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Effluent that infiltrates and percolates through this fine soil material (clay and silt sized particles) will undergo biological treatment of the effluent before reaching the water table (�73 ft below grade). Biological treatment includes the destruction of bacteria and viruses. For percolation test purposes, the property was divided into three separate areas of approximately .2.07 acres each to represent three proposed parcels.. These three areas are illustrated on the enlarged Assessor's Parcel Map and referenced as the "West Parcel," "Middle Parcel," and "East c-J Parcel." The remaining 1.03 acre area where the above-referenced house is located, could not be perc tested due to "distance from well" constraints. There is a domestic well and a non-functioning irrigation well near the house. Consequently, a .150-foot distance could not be maintained from these two wells. In addition; there are no domestic wells to the north or east of the subject property within 50 feet of the border, and therefore, not within 150 feet of the percolation tests. The surface and subsurface investigation of the property soils under the three proposed parcel areas began with the use of a truck-mounted drill rig. Solid stem auger and a split-spoon sampler were used to drill the percolation test borings and to.sample soil at the prescribed depths. Logs of boring for each of the three test borings are found in Appendix 4 and illustrate the / M subsurface soil characteristics encountered in each of the three 24.5 foot percolation test borings. i A Standard Penetration Test (SPT) was conducted at the referenced depths to illustrate the physical condition of the both cohesive soils (silts and clays), and cohesionless soils (sand and gravels) found at the deeper depths. All of the SPT test results indicate the subsurface soils to consist of dense and very dense cohesionless soils, and hard cohesive soils. The logs illustrate the variability of the strata encountered. Classification-by the USDA and Unified Soil Classification System (USCS) includes a sandy loam(sandy silt - SM), a loam (silt - 3� ML), a clay loam(clayey silt - CL-ML), and a silty clay (ML-CL). The surface soils at the west i end of the.property have a lower clay content, which becomes increasingly heavier to the east of the-property, as noted: The West Parcel soils contain a comparatively lower clay content soil of 14%, which increases to 28% for the Middle Parcel, and to a very high clay.content of 42%.for the East Parcel. The deeper subsoils show a reverse of this trend with the Middle Parcel and East Parcel having lower-clay content and higher sand content subsoils down to the 24-foot depth. Although the deeper subsoil clay content decreases from west to east, there still remains sufficient clay at the deeper depths to maintain biological activity. A'Water Well Drillers Report (Well Log) for a well drilled at 7425 Orford Road can be found in . Appendix 7, along with other surrounding Well Logs. The Orford Road Well Log illustrates the underlying lithology to be clay from the surface to 64`feet. As referenced above, soil borings completed for perc testing indicate a sandy loam at.the 10 to 24 foot depths at the middle and-east sides.of the property. From 64 feet to 70 feet, which is the near the depth of the current static _ water level, is a fine sand stratum. Below this stratum are intervening strata of clay and sand down to a blue clay stratum at 250 feet. This may be the top of the Corcoran Clay layer. Particle Size Analysis discussed above, and Nitrogen Contents for each of the tested soil samples are summarized in the following Table. (Note: Samples from the intermediate (-12 feet) depth and the deep depth (24 feet) were not tested for the Middle Parcel since these deeper soil physical characteristics were very similar to the East Parcel). Che mey ConsultiV