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FFFlood WATER INFORMATION epths and elevations are illustrated on maps published by the San Joaquin County and Water Conservation District. Unfortunately, The 1999 Lines of Equal Depth Maps do not illustrate the groundwater depth under the property in this locale. Consequently,the on-site domestic well was sounded to estimate groundwater depth. Mr. Pombo's well has a 10 ft high well casing riser, extending above the concrete wellhead. By standing on the pickup tailgate, I was able to insert the sounder into the well. The static water level was measured at 17.5 ft from the top of the well casing, indicating the water level is approximately 7.5 ft below grade. Considering that the filter bed area has been built-up three feet above existing grade, this places the depth to the water table at: 3 ft+ 7.5 ft= 10.5 ft below the top of the filter bed. If the filter 1� bed is typically constructed to be 18 to 24 inches in depth, then there will be sufficient distance between the soil/effluent interface and the existing depth to the water table: 7.5 ft + 3 ft = 10.5 ft above water table minus 2 ft at the soil/effluent interface= 8.5 ft between soil/effluent interface and the water table. Separation distance is generally accepted to be five feet. CONCLUSIONS The percolation tests reveal mediocre percolation rates of 31.3 min/in and 35.7 min/in for the filter bed as it currently exists. The percolation tests also reveal that there has been no significant soil compaction from the construction of the filter bed area to an appreciable extent. However, once effluent flows begin, in conjunction with rainfall, this constructed filter bed area will lose permeability. To what degree this loss in permeability will be, is indeterminable. Therefore, sufficient replacement area must be reserved, or be constructed at the time the filter bed is installed. The filter bed is currently 50 feet long by 50 feet wide. This should accommodate the primary filter bed, and possibly the reserve area. A large, open area exists to the west of the filter bed, so more than sufficient area exists for reserve or replacement. The existing filter bed is 120 feet from an irrigation ditch to the north and 350 feet from Mr. Pombo's domestic well. It is my understanding that Mr. Pombo's domestic well is on an adjacent parcel; therefore, a well will have to be installed on the subject parcel to serve this new home. It is important to recognize that all septic systems have a lifespan, which is dependant on several factors and is therefore difficult to determine. This lifespan can be from months to years. Septic system failure would primarily result from soil compaction from the introduction of septic effluent and rainfall, and the advanced formation of a"biomat" or"clogging mat" on the wetted soil/effluent interface. This mat is composed mostly of aerobic and anaerobic bacteria and bacterial products consisting of a slime of polyuronides and polysaccharides. If the soil/effluent interface is well aerated, a variety of soil microfauna such as nematodes and protozoa may digest the clogging mat bacteria. Since the import soils consist of fine-grained soil materials (primarily silts and clays), anaerobic conditions may prevail over time because of oxygen diffusion difficulty. This may decrease the expectant life of the filter bed. Page 3 of 4 Chesney Consulting