ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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consolidation of soft clays following the lowering of the water table or the placement of fill. The Galt Clay soil type south of the WQCF site(see Exhibit 4.7-1)is considered expansive because of its high clay content,high plasticity index, and high shrink-swell potential(MRCS 1992). In addition,the Arents soil type south of the WQCF, and the Guard the Egbert soil types along the effluent outfall pipeline alignment are also considered expansive soils (San Joaquin County 1999). SEEPAGE AND SOIL MOISTURE As described above, groundwater at the WQCF site was encountered at depths of 8 to 12 feet below the existing site grade and was encountered as high as three feet below grade in previous investigations. Throughout the project area, soil permeability is generally rapid,but surface runoff is slow. Combined with high groundwater levels during the winter and spring months, slow surface runoff could create saturated surface soil conditions and high soil moisture content. CORROSION POTENTIAL Corrosion is the gradual degradation of materials through electrochemical processes resulting from the interaction between chemical properties of the soil(e.g.,pH,resistivity, and sulfate and chloride concentrations)and metal, concrete, or stone. Based on a review of available geotechnical reports,no soil testing to evaluate the potential for corrosion has been conducted at the WQCF site and along proposed collection system alignments. In addition,it does not appear that any laboratory testing by a corrosion engineer has been completed, so no definitive conclusion can be reached regarding the soil corrosion potential in the project area. MINERAL RESOURCES There are a number of natural gas fields within San Joaquin County, although the majority are located in and around the Sacramento-San Joaquin River Delta. The project area is approximately 4 miles southeast of Lathrop Gas, a large natural gas field that was actively producing 1,121,100 Mcf(a unit of measurement equal to 1,000 cubic feet)in 1998. McMullin Ranch Gas, approximately 2 miles south of the project site, is another large natural gas field which produced 63,258 Mcf in 1998. Given the uncertainty in locating oil and gas reserves,the high cost of exploratory well drilling,the fact that the project area does not lie within an existing oil or gas production field, it is unlikely that natural gas reserves would be encountered. In compliance with the California Surface Mining and Reclamation Act(SMARA),the California Department of Conservation,Division of Mines and Geology(CDMG)has established the classification system shown in Table 4.7-4 to denote both the location and significance of key extractive resources. Lands are included in one of four categories based on available information indicating their potential to contain mineral deposits.Not all lands in the state have been classified by the CDMG. Mineral Resource Zones (MRZs)have been designated to indicate the significance of mineral deposits. Table 4.7-4 CDMG Mineral Land Classification System Classification Description MRZ-1 Areas where adequate information indicates that no significant mineral deposits are present or where it is judged that little likelihood exists for their presence MRZ-2 Areas where adequate information indicates that significant mineral deposits are present or where it is judged that a high likelihood for their presence exists MRZ-3 Areas containing mineral deposits,the significance of which cannot be evaluated from existing data MRZ-4 Areas where available data is inadequate for placement in any other MRZ zone Source:CGS 2000 EDAW Manteca WQCF and Collection System Master Plans EIR Geology, Soils,and Seismicity 4.7-12 City of Manteca