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i r t G.7 No problems are anticipated for th`is septicsystem, (§ ) p p � pother than typical lifespan concerns. An engineered septic system will not have to be installed for this project unless there is a failure, or if depth to the water table and/or flooding becomes a concern. A 50% standby replacement area is located directly to.the northwest of the proposed letchfield area. Bec of 7.5 ecp water table determination, the leachlines cannot be installed any deeper th n 30 i hes e ow grade so that a five- foot separation distance is maintained between what can E be considered thelighest depth to groundwater and the soil-effluent interface. The highest depth of groundwater is based on the surrounding topography of the disposal area, and the recent heavy rains that certainly would have had an effect on raising the water table elevation. The domestic well proposed to serve Manufactured Home Unit#4 is to be drilled next to the building pad for this structure, with concurrence from EHD. Found in Appendix D is the Draft Log of Boring completed near the domestic well location for Unit#4. It appears from this Log that two permeable strata may be conducive for acceptable well water production. Te depth intervals are from 52 to 57 ft and from 72 to 78 ft below grade. EHD will require a 15 t,! 20 of cement seal in this well. - If unusual or unforeseen conditions are encountered during emplacement of the septic system for Manufactured Home Unit#4, Chesney Consulting must be contacted for assessment of the situation. These conditions may include, but are not limited to: 1.) Encountered groundwater during septic system installation, 2.)Unusual soil conditions in the leachline trenches such as high moisture content, peat or highly organic/clayey soil, and 3.) Any changes that may be made to the system, as proposed. It is important to recognize that all septic systems have a lifespan, which is dependant on several factors and is therefore difficult to determine. 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 in the disposal area consist of sand, silts, and some clays, marginal aerobic conditions may prevail over time which may allow biomat formation to remain in g Yp Y equilibrium. Since the leachlines will be installed higher in elevation than typical (30 inches vs. 42 inches), there will be a greater opportunity for oxygen intrusion from the atmosphere, thus theoretically assisting in biomat degradation. However, soil moisture content of the subsurface soils will play an important role in septic system operation and lifespan. For example, if heavy rains are experienced in any given winter, subsurface soil moisture content will increase dramatically, thus decreasing permeability. In unsewered areas and/or areas that have been, or currently are under agricultural production, it is highly recommended that bottled water be used for drinking and cooking purposes. It is my understanding that C.C.R.C. Farms provides bottled water for drinking and cooking purposes for all their on-site employees who reside on Mandeville Island. Page -6- Chesney Consulting i