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DTSC COMMENTS REMEDIAL ACTION REPORT MOUNTAIN HOUSE NEIGHBORHOOD C & D PRPOSED MOUNTAIN HOUSE HIGH SCHOOL TRACY, CALIFORNIA The Remedial Action Report (RAR) was developed on behalf of Shell and submitted to the Central Valley Regional Water Quality Control Board (CVRWQCB). The CVRWQCB is overseeing the investigation and clean-up of the entire pipeline. DTSC coordinates with the CVRWQCB on this review because a portion of the pipeline investigation is on the proposed Mountain House High School (MHHS) site. The Shell pipeline was located in the Mountain House area of Tracy, California. The 5,200 feet portion of pipeline currently under investigation is in the section of Mountain House referred to as Neighborhood C & D. When Shell removed the pipeline in 1960, contamination in soil and groundwater were identified. DTSC's review has focused on a 1 ,000 foot segment of pipeline that transects the proposed MHHS. The report refers to this portion of the pipeline as Area 3, 4 and 5. The adjacent properties will become the Mountain House residential development. Initial investigation of the pipeline alignment involved digging several test pits to verify the location of the former pipeline; advancing soil borings eight feet below ground surface (bgs) every 25 feet along the pipeline alignment, removal of 72,000 cubic yards (17,000 cubic yards from the proposed MHHS) of soil contaminated with total petroleum hydrocarbons (crude and diesel range, TPHc and TPHd) and benzene, toluene, ethylbenzene and xylene (BTEX). Excavation depths varied between 10 and 24 feet bgs and the trench was backfilled with soil from the general area. Prior to using the surrounding soil for backfilling the excavated areas, Science Applications International Corporation (SAIC) collected twenty six samples and analyzed them for TPH and BTEX. No BTEX was detected, however low levels of TPH were found (TPH -maximum 360 mg/kg; TPHd -maximum 5.1 mg/kg). The RAR indicates that a total of 34,384 cubic yards of soil was removed and 47 confirmation samples were taken from the floor and sidewalls of the excavations. Confirmations samples were analyzed for TPH , TPHd, and BTEX. The results of the confirmation samples in Area 3 are five samples had detections of TPHd concentrations ranging from 2.1 mg/kg to 1,700 mg/kg and TPHc concentrations ranging form 300 mg/kg to 2,400 mg/kg. BTEX was not detection in any sample. Area 4 had five samples with TPHd concentrations ranging from 2.1 mg/kg to 1 ,700 mg/kg and TPHc concentrations ranging from 300 mg/kg to 2,400 mg/kg. BTEX was detected. Area 5 had two samples with detections of TPHd (2 mg/kg, 150 mg/kg) and TPH (10mg/kg, 360 mg/kg). No BTEX was detected. Soil gas samples were collected within and adjacent to the backfilled areas at depths ranging from 5 to 24 feet bgs. The samples were analyzed for BTEX, naphthalene and Freon-134a. Freon-134a was used as a leak-detection compound in the soil gas samples, and breakthrough was found in 4 out of 18 samples. Naphthalene was not