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8.C.1. PRSR 09 08 2004ITEM # S.C.1. ver MEMORANDUM TO: Parks and Recreation Commission FROM: Bill Maertz, Parks and Recreation Director DATE: August 30, 2004 SUBJECT: Rain Garden at Lake Orono A representative of the Sherburne County Soil and Water Conservation District has approached the City of Elk River about the possibility of constructing a Rain Garden in Elk River as a demonstration site. After discussing several sites, staff determined that the north parking lot at Orono Park was a good potential location for a rain garden. This site was selected because a large area of impervious surface currently drains directly into Lake Orono upstream of the beach. Goose droppings, grass clippings, and automobile byproducts are flushed into the lake with each storm event. A rain garden uses native and locally adapted plants to retain and filter storm water. The Soil and Water District can cover 75% of the cost of a rain garden. The Cities 25% share could consist of in house labor. The purpose of discussion on August 30 is to seek direction from the Commission whether to move forward and further study this potential project. ITEM / $.C.1. SHERBURNE C~!~; SOIL ANA WATER CONSERVATION DISTRICT August 31, 2004 To: Bill Maertz, City of Elk River From: Mark Basiletti, Sherburne SWCD 14855 Highway 10 Elk River, MN 55330 Tel. (763) 241-1170 ext. 3 Website: www.sherbu rneswcd.org Re: Lake Orono Park rain garden and shoreline buffer demonstration project. Purpose: Currently storm water runs directly from the park impervious areas to the lake. This untreated storm water is a source of pollutants such as nutrients and fecal coliform bacteria. Much of the storm water can be treated by a system of rain gardens, swales and buffer areas. Rain gardens are designed to infiltrate most of the runoff. Vegetation in the rain gardens will tie up nutrients and filter pollutants from the runoff. For large runoff events, excess runoff will overflow into a buffer area which will provide further treatment. The SWCD's preliminary assessment is that storm water from most of the impervious surface could be treated by rain gardens and buffer areas. A rain garden was not planned for the parking lot adjacent to the beach because of possible future relocation of this parking lot. Three possible garden and buffer locations were identified (see attached map). The estimated areas of the proposed rain gardens would come within the guideline that the size of the rain garden be approximately 8% of the drainage area being treated. Water would enter the rain gardens via curb cuts where concrete gutters currently exist in the parking areas. Overflow from RG 1 would flow through buffer 1. Overflow from location RG 2 would flow via a Swale to location RG 3 and then through Buffer 2 to the lake. 2. Depth to the water table: The depth to the water table was estimated under the assumption that the water table is approximately at the lake level. Information from MPCA's "Protecting Water Quality in Urban Areas" states that the bottom of an infiltration basin should be 2 to 4 feet above the water table. The locations labe]ed RG 1 and RG 2 would most likely meet this criteria. The lowest point of RG 3 is only about 13 feet above the water table. The design for this treatment area should take this into account. An existing ice ridge at this location already provides a shallow depression. It may be desirable to create only a buffer at this location and design the buffer to avoid ponding to the extent possible. Depth to the water table will need further assessment for all locations. Soil borings should be done for each. Rain Garden Assessment Page 2 3. The design should allow for infiltration of stored runoff within 48 hours to avoid mosquito breeding. 4. Long term maintenance needs to be investigated. How will accumulated silt be removed? 5. Compatibility with recreational use needs to be assessed for each location. In some cases, walking paths may need to be incorporated into the design. Barriers such as wood rail fencing may be advisable in some locations. 6. The size and shape of each of the proposed rain gardens is approximate but is based on measurements of available space at each site. In all cases, it is planned that excavation will be done so as to minimize impacts to tree root systems. Funding: The Elk River Watershed Association through a Section 319 grant can provide funding for innovative storm water treatment such as rain gardens and associated buffer/filter strips. Cost share is up to a maximum of 75% of total project cost. The cooperator's share can consist of in-kind goods and services. Volunteers may be used to plant vegetation, which can go toward the cooperators 25%. Funded projects must be completed by September 30, 2006. Projects must be maintained for 10 years. 8. Signage: For projects funded through the 319 Grant, we require that a sign identifying the practice as a water quality improvement project be placed at the site. The Elk River Watershed Association can provide an appropriate sign. We can also provide a literature box with fact sheets explaining the purpose of the practice. 9. The SWCD proposes that the city engineer would do design work including calculations for drainage area, pond dimensions, inlet and outlet design etc. The SWCD would plan for the plant materials part of the project. WHAT IS A RAIN GARDEN? Every time it rains, gallons upon gallons, of polluted runoff flows from our yards, sidewalks, and driveways into Strom sewers or road ditches. This polluted runoff is carried as conduit flow directly into our lakes, rivers, and streams. You don't think about it but around every home and yard their are spots of lutants on the landscape that are waiting to be washed away. Nutrients are found around the yard as lawn fertilizer, grass clippings, and pet waste left on the landscape. Heavy metals and complex organic compounds are deposited in the lawn from roofing materials, metal plating in downspouts, and pesticide applications. Even exposed soil on the landscape can wash down storm sewers causing sedimentation problems in surface waters. The runoff carrying pollutants from our yards may not cause much harm but the pollutants washing into our storm sewers and drainage ditches from all of our yards has a cumulative effect on our water resources. Rain Gardens use native and locally adapted plants to retain and treat stromwater on the landscape before it reaches a storm drain or road ditch. The plants used in Rain Gardens have deep root systems which allows them to retain runoff and filter pollutants in stormwater. Basically, the plants capture and treat runoff from your yard and allows the water to infiltrate into the subsurface rather than having it flow across the landscape as storm- waterwhere it has the ability to pick up additional pollutants. Rain Gardens are placed at the end of downspouts or in low-lying areas of a yard where water collects. The native and i~~ally adapted plants used in these gardens are a to tolerate a mix of dry and wet conditions and even prosper when they are regularly flooded. These gardens are cost effective, too. Rain Gardens require less maintenance than your typical turfgrass. This means less mowing, no watering, and no fertilizer or pesticide applications. They can also provide a great habitat for birds and buttertlies. Rain Gardens areaway of using nature to protect our natural resources. They are attractive landscapes that treat and filter storm- water. ~ ;,;' ~ ain Colter ., , r, ; ;v, ' ~ Downspout -,i~ ,,, ./ r -r „ -, . .. ~, ~~YMI~A~¢/1 l~~~Y~~ Ii ~ ~ i ~ M / }t ~~~ Rain Ga` ~n j Several communities around the nation and in Minnesota are promoting the use of Rain Gardens for the purpose treating urban stormwater. The city of Maplewood, a northern suburb of St. Paul, used Rain Gardens to retrofit a 1950's era subdivision during a street resurfacing and storm sewer construction project. The city used the gardens to downsize storm sewer piping and street gutters in a suburban neighborhood that was under construction. The University of Minnesota estimated a cost saving of $13,000 for the community in the two-block area where the residents installed Rain Garden amenities rather than using the conventional stormwater system approach that uses street gutters and underground piping.' In addition, the neighborhood was interested in protecting a downstream wetland from pollutants associated v urban runoff. The existing piping from the storm sewer system emptied near an existing wetland cam, ~ iplex. The gardens will benefit the wetland area by allowing runoff water to infiltrate into the subsurface rather than directing it towards the sensitive ecosystem. Rain Gardens provided the city of Maplewood with an overall cost saving and assisted the neighborhood with an environmental alternative to reduce pollution 2 ~~ ~A ~~~~~ The natural solution to stormwater pollution ~~ ~_ ~ £ south zumbro watershed partnership Page I of 1 file://C:\Documents%20and%20Settings\dhuebner\Local%20S ettings\Temporary%20Intern... 9/1 /2004