SU0007861 - Laserfiche WebLink

Home Browse Search

Draft Environmental Impact Report Page IVY-6 Forward Inc. Landfill Expansion and domestic wells, and most wells in the vicinity are generally drilled to a depth of several hundred feet. Groundwater recharge to the unconfined aquifer, both regionally and locally, is fromm local rainfall and stream infiltration, while the deeper, confined aquifers are recharged by rivers, reservoirs, and surface runoff along the western base of the Sierra Nevada. The project area is not in a General Plan-designated substantial groundwater recharge area, although some infiltration and percolation to the groundwater system is expected along the north branch of the south fork of Littlejohns Creek as well as the Landill's artificial recharge program.' .� Before the early 1960's, groundwater in the area typically flowed to the west. Since that time, San Joaquin hydrologic basin has experienced overdraft as a result of heavy pumping. In the Central San Joaquin Irrigation District, which encompasses Forward Landfill, water levels have dropped approximately 70 feet in the past 30 years. Based on groundwater elevation contours published by the San Joaquin County Flood Control and Water Conservation District, the regional groundwater in the vicinity of the site is now typically 20 to 30 feet below msl (approximately 60 to 80 feet below ground surface) and flows to the north-northeast. I ' Beyond the trend of historical over-drafting (removing more groundwater than is naturally recharged)from the aquifer, the San Joaquin Valley's groundwater basins has been the tendency for water levels to show seasonally variations. Seasonal fluctuations reflect the rainy and dry seasons. Rainy season infiltration raises the water table, and dry season pumping ' lowers the water table. Seasonal fluctuations in the project area are on the order of 5 to 10 feet .. due to a distinct rainy season and dry season. During the rainy season infiltration raises the water table and during the dry season drawdown by water well users lowers the water table. The declining water levels throughout the Stockton area have induced the eastward movement of poor-quality water from the delta sediments. Migration of these saline waters had already impacted the utility of groundwater as far east as Stockton at the time of a 1981 study by the U.S. Geological Survey (USGS) (San Joaquin County Flood Control and Water Conservation District, 1990). The San Joaquin County Flood Control and Water Conservation District has documented a decline in water quality for the Stockton area due to a general increase in chlorides. The regional water quality in the area around Forward Landfill meets the State's Drinking Water Standard. The water is a calcium-magnesium/bicarbonate water type, with total dissolved solids (TDS) concentrations under 500 mg/l. The sedimentary formations underlying the Victor formation have many productive confined aquifers. In order to develop adequate flow, most of the agricultural irrigation wells in the area are at least 500 feet. The unconfined aquifers are recharged by rainfall and local stream infiltration. Rivers, reservoirs and surface runoff along the slopes of the western Sierra Nevada Foothills recharge the deeper confined aquifers. Groundwater Resources and Supply The designated beneficial use of the groundwater in the landfill area, as specified in the basin Plan, are domestic and municipal supply, agricultural supply, industrial service supply, and industrial process supply. 1 Hydrogeological investigations at the Forward Landfill show that recharge along the course of the south fork of Littlejohn Creek,which crosses that property,has a significant influence on water table depth,gradient,and flow direction. E. ,