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6.0 GREAT Program Groundwater FlowModelingThis section evaluates those elements of the GREAT Program that will have a cumulative(year-to-year) regional effect on groundwater elevations within the aquifers underlying theOxnard Plain and Pleasant Valley areas. These are the project elements related to creatingthe new sources of water supply, which would be created by reusing treated effluent fromthe City WWTP that is currently being discharged to the ocean. These consist of thefollowing elements, as summarized in Section 1.0 and described in Section 4.0:• In-Lieu Groundwater Recharge using Recycled Water• Direct Injection Groundwater Recharge using Recycled Water• Groundwater Recovery for Potable UseThe methodology used to evaluate the regional effects from implementing GREAT Programelements and the results of that evaluation are presented below.6.1 MethodologyThe regional effects on groundwater elevations are evaluated by developing and simulatingdetailed Phase 1 and Phase 2 operating scenarios for the GREAT Program using the updatedUWCD model of the USGS groundwater flow model of the Santa Clara-Calleguas Basin.The USGS model and the UWCD update to that model are described in Section 5.0.6.1.1 Development of ScenariosDetailed scenarios are developed for operation of Phase 1 and Phase 2 elements of theGREAT Program to (1) evaluate the cumulative effects on groundwater elevations and(2) evaluate extraction well locations to minimize coastal drawdown during groundwaterrecovery. The results of these scenarios are compared to a Base Case scenario, which wouldrepresent conditions without the GREAT Program. The Base Case, and the Phase 1 andPhase 2 scenarios, are described below and summarized in Table 6-1.Base Case ScenarioThe objective of the Base Case is to develop a No Project scenario against which the effectsof the proposed GREAT Program Phase 1 and Phase 2 scenarios are compared. The BaseCase is developed and consists of the following elements:• Inland Saline Intrusion Assessment Project – Scenario 3. Scenario 3 from the InlandSaline Intrusion Assessment Project is used as a starting point. The scenario is describedin Section 5.0 and consists of the following:−Water deliveries from the UWCD Saticoy wellfield used as in-lieu deliveries to offsetpumping demand in PTP and PVCWD wells.W112003002SCO LW1458.DOC/ 033390002 73