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RECEIVED <br />'ri&DA <br />ENGINEERS • ARCHITECTS • PLANNERS <br />MEMORANDUM <br />To: Jim McNamara <br />Copies To: Martin Rafferty <br />From: Thomas D. Prew, P. E. <br />Date: June 20, 2006 <br />"UN 2 1 M <br />1500 Piper Jaffray Plaza <br />444 Cedar Street <br />Saint Paul, MN 55101-2140 <br />(651)292-4400 <br />(651) 292-0083 Fax <br />www.tkda.com <br />Reference: Septic Pen -nit <br />5751 Hvtrail Avenue <br />Proj. No.: <br />Routing: <br />City of Lake Elmo, Minnesota <br />13593.000 <br />As requested, we reviewed the Pen -nit Application for a septic system at the above address. Because of the <br />history on this lot, a review of the previous work done and previous approvals is needed. <br />History <br />Because of previous filling and poor soils, this lot and the two to the south, received City Council approval <br />for a performance based septic system in 2000. This plan was designed by North American Wetland <br />Engineering (NAWE). Included in the approval was a plan for monitoring and mitigation. The mitigation <br />plan included procedures for repairing and expanding the system should it not perform correctly. <br />According to NAWE this system was not built according to the plan. As a result, mechanical difficulties <br />have plagued this system and created a difficult situation for the property owners. <br />Current Proposal <br />The property owners have submitted a Permit Application asking to abandon the existing pretreatment <br />system and drainfield and construct just a drainfield. The septic tanks would remain, with one tank being <br />converted to a filter tank. They have submitted a completed site design and wish to have it approved. <br />Design Review <br />The soils on this site have always been the concern. The original design, approved by the City Council, was <br />conservatively designed to allow for variations in the fill soil. A review of the two designs is listed below. <br />Proposed Design <br />Approved Design <br />Design Flow <br />450 GPD <br />750 GPD <br />Disposal Area <br />1,000 SF <br />10,000 SF <br />Pretreatment <br />None <br />Sand Filter <br />The soil borings between the approved system and the proposed system differ somewhat. The approved <br />design lists the soil as fill with a high water table and clay below the fill. The proposed design does not list <br />the area as fill, does not specifically detail the water table and shows sand below 48 inches deep. Based on <br />An Employee Owned Company Promoting Affirmative Action and Equal Opportunity <br />