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Manteca Bean Facility, 229 Moffat Boulevard, Manteca, California April 2, 1993 Golden Grain Company Page 2 November 18, 1993 The groundwater movement beneath the site is generally in a northerly direction at an average gradient of 0 0018 ft/ft The gradient at the southern portion of the site is substantially greater and exhibits the effects of the groundwater extraction well on the site groundwater Previous potentiometric surface maps have not shown the effects of pumping during drought conditions The average increase of 4 67 ft in groundwater elevation across the site during the last two quarters has z/ brought groundwater back into all but one site monitoring well GROUNDWATER SAMPLING Groundwater samples were collected from 12 of the 14 monitoring wells on site in accordance with the LUFT guidelines Monitoring well MW-3 did not contain groundwater and well MW-9 was not accessible for sampling Field data sheets from monitoring well gauging and sampling work are included in Attachment 1 The samples were submitted under a chain-of-custody manifest to GTEL Environmental Laboratories in Concord, California, and analyzed for benzene, toluene, ethylbenzene and xylene (BTEX), and total petroleum hydrocarbons-as-gasoline (rPH-G) by Environmental Protection Agency (EPA) methods 5030/8015/8020 Historical and recent analytical data from groundwater analyses are summarized in Table 2 The laboratory analyses reports, and the chain-of-custody manifest for the water samples collected on February 18, 1993, are included in Attachment 2 Maps showing reported values of dissolved TPH-G and benzene concentrations are included as Figures 2 and 3, respectively Of the 12 monitoring wells sampled in February 1993, dissolved TPH-G was detected in MW-1, MW-2, MW-4, MW-5 and MW-7 Dissolved hydrocarbon concentrations detected were lower than historical concentrations detected during previous sampling events The concentrations reported in water from MW-7 are lower than those observed last quarter, but the values are within the same order-of-magnitude as detected during previous quarters TREATMENT SYSTEM OPERATION AND MAINTENANCE From September 14 through October 13, 1992, influent and effluent groundwater samples were collected each week from the Air Stripper/Groundwater Treatment unit Beginning October 13, 1992, this sampling frequency was changed to quarterly in accordance with permit conditions and following notification of the City of Manteca Public Works Department Samples were collected from the groundwater treatment system on February 18, 1993 and analyzed for TPH-as-gasoline, BTEX, total lead, organic lead, and ethylene dibromide at a state certified laboratory Laboratory analysis reports and corresponding chain-of-custody manifests for the sampling event on February 18, 1993, are included in Attachment 2 Results of system historical analyses are summarized QTR1 MCS F1[]9GROUNDWATER � TF.CHN0L0C,Y,INC I