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w Draft Supplemental Environmental Impact Report Page IV.G-11 Forward Inc. Landfill 2018 Expansion Project • area. Most of the production wells are constructed to depths on the order of 500 feet or more and produce water from the Laguna Formation. • Groundwater at the Forward Landfill is monitored by 48 groundwater monitoring wells, three domestic wells, and five piezometers. The monitoring wells are used to collect water level elevations as well as water quality data. In addition, the current Corrective Action Program • (CAP) includes four active groundwater extraction wells. Data from these wells and • piezometers indicate uppermost groundwater beneath the landfill occurs at depths that range from about 50 to 80 feet bgs in the younger alluvium and is unconfined. Groundwater gradient (the steepness of the slope of the groundwater flow) varies seasonally, being reflective of the weather cycles and pumping,with a steeper,north-trending gradient in dry years and a more gentle, northeast gradient in wet years. The groundwater gradient in the 2016 monitoring (GLA, 2017c) was relatively flat at 0.002 ft/ft. Quarterly groundwater monitoring data for the landfill indicate groundwater in this zone flows to the north-northeast • at a hydraulic gradient ranging from about 0.001 to 0.003 feet per foot(ft/ft), reflecting the • seasonal variation. Pump testing performed for extraction wells EW-1 and EW-2 at the Forward Landfill resulted in • an estimated hydraulic conductivity of about 250 feet per day (ft/day) for the uppermost • aquifer beneath the landfill (CDM, 1999). Assuming an effective porosity of 0.35, the groundwater flow rate is estimated to be about 0.7 to 2.1 ft/day. Depth to water measurements in shallow and deeper well pairs in the Evaluation Monitoring Program (EMP) wells for the • Austin Road Unit (ARU) indicate there is no appreciable vertical hydraulic gradient below the • Forward Landfill. Groundwater Ouality • Groundwater quality has been impacted by Forward (including Austin)Landfills historical operations. The discussion of groundwater quality at the Forward Landfill is provided for background information regarding the overall site setting. Refuse accumulated at landfills can • impact groundwater by leaching out chemicals over time. In the case of the unlined units at the • Forward Landfill, the leachate generated had a direct path to the subsurface environment and groundwater. Landfill gas can also move VOC form the vapor to dissolved groundwater phase. The lined portions of the Forward Landfill have not measurably impacted groundwater. Data acquired by Geo-Logic Associates (GLA)between 2003 and 2014 indicate that, groundwater generally flows to the north and northeasterly at a gradient between 0.001 and 0.003ft/ft. Locally, a southeast gradient has been noted in the southern area of the Original Forward Landfill beginning in May 2011 that is believed to be the result from adjacent • agricultural pumping. The groundwater in the northern proposed WMU FU-19 expansion area shows the most impact from contaminants of concern. Since 2016, low level VOCs have been detected in point of •