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4.3 GEOLOGY AND SOILS • Three of the proposed septic system sites are in an area determined to have severe septic system constraints due to high groundwater conditions. Based on these findings it can be concluded that the present project design does not adequately provide for suitable septic system easements for all of the proposed building sites. This is because the septic system has been prepared without the benefit of adequate field testing. The impact of this is that, as proposed, many of the septic systems would be located in areas not well suited for subsurface sewage disposal. Possible consequences of this could include: • surface failure of septic systems in the immediate leachfield area, with attendant nuisance and contamination hazards, due to shallow soils and localized saturation above the hardpan layer; • lateral seepage of inadequately treated sewage effluent at vernal pools and lakeshore areas; and, • deep percolation of sewage effluent into the regional groundwater aquifer, without proper treatment through a sufficient unsaturated soil zone. These are all potentially significant impacts to public health and water quality. Alternatives to the proposed wastewater plans for the project could include clustered leachfields serving groups of houses, or possibly a central collection system with community leachfields and/or a package type treatment plant with leachfield or spray disposal. Any of these options would require the formation of a special sanitation district, zone or service area to bring the sewage treatment and disposal operations under the authority of a public entity. A homeowner's association could be charged with the responsibility for individual leachfields on commons;but the operation and maintenance of a community treatment facility, even for 26 homes, would require a public agency with sewerage authority, The alternative of community or clustered systems may or may not be more economical, and it could produce reclaimed wastewater for irrigation purposes (e.g.,pasture irrigation). However, it would not necessarily be more feasible than the proposed use of individual leachfield easements, provided they are properly sited, constructed and maintained. Miti a� t 4.3-1 Conduct a soil suitability study prior to tentative map approval to identify and document the suitability of each proposed on-site sewage disposal site. Investigations shall include soil profiles, percolation testing and winter (wet weather) groundwater observations to verify conformance with current on-site sewage disposal regulations of the County. Studies must be approved by the Environmental Health Services Division of the San Joaquin County Public Health Services Department. 4.3-7