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• • Hailey Manor Page 2 August 26, 2003 City of Lino Lakes, Minnesota Drainage and Stormwater Comments 1. The minimum building elevation floor elevation (including basement), must be the greatest of the following: 2 feet above the design flood elevation, 4 feet above the water table, or 1 foot higher than the emergency overflow elevation. Based upon the information provided, it would appear that several of the proposed units around the land locked drainage basin would need to be raised significantly, based upon the 10 year snow melt elevation. The groundwater elevations may also dictate adjustments to the proposed elevations. In addition, there are existing homes that do not meet the above criteria; one located just west of the property on Lois Lane, and the other on Lois Lane within the proposed development (both properties are adjacent to the existing landlocked basin). In this case, the developer must provide written assurance (technical proof) that he is not making an existing non - conforming situation worse (potential for drainage problems) by constructing the proposed improvements, described further as follows: The governing design elevation for the proposed development (according to the calculations submitted) is the 10 -day snow melt elevation of 906.8. Under the existing conditions and according to the survey, this is already a land lock detention basin, and without an emergency overflow. The lowest elevation (bottom) of the existing land locked basin appears to be at an approximate elevation of 906.7. One may argue that under the existing conditions, the highest flood elevation (particularly for snowmelt) would be higher than 906.7. However, this would need to be confirmed by calculations provided by the developer. Calculations for the existing 100 -year rainfall event have not been submitted as required. Calculations for the existing 10 -day snowmelt event must also be submitted. It must also be mentioned that the existing groundwater elevation (per the borings submitted) show a groundwater elevation of 902.5 near the two houses mentioned. The basement elevation of 904.2 for the house west of the property line is therefore less than the 4 -foot separation required. In summary, the existing house already fails to meet the City's criteria. Again, the developer must demonstrate that he is not increasing the chances for drainage or other water related problems for the existing houses. 2. New existing condition computations were not submitted. Previously submitted computations were used for the comparison of rate control. 3. An infiltration basin along Country Lane is proposed by constructing a 5 -foot gap in the curb. The City may feel that a 5 -foot gap in the curb is not acceptable. Therefore, the alternative (building a sump next to the existing CB) may be a more desirable option. 4. A Conditional Approval has been granted by the RCWD. Completion and conformance with all • outstanding conditions of the Rice Creek Watershed District must be adhered to, including the following: • The City and Developer must sign an agreement addressing the maintenance and management of stormwater facilities.