ARCHIVED REPORTS_2014 - Laserfiche WebLink

Home Browse Search

Non-Water Release Corrective Action Plan North County Recycling Center and Sanitary Landfill ranges. The geology of the eastern portion of the San Joaquin Valley is characterized by alluvial sediments deposited by rivers and streams emanating from sources in the Sierra Nevada Mountains to the east. The NCRCSL is situated at the western edge of what Piper et al. (1939) designated as the Arroyo Seco Pediment. This geomorphic feature was produced by the Mokolumne River and other streams originating in the Sierra Nevada Mountains. The sediments were described as fluviatile (stream or river) deposits consisting of sand, gravel, silt, and clay. The youngest geologic units underlying the site are semiconsolidated alluvial deposit of the Turlock Lake and Riverbank Formations. The Turlock Lake and Riverbank Formations consist of arkosic alluvial deposits of gravels, sands, silts, and clays. These deposits show coarsening upward patterns, as is seen in most of the alluvial systems flanking the western Sierra Nevada. On a more local level, the site is situated within an area of gently rolling topography. Surficial soils consisting of silts and clays extend from the ground surface to a depth of 2 to 3 feet, commonly underlain by a 1/2-foot layer of cemented soil referred to as hardpan. The landfill foundation soils to a depth of 100 feet consist of medium sense silty sand and clayey sands with occasional medium stiff, sandy silt and sandy clay interbeds. The Standard Penetration Test (SPT) resistance (or N Values), vary from approximately 20 to 70 with an average of 40 blows per foot. Below 100 feet, the soils generally consist of medium dense to dense, poorly graded sand and gravelly sands with an average SPT of 50 for 2 inches. Groundwater is found in site wells at depths ranging from 150 to 160 feet (CB&I, 2013). Groundwater underlying the landfill occurs under unconfined or partially confined conditions within gravelly or silty sands. Static water levels are higher than levels at which ground water was first encountered during drilling, indicating some limited confinement. Depth to ground water beneath the base of the landfill ranges from 100 to 120 feet. 2.2 Surface Water Hydrology The NCRCSL is located within the San Joaquin Valley flatlands. The natural drainage courses include a tributary to Paddy Creek which runs from east to west along the north side of the site and an unnamed drainage on the south side of the site. Due to the location of the landfill and surrounding land uses, run-on to the site is contained within Paddy Creek tributary in the mitigation area of the site. Run-off from the landfill is controlled by a series of top-deck berms, drainage benches, and downdrain pipes which will direct flow into perimeter ditches. Runoff from the top deck, west, east, and north side slopes is directed to the northern sedimentation basin and runoff from the south side slopes is directed offsite in an unnamed drainage ditch. The final grading for the NCRCSL is shown in Figure 2. 2013.A135 I N:\San Joaquin\North County\Non-Water Release CAP\Final Report\North County_NWCAP_Report_Final.docx July 2014,Rev.0 2