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_ Upgradienr Environmental Ctnsu tants �!ifn f. f May 10, 1996 Mr. Michael Infurna,REHS Public Health Services Division of Environmental Health San Joaquin County 304 E. Weber Street Stockton, CA 95201 Subject: Results of April 23, 1996 Investigation Swett & Crawford Building 711 N. Pershing Avenue Stockton,CA Project No. 96011 Dear Mr. Infurna: The purpose of this letter is to summarize a limited investigation that was performed by Upgradient Environmental at the referenced property on April 23, 1996. The purpose of the investigation was to re-sample that area of the property where heptachlor epoxide had been detected in a groundwater sample that Upgradient collected in January 1996. Boring SP-12 was drilled adjacent to previous borings SP-8, SP-10. and SP-11 (Figure 1). A portable, gasoline-powered drilling rig equipped with 3-inch-diameter hollow-stem augers was used to drill to 12 feet. The augers were raised slightly but left in place to allow groundwater to flow into the bottom of the hole. Within 5 minutes, groundwater had risen to a depth of approximately 9 feet below grade, and a small-diameter plastic bailer was used to collect a groundwater sample. Two liters of moderately turbid water were collected. Per prior agreement with Mr. Michael Infurna, both liters were filtered of all sediment before being transported to the laboratory. One liter was transported to Sequoia Analytical Laboratory, the other was taken to Sparger Technology. Both laboratories analyzed the samples using EPA method 8080 for pesticides. No heptachlor epoxide or other pesticides were detected by either laboratory. The laboratory reports are attached. This sampling event did not confirm the previous results, in which heptachlor epoxide was detected above reporting limits. High turbidity, laboratory error, or sampling error may have led to a false positive result in the January 1996 sample. Based on the localized occurrence of chlordane, 4,4-DDT, and diesel-range hydrocarbons in the soil around RESNA's boring B-4, we conclude that a small amount of pesticide (5-10 gallons) may have been used or spilled in the vicinity at some time in the past. These contaminants have been detected to a depth of 6 feet. Below that, no hydroccarbons were detected in the soil, but heptachlor epoxide and diesel were reported in a groundwater sample that was collected in January 1996. However, subsequent sampling in April 1996 did not confirm that result. Therefore, Upgradient recommends removing the soil to a depth of 7 feet in a small area surrounding B-4, SP-8, SP-10, and SP-11. In his June 14, 1995 letter, Mr. Michael Infurna directed that sidewall samples should be collected from the 4111 82nd Street 3369 Kimberly Road Sacramento, CR 95826 Cameron Park, CA 95682 (916) 452-2891 (916) 677-3055 \ Fax: 457-1817 Fax: 677-3055