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�>�� ANNE @ Science Applications International Corporation An Employee-Owned Company 06-6102-00-2931-120 April 29, 2003 Mr. M. Scott Mansholt Chevron Environmental Management Company P.O. Box 6012 San Ramon, California 94583-2324 > Work Plan for the Implementation of Quarterly Monitoring Surland Homes (Laurelbrook) Property Tracy, San Joaquin County, California Dear Mr. Mansholt: Science Applications International Corporation (SAIC) is pleased to present this Work Plan for groundwater sampling at the Surland Homes Property, Tracy, California. The proposed scope of this work is provided in response to the California Regional Water Quality Control Board, Central Valley Region (RWQCB) letter, dated February 28, 2003. A generalized site location map is shown on Figure 1. An initial soil and groundwater investigation was conducted by Geomatrix Consultants at the site in July 1998. The investigation included advancing eight soil borings and the collection and analysis of soil and grab groundwater samples. Results of the investigation indicated that petroleum hydrocarbons are present in the subsurface, and that the lateral and vertical extent of petroleum hydrocarbon-affected soil is constrained. Grab groundwater data suggested that the residual petroleum present in soils is not providing a source of dissolved petroleum to the groundwater that poses a threat to human health or the environment. Two monitoring wells were installed and sampled in September 1998 at the request of the San Joaquin County Public Health Service. A third well was installed in July 1999 and quarterly monitoring activities were conducted through April 2000. Monitoring well TW-2 was destroyed in the process of development of the surrounding property as a residence. Total petroleum hydrocarbons as crude oil (TPHc), benzene, toluene, ethylbenzene, and total xylenes (BTEX), and specific polynuclear aromatic hydrocarbons (PAHs) were detected in soil samples from the site. Low concentrations of total petroleum hydrocarbons as gasoline and as diesel (TPHg and TPHd), toluene, ethylbenzene, and xylenes, and specific PAHs were detected in groundwater. A petroleum sheen was observed on groundwater in the later-destroyed TW-2, in 1998. The RWQCB requires additional groundwater monitoring for one quarter, to confirm that TPHd concentrations are stable (or less than the WQO for the TPHd [without silica gel] taste and odor threshold), and/or attenuating in the two remaining monitoring wells. 3800 Watt Avenue, Suite 210, Sacramento, CA 95821 (916)974-8800•Fax.(916)974-8830• www.saic.com