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1%WW ..00 FFwell er is 45 ppm. The construction details and depth of this domestic well were These test results follow the general trend of lower nitrate concentrations the closer roximity to a river. The agrichemicals DBCP and EDB were below detection limits h is equivalent to non-detect(ND). CONCLUSIONS The perc test result for Parcel "1" suggests absolute minimal percolation of septic effluent at the typical leachline depth of 42 inches. As stated by Mr. Pombo, there have not been problems with his septic system, which may be attributed to keeping an extremely close watch on water usage. This shallow test depth also reveals there will be sufficient distance for "treatment" of septic effluent before it encounters the groundwater table. It was also evident that percolative capacity decreases with soil saturation, over time. Since the perc rate obtained was extremely poor, the San Joaquin County Environmental Health Department will require that if a new structure is built, or moved onto the subject properties (both Parcel "1" and/or the Designated Remainder), there must be two and preferably three percolation tests conducted in the exact location of the proposed leachfield area. The average perc rates obtained from these tests must be exceptionally good (less than 60 min/in) for a conventional system to be installed. Given the perc test results completed for this study, it is highly doubtful that favorable rates can be achieved. Therefore,the Environmental Health Department will stipulate that an engineered system must be installed for any fixture dev An engineered system is commonly referred to as a "mound system." The leachfield is built above grade, consisting of gravel and sand, which must be hydraulically protected during the rainy season to prevent inundation. It is imperative to keep wastewater flows to an absolute minimum with this design. A 50% standby replacement area must be incorporated into this type of system and all related septic system structures and a possible new domestic well must comply with the published "distance" requirements from property borders, roads, irrigation fields, etc. It is important to note that all septic systems have a lifespan. This lifespan is dependant on several factors and is therefore difficult to determine. Although repairs and additions were not on record at the Environmental Health Department, it is evident that septic systems in this area will have a definite lifespan due to the indigenous clay soils. Septic system leachline failure would primarily result from 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 shallow subsurface soils consist mostly of clay soil material, anaerobic conditions will prevail over time which may hasten leachfield failure. Page -3- Valky Ag Research