SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Mr. Maurice Benson 2 5 April 2011 Defense Logistics Agency diesel-range TPH was 18,200 milligrams per kilogram (mg/kg) in soil and 478,000 micrograms per liter (µg/L) in groundwater. In 1998, DLA collected soil and groundwater samples from borings located at the south, east, and north sides of the UST excavation area and performed laboratory chemical analyses. The maximum concentration of diesel-range TPH was 17,000 mg/kg in soil and 650,000 gg/L in groundwater. In 2003, DLA collected a soil sample at the former UST location and a groundwater sample approximately 30 feet north. The diesel- range TPH concentration in the soil sample collected at 15 feet below the surface was 16,000 mg/kg and the water sample was 20,000 gg/L. At that time, DLA estimated that approximately 40&cubic-yards of soil contaminated with approximately 200 kilograms of - diesel-range TPH remained in soil beneath the site. In January 2009, DLA again collected soil and groundwater samples from borings at and near the former UST location. The maximum concentration of diesel-range TPH was 7,200 mg/kg in soil and 1,100,000 µg/L in groundwater. In February 2010, DLA collected groundwater samples from soil borings. The maximum concentration of diesel-range TPH was 619,000 µg/L. In May 2010, DLA installed groundwater monitoring wells LM198AU through LM202AU, screened across the water table. Laboratory chemical analyses results on groundwater samples collected during the second, third, and fourth quarters of 2010 using low- flow techniques detected diesel-range TPH at concentrations up to 1,150 gg/L. Comments Central Valley Water Board staff consulted Department of Toxic Substances Control (DTSC) technical staff of the Sacramento Office of Military Facilities and the Chatsworth Geological Services Unit. We have incorporated comments from DTSC staff with our comments below. 1. DLA modeling utilized a soil lithology default value for silt. That value may be more typical of Midwest wind-deposited silt rather than Central Valley fluvial silty sand or sandy silt. DLA should collect site-specific soil data for use in final risk evaluations. 2. DLA soil modeling did not include naphthalene and 2-methylnaphthalene. These should be included in final risk evaluations. 3. The highest concentrations of diesel-range TPH, naphthalene, and 2- methylnaphthalene in soil and groundwater were detected in 2009. DLA should utilize those concentrations for modeling. 4. DLA should comment on why the diesel-range TPH in groundwater samples collected from monitoring wells in 2010 were several orders of magnitude lower than the saturation-level concentrations detected in soil boring samples collected between 1993 and 2009. 5. The soil boring logs in Appendix A do not use appropriate USCS terms and symbols. DLA should revise the logs and make sure that they are reviewed by a California licensed Geologist. California Environmental Protection Agency �aRecycled Paper