11-12-1996 Council Packet - Laserfiche WebLink

Home Browse Search

TO: FROM: DATE: Mayor and City Council Ron Moorse, City Administrator May 30, 1996 '» •’ SUBJECT: MCWD Chanees to Storm Water Management Rules Funding for "Regional" Water Quality Ponding Facilities Staff recently met with MCWD representatives to discuss a recent change in MCWD rules which affects projects in Orono. The rule change allows for developers of sites smaller than 40 acres to pay into a district storm water fund in lieu of providing the ponding facilities necessary for water quality purposes on site (at MCWD’s discretion). At this time it is not possible for developers in Orono to take advantage of this change because it requires a cooperative agreement to be in place between the MCWD and the city for regional stormwater ponding facilities. The reasoning behind this rule change is that on small sites (less than 40 acres, and particularly less than 10 or 20 acres) it is either not possible to construct a pond which adequately handles storm water in terms of water quality or it is not efficient to do so, or both. In order tor a pond to be effective regarding water quality it must have certain depth and slope characteristics which require a minimum 1/2 acre foot print. Water quality ponds that are larger (1 to 5 acres in area) have been found to be much more effective at enhancing water quality than smaller ponds. Current stormwater rules require ponding that meets water quality standards. On small sites or subdivisions, it may not be practical to require a pond meeting water quality standards. Rather than simply allowing the developer to avoid this requirement, the MCWD rule provides an alternative that does address water quality needs. The developer pays the amount it would have cost to build the water quality pond into a fund to be used to construct larger water quality ponds to serve wider sub-regional needs. Currently on small parcels, or in relation to small subdivisions, the stormwater ponds are developed to meet storm water quantity control requirements. These ponds do not meet the size and other requirements needed for effective water quality treatment. The amount of land required for a water quality pond is substantial in relation to the land area of small subdivisions. The water quantity ponds provide some level of treatment to the water prior to discharge. However, what happens in fact is that because the water quantity ponds do not adequately treat the water in terms of water quality, the city’s wetlands are serving this purpose. Although this is as called for by the city’s Comprehensive Plan (which dictates use of our wetlands to filter stormwater before it reaches the lakes) and was state-of-the-art at the time it was put into effect; this has been replaced by new thinking that calls for stormwater to be substantially filtered in a water quality pond prior to being discharged to a wetland. The concern is that if wetlands are serving heavily as filters of stormwater they will over time be degraded by the sediment and debris which they are filtering from the stormwater. The concept of larger water quality ponds serving substantial portions of sub-watersheds has substantial potential benefits. However there are also substantial obstacles to this approach. These include the fact because there are so many wetlands in Orono it may be difficult to get