11-07-1977 Planning Packet - Laserfiche WebLink

Home Browse Search

Page -9* POTENTIAL OF SOILS FOR ON-SITE WASTE TREATMENT According to the reconroended "Ordinance and Code Regulating Individual Sewage Disposal Systems" published by the Minnesota Department of Health in 1971 **No soil absorption system shall be installed in an area i^ere the watertable is at any time less than 6 1/2 feet below ground level or 4 feet below the bottom of the drain field trench". This line of thinlcing 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 WPC-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 trmich system to meet this recjuirement. An example of the innovative systems is the mound system. In the mound systm the seepage bed or trench is elevated by the use of sand fill to provide the 3 foot separation distance between the bottom of ^e seqpage trench and a barrier layer such as the watertable or bedrock. In the preliminary *'Recomn^ed 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 system. Concern about tMs minimum separation distance is due to the fact that it takes approximately 3 feet of unsaturated soil material to properly treat the septic tank effluent, toce the septic tank effluent reaches a watertable treatment of the effluent ceases. This results in the ores ence of a polluted water body near the surface. Additional iiqjuts of effluent and natural water in the area may result in surfacing of the effluent and/or the backing up of the effluent into the house. TTiis ere ates not only a nuisance to the home owner, but can also pose a health hazard if the surrounding area is well populated. The best indicator available for determining the maximum height of a seasonal watertable which often occurs in the soils of Hennepin COunty is the presence of soil mottles. Mottling is a distinctive coloration of grey with red and yellow splotches in the subsoil. Any investigation of a proposed soil absorption (treatment) system site should include a determination of the depth at i^ich soil mottles occur. With this back ground the potential of the original soils mapped in this development ar< for treatment of septic tank effluent will be discussed. Areas of Peaty muck soils indicated by dark blue on the accompanying soils werlay are found in wetlands. The watertable in these organic soils is above or near the surface the entire year. These areas are unsuitable for the installation of any soil absorption system. >1 ' • .• f; a r;;-: 4;'-A f..■Mi mm The C soils with! durir in tY The n Howev for t absoi Areas on t> this 3 fee of ar at a Nessc seasc dical atior be ms recon mott] shall The I the n tabl< of tl evid< the ] mean* stanc Shor< seas( rate* this eith< Erin high in e: an ii canni a se: m