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<br />Ms. Anne Norris <br />page 2 <br /> <br />Mav 14, 1986 <br /> <br />", <br /> <br />GrOWld water impact from the proposed on-site systems <br /> <br />'!'he staff recOlll1ll!nds the following measures be implemented to prevent <br />contamination of ground water by the proposed on-site wastewater disposal <br />systems. '!'he final EIS should contain a section which addresses these issues. <br /> <br />1. '!'he Agency has no rules regulating the density of on-site systems. <br />However, the issue of density is of significant concern due to the 1 <br />likelihood of nitrate contamination of grOWld watllr. Based upon the <br />results of a high rate soil absorption report prepared by MPCA staff in . <br />1984, we recCllllllend that the separation distance between drainfields be the <br />same as the separation distance between drainfields and wells. '!'his <br />measure should get the on-site systems spread out so that nitrate will be <br />IllOre effectively diluted. However-, this measure alone roay not COlllPletely <br />mitigate problems. <br /> <br />2. '!'he average lot size is 2 1/2 acres for the project, and the overall <br />project density is roughly one unit per five acres. '!'his overall density <br />exceeds the Metropolitan council's lo-acre rural density guideline <br />included in its Water Quality Management policy plan. '!'he overall density <br />also exceeds the density guideline of one unit per 10 acres for a rural <br />area contained in the city of RamSey'S comprehensive plan. However, the <br />city has interpreted this guideline to mean that the densities apply to <br />total existing acreage in the entire rural service area. We recCllllllend <br />that the Metropolitan council's density guidelines be adhered to for the <br />project or a site specific hydrogeologic study be conducted to evaluate 2 <br />the potential impacts due to the proposed residential density and on-site <br />systems. More stringent programs covering operation, maintenance. and <br />post-installation inspection for private sewer systems should be <br />implemented as required by the water Quality Chapter of the Metropolitan <br />council's Developuent Guide if the project density exceeds one unit per 10 <br />acres. <br /> <br />3. '!'he on-site systems should be designed and constructed according to <br />Minnesota Rules Part 7080, Individual sewage Treatment system standards. <br />'!'he city should have this rule incorporated into its local construction <br />ordinances. Moreover, construction at each hauesite must be IIIOnitored to 3 <br />ensure that precautions are taken to protect the wastewater disposal site . <br />from detrimental construction practices. '!'he drainfield site should have <br />litUe construction activity. Soil fill from site excavation cannot be <br />disposed of on the drainfield area to ensure homogeneous soil conditions <br />or as close to naturally occurring soil conditions as possible. <br /> <br />4. It is not possible to determine from the soils data presented in the draft <br />EIS that all lots are suitable for placement of an on-site system. Site <br />specific data must be collected to do so. '!'he soils maps only give a good <br />general indication of the feasibility for placement of on-site systems. 4 <br />'!'he biggest problem regarding the feasibility of on-site systems is <br />identification of the water table. For example, a number of lots, as <br />platted in Figure 27 at page 66 with the soil overlay, show a large <br />portion of the lot on marginally or seriously severe limiting soils. <br />Because of gradual transitions and the degree of accuracy of mapping, <br /> <br />. ! <br /> <br />r <br />I <br />\ <br /> <br />-- <br /> <br />l <br /> <br />\ <br /> <br />I <br />i <br /> <br /> <br />I <br />I <br /> <br />-73- <br /> <br />