View File - Development Services - City of Oxnard

WATER RESOURCES TECHNICAL REPORTClara River system. The base of the aquifer extends from about 200 to 400 feet bgs. In thePleasant Valley area, the Mugu aquifer is finer grained because the aquifer sediments werelocally derived instead of from the Santa Clara River. Consequently, few wells arecompleted solely in the UAS in the Pleasant Valley area. The silt and clay layers retard thevertical movement of water thorough the Mugu aquifer.Lower Aquifer SystemThe LAS consists of folded and faulted Pleistocene continental marine deposits of theSaugus, Sand Pedro, and Santa Barbara Formations. Localized fine-grained deposits occur inareas along the coast line between Port Hueneme and Point Mugu, which are attributed tothe backfilling of ancestral submarine canyons. Regional fault systems segregate the LASinto many parts and affect the flow of water between and within the sub-basinsUpper and Lower Hueneme Aquifers. The Hueneme aquifers constitute the upper part of theSan Pedro Formation beneath the Oxnard Plain. These deposits consist of lenticular layers ofsand, gravel, silt, and clay. These deposits are divided into upper and lower aquifers basedon data from electric logs that show a decrease in electrical resistively at the contact betweenthe aquifers. The decrease is attributed to the presence of more fine-grained deposits in theLower Hueneme aquifer than in the Upper Hueneme. The Upper Hueneme aquifer ispredominately fine grained in the Oxnard Plain basin.Fox Canyon Aquifer. The Fox Canyon aquifer constitutes the basal part of the San PedroFormation. The aquifer consists of weakly indurated very fine- to medium-grainedfossiliferous sand with occasional gravel and clay layers of shallow marine origin. Themarine deposition of the sediments of the Fox Canyon aquifer results in a relatively uniformseries of layers, which can be correlated by electric logs over large areas.2.6.2 Groundwater Levels and MovementPredevelopment ConditionsUnder predevelopment conditions, groundwater levels were well above sea level in theinland recharge areas and gradually decrease toward the ocean, the natural discharge areafor groundwater. Artesian conditions existed in the coastal areas. In the 1970s, wells near thecoast were reported to deliver water to the second floor of homes under natural artesianpressures of the Oxnard aquifer. Groundwater would have moved from the inland rechargeareas towards the west /southwest to the regional offshore discharge areas along thesubmarine outcrops into the Pacific Ocean.Sources of recharge to and discharge from the groundwater system under these naturalconditions would have included the following components, which the USGS quantifiedusing the groundwater flow model of the Santa Clara-Calleguas Basin:• Recharge Components− Stream flow infiltration− Mountain-front and bedrock recharge− Precipitation on valley floor• Discharge Components− Stream base flow− Evapotranspiration− Coastal outflowW112003002SCO LW1458.DOC/ 033390002 18