SITE INFORMATION AND CORRESPONDENCE_1993-1996

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San Joaquin County Utilities,part of the SJCPWD,owns the Lincoln Village Maintenance District wells. In the summer of 1992, San Joaquin County Utilities destroyed four LVMD wells because the high concentrations of iron and manganese detected in these wells exceeded the State of California minimum contaminant levels for drinking water. San Joaquin County Utilities currently purchases water from the City of Stockton Water Department to provide drinking water to the Lincoln Village Shopping Center. (15) 3.0 HAZARD RANKING SYSTEM FACTORS 3.1 Sources of Contamination Past business activities conducted on site by Lincoln Village Cleaners have generated hazardous wastes. There is one potential source of contamination at the Lincoln Village Cleaners site: • Soil and groundwater beneath the site have been contaminated with PCE as a result of previous discharges of dry cleaning wastewater and/or PCE solvent to the municipal sewer system. 3.2 Groundwater Pathway 3.2.1 Hydrogeologicrl Setting. The Lincoln Village Cleaners site is located in the City of Stockton,within the Central Valley geologic province in northern San Joaquin County. To the east occur the metamorphic and igneous rocks of the Sierra Nevada geologic province. The Stockton area is underlain by continental rocks and deposits from the Miocene to Holocene age. Heterogeneous mixtures of poorly sorted clay, silt, sand, and gravel, as well as some beds of claystone, siltstone, sandstone, and conglomerate, are present beneath the area to a depth of about 2,000 feet. Informal units of significance to fresh water supplies in the Great Valley include from ground surface downward: the Younger Alluvium, Older Alluvium, Turlock Lake Formation, Laguna Formation, Mehrten Formation, and the Valley Springs Formation. Continental and marine rocks and deposits occur below a depth of about 2,000 feet. These deposits are predominantly sandstone with some conglomerate and shale, marine rocks, and deposits of clay, shale, siltstone, and sandstone. (16, 17) The younger sedimentary units of the alluvial deposits, and Turlock Lake and Laguna formations are the most widely used for groundwater in the Great Valley. The Mehrten Formation has been less developed because of generally higher concentrations of iron and manganese. High concentrations of these elements in the minerals present are caused by the volcanic-source rocks that dominate the Mehrten Formation. The older Valley Springs Formation is relatively undeveloped because of its fine-grained nature and its depth of occurrence. However, some production is made from this formation especially along the eastern boundary of the Great Valley. (16, 17) In the Stockton area, the Turlock Lake and Laguna formations are the main water-producing zones. The Younger Alluvium unit occurs along the Calaveras River Valley as a thin complex of terrace and flood plain deposits. The Younger Alluvium's importance is as a route for groundwater percolation from the river and stream channels to the deeper and older formations. (16) Most of the groundwater in the Younger Alluvium, Turlock Lake, and Laguna formations for the Stockton PA Linmin Village Cleans V (F) • SM 7 Piloted w 50% recycled paper.