1975-03-11 Report on Variance - Laserfiche WebLink

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645-3601 TWIN CITY TESTING AND ENGINEERING LABORATORY, INC, REPORT OF: LABORATORY No. 9-5984 ENGINEERS AND CHEMISTS 662 Cromwell Avenue - St. Paul, Minn. 55114 The site is a residential lot and southern end of the lot, where a Minnetonka below. As previously garage with a walkout basement. WATER SHED INVESTIGATION SITE CONDITIONS DATE: March 7, 1975 PAGE. 2 slopes gently toward the south except at the extreme near vertical face drops approximately 30' to Lake stated, the site is now occupied by combined house and SOIL. CONDITIONS The soils encountered were lean and sandy clays to the depths of our boring These soils are generally typical of the Lake Minnetonka area and are not conducive LG the absorption of surficial runoff. That is, precipitation falling on the existing lot would normally fcilow the tupography and move directly to Lake Minnetonka with very little water actually being absorbed by the grassed areas. ANALYSIS AND RECOMMENDATIONS One method of controlling surficial drainage, which allows for the water to be returned to the groundwater system with minimal sedimentation, would be the installation of a French drain. This system consists of an excavation filled with clean granular material, which allows for surficial, runoff to be returned to the groundwater system while filtering out any sediment. However, this system would only be effective if connected to moderately permeable to permeable soils as opposed to the generally impervious (cohesive) soils encountered at the site. As the soils encountered at the site are cohesive, an alternate type of drainage system will have to be employed The use of a collection settling pond with an underlying drain- age trench system would appear to be the most practical approach from the standpoint of useability of the lawn area. With thissystem,the rear lot area would be contoured to a low swale to prevent the majority of the surface water runoff from draining directly to the lake. Then a series of sand filled trench containing perforated drain tele would be placed across the Swale with the pipes daylight)ng on the steep vertical face to the south The Swale and trench system would then be landscaped with a sandy topsoil as opposed to the cohesive material presently on the site. The sand topsoil and sand filled trenches would then drain and filter any water trapped within the swale area. The size of the Swale and number and dimensions of the underlying trenches would have to be based on such parameters as annual rainfall and vulumes of water directed to the ponding area Therefore, a competent engineering hydrologist f!rm, familiar Nith municipal drain fields and other related water, problems, should be contacted for the design of this system or other such systems adaptable to this structure. REMARKS The recommendations and suggestions contained in this report are our opinions based on the data which are assumed to be representative of the site explored, but because the area of AS AMUTUAL PROTECTION TO CLIENTS. THE PUBLIC AND OURBELVEE. ALL RC►ORTS ART SUBMITTED AS TNR CONFIOENTIAL PROPERTY OF CLIENTS. AND AUTHOR IZA TION FOR PUBLICATION OF STATEMENTS, CONCLUSIONS 00 EETRACTS FROM OR REGARDING OUR REPORT■ IB Rl SERvED PFNDING OUR WRITTEN APPROV11