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amec <br /> the ponds available for infiltration was 10 acres, then a combined flow of domestic and <br /> industrial wastewater of approximately 270 gpm would be sufficient to maintain the ponds at <br /> capacity; a combined flow of approximately 540 gpm would be sufficient to keep 20 acres of <br /> ponds filled assuming the 27 gpm/acre value is valid. Assuming the latter is true, and estimate <br /> of industrial sewer discharge for 1957 would be approximately 540 gpm — 186 gpm of <br /> domestic influent = 354 gpm. This value appears to be reasonable given that Nestle <br /> groundwater use was on the order of 340 — 500 gpm and sometimes higher, and other <br /> industries also used the industrial sewer. <br /> As the population increased, the rate of domestic sewage inflow relative to industrial inflows <br /> also would have increased. The "egg plant", presumably Nulaid Foods, began discharging to <br /> the industrial sewer in 1972, according to Feightmeir's accounts. Discharge from this facility <br /> was very high in biological oxygen demand (BOD, a characteristic of organic-rich wastewater); <br /> the BOD concentration from the egg plant was similar to that of domestic sewage when it was <br /> tested in 1974, according to Feightmeir. <br /> 4.5.3 Historical Groundwater Flow Regimes <br /> A two-step process was used to infer past historical groundwater flow patterns: 1) historical <br /> water level information for Nestle monitoring wells was used to prepare potentiometric surface <br /> maps for corresponding pumping and recharge scenarios to assess the groundwater flow <br /> regime under different hydraulic stress periods, and 2) the hydrogeologic inferences drawn <br /> from the first step were used in conjunction with historical information on pumping and <br /> recharge to infer historical flow regimes prior to the implementation of the monitoring program <br /> in 1990. <br /> Figures 16 through 26 show potentiometric surface maps for the Intermediate Aquifer at <br /> different configurations of groundwater pumping and recharge as summarized below, going <br /> backwards through time, from more recent times in which water level information is available <br /> to assess flow directions beneath the Study Area, to pre-1990 times, during which <br /> groundwater flow is inferred from estimated groundwater pumping and recharge rates. <br /> July 2006 (Figure 16): The Stanislaus River stage was approximately 2 feet below <br /> Intermediate Aquifer groundwater levels (Figure 12) in July 2006, and a hydraulic mound is <br /> evident based on water levels at M-20C1 and M-23C1, north of the clay-lined WWTF aeration <br /> ponds. Flow is to the south towards the Stanislaus River from beneath the WWTF ponds, and <br /> southwesterly beneath the Stanislaus River. This southerly flow may be enhanced by irrigation <br /> pumping south of the Stanislaus River. The combined local anthropogenic recharge from <br /> Neenah Paper (Upper West Percolation Field) and the WWTF ponds can explain the elevated <br /> hydraulic heads in this area. Groundwater flow is northward from the WWTF area towards a <br /> AMEC Geomatrix, Inc. <br /> hDoc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 40 <br />