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2 Fourth Quarter 1995 Status Report Golden Grain Company,Manteca Bean Facility,229 Moffat Boulevard Manteca,California December 21,1995 ny The water table elevations recorded on November 17, 1995,were used to prepare a potentiometric surface map for the site(figure 2) The groundwater elevation from MW-3 was not used because an accurate measurement could not be collected The potentiometric surface elevations measured in the site groundwater monitoring wells increased an average of 0 79 feet since the August 18, 1995, monitoring event The groundwater gradient direction beneath the site is generally to the north at an average gradient of 0 002 foot per foot(Rift) 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 13 of the 14 monitoring wells on the site in accordance with the LUFT guidelines A sample was not collected from MW-3 because adequate groundwater was not retrievable A copy of the field data sheet from 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 Concord, California 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 503018015/8020 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 November 17, 1995,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 November 1995,dissolved TPH-g and benzene were detected in wells MW-1,MW-2, MW-4, MW-5, and MW-7 The dissolved TPH-g concentrations detected in groundwater samples from MW-1 were higher than the results from the previous quarterly sampling performed on August 18, 1995 Concentrations of TPH-g detected in groundwater samples from MW- 2, MW-4, MW-5,and MW-7 were within the range reported in the previous quarter Benzene concentrations detected in groundwater samples from MW-7 were higher than the results from the previous quarter The remaining monitoring wells with detectable concentrations of benzene were within the ranges reported In the previous quarter TREATMENT SYSTEM OPERATION AND MAINTENANCE The sod treatment system operated in pulsed mode this quarter until November 16,when it was turned off because no hydrocarbons were detected in the extracted soil vapor The pulsed mode of operation consists of operating the soil vapor extraction system for one week and turning it off for three weeks The pulsed operation is being used to more efficiently remove hydrocarbons from the vadose zone by Ll ❑❑❑ TECHNOLOGY Y