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v J The density of the one mile radius surrounding study area can be considered low. According to the attached USGS topographical map, there are approximately eleven structures per square mile. Population density is one of the most important factors to take into consideration when assessing the potential for nitrate contamination from septic systems. There is however, a small community south of the dairy facility known as River City. Permit applications for repairs and additions on record at the Environmental Health Department indicate over 20 applications for this subdivision. This is further evidence that the soil in the general locale is unsuitable for proper effluent management. PERCOLATION TEST RESULTS Percolation testing was performed under San Joaquin County and Environmental Protection Agency (EPA) guidelines. Due to the homogeneity of the subject site soils, only one perc test procedure was conducted in the front yard of the main residence, located northwest of the milk barn. Septic systems for each structure had been installed at the time of our test. The test boring was drilled to four feet in depth and the sidewalls scarified to open the smeared soil surfaces from the drilling process. This four-foot depth represents percolation which takes place in the leachfield area. A three-inch O.D. perforated PVC pipe was used to maintain test hole integrity and gravel was placed in the bottom of the hole. The perc test results performed on February 12, 1996 indicate there is very slow percolation which will occur in the leachfield area. The soil clay content is too high to allow the septic effluent to effectively and efficiently percolate through the soil pores. To assist in effluent disposal management, there are sumps located at the ends of the leachlines for each of the on-site systems. From our investigation of the subsurface soils, it can be reasonably concluded that the bottom and sides of the sumps also contain the same high clay content soil. Although there is documented evidence of intermittent sand strata existing in this general locale, it is unknown during the sump emplacement if a sandier material was encountered. The septic tanks should be pumped out on a periodic basis to prevent sludge or scum from entering the leachfield and sump system and decreasing permeability even further. Every effort should be made to reduce the volume of influent from all sources such as showers, sinks, toilets, washers and disposals. Therefore, due to the high clay content subsurface soil, we are recommending the owners may want to consider creating a fund in which money is saved specifically to install an above ground septic system, commonly referred to as a "mound system" at some time in the future. The mound 3