SITE INFORMATION AND CORRESPONDENCE

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Duncan Austin, P.E. 0 - 2 - 9 20 September 2012 compounds, pesticides, herbicides, and metals. DLA utilized the petroleum constituent sampling results from SWMU 20 and SWMU 33 to supplement UST Site 13 data. During a 1993 investigation of the industrial waste pipeline at SWMU 33, DLA detected concentrations of total petroleum hydrocarbons in the diesel range (TPHd) in soil samples. Concentrations ranged up to 15,000 milligrams per kilogram (mg/kg). During a 1994 investigation of the former sump at SWMU 20, DLA detected TPHd concentrations in soil samples up to 500 mg/kg. Removal Actions and Extent of Residual Contamination in Soil In 1997 and again in 1999, DLA excavated soil at UST Site 13, and at SWMUs 20 and 33 as part of the selected remedies for those units. The excavated soil included TPHd-contaminated soil from UST 13. Following the second removal action in 1999, residual concentrations of TPHd in eight of nine confirmation soil samples were less than the laboratory reporting limit of 12 mg/kg. The laboratory estimated the TPHd concentrations below the reporting limit in four of the eight samples; the results ranged from 2 mg/kg to 6 mg/kg. The ninth confirmation soil sample, collected from the south excavation sidewall beneath the north wall of Warehouse 10, contained TPHd at 48 mg/kg. DLA performed a TPH-d analysis on this sample utilizing the deionized water waste extraction test method. The laboratory result was less than 0.1 mg/L. In December 2007 prior to the demolition of the warehouse, the USACE advanced eight borings and collected eight soil samples for laboratory chemical analyses. The USACE advanced one of the borings at the north wall of Warehouse 10, near the location of the 1999 soil sample that contained 48 mg/kg TPHd. The laboratory analysis of the sample from this boring did not detect TPHd above its reporting limit of 6 mg/kg. Threat to Groundwater DLA has not detected TPHd contamination in water table monitoring well LM093AU, located approximately 15 feet down-gradient of former UST 13. Furthermore, laboratory analyses of groundwater samples collected from other nearby monitoring wells between 1993 and 2008 did not detect TPHd. Threat to Human Health The threat to human health from residual concentrations of heating oil constituents released from UST 13 is negligible. However, land-use controls continue to be in place for SWMU 20, which surrounds the UST 13 Site, while remediation of TCE by soil vapor extraction continues. Threat to Ecological Receptors Pavement completely covers UST Site 13 and does not provide habitat for support of ecological receptors. Summary Central Valley Water Board staff concurs with the DLA's conclusion that it has completed the required removal actions at UST Site 13 and that it should close the site.