Agenda Packets - 1994/11/07 - Laserfiche WebLink

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COMSTOCK &DAVIS, INC. Consulting Engineers&Land Surveyors November 2, 1994 1446 County Road J (85th Ave.N.E.) Minneapolis, Paul Harrington Minnesota Community Development Director 55432 City of Mounds View 2401 Highway 10 Mounds View, MN 55112 • 612 784-9346 Tel. • 612 784-9395 Fax. Re: Sherwood Estates Preliminary Plat Dear Paul, I have reviewed the concerns expressed by Rocky Keehr in his letter of October 24, 1994 to you. The specific concerns to be addressed are the possibility of problems in house basements, or non-stop pumping (sump pumps) , and saturation and weakening of the subgrade of the street. Existing homes outside the plat will not be adversely affected by the runoff from the plat, or runoff changes as a result of the plat. This is due to the fact that the theoretical 100 year - 24 hour storm, and the theoretical 100 year - 10 day runoff elevations will not be changed by the proposed plat. In fact, the actual volume of water that needs to soak into the ground will be reduced. Also, the roadway construction and storm drain construction will provide an additional overflow for the landlocked area. The soil (coarse Alluvium) in the area of the ponds has a high permeability rate and will allow any water that does pond to quickly soak into the ground. Observation of the soils in soil cores has shown the soils to remain relatively dry or moist and not saturated, even immediately after heavy rainfalls. To my knowledge, no ponding has been observed in the low areas. The water table in the area of the ponds is at elevation 901 to 903. The lowest floor elevation allowed in this area shall be 907 (per Rice Creek Watershed District) . It is anticipated that because of the permeability rate of the soil, the water will not be in the ponding areas long enough to cause any problems in most of the basements. In the case of Lot 4, Block 1; Lot 2, Block 2; and Lot 4, Block 3, the close proximity to the ponds may necessitate raising the lowest floor elevation and/or providing sump pumps. Because of the history of the water table for the entire Mounds View area, it may be prudent to provide sump pumps (as most builders do routinely) in all the houses or raise the lowest floor elevation. The lowest point in the roadway (909.75 at centerline) is over 50' from the nearest ponding area. Coarse Alluvium soils are relatively stable, even when saturated. Since fill for the roadway will either be granular borrow or the coarse Alluvial soils from on-site, no problems with saturated or weakened subgrade are anticipated.