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Appendix I• APPENDIX I Phosphorus Removal Study • PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD MARCH 2008 Prepared by: WSB & Associates, Inc. 701 Xenia Avenue South, Suite 300 Minneapolis, MN 55416 • (763) 541 -4800 (763) 541 -1700 I hereby certify that this report was prepared by me or under my direct supervision and that I am a duly registered professional engineer under the laws of the State of Minnesota. Steven G. Gurney, PE Date Reg. No. 40497 PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD TABLE OF CONTENTS • I. INTRODUCTION AND PURPOSE II. PROCEDURES AND METHODS FOLLOWED III. DISCUSSION / EVALUATION OF RESULTS IV. RECOMMENDATION List of Tables Table 1 Annual Phosphorus Loads by Land Use Table 2 Reductions to Phosphorus Loads Already in Place Table 3 Potential BMPs and Other Operational Strategies to Meet MCWD Load Reduction Requirement • List of Figures Figure 1 Location Map List of Appendices Appendix A Load Calculations for Redeveloped Properties within Shorewood • PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD TOC I. INTRODUCTION AND PURPOSE • This report provides the results of a Phosphorus Loading Assessment that was completed for the City of Shorewood. This report provides the results of a very basic water quality modeling and stormwater treatment analysis for systems that are in place within the City of Shorewood. The report provides the results of the assessment which has been performed to estimate the changes in annual phosphorus loadings that may have occurred from 2000 to the present. Section II provides a detailed outline of the procedures and methods that were used to perform the loading assessment and to estimate stormwater BMP treatment efficiencies. Section III presents and discusses the results of the loading assessment. 0 • PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD 1 -1 II. PROCEDURES AND METHODS FOLLOWED • This section of the report provides the procedures and methods followed for the loading assessment and analysis. The loading assessment estimates the changes in annual phosphorus loads for areas that were redeveloped within the City of Shorewood between 2000 and 2007. This time frame was chosen to coincide with the MCWD studies. Likewise, areas that redeveloped prior to 2000, or have not redeveloped, are not included in this study. A method based on land use has been applied to determine the change in phosphorus loadings as described in the Steps listed below. This method is similar to that outlined in the July 1, 2005, Technical Memorandum from Wenck Associates, Inc. entitled "Methodology for HHPLS -P -Load model Application to Development of Subwatershed Rules Under Performance -Based Management." The redeveloped areas evaluated as part of this study are identified in Figure 1. A detailed description of the procedures and methods used follows: • • PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD II -1 Step 1. Compare 2000 and 2007 land uses. • Information was gathered from past redevelopment reviews and from staff input regarding areas of the City in which stormwater improvements have been constructed since 2000. Step 2. Estimate annual phosphorus loading based on land use. The annual phosphorus loading used for this study for various land uses are summarized in Table 1. Table 1 Land Cover Type for Selection of Imperviousness Annual TP Load (lb/ac Undeveloped Land, or Pre-develop ment H dric soils — row cropland or close grown cropland 0.259 Upland soils — row cropland or close grown cropland 0.109 Forest, woodland, upland shrubland, savanna, grassl and 0.014 Developed Land, or Post - Develo ment Rural /Residential 4 -10% Impervious 0.300 Residential Low /Residential 11 -25% Impervious 0.563 Residential Medium /Residential 26 -50% Impervious 0.724 Residential High/Residential 51 -75% Impervious 1.140 Commercial 76 -90% Impervious 1.288 Step 3: Compute annual phosphorus load generated by land use. The average phosphorus load generated from each land use in the pre- and post - development condition was computed based on the data gathered in Step 1 and Step 2. Annual loading is calculated using the following equation on a per acre basis: Redevelopment Size x Loading by Land Use = Total Phosphorus Load (lbs /year) Step 4: Define treatment practices and removal efficiencies employed in 2000 and present. Treatment practices and BMPs that have been constructed since 2000 were identified and evaluated for this study. Identified below is a discussion of the BMPs considered for the analysis: • Stormwater Ponds This analysis considers that newly created ponds will retain 60% of TP loads prior to discharging downstream. This TP removal rate is supported by information presented in "Phosphorus Removal by Urban Runoff Detention Basins" (Walker). This document indicates that basins built to the NURP design standards that average four feet in depth provide TP removal efficiencies of 60% or greater. To be conservative, a 50% removal • rate is used in this study, except where otherwise demonstrated during the design review of individual redevelopment projects. PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD II -3 • Structural BMPs Significant structural BMPs within the City include: • 1. The underground alum treatment system at Shorewood Mall, constructed in 2002 as part of the Cub Foods expansion. Further discussion of this system is presented in Section III of this study. 2. The grit chamber installed as part of the County Road 19 project. This structural BMP was one part of the treatment train for the Gideon Glen demonstration project. Other BMPs In addition to storm water ponds, other BMPs may reduce volumes of runoff and pollutant loadings within the City. Some common BMPs that exist in the City are infiltration areas, sump catch basins, street sweeping, restrictions on phosphorus fertilizer, and vegetated buffers. These BMPs further reduce increases in annual runoff volumes and pollutant loading discharges that may have occurred between 2000 and 2007. L • PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD II-4 III. DISCUSSION /EVALUATION OF RESULTS • This section provides the results of the phosphorus load analysis that was completed as part of this study. This section also provides a description of possible methods to further reduce the phosphorus load on downstream waters. The information presented in this section was determined utilizing the methods outlined in Section II of the report. Results The redeveloped areas constructed since 2000 that have reduced the phosphorus load to downstream water bodies are shown in Table 2. Table 2 — Load Reductions for New Developments between 2000 and 2007 • There were several other properties within the City of Shorewood that have been redeveloped since 2000, but were not included in Table 2. Arbor Creek and Lake Virginia Woods were two subdivisions that were created from open space. While the NURP ponds constructed for these projects provide the required treatment for the site, there is a slight increase in the phosphorus loads from each site because open space was converted. Since the MCWD load reduction allocations for each City are already based on some areas of the City being redeveloped, these developments are ignored in this study. Two other redevelopments are not included since they were constructed in landlocked basins and, therefore do not discharge downstream. These basins are identified as LMC -7 and LMC -8 in the MCWD Plan. Redevelopment in the basins includes the Bosworth Planned Unit Development and the Shorewood Mall Expansion that included the new Cub Foods building. • As part of the construction of the Cub Foods store, an alum injection system was installed in the underground chamber constructed beneath the parking lot. The PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD III -1 Post- Post - development development Pre- Load Prior Treated Load Redevelopment Area development to Treatment Load Reduction Name ac Load Ibs ) (Ibs) (Ibs) (Ibs) Subwatershed Parkview 5.88 3.3 4.3 2.1 1.1 Minnetonka Crossin Shorewood 2.2 2.4 2.7 1.1 1.3 Minnetonka Nursery Site Gideon Glen 15.8 20.4 20.4 10.2 10.2 Minnetonka Barrington 5.4 5.9 3.9 2.0 3.9 Minnetonka Excelsior- 2.4 3.1 3.1 1.5 1.6 Minnetonka Covenant Church Total Reduction 18.1 There were several other properties within the City of Shorewood that have been redeveloped since 2000, but were not included in Table 2. Arbor Creek and Lake Virginia Woods were two subdivisions that were created from open space. While the NURP ponds constructed for these projects provide the required treatment for the site, there is a slight increase in the phosphorus loads from each site because open space was converted. Since the MCWD load reduction allocations for each City are already based on some areas of the City being redeveloped, these developments are ignored in this study. Two other redevelopments are not included since they were constructed in landlocked basins and, therefore do not discharge downstream. These basins are identified as LMC -7 and LMC -8 in the MCWD Plan. Redevelopment in the basins includes the Bosworth Planned Unit Development and the Shorewood Mall Expansion that included the new Cub Foods building. • As part of the construction of the Cub Foods store, an alum injection system was installed in the underground chamber constructed beneath the parking lot. The PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD III -1 • underground system could be utilized to reduce the phosphorus load to Lake Minnewashta and ultimately Lake Virginia, if an outlet from these landlocked basins becomes necessary. Potential Additional Load Reductions There are several options available to further reduce the phosphorus loads to each watershed. The following is a list of potential BMPs or operational procedures that could possibly be used to reduce the phosphorus load to downstream water bodies within MCWD. 1. Street Sweeping A study completed by the Coon Creek Watershed District in June 2007 indicates that the average concentration of phosphorus in street sweepings is 215 mg per kg of sweepings (or 0.35 lbs per ton of sweepings). Based on the City's past records, approximately 400 tons are removed annually in the spring by sweeping. 0 2. 3. If a second sweeping was added in the fall, it is estimated that an additional 200 tons will be removed. Based on 50 miles of City- maintained streets, the average phosphorus removal will be 1.4 pounds per mile. By strategically sweeping select areas of the City (i.e. those directly tributary to the lakes targeted) the City can reach it easily meet its load reduction allocation. The This represent an additional 70 pounds of phosphorus can be reduced annually. Table 3 — Recommended Fall Sweeping Activities BMP Road Miles to Be Swept Estimated Load Reduction Subwatershed Street Sweeping 22.9 mi 32 lbs. Lake Minnetonka Street Sweeping 2.9 mi 4 lbs. Lake Virginia Street Sweeping 2.1 mi 3 lbs. Christmas Lake Because fall sweepings collect mostly dead leaves and lawn clippings, it is likely that this reduction is under - estimated. Construction of Additional NURP Ponds Since the City is fully developed, there are limited opportunities to construct new stormwater treatment ponds. Should areas redevelop, the City will require new developments to install treatment facilities at that time. Use of Active Treatment Systems This option involves using a portable alum treatment unit to treat standing water in storm water ponds. is 3. Infiltration Basins Due to the nature of the soils in this area, this is not considered a good option; however, if a developer proposed this type of PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD III -2 system, the City would allow it, provided treatment to NURP standards have been demonstrated. • 4. Water Reuse A water reuse system to reuse stormwater runoff as irrigation water in City parks may be a feasible system to reduce both runoff volume and annual phosphorus load to downstream waterbodies. The above methods are presented to demonstrate that there are potential options available to reduce phosphorus loads to downstream water bodies. • • PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD III -3 IV. RECOMMENDATION This report demonstrates that the City will be able to meet the phosphorus load reductions set forth • by MCWD (57 pounds, overall, annually). The report is based on several general assumptions, using data from a variety of other studies. Since this data may or may not relate to the City of Shorewood Storm Water Management Program, it is recommended that a complete Feasibility Report b e undertaken to incorporate data that relates to the City of Shorewood. Based on the results of the Feasibility Report, the most cost - effective methods for phosphorus removal can be implemented in the City of Shorewood. • • PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD III-4 0 APPENDIX A Load Calculations for Redeveloped Areas within Shorewood 0 • PHOSPHORUS LOAD REDUCTION STUDY CITY OF SHOREWOOD OEM m-- 701 Xenia Avenue South, Suite 300 Project Description SCIOVQI? 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