COMPLIANCE INFO_FILE 8 - Laserfiche WebLink

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Mr. James Diel -2- 17 March 2011 UP Former Tracy Maintenance Facility San Joaquin County The CAO establishes a cleanup goal for total PAHs as extractable concentrations from soil based on a one-in-one-million incremental cancer risk (total PAH _< 0.0028 pg/L). ARCADIS has provided copies of data tables summarizing soil and groundwater results or PAHs. These results date from the early to Iatel990s, and were originally presented in the 1994 Remedial Investigation (RI) Report and other site documents. The summary tables show that PAHs were present below the cleanup goal in both baseline and confirmation soil sampling in the biotreatment beds in 1996. Monitoring wells MW-01, MW-04, and MW-07 were the wells closest to the biotreatment beds; in 1996, each contained PAHs in concentrations at or near the method detection limits. The biotreatment bed soils do not appear to be a source of PAHs, to groundwater. The CAO establishes cleanup goals for VOCs, chromium, and lead as extractable concentrations from soil, although these constitutents were not determined to be constituents of concern in the RI for the biotreatment beds. VOCs present at the site are not associated with the biotreatment beds, and are not present in groundwater downgradient from the biotreatment beds or former pond. Chromium and lead were evaluated in soil and groundwater samples from the late 1980s through the 1990s. The biotreatment method was not intended and is not effective for remediation of metals. Maximum concentrations of lead (19 mg/Kg) and chromium (51 mg/Kg) are consistent with samples taken from other locations, and are representative of background levels found at the site. In their August 2010 Biotreatment Beds Post Remediation Investigation Report, ARCADIS compared the 2009 maximum soil TPHd concentration to the Regional Water Quality Control Board San Francisco Bay Region Environmental Screening Levels (ESLs) for shallow soil dermal contact, inhalation, and ingestion. The maximum soil concentration of TPHd (620 mg/Kg) exceeds residential land use ESLs. For commercial/industrial worker exposures, however, the maximum concentration is below the direct contact exposure screening level for a hazard quotient of 1.0 (2,200 mg/Kg). Historical groundwater sampling results show, and the March 2010 sampling data confirm, that the concentrations of TPHd and other constituents have declined to below Water Quality Objectives in the wells situated in and immediately downgradient from the biotreatment beds. As such, we concur with UP that they have satisfied the requirements of the CAO with regard to the biotreatment beds. No further remedial action is required for the biotreatment bed areas. However, because TPHd remains in shallow soils at concentrations above the residential ESL of 50 mg/kg, UP must implement either a soil cleanup to reduce TPHd to levels protective of unrestricted use, or a land use covenant to restrict the use of the site to commercial or industrial uses, and to restrict excavation and disposal of soils. Please respond in writing by 18 April 2011 with a plan and schedule for your selected course of action. The CAO addresses other on-site pollution sources in addition to the TPCA pond. The light non-aqueous phase liquid and dissolved-phase diesel plume remain on site and are actively California Environmental Protection Agency �aRecycled Paper