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! c 1117 Lorre Palm Avenue, Suite B Modesto, CA 95351 4 http I/www atcassoclates corn 209 579 2221 A S S O Fax 209 579 2225 C I A T H S I N C July 12, 2005 54 62596 0001 Mr Jeff Wong JUL 18 ZQQS San Joaquin County ENV'RONVENT Environmental Health Division AER[V"T ;_ CESHEALTH IE 304 E Weber Street, Third Floor RVICES Stockton, California 95202 Subject Monitoring Report First Quarter 2005, Farmer Property, 610 North Hunter Street, Stockton, California Dear Mr Wong This report presents the results of quarterly groundwater monitoring and sampling performed on March 1 and 2, 2005 at the site located at 610 North Hunter Street in Stockton, California (Figure 1) Quarterly groundwater monitoring and sampling was performed to evaluate the distribution of petroleum hydrocarbons in groundwater and to evaluate the groundwater flow direction and the hydraulic gradient in the uppermost aquifer During the reporting period the soil vapor extraction/air sparge (SVE/AS) remediation system was not operational SITE HISTORY On October 6, 1987, Al Williamson, General Contractor, removed two 1,000-gallon leaded gasoline tanks and one 550-gallon waste oil tank from the locations shown on Figure 2 Soil samples collected after the tank removals contained elevated concentrations of petroleum hydrocarbons and volatile organic compounds (VOCs) On January 21, 1988, Falcon Energy, attempted to remove all VOC contaminated soil by over-excavating the former tank locations The former tank locations were excavated to approximately 22 feet below ground surface (bgs) The excavation was limited to the north by the on-site building The confirmation samples collected from the base of the over-excavation still contained elevated concentrations of volatile organics The over-excavated soil was disposed of at Forward Landfill near Stockton, California On June 30 and July 1, 1997, Smith Technology personnel supervised advancement of seven soil borings, SB 1 through SB7, at the site to depths ranging from approximately 40 to 45 feet bgs to investigate the horizontal and vertical extent of petroleum hydrocarbon soil and groundwater contamination Three of the soil borings were completed as groundwater monitoring wells and two of the soil borings were completed as vapor extraction wells The soil boring, groundwater monitoring well, and vapor extraction well locations are shown on Figure 2 On July 3, 1997, the monitoring wells were developed and sampled for petroleum hydrocarbons along with the adjacent property owner's well (CW) The samples from MW1, MW2, and MW3 contained concentrations of total petroleum hydrocarbons as gasoline (TPHg) and benzene ranging from 3,200 micrograms per liter (ug/1) to 130,000 ug/1 and 920 to 11,000 ug/l, s lenviro1625961quardyU qr-2005 doc 1 ATC ASSOCIATES INC ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS