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3. Consider construction of Stormwater Improvements at Kerber Park Pond CITY OF CHANHASSEN 7700 Market Boulevard PO Box 147 Chanhassen, MN 55317 Administration Phone 952.227.1100 Fax 952.227.1110 Building Inspections Phone: 952.227.1180 Fax: 952.227.1190 Engineering Phone 952.227.1160 Fax: 952.227.1170 Finance Phone: 952.227.1140 Fax: 952.227.1110 Park & Recreation Phone 952.227.1120 Fax 952.227.1110 Recreation Center 2310 Coulter Boulevard Phone: 952.227.1400 Fax 952.227.1404 Planning & Natural Resources Phone: 952.227.1130 Fax: 952.227.1110 Public Works 1591 Park Road Phone 952.227.1300 Fax: 952.227.1310 Senior Center Phone 952.227.1125 Fax: 952.227.1110 Web Site www.ci.chanhassen.mn.us 3 Memorandum To: Park and Recreation Commission From: Terry Jeffery, Water Resources Coordinator r Todd Hoffman, Parks and Recreation Director -/II DATE: April 22, 2008 RE: Kerber Pond Water Quality Improvements - City Project No. 08-01 REQUESTED ACTION (Simple Majority Vote Required) Staff is recommending that the Park and Recreation Commission recommend the City Council approve Bid Alternate No.3 to the 2008 Laredo Street Reconstruction Project for construction of stormwater improvements in Kerber Pond Park. BACKGROUND The Lotus Lake Watershed is a fully developed watershed. The majority of the development occurred prior to National Urban Runoff Program recommendations. As a result, there is approximately 22 acre feet of storage in a watershed that has upwards of 210 acre feet of runoff during a 10 year rain event. This lack of treatment for stormwater runoff has led to degradation of the water quality of Lotus Lake and other surface waters in the watershed including wetlands and shallow open water features. In addition, the lack of storage has resulted in pond failures, accelerated erosion in channels and along shorelines, surcharging of stormsewer conveyance systems and backyard flooding. All of these factors prompt the need to identify areas where stormwater treatment can occur. A neighborhood meeting was held on March 20, 2008. Several members of the Lotus Lake Water Quality organization and two neighbors attended this meeting. A public hearing was held before the Park and Recreation Commission on March 25, 2008. Over fourteen residents were in attendance at this meeting. Many of them spoke against the plan due to a variety of concerns. These concerns included: 1. Safety due to depth of water and duration of inundation; 2. Access to trail through the backyards; 3. Privacy issues due to the proximity of the trail and removal of screening vegetation that currently exists; 4. Pollution in the ponds; 5. Long term maintenance; The City 01 Chanhassen . A growing community with clean lakes, quality schools, a charming downtown, thriving businesses, winding trails, and beautiful parks. A great place to live, work, and play. Park and Recreation Commission Kerber Pond Water Quality Improvements April 22, 2008 Page 2 6. The effect on property values; and 7. Why Bid Alternate 2 wasn't the preferred choice. We have worked with the consulting engineer, Kimley-Horn & Associates, to address these comments. The following is a discussion of how these items were addressed: 1. Pond Safety The ponds are designed to drain in 48 hours. This is accomplished by installing engineered soils which provide for a rapid infiltration rate, a layer of coarse aggregate material which provides additional storage underground, and the installation of drain tile which will route water into the stormsewer system. Rainwater garden 1 has a bottom elevation of 986 feet and an outlet elevation of 987.5 feet. Rainwater garden 2 has a bottom elevation of 987 feet and an outlet elevation of 988.5 feet. There is a portion of the garden with a bottom elevation of 986. So while a portion of the second feature will have a maximum depth of 2.5 feet, the majority of the two features will be no greater than 1.5 feet in depth. It is important to note that these are maximum depths and under most circumstances, the depth of inundation, as well as, the duration of inundation will be considerably less. The consulting engineer is working to minimize the slope of the grades into the features to the greatest extent possible. Large rock features will be intentionally installed into the side slopes to break up the grade. These will act similarly to small retaining walls. 2. Access The second feature will have a landscaped earthen berm which will act as a pathway through the rainwater garden swale. In addition, access will be possible between the first and second garden as well as to the north of the second garden. Every house which currently has direct access to the existing trail will have at least one access point in the final design. 3. Privacy One homeowner was concerned that the trail would be immediately adjacent to his property and that the hedgerow adjacent to his lot on park property would be removed. The trail has been aligned such that there is no need to remove this hedgerow. Further, the trail will be between 10 feet and 17 feet from the property line. The entire corridor will be landscaped with 6 foot balsam firs which will provide immediate screening. Other deciduous trees including bur oak, paper birch, river birch, trembling aspen and sugar maple will be planted throughout the corridor to provide additional screening and canopy coverage over time. Finally, shrubs such as highbush cranberry, viburnum and G:\ENG\PUBLlC'-2008 Projects\08-012008 Street Improvements\Kerber Park Pond\Memo_THoffman_042208.doc Park and Recreation Commission Kerber Pond Water Quality Improvements April 22, 2008 Page 3 dogwood will be planted to offer additional screening, aesthetics and wildlife habitat. All of this will be in addition to the perennial forbs and no mow grasses which will be included within the raingarden features. 4. Pollution There is no evidence that these features will accumulate hazardous materials and pose any threat to public safety. Ponds have been commonly installed in residential areas since 1989 with no documented safety risk due to environmental hazards. 5. Long Term Maintenance Staff has requested bids from four different companies which specialize in the installation and maintenance of naturally landscaped areas. A company will be selected from this pool to provide immediate maintenance to assure that the rainwater gardens establish well and long term maintenance to assure their long term success. This maintenance will include watering the features during the establishment period in an absence of adequate rainfall, replacement of failing plants, pruning of woody vegetation, spot spraying of noxious weeds and invasive species, replacement of mulch, removal of debris from within the features, evaluation of any erosive conditions which may develop, and other maintenance requirements that may arise. 6. The effect on property values To date, no comprehensive study on property values has been performed pertaining specifically to rainwater garden features. I have had discussions with developers who are looking at using these features or have already incorporated these features into their developments. Anecdotally, they have said that lots adjacent to rainwater garden features have sold faster than other lots. Another developer felt that these features can be used to market the property. A 2005 survey conducted by Embrace Open Space found that in the eleven county metropolitan area, 68% of residents were willing to pay 10% more for their property if it was located within walking distance of a trail or bikeway. This survey also found that 66% were willing to pay 10% more for their property if it was located within walking distance of a wetland. This study had a margin of error :t4.5%. Similar studies have been done in Concord, MA, Boulder, CO, Salem, OR, Dayton, OH, Philadelphia, PA, and other U.s. Cities and have all shown a positive correlation between the proximity of a property to trails and open space and home value. G:\ENG\PUBLlC'-2008 Projects\08-01 2008 Street Improvements\Kerber Park Pond\Memo_THoffman_042208.doc Park and Recreation Commission Kerber Pond Water Quality Improvements April 22, 2008 Page 4 A 1988 study performed by Kansas State University found that 87% of the land owners adjacent to the Luce Line rail-trail corridor felt the trail increased or had no effect on their property value. Of those property owners in a suburban setting, 61% "noted an increase in their property value as a result of the trail." It is the staffs' contention that, with proper installation and maintenance, these features will be amenities which will ultimately add to the aesthetics of the park and those adjoining properties. 7. Bid Alternate 2 When comparing the cost benefits of the two alternates, Bid Alternate 2 was not nearly as cost effective as Bid Alternate 3. Bid Alternate 2 has a cost of $135,314.50 while Bid Alternate 3 has a cost of $189,602.20. In other words, Bid Alternate 2 is more than 71% of the cost of Bid Alternate 3 to get 40% of the treatment. This does not make sense economically or from a water quality point of view. Further, there would be limited landscaping along the trail and we would still need to remove the vast majority of the trees along the trail in order to accommodate the open trench. For these reasons, staff does not feel it is prudent to pursue Bid Alternate 1. SCHEDULE This project would move forward concurrently with the Laredo Drive reconstruction project. Award Contract May 12, 2008 Begin Construction May 19, 2008 Request for Proposal - Landscaping July, 2008 Landscaping Fall 2008jSpring 2009 The timing of the landscaping will be contingent upon when the grading and pipe installation is completed. If the grading is finished by August of 2008, landscaping can be done in September of 2008. In the event that grading is not completed by this time, a cover crop of winter wheat will be established and the landscaping will be performed in May of 2009. FUNDING This project is to be funded from Capitol Improvement Project SWMP-019. Any additional costs beyond what is in the CIP will be funded through CIP SWMP-012. G:\ENG\PUBLlC'-2008 Projects\08-01 2008 Street Improvements\Kerber Park Pond\Memo_ THoffman_042208.doc Park and Recreation Commission Kerber Pond Water Quality Improvements April 22, 2008 Page 5 Discussions with the Riley-Purgatory-Bluff Creek Watershed District have been ongoing since January of 2008. The City of Chanhassen is requesting a 50% cost share with RPBCWD. Staff will present the request to the RPBCWD on May 7, 2008. RECOMMENDATION Move to recommend Bid Alternate No.3 for the construction of stormwater improvements within Kerber Park Pond as part of the Laredo Drive Reconstruction Project 08-01. ATTACHMENTS . Bid Alternate No.2 . Bid Alternate No.3 . Landscape Plan G:\ENG\PUBLlC'-2008 Projects\08-01 2008 Street Improvements\Kerber Park Pond\Memo_THoffman_042208.doc New -, Traj( , / /// ,>/ //// ~~ \ / , / ,\ / , \ , \ /,>v \ Kerber Pond \t!,',,~' ~' / '- r.A Ash/Maple/Elm Forest , .___,r I I , -.--1-- I I ;- i._~""" / , / \ \ I " \ , "' '-, / (-, ).--~ '.' f.... .1, I f'I _' ..' -.' --11, \ --<- - - I ) _1.------ ( I') ,- - - \ \-''-..j\,_.AJjj I '\ \ I J /' 1"\ ). 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