Project Packet - Laserfiche WebLink

Home Browse Search

Page W. 1'UTEVI'IAl. OF SOILS FUR oN-5IT1: iv.xsTi. 'rPj..xr�axj According to the recommended "Ordinance and Code Regulating! Individual Stwage Disposal Systems" published by thc Minnr_aota Department of Health in 1971 "No soil absorption system si-u*: ' ' e installed in an area where the watertable is at any time less than ti 112 feet below ground level o- 4 feet below the bottom of the Grainfield trench'. '111is line of oiriki.ng has changed somewhat over the past 6 years to re- flect research results conducted in various areas of the county. The proposed Minnesota Pollution Control Agency WK-40 "Individual Sewage Treatment Systems Standards" states only that ;The bottom of trenches and beds shall be at least three feet above the watertable or bedrock" and allows for installation of additional innovative systems other than the standard subsurface trench system to meet this requirement. An example of the innovative systems is the mound system. In the mound system the seepage bed or trench is elevated by the use of sand fill to provide the 3 foot separation distance between the bottom of the seepage trench and a barrier layer such as the watertable or bedrock. In the preliminary "Recommended Practices for On -Site Sewage Treatment Systems" prepared by the City of Orono the 3 foot separation distance is implied when the highest point of groundwater must be greater than 5 feet for installation of a standard soil absorption sN•-tem. Concern, about this minimum separation distance is due to the fact that it takes approximately 3 feet of unsaturated soil material to properly treat the septic trunk effixnt. Once theseptic tank effluent reaches a water - table treatment of the effluent ceases. This results in the presence of as polltiml water b6ly near t e sup ace. Additional inputs of effluent .ur' natural water in the area may result in surfacing of the effluent and/or the backing up of the effluent into the house. This creates not onl}• a nuisance to the home owner, but can also pose a health hazard if the sur- rounding area is well populated. The best inaicator available for determining; the maximum heir:ht of a sea- sonal watertable which often occurs in the soils of tlennerin County is the presence of soil mottles. Mottling; is a distinctive coloration of grey with red and yellow splotches in the subsoil. Any inveetig;ation of a pro. Ix)sed soil ahsorpt ion (treatment) tiYston site should a determ- ination of the depth at which soil nettles occur. With this backgtt'' ind the potential of the original soils mappcxt in this de elo;ner.t ..rea for treat.. :cant of septic tank effluent will be discussed. The areas of tkimel soils .uia i�iiclit-6 ;h+ .he medium blue color on the soils overla%- ii;ive the hi -hest watvtt.c ,i. i,ithin 1 foot of the surface. This water may persist for several month, during the year.