FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

Mr.M. Scott Mansholt—CEMC First Quarter 2006 Groundwater Monitoring and Sampling Report April 18,2006 US Can-Welty Road Page 2 of 5 Currently,Kinder Morgan Energy Partners,L. P., operates a pipeline that reportedly transports gasoline,jet fuel, and diesel and is located between the US Can-Welty Road site and Highway 33. Western Farm Service(WFS)is located directly northeast of the site across Highway 33 and has stored and distributed bulk liquid and dry fertilizers since 1969. In addition, a former Union Oil gas station,reportedly located northeast of the site, operated from approximately 1972 until the mid 1980s. REGIONAL/LOCAL HYDROGEOLOGY Regionally,the site is encompassed within the Tracy sub-basin(Groundwater Basin Number 5-22.15)and is defined by unconsolidated to semi-consolidated sedimentary deposits that are bounded by the Diablo Range on the west,the Mokelumne and San Joaquin rivers on the north, the San Joaquin River on the east, and the San Joaquin-Stanislaus County line on the south. The Tracy sub-basin is located adjacent to the eastern San Joaquin sub-basin on the east and the Delta- Mendota sub-basin on the south.' The above-mentioned sub-basins are located within the larger San Joaquin Valley Groundwater Basin. The Tracy sub-basin is comprised of continental deposits of Late Tertiary to Quaternary age, including the Tulare Formation, Older Alluvium,Flood Basin Deposits, and Younger Alluvium. The thickness of these formations ranges from a few hundred feet in the western foothills to about 3,000 feet near the eastern margin of the basin. The Tulare Formation is comprised of semi- consolidated,poorly sorted,discontinuous deposits of clay, silt, and gravel. The Corcoran clay is situated near the top of the Tulare Formation, separating groundwater in the basin in what has been reported as two primary aquifers. The upper aquifer is reported to range in thickness from 15 to 250 feet below ground surface(bgs), and the lower aquifer is reported at 600 feet bgs.l Locally,the site is within the Central Valley Physiographic Province of California, is situated at an approximate elevation of 103 to 105 feet above mean sea level, and has a relatively flat topography that slopes gently downward to the northeast. Groundwater in the upper water-bearing zone flows in a northeasterly direction at an approximate gradient of 0.001 feet per foot(ft/ft)and is hydraulically controlled by low-permeable,unconsolidated sediments. Generally, depth to groundwater at the site varies from 20 to 40 feet bgs. Soils encountered appear to be fine-grained unconsolidated sediments, consisting mainly of lean clays and silts (CL, ML)and clayey and silty sands, (SC, SM)with smaller quantities of poorly graded sand and gravel(SP, GP). PETROLEUM DISTRIBUTION IN GROUNDWATER During 2005, a sheen was observed in well MW-1, and a petroleum odor was observed in MW-2. Dissolved-phase crude oil was indicated by total petroleum hydrocarbons quantified as diesel (TPHd)analyses. TPHd have been detected in wells MW-3 and WFSMW-I at concentrations of up to 6,700 and 240 micrograms per liter(gg/L),respectively. No dissolved-phase TPH quantified as gasoline (TPHg) or benzene,toluene, ethylbenzene, and total xylenes (BTEX)have been detected in the groundwater from the site wells. TPHg and TPHd were detected in the separate-phase oil(SPO) from well MW-2 in 2005. Low levels of PAHs have been detected in groundwater from MW-3 and WFSMW-I since 2005. 1. California Department of Water Resources,2003. California's Groundwater,Bulletin 118,2003 Update.