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California Itional Water Quality CoV l Board Central Valley Region ' Katherine Kart, Chair 3685 E Street, Fresno, California 93706 Linda S.Adams (559)445-5116 • Fax(559)445-5910 Edmund G. Brown Jr. Acting Secretary for http:]/www.waterboards.c@.gov/centraivalley Governor Environmental Protection To: Shelton R. Gray FROM: C. Dean Hubbard Senior Engineering Geologist Engineering Geologist P. G. No. [TATE: 25 January 2011 SIGNATURE: SUBJECT: REQUEST FOR NO FURTHER ACTION REQUIRED, MOUNTAIN HOUSE DEVELOPMENT SITE #3, MOUNTAIN HOUSE, SAN JOAQUIN COUNTY Chevron Environmental Management Company (Chevron) submitted a request for No Further Action Required (NFAR; Report), Mountain House Development Site #3, Mountain House, San Joaquin County (Site). The Report, dated 22 October 2010, was prepared for Chevron by Science Applications International Corporation -- Benham Companies, LLC (SAIC). I have reviewed the Report and related 2001 to 2008 documents contained in project files. My comments are provided below. Background The area of crude oil affected soil is delineated at approximately 150 feet by 300 feet. The vertical extent is defined by non-detect (ND) analytical results for total petroleum hydrocarbons as crude oil (TPHc) in a sample from a depth of 54 feet below ground surface (bgs). A smaller area of separate phase crude oil in soil of approximately 100 feet across and 35 feet bgs is noted in the northern part of the affected area. A portion of the crude oil affected soil occurs along the southern edge of Byron Road extending into an adjacent agricultural field. In the remaining portion of the delineated area, affected soil was noted at approximate depths of 15 to 35 feet bgs with TPHc detected at concentrations ranging from 2,600 milligrams per kilogram (mg/kg) at 23 feet to 1 ,900 mg/kg at 33 feet. Generally, the elevated TPHc concentrations in soil found below the water table occur with affected groundwater. The extent of affected groundwater is slightly larger than the area of affected soil and has approximate dimensions of 400 by 500 feet. Approximately one-third of the affected groundwater lies within/beneath the agricultural field adjacent to the south. The remainder is downgradient (north) beneath Byron Road, the former OVP/TAOC pipelines, UPRR tracks, and two existing active pipelines. TPH as diesel (TPHd) in groundwater was detected at concentrations up to 500,000 micrograms per liter (pg/L). Additionally, elevated concentrations of polynuclear aromatic hydrocarbons (PAHs) reported, correspond to samples reporting high levels of TPHc. Groundwater samples from two nearby private wells more than 1 ,000 feet crossgradient to the east of the Site (Pombo and Fish), were obtained. Analytical results from the Pombo supply well reported ND for TPH constituents. Analysis of the water sample from the Fish family supply well reported TPHd at a concentration of 170 pg/L. According to information obtained California Environmental Protection Agency aRecycled Paper