EP 1110-1-19
30 Jun 01
4-3. Operable Unit Background. This section should summarize the requirements specified
in the ROD for the subject OU. It should include information on the cleanup goals, institutional
controls, monitoring requirements, O&M requirements, and other parameters applicable to the
design, construction, operation, and performance of the RA. Additional information regarding
the basis for establishing the cleanup goals/remediation objectives, including planned future land
use, should be provided. A summary of the RD, including any significant regulatory or technical
considerations or events occurring during the preparation of the RD, should also be included in
this section. Any ROD amendments, explanation of significant differences, or technical
impracticability waivers should also be identified and briefly discussed. An example
background section is provided in Exhibit 4-3.
Exhibit 4-3
Example Operable Unit Background (Section 2)
The remedy described in the ROD for OU2 included:
♦
On-site biodegradation of remaining, less-severely contaminated soils in a land treatment area
constructed with a liner, internal drainage, and spray irrigation system;
♦
Activities necessary to the proper functioning of the land treatment process;
♦
After treatment, covering the land treatment area with clean fill and re-vegetating; and
♦
Five years of groundwater monitoring to verify that it remains uncontaminated.
The remediation objectives in the ROD were: Within two years from initial seeding, the land treatment
process must reduce the concentration of TCIC to 100 mg/kg throughout the volume of the material treated.
The goals were based upon a risk assessment that focused on attaining at least a 1 x 10-6 risk for ingestion of
contaminated soil by a child. The risk assessment assumed a future industrial land use scenario, with no
institutional controls. Remediation objectives were described by the total concentration of six carcinogenic
indicator constituents of creosote -- benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, chrysene,
dibenzo(a, h)anthracene, and indeno(1,2,3-c,d)pyrene referred to as total carcinogenic indicator chemicals
(TCIC). EPA selected the six of the approximately two hundred compounds that make up creosote because of
their concentrations in sludge and soil at the site and their carcinogenic nature. The concentrations of TCIC
in the soil to be treated ranged from 100 to 208 mg/kg.
The September 15, 1996, ROD amendment included:
♦
Soils contaminated at levels exceeding 100 mg/kg, but less than 5,000 mg/kg TCICs, were to be
biodegraded in the on-site land treatment area.
♦
Soils found contaminated at levels exceeding 5,000 mg/kg TCICs were to be removed, stabilized, and
disposed of at an EPA-approved hazardous waste disposal facility along with the solidified, OU 1 waste
(7,500 yd3).
♦
If the land treatment process did not attain the remediation objectives for the TCIC within two years, but
quarterly monitoring showed substantial progress toward meeting the remediation objectives, EPA
would consider extending the treatment period. However, if substantial progress could not be identified,
EPA would consider alternative means of addressing the contaminated soils, such as capping, removal,
incineration, solidification, or vitrification.
♦
Groundwater monitoring would begin upon completion of construction of the land treatment area.
Based on the original ROD and the ROD amendment, the remedial design was prepared for construction of
the remedy. The design was completed in five months and approved by EPA September 15, 1996, for
implementation of the remedial action.
4-5
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