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0 <br /> �Ar no <br /> w <br /> From Science to Solutions,- <br /> HPP-BTR MP#220.71223.4 <br /> Mountain House Development <br /> Agency Correspondence-RWQCB <br /> DCN:C20-SAI-Mountain-House-01-11952 <br /> May 15, 2007 <br /> Mr. C.Dean Hubbard JED <br /> Engineering Geologist <br /> Regional Water Quality Control Board 6 2007 <br /> Central Valley Region <br /> IVL'1" <br /> 1685 E Street °w t,A41I61 T hEALTy <br /> Fresno, California 93706 �``RACES <br /> Subject: Environmental Risk Evaluation <br /> Mountain House Development Site#1 <br /> Byron Road,Mountain House, California <br /> Dear Mr. Hubbard: <br /> This letter was prepared by Science Applications International Corporation(SAIC) on behalf of <br /> Chevron Environmental Management Company(CEMC) in response to your letter dated March <br /> 26, 2007, concerning SAIC's Environmental Risk Evaluation(ERE) report for the above- <br /> referenced site. In the letter,you requested an evaluation of whether elevated concentrations of <br /> total petroleum hydrocarbons quantified as gasoline (TPHg) in groundwater samples collected <br /> and tested during SAIC's 2005 site investigation could have been caused by TPH quantified as <br /> diesel (TPHd) detections in groundwater or TPH quantified as crude oil (TPHc) in soil. <br /> Additionally, you requested a schedule for the completion of a site Soil and Groundwater <br /> Management Plan. This letter presents the results of SAIC's evaluation of TPHg in groundwater <br /> and a schedule for the completion of a Soil and Groundwater Management Plan. <br /> The 2005 site investigation found elevated TPHg(380 to 6,400 micrograms per liter [pg/L]) and <br /> TPHd(68,000 to 2,400,000 pg/L)in groundwater and elevated TPHc (900 to 29,000 milligrams <br /> per kilogram) in soil. To determine whether elevated TPHg concentrations in groundwater were <br /> due to the presence of gasoline or to overlap/interference between the analytical methods for <br /> TPHg and TPHd, and consequently related to TPHc of Chevron's Old Valley Pipeline (OVP) or <br /> Tidewater Associated Oil Company(TAOC)pipelines, SAIC requested that Lancaster <br /> Laboratories and Chevron Energy Technology Company(ETC) evaluate the chromatograms of <br /> samples MH 1-1, MH I-3, MH 1-10, MH 1-19, and MH 1-24. Based on the evaluation, the <br /> conclusions are as follows: <br /> • Results of SW-846 Method 8015M for TPHc (Co-C36) and TPHd (C10-C28), and SW-846 <br /> Method 8260 for TPHg (C6-C12) represent overlapping carbon ranges. These methods <br /> alone could not definitively identify a specific petroleum product such as crude oil, diesel, <br /> or gasoline in a sample. <br /> • The chromatogram patterns are consistent with TPHc, based on the broad range of carbon <br /> chain lengths noted. <br /> Science applications International Corporation <br /> 1000 Broadway I Suite#6751 Oakland. CA 94607?tel; (510)43 3-083 5 1 fax:(510)446-7919 k saic.com <br />