and
approved by ATSDR. Table 5 lists the remediation levels that
will be used for ground water remediation at this site, including
the practical detection limits for the carcinogenic PAHs.
4.7
ENVIRONMENTAL RISKS
The u.S. Fish and Wildlife Service (USFWS) manages 194,000
acres of the upper Mississippi River from Wabasha, Minnesota to
Rock Island, Illinois as the Upper Mississippi Wildlife and Fish
Refuge. Although the industrial corridor of Dubuque is not
managed as part of the refuge, areas in Wisconsin and Illinois
directly across form Dubuque are included in the refuge. The
USFWS has identified two endangered species that may be located
in the general vicinity of Dubuque. These species are the Hig-
gins eye pearly mussel and the bald eagle. The USFWS indicated
that the selected remedy will not impact these species or other
aquatic organisms associated with the Mississippi River if dis-
charged site-related waters are treated to meet ARARs.
The principal threat to ground water is coal tar contaminat-
ed source materials which will be treated in the selected remedy.
Remediation of the source materials will also diminish environ-
mental exposures by removing the direct contact threat to contam-
inated soils. .
5.0
SUMMARY OF ALTERNATIVES
The National Contingency Plan (NCP), 40 CFR Part 300,
requires that certain alternatives be developed for evaluation in
the Proposed Plan:
. An alternative that removes or destroys the hazardous
constituents to the maximum extent feasible and eliminates the
need for long-term monitoring and management:
. One or more additional alternatives that reduce the
toxicity, mObility, or volume of the hazardous constituents;
. One or more alternatives that involve little or no
treatment, but provide protection of human health and the
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environment by containing the hazardous constituents to control
exposure to the wastes 1
. One or more innovative treatment technology alternatives
if those technologies offer the potential for comparable "or
superior performance or implementability, fewer adverse effects,
or lower costs than demonstrated technologies 1
. A limited number of remedial alternatives for ground water
that attain site-specific remediation levels within different
restoration time periods utilizing one or more different
technologies 1 and
. The no-action alternative.
The alternatives that were evaluated in detail in the
Feasibility study are described in this section. Five
alternatives were determined to be appropriate for consideration
at this site. These alternatives provided a range of various
remedial options to satisfy the requirements in the NCP. The
following descriptions summarize the alternatives, including
their treatment components, implementation requirements and the
estimated time for completion and costs.
5.1
NO ACTION
The NCP requires that the no-action alternative be evaluated"
for every site. This alternative (Alternative 1) provides a
baseline for comparing the effectiveness of other remedial
options. This alternative involves no further action at the site
to prevent the migration of contaminants from the site. There
would be no costs associated with this alternative.
5.2
REMOVAL ACTION WITH GROUND WATER MONITORING
Alternative 2 does not include any remedial action beyond
the removal action currently being completed in the highway
corridor. This alternative would also include ground water
monitoring involving periodic collection of ground water samples
from upgradient and downgradient wells in both the silty sand and
alluvial a~ifer. The objective of ground water quali~y monitor-
ing for Alternative 2 would be to provide a quantitative assess-
ment of the effectiveness of the technologies implemented in the
removal action toward minimizing the migration of coal tar con-
taminants to the aquifers.
The technologies previously incorporated as part of the
removal action include: removal and treatment of contaminated
soils in the highway corridorl incineration of excavated soils 1 a
leachate collection system for residual contamination and
gradient control in the silty sand aquifer: and institutional
controls for the site that include deed restrictions.
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It is estimated that the ground water monitoring plan would
include semi-annual collection of samples for analysis of vola-
tile organic chemicals (VOCs) and annual collection of samples
for analysis of PAHs and other contaminants for a total. of thirty
years. It is assumed that samples would be collected from one
upgradient and five downgradient wells in the alluvial aquifer
and one upgradient and three downgradient wells in the silty sand
aquifer. The present worth total cost for the ground water
monitoring program is estimated to be $370,000 (excluding cost of
the removal action).
5.3 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATER
EXTRACTION AND TREATMENT.
Alternative 3 includes remedial actions to address the two
major potential routes of exposure; direct contact with coal tar
derived contamination in the soils and ingestion of contaminated
ground water.
Surface soils would be excavated and removed from the site
for treatment or disposal. It is estimated that 5,500 cubic
yards of soil would be removed and treated or disposed offsite
using one of three options. These options for treatment or
disposal of excavated soils are incineration, land disposal, and
biological treatment. Biological treatment of excavated soils
would consist of either land treatment or aerobic biological
reactor treatment. During excavation air monitoring would be
conducted to determine potential contaminant exposure to area
residents and workers. Berms would be constructed to collect
surface runoff from excavation and soil storage areas.
Alternative 3 includes land disposal and biological treat-
men~ as options fo~ disposal and/or treatment of excavated soils.
. This is a flexible alternative with regard to treatment of soils.
If soil is treated biologically and replaced in the excavated
areas, some residual contamination may be present in the soil
after treatment thus reducing but not eliminating PAH contamina-
tion. . Current technologies for biological treatment of PAHs in
soil have not been demonstrated to effectively reduce concentra-
tions of all PARs to environmentally acceptable concentrations
for the quantities of excavated soils which would be generated by
Alternative 3. Biological treatment technologies are in develop-
ment which may effectively reduce PAH concentrations to environ-
mentally acceptable concentrations in large quantities of soil.
A ground water extraction system would be installed to
remove contaminated ground water from the alluvial and silty sand
aquifers. Ground water would be treated to achieve the remedia-
tion goals listed in Table 5. Extracted water from the alluvial
aquifer would be treated with an air-stripper to remove VOCs and
discharged. to the storm sewer. Extracted water from the silty
sand aquifer would be discharged to the sanitary sewer. This.
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ground water extraction system would minimize the miqration of
contaminants to the alluvial aquifer from either the silty sand
or the contaminated soils above the silty sand.
The ground water monitoring system described in Alternative
2 would be operated to determine the effectiveness of the soil
removal and ground water extraction system in preventing migra-
tion of contaminants to the alluvial aquifer. The alluvial
aquifer would be monitored for 10 years and the silty sand aquif-
er would be monitored for 30 years.
It is estimated that the soil could be excavated and removed
from the site in 6 to 12 months at a cost of $720,000 for
excavation and $700,000 for soil treatment or disposal. Ground
water extraction and treatment systems could be placed in
operation in approximately two years. It is estimated that the
alluvial aquifer extraction system would be operated for 10 years
and the silty sand system for 100 years. The present worth cost
for the extraction system is estimated at $790,000 (cost assumes
30 years operation and maintenance for silty sand system). The
present worth cost for Alternative 3 with incineration is esti-
mated at $2,800,000 (excluding cost of the removal action). The
present worth cost estimate for Alternative 3 with land disposal
is $2,600,000 and with biological treatment of excavated soils is
$2,700,000.
5.4 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATER
EXTRACTION AND TREATMENT, CAPPING OF SOURCE SOILS, AND IN SITU
BIOREMEDIATION
Alternative 4 includes all the elements of Alternative 3
plus in-situ bioremediation and capping of source soils. This
would provide further reduction of contaminated source areas and
decrease infiltration of water into the ~ource areas. The opera-
tional lifetime of the ground water extractions systems presented
in Alternative 3 would be reduced with biological treatment of
source soils at depth. .
In-situ bioremediation of contaminated soil and ground water
would be conducted in the silty sand layer. An injection and
. extr~ction system would be developed to reduce the concentration
of coal tar derived contaminants through biological degradation.
Bioremediation should treat coal tar derived contamination in the
ground water and contamination sorbed to the soil particles.
Although capping and ground water extraction and treatment might
achieve the remedial action objectives for the ground water,
bioremediation should significantly reduce the time required to
meet these objectives. .
Capping is included in Alternative 4 to reduce leachate
production by limiting infiltration. This would reduce the rate
of release to t~e underlying silty .sand and alluvial aquifers.
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The cap would include a low permeability zone of compacted clay
and a high density polyethylene (HDPE) membrane which is estimat-
ed to reduce infiltration by a minimum of 99 percent.
It is estimated that construction of the cap would require 4
to 8 months after completion of the soil excavation described in
Alternative 3 and would cost $64,000. The time required for
in-situ bioremediation would depend on completion of treatability
studies to determine site-specific requirements. It is estimated
that" treatability testing and initial implementation of an
in-situ bioremediation could be completed in two years at a
present worth cost of $765,000 including 10 years of operation.
The present worth cost for Alternative 4 with incineration of
excavated soils is estimated at $3,500,000 (excluding cost of the
removal action). The present worth cost estimate for Alternative
4 with land disposal is $3,300,000 and with biological treatment
of excavated soils is $3,400,000. .
5.5 LIMITED SOIL REMOVAL AND TREATMENT WITH GROUND WATER
EXTRACTION AND REMOVAL OF SOURCE SOILS.
Alternative 5 would include all the elements of Alternative
3 with additional removal of coal tar contaminated source soils
at depth (greater than 6 feet below surface). Compared to
Alternative 3, the operational lifetime of the ground water
extraction systems would be reduced with removal of the source
soils at depth.
This alternative includes the additional removal of coal tar
contaminated soils at depth that may contribute contaminants to
the silty sand or the" alluvial aquifer. This removal would
reduce the total mass of contaminants on the site and would
result in a shorter operation of the silty sand ground water
extraction system.' The soil volume calc~lation includes
excavation of all visibly contaminated soils as described in the
boring logs. This soil volume estimate exceeds that provided in
the RIfFS because it includes excavation to the lower confining
unit.
~t is estimated that 24,200 cubic yards of source soils
would be removed and disposed or treated for this alternative.
The overall present worth cost for Alternative 5 with incinera-
tion is estimated at $8,000,000 (excluding cost of the removal
action). The present worth cost estimate for Alternative 5 with
land disposal is $7,200,000 and with biological treatment of
excavated soils is $7,500,000.
6.0
SUMMARY AND COMPARATIVE ANALYSIS OF ALTERNATIVES
The NCP has established nine criteria that are used to
evaluate remedial alternatives. These criteria serve as the
basis for conducting detailed analyses during the Feasibility"
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study and subsequently are used to determine the appropriate
remedy for the site.
A detailed analysis of the remedial alternatives was con-
ducted, consisting of an assessment of the individual alterna-
tives against each of the. nine criteria and a comparative analy-
sis that focused on the relative performance of each alternative
against those criteria. As a result of this detailed analysis,
EPA has determined that a combination of Alternatives 4 and 5
provides the best balance among the alternatives with respect to
the criteria.
When conducting the analysis, the nine criteria are
organized into three categories. The first such category is
threshold criteria. An alternative must meet the following two
requirements to be considered as a final remedy for the site:
6.1
OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
The selected remedy would involve the excavation and
incineration of the source soil areas and contaminated soil
areas. The highly contaminated soil areas remaining in the silty
sand unit would also be addressed by in-situ bioremediation.
Ground water from the alluvial aquifer would be treated with an
air stripper and discharged to the storm sewer and the ground
water from the silty sand aquifer would be discharged to the
sanitary sewer. This would reduce exposure to contaminated soils
and ground water to protective levels and also minimize the
potential for contaminant migration. Air monitoring would be
conducted to determine if concentrations of airborne contaminants
exceed air quality criteria. If these criteria are exceeded
control measures will be implemented. Access restrictions would
prevent direct exposure to site soils by the general population.
The no-action alternative does not provide overall
protection to human health and the environment and therefore will
not be evaluated further because this threshold criteria is not
attained. The alternatives involving incineration, 3 - 5, pro-
vide the permanent elimination. of long-term residual risk. The
long-term residual risk would also be eliminated by in-situ
biological treatment in the silty sand unit to health-based
levels of the contaminated soil in alternatives 4 and the select-
ed remedy. Alternative 2 would not permanently eliminate residu-
al risk and therefore does not provide for protection of human
health and the environment. The alternatives which include
ground water treatment and the selected remedy, provide for
overall protection of human health and the environment.
6.2
COMPLIANCE WITH ARARS
The selected remedy would comply with all federal and stat.
applicable or relevant and appropriate requirements (ARARs).
'.-
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Applicable requirements are those state or federal requirements
legally applicable to the release or remedial action contemplated
that specifically address a hazardous substance, pollutant,
contaminant, remedial action, location, or other circumstance
found at the site. If it is determined that a requirement is not
applicable, it may still be relevant and appropriate to the
circumstances of the release. Requirements are relevant and
appropriate if they address problems or situations sUfficiently
similar to the circumstances of the release or remedial action
contemplated(, and are well-suited to the site.
Applicable chemical-specific requirements associated with
this alternative include the National Ambient Air Quality
Standards, promulgated under the Clean Air Act. Source control
on emissions from the air-stripper would be implemented if air
monitoring indicate exceedances of applicable air quality crite-
ria. The MCLs for this site would be applicable and would have
to be achieved. Also identified as applicable for this site are
the Iowa Administrative Code Chapter 133 standards discussed in
Section 4.6. .
No location-specific ARARs were identified for the site.
The federal action-specific ARARs that the selected remedy would
have to comply with are: all pertinent Occupational Safety and
Health Act requirements and all Hazardous Materials
Transportation Act regulations: the Resource Conservation and
Recovery Act (RCRA) regulations applicable to solid wastes, 40
C.F.R. 257: the Clean Water Act regulations applicable to dis-
charge to POTWs and surface waters: and the Clean Air Act re-
quirements applicable to incinerators. The action-specific state
ARARs include the Iowa Environmental Quality Act regulations: the
Iowa Air Pollution Control Regulations, Sections 22.4, 22.5,
23.1, 23.3, and 23~4: and the Iowa Water Pollution Control regu-
lations, Sections 61.3, 62.1, 62.6, 62.8, 62.9 63, 64.2 and 64.3.
The hazardous waste treatment storage and disposal regula-
tions under RCRA are applicable to wastes at this site where coal
tars, when tested by the toxicity characteristic leachate proce-
dure (TCLP), are found to contain concentrations of hazardous
constituents in excess of regulatory values. Otherwise, RCRA
regulations are considered relevant and appropriate, due to the
hazardous nature of coal tars. Therefore the substantive re-
quirements of RCRA, specifically 40 C.F.R. Parts 264 and 270,
must be met for non-TCLP wastes, including the requirement that
an incinerator destroy the contaminants at an efficiency of
99.99'. A trial burn was conducted and demonstrated this removal
efficiency. Both the administrative and substantive requirements
of Subtitle C of RCRA must be met for those hazardous constitu-
ents that exceed regulatory levels.
All waste generated as a result of remedial actions at the
Peoples site are subject to requirements of the EPA off-site
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pOlicy. The off site pOlicy, as stated in CERCLA 1121(d)(3),
requires that hazardous substances, pollutants, or contaminants
transferred off site for treatment, storage, or disposal during a
CERCLA response action be transferred to a facility operating in
compliance with 13004 and 13005 of RCRA and other applicable laws
and regulations.
Alternative 2, which calls only for ground water monitoring
rather than treatment, does not reduce the spread of contaminants
in ground water and therefore does not provide adequate protec-
tion of human health and the environment. Also this alternative
does not meet the chemical-specific ARARs associated with this
site. Therefore, this alternative will not be further considered
based on the threshold criteria.
Alternatives 3 - 5 would meet the ground water cleanup
standards previously identified. Other chemical-specific ARARs,
such as the Clean Air Act, would be met for all other alterna-
tives. Air monitoring would be conducted to assure compliance
with applicable air standards.
The action-specific ARARs would be met for all other
alternatives considered. These ARARs include all OSHA
requirements, all Hazardous Materials Transportation Act
regulations, and the RCRA requirements previously discussed.
The second category of criteria is Drimarv balancina
criteria. The following five criteria are used to evaluate the
alternatives to determine the option that provides the most
balance for the final remedy for the site:
6.3
LONG-TERM EFFECTIVENESS AND PERMANENCE
The incineration of the contaminated soils and the treatment
of ground water in "alternatives 3 - 5 and the selected remedies
. would eliminate the long-term risks associated with.direct
contact and potential migration of these areas, providing a
permanent solution. Highly contaminated source soil areas would
continue to leach contaminants into the environment if not
treated or removed. The source soil removal of Alternative 5 and
the enhanced in-situ biodegradation process of Alternative 4
would reduce contamination in these areas, adding to. the long-
term effectiveness of these alternatives. The selected remedy
involves a combination of these technologies which would reduce
contamination and provide for long-term effectiveness.
The alternatives involving incineration as a soil disposal
option, 3 - 5 and the selected remedy would eliminate the risks
associated with source areas and provide a permanent remedy for
contaminated soils. The residual risk associated with
contaminants in qround water above health-based levels would be
eliminated by alternatives 3 - 5 and the selected remedy. Long-
-
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term ground water monitoring would be required for all
alternatives. Alternative 3 does not involve excavation of
contaminated soils at depth and would not permanently eliminate
residual risk, requiring long-term control measures throughout
the life of the alternative, estimated at 100 years.
Alternative 4 would reduce contamination in the silty sand
unit through the in-situ biodegradation process. However, this
alternative does not remove highly contaminated source soil areas
from 6 feet below surface to the top of the upper confining
layer. This would leave a large volume of contaminated soils as
a source of "chemicals of concern that could potentially leach
into the ground water over time. Alternative 5 relies on ground
water extraction to remove contaminants form the silty sand unit
which would require a much longer period to reduce contaminant
concentrations to acceptable levels.
6.4
REDUCTION OF TOXICITY, MOBILITY, OR VOLUME
The selected remedy treats contaminated surface soils
(surface to 6 feet below surface), highly contaminated soil
areas, and ground water to achieve reduction of toxicity,
mobility and volume of contaminants at the site. The
incineration of these soils provides permanent treatment. The
excavated nonhazardous waste materials would be incinerated
offsite in accordance with the substantive requirements of RCRA,
with a 99.99% destruction and removal efficiency (DRE) of contam-
inants. Those materials that exceed TCLP levels would be managed-
in accordance with all RCRA requirements. The enhanced in-situ
bioremediation process would reduce the toxicity, mobility, or
volume of the highly contaminated soils in the silty sand unit.
This would also reduce the volume of contaminated ground water
that will eventually need to be treated at the site, since these
highly contaminated' areas will continue to leach contaminants
into the environment. The biodegradation process would treat
these areas.
The other alternatives involving incineration (3- 5), would
provide a permanent treatment for the excavated contaminated
soils. The ground water treatment alternatives would also pro-
vide a permanent treatment. Alternative 3 would not treat highly
contaminated source soils and therefore not provide for the
permanent reduction of the toxicity, mobility or, volume of the
contaminants in the source soil areas. Alternative 4 does not
remove a large volume of contaminated soil above the silty sand
unit and relies on a cap to reduce mobility which will require
long-term maintenance.
Alternatives 3 - 5 include land disposal and biological
treatment as options for disposal and/or treatment of excavated
soils. If soil is treated-biologically and replaced in the
excavated areas, some residual contamination "may be present in
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the soil after treatment thus reducing but not eliminating PAH
contamination. CUrrent technologies for biological treatment of
PAHs in soil have not been demonstrated to effectively reduce
concentrations of all. PAHs to environmentally acceptable concen-
trations for the quantities of excavated soils which would be
generated by Alternatives 3 - 5, or the selected remedy.
Biological treatment technologies are in development which may
effectively reduce PAH concentrations to environmentally accept-
able concentrations in large quantities of soil. Land disposal
of contaminated soils would not provide a reduction of toxicity
or volume, but would reduce mobility. Land disposal would not
provide treatment of excavated soils. .
6.5
SHORT-TERM EFFECTIVENESS
The short-term risks associated with the selected remedy
would involve the normal construction hazards associated with the
excavation of source and soil areas and with the construction and
installation of wells. Volatile emissions might also be released
during excavation and materials handling, and during the drilling
and sampling of wells. This alternative would involve the
transportation of wastes and would have short-term risks
associated with offsite transport. .
Any potential for exposure can be effectively minimized or.
controlled by compliance with the action-specific ARARs and by
implementing engineering controls at the site, such as .
restricting access to the site, monitoring for volatile
emissions, and adhering to a site-specific safety plan. In
conformance to OSHA standards, all site workers would be health-
and-safety trained, wear the appropriate protective clothing, and
participate in a medical monitoring program.
Workers at the City of Dubuque public w~rks garage may be
working on the Peoples site during excavation of contaminated
50i15. Air monitoring would be conducted during soil excavation
activities to determine airborne concentrations of PAHs and
BETX5. If levels of these contaminants exceed OSHA standards the
City of Dubuque would be notified.
. .The selected remedy would require 24 to 36 months to
complete the removal and treatment of source areas and contami-
nant soil. Incineration of excavated soils is estimated to
require 24 months. The time estimated for installation of the
ground water extraction system and the establishment of the plume
containment is 24 months. The time necessary to achieve a reduc-
tion in contaminant levels to the health-based standards is
estimated at 10 to 20 years. Installation of the biological
remediation system is estimated at 24 months.
Alternative 5 will require ~xcavation of larger soil volumes
than the selected remedy or Alternatives 3 and 4. Incineration
20
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would require storage onsitewhile soil is transported offsite
for incineration. It is estimated that soils may be stored on
site for a period of 8 months longer than the selected remedy.
As previously noted, compliance with the action-specificARARs
would effectively minimize and control the potential exposure
during implementation of the alternative. .
Incineration for alternatives 3 and 4 would require 6 to 12
months to complete the removal and treatment of contaminated
soil. Construction of the cap in alternative 3 would require 4
to 8 months. All the remaining alternatives would require 24
months for installation of the ground water system and the estab-
lishment of the plume containment. The biological treatment of
the soil areas in Alternative 4 is estimated to take 24 months.
6.6
IMPLEMENTABILITY
Implementation of the selected remedy would involve
conventional construction technologies. Excavation, pumping,
decontamination, and gradient control are frequently used
technologies that have been proven to be effective. Incineration
is a proven technology for coal tar wastes and a trial burn
conducted at a power plant boiler has demonstrated it can achieve
the RCRA destruction efficiency for site derived coal tar wastes.
The enhanced in-situ bioremediation process has not been exten- .
sively used at coal gas sites and therefore would be implemented
after conducting an extensive treatability study.
The other alternatives involving incineration and the ground
water treatment system would have the same ease in implementabil-
ity. Capping is also a frequently used technology. Excavation
below the upper confining unit would not be practical near the
public works garage and Kerper Boulevard as it would require
excavation to approximately.30 feet. Insufficient space is
available on the site for the setback requirements to excavate to
this depth. Sheet pilings may not provide sufficient stability.
Biological treatment of excavated soils would require suffi-
cient space onsite to construct a biological reactor system. It
would be difficult to locate this system on the site due to space
limitations. Biological treatment by land farming technologies
would require offsite facilities in order to.have the necessary
space to implement this technology.
6.7
COST
The cost. of the selected remedy would be the cost for
alternative 4 plus the additional cost for source soils removal
less construction costs for capping. The present worth cost for
the selected remedy is estimated at $8,000,000 (excluding cost
for the removal). This includes .operation and maintenance costs
~or 10 years of operation.
21
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The selected remedy would remove highly contaminated source
soil areas below 6 feet to the top of the upper confining layer.
This would remove a source of chemicals of concern that could
potentially leach into the ground water. Alternative 4 would not
remove these source soil areas below 6 feet potentially causing
an increase in the time requirements for ground water
remediation.
The range of total present worth costs for the alternatives
is from $370,000 for alternative 2 to $8,000,000 for alternative
5 {excluding costs for the removal action).
The present worth cost estimates stated above include incin-
eration as the disposal method for excavated soils. Costs for
biological treatment or land disposal of soils do not differ
significantly from those for incineration.
The third category of criteria is modifvina criteria. . The
following two criteria are considered when evaluating the
alternatives and are used to help determine the final remedy for
the site:
6.8
STATE ACCEPTANCE
The State of Iowa supports the remedy selected for the
cleanup of contaminated soils and ground water at the Peoples
site.
6.9
COMMUNITY ACCEPTANCE
Community acceptance of the selected remedy was evaluated
during the public comment period. The comments received are
contained in the Responsiveness Summary, Appendix A.
7:0
SUMMARY OF SELECTED REMEDY
Based on the evaluations prepared for each of the proposed
alternatives, EPA has made a determination that the appropriate
remedy for the Peoples site is a combination of Alternatives 4
and 5 described as follows: excavation and incineration of
contaminated soil trom surface to 6 feet below grade that exceed
100 mg/kg carcinogenic PARs and 500 mg/kg total PARs: excavation
and incineration of contaminated source soils that have visible
coal tar contamination from 6 feet below grade to the surface of
the upper confining unit: enhanced in-situ bioremediation to
treat the contaminated ground water and contaminated source soils
in the silty sand unit: ground water extraction of both the silty
sand and alluvial aquifers to reduce concentrations to levels
required by the state of Iowa Administrative Code Chapter 133:
and ground water monitoring of both the silty sand and alluvial
aquifers to assure successful implementation of ground water
-,
22 .
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treatment systems. This alternative provides the best balance of
the factors identified by the nine criteria.
The selected remedy would require 24 to 36 months to com-
plete the removal and treatment of source areas and contaminated
soil. Incineration of excavated soils is estimated to require 24
months. The time estimated for installation of the ground water
extraction system and the establishment of the plume containment
is 24 months. The time necessary to achieve a reduction in
contaminant levels to the health-based standards is estimated at
10 to 20 years. Installation of the biological remediation
system is estimated at 24 months.
It is estimated that 18,500 cubic yards of contaminated
soils would be removed and treated by incineration. It is esti-
mated that operation of the alluvial extraction system would
continue for 10 years,S years for the silty sand aquifer extrac-
tion system, and 5 years for the bioremediation system. However,
the operation of these systems would continue as long ,as neces-
sary if results of the ground water monitoring indicate contami-
nant concentrations have not attained the remedial criteria.
Injection of ground water into any aquifer would not be used, as a -
method of disposal for qround water. Ground water removed from
the silty sand extraction system will be discharqed to the City
of Dubuque sanitary sewer system. Ground water removed from the
alluvial extraction system will be treated and discharqed to the
City of Dubuque storm sewer system.
The selected remedy is in addition to the removal action
completed in July 1991 which eliminated contamination sources in
the Hiqhway 61 corridor on the western portion of the site. The
provisions of the r.emoval order require institutional controls
includinq restriction of site access and deed restrictions allow-
inq only commercial use of the property. The site will remain
secured to prevent access by the qeneral population. The tech-
noloqies previously incorporated as part of the removal action
include: removal and treatment of contaminated soils in the
hiqhway corridor: incineration of excavated soils: a leachate
collection system for residual contamination and qradient control
in the silty sand aquifer. '
The horizontal extent of excavation will be determined usinq
the 100 mq/kq carcinoqenic PAH/500 mq/kq total PAH level. The
vertical extent of excavation may also be adjusted in the field,
with a maximum vertical excavation of 6 feet based on this level.
Excavation from 6 feet below qrade to the top of the upper con-
fininq unit will be based on visible coal tar contamination. A
procedure will be developed to determine the existence of visible
coal tar contamination. Excavation will cease at the top of the
upper confininq unit. The base of each excavation area will be
divided into sections and sampled to determine the concentration
of contaminants that remain. The base of the excavation areas
23
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will be determined by either the 100 mg/kg carcinogenic PAR/
500 mg/kg total PAH level or the visible coal tar standard
depending on which is applicable as previously described.
This cleanup level of 500 mg/kg total PAR/100 ig/kg.
carcinogenic PAR calculates to a risk of 5.8 x 10 - for
incidental soil ingestion by pUblic works garage workers, the
population with the highest potential for incidental exposure.
PAR contaminants below 6 feet are not considered by EPA to
constitute a direct contact threat to persons at the site. The
purpose of clean up of soils below 6 feet would be to protect
ground water from contamination from coal tar materials.
Excavated material will be separated to remove materials not
compatible with the incineration process. All material greater
than 2 inches in diameter will be separated. Materials less than
2 inches in diameter will be placed in the contaminated soil
storage area, along with source tars, before being transported to
the incinerator. This pad will meet the substantive requirements
of RCRA. All material that cannot be reduced to a manageable
size will be steam-cleaned and sent for disposal in accordance
with RCRA. The proper transportation requirements will be met
and the trucks will be decontaminated. .
Chemical dust-suppressants and/or water will be used for
dust control during activities at the site. Volatile emissions
will be monitored during all operations. Berms will be con-
structed and grading performed to control water run-on and run-
off, and sumps will collect water for treatment. Clean fill will
be added to excavated areas. storage piles of contaminated
excavated soils will be covered with 60-mil high density polyeth-
ylene (HDPE) until removed for incineration.
Monitoring wells will be installed at various locations at
the site to confirm the efficacy of the ground water extraction
system. Extraction wells will be installed in both the silty
sand and alluvial aquifers for the removal of ground water and
subsequent treatment. The goal of the treatment Piocess will be
1 uq/l (ppb) benzene, which corresponds to the 10- risk level.
The process will also meet the ground water remediation levels
listed in Table 5, which includes the current practical detection
limits for carcinogenic PARs. If, in EPA's judqment~ implementa-
tion of the selected ground water remedy clearly demonstrates
that it will be technically impracticable to. achieve and maintain
the ground water remediation levels established in this ROD, EPA
will re-evaluate those levels. For example, the cleanup levels
for ground water may be re-evaluated if it has been demonstrated
that contaminant levels have ceased to decline over time and are
remaining constant at some statistically significant level above
remediation goals. In such a case, an alternate concentration
level may be established and/or a chemical-specific ARAR waiver
maybe invoked... Any newly established remediation levels must be
24
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protective of human health and the environment. The ROD will be
amended or an explanation of Significant Differences will be
issued to inform the public of the details if such actions occur.
The water pumped from the alluvial aquifer will be treated
using air stripper technology and discharged to the City of
Dubuque storm sewer system. Water pumped from the alluvial
aquifer will be analyzed as required by the Clean Water Act (CWA)
prior to discharge to a surface water body. Water discharged to
the storm sewer must meet all applicable CWA requirements and
must be treated as necessary to remove contaminants as required
by the CWA. Air modeling and/or analysis will be conducted to
determine potential requirements for emission controls on the air
stripper. Emission controls will be installed as required by EPA
and State of Iowa regulations.
The water pumped from the silty sand aquifer will be dis-
charged to the City of Dubuque sanitary sewer system for treat-
ment at the publicly-owned treatment works (POTW). Water dis-
charged to the sanitary sewer must meet all CWA pretreatment
requirements for discharge to the POTW through the sanitary sewer
system.
Air monitoring will be conducted in connection with both the
excavation activities and the air stripping of water pumped from
the alluvial aquifer. All applicable National Ambient Air Quali- "
ty Standards, promulgated State of Iowa air standards, or other
promulgated federal air standards must not be exceeded at the
site boundaries. Appropriate control measures will be implement-
ed as necessary to achieve all applicable air quality standards.
Air monitoring and/or modeling will be conducted to determine air
quality con~rol measure requirements.
The in-situ bioremediation process will begin with a pilot
study to determine the proper types and amounts of nutrients and
possible engineered organisms to inject into the aquifer for
stimulating natural biological degradation. The nutrients,
dissolved oxygen, and organisms will be added to treated ground
water and reinjected into the aquifer using injection wells.
Injection well placement will be determined through ground water
modeling. The system will use injection and extraction wells as
determined"through ground water modeling and treatability stud-
ies. Procedures for determining the efficacy of the bioremedia-
tion system will be determined and implemented. The system will
be modified as necessary to reduce concentrations of contaminants
in the silty sand unit.
" The goal of this remedial action is to restore the ground
water to its beneficial use as required by IDNR regulations.
Based on information obtained during the remedial investigation,
and the analysis of the remedial alternatives EPA and the State
of Iowa believe that the selected remedy may be able to achieve
25
-------
this goal. Ground water contamination may be especially persist-
ent in the immediate vicinity of the contaminants' source. The
ability to achieve cleanup levels throughout the area of attain-
ment, or plume, cannot be determined until the extraction system
has been implemented, modified as necessary, and plume response
monitored over time. If the selected remedy cannot meet the
specified remediation at any or all of the monitoring points
during implementation, the contingency measures described in this
section may replace the selected remedy and the remediation
levels for these portions of the plume. These measures are
considered to protect human health and the environment, and are
technically practicable under the corresponding circumstances.
The selected remedy will include ground water extraction for
an estimated period of 10 years for the alluvial aquifer and an
estimated 5 years for the silty sand aquifer, during which time
the system's performance will be monitored on a regular basis and
adjusted as warranted by the performance data collected during
operation. Modifications may include any or all of the
following:. . . .
.
Discontinuing pumping at individual wells where cleanup
goals have been attained
.
Alternating pumping at wells to eliminate stagnation
points
Pulse pumping to allow aquifer equilibrium and encourage
adsorbed contaminants to partition to the ground water
.
Installing additional extraction wells to facilitate or
accelerate cleanup of the contaminant plume
To ensure that cleanup levels are maintained, the aquifer
will be monitored at those wells where pumping has ceased follow-
ing discontinuation of ground water extraction.
.
If it is determined, on the basis of the preceding criteria
and the system performance data, that certain portions of the
aquifer cannot be restored to their beneficial uses, all of the
following measures involving long-term management may occur, for
an indefinite period of time, as a modification of the existing
system:
.
Engineering controls such as physical barriers or long-
term gradient control provided by low level pumping, will
be implemented as containment measures
Chemical Specific ARARs will be waived for cleanup of
for those portions of the aquifer based on the technical
impracticability or achieving further contaminant
reduction .
.
26
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.
Institutional control will be provided and maintained to
restrict access to those portions of the aquifer that
remain above remediation levels
.
Monitoring of specified wells will continue
Remedial technologies for ground water restoration will
be reevaluated periodically
.
The decision to invoke any or all of these measures may be
made during a periodic review of the remedial action, which will
occur at a minimum of 5 year intervals in accordance with section
121(c) of CERCLA.
The site will be.fenced and ground water and land-use re-
strictions will be implemented to minimize activities which would
provide direct contact with contaminants. Initially, well-moni-
toring will be performed bimonthly after the remedy is implement-
ed. After the first year, monitoring will be performed quarterly
for 5 years, then biannually for the next thirty years, to ensure
that the remedy was successful.
A review of the effectiveness of the selected remedy will be
conducted each five years following completion of construction
activities as required for implementation of the selected remedy.
Five year reviews are conducted pursuant to section 121(c) of
CERCLA which requires the review of remedial actions no less
often that each five years for sites where the remedial action
results in any hazardous substances, pollutants, or contaminants
remaining at the site. The purpose of the five review is to
assure that human health and the environment are being protected
by the implementation of the selected remedy.
Table 17 lists the capital costs for each major component of
the selected remedy. The total construction costs are estimated
to be $7,000,000 and the total operations and maintenance costs
are estimated to be $1,000,000 giving a total present worth of
$8,000,000.
Changes may be made to the selected remedy during remedial
design work and the processes of construction.
8.0
STATUTORY DETERMINATIONS
The selected remedy satisfies the statutory requirements of
Section 121 of CERCLA, 42 V.S.C. S 9721, as follows:
8.1
PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT
The selected remedy will be protective of human health and
the environment by providing for .the permanent destruction of
contaminated soil areas. These areas will be excavated to a
27
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level protective if human health and the environment that corre-
sponds to the 10- risk level. Proper institutional controls
will be taken at the site, including site fencing, ground water
use restrictions and land use restrictions.
The groundwater will be treated until the off-site
contaminants are belol health-based standards, providing 4
protection to the 10- risk level for benzene and the 10- risk
level for carcinogenic PABs. Ground water from the alluvial
aquifer will be treated with an air stripper and discharged to
the storm sewer. Air monitoring will be conducted to determine
if concentrations of airborne contaminants exceed air quality.
criteria and if these criteria are exceeded control measures will
be implemented. The enhanced in-situ bioremediation process will
address contaminated soil areas that will not be excavated.
The selected remedy will provide maximized long-term
effectiveness and will reduce the toxicity, mobility and volume
of wastes to the greatest extent practicable. . The selected
alternative will also have minimal short-term risks and the
proper controls will be taken to minimize these risks.
8.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REQUIREMENTS
The selected remedy complies with all ARARs associated with
this site. All chemical-specific ARARs will be met, including
CAA, RCRA and the Iowa Administrative Code Chapter 133, which
requires one of three standards, MCLs, HALs, or NRLs. All
action-specific ARARs, including all OSHA, RCRA, and DOT
requirements, will also be met. No location-specific ARARs were
identified at this site.
8.3
COST-EFFECTIVENESS
. The overall effectiveness of the selected remedy is
proportional to its estimated cost of $8,000,000. The soi1
excavation and incineration and the ground water treatment proc-
ess are necessary to provide protection of human health and the
environment. The added cost of the bioremediation system is
reasonable when considering the added protection that will be
provided for human health and the environment in addressing the
contaminants. There would be a reduction in the time needed for
treatment of the aquifer, resulting in a decreased cost.
8.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE
TREATMENT TECHNOLOGIES TO THE MAXIMUM EXTENT PRACTICABLE
The EPA has determined that the selected remedy represents
the maximum extent to which permanent solutions and treatment
technologies can be utilized in a cost-effective manner for the
Peoples Natural. Gas Site. Of those alternatives that are protec-
28.
-------
tive of human health and the environment and comply with ARARs,
EPA has determined that this selected remedy provides the best
balance in terms of long-term effectiveness and permanence,
reduction in toxicity, mObility, or volume achieved through
treatment, short-term effectiveness, implementability, and cost.
Also EPA considered the statutory preference for treatment as a
principal element, and considered input from the community. The
state of Iowa agrees with these determinations.
The selected remedy utilizes proven technologies in
incineration and the ground water treatment system that can be
effectively implemented. These processes provide the best solu-
tions in addressing the contaminants at the site. The enhanced
in-situ bioremediation process will provide treatment for the
contaminated silty sand unit which would otherwise have to be
left unattended and therefore significantly add to the time
required for treating the ground water. Therefore this remedy
provides treatment technologies to the maximum extent practicable
at this site.
The selected remedy permanently destroys the contaminated
soil areas and treats the off-site ground water to below health-
based standards, providing for long-term effectiveness and perma-
nence. Alternatives 2 does not permanently eliminate risks at
the site. All other alternatives provide permanent protection.
The selected remedy provides maximum reduction of toxicity,
mobility, and volume. The other alternatives involving
incineration, 3, 4, and 5, also provide for the reduction of
toxicity, mobility, or volume, however alternative 2 would not
treat the contaminated ground water. The other alternatives
involving incineration (3 - 5), would provide a permanent treat-
ment for the excavated contaminated soils. The ground water
treatment alternatives would also provide a permanent treatment.
Alternatives 3 would not treat highly contaminated source soils
and therefore not provide for the permanent reduction of the
toxicity, mobility, or volume of the contaminants in the source
soil areas. Alternative 4 does not remove a large volume of
contaminated soil above the silty sand unit and relies on a cap
to reduce mobility which will require long-term maintenance.
The short-term risks associated with the selected remedy are
minimal and will be attended to with the proper controls at the
site. The same general short-term risks apply to all
alternatives utilizing excavation and transport of waste which
involve more short-term risks. These risks will be minimized
through compliance with ARARs.
The selected remedy utilizes proven and implementable
technologies in excavation, incineration, and ground water treat-
ment. The in-situ biological alternative portions provide added
reduction in the toxicity, mObility, and volume at a 'reasonable
29,
-------
cost. Alternative technologies for biological treatment of PAHs
in excavated soils will require further development before being
considered for implementation at the site.
In order to satisfy the preference for a permanent solution,
alternatives 2 was eliminated. The incineration of the contami-
nated soils and t~e treatment of ground water in alternatives 3 -
5 and the selected remedy would eliminate the long-term risks
associated with direct contact and potential migration of these
areas, providing a permanent solution. Highly contaminated
source soil areas would continue to leach contaminants into the
. environment if not treated or removed. The source soil removal
of Alternative 5 and the enhanced in-situ biodegradation process
of Alternative 4 would reduce contamination in these areas,
adding to the long-term effectiveness of these alternatives. The
selected remedy involves a combination of these technologies
which would reduce contamination and provide for long-termeffec-
tiveness.
The alternatives involving incineration as a soil disposal
option, 3 - 5 and the selected remedy, would eliminate the risks
associated with source areas and provide a permanent remedy for
contaminated soils. The residual risk associated with
contaminants in groundwater above health-based levels would be
eliminated by alternatives 3 - 5 and the selected remedy. Long-
term ground water monitoring would be required for all
alternatives. Alternative 3 does not involve excavation of
contaminated soils at depth and would not permanently eliminate
residual risk, requiring long-term control measures throughout
the life of the alternative, estimated at 100 years.
Alternative 4 would reduce contamination in the silty sand
unit through the in-situ biodegradation process. However, this
alternative does n6t remove highly contaminated source soil areas
from 6 feet below surface to the top of the upper confining
layer. This would leave a large volume of contaminated soils as
a source of chemicals of concern that could potentially leach
into the ground water over time. Alternative 5 relies on ground
water extraction to remove contaminants form the silty sand unit
which. would. require a much longer period to reduce contaminant
concentrations to acceptable levels. Alternative 5 would involve
the excavation of 24,200 cubic yards of soil as opposed to 18,500
cubic yards for the selected remedy.
For these reasons, the selected alternative provides the
best balance of trade-offs with respect to these criteria.
8.5
PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT
The selected remedy involves treatment of the contaminated
soil and source areas by incineration. The ground water is
treated by the City of Dubuque POTW or by other technologies yet
30
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to be determined. The un excavated source areas will be treated
by the in-situ enhance bioremediation process. Therefore, the
statutory preference for remedies that employ treatment as a
principal element is satisfied.
9.0 DOCUMENTATION OF SIGNIFICANT CHANGES
No significant chanqes were made in selectinq the preferred
alternative as described in the Proposed Plan. '
31
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FIGURES
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Figure 2
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Figure 6
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DECONTAMINATION PAD
~
SECOHIWrt'
0\IER8UR0EM
STOCKPU
NI£A
F1sure 7
COUPlETEO REUOVAl ACTION SrTE PlAN,1990
Peoples Natural eo. Site
lVN't)'~O "-
J.lnvnb ~ooCt
-------
......
""'6
X--17
~
"-3'
-
.
~
t
.1
--
-
~'
--25
X
.....
I
I
lImlta of $0" In the F1R Unit wfth c-tratIon8
of Totol PAHa >500 ma/k~).
Cordnogenlc PAHa >100 ~ (Laboratooy). fW
>1,000 "'9/kv Total PAHa with
FIeld ScrMnIn9 Method.
lEGEND
A W-4 ~WD1.
D 1'-118 ~ ~CIM[IUt
M.LIM\l AGIIfUI
~ WD1.
----
AUGUST 1-
----
_1- '
. W-12
.....
""'28
X 5&-30
......n
. ...-n
IDOf
-- IIOI8ID
.....311
X.....
- 5.000 "'9/k9- 1UW.-
--n
\
..
I
I
/, -,
,
I ....'~
CAJ ItaUIOt I'
\ ,
" /
,-_/
,
laTYOI~
,----
... ,
"'-'"
58-.J3
58-13
.:.. {"
fIIU. -
c:~
C:::J
em' 01 --
fIIU. N8'S
--
c-->
~
o 50 100
1.11. I.... .1
SCAlE IN n:ET
...... """'28
- ... 0-
.1
Pisure 8
LOCATION OF TAR/AMMONIA TANKS
AND GAS PLANT WASTE DISPOSAL AREA
Peoples Natural Gas Site
-------
....
"6
...211
X
X"'''
...n
....,.
8if
-.
--
.
~
.
I
-III....
--
-
- ... 0-
c:z=:: <
iVNI~I~O "
AIIlVnb ~ooa
lEGEND
6 W-4 =-~
8.1Y WID
UMS PlEZGC1III
~ IIIIIIfIII
-- WI1.L
---
MIIIUST ,-
---
MAY ,-
IJCJf
---
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101'.0&. "'" >2,tOO ..JIo8 011
- "'" >flID-""""
D 1'-'"
...
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I
I
--IS
. W-12
....
)( 58-30
....n
. e-oIIJ2
...JII
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- 2.800 moIIco-
lAST II. 81IIEIT
88-11
. X
)(...17
)(...11
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/ "6-
I \
w HIIUJUI ,
J
/
-_/
88-111
III-IJ
CI1Y fI1 -
---
--,r
.1
--
~~
a
o 50 100
1.11. II 1.11 ..
SCAlE If nET
Figure 9
ESTIMATED LIMITS OF PAH SOIL
CONTAMINATION (SILTY SAND UNIT)
Pebple. Natural Ga. Site
-------
610
600
590
. 580
560
550
..-
WEST
N
...
o
o
I
o
4'
EAST
- ...
..,
olD
crill
o
.
1
ID
III
o
N
1
ID
VI
<
...
j'
~
-
N
I
ID
VI
N
I
ID
VI
N
N
I
ID
III
-N
"'-
I-
~d. HYDROCEOLOGIC
UNIT
Or .nle Clay
Lean Clay
~----
----
-- Lean 10 -Silty Clay
--
--
Sand
o
100
200
"00
DiStance. feet
300
500
600
700
800
Fill
Upper Confining
Unit
Silty Sand Unit
Lower Confining
Unit
Alluvial Aquifer
. U.lts of SoIl With Concentrations
of Total PAHs =- 500 mg/kg or Carcinogenic
PAHs =- 100 1119/kg
$- U.lts 0' SoIl With Conc8ntntlons
0' Total PAHs=-2.too 89/kg. or
Cardnogenlc PAHs >2" 89/kg
Fi8ure 10
PAH CROSS SECTION.....'
Peoples Natural Cas Site
-------
LmEt4D
- n-, 1ISf 1IIOICII
A W-4 -TOt ~
-- 0101
a P-118 atV -
LOIS PtElIJII[TOI
. W-12 M.L\MOL--
-- IIUJ.
X S8-JO ....-c
MIGU5'I 1-
8...11 ...-
_I-
. ~ IDGf
--
X ...a
....
I
I
---
>W....
o
......
....
...28
-
x"'l1
.,
-'ar-
. UN[
...311
x......
~
--11
8-1&
_1.
ESTIMATED LIMITS
OREATER THAN OF SOn..S WITH
y ~~ TOTAL 8ET~olNm::8FI.L
"-12 6 ""'18 ..UNIT
.
~ ";'~8 ~r-;,tA ./ ./ n-1 ..or
1MF1l~ .:1 88-:1 I V~'" ;::=-r
T£Si11OH~ ,~, ~ r n""ln- n In...
. ~' ,n;;ur _"
1,8YH h
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n,1 ~, 0""
f 8...,
,
I '-::
. ....
-:~~
--
co- -)
(N)
.
I
~.~.:
~ ,.'~ ":.~~
200
I
. Plsure 11
ESTIMA T
BETX SOil ~D LIMITS OF
Peoples N ONTAMINATION.
eturel Cel SUe
, 1VN'!)'~O
A...!l'tnD ~OOd
-------
..."
0.00!6/O.0"
""6
...
O. './0.18
,
I
10
.
I
---
-
~.
...
ND/O.O"
...
I
I
......
a
0-."
ND/O.OO".
\£Gf'Nn
6 W-4 ~1IDL
a P-'" ::: ::r0Mmll
. W-t2 ~~
'/8'0 IUSP£cna CMCINOOEI8C
"""IIfOT"L "AtIo
., NOT DmcnD
-ar-
- \II[
.N~O.U
lAIr 11. swn
[]
....
ND/'" .
.-
..6
....
,
,
I
o
U/"O ....
0.27/'.'"''
ND/O...::,"
(f'/f
--{
~"3n
cmar--~
NIl. r\U'S
aTf Of--
~--
--
(Do. ..,
~
o
100
200
I
I.. 1;. t ,. III
......
SCAl£ IN FEET
-. .
. . ..I
. Figure 12
DISTRIBUTION OF PAHs IN
THE GROUND"A TER
FEBRUARY Z2 AND 23. 1"0
(Concentrations In ug/L)
Peoples Natural Gas Site
-------
.... 6
lID
lID 8-
... D
lID I .....
I
-W-
_1M .....
lID
I6If fl. nuT
...n
.20
......
~ .O a
lID ,
I .....
.....
10 0
I
,
, ..0....
=8:::
.~.
n aTfW-
PUaJC - --
--{
c~
aTfW-
FUll. PIAI'S
t
I Ji8.
-- .~I
- ~ .. -.~ A
u:oom
6--. ~W01
D"""'=~
. W-12 ==--=
lID
NOT DETtCY1!D
--
(Dolo -»
(N)
o
100
200
I
I.. 1&111111 .1
SCAlE IN FrET
Figure 13
DISTRIBUTION OF BETX IN
THE GROUNDWATER
NOVEMBER .,.,
(Concentr8Uons In ug/L)
Peoples N8tur81 G.. SI te
'VN1~I~O
A1.11V(1f.) ~OOd
-------
....
-,
ND
~
,
I
10
.
.,
--
--
~.
c
_A
-.
I
,
I
o
n
--{
cSn
em fIT -- ....)J
FUll. ~
;;;.
. .
- . . ;.
...
.
...,
,
I
~i:o,../I./'O]
...,,,
NO
lECF'MO
6. '11-4 ~WU1.
o 1'-111 :: ~
. '11-12 =--=
"" IIOf DI11!CftD
-fIT..,
_1M
......
,
lAST ".. I1IIHT
..."
.70
.....
em fIT --
--=--
--
(Dooo ~
(i)
o 100
I... .1. I. .1
SCALE IN f[[T
200
I
1'1sure 14
DISTRIBUTION OF BETX IN
THE GROUNDWATER
JANUARY '''0
(Concentr.tlon In ug/LJ
Peoples N.tur.' G.I Site
-------
-
TABLES
-------
TABLE 1
SUMMARY OF MAXIMUM CONTAMINANT CONCENTRATIONS FOR WASTE DISPOSAL AREA
PEOPLES NATURAL GAS SITE
DUBUQUE, IOWA
WASTE DISPOSAL AREA
Boring 12- Boring 21 Boring 22 Boring 34
Compound of Concern Soil Soil Soil Soli
Total Carcinogenic PAHs (In mglkg) 920 1800 240 44
Total PAHs (In mg/kg) 8,000 5,400 2,700 350
Sum 01 VOCs (In ppb) 140,000 98,000 560,000 14,000
Total Cyanides (In mglkg) 870 41 1,100 38
Data Source: Barr Engineering Company, May 1991 (Table 2.1-2)
. Barr Engineering Company, January 1991 (Table 8)
PAHs - Polynuclear Aromatic Hydrocarbons
VOCs - Volatile Organic Compounds
-------
TABLE 2
SUMMARY OF MAXIMUM CONTAMINANT CONCENTRATIONS IN GROUNDWATER
PEOPLES NATURAL GAS SITE
DUBUQUE. IOWA
(Concentration in ugll)
WATER TABLEJUPPER
CONANING UNIT ALLUVIAL AQUIFER SIlTY SAND AQUIFER
COMPOUND OF CONCERN Well W2 WellW8 Well W9 Well W12 Well W16 Well W17 Piezometer 112
Total Carcinogenic PAHs 52 350 ND ND ND ND ND
Total PAHs 580 9300 48 0.56 8 43 4
Sum 0' Volatile Organics (BETX) 250 7500 - 21 360 500 . 8100
Total Cyanides 620 47001 181 100 - 160 30
Data Source: Barr Engineering Company. May 1991 (Table 2.5-4,2.5-6,2.5-7)
BETX . Benzene. Ethyl Benzene, Tohlene. Xytene
ND - Not detected
- - Not analyzed
- Estimated Value
rodlbl-2.wk1
-------
TABLE 3
(continued)
SUMMARY STAT1snCS FOR ANAL YneAL DATA
DETECTED COMPOUNDS - SOIL
. PEOPLES NATURAL GAS SITE
DUBUQUE, IrINA
PARAMETER
VOLATILE ORGANIC COMPOUNDS
Benzene
Ethyl Benzene
Toluene
Xylene
CYANIDE
Cyanide
""""'.."""""""""""""""""""''''''''..".,..",......."....,....
sQr~p~fA:.~g9~~~gr:;::::::::::::::::::;:::::;
BASE/NEUTRAL COMPOUNDS
Acenaphthene
Acenaphthylene
Anthracene
Benzo(a)anthracene
Benzo(a)pyrene
Benzo(b)fluoranthene
Benzo(ghi)perylene
Benzo(k)fluoranthene
Chrysene
Dibenzo(ah)anthracene
Ideno(1 ,2,3,cd)pyrene
Fluoranthene
Fluorene
Phenanthrene
Pyrene
Naphthatene
2-Methylnaphthalene
Dibenzofuran
.
Posltivel
Total
1 /
1 /
1 /
1 J
7 J
........
.......
37 / 101
35 I 101
34 / 101
32 / 101
25 /101
20 / 101
11 / 101
19 /101
36/ 101
3 / 101
14 /101
40 / 101
35 / 101
45 J 101
42 / 101
56 / 101
47 J 101
33 / 101
Range of
Positives
(ugIKg)
1
1
1
1
29 -
1,100 -
140 -
2,600 -
29
1,100
140
2,600
8
1,200 - 1,100,000
64 - 360,000
53 - 2,500.000
51 - 1,300,000
46 - 610,000
52 - 360.000
60 - 290,000
260 - 170,000
34 - 260,000
49 - 520,000
800 - 3,200
42 - 160,000
63 - 1,700,000
120 - 2,200,000
67 - 3.600.000
64 - 1,100,000
74 - 7,700,000
58 - 3,400,000
47 - 1,000,000
Data Source: Barr engineering Company. May 1991 (Table 4.1-1)
Arithmetic means.were calculated assuming a concentration of half the detection limit for
compounds below the detection limit.
ArIthmetic
Mean
(ugIKg)
29
1,100
140
2,600
222,000
10.950
40,866
21 ,677
10,224
6,573
6,644
4,519
5,979
9,122
7,474
4,381
28,351
37,258
63.100
20,007
134,039
67,888
15,341
-------
TABLE 3
SUMMARY STAT1STICS FOR ANALYnCAL DATA
DETECTED COMPOUNDS - SOIL
. PEOPlES NATURAl GAS SITE
DUBUQUE.IONA
Range of Arithmetic
Positivel Positives Mean
. PARAMETER Total (ugIKg) (ugIKg)
.......,.,..tC'.""""""."""""'b;:,fFEEt"::'[[[';';'
$.:Qt.:P.~TA:::..::::::......:::,:/::::::://::/:::J::::::::/:::::::::r:::::::,/:;)
BASeNEUTRALCOMPOUNDS
Acenaphthene 6 I 18 470 - 850,000 16,000
Acenaphthylene 14 I 18 200 - 380,000 42,474
Anthracene 15 I 18 190 - 360,000 36,152
Benzo(a)anthracene 16 I 18 70 - 240,000 34,521
Benzo(a)pyrene 14 I 18 150 - 420,000 39,641
Benzo(b)fluoranthene 13 I 18 990 - 310,000 35,567
Benzo(ghi)perylene 12 I 18 590 - 230,000 26,712
Benzo(k)fluoranthene 13 I 18 910 - 330,000 37,952
Chrysene 16 I 18 71 - 240,000 33,519
Dibenzo(ah)anthracene 9 I 18 190 - 64,000 12,976
Indeno(1,2.3,cd)pyrene 12 I 18 520 - 250,000 27,180
Fluoranthene 17 I 18 100 - 770,000 91 ,198
Fluorene 13 I 18 100 - 410,000 40,854
Phenanthrene 17 I 18 110 - 820,000 97,716
Pyrene 17 I 18 66 - 480,000 67,318
Naphthalene 16 I 18 79 - 2,800,000 283,884
2-Methylnaphthalene 10 I 18 210 - 720,000 89,599
Dibenzofuran 11 I 18 200 - 230,000 . 23,235
Benzo(e)pyrene 1 I 1 5,000 - 5,000 5,000
Carbozole 1 I 1 370 - 370 370
Indene 1 I 1 770 - 770 770
Perylene 1 I 1 1,700 - 1,700 1,700
Triphenylene 1 I 1 4,700 - 4,700 4,700
Bis(2-ethylhexyl)phthaJate 2 I 9 140 - 160 19,753
Di-n-butyl phthalate 1 I 9 41 - 41 19,802
PHENOLS
Benzoic acid 1 I 9 140 - 140 94,321
Data Source: Barr engineering Company. May 1991 (Table 4.1-1)
-------
TABLE 4
SUMMARY STATlsnCS FOR ANAL YT1eAL DATA
DETECTED COMPOUNDS - GROUNDWATER
PEOPlES NATURAL GAS SITE
DUBUQUE. tONA
Range of ArIthmetic
Positive I Positives Mean
PARAMETER Total (ugIKg) (ugIKg)
BASEINEUTRAL COMPOUNDS
. .
2.3-Benzofuran 8 I 22 0.0054 - 8 1.08
2.3-Dlhydrolndene 14 I 22 0.0021 - 18 2.2
Indene 17 I 22 0.0064 - 33 4.42
Naphthalene 26168 0.0052 - 5.800 207.14
Benzo(b)Thiophene 13 I 22 0.0064 - 22 3.04
Quinoline 2 I 22 3 - 4 0.74
Isoqulnollne 3 I 22 2 - 18 1.64
2-Methylnaphthalene 12 I 68 0.0023 - 830 17.13
1-Methylnaphthalene 16 I 22 0.0012 - 22 3.23
Biphenyl 10 I 22 0.0012 - 39 2.52
Acenaphthylene 11 I 68 0.043 - 630 15.73
Acenaphthene 26 I 68 0.0028 - 380 19.21
Dibenzofuran 11 I 68 0.033 - 200 13.52
Fluorene 13 I 67 0.0045 - 300 12.96
Dibenzothiophene 5 I 22 0.0069 - 13 1.14
Phenanthrene 18 I 68 0.0037 - 520 19.57
Anthracene 11 I 68 0.0016 - 180 9.09
Carbozole 9 I 22 0.0024 - 65 4.49
Fluoranthene 16 I 68 0.0036 - 220 11.56
Pyrene 16 I 68 0.0028 - 170 10.08
Triphenylene 7 I 22 0.0011 - 9 0.93
Benzo(e)pyrene 3 I 22 0.02 - 5 .0.79
Peryiene ' 2 I 22 0.0049 - 2 0.65
Benzo(ghQperyiene 2 I 68 0.028 - 5 7.61
Bis(2-ethylhexyl)phthalate 8 I 27 1. - 1,100 56.67
Benzo(a)anthracene .' 8 I 68 0.017 - 100 7.66
Chrysene 8 I 68 0.0011 - 78 7.33
Benzo(b)fluoranthene 6 I 68 0.0024 - 92 7.65
Benzo(k)fluoranthene 5 I 68 0.0024 - 15 7.77
Benzo(a)pyrene 4 I 68 0.026 75 7.26
Ideno(1,2,3,cd)pyrene 3168 0.019 6 7.61
Data Source: Barr Engineering Company. May 1991 (Table 4.1-1)
Arithmetic means were calculated assuming a concentration of half the detection limit for compounds
below the detection limit.
-------
TABLE 3
(continued)
SUMMARY STAllsnCS FOR ANAL YneAL DATA
. DETECTED COMPOUNDS - SOIL
PEOPLES NATURAL GAS snc
DUBUQUE.IONA
Range of Arithmetic
Pos1tiv81 Positives Mean
PARAMETER Total (ugIKg) (ugIKg)
Methylnaphthalene 4 I 4 80 - 49,000 9,926
2,3-Dlhydrolndene 1 I 1 180 - 180 3,944
Benzo(b)thlophene 2 I 2 210 - 700 3,758
Biphenyl 1 / 6 1,200 - 1,200 3,843
Dibenzothiophene 1 / 6 1,500 - 1,500 3,893
Indene 4 / 6 100 - 35,000 6,578
Isoquinollne 2 / 6 61 - 62 3,901
Triphenylene 1 / 6 1,200 - 1,200 3,843
Bis(2-ethylhexyl)phthalate 11 / 40 46 - 610 14,834
Butyl benzyl phthalate 5 / 40 66. - 410 14,831
Dlethyl phthalate 7 / 40 130 - 89,000 16,365
Di-n-butyl phthalate 1 / 40 38 - 38 14,851
PHENOLS
2,4-Dlmethylphenol 23 / 101 170 - 270,000 10,248
4-Chloro-m-cresol 1 I 47. 2,100 - 2,100 13,167
o-Cresol 8 I 47 250 - 55,000 13,521
p-Cresol 8 / 47 770 - 160,000 16,194
Phenol 2 /101 200 - 13,000 7,705
VOLATILE ORGANIC COMPOUNDS
Benzene 24/43 1 - 55,000 1,839
Ethyl Benzene 21 / 43 2 - 110,000 3,149
Toluene 15 / 43 2 - 29,000 2,255
Xylene 22 I 43 5 - 390,000 11,138
CYANiDE
Cyanide 8 I 27 1,000 - 48,000 4,600
Data Source: Barr engIneerIng Company, May 1991 (Table 4.1-1)
ArIthmetic means were calculated assumIng a concentratIon of half the detectIon limIt lor
compounds below the detectIon limIt.
-------
TABLE 5
REMEDIATION LEVELS IN GROUNDWATER
PEOPLES NATURAL GAS SITE
DUBUQUE. IOWA
Remediation
Contaminant Level (ppb) StandardlDetection UmJt
Benzene 1 Negligible Cancer Risk Level
Ethylbenzene 700 Ufetime Health Advisory Level
Toluene 2,000 Ufetlme Health Advisory Level
Xylene 10,000 Ufetime Health Advisory Level
Naphthalene 20 Ufetime Health Advisory Level
Benzo(a)pyrene 0.2 Practical Detection Umlt
Benzo(a)anthracene 0.1 Practical Detection Umit
Benzo(b)fluoranthene 0.2 Practical Detection Umit
Benzo(k)fluoranthene 0.2 Practical Detection Limit
Chrysene 0.2 Practical Detection Limit
Dibenz(a.h)anthracene 0.2 Practical Detection Limit
Indenopyrene 0.4 Practical Detection Limit
-------
TABLE 4
(continued)
SUMMARY STAllST1CS FOR ANAl Y11CAL DATA
DETECTED COMPOUNDS - GROUNDWATER
PEOPLES NATURAL GAS SITE
DUBUQUE. teNiA
Range of Arithmetic
Positive I Positives Mean
PARAMETER Total (uglKg) (ugIKg)
PHENOLS.
Phenol 4 , 46 5 9,800 231
2,4-Dlmethylphenol 8 , 41 4 - 25,000 634
VOLATILE ORGANIC COMPOUNDS
Benzene 19 , 59 1 - 4,400 175
Ethyl Benzene 11 , 59 3 - 1,500 34
Toluene 11 , 59 1 - 2,000 63
Xylene 15 , . 59 1 - 5,000 117
CYANIDE
Cyanide 33 , 41 10 - 4,700 373
Data Source: Barr Engineering Company, May 1991 (Table 4.1-1)
Arithmetic means were calculated assuming a concentration of half the detection limit for compounds
below the detection limit.
-------
TA, . =. 7
CALCULATED INCREMENtAL LIFETIME CANCER RISKS AND GLOBAL HAZARD INDICES
BASELINE ENDANGERMENT ASSESSMENT
PEOPLES' NATURAL GAS SITE
DUBUQUE. IOWA
RISKSIHAZARD INDICES
Exposure Scenario
Municipal
Worker
CARCINOGENIC RISKS
VOC Inhalation During Excavation Activities
VOC Inhalation During Routine Activities
Ingestion 01 On-Site (Alluvial Zone) Groundwater
Ingestion 01 Site Solis
Dermal Contact with Site Solis
1.17E-07
1.09E-02
2.92E-06
RECEPTOR
I Local Resident I Construction
(Adult) I Worker
I
Local Resident
(Child)
9.69E-10
5.64E-10
1.70E-04
8.83E-04
5.47E-08
3.40E-05
4.10E-08
2.85E-09
5.83E-05
1.20E-03
2.50E-04
l~~g:lt~iiI[QIII[ftm:ii[:::::::::::::i::::i:::I::iiili::::.::i:i:i:I:::ii::::i:iii:::ii:ii:i::::::::::I::':iiI::~::~ii':i:'I:::i:ii::::i:::::':i.1.~Pf~g::ii::'~::::':::::::::ii::ii:::tji:1.~!i~t9I:I':I::::::::::::i:::i:i:i:t:::::i::i;::iii::i1i::iil.~Il~.::::i:l:i::III:::::::::::i:::::;:i:::::i::i':i:i:!lt:III.::
NONCARCINOGENIC HAZARDS
VOC Inhalation During Excavation Activities
VOC Inhalation During Routine Activities
Ingestion 01 On-Site (Alluvial Zone) Groundwater
Ingestion 01 Site Soils
Dermal Contact with Site Solis
ND
1.40E-01
9.68E-01
ND
ND
2.27E-01
3.51 E-03
2.42E-02
6.12E-02
9.17E-01
ND
2.34E-01
6.26E-02
6. 26E-02
~~:H~:~m:".::::::::::::::::::::iii::::::::::::::::::::::::::::::i::::i:i~:::::::)~:::i:::i:i::i::::i:::i:iii:i::::i:"i,,:ii:i::::::::::i::I:::i::ii:i::::::'i:::::i'::i::Iii::i::::::::~:::::i:i:i:::::::':':.j.~l',.~~:::ii:i~'::::':i::::i,:,i::::::i:::g~igI1.::i:::'I::i.:'::::ii:::::::::i::i:::i:::::ii::::i;i'I~7!~11::i'::::i:::::::i:::::i:::i::::::::::::::::::::i:::::::::i:::::l.i'~!lPii:
Data Source: Barr Engineering Company, May 1991 (Table 4.6-1)
-------
TABLE 6
INDICATOR COMPOUNDS USED FOR RISK ASSESSMENT CALCULATIONS
PEOPLES NATURAL GAS SITE
DUBUQUE. IOWA
CARCINOGENIC INDICATOR COMPOUNDS
- Benzene \ .
- Benzo(a)anthracene
- Benzo(a)pyrene
- Benzo(b)fluoranthene
- Benzo(k)fluoranthene
- Chrysene
- Dibenzo(a,h)anthracene
- Indeno(1.2,3-C,d)Pyrene
NONCARCINOGENIC INDICATOR COMPOUNDS
- Fluorene
- Fluoranthene
- Pyrene
- Acenaphthene
- Anthracene
- Naphthalene
- Cyanide
Reference: Barr Engineering Company, May 1991
-------
TA~8
CARCINOGENIC RISKS
, .
r
RESIDENTIAL EXPOSURE INGESTION OF CHEMICALS IN SOIL BY CHILDREN
PEOPLES NATURAL GAS SITE
DUBUQUE, IOWA
CONTAMINANT
CS. IR CF R EF ED BW AT INTAKE CPFu
(MGIICO) (MGIDAY) (10-61
-------
LIST OF ACRONYMS
PEOPLES NATURAL GAS SITE
DUBUQUE, IOWA
TABLES 8, 9,10, AND 11
AT - Averaging Time (ED years x 365 days/year; days)
BW - Body Weight (kg)
CF - Conversion Factor
CPF - Cancer Potency Factor (mglkglday)-1
CS - Chemical Concentration In Soli (mglkg)
ED - Exposure Duration (years)
EF - Exposure Frequency (dayslyr; eventslyr)
FI - Fraction Ingested (unitless)
IR - Ingestion Rate (Uday)
RfD - Reference Dose (mg/kg/day)
-------
TABLE IV
CARCINOGENIC RISKS
INGESTION OF CHEMICALS IN SOIL FOR MUNICIPAL GARAGE WORKERS
. PEOPLES NATURAL GAS SITE
DUBUQUE. IOWA
CONTAMINANT
CS* IR CF FI EF ED BW AT INTAI
-------
TABLE 9
CARCINOGENIC RISKS
RESIDENTIAL EXPOSURE INGESTION OF CHEMICALS IN SOIL BY ADULTS
PEOPLES NATURAL GAS SITE
DUBUQUE, IOWA
.
CS. IR CF R EF ED OW AT INTAKE m=..
(UGIICO) (UGlDAV) (10-6 KGIMG) (UNrTlESS) (EVENTSIYR) (VAS) (KG) (DAYS) (MGII
-------
TABLE 12
. GROUND WATER RESULTS FOR RISK ASSESSMENT PURPOSES
PEOPLES NATURAL GAS SITE
DUBUQUE, IOWA
HIGHEST CONCENTRATION FOR ALL SAMPLING ROUNDSIALL WELlS (UGIL)* .
WATER TABLE WELlS ALLUVIAL AQUIFER WELlS
CHEMICAL (W1 THRU W7) WELL NO. (W10THRU W15, W17, W18) WELL NO.
BENZENE 230 W2 410 W17
BENZO(A)ANTHRACENE 0.045 W6 0.12 W10
BENZO(A)PYRENE ND 0.028 W10
BENZO(B)FLUORANTHENE ND ND
BENZO(K)FLUORANTHENE ND ND
CHRYSENE ND ND
DIBENZO(A,H)ANTHRACENE ND ND
INDEN0(1,2,3-C,D)PYRENE ND 0.019 W10
FLUORENE 130 W2 0.051 W10
FLUORANTHENE 110 W2 0.61 W10
PYRENE 86 W2. 0.47 W10
ACENAPHTHENE 380 W2 9 W17
ANTHRACENE 23 W2 0.035 W10
NAPHTHALENE 5100 W2 31 W17
CYANIDE 1.3 W4 0.16 W17
DATA SOURCE:
BARR ENGINEERING COMPANY, MAY 1991
SEMIVOLATILE ORGANIC COMPOUNDS TABLE 2.5-4
VOLATILE ORGANIC COMPOUNDS TABLE 2.5-8
INORGANIC COMPOUNDS TABLE 2.5-7
ND - NOT DETECTED ABOVE QUANmATION LIMIT OR WITHOUT A DATA QUALIFIER
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TABLE 11
CARCINOGENIC RISKS
ING~STlON OF CHEMICALS IN SOIL FOR CONSTRUCTION WORKERS
PEOPLES NATURAL GAS SITE
DUBUQUE, IOWA
CONTAMINANT
CS. IR CF FI EF ED OW AT INTAI
-------
LIST OF ACRONYMS
PEOPLES NATURAL GAS SITE
DUBUQUE, IOWA
TABLES 13, 14, 15, AND 16
AT - Averaging Time (ED years x 365 days/year; days)
BW - Body Weight (kg)
CPF - Cancer Potency Factor (mglkglday)-1
CW - Chemical Concentration In Water (mglL)
ED - Exposure Duration (years)
EF - Exposure Frequency (dayslyr; eventslyr)
IR - Ingestion Rate (Uday)
RfD - Reference Dose (mglkQlday)
-------
TABLE 13
CARCINOGENIC EXPOSURE CAlCUl.AllON FOR INGESTION OF CHEMICAlS IN DRlNIONG WATER
AllUVIAL AQUIFER
INClUSION OF All CHEMICAlSlON-SITE CONCEN1RAllONS
PEOPlES NATURAL GAS SITE, DUBUQUE,IOWA
IR EF ED BW AT INTAKE QJF
(MGIl) (lJDAY) (DAYSIYR) (VAS) (KG) (DAYS) (MGII
-------
TABl 14
CARCINOGENIC EXPOSURE CALCULAT10N FOR 1r«:ar::"STION OF CHEMICAlS IN DRlNI
-------
TABLE 15
DiRONIC NONCARCINOGENIC EXPOSURE CAlCULAl10N FOR INGES110N OF Dia.ICAlS IN DRINKING WATER
AllUVIAl AQUIFER WELlS
INa.USlON OF ALl DiEMICAlSION-S81E CONCENTRATIONS
PEOPlES NATURAL GAS SITE. DUBUQUE, IOWA
EF ED BW AT INTAKE RID
(DAYSIYR) (VAS) (KG) (DAYS) (MGII
-------
TAli
;16
CHRONIC NONCARCINOGENIC EXPOSURE CAlCUL\TmR FOR INGES110N OF CHEMICALS IN DRINKING WAtER
WATER TABLE WElLS
INClUSION OF ALL CHEMICAlSION-SITE CONCENTRAl1ONS
PEOPlES NATURAl GAS SITE. DUBUQUE. IOWA
CW(a) IR EF ED BW AT INTAKE RID
(MGIl) (lJDAY) (DAYSIYR) (VRS) (KG) (DAYS) (MGII
-------
no
IV.
- V.
VI.
I.
II.
111.
!'ABLB 17
COS!' ESTIKA!'E SUMMARY ~OR SELECTED RBKBDY
site Work
soil Transportation and Treatment
Ground Water Extraction and Treatment
1.
Alluvial Aquifer
Capital
o & M: Present Worth (10 Yrs. @ 9%)
2.
silty Sand Aquifer
capital
o & M: Present Worth (5 Yrs. @ 9%)
3.
Bioremediation System
Capital
o & M: Present Worth (10 Yrs. @ 9%)
Ground Water Quality Monitorinq
~
2,200,000
3,700,000
240,000
313,000
13,000
130,000
195,000
345,000
2.
Silty Sand: Present Worth (10 Yrs. @ 9%)
Alluvial Aquifer: Present Worth (10 Yrs. @ 9%). 106,000
1.
Subtotal Cost of .Selected Remedy
continqency for Commercial Soil Disposal
Total Estimated Cost for Selected Remedy
129,000
7,341,000
, 629,000
8,000,'000
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