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WATER RESOURCES TECHNICAL REPORT• Detailed Phase 1 and Phase 2 scenarios for the GREAT Program were developed,simulated, and evaluated using the UWCD update to the USGS groundwater flowmodel.The USGS developed the groundwater flow model to better define the hydrogeologicframework of the regional groundwater flow system and to help analyze the majorproblems affecting water resources management of a typical coastal aquifer system, theSanta Clara-Calleguas Basin (USGS, 2003). The USGS calibrated the model to historicalsurface water and groundwater conditions for the period 1891 to 1993. UWCD updated themodel for a study related to the nature of recent inland saline (seawater) intrusion in thePleasant Valley groundwater basin and developed specific recommendations to controlor limit water quality problems associated with the migration and pumping of salinegroundwater. UWCD updated the model and extended the calibration period through 2000.It is the policy of UWCD that only UWCD have custody of the updated groundwater flowmodel and that only UWCD staff can run the model. Therefore, the actual simulations of thedetailed GREAT Program Phase 1 and Phase 2 scenarios were performed by Mr. SteveBachman, Ph.D., Groundwater Resources Manger of UWCD. CH2M HILL developed thedetailed Phase 1 and Phase 2 scenarios and evaluated the results of the model simulations incollaboration with Mr. Bachman. Mr. Bachman performed the model simulation work undercontract to the City.1.3 OrganizationThis technical report is organized into the following sections:• Section 1.0, Introduction. This section provides background, the purpose, and scope ofwork related to evaluating potential impacts to groundwater elevations within theOxnard Plain hydrogeologic system as a result of implementing the GREAT Program.• Section 2.0, Environmental Setting. This section summarizes the environmental settingof the Oxnard Plain and vicinity as it relates to the GREAT Program, includingphysiography, climate, surface water resources, and groundwater resources.• Section 3.0, Water Supply and Demand. This section describes the currently availableregional water supplies and the current and projected water demands related to theGREAT Program.• Section 4.0, GREAT Program Project Description. This section provides a summary ofthe GREAT Program elements.• Section 5.0, Historical Groundwater Flow Modeling. This section summarizes theUSGS numerical groundwater flow model of the Santa Clara-Calleguas Basin and theUWCD update to that model.• Section 6.0, GREAT Program Groundwater Flow Modeling. This section provides themethodology and results of the model development and simulation of the detailedPhase 1 and Phase 2 scenarios for the GREAT Program.W112003002SCO LW1458.DOC/ 033390002 4