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S E C 0 R Ms Lori Duncan ARCO Station 4493 Site Closure Report . July 31,2006 Page 4 Groundwater elevations in the site wells generally decreased relative to the previous quarter The inferred groundwater flow direction and gradient were consistent with previous quarters SENSITIVE RECEPTORS Low concentrations of residual and dissolved petroleum hydrocarbons are situated beneath an open ground surface Normal surface air movement is likely to dilute and remove impacted sod vapors from the site before concentrations reach risk levels The area surrounding the site utilizes a municipal water source supplied by California Water Service Company(CWSC) SECOR contacted CWSC on May 5,2006,to verify that municipal water supply wells were not situated in the immediate site vicinity According to the CWSC web site,"Cal Water's Stockton District was formed in 1926 with the purchase of the water system from Pacific Gas and Electric Company To meet the needs of our 42,000 customers, we use a combination of local groundwater and water purchased from the Stockton East Water District,which is imported from the Stanislaus and Calaveras Rivers The Stockton system pumps 28 million gallons of water per day and includes 56 wells, 17 booster pumps, 12 storage tanks,and one imported water connection Cal Water proactively maintains and upgrades its facilities to ensure a reliable, high-quality supply' (http llwww calwater coml) According to the sensitive receptor survey conducted In 2004,eight wells are located within a 2,000- foot radius of the site The records included information about one municipal well, one "air conditioner' well, one irrigation well, and five wells of unknown use The closest identified well is located approximately 1,000 feet southeast of the site and is located in the basement of the City of Stockton Police Department This well Is screened between 170 feet and 215 feet deep Copies of these reports, and a figure illustrating approximate well locations, are provided in Attachment D During preparation of the sensitive receptor survey in 2004 URS contacted CSMUD to ascertain whether they operated any wells In inity of the ARCO site According to Mr Larry Deimler with CSMUD, there are no city wells perating ithin 2,000-feet of the site URS contacted the Stockton office of CWSC in 2004 to determine whether they operated any wells in the vicinity of the ARCO site According to Mr Eric Mar with CWS there are no active wells with 2,000 feet of the site, and groundwater in the vicinity Is not usable due to Impacted water quality Z On December 6,2004, URS performed a 500-foot reconnaissance of the site to Identify and/or venfy the location of wells, water bodies, and schools No municipal, domestic, or Irrigations wells were visible The ARCO site Is located In Stockton's CBD and Is predominantly commercial offices and retail The Port of Stockton extends to Weber point, Immediately west of the site Eight water supply wells were located In the vicinity of the ARCO site in DWR well searches Inquiries at CSMUD and CWS revealed that all production wells In the vicinity of the site are currently inactive due to existing water quality Issues No other sensitive receptors were Identified a,