SU0006676_SSNL - Laserfiche WebLink

Home Browse Search

l ! From observations made by EHI, commercial facilities on conventional septic systems along the Highway 99 Corridor have been roblematic. One reason being the State of California requirement (� that gas stations and other types of commercial facilities must provide public restroom services. The project site has level terrain; consequently, there will be no need to incorporate design considerations for slopes for any future disposal area. Potential wastewater discharge possibilities are discussed in the Conclusions Section. Under EHD requirements and regulations, a mound system for effluent disposal would not be allowed for a future project even though tight clayey surface soils exist. B. SOIL PHYSICAL CHARACTERISTICS AND ANALYTICAL TEST RESULTS The United States Department of Agriculture - Soil Conservation Service(USDA-SCS) indicates the property soils for the northeast half of the property are Galt clay(#160) and the soils for the southwest half are Jacktone clay(#180). The Soil Survey of San Joaquin County states that permeability is slow in these two soils,which was observed in the top four feet of soil by the percolation tests conducted. As referenced, the deeper soils below six feet are permeable. SSS§5.2. The surface and subsurface soil investigation began on September 25, 2007 with the drilling of four percolation test borings and a 25 feet deep exploratory boring with a truck mounted drill rig and solid stem auger. The test borings were drilled near the northeast comer of the property as illustrated on the S.J.C. District Viewer Map. This test location was chosen since it is probable that a wastewater disposal area for any future commercial development may take place in this area of the property, and given the triangular shape at the northeast corner, this is a logical location. NLS§ 1.1, 1.2. Soil cutting samples from the 25-ft exploratory test boring were retrieved from the surface and every five-foot depth for physical and chemical analysis. As the noted on the A&L Laboratory Soil Analysis Reports in Appendix B, chemical analyses of the six soil samples quantify several constituents that influence nitrate loading for this project. The important parameters for nitrate loading assessment are the organic matter,pH,cation exchange capacity(CEC), clay content percentage, along with nitrate-nitrogen content of the soil. As noted, the organic matter in the surface soils is higher than the subsoils, which is to be expected 2. given the property was once farmed. The nitrate-nitrogen concentration is medium at the surface, again to be expected,but decreases in concentration in each of the subsequent deeper depths. However, at 15 ft, the nitrate-nitrogen concentration increases from 7 ppm at 10 ft to 11 ppm at 15 ft. Looking at the soil texture, we find the soil changing from a loamy sand to a clay loam, respectively, at these depths. It is theorized that downward migration of nitrogen is impeded and congregates around this 15-ft depth due to a change from a coarse-grained soil to a fine-grained soil. Below 15 ft at the 20 and 25 ft depth, there is a decrease in nitrate-nitrogen concentrations which Z'J suggests the denitrification potential within the soil profile may also play a role in reducing the nitrogen concentrations. 3 Chesney Consulting