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PACIFIC GAS AND ELECTRIC COMPANY <br /> IP U' 1M 4040 WEST LANE • P. O. BOX 930 • STOCKTON, CALIFORNIA 95201 • (209) 942-1440 <br /> RON GIRARD <br /> DIVISION MANAGER <br /> September 29, 1987 <br /> Ms. Laurie Cotulla, R. S. <br /> Environmental Health Division SEP 3 0 1987 <br /> San Joaquin Local Health District <br /> 1601 East Hazelton Avenue ENVIROMENTAL HEALTH <br /> Post Office Box 2009 PERMIT/SERVICES <br /> Stockton, California 95201 _ <br /> Dear Ms. Cotulla: <br /> Enclosed are two attachments to supplement the information you have <br /> already received concerning the underground tank investigation at <br /> PGandE's Tracy Service Center. Attachment 1 to this letter addresses <br /> comments from the Central Valley Region of the California Regional Water <br /> Quality Control Board (letter of June 16, 1987) regarding our work plan <br /> for this investigation. Attachment 2 is the report containing the <br /> results of the soil vapor survey performed at the service center on June <br /> 24, 1987 as Phase I of the investigation as outlined in the work plan. <br /> The purpose of Phase I was to determine if the petroleum-range <br /> hydrocarbons found in the soil at the service center originated from the <br /> on-site underground gasoline storage tank. Three of the soil vapor <br /> samples collected in the vicinity of the tank contained detectable <br /> levels of petroleum-range hydrocarbons. These sampling locations were <br /> surrounded by sampling locations in which no hydrocarbons were detected. <br /> This data indicates that the source of the hydrocarbons is likely to be <br /> the underground gasoline storage tank. Therefore, Phase II, as outlined <br /> in the work plan, will be initiated. <br /> The first step in Phase II is the installation of observation wells to <br /> determine groundwater flow direction. In accordance with the work plan <br /> we are proposing four observation wells. Construction details of these <br /> wells are contained in the work plan and the well locations are shown on <br /> Figure 1 of this letter. Observation wells OW-1, OW-2 and OW-3 are <br /> located near the three vapor sampling locations where the soil vapor <br /> contained hydrocarbons. This placement will maximize the potential for <br /> using at least two of the observation wells as monitoring wells while at <br /> the same time providing gradient information when used in conjunction <br /> with OW-4. <br />