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• Mr. Harlicker May 21, 2003 Page Two ➢ The drainage area of Structure #1 is approximately 253 acres. The hydrologic factor provided for the area is represented by the NRCS methodology and is provided with a Curve Number(CN) of 49 and a Time of Concentration of approximately 2.07 hours. Since the ponding limits downstream of this area are primarily influenced by this drainage area size, is the long term land-use of this 253 acres designated to remain the same? ➢ It appears that the Time of Concentration shown on your Curve Number calculation sheets is not the same as the number used in TR-20 for areas Pre-8 and Post-8. The number used in TR-20 appears to be the more suitable Tc for area 8. This will not affect the calculations if the number used in the program is the correct number. ➢ The Structure#5 ponding area appears to include area Post 31 in the ponding calculations of the Post-developed conditions. The street and planned culverts for the crossing of the ponding area shall have sufficient capacity to convey flows to maintain fairly equal pond levees on each side of the street. ➢ The 100-yr. HWL for Post 33 (888.50) does not meet the required 1.0 feet of freeboard to the low point on Xerxes St. NW (888.86) > The existing 100-year elevation of area Post 2 is listed as 888.6. Please submit the calculations used to determine this elevation. • > The total off-site discharge for the proposed conditions is greater than the total off- site discharge of the existing conditions. Any excess discharge must be detained on-site. > Storm sewer calculations should be submitted during the final design phase. The preliminary layout appears to be adequate for the proposed improvements. > The quality control ponds need to be designed using N.U.R.P. standards, found in Ch. 4 of"Protecting Water Quality in Urban Areas—Best Management Practices for Minnesota" B. Preliminary Utility Plan • This entire development will be a long dead end serviced off of Waco Street until such time that the seven-acre site to the north is developed and watermain can be looped back to Waco Street. Therefore, we will require an additional looping of the watermain to the existing watermain in Waco Street off of 184th Circle to provide some redundancy to the system. • The Elk River Municipal Utilities water model is being investigated to determine if any of the watermain in the West Oaks development needs to be oversized for fire flow since the development is on the far end of the existing water system. If any does need to be upsized, we will provide that information to the developer's engineer so that is can be shown that way in the final construction plans. • At the west end of 183rd Avenue, an additional catch basin should be added between the last two structures to ensure that the storm sewer is maintained in the public right- of-way. • • Hydrant and valve locations will be reviewed and commented on at the final plan stage. Ltr-051903 Harlicker Howard R. Green Company