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k, II. SOIL INVESTIGATION FINDINGS j' A. SUBJECT PROPERTY AND SURROUNDING STUDY AREA INFORMATION 'k The subject property was owned by Mr. Rinauro's father until recently purchased by Larry and Sharon Rinauro. It is located near the northeast corner of Etcheverry Drive and MacArthur Drive. It is bound to the north, south, east and west by single family residences, mostly on 1.5 acre parcels, and to the west by a new housing subdivision that is sewered and with much higher densities. The wide- range surrounding land use, and in particular upgradient land use, has been primarily in gravel mining and agricultural production for many decades. This is evidenced by the United States Department of Agriculture (USDA) Soil Maps for San Joaquin County for this area. Applications on file with the County Environmental Health Department reveal that there have been no permits issued for additions to existing systems in the one-half mile radius study area, which primarily includes Etcheverry Drive to the south and Almendra Way to the north. The apparent non-existent septic system failures in this area may be attributable to most systems having pits and sumps installed. However, the Environmental Health Department no longer allows sumps and pits in this area. , l B. SOIL PHYSICAL AND CHEMICAL CHARACTERISTICS E 1. SURFACE AND SUBSURFACE SOILS The shallow soil profile was determined during the drilling of the percolation test boring. Particle Size and Chemical Analysis was done on a soil sample from the bottom of the percolation test boring at 42 inches. The test results are denoted on the attached SOIL ANALYSIS REPORT. The soil has been classified by the laboratory as a loam, which correlates with the United States Department of Agriculture -Natural Resources Conservation Service (USDA-NRCS) classification of the on-site soils as a Stomar clay loam (#252). The Unified Soil Classification System (USCS) identifies this soil as a clayey silt(CL-ML). The fine soil material (clay and silt sized particles) promote biological treatment of the effluent. Biological treatment includes the destruction of bacteria and viruses, as well as promotion of denitrification. Gravel strata encountered at approximately eight feet below grade are illustrated on the attached logs of boring for water wells drilled in this area. Since septic effluent is composed predominately of ammonium (NHg) ions, the pH, along with the Cation Exchange Capacity, have significant influence on ammonium molecules. The pH of the soil, which is somewhat alkaline at a pH of 7.6 and may inhibit ammonium formation and stability. Secondly, the CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. The clayey subsurface soils have a comparatively high CEC of approximately 21.4, which should increase the retention of ammonium molecules for microbial uptake and nitrification suppression(nitrate formation). In cation exchange, a positively charged ion within the clay complex is replaced and released by another type of ion. Ionic exchange,through its effects on nutrient availability and acidity, has a tremendous effect on biological and chemical Page -2- { Chesney Consufting