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GROUNDWATER INC.TECHNOLOGY, INC. 4057 PrirtCA9U,2ul41:u6—)-23ti7 E-A\.i41;i+�ti February 22, 1991 Job No.203 175 3289.01 Mr.Clint Rodgers Chevron USA Inc. 2410 Camino Ramon San Ramon,CA 34583-0804 MA� VED Subject: Groundwater Monitoring and Sampling �NV�RNM�z 19$; Chevron 4 So th El Dorado Streets 0342 PERU�r�s�'9v'HEA L raj Stockton,California This Monitoring and Sampling Letter Report summarizes the results of the groundwater monitoring and sampling condt:cted by Groundwater Technology, Irr.:.at Chevron Service Station No.9-ON2, located at 1374 South Et Dorado Street in Stockton,California(Figure 1 attached). This report documents the first in a series of quarterl,monitoring and sampling events performed under work release order number 430-4820, Issued by Mr.Clint Rodgers of Chevron U.S.A. Inc.(Chevron). The site layout and locations ' of the three monitoring wells are shown on the attached Site Plan(Figure 2). The three monitoring wells were monitored on January 9, 1991,to determine depth to-groundwater, hydraulic gradient and groundwater-flow direction,and to check for the presence of separate-phase hydrocarbons. Standard Operating Procedure(SOP) 8, (Appendix A),describes the groundwater-monitoring procedures. Monitoring was performed ush,g a water-level Indicator graduated to i/100th of a foot,and the depth-to-water(DTW)measurements were taken from the top of the well casings. These monitoring data are shown on the standard monitoring data form(attached). The DTW data collected during well monitoring were combined with wellhead survey information to produce the Groundwater Contour Map presented as Figure 3. Compared with the August 1990 water- ievel data,the groundwater level has dropped 3 feet. The groundwater gradient measured for the January 9, 1991,event is approximately 0.002 toot-per-foot(ft/ft), in a mrtheasteriy direction.Phis compares with a 0.02 ft/ft gradient to the northwest,which was rnaasured in August 1990. Changes of water level,direction of groundwxler flow,and grounccwater gradient are not unusual for the Stockton area,due to the presence of active wells and variable recharge areas. Groundwater behavior will be monitored In subsequent quarters and compared for sign-.or seasonal trends. Table 1 summarizes the August 1990 and the January 1991 groundwater-elevation data(attached). Sepa(ate-phase hydrocarbons were not detected In any wells monlored in August 1990 or January 1991. Ofarrs r!v,:ruh.rut Me i:S..Canada und r::re"us