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Fat is yet to be enforced may restrict the installation of seepage pits (Assembly Bill 885). aw is implemented, EHD may require the installation of seepage pits for this project for g reasons: 1.) They are the typical and principle effluent management structure installed 2.) There is a distance of approximately 70 - 25 =45 feet between the bottom of a t 25 feet b.g.s. and the current groundwater depth of 70 feet, 3.) It is unlikely that groundwater will ever approach within 10 feet of the bottom of a seepage pit in this area (groundwater at 35 feet), 4.) Seepage pits allow head pressure buildup to force effluent into the underlying soils. The underlying soils possess increasing moisture content with increasing depth. This may be due to last winters' heavy rainfall during 2004/2005. High moisture content soils are beneficial for the suppression of nitrification, and the promotion of denitrification of nitrate molecules that may have formed through nitrification in the upper,more favorable soil environments. EHD requires that there be sufficient distance for"treatment"of septic effluent before it encounters the groundwater table. This distance is normally regarded to be five feet in leachlines and 10 feet with seepage pits. Therefore, sufficient distance exists between the bottom of a maximum depth seepage pit of 25 feet and the current groundwater depth of 70 feet. (§ 6.8) The number of leachlines, sumps and/or seepage pits, and septic tank sizes are unknown at V this time for any future residential structure since the number of bedrooms is unknown. (§ 6.7) No problems are anticipated for any future septic system on the property, other than typical lifespan concerns. Engineered septic systems will not have to be installed for this proposed subdivision unless there are continual failures. Each new system must have at least a 50% standby replacement area incorporated into the design of the septic system. All related septic system structures and the new domestic wells must comply with the "distance" requirements from property borders, roads, irrigation fields and irrigation ditches, etc. It is important to recognize that all septic systems have a lifespan, which is dependant on several factors and is,therefore,difficult to determine. 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 on the property consist of silts, clays and hardpan, anaerobic conditions may prevail over time which may decrease the expectant life of any new leachfield. Lifespan will be dependant upon the efficiency of the deep septic system structures (i.e., sumps or seepage pits) to manage effluent flows. If the leachlines are installed high in elevation, or by using Infiltrator Chambers, there will be a greater opportunity for oxygen intrusion from the atmosphere, thus theoretically assisting in biomat degradation, along with promoting evapotranspiration. in addition, soil moisture content of the subsurface soils will play an important role in septic system lifespan. For example, if heavy rains are experienced in any given winter, subsurface soil moisture content will increase dramatically,thus decreasing permeability. Page -5- Chesney Consulting