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• • Thomas E. Wohlleber January 31, 1994 Page 2 soils and the western two-thirds being moderately well drained. Soil properties observed in the profile of TP7 typify those existing within the zone of well drained soils. The surface horizon is a plow layer and consists of silt loam to a depth of 13 inches. The silt loam subsoil occurs between 13 inches and 67 inches and is underlain by a horizon of loamy sand. Structure of the surface horizons is well defined. Properties observed in the profile of TP9 are typical of soil within the moderately well drained zone. The surface horizon consists of 12 inches of silt loam. The subsoil extends to a depth of 73 inches and has a texture of silt loam to heavy silt loam. Sandy substratum lies below. Structure of the profile is well defined to a depth of 35 inches below which it becomes weak. Soil mottling, localized zones of color differing from that of the soil matrix, was observed between depths of 35 inches and 73 inches. These mottles were orange to red-orange in color and were formed under unsaturated conditions following periods of saturation. Detailed soil profile descriptions are also attached. Conclusions and Recommendations Based on the observed soil conditions, use of the site for subsurface wastewater infiltration should be possible. The type of system required will be dependent on location of the infiltration portion of the system. Shallow conventional subsurface infiltration trenches installed in native soil would be suitable for the well drained zone in the eastern third of the site. System size would be determined using a hydraulic loading rate of 0.3 to 0.4 gallons of wastewater per day per square foot (gpd/ft2) of infiltrative surface bottom area. Use of the moderately well drained zone will necessitate use of a mound. This system requires installation of the subsurface infiltration area in sand fill placed on top of native soil. Infiltrative surface area of a mound would be sized using a 1.0 gpd/ft2 hydraulic loading rate. Cost of system installation would be determined by system type and the design flow. As previously indicated, system type would be determined by siting choice. Both conventional and mound systems would require multiple cells for long-term operation. However, use of a conventional system would require that a replacement area, equal to 100 percent of the constructed infiltration area, be identified and reserved for future use should the need arise. This area could not be used for other purposes which would result in compaction of the native soil. A mound system can be reconstructed in position should hydraulic failure of the infiltrative surface occur. Thus, the need for replacement area is unnecessary. Wisconsin regulations in the ILHR 83 code require a design flow of 750 gpd per classroom for a school which serves meals and has shower facilities. Utilizing information you provided for a previous feasibility study recently conducted, a design flow of 15,000 gpd would be required for a 20-classroom school. A design flow of greater than 5,000 gpd requires installation of two complete systems, each having a capacity no less than 75% of the infiltrative surface area required for a single system. Based on past experience, actual wastewater volume generation for such a facility is much less (i.e. 3,500 gpd at West Middleton Elementary School). It may be possible to obtain a variance through the Wisconsin Department of Industry, Labor and Human Relations to reduce the design flow. hwyklrep.doc 18-0132.00