SU0012793 - Laserfiche WebLink

Home Browse Search

Page 95 A. ° compliance with the various regulatory requirements that have emerged. These include the RWQCB orders, Board-required Solid Waste Water Quality Assessment Test(SWAT),National Pollutant Discharge Elimination System(NPDES)permits,workers right-to-know,Hazardous Materials Management Plan(HMMP),Surface Water Pollution Prevention Plan(SWPPP),and most recent E Corrective Action Plan(CAP). The City of Stockton and Austin Road Landfill implemented a hazardous materials screening procedure to inhibit any hazardous materials from being initially collected for F disposal to the landfill and a second screening at the landfill to check for potential hazardous materials that were carried to the landfill. In February 1999 a updated SWPPP was completed, i a The RWQCB is the lead regulatory agency for the oversight of Austin Landfill with the City of Stockton being the Responsible Party(RP). Groundwater Conditions Y Underlying San Joaquin County is a portion of the vast subsurface groundwater aquifer system of the Central Valley of California. Groundwater occurs in unconfined and confined conditions. The upper F', regional aquifer is typically an unconfined aquifer within the Victor Formation geologic unit. The Victor formation consists of over 100 feet of clay,silt,and fine to coarse sand andgravel. Sedimentary 1 formations underlying the Victor formation include additional,productive confined aquifers. Y S Groundwater within one mile of the site is tapped by irrigation and domestic wells, and most wells in the vicinity are generally drilled several hundred feet deep. FGroundwater recharge to the unconfined aquifer,both regionally and locally,is from 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 one of the General Plan- F designated substantial groundwater recharge areas,although some infiltration and percolation to the groundwater system is expected along the North Branch of the South Fork of Little Johns Creek (Hydrogeological investigations at the nearby Forward,Inc. Landfill show that recharge along the course ,. of the South Fork of Little Johns Creek,which crosses their property,has a significant influcnce on water table depth,gradient,and flow direction). A characteristic of the San Joaquin Valley's groundwater basins has been the tendency for water levels to vary,both seasonally and annually,over short periods of time. Seasonal fluctuations reflect the rainy and dry season. Rainy season infiltration raises the water table, and dry season pumping lowers the water table. The 1994 EIR reported that,in the project area,water levels have dropped over the last 20 years by approximately 10 feet due to agricultural pumping demand and drought. The 1994 EIR identified the ti uppermost water bearing formation as approximately 70 feet below the base of the landfill,with the hydraulic gradient to the north-northeast. The beneficial uses of project area groundwater are domestic,municipal, and agricultural. A Solid Waste 7 Water Quality Assessment Test(SWAT)in 1989 found a significant groundwater quality impact by i ' regulated volatile organic compound(VOC)chemicals at contamination levels above the drinking water standard. The 1994 EIR reported the key VOC contaminants as: tetrachloroethene(PCE);trichloroethene F (TCE);cis-l,24chloroethene(DCE);and vinyl chloride(VC). Table K-1 shows the key VOC concentrations detected. VOC concentrations found in the downgradient monitoring wells included: VC (l l µg/L);PCE(210 pg/L);TCE(39 pg/L);and DCE(36 pg/L). k P, Supplemental sampling results indicated that VOCs were detected in CYA wells CYA-1 and CYA-2 at levels equal to or slightly above drinking water action levels. These wells are shown on Figure K-1. GR4SSETTI ENMONMENTAL CONSULTING i