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VALON `' 20 CORe RATE PI A7A NE�VEoaT Bcncx,CAIIFORMA 92660 ENVIRONMENTAL ,�_ry �' TEL:(949)644-2690 • Fnx:(949)644-2691 CONSULTANTS S4 October 6, 1999 Public Health Services,San Joaquin County Attn: Ms. Carol Oz 304 East Weber Avenue, Third floor Stockton, California 95201 Subject: Work Pian for Groundwater Assessment and Monitoring Well Installation at Joe's Truck Stop, at 15600 South Harlan Road, Lathrop, California. Ms. Oz: Pursuant to your request, Avalon Environmental Consultants (Avalon) is pleased to submit this work plan to perform a Groundwater Assessment and Monitoring Well Installation at Joe's Truck Stop at 15600 South Harlan Road in Lathrop, County of San Joaquin, California. This investigation will consist of installing six groundwater monitoring wells on the subject property. The purpose of this investigation is to establish the groundwater gradient, and to monitor levels of Methyl Tertiary Butyl Ether (MTBE) and other hydrocarbon contamination in the groundwater. The impact was previously identified through groundwater grab samples collected by Avalon, during a Phase II Site Assessment dated December 17, 1998. Elevated levels of diesel at 11,000 parts per billion (ppb) and 5,200 ppb were identified in the groundwater samples from two borings in the area of the former diesel tank pit in the southern portion of the property. Elevated levels of MTBE, were identified in groundwater samples taken from borings in the northern tank pit area. Levels in the groundwater were as high as 1,700 ppb. Due to these elevated levels of hydrocarbons, additional characterization was recommended by the consultants. This investigation will consist of drilling and sampling six groundwater monitoring wells on the subject property. The levels of contamination identified in Avalon's Phase II report suggests that the gradient is to the north, however, a true gradient direction on the subject property has not been established. We recommend placing one monitoring well in the center of each of the tank areas (One in the northern tank area and one in the southern tank area). Additionally, one monitoring well is recommended north of the northern tank area and three monitoring wells are recommended in the remaining three corners of the property. Once monitoring well construction is complete, and the monitoring wells have been developed, the locations and top of casings will be surveyed by a State Licensed Land Surveyor. Once this is complete, the wells will be given one week to stabilize, prior to measuring and sampling. This will allow groundwater levels to stabilize, thereby giving accurate data.