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• Mr. Scott Harlicker February 20, 2002 Page Two • The proposed improvements require some filling of the wetland area. These are noted on the plan with identified mitigation areas. Obviously, this project will need to go through a Technical Evaluation Panel for the wetland issues. B. STORM DRAINAGE Detailed storm drainage calculations were provided. These have been reviewed. In general, the storm drainage concept is fine. However, there are a number of questions and modifications that need to be answered or made. These include the following: • The report does not clearly show a comparison of the total of pre and post total site discharge rates. It appears as though the post-development rate is less than the pre-development rate for the 100-year event. • The 100-year peak pond elevations are summarized in the drainage report. The 100-year high water elevations (100-year HWL) are shown on the preliminary grading plan for ponds 40, 42, 43, and 44. The grading plan should show the 100- year HWL for all ponds in the development. • The 100-year HWL for pond 66 is shown in the report as 945.4; the calculations submitted show this elevation to be 945.0. This should be corrected in the report. • The calculations should be revised to show the normal water level to be at the outlet • elevation at the beginning of the 100-year event. This will affect the calculated 100- year HWL for most of the ponds. • Pond 8 along Ranch Road is shown to have no outlet other than overflowing the curb onto 215th Avenue. Storm sewer is shown in the area. An inlet should be added behind the curb to drain this area. • The trail crossing the ditch between Ranch Road and 215th Avenue will require a culvert within the ROW of Ranch Road. • The EOF between Lots 10 and 11, Block 1, is shown at an elevation of 947.0. The low point at the intersection of 214th Avenue and Queen Street is 945.0, leaving a potential pond depth of 2.0 feet in the road should the storm sewer become obstructed. The low point should be raised or the EOF should be lowered to allow a maximum ponding depth of 1.0 foot. • The EOF between Lots 19 and 20, Block 1, should be moved to the lot line between Lots 18 and 19. • Details of the pond outlets should be provided in the drainage report. Many of the ponds in this development have a weir outlet. Are these constructed with rip-rap, treated timbers, or some other materials? • No water quality calculations have been provided to determine if adequate dead storage has been provided. • No analysis of the 1-year or 10-year events has been provided. • The calculations show a curve number of 39 for lawn (good) soil type A in the developed condition in the yard area of the lots. Typically, residential developments import topsoil for lawn and the soil type in the yards is more characteristic of type B soils. The curve number for this case would be 61. The calculations should be • revised to show a curve number of 61 for yard areas. Howard R. Green Company Ltr 2-20-02 Harlicker.rev CONSULTING ENGINEERS