ARCHIVED REPORTS BIOTREATMENT BEDS POST REMEDIATION INVESTIGATION REPORT

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' ARCADIS Ms. Kathryn Dominic August 24, 2010 ' 1997a). The 11,000 cubic yards of stockpiled sludge and soil along with 2,000 cubic yards of soil from regrading the Site were spread into two Biotreatment Beds (Figure ' 2)with RWQCB approval. Three phases of bioremediation activities occurred from 1994 to 1997. Each phase included application of nutrients and water, soil tilling, and soil sampling for TPH and PAHs (Terranext 1997a). Results from sampling of ' Biotreatment Beds associated with each phase of bioremediation are presented in the Work Plan. ' Cleanup and Abatement Order Cleanup Requirements CAO No. 92-707 amends CAO No. 91-720 and No. 90-715, which together comprise ' the cleanup requirements for the site, but CAO No. 92-707 specifies cleanup levels for soil and insitu groundwater. Based on a review of CAO 92-707 and the RWQCB February 2010 E-mail, the following must be met: ' Soil remaining on site must contain less than 50 mg/kg of TPH-d • Groundwater beneath the downgradient limit of the TPCA impoundment (or in this case, the biotreatment bed) must contain less than 100 mg/I of TPH-d Cleanup and Abatement Order Cleanup Requirements and Alternative ' Risk-Based Cleanup Levels for Soil The cleanup requirement for TPH-d is 50 mg/kg, as stipulated in CAO No. 92-707. ' This cleanup level was based on the RWQCB's experience that"several underground cleanup cases have demonstrated the feasibility of excavation and treatment of diesel contaminated soils to below 50 mg/kg TPH-d within a single dry ' season."An alternative cleanup level is for TPH-d is recommended, as allowed in accordance with the CAO, based on the following: ' • CAO No. 92-707 was executed nearly 20 years ago prior to the existence of risk- based cleanup levels for TPH • The primary intent of the CAO requirements is to achieve site cleanup that is ' protective of human health and the environment • Conservative risk-based screening levels for TPH have been developed by the San Francisco Bay RWQCB (SFB-RWQCB 2008) since CAO No. 92-707 was executed in 1992 The SFB-RWQCB developed three THP-d screening levels, commonly known as environmental screening levels(ESLs)for shallow soils, applicable to commercial/industrial land use where groundwater is not a drinking water source. These ESLs are the following: Page: ' 3/12