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07-03-1995 10:24 784 3114 MOUNOSVIEW - PUBLIC WORKS P.02 o T.O3.'9S 11:19 FAX SEH ST. PAUL Q002:002 • i • t MEMORANDUM ST PAUIL.MN 0 MINNEAPOLIS.MN 0 ST.CLOUD.MN u CHIFPEWAPALLS M O M OISON.W! TO: Paul Harrington,City of Mounds View FROM: Rocky J. Keehn,Water Resources Engineer DATE: July 3, 1995 RE: Mounds View,Minnesota Review of Item 13.5 in the Purchase Agreement Between the City of Mounds View and Watson Investment SEH No. A-MOUND94O2.00 • We have completed a preliminary review of the above mentioned item in the purchase agreement. • The agreement states that"the future detention pond to be constructed on the northern portion of Oudot A will be constructed at Seller's sole cost and expense and will be constructed according to Buyer's specifications". There are two types of ponds that may be required as part of the development projects in the City. The first is a retention pond or basin for water quality improvements and the second a detention pond for rate control. Since the agreement was signed after the Local Water Management Plan(LWMP) was approved, definitions in the LWMP describe what is a detention pond and what is a retention pond (unless stated otherwise in the purchase agreement). In the LWMP, a detention pond Is defined as: "Any area that temporarily detains storm water runoff for the purpose of storm water management. The area does not have a normal surface water elevation, that is it is dry during periods of low precipitation." A retention basin is defined as:"Any area that retains all runoff to that area, that is, an area without an outlet. A retention area is referred to as a landlocked area." Detention and retention ponds can also be used in combination to provide both water quantity and quality benefits. Based on the language in the purchase agreement, the City may allow Outlot A to be used for a detention pond for the developments,but not as a retention pond. Retention ponding, therefore, is the responsibility of the developer. The developer can provide on-site retention ponding or work with the City and permitting authorities to provide retention ponding in Outlot A. Kelly Bettendorf reviewed Item 13.5 to determine permit requirements if the City constructs a detention pond in Outlot A. Her review(a memorandum to Rocky Keehn) is attached. It appears • that any work done in Outlot A would require permitting We also estimated the amount of on-site retention ponding required for Lots 1, 2 and 3. The analyses was done using a Lotus spreadsheet called PONDSIZE developed for the Vadnais Lake