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Section 5 <br />approach described above but using the model - derived particle 4 -month travel <br />time area. This is based on CDPH's approval of a four-month secondary buffer <br />for the recharge of GWRS water in the Anaheim Forebay. The model shows that <br />no existing active drinking water production wells would lie within the three-month <br />or four-month buffer areas. <br />Mounding Analysis <br />Mounding (increase in groundwater levels) and potential effects on groundwater <br />flow conditions that could occur as a result of the injection in the mid-basin <br />project area were estimated using an existing numerical groundwater flow model <br />that encompasses the project area and the Talbert Gap Barrier Model. <br />The proposed injection would occur in the Omicron/Upper Rho (Layer 9) and <br />Main aquifers (Layer 11), which are confined aquifers. It was assumed that three <br />million gallons per day (MGD) would be injected at each well location in model <br />Mayers 9 and 11. The injection rate was based on the hydrogeological condition of <br />the area and the availability of GWRS water. Additionally, to be conservative, a <br />twelve-month continuous injection period was assumed to reach, maximum <br />mounding potential. During this period, production wells around this area were <br />operated within their typical historical capacities. <br />To evaluate potential mounding from the injection wells, two simulations were <br />performed: A baseline simulation, in which no mid-basin injection was <br />considered, and an injection Simulation, in which a constant injection amount of 3 <br />MGD was applied to each of the one existing and four proposed mid-basin <br />injection wells. <br />For visual comparison, the simulated water level contours in the Omicron/Upper <br />Rho aquifers (Layer 9) are shown in Figure 18 for both the baseline and <br />proposed injection simulation. Figure 18 shows that, although the shapes of the <br />groundwater contours are different between the two simulations in the immediate <br />vicinity of the injection area, the general direction of groundwater flow would be <br />to the south /southeast in the two simulations. Although the general groundwater <br />flow direction did not appreciably change, the steepness of the hydraulic gradient <br />caused by the mounding was estimated to increase by 1.1 x10`' feet/feet within a <br />1 -mile radius of the injection area. This represents an increase of 30 percent <br />from the baseline hydraulic gradient of 3,6xl 0-3feet/feet in this area. The <br />estimated hydraulic gradient increase is minimal beyond one mile from the <br />injection site, <br />Mid Basin Centennial Park2jSGr247Project Final EIR 5-116 <br />