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y rl Second Quarter 1996 Status Report 2 Golden Grain Company, Manteca Bean Facility,229 Moffat Boulevard, Manteca,CA June 14, 19% The depth to water measurements recorded on May 21, 1996, were used to calculate the groundwater elevations for preparation of a potentiometric surface map for the site (figure 2) The depth to water measurement from MW-3 was not used because a bent well casing did not allow an accurate measurement The potentiometric surface elevations measured on May 21, 1996, showed an average increase of approximately 1 foot since the February 20, 1996, monitoring event The groundwater gradient direction beneath the site is generally to the north at an average gradient of 0 0017 foot per foot The general gradient at the southern portion of the site is slightly greater than that for the northern portion GROUNDWATER SAMPLING Groundwater samples were collected from all of the 14 monitoring wells on site in accordance with the LUFT guidelines A copy of the field data sheet for monitoring well gauging and sampling work is included In attachment 3 The samples were submitted under chain-of-custody protocol to American Environmental Network in Pleasant Hill, California, for chemical analyses The samples were analyzed for benzene,toluene, ethylbenzene, and total xylenes (BTEX), and for total petroleum hydrocarbons as gasoline (TPH-g) using Environmental Protection Agency (EPA) Methods 50301801518020 Historic and recent groundwater analytical data are . summarized in table 2 The laboratory analytical reports and the chain-of-custody record for the water samples collected on May 21, 1996, are included in attachment 4 Maps showing reported values of dissolved TPH-g and benzene concentrations are included in attachment 1 as figures 3 and 4, respectively Of the 14 monitoring wells sampled in May 1996, dissolved concentrations of TPH-g and benzene were detected in wells MW-1, MW-4, MW-5, and MW-7 The dissolved TPH-g concentrations detected in groundwater samples from MW-1, MW-4, and MW-7 were lower than the results reported for the previous quarterly sampling performed on February 20, 1996, but within historic ranges Concentrations of TPH-g detected in groundwater samples from MW-5 were slightly higher than the results reported in the previous quarter Benzene concentrations detected in the groundwater sample from MW-1 was lower than the results from the previous quarter Concentrations of benzene detected in groundwater samples collected from MW-4, MW-5 and MW-7 were slightly higher, but within historic ranges Concentrations of dissolved TPH-g and benzene in the sample collected from MW-2 were not detected above the method detection limit this quarter Due to a matrix interference, however, the detection limits for dissolved TPH-g and benzene were elevated for this sample This is caused by elevated levels within the sample of other target compounds in the analytical method (EPA 8020-see lab report for MW-2) Historically, MW-2 has had detectable concentrations of dissolved TPH-g and benzene • 42=13 QS2 F4u001 ®AR11ML GTI