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i Manteca Bean Facility, 229 Moffat Boulevard, Manteca, California February 9, 1993 Golden Grain Company Page 2 summarized in Table 1 The water table elevations for November 18, 1992, were used to prepare a potentiometric surface map for the site (Figure 1) The potentiometric surface elevations in the site- related groundwater monitoring wells Increased in 7 of the wells an average of 2 18 feet since the last monitoring event-conducted on August 21, 1992 The groundwater movement beneath the site Is approximately east-northeast at an overall gradient of 0 002 ft/ft The gradient on the southern end of the site is slightly steeper compared to the gradient in the central and northern portion of the site In general, the potentiometric surface and hydraulic gradient are similar to the last quarterly gauging event MONITORING WELL SAMPLING Groundwater samples were collected from 7 of the 14 monitoring wells on site in accordance with the LUFT guidelines Because the groundwater surface has declined since Installing the monitoring wells, six of the monitoring wells (MW-1 through MW-6) do not contain groundwater Well MW-14 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 . Sequoia Analytical Laboratories in Sacramento, California, and analyzed for benzene, toluene, ethylbenzene and xylene (BTEX), and total petroleum hydrocarbons-as-gasoline (TPH-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 November 18, 1992, 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 seven monitoring wells sampled In November 1992, dissolved TPH-G was detected only in the MW-7 sample at a concentration of 30,000 parts per billion (ppb) The benzene concentration in the well was 2,300 ppb The concentrations detected in MW-7 are higher than those observed last quarter, but consistent with the concentrations detected In the first two quarters of 1992 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 All samples collected from the groundwater treatment system were analyzed for TPH-as-gasoline, BTEX, and total lead at a 10466a1 cd/nk GROUNDWATER TECHNOLOGY,INC