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I I I Council Meeting Minutes June 9, 1992 Page 3 Public Hearina. continued Staff investigated constructing the storm sewer to Oakwood Drive's low point, and directing drainage to the low outlot in the back of homes on the east side of Oakwood Drive. Also, staff investigated reduction of assessments for previously assessed properties. The top sub-area is the Sky High area and has 4.4 cubic feet per second (cfs) of run-off. The existing storm sewer has 6.0 cfs of capacity and is more than adequate, however, problems arise when the small catch basin grates are plugged. This is why staff recommends installation of larger grates and berming of the boulevard to force the water to the catch basins. The next sub-area is the north end of Oakwood Drive. The combined run- off is 8.1 cfs and the storm sewer capacity is 7.5 cfs. The storm sewer here is a little undersized, but within reasonable limits. At the third sub-area, the combined run-off increases to 18.5 cfs, but system capacity drops to 4.8 cfs because the pipe slopes less going south of 3rd St. From 3rd St. south, the run-off not carried in the storm sewer is running 4 inches deep and extends to the center of the street. The fourth and fifth sub-areas add a total of 31. 1 cfs and is six times the storm sewer capacity. The alternate plan proposes construction of the same 30 inch storm sewer to the low point, but extends the 27 inch pipe to the park's southeast corner. A shallow basin would be excavated to collect the park runoff and funnel it to a device which sits six inches above the manhole. The plan includes six large catch basins on Oakwood, one on Silver Lane and one in the condominium parking lot. Estimated costs would be $55,000 and an assessment rate of $1,940 per acre, and is 65% of the original plan cost. Proper said the alternate plan is unreliable due to difficulty in catching runoff which runs fast and deep, The alternate storm sewer could be extended in the future, however, then the many catch basins are no longer needed and there is wasted costs. Another concern is the park's drainage basin near the sliding hill which poses a safety hazard. Also, the alternate plan does not correct the backyard drainage at 1827 and 1853 3rd St. Proper addressed directing drainage to an outlot behind the homes on the east side of Oakwood. While runoff could be discharged, there is no cost savings, and may increase costs, The same amount of pipe is required and water would end up in the same 60 inch storm sewer. The only area with sufficient clearance is between the homes on 301 and 349 Oakwood. Putting water in this low area may create problems for surrounding homes. Proper said Option A is to construct the original $84,000 project, and reduce the assessments by setting a $ 500 cap on individual assessments. The City would pick-up any amount over $500 which equals an additional $8,278.15. The assessments would range from $202.43 to $500, as compared to $202.43 to $1,235.03 for the original plan. Public Hearing Storm Sewer Improvement - Oakwood Drive Report 92-136 Resolution 92-061 Resolution 92-062