04-21-14-WS - Laserfiche WebLink

Home Browse Search

ARDEN HILLS CITY COUNCIL WORK SESSION—APRIL 21, 2014 12 There have been illustrative drawings showing how a regional storm water feature can be an amenity to the area providing passive recreational opportunities. But thus far there has been very little discussion with the Council about what their goals are for making this regional storm water feature a real amenity to the site and the City. The purpose of this agenda item is to begin this goal discussion. Public Works Director Maurer commented that before a real goal discussion can be conducted it is important to provide some detail regarding the various Federal, State and Regional agencies that may have jurisdiction over at least a portion of the things happening in the blue/green spine area. The first of these items is wetlands. Public Works Director Maurer noted that as discussed in the AUAR, there are 14.4 acres of wetlands on the TCAAP site. The largest single wetland, and possibly the most undisturbed wetland, is within the blue/green spine. It is a type 2/3 wetland approximately 4 acres in size. Examples of typical type 2 and 3 wetlands from the RCWD website are attached to the staff memo. This type of wetland generally does not have standing water but can be flooded seasonally. It is generally saturated ground a few inches below the surface. Vegetation is typically grasses, sedges and rushes. Public Works Director Maurer reported that there are two agencies that could have jurisdiction over each wetland. The first is the Army Corps of Engineers (COE) that has authority if the wetland is determined to be "jurisdictional" which generally means it is navigable or connected to navigable water. The second agency is the State Wetland Conservation Act (WCA) which is administrated by RCWD as the Local Government Unit (LGU). A Technical Evaluation Panel (TEP) would review the County's application to address the wetlands on the site. WCA rules require what is called sequencing whereby the applicant must show efforts to avoid, minimize, rectify, reduce and replace in that order. So even if the County tries to remove all wetlands from TCAAP (most of the 14.4 acres are degraded areas), the final say on what happens to the 4 acre wetland in the blue/green spine rests with possibly the COE and WCA. Public Works Director Maurer indicated that the next agency that will have say over how the blue/green spine looks and operates is the Rice Creek Watershed District (RCWD). They are the agency responsible for storm water runoff quality, volume control, and runoff rate control. Generally the RCWD water quality requirement is to provide storage for 1.1 inches of rainfall over the impervious area of the entire site. This will result in a fairly large volume of water; approximately 20 acre-feet of infiltration area or 40 acre-feet of ponding. In addition, as detailed in the AUAR, the rate control requirement imposed by RCWD for TCAAP will be 80% of the predevelopment peak runoff rate. This again will result in a significant amount of ponding to detain the runoff and meter it out at the maximum allowable rate (the actual maximum rate will depend on what RCWD determines is the pre-existing condition). As much as possible these ponding and quality control requirements are expected to be met utilizing the blue/green spine area(actual calculations for these requirements are part of the City/County RFP). Public Works Director Maurer stated that as part of our new MS4 permit, the City will be required to come up with policies and regulations for storm water management dealing with Total Phosphorus and Total Suspended Solids in the runoff stream (RCWD will be doing the same). These requirements could possibly be more restrictive than the current RCWD regulations.