6    DESIGN AND IMPLEMENTATION OF A RISK-BASED
REMEDIAL ACTION PROGRAM FOR UNDERGROUND
TANK REMOVAL AT A DIOXIN-CONTAMINATED SITE
Jonathan R. Spencer, Director of Engineering REACT
Division of D. W. Ryckman and Associates
St. Louis, Missouri 63146
INTRODUCTION
Risk assessment has been defined by the National Academy of Sciences as "the use of available
scientific information and reasonable scientific assumptions to evaluate the health risk to people from
exposure to hazardous materials and situations in the environment."1 The unknown or uncertain
conditions often inherent in hazardous waste site remediation projects complicate the job of the
responsible professional to adequately assess and manage associated risks. This paper describes the
design and implementation of a risk-based remedial action program for the removal of pentach-
lorophenol sludges at a dioxin-contaminated site in the midwest.
SITE HISTORY
A midwestern solvent transfer terminal was the focus of a 1984 dioxin investigation initiated by the
United States Environmental Protection Agency (EPA) after records revealed that the site had been
used by a previous owner for the production of Agent Orange. The presence of 2,3,7,8-TCDD, a
contaminant found in Agent Orange, was allegedly confirmed by two sampling and analysis tasks
performed by EPA showing levels up to 160 ng/L on the site. In late 1984, the current owner noticed a
black tar-like substance surfacing on the property. Subsequent excavation of the affected area uncovered a large underground steel tank containing similar type sludges. These sludges were later found to
contain significant levels of pentachlorophenol and other poly-aromatic hydrocarbons (PAH's).
An initial attempt by the owner to remove the tank proved unsuccessful and also resulted in the
release of these sludges to the surrounding soil matrix. Because of the presence of TCDD in the
vicinity of the tank, no additional excavation work was attempted at that time.
In March of 1986, EPA notified the current owner and other potentially responsible parties (PRP's)
(including former owners and operators) that it was considering spending public funds appropriated
under section 104 of CERCLA to remediate the site. An initial engineering evaluation and cost
analysis, prepared for EPA under the Federal REM II program, recommended the excavation, containment, and interim storage of all soils where TCDD concentrations exceeded 5 /ig/L. Soils were
eventually to be transported off-site and incinerated. This alternative would have necessitated the
suspension of on-site operations during the 3-month project performance period and also required the
construction of two large storage buildings. The owner rejected these recommendations as cost-
prohibitive, and the PRP's elected to initiate their own remedial investigation/feasibility study (RI/
FS).
INVESTIGATIONS AND PRIORITY REMEDIAL ACTION
REACT was retained by the site owner to perform an engineering study and to recommend a
remedial action program addressing both the leaking underground storage tank and the dioxin-
contaminated soils on-site. The program was intended to provide the site owner with a cost effective
solution through which the health and safety of on-site personnel and the general public would be
insured. The proposed program consisted of two priority items: 1) construction of a surface cap to
entomb dioxin-contaminated soils; and 2) removal of the underground storage tank and associated
soils.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers. Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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