View File - Development Services - City of Oxnard

WATER RESOURCES TECHNICAL REPORT• Moderate decline in groundwater elevations in the vicinity of the City Water Yard in theUAS and LAS as a result of extracting 15,429 AFY (80 percent) of the 19,286 AFY ofin-lieu recharge from the City Water Yard wells: two LAS wells (Nos. 20 and 21),two UAS wells (Nos. 22 and 23), and three UAS wells. Water levels decreased up to30 feet in the UAS and up to 15 feet in the LAS in the vicinity of the City Water Yard,and decreased up to 20 feet in the UAS and up to 10 feet across the northern OxnardPlain. These water level decreases will result in the following:−−In the UAS, these moderate decreases, combined with the declines from the UWCDEl Rio wellfield extractions, will increase the potential to induce brief periods ofcoastal landward flow during extended, drier climatic periods (see Scenario 2chydrograph for coastal well 05G02, which twice briefly drops below sea level forsimulation period [Figure 6-27]).In the LAS, these moderate decreases will increase the moderate potential forlandward flow that exists, particularly during drier years and in the fall when waterlevels are seasonally low.• Moderate decline in groundwater elevations in the Forebay area as a result of extracting3,857 AFY (20 percent) of the 19,286 AFY of in-lieu recharge from the UWCD El Riowellfield. Water levels decreased up to 20 feet in the UAS and up to 10 feet in the LAS.The water level decline in the LAS is mostly due to interference from drawdown at theCity Water Yard. These water level decreases will result in the following:−−In the UAS, these moderate declines will not interfere with pumping operations atthe Forebay spreading grounds. However, combined with the declines from CityWater Yard extractions, these moderate declines will contribute to the increasedpotential to induce brief periods of coastal landward flow during extended, drierclimatic periods (see Scenario 2a hydrograph for coastal well 05G02, which twicebriefly drops below sea level for simulation period [Figure 6-27]).In the LAS, these small declines are attributed mostly to drawdown from theextractions at the City Water Yard and, consequently, will have no significant effect.These changes will result in the following reductions in overdraft:• For the UAS, the average height above the coastal water level goal will decrease to3.8 feet compared to 5.7 feet for the Base Case.• For the LAS, the reduction in overdraft will be 36 percent compared to the Base Case.Scenario 2bScenario 2b results in the following changes relative to the Base Case:• Virtually the same large rise in groundwater elevations across the southern OxnardPlain and Pleasant Valley areas as for Scenario 2a (the in-lieu recharge assumptions arethe same for Scenarios 2a and 2b).• Small to moderate decline in groundwater elevations in the vicinity of the City WaterYard in the UAS and LAS as a result of extracting 3,857 AFY (20 percent) of the 19,286AFY of in-lieu recharge from the City Water Yard wells: two LAS wells (Nos. 20 and 21),W112003002SCO LW1458.DOC/ 033390002 90