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SECOR vvww secar Com (� INTERNATIONAL 3017 Kilgore Road Suite 100 S E CO R INCORPORATED Rancho Cordova,CA 95670 916-861-0400 TEL . 916 861 0430 FAX January 29, 2003 l� �1�C I I��/]E D JAN 3 1 2003 Michael J Infurna San Joaquin County Environmental Health Department ENVIRONMENT HEALTH 304 East Weber Avenue, Third Floor PERMIT/SERVICES Stockton, CA 95201-0388 RE Quarterly Monitoring and Sampling Report Ranch Market 23569 South Santa Fe Road Riverbank, CA SECOR Project No 770T 43627 00 0004 Dear Mr Infurna SECOR International Incorporated (SECOR) submits this quarterly report to summarize the methods and results of fourth quarter 2002 groundwater monitoring and sampling for the above referenced site (Figures 1 and 2, Attachment 1) Groundwater monitoring and sampling were conducted on October 1, 2002, to determine water table elevation and the distribution of dissolved hydrocarbons in the site-related groundwater monitoring wells Domestic well DW-1 was also sampled monthly to monitor for the presence of dissolved petroleum hydrocarbons The site is located at the southwestern Intersection of South Santa Fe Road and Henry Road in Riverbank, California (Figure 1) Facilities onsite consist of a single story brick building with a septic tank and leach field The remainder of the Site is covered with asphalt paving Currently the Site is being used as a mini-market without gasoline service Underground Storage Tank Removal On May 20, 1991, three underground storage tanks (USTs) were removed from a common tank pit (Figure 3) Strong hydrocarbon odors and discolored soil was observed by SJCEHD in the tank pit following removal of the tanks Tank pit floor soil samples collected at depths of 9 to 11 feet below ground surface (bgs) contained reportable concentrations of gasoline range petroleum hydrocarbons (Attachment 2, Table 1) Soil and Groundwater Assessment In January 1998 soil boring B-1 was advanced into the former tank pit to a depth of 30 feet bgs Analyses of soil samples collected from soil boring B-1 at 20, 25, and 30 feet bgs showed a decline in total petroleum hydrocarbon as gasoline (TPHg) concentrations from 4,140 milligrams per kilograms (mg/kg) at 20 feet bgs to 6 mg/kg at 30 feet bgs (Table 1) A grab water sample was also collected from boring B-1 that contained elevated concentrations of benzene, toluene, ethylbenzene, xylenes (BTEX), and TPHg (Table 2 and 3) In November 1998, Arrowhead Consultants oversaw the installation of four groundwater monitoring wells at the site MW-1 in the former tank pit and MW-2, MW-3, and MW-4 centered around the �) former tank pit (Figure 2 and Table 2) Soil samples collected during monitoring well Installation contained reportable concentrations of BTEX and TPHg (Table 1) The first monitoring and sampling Riverbank-02-4Q doc