PB95-963131
EPA/ESD/R10-94/103
March 1995
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Harbor Island (Soil and Groundwater
Operable Unit), Seattle, WA
7/26/1994
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United States Region 10 Alaska
Environmental Protection 1200 Sixth Avenue Idaho
Agency Seattle WA 98101 Oregon
" Washington
&EPA
EXPLANATION OF SIGNIFICANT DIFFERENCE
INTRODUCTION
Site Name and Location:
Harbor Island, Soil and Groundwater Operable Unit
Seattle, Washington
Lead and Support Agencies:
U.S. Environmental Protection Agency (EPA)
Washington State Department of Ecology (Ecology)
Statute that requires an Explanation of Significant Difference
(ESD):
Comprehensive Environmental Response, Compensation, and Liability
Act (CERCLA), Section 117(c) and the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP), Section
300.435(c)(2)(i).
Need for an ESD:
One of the components of the selected remedy in the Record
of Decision (ROD) for the Soil and Groundwater Unit of the Harbor
Island Site (Site) was thermal desorption with condensate
collection to treat petroleum contaminated soil. However, after
further evaluation of the performance of this technology, it
became apparent that it would not meet air emission standards for
volatile organic compounds set by the Puget Sound Air Pollution
Control Agency (PSAPCA).
Administrative Record:
This ESD will become part of the Administrative Record for
the Harbor Island Superfund Site, which is available to the
public at the following location:
U.S. Environmental Protection Agency
Record Center, 7th Floor
1200 Sixth Avenue
Seattle, Washington 98101
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SITE BACKGROUND
Harbor Island is located approximately one mile southwest of
downtown Seattle, in King County, Washington, and lies at the
mouth of the Duwamish River on the southern edge of Elliott Bay.
The island is approximately 400 acres in size and is bordered by
the east and west waterways of the Duwamish River.
From 1903 to 1905, Harbor Island was created from marine
sediments dredged from the Duwamish River. Dredged sediment was
placed across the Duwamish tidelands to form a generally
homogeneous sandy fill which is now Harbor Island. Since
construction, Harbor Island has been used for commercial and
industrial activities including shipping, railroad
transportation, bulk petroleum storage and transfer, secondary
lead smelting, lead fabrication, shipbuilding, and metal plating.
Warehouses, laboratories, and office buildings have also been
located on the island. Harbor Island was placed on the National
Priorities List as a Superfund Site in 1983 due to elevated lead
concentrations in soil from the former lead smelter on the
island, (which ceased operation in 1984) as well as elevated
levels of other hazardous substances identified at the Site.
EPA has divided the Site into four operable units: 1) the
petroleum storage tank facilities operable unit, 2) the marine
sediment operable unit, 3) the Lockheed Shipyard facility
operable unit, and 4) the "soil and groundwater" operable unit
which covers the rest of the island. EPA is the lead agency for
the Lockheed, marine sediments, and soil and groundwater operable
units. EPA has designated the Washington Department of Ecology
(Ecology) as the lead agency for the petroleum storage tank
operable unit because the primary contaminant there is petroleum,
which is excluded from the federal Superfund statute but is a
regulated substance under the State's Model Toxic Control Act
(MTCA).
EPA completed a Phase I Remedial Investigation of Harbor
Island in 1990. EPA initiated a Phase II investigation in May,
1991, and completed the RI/FS reports for the soil and
groundwater operable unit in February, 1993. A Proposed Plan for
this unit was issued in June 1993, and the ROD for this unit was
completed in September 1993.
On May 2, 1994, EPA sent special notice letters to 55
Potentially Responsible Parties (PRPs) for the soil and
groundwater operable unit requesting that they perform the remedy
selected in the ROD. EPA intends to sign a Consent Decree with
these PRPs by September 1994.
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SITE CONTAMINATION
The most significant organic contaminant in soil is
petroleum. The range of petroleum concentrations were between
approximately 20 mg/kg and 51,000 mg/kg. Also present in smaller
quantities in surface soil were polycyclic aromatic hydrocarbons
(PAHs). The highest concentrations of heavy PAHs found in surface
soil ranged between 10 and 50 mg/kg. Polychlorinated biphenyls
(PCBs) in surface soil ranged from 2 to 420 mg/kg.
The most significant inorganic contaminant in the soil is
lead, which is found over most of the island and originated
primarily from the lead smelter. The majority of samples with
elevated lead in the range from 5,000 to 200,000 mg/kg, occurred
in the central portion of the site. The highest concentrations
of other inorganics are found in soil include: arsenic at 1,830
mg/kg, cadmium at 131 mg/kg, and chromium at 791 mg/kg.
Floating petroleum product was found at one location
adjacent to the shoreline on the north end of the island.
Groundwater at several locations along the shoreline on the
northern portion of the island also contained benzene,
ethylbenzene, and xylene, vinyl chloride, and other compounds
associated with petroleum products. Elevated levels of inorganic
contaminants including mercury, nickel, cadmium, lead, and zinc
are also found in groundwater across the island.
REMEDY SELECTED IN THE RECORD OF DECISION (ROD)
The selected remedy in the Harbor Island ROD includes the
following components:
Excavate and treat or dispose soil containing the
highest levels of contamination ("hot spots"). These
soil hot spots are defined as Total Petroleum
Hydrocarbons (TPH) greater than 10,000 mg/kg, PCB
greater than 50 mg/kg, and soil with mixed carcinogens
with a total risk greater than 10~\ TPH hot spot soil
would be treated on-Site by thermal desorption with
condensate collection= PCB and carcinogenic hot spot
soil would be disposed in an off-Site hazardous waste
disposal facility.
Contain exposed contaminated soil exceeding inorganic
or organic cleanup goals. Containment would be
achieved with a three inch asphalt cap which would
prevent infiltration of rainwater and reduce
contaminant migration into the environment. Existing
asphalt and concrete surfaces would be repaired to
prevent infiltration of rainwater.
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Invoke institutional controls which would require long
term maintenance of new and existing caps, warn future
property owners of remaining contamination contained
under capped areas on their properties, and specify
procedures for handling and disposal of excavated
contaminated soil from beneath the capped areas if
future excavation is necessary.
Remove and treat floating petroleum product and
associated contaminated groundwater at Todd Shipyards
to prevent its migration into the marine environment.
Monitor groundwater quality for 30 years and review of
groundwater quality data every 5 years to assess the
effectiveness of the selected remedy.
BASIS FOR SIGNIFICANT DIFFERENCE
This ESD modifies the technology selected to treat petroleum
contaminated soil from thermal desorption with condensate
collection to thermal desorption with an afterburner. Thermal
desorption with condensate collection was selected in the ROD
because it was believed that this technology would minimize air
emissions. However, after further evaluation of this technology,
it became apparent that condensate collection would not be able
to meet one of the Applicable or Relevant and Appropriate
Requirements (ARARs) for the Harbor Island Site. This ARAR is
the PSAPCA regulation which sets a destruction efficiency of
greater than 99% for volatile organic compounds in a thermal
desorption system. PSAPCA also identifies the best available
technology for treating petroleum contaminated soil as thermal
desorption with an afterburner. According to bulletins issued by
EPA's Office of Research and Development, thermal desorption with
an afterburner has a destruction efficiency of 99.99% for
volatile organics, which exceeds PSAPCA's requirement by about
two orders of magnitude.
To verify that the operation of a thermal desorption system
with an afterburner on Harbor.Island would not pose a significant
health risk to workers operating the system, an exposure estimate
was calculated (attached). Such workers would be the individuals
receiving the maximum potential exposure to contaminants in the
air emissions from the thermal desorption system. Because of the
short duration of the exposure (3-6 months), the only significant
potential health effects to these workers would be non-
carcinogenic effects from exposure to low levels of benzene and
polyaromatic hydrocarbons (PAHs). The exposure estimate
calculates concentrations of benzene and PAHs at the stack exit
of the thermal desorption system, which is the point of maximum
possible exposure. Based on the assumptions used in this
estimate, the concentrations of benzene and PAHs in the stack air
emissions would be about four orders of magnitude below the
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industrial threshold limit values (TLVs), for benzene and PAHs.
The TLVs are values identified by the American Conference of
Government Industrial Hygienists as safe exposure limits for an
8-hour per day, 40-hour per week worker exposure. Based on this
comparison to these TLVs, it was concluded that the operation of
a thermal system on Harbor Island will not pose a health hazard
to workers.
In summary, the complete PSAPCA requirements for thermal
desorption are: 1) greater than 99% destruction efficiency for
volatile organic compounds, 2) the afterburner operates at a
minimum temperature of 1400° F, 3) particulate emissions from the
stack cannot exceed 0.02 grains/dry standard cubic feet, 4)
opacity from the exhaust stack cannot exceed 5% for three minutes
in any hour, and 5) fugitive emissions from any other part of the
equipment or control equipment is prohibited. In addition to
these requirements for the thermal desorption system, EPA will
require that the dust collected in the baghouse be sampled for
TPH concentration to determine if it is below the cleanup goal of
600 rag/kg before being mixed with treated soil. Dust which
exceeds this goal will have to be retreated or taken off-Site for
disposal in compliance with Ecology's regulations.
EPA will also require soil sampling before and after thermal
desorption treatment to verify that treated soil is not a RCRA
characteristic hazardous waste. The main concern is high
concentrations of lead in some of the untreated soil which may
cause it to become a characteristic hazardous waste after
treatment. To prevent on-Site disposal of treated soil which may
constitute a hazardous waste, EPA will require that: 1) in areas
where lead concentration are suspected to exceed 1,000 mg/kg,
soil will be tested for lead concentration prior to treatment,
and 2) untreated soil which exceeds lead concentrations of 1,000
mg/kg will be tested after treatment by the EPA's TCLP leachate
procedure to determine if it is a hazardous waste. Any soil
which is identified as a hazardous waste will be disposed off-
Site at a permitted hazardous waste disposal facility.
The cost estimate for thermal desorption with condensate
collection provided in the Soil and Groundwater operable unit ROD
was $125 per cubic yard ($100 per cubic yard plus a 25%
contingency). However, cost estimates from vendors post-ROD
indicate that on-Site thermal desorption with an afterburner will
cost about $60-$70 per cubic yard, which is about half the cost
estimate in the ROD.
AFFIRMATION OF STATUTORY DETERMINATIONS
Considering the new information on the performance and cost
of thermal desorption collected since the ROD was completed, EPA
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believes that the revised remedy is more protective of human
health and the environment and achieves cleanup goals more cost
effectively. The revised remedy utilizes permanent solutions to
the maximum extent practicable for this Site. It complies with
the NCP and other federal and state requirements that are
applicable or relevant and appropriate to this remedial action.
PUBLIC PARTICIPATION ACTIVITIES
This ESD will become a part of the Administrative Record .for
the Harbor Island Site. The availability of the ESD and a
summary of it impact on the site remedy will be announced in a
public notice and in a fact sheet sent to the mailing list. For
additional information regarding this ESD, please contact the
Superfund Site Manager for the Harbor Island site:
Keith Rose
1200 Sixth Avenue, HW-113
Seattle, Washington 98101
(206) 553-7721
Approval:
Carol Rushin, Chief, date
Superfund Remedial Branch
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Attachment
EXPOSURE ESTIMATE FOR THERMAL DESORPTIOK OF
PETROLEUM CONTAMINATED SOIL AT HARBOR ISLAND
It is proposed that petroleum contaminated soil at Harbor
Island be treated by thermal desorption with an afterburner. In
order to determine if such a treatment system would produce air
emissions which are safe for the system operators, who would be
the individual with the greatest chance of exposure, the
following calculations were performed. The petroleum constituents
with the greatest potential for health effects were identified as
benzene and PAHs. The air concentrations of these constituents
are estimate at the point where the stack vents to the
atmosphere, which would be the maximum possible concentration
before mixing with ambient air. Finally, the industrial threshold
values for these constituents are provided for comparison. These
threshold values are based on an 8-hour work day and 40-hour work
week, which are the assumed exposure durations for this case.
1. Assumptions
a. Soil process rate: 100 tons/hr (22,500 kg/hr)
b. Stack air flow rate: 600,000 ft3/hr (22,222 m3/hr)
c. Afterburner Destruction Efficiency (DF): 99.99%
d. Average concentration of benzene in soil: 2.0 mg/kg
e. Average concentration of PAHs in soil: 30 mg/kg
2. Calculated Air Concentrations at Stack
a. Formula:
[C]«ir = ([C]soii) (process rate) (1-DF)/stack flow rate
b. Benzene Concentration:
[Benzene]air = (2 mg/kg) (22 , 500 kg/hr) (10"*)/(22 ,222 m3/hr)
= 2x10'* mg/m3
c. PAH Concentration:
[PAH]air = (30 mg/kg) (22,500 kg/hr) (10'A)/(22, 222 m3/hr)
3xlO"3 mg/m3
3. Threshold Limit Values fTLVs)
[ Benzene ]TLV = 30 mg/m3
[PAH (naphthalene) ]TLV = 50 mg/m3
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