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amec�9 <br /> the Upper and Intermediate Aquifer have been higher than river stage since the second <br /> quarter of 2006. Before that time, river stage was generally higher than groundwater levels <br /> during the winter months, but lower during the summer months. The very high river stage <br /> observed in the winter of 2006, when river stage increased by approximately 15 feet, appears <br /> to correspond with an increase in water levels in the nearby Upper Aquifer monitoring wells, <br /> which increased by approximately 8 to 10 feet since the previous fall 2005 monitoring event. <br /> These fluctuations indicate that groundwater flow near the Stanislaus River is highly variable, <br /> and that there are times when the river water replenishes the aquifer system, and vice versa. <br /> A hydrologic evaluation was conducted by ECO:LOGIC Engineering on behalf of the City of <br /> Ripon in 2006 (ECO:LOGIC, 2007). That study involved placing transducers to measure and <br /> record water levels in shallow (B-zone) monitoring wells on WWTF property for comparison <br /> with the corresponding river stage. The data from that study supports the conclusion that the <br /> water table beneath the WWTF ponds fluctuates with river stage. <br /> 4.3.2 Groundwater Recharge <br /> Recharge by infiltration of surface water is enhanced by municipal and industrial lagoons and <br /> irrigation fields at the southern limits of the City of Ripon, near the Stanislaus River, where <br /> soils are associated with moderate to high infiltration rates (ECO:LOGIC, 2007). The influence <br /> of the lagoons and the role of the Stanislaus River greatly outweigh rainfall infiltration as <br /> sources of recharge. Leakage from irrigation canals are likely important sources for recharge <br /> in the agricultural areas south of the Stanislaus River. The direct percolation of irrigation water <br /> purchased by the City of Ripon at the recharge basin in the vicinity of the WWTF is also an <br /> important anthropogenic recharge source. Water loss from the potable and non-potable water <br /> distribution systems and sewer systems may also be important for recharging groundwater <br /> over a large area, however, the effects of these potential recharge sources are difficult to <br /> assess and their influence on groundwater movement are likely small compared to the <br /> municipal and industrial lagoons. <br /> Municipal Wastewater Treatment Lagoons <br /> There are three sources for recharge in the WWTF area: <br /> 1. Rapid infiltration of treated domestic wastewater, <br /> 2. Rapid infiltration of untreated industrial wastewater, <br /> 3. Seasonal recharge of irrigation water. <br /> Infiltration of Treated Domestic Wastewater(summarized from ECO:LOGIC (2007)): The <br /> WWTF accepts an average flow of approximately 1.2 million gallons per day (MGD) of <br /> AMEC Geomatrix, Inc. <br /> hDoc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 29 <br />