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y f� ti \� Second Quarter 1994 Status Report 2 Golden Grain Company, Manteca Bean Facility, 229 Moffat Blvd , Manteca, CA July 18, 1994 The water table elevations recorded on May 20, 1994, were used to prepare a potentiometnc surface map for the site (figure 2) The potentiometric surface elevations measured in the site groundwater monitoring wells decreased an average of 1 44 feet since the February 18, 1994, monitoring event The groundwater movement beneath the site flows generally to the north at an average gradient of 0 0014 foot per foot (ft/ft) The gradient at the southern portion of the site is greater and exhibits the effects of pumping from the groundwater extraction well on the site groundwater GROUNDWATER SAMPLING Groundwater samples were collected from 13 of the 14 monitoring wells on-site according to the LUFT guidelines Monitoring well MW-3 did not contain adequate groundwater to obtain samples Field data sheets from monitoring well gauging and sampling work are included in attachment 3 The samples were submitted under chain-of-custody protocol to GTEL Environmental Laboratories in Concord, California The samples were analyzed for benzene, toluene, ethylbenzene, and xylene (BTEX) and for total petroleum hydrocarbons-as-gasoline (TPH-g) using 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 record for the water samples collected on May 20, 1994, are included in attachment 4 Maps showing reported values of dissolved TPH-g and benzene concentrations are Included as figures 3 and 4, respectively Of the 13 monitoring wells sampled in May 1994, dissolved TPH-g was detected in wells MWA, MW-2, MW-4, MW-5, MW-7, and MW-13 The dissolved TPH-g concentrations detected in groundwater samples from these wells were within the same range reported in the previous sampling event on February 18, 1994, except in the sample from well MW-13, where dissolved TPH-g was detected for the first time Benzene concentrations were detected in samples from wells MW-1, MW-2, MW-4, MW-5, MW-7, and MW-13 Concentrations of benzene less than 1 part per billion (ppb) were also detected in groundwater samples collected from wells MW-10, MW-11, and MW-14 The benzene concentrations detected in groundwater samples from these wells were within the same range reported in the previous sampling event on February 18, 1994, except for the following (1) benzene was detected at lower concentrations in wells MW-1 and MW-2 than had been previously reported, (2) benzene was detected for the first time in well MW-11 Monitoring wells MW-10, MW-13, and MW-14 are located upgradient and/or cross-gradient from the original source area for hydrocarbon concentrations on the site Groundwater monitoring data collected prior to the beginning of pumping from RW-1 (September 1992) indicate that these wells are also upgradient or cross-gradient from the site under nonpurnping conditions Groundwater 551OR024 020 GROUNDWATER TECHNOLOGY,INC