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Mr. Harlin Knoll,SJCEHD June 18,2007 Well Installation Work Plan A.Teichert and Sons Property, Stockton,CA Page 6 Overexcavation was also performed following removal of Tank D by Elder in 1988. Information regarding the volume of soil excavated was not available in the documents reviewed for this report. Additional excavation was performed after Tanks T-5, T-6, and T-8, and the associated I dispenser island, were removed by Town and Country in 1999. Approximately 560 to 700 cubic yards of soil were subsequently transported to the Teichert facility in Tracy for bio- remediation prior to disposal. � Soil Va or Extraction� p A subgrade SVE manifold was installed in the excavated area north of the lubrication station and warehouse. EMCON utilized this manifold and well MW-13 to perform an SVE test in October 1992. BCR installed well MW-14 in March 1994, and initiated SVE from well MW-14 at that time. Anderson reconstructed well MW-13 for vapor extraction, and simultaneous extraction from wells MW-13 and MW-14'began in January 1995. EMCON installed air sparge well AS-1 in.May 1995. Concurrent air sparging and SVE was initiated in June 1995. Use of the SVE/air sparge system was discontinued in December 1995. EMCON estimated that approximately 13,400 pounds of GRO have been removed via excavation and SVE. Stratus estimates that less than 50 pounds of GRO remain beneath the site. Bioventinl~ Bioventing activities were initiated on November 16, 2004, and are on-going. An oil-less compressor is utilized to pump air into wells MW-13, MW-14, and AS-1. In wells MW-13 and MW-14 the air is delivered via droptubes installed to approximately 1 foot above the pp Y bottom of the well. In well AS-1, the air is applied directly to the well casing, as in conventional sparging. Airflow from the compressor to the wells has ranged from 40 to 65 liters per hour, at pressures ranging from 24 to 30 pounds per square inch. Potential Sensitive Receptors The only potential off-site receptors appear to be water supply wells in the area. The depth of the groundwater beneath surface grade suggests it is unlikely that the dissolved hydrocarbons will impact surface waters. Analytical data collected to date suggests that the dissolved plume is not migrating vertically, and with the exception of 1,2-DCA, the dissolved plume appears restricted to the site. EMCON completed a water supply well survey in the second quarter of 1996. The nearest water supply wells appear to be situated in the vicinity of Fremont Street, approximately K:%TeichertlStockton-1031Work Plans4eichert-well install work plan 06-2007.doc SIMMS l