SU0012885 - Laserfiche WebLink

Home Browse Search

B. PUBLIC SERVICES AND UTILITIES S_ew-age Disposal 1 . Environmental Setting Sewage disposal for the Morada Area and the project vicinity is handled entirely on-site. The majority of these systems utilize septic tanks along with leachfields or seepage pits, depending on soil conditions. The applicant has conducted a geotechnical investigation for the site. Borings performed for this study revealed surface soils generally consisting of "medium stiff to stiff black to dark brown silty clays" to depths of four feet. Beneath these surface clays; most borings encountered stiff to hard silts and clays. No soil percolation testing was performed at the site during this investigation, however, these soil types generally exhibit very slow percolation rates. Soils found at the site are either Jacktone clay ,or Clear FA !Lake clay ha-rdpan -as described in the Soil- Conservation Service Soil Sur.vey , 2 Tfiis survey also rates both soils as having slow percolation rates, which may limit the use of leachfield systems. The groundwater level in the fall of 1986 was determined to be 60 _ ' to 70 feet below the surface. 3 Soil descriptions in the applicant ' s investigations included descriptions of orange and grey silty clays.. These soil conditions often indicate seasonally high groundwater, with oxidation and reduction causing the soils to take on this appearance. The presence of an underlying hardpan ' with stiffer clay might also contribute to a higher water table in the winter months. 2. Environmental Impacts FThe use of individual on-site sewage disposal has been proposed for this project. The effectiveness of on-site sewage disposal will be primarily dependent upon . adequate soil percolation. The San Joaquin . Local Health District. is the regulating agency and County Ordinance No. 549 has established a maximum acceptable percolation rate of 60 minutes per inch (mpi ) ' for leachfield .disposal . At sites where '~this rate is exceeded, a seepage pit may be used in lieu of a leachfield, . providing the f percolation rate is less than 30 mpi. _Fo-r the project site, it is likely that perco.l.at-io-n rates will .b.e _n_ea_r the. maximum acceptable value.TEach p op~osed le hf.ieI site w•i�l�l requare a't feast one � . p` rc�`a__on test to comply wYth County Ordinance No. 5u9 goverining i-ndividual sewage disposal systems. To estimate theotential for nitrate impacts on p p groundwater, an analysis was made for this EIR . This analysis involved the application of a simplified water-chemical mass balance model . In this model the long-term concentration of nitrate-nitrogen (NOS - F43