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2. Poorly designed systems <br />a. Deep cesspools (up to 15-20' deep) used as septic tanks, <br />with or without drainfi.eld. <br />b. Tank capacities extremely small for 1980's water use <br />habits. <br />C. Single tank systems of inadequate capacity or retention <br />times to treat the current flows. <br />d. Drainfields with inadequate hydraulic capability to <br />dispose of current flows, due to small size or natural <br />biomat buildup due to age of system. <br />e. Drainfields with inadequate piping, little or no rock, <br />or both. <br />3. Poorly located systems <br />a. Drainfields and non -sealed tanks located near or within <br />high water tables, causing premature system failures. <br />b. Drainfields located near hardcover which drains excess <br />surface runoff onto the drainfield. <br />4. Old systems subject to groundwater inflow and infiltration <br />especially where tanks are deep and a pump is used to discharge <br />effluent to elevated drainfiel9 sites. <br />As stated previously, a number of systems either discharge to the <br />surface or have backed up into basements. In both instances, a poten- <br />tial health problem is created as well as an odor problem. Add°- <br />tionally, althougr no ( ^*_amination problems have been documented, <br />well water contaminatioi. -ild occur since more than 1/3 of the exist- <br />ing wells are less that the Minnesota Health Department required <br />minimum of 50' from non -sealed septic tanks or drainfields. In fact, <br />3 wells are located only 15' from septic tanks or drainfields. The <br />potential exists for untreated septic tank effluent to migrate to the <br />well casing and then follow the casing down to the subsurface aquifer, <br />contaminating the water supply at its source. Note that well records <br />are on file for 37 of the 73 existing wells, with depths generally <br />100-150' deep in the northerly and easterly portions of the study <br />area, but 200-320' deep in the southwesterly quadrant. <br />Soil conditions in the area are documented in the Hennepin County <br />Soil Survey, which indicates that about 60% of the area is Anoka loamy <br />fine sand, with the remaining 40% consisting of various loamy and <br />wetland soils. In general, the soils on ti h, dry ground are suitable <br />for septic systems, although the actual ,il types observed by staff <br />in the field include inconsistent pockets of more clayey soils within <br />*.he Anoka mapping unit. As a general rule, a specific site shown as <br />)ntaininq Anoka soils on the soil survey may not necessarily contain <br />.pose soi Is. <br />4 <br />