CORRESPONDENCE_2020 - Laserfiche WebLink

Home Browse Search

Former San Joaquin Cogeneration - 2 - 17 December 2020 Lathrop, San Joaquin County • The Site consists of sand and silty sand near the surface grade to approximately 14 feet below ground surface (bgs) underlain by 1 to 6 inches of clay in most locations. In the former power plant area, the sand extended deeper than the investigative borings which were terminated at approximately 20 feet bgs. Hydrocarbon odors were noted in boring B40 between 13 and 17 feet bgs. • Monitoring wells MW-1 through MW-4 were installed to total depths of approximately 20 feet bgs to determine flow direction and gradient. Depth to water ranged from approximately 12.5 to 14.3 feet below top of casings (roughly 10 to 12 feet bgs). Based on calculated groundwater elevations, groundwater flow was to the southwest at an average gradient of 0.003 foot per foot across the Site. • The remaining portions of the North Waste Cell along the eastern property boundary was located and defined with step-out borings. Waste Cell 1 was identified as part of the former North Waste Cell extending from the neighboring property at 500 E. Louise Ave in Lathrop. • A small pocket of glass waste material extended from the property boundary to the area between borings B9 and B8 where the northern part of the South Waste Cell was anticipated to extend across the property boundary. Boring B8 and B9 are the only borings located along the property boundary where the South Waste Cell was observed to extend onto the property from previous investigation and remediation work on the neighboring property. • A waste cell was discovered during the investigation beneath the southeastern portion of the former power plant. This cell was designated as Waste Cell 2 and is approximately 3,900 square feet. • Total petroleum hydrocarbons (TPH) as gasoline (TPH-g), TPH as diesel (TPH-d), and TPH as motor oil (TPH-mo) were detected in several soil samples, however, only TPH-d in two soil samples exceeded the San Francisco Regional Water Board (SFRWB) Environmental Screening Level (ESL) in a commercial scenario. • PCBs were detected in four soil samples and one waste sample at concentrations exceeding the United States Environmental Protection Agency (USEPA) Regional Screening Level (RSL) in a commercial scenario of 0.97 milligrams per kilogram (mg/kg). • Dioxins/Furans were detected in several soil samples. Only one of the 12 samples analyzed exceeded the SFRWB commercial ESL of 22 picograms per gram (pg/g) with a toxicity equivalence (TEQ) concentration of 52.2 pg/g. The data indicates that the glass processing waste is the source of the dioxin/furan impact. • Concentrations of barium, chromium, cobalt, copper, vanadium, and zinc were detected in all soil samples below screening levels. Antimony and nickel were also detected in a few soil samples at concentrations below screening levels. One of twelve soil samples with chromium detected was selected for leaching