EPA/ESD/R10-95/117
August 1995
EPA Superfund
Explanation of Significant
Differences for the
Record of Decision:
Commencement Bay
Near Shore/Tide Flats,
Tacoma Tar Pits, WA
5/09/95
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REVISION OF
EXPLANATION OF SIGNIFICANT DIFFERENCES
INTRODUCTION
Datc of Revision of Explanation of Significant Differcnccs (Revised ESD):
March 31, 1995
Site Name and Location:
Tacoma Tar Pits Operable Unit (Tar Pits site)
Commencement Bay-Nearshoreffideflats Superfund Site
Tacoma, Washington
Lead and Support .Agencies:
U.S. Environmental Protection Agency (EP A) -- Lead Agency
Washington State Department of Ecology (Ecology) -- Support Agency
Authorization for Revised ESD:
Section 117(c)of the Comprehensive. Environmental Response, Compensatipn, and
Liability Act (CERCLA) 42 U~S>c. ~9617(c), .and Section 300.435(c)(2)(i) of the
National Oil and Hazardous Substances Pollution Contingency Plan (NCP).
Need for Revised ESD:
On December 20,1987, EPA signed and issued a.Record of Decision (ROD) for the Tar
Pits site, located within the Commencement Bay-Nearshoreffideflats Superfund Site. A
number of changes to the remedy described in the ROD were developed based on studies
conducted ~ubsequent to the ROD. These changes are discUssed in the Explanation of
Significant Differences (ESD) dated November 10, .1991, and also in this revised ESt>.
This revised ESD is necessary because.there have been additional changes in the remedy
since the ESD was prepared. .
Administrative Record:
This Revised ESD will become part of the Administrative Record for the Tar Pits site.
The Administrative Record is available at the following locations:
U.S. Environmental Protection Agency
1200 Sixth Avenue, HW -113
Seattle, Washington 98101
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Tacoma Public Library
Main Branch
1102 Tacoma Avenue, N.W. Room
Tacoma, Washington 98402
SITE BACKGROUND
A coal gasification plant operated at the Tar Pits site from 1924 to 1956. Waste materials
from the coal gasification process, including coal tar liquors, coal ash, and coal tars were
disposed on site. The waste compounds included aromatic hydrocarbons, (e.g., benzene
and toluene, polynuclear aromatic hydrocarbons (P AHs)(e.g., naphthalene, .
benzo(a)pyrene), other classes of hydrocarbons, and cyanide). Heavy metals including
arsenic, mercury, and lead were also common in the plant waste streams. In 1966,
Washington Natural Gas (WNG), the site owner, demolished the plant. Most structures
were removed but some demolition debris and below-grade structures, including pipelines.
containing tars and tank bottoms and foundations, remained.
In 1967, Joseph Simon & Sons (JS&S) began a metal recycling operation at the Tar Pits
site. The JS&S operation recycled a variety of metals, including car bodies and electrical
transformers. The scrapping of these products released heavy metals and polychlorinated
biphenyls (PCBs) on to the surface and the subsurface. Shredded non-metal automobile
waste (auto. fluff) was also disposed at the site. The auto fluff, consisting primarily of
shredded automobile interiors, .became fill material at the southern perimeter of the JS&S
property as well as for the surrounding property owned by Burlington Northern Railroad
Company (BN) and Hygrade Foods Product Corporation (Hygrade).
In 1981, EP A and Ecology discovered tar with a P AH content of 4 percent (40,000
mg/kg) at the Tar Pits site. In 1982, the EPA Field Investigation Team's site inspection
lead to ~ EP A Potential Hazardous Waste Site Preliminary Assessment. In September' of
1984, EP A began a Remedial Investigation (RI) which, in November of 1984 as part of an
Administrative Order on Consent, was continued and completed by JS&S,WNG, .
Hygrade, and BN. These parties also prepared a Feasibility Study (FS). The RI/FS was
completed in 1987. The ROD was issued by EPA on December 30, 1987. In September
1988, EP A issued a Unilateral Administrative Order (UAO) to WNG and JS&S requiring
these parties to implement the remedial design/remedial action (RD/RA) set forth in the
ROD. .
EPA, with assistance from Ecology, provided oversight during implementation of the
remedial activities. In 1991, as a result of an alleged failure of WNG and JS&S to fully
comply with the UAO, EP A filed a law suit in Federal District Court to enforce the
requirements of the UAO. This action resulted in a settlement pursuant to which WNG
has agreed to be responsible for implementing RA at the Tar Pits site.
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RA began in June 1992 and Phase I was completed in June 1993. . Phases II and 111,
known as the "Balance of Remediation Activities," commenced in June 1993 and WNG
has projected completion in June 1995. The RA requirements are discussed below.
REMEDY SET FORTH IN THE RECORD OF DECISION (ROD)
The RA set forth by the ROD requires the. following:
.
Excavation and treatment of all contaminated soils considered to be
Extremely Hazardous Wastes (EHW), which are defined for the Tar Pits
site as exceeding 1 percent (10,000 mg/kg) total P AHs (Ecology Applicable
or Relevant and Appropriate Requirement)
.
Excavation and ti-eatment (stabilization) of all surface .soils (less than 3-foot
depth) containing contaminants identified in the ROD (lead, benzene, PCBs, .
and PAHs) that exceed a 1O~ lifetime cancer risk level.
.
Reduction of surface water infiltration and potential human exposure to
stabilized soils by capping the stabilized matrix with a low-permeability
asphalt cap
.
Reduction .of surface water transport of contaminants by channeling and
managing. surface water run-on and run-off
.
Provision for continued groundwater monitoring to evaluate the
effectiveness of the RA and evaluate the need for potential groundwater
extraction and treatment. . .
.
: Removal and treatment of ponded water to achieve cleanup goals
.
Provision for institutional controls to ensure cap integrity and prevent future
use of contaminated onsite groundwater.
SIGNIFICANT DIFFERENCES
Nine significant differences from the remedy specified in the ROD were discussed in the
ESD. Five of these significant differences have changed in nature since the ESD. In .
addition, a new significant difference has developed since the ESD, resulting in a total of
10 significant differences from the remedy set forth in the ROD. A discussion of each of
the 10 significant differences is provided below,. including a summary of each significant
difference contained iri the ESD and the subsequent changes thereto..
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,II
L
Consolidation of Hot Spots from the Peripheral Areas
Summary of Discussion in the ESD:
An extent-of-contamination (EOC) investigation was conducted in April 1990~and
an EOC report was prepared in August 1990 (Ebasco, 1990). The purpose of the
EOC investigation was to determine the nature and extent of additional
contamination beyond the proposed cap area delineated in the ROD. The EOC
report indicated that various levels of contaminants identified in the ROQ existed
in the peripheral areas of the Tar Pits site. Based on review of the EOC report,
EP A determined that if the most contaminated soils were removed from the
peripheral areas and replaced by clean fill, the ROD action level requirements
would be met. It was further concluded that capping of the peripheral areas would
not b,e necessary. '
Changes Since the ESD:
There have been no changes to this significant difference since the ESD.
2.
Consolidation and Stabilization of Area C. JS&S Operating Area East.
Summary of Discussion in the ESD:'
The JS&S Operating Area East (OAE) waS not specifically identified in the ROD
as an area requiring remediation. However, the EOC report (Ebasco, 1990)
indicated the presence of contaminated soils in this area. , Therefore; remediation of
OAE was determined to be necessary by EPA. Such remediation would be similar
to that of other peripheral areas such that "hot spots" in the JS&S OAB would be
excavated, stabilized, and placed within the cap area identified in the ROD. In
addition, OAB would be capped (paved) with a low-permeability material suitable
for JS&S operations.
Changes Since the ESD:
There have been no changes to this significant differep.ce since the ESD.
3.
Importation of Clean Fill To Place Treated Material Above the Seasonally High
Water Table' .
, Summary of Discussion in, the ESD: .
,The ROD specifies that certain material is to be stabilized, and placed back into the
excavated areas. However, during remedial design EP A determined that the
stabilized material should be placed above the seasonal high groundwater level to
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reduce the potential for leaching of contaminants from. the stabilized. material to
groundwater. Therefore, EP A also determined that imported clean fill should be
placed in excavated areas to raise the bottom of stabilized fill above .the seasonal
high groundwater level. . .
Changes Since the ESD:
There have been no changes to this significant difference since the ESD. .
4.
Modification of Treatabilitv Mixes
Summary of Discussion in the ESD:
The stabilization process generally prescribed by the ROD would include a
cement/polymer mix added to a homogenous mixture of soil, auto fluff, and tar in
order to produce a stabilized matrix. Bench- and pilot-scale treatability studies
were conducted in accordance with the ROD in order to demonstrate the
effectiveness of various mixes and allow for the selection of the stabilization.
process. Review 01 the treatability study results indicated that not all contaminants
required the same level of stabilization in order to meet cleanup criteria for.
groundwater at the .site boundary. Therefore, different stabiliZation mixes and
processes were appropriate for each of the predominant components: auto fluff,
tarry soils, and non-tarry soils. . .
Changes Since the ESD:
Additional treatability studies were conducted subsequent to the ESD in order to
select the proper stabilization mix for each of the components at the site.
T~eatability. The results from these studies are reported in the following
documents:
1)
2)
3)
Batch Plant Demonstration Repor~ (Ebasco, March 1991).
Phase II Treatability Study (Ebasco, May 1992).
S-4 Optimization and STC Stabilization M.ix Design Report (Ebasco,
November 1992). ... .
S-4 Elimination Treatability Testi,!g & STC Stabilization Mix Design
(Ebasco, September 1993).
Results of Fluff Treatability Optimization Study (Letter from Ebasco to
EPA dated February 10, 1993). .
4)
5)
Stabilization has been completed. Auto fluff and non-tarry contaminated soil was
stabilized in a pug mil" using Portland cement as the active stabilization ingredient.
Tarry materials were stabilized using a proprietary mixture of ingredients provided
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by Silicate Technology Corporation (STC). The STC ingredients were mixed with
contaminated material in an-on-site batch mixer.
5.
Change in the Leaching ReQuirements
Summary of Discussion in the ESD:
In order to meet "the post-remediation cleanup criteria established in the ROD, the
leaching requirements and treatment levels were modified to take into consideration"
the final Batch Plant Demonstration Report (Ebasco, 1991), the
Dilution/Attenuation Factor (DAF) Quantification report (Ebasco, 1991), available
bench scale treatment data, and attenuation characteristics. Additional treatability
testing at both bench and batch scales were planned to further optimize mix
. constituents. .
Maximum values for leaching characteristics (TCLP) were established for each of
the parameters set forth in the ROD, using information obtained in the following
documents: .
1)
2)
3)
4)
5)
Dilution/Attenuation FaCtor Quantification Report (Ebasco, April 1991).
Bench-Scale Treatability Study Report (Ebasco, January 1990).
Bench-Scale Screening Study (Ebasco, November 1990). "
Batch Plant Demonstration Report (Ebasco, March 1991). .
. Final Framework for Remediation Document (WNG, September 1991).
The maximum leaching values (TCLP) for stabilized" material are as follows:
.
Tarry Materials:
Lead, 650 ugll
PCBs, 2.6 ugll
ROD P AHs (total), 390 ug/l
ROD PAHs(individual compounds), 65 ug/1
Benzene, 500 ugll .
.
Soils and auto fluff:
Lead, 5000 ug/l
PCBs," 20 ug/l .
ROD P AHs (total), 3000 ug/l
ROD P AHs (individual compounds), 500 ug/l
Benzene, 500 ug/l
.. In addition, groundwater monitoring performed during the implementation of, and
following, the RA was required to determine the long-term effectiveness of the
remedial action. As provided in the ROD, an expanded groundwater monitoring
system has been designed and installed at the site. Pre-remediation groundwater
quality data was collected during the RA. Groundwater and surface water data will
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continue to be collected after the RA is ,complete. The ROD states that if cle~up
levels are not achieved in the aquifers at the site boundary within a reasonable
period of time following completion of RA, and during a subsequent 2-year
monitoring period, alternative RAs are to be evaluated and additional RA is to be
implemented. Groundwater extraction and treatment is one such alternative.
Changes Since the ESD:
The maximwn leaching criteria discussed in the ESD have not changed. However,
treatment mixtures have changed based on treatability results, as discussed for
significant difference No.4 above. .
6.
Increase in the V olwne of Material to be Treated i
Summary of Discussion in the ESD:
, According to the ROD, an estimated'45,000 cubic yards (yd3) of material would be
excavated and stabilized at the site. This estimate asswned "areas of clean'" within
the proposed cap boundary, and did not ' account for additional contaminated
material in the peripheral, and 1S&S operating areas. Based on post RIffS,
characterization of the site within the cap area and data from the EOC report; the
excavation/stabilization volume estimate was revised to 78,600 yd3, including soil,
c;luto fluff, and tar. This volume estimate was subject to revision based on
'additional testing conducted during the exCavation of "hot spots", or as previously'
unknown EHW (i:e. tarry materials with a PAH content above 1 percent [10,000 "
mg/kg]) was identified. '
Changes Since the ESD:
Excavation and stabilization' is complete. BecaUse of the expansion of "hot spot"
excavations and identification and excavation of more EHW tarry material than
originally estimated (based on testing and visual observation), a total of 185,170
yds3 of soil, auto fluff, and tar was excavated and stabiliz~d. Another 14,869.78 '
tons (11,335.61 hazatdous and 3,534.17 nonhazardous) were disposed at offsite
landfills (offsite disposal included over-size debris too large to stabilize and
residual soil from batch mix plant cleanup). ' '
7.
Increase in Cap Area
Summary of Discussion in the ESD:
A cap area of approximately 75,000 square yard (yd2) was specified in the ROD.
The cap area was to be expanded to include an additional surface area up to a total
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8.
of approximately 100,000 yd2,if necessary. The capped area was to include the
entire JS&S operating area.
Changes Since the ESD:
There have been no changes to this significant difference since the ESD.
Increase in Capital Cost for Remediation
Summary of Discussion in the ESD:
At the time of the ESD, the estimated capital cost for the RA was $15 to $18
million, an increase from the $3.4 milli~m estimate in the ROD. The major
components affecting cost included increases in:. the unit cost of remediation and .
chemical additives,. the volume of material to be stabilized, the capped area, the
associated materials handling effort, and the scope for the engineering and
management of the projeCt. .
Changes Since the ESD:
The estimated capital cost for the RA has increased to approximately $37 million.
As was the case with the cost increase explained in the ESD, the.cost increase is .
primarily the result of extra costs associated with excavation and stabilization of .
the additional volume of material (see significant difference No.6 for a discussion
of the volume increase).
9.
. Change in Remediation Schedule
Summary of Discussion in the ESD:
In September 1988, EP A issued the UAO to WNG requiring implementation of the
remedy set forth in the ROD. The UAO required completion of construction of
the RA by September 1990. The UAO was amended on June 6, 1989, with a new
schedule requiring completion of the RA by September 26, 1991. The schedule
was revised again when EP A and WNG entered into the Consent Decree in
February 1992. ~e schedule in the settlement specified that remediation was to
have been completed by November 1, 1993. However, the settlement allowed for
a third construction season as a cQntingency; the third construction season and RA
was to have been completed by the end of 1994. .
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Changes Since the ESD:
.
EPA approved an extension of the schedule in a letter dated August 16, 1993. The
extended schedule allowed use of the contingency construction year and designated
December 31, 1994 as the RA completion date. The schedule was extended
primarily because of the increase in excavation and stabilization volumes (see.
significant difference No.6 for a discussion of the volume increase). At this time,
remediation is not yet complete~ however, WNG has committed to completion of
the remediation by June 30, 1995 (WNG letter to EPA dated January 12, 1995).
~
10.
Addition of a Multi-Lavered Geosvnthetic Cover and Cement Concrete Pavement
This significant difference has developed since the ESD. The ROD specifies that a
low-permeability asphalt cap be installed over the stabilized waste. However,
concerns regarding the ability to meet the permeability requirement (lxl0-7 cm/s)
on the side 'slopes of the waSte pile and .the long-term durability of asphalt
pavement led to the use ofa multi-layered geosynthetic cover for the waste pile'
area (Ebasco, August 19, 1994~ September 1994a; and September 1994b). Also,
1S&S had concerns about the long-term wearability of asphalt pavement in parts of
the JS&S operating area; therefore, cement concrete pavement was constructed in
certain areas of the 1S&S areas. Low-permeability asphalt pavement was installed.
in other portions of the 1S&S areas ,and around the waste pile perimeter. All of
the paving alternatives, including the geosynthetic cap; have been designed,
installed and'tested to meet the permeability requirements specified in the ROD.'
SUPPORT AGENCY COMMENTS
. '
. '
Ecology has been informed of the developments in the RA approach and has had an
opportunity to comment on project documents, including this Revised ESD. . Ecology
,concurs with this Revised ESD. "
AFFIRMATION OF STATUTORY DETERMINATIONS
After consideration of the new information developed subsequent to the ROD, EP A and
Ecology have determined that the changes to the remedy will continue to provide for the
pro~ection of human health and the environment. The remedy continues to be cost.
effective and uses permanent solutions to. the maximum extent practicable for this site.
The remedy is also in compliance with th.e NCP, and Federal and State requirements
'identified in the ROD that are applicable or relevant and appropriate to this RA. .
PUBLIC PARTICIPATION ACTIVITIES
D
A notice of the approval and issuance of the Revised ESD will be published in the
Tacoma News Tribune. This Revised ESD, the supporting information, and EPA's
.
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response to any commeuts from the public will become part of the Administrative Record
for the Tar Pits site. For additional information regarding this Revised ESD, please
contact the Superfund Site Manager for the Tar Pits site:
Lee Marshall
1200 Sixth Avenue, HW-113
Seattle, Washington 98101
(206) 553-2723
APPROVED:
DATE:
T\~~
5/ iJ9S-
Randall F. Smith
Director
Hazardous Waste Division
,
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REFERENCES
Ebasco, January 1990. Benc.h-Scale Treatability Study Report.
Ebasco, November 1990. Bench-Scale Screening Study.
4
Ebasco, November 1990. Extent of Contamination Field Study.
Ebasco, March 1991. Batch Plant Demonstration Report.
Ebasco, April 1991, Dilution! Attenuation Factor Quantification.
Ebasco, May 1992. Phase II Treatability Study.
Ebasco, November. 1992. S-4 Optimization and STC Stabilization Mix Design.
Ebasco, February 10,1993. Letter addressing results of Fluff Treatability Optimization
Study. Letter from A. Rossi/Ebasco to L. MarshalllEPA. .
Ebasco, September 1993. S-4 Elimination Treatability T.esting & STC Stabilization. Mix
Design.
Ebasco, August .19, J994. Technical Memorandum Waste Pile Cover Design, Revision 1..
. Ebasco, September 1994a. Design Drawings for the Waste Pile Alternative Cover.
Ebasco, September 1994b. Technical Specifications for the Waste Pile Alternative Cover.
Enviromnental Protection Agency, November 1, 1991. Explanation of Significant
. Differences for the Tacoma Tar Pits Site.
WaShington Natural Gas Co., September 1991. Final Framework for Remediation
Document.
Washington Natural Gas Co., January 12, 1995. Letter addressing schedule for remaining
RA work. From T. HoganfWNG to R. MednicklEP A. .
Washington Natural Gas Co.; September 28, 1994 and March 17, 1995. Memoranda from
Matthew Dalton with preliminary cost projections.
"
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