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amec— <br /> domestic <br /> sewage that is screened and discharged to a series of four clay-lined aeration ponds <br /> shown in Figure 13 (these ponds were unlined prior to 2001). Effluent from the aeration ponds <br /> is infiltrated to the water table at two unlined storage ponds (ponds 8 and 9) adjacent to the <br /> lined ponds, and to a series of seven percolation basins to the west. The inflow rate from the <br /> domestic sewer is relatively consistent over the course of the year (not seasonally variable). <br /> Percolation rate is dependent upon the pond water level, the permeability of the soil and depth <br /> to the water table; higher percolation rates occur during times of lower water table for <br /> equivalent pond water level. Area weighted average percolation rates for the ponds varied <br /> from 43,000 gallons/acre/day (g/a/d), when the separation between the water table and base <br /> of the ponds was approximately 3 to 5 feet, and 188,000 g/a/d with approximately 8 to 10 feet <br /> of separation between the water table and base of the ponds. <br /> Water levels in shallow monitoring wells installed adjacent to the ponds quickly began to rise <br /> as the ponds were filled, and the ponds rapidly drained when filling stopped. The rapid <br /> dissipation of the mound was inconsistent with the relatively low hydraulic conductivity values <br /> obtained from three aquifer tests near the ponds, leading ECO:LOGIC (2007) to conclude that <br /> a high degree of anisotropy complicated the interpretation of the hydraulic mounding condition, <br /> implying much higher hydraulic conductivity would be needed to explain the mound formation <br /> and dissipation. In the winter of 2006, the bottoms of the ponds were below the water table <br /> and Stanislaus River stage, indicating that groundwater can "daylight" within the ponds during <br /> very high river stage unless they are being actively filled. Most importantly, ECO:LOGIC <br /> (2007) established a clear hydraulic connection between the Stanislaus River, the water table, <br /> and the City of Ripon WWTF ponds. <br /> The unlined treated domestic wastewater disposal ponds are capable of high rates of <br /> recharge, with recharge rates on the order of 40,000 g/a/d (approximately 27 gpm/acre) on <br /> average. These high recharge rates are spread out over an area between 29.4 acres and <br /> 39.2 acres (if storage ponds 1 and 2 are full), and represent a situation of diffuse but high <br /> recharge rates which contributes to the hydraulic mound that is commonly observed <br /> throughout the year during monitoring events. <br /> Infiltration of Untreated Industrial Wastewater: <br /> The City of Ripon operates a separate industrial sewer system that originates near the <br /> northern end of Industrial Avenue, and runs south to 4th Street, west to Stockton Avenue, and <br /> south to the WWTF. Three current contributors to water in the industrial sewer system are: 1) <br /> treated groundwater pumped from the former Nestle facility property at 230 Industrial Avenue <br /> (currently approximately 60 gpm from combined treated effluent from IRAP extraction wells <br /> EU-3 and EU-4, but previously on the order of 150 gpm during EI-1 and EW-1 pumping), 2) <br /> AMEC Geomatrix, Inc. <br /> hDoc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 30 <br />