South Bald Eagle Lake Subwatershed: Urban Stormwater Retrofit Analysis

Transcription

1 South Bald Eagle Lake Subwatershed: Urban Stormwater Retrofit Analysis Prepared for Rice Creek Watershed District by: Ramsey Conservation District, June 2016

2 South Prepared for RCWD by: Andrea Prichard, Ramsey Conservation District with support from the Clean Water Fund Front Cover: Bald Eagle Lake with County borders and Subwatershed delineation Abbreviations Used in this Report: BMP Best Management Practice DNR Department of Natural Resources IESF Iron-Enhanced Sand Filter JD-1 Judicial Ditch 1 MPCA Minnesota Pollution Control Agency O&M Operations & Maintenance RCD Ramsey Conservation District RCD-11 Ramsey County Ditch 11 SAFL Saint Anthony Falls Laboratory TMDL Total Maximum Daily Load TP Total Phosphorus TSS Total Suspended Solids

3 4 Executive Summary This analysis identifies optimal locations for implementing cost-effective best management practices to improve environmental water quality in the Bald Eagle Lake subwatershed of Ramsey County. These practices consist of general recommendations as well as retrofits to the existing drainage system to filter stormwater runoff, thereby reducing the amount of total phosphorus (TP) and total suspended solids (TSS) reaching the lake. Bald Eagle Lake was classified by the Department of Natural Resources (DNR) in 2002 as impaired for nutrients and eutrophication, with TP concentration as a leading factor to this impairment. In spring of 2014 and 2016, the Rice Creek Watershed District applied an alum treatment to Bald Eagle Lake, which reduced the average TP level to within the Minnesota Pollution Control Agency (MPCA) standard s 40 μg/l maximum level for the first time in many years (RCWD, 2014). This study was conducted with the objective of furthering clean water stewardship in line with the goals of Rice Creek Watershed District. This subwatershed was divided into 7 major catchments using Area of Interest delineations by Wenck from the Total Maximum Daily Load (TMDL) Implementation Plan, and modified based on the drainage path of runoff into the lake. The catchments were then modeled using WinSLAMM software to determine base loading of TP and TSS. Based on initial results, certain catchments were prioritized for best management practice (BMP) retrofitting. After desktop and field analyses, potential projects were identified, designed, and given a price estimate. Retrofits were modeled for their capacity for pollutant reduction, and the final result is a ranked list of these projects in order of lowest cost per pound of phosphorus removed. Additional priority areas and alternative BMP recommendations are discussed in the Catchment Results section under the heading for each catchment. Contaminant loading values and costs presented are estimates based on models and pricing for comparable projects. More detailed studies should be completed prior to the implementation of any individual project presented herein. In areas with sandy soils, bioretention systems (rain gardens) were generally found to be the most effective practice, given the high infiltration rates of the native soil of the suggested areas. While the institutional and commercial areas (near parking lots of schools, churches, or shopping centers) have higher costs due to the larger sizes and extra construction complexity, they also carry the benefits of greater pollution reduction, higher likelihood of appropriate maintenance, and stronger potential to raise awareness on clean water efforts due to their elevated visibility. Streambank and shoreline stabilizations, too, would have large benefits in areas of degraded land with constant contact with water. Turf to native buffer conversions along shorelines have lower modeled benefits, though the benefit would increase dramatically on eroded shorelines. Alternative BMPs suggested include stormwater ponds, SAFL Baffles, tree trenches, swales, underground storage, permeable pavement, and iron-enriched sand filters. This document includes background information, methods, assessment results, conclusions and recommendations. When implemented, these projects will help improve existing water quality and benefit the lake ecosystems.

4 The following table, also found in the Results section, shows the proposed retrofits in order of cost-forbenefit ranking, as determined by the modeled phosphorus reduction and estimated cost for the 30-year life cycle of the project. Colors correspond to the project type, as displayed in the legend of the map below, which shows the locations of each of the proposed retrofits in their respective catchments for the south Bald Eagle Lake subwatershed. 5 ID Catchment BMP Rain Garden Complexity TSS removed lb/year TP removed BMP area ft2 Total Initial Cost Annual O&M Cost/lb P removed/yr (30 yr) Stormwater pond $ 53,970 $ 3,238 $ Streambank Stabilization $ 9,800 $ 950 $ Shoreline Stabilization $ 2,600 $ 950 $ Iron Enhanced Sand Filter $ 250,000 $ 5,000 $ Rain garden simple $ 9,800 $ 525 $ Vegetated Swale $ 5,850 $ 225 $ Shoreline Stabilization $ 26,000 $ 9,500 $ Rain garden moderate $ 8,750 $ 375 $ SAFL Baffle n/a $ 10,000 $ 240 $ SAFL Baffle n/a $ 10,000 $ 240 $ Rain garden complex $ 11,500 $ 375 $ Rain garden moderate $ 8,750 $ 375 $ Shoreline Stabilization $ 2,600 $ 950 $ Rain garden simple $ 5,250 $ 225 $ Rain garden simple $ 5,250 $ 225 $ Rain garden simple $ 6,125 $ 263 $ 1, Rain garden simple $ 7,000 $ 375 $ 1, Rain garden moderate $ 7,500 $ 225 $ 1, Rain garden simple $ 5,250 $ 225 $ 1, Rain garden moderate $ 17,500 $ 750 $ 1, Rain garden simple $ 5,250 $ 225 $ 1, Underground Storage System $ 30,000 $ 425 $ 1, Underground pipe n/a $ 25,000 $ - $ 1, Stormwater pond $ 8,711 $ 523 $ 1, Rain garden moderate $ 31,500 $ 1,350 $ 1, Tree trench $ 29,450 $ 500 $ 2, Rain garden complex $ 17,250 $ 563 $ 2, Permeable Pavement $ 11,196 $ 555 $ 2, Rain garden moderate $ 8,750 $ 375 $ 2, Rain garden simple $ 5,250 $ 225 $ 2, Rain garden simple $ 10,500 $ 563 $ 2, Rain garden simple $ 3,063 $ 131 $ 2, Rain garden moderate $ 7,500 $ 225 $ 2, Rain garden complex $ 15,000 $ 300 $ 3, Native Buffer $ 8,016 $ 380 $ 6, Native Buffer $ 5,344 $ 275 $ 7, Native Buffer $ 6,680 $ 380 $ 7, Native Buffer $ 5,344 $ 275 $ 9,061

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6 7 Table of Contents Executive Summary... 2 Introduction... 9 Methods...13 Retrofit Scoping Desktop Retrofit Analysis Retrofit Reconnaissance Field Investigation Treatment Analysis Retrofit Neighborshed Delineation Retrofit Modeling & Sizing Retrofit Types Retrofit Cost Estimates Results...18 Catchment Comparison Catchment Results Catchment Catchment Catchment Catchment Catchment Catchment Catchment Conclusions and Recommendations...51 Appendix A. WinSLAMM Modeling Parameters and Land Use Codes...53 Appendix B. Bioretention design...55 References...57

7 8 Figure 1. Boundary of Bald Eagle Lake Subwatershed within Ramsey County, MN showing Ramsey Washington Judicial Ditch 1 (RWJD 1) and Ramsey County Ditch 11

8 9 Introduction Bald Eagle Lake is a 1017-acre recreational water body in northern Ramsey County, MN extending northward to Anoka and Washington Counties, ultimately discharging to the north into Clearwater Creek. The full watershed for Bald Eagle Lake is 10,835 acres, giving the watershed-to-lake area about a 10:1 ratio, making it moderately sensitive to nutrient inputs from watershed runoff (TMDL, 2012). For the purposes of this study, however, the area evaluated (the South Bald Eagle Lake subwatershed) is the most densely populated area of the watershed, located in Ramsey County. This urban subwatershed is a acre area (including the lake) located in north central Ramsey County, Minnesota (Figure 1). Improving water quality within the south Bald Eagle Lake subwatershed is what prompted this study. Specifically, the objectives are to reduce: Total Phosphorus (TP): a nutrient that can contribute to the eutrophication of surface water bodies Total Suspended Solids (TSS): particles suspended (not dissolved) in water that can cause turbidity and harm aquatic life Watershed and Subwatershed Land Cover Of the 1665 acres of land in this subwatershed, about half is composed of residential land use, with 40% composed of parks or undeveloped open space, and remaining land cover composed of highway, industrial, commercial, and institutional land use (Figure 2). Bald Eagle Lake Subwatershed Land Use 40% 1% 5% 2% 3% 49% Residential Industrial Institutional Parks and Open Space Commercial Highway Figure 2. Land Cover in south Bald Eagle Lake subwatershed. Data Source: Met Council land cover GIS shapefile, updated by Ramsey Conservation District (RCD) staff using 2015 aerial imagery.

9 10 Outside Ramsey County, most of the 8,317 acres composing the remaining Bald Eagle Lake watershed lies in Washington County, and is composed of agricultural land, golf courses or undeveloped/preserve land. This land was excluded from the study in order to focus on urban land use and retrofits, to which the WinSLAMM pollution modeling software is better suited. Additionally, the majority of the lake s phosphorus load originates in Ramsey County, according to the 2012 TMDL report on Bald Eagle Lake; therefore, this report focuses on the most effective retrofits that can be implemented Figure 3. DNR Level 08 watershed boundaries and Judicial Ditch 1 within Ramsey County to improve the lake s water quality. There is, however, one large source of nutrients and sediment originating from outside the subcatchment area, which is Ramsey-Washington Judicial Ditch 1 (Figure 3). This ditch conveys runoff from a vast drainage area in Washington County westward into Ramsey County, bringing 25% of the phosphorus load to Bald Eagle Lake (TMDL, 2012). Figure 3 shows the DNR Level 8 watershed boundary, as well as Judicial Ditch 1, a high-flowing ditch monitored for water quality at its outlet into Bald Eagle Lake. Although the subwatershed was based generally on the DNR watershed boundary (confined by Ramsey County boundaries), several modifications to these boundaries were chosen based on stormwater infrastructure, which carries stormwater from southeast of Bald Eagle Lake northward toward the lake. Runoff in the northeast of Bald Eagle Lake is conveyed westward, ultimately crossing underneath Highway 61 and the railroad tracks and discharging into Bald Eagle Lake. Water Quality Though Bald Eagle Lake was only classified by the DNR in 2002 as impaired for nutrients and eutrophication, it has consistently exceeded the state eutrophication standard of 40 μg/l for almost 30 years. (TMDL, 2012). This impairment is based on three factors: phosphorus, chrolophyll-a, and secchi depth transparency. With a maximum depth of 39 feet, Bald Eagle falls under the MPCA s deep lake classification and corresponding standards for nutrient loading (MPCA, 2008). State standards for this lake are 40 μg/l for phosphorus, 14 μg/l for chlorophyll-a, and greater than 1.4m for secchi depth transparency. During intensive monitoring between , the average summer values in Bald Eagle Lake were were 90 μg/l for total phosphorus, 34.2 μg/l for chlorophyll-a, and 1.2 meters for Secchi depth (TMDL, 2012). These values are consistent with high incidences of algal blooms. Table 1 shows average values of TP from The MPCA standards listed below are for lakes in the Central Hardwood Forest (CHF) ecoregion (MPCA-EDA, 2014).

10 11 Table 1. Average TP values for Bald Eagle Lake, Data Source: Minnesota Pollution Control Agency Environmental Data Access website Sampling Location Total Phosphorus (µg/l) - Averages from MPCA data MPCA Standard Average Value Sampling Period (May-September) Bald Eagle Lake The Total Phosphorus (TP) average dropped from 90 to 62 from the time period to the time period, due in part to elevated awareness and pollution reduction efforts by the cities, watershed district, golf courses, and other organizations in the form of construction permits, restrictions, best management practices, and new projects to reduce nutrient loading in the watershed. TP Load 2012 TMDL and updates The largest contributor of phosphorus at the time of the 2012 TMDL study was internal loading, with accumulated sediment in the lake bottom releasing phosphorus (Figure 4). A 91% reduction in internal phosphorus loading was needed to meet standards. In order to address this, Rice Creek Watershed District in partnership with the Bald Eagle Area Association applied a 2-installment aluminum sulfate treatment to Bald Eagle Lake in 2014 and 2016, quickly reducing the TP level of Bald Eagle Lake to meet the MPCA standard s 40 μg/l standard (RCWD, 2014). While this project has had immediate and positive impact on the lake s water quality, external loading will threaten the positive impact of the alum treatment administered. This report is an analysis of land-based treatments to treat stormwater before entering Bald Eagle Lake. Figure 4. Bald Eagle Total Phosphorus Load ( Average) (TMDL, 2012).

11 12 The TMDL stated that 25% of the lake s phosphorus load was estimated to come from Judicial Ditch 1 (JD- 1), which carries runoff from about 75% of the land area draining to Bald Eagle Lake. However, since the time of the TMDL, improvements have been made to reduce this load. A large percentage of the phosphorus loading from JD-1 originated just north of Schuneman marsh, just downstream of Oneka Ridge Golf Course and Fish Lake. In 2014, however, the Oneka Ridge Golf Course completed an irrigation project collecting and reusing stormwater runoff from a 915-acre subwatershed, thereby reducing the golf course s phosphorus output by 75 lbs/year (RCWD, 2014). Ramsey County Ditch 11 (RCD-11), which carries an estimated 8% of the lake s total phosphorus load, gets a great deal of this loading from the southern-most section of the subwatershed composed of commercial land use and highway, which drains north into RCD-11 before passing through medium-density residential land cover and discharging into the lake. Many retrofits are suggested in this area, and for the Bald Eagle Direct loading section (seen as 14% in Figure 4), which corresponds to direct drainage via overland flow as well as water collected in stormwater infrastructure and discharged through outfalls into the lake. Two upstream lakes (Pine Tree and Fish Lakes, Figure 3) were modeled to account for 3% of the total phosphorus load. The modeled influx of nutrients from these lakes was estimated to be 99 lbs/year from Pine Tree Lake and 33 lbs/year from Fish Lake (impaired since 2006 for nutrients). Water from both of these lakes enters the subwatershed from the east via Judicial Ditch 1 (TMDL, 2012). Retrofits to Pine Tree and Fish lakes were not included since they are outside the study area. Note: Otter Lake and White Bear Lake are connected to White Bear Lake by surface water in times of flooding, but they are not considered upstream lakes because 2012 TMDL concluded that water flows from Bald Eagle Lake toward Otter Lake, and that White Bear Lake water only reached Bald Eagle Lake in a 100-year flow event, so neither was considered as a significant source of nutrients. Modeling Pollutant modeling in this analysis is based on surface runoff within catchment boundaries. Primary factors used for contaminant modeling were local precipitation, land use, and soil type. The predominant soil type in most retrofit areas is sand, which is beneficial for rain gardens and other infiltration stormwater BMPs due to its high infiltration rate. Treatment from pre-existing BMPs was modeled and taken into account when generating base loads in each catchment. In newer areas of development, Rice Creek Watershed District issues permits for construction sites, which requires the implementation of permanent stormwater control and local treatment of runoff from impervious surfaces. For this reason, older areas in the south of the subwatershed were prioritized for retrofits, since they were built prior to Rice Creek Watershed District s permit regulations requiring stormwater BMPs. Public land including rightof-ways was prioritized for projects due to the cities collaboration, cooperation, and efficiency in construction and maintenance of public projects. Commercial and institutional land was also prioritized due to the high visibility and maintenance probability for these sites, since landscapers are often hired to maintain these green spaces.

12 13 Methods In this analysis, the methods used were based on models developed by the Center for Watershed Protection. In summary, these investigative methods include Retrofit Scoping, Desktop Retrofit Analysis, Retrofit Reconnaissance Field Investigation, Treatment Analysis, and Retrofit Cost Estimates for use in project ranking. A summary of the methods used is described below. Retrofit Scoping The subwatershed was divided into seven catchments based on lesser drainage basins leading to Bald Eagle Lake (Figure 5). Each catchment was then analyzed using standard land use files in WinSLAMM software to determine a base load of TP and TSS. The WinSLAMM parameters and standard land use files used can be seen in Appendix A. These base loads were used to identify and prioritize catchments with a greater pollutant load for retrofits. The modeling takes into account existing treatment, such as bi-annual street-sweeping and stormwater ponds. The natural treatment system consisting of a network of wetlands and stormwater ponds was also accounted for. All steps used to calculate the base load modeling were done consistently for all the catchments so that an overall precise comparison could be made between them. More precise pollutant loads for each retrofit opportunity found within the drainage areas are presented below in the results. Desktop Retrofit Analysis A desktop search for potential retrofit locations was conducted for each catchment to identify potential retrofit opportunities. GIS layers including land use, elevation, soils, hydrologic boundaries, cadastral information, highresolution aerial photography, water quality data, and storm drainage infrastructure were reviewed to determine potential retrofit placement. Some modifications were made to the soil layer in order to include the highest infiltration potential areas as identified within the TMDL. Several BMP retrofits in this study were concentrated around areas with stormwater infrastructure in order to intercept untreated urban runoff before entering into underground stormwater conveyance systems. In other areas, BMPs were suggested to treat surface water drainage before entering the lake or stormwater ponds. Areas already equipped with stormwater treatment, such as Catchment 2, were less prioritized than areas with minimal existing treatment. Figure 5. Catchment division

13 14 Retrofit Reconnaissance Field Investigation After identifying potential retrofit sites through the desktop search, a field investigation was conducted to evaluate previously identified sites, identify additional sites, and determine the appropriate BMP type based on the onsite conditions. During the investigation, roads in the study area were driven, and the drainage area and stormwater infrastructure mapping data were verified. Site constraints were assessed to determine the most feasible retrofit options as well as to eliminate unfeasible sites from consideration. Most of the lake s shoreline and the length of the public ditches were not visited due to restricted access on private land and time limitations. A more in-depth study of these locations is recommended to evaluate shoreline and streambank stability and to implement any stabilization necessary to prevent erosion into the water body. Treatment Analysis Retrofit Neighborshed Delineation After the retrofit sites were identified, the BMP s individual drainage areas or neighborsheds, consisting of runoff from surrounding streets, buildings, and landscaped areas, were delineated using GIS and contour data. See an example in Figure 6. This information, in conjunction with land cover and NRCS soil survey data, was used to model the pollutant loads from these sites. The neighborshed acreage was entered into the WinSLAMM program along with its corresponding land use and soil type. To maintain consistency, all standard file data used in WinSLAMM, listed in Appendix A, was the same for each site modeled, though different types of land use were specified for modeling. Figure 6. An example neighborshed and the source areas that are entered into WinSLAMM Retrofit Modeling & Sizing Appropriate retrofits were identified and customized, depending on the neighborshed size, the soil type, the type of infrastructure present, and the slope of the retrofit area. The retrofit/treatment types identified, to be described in the next section, include: swales, alum treatment, iron-enhanced sand filtration, shoreline stabilization, bank stabilization, stormwater ponds, permeable pavement, tree trenches, SAFL Baffles, and bioretention (rain gardens). Designs and sizes of retrofits vary, depending on the properties of individual sites and landowner s preferences. Retrofits were then entered into each neighborshed WinSLAMM model to determine their capability to reduce TP and TSS for the given area.

14 15 Retrofit Types Alum treatment (Aluminum Sulfate) This chemical treatment is already in use for Bald Eagle Lake in order to precipitate out phosphorus, rendering it unavailable for algae, and thus improving water clarity as it reduces total phosphorus. This treatment is most effective in water bodies with predominantly internal nutrient loading. Iron-enhanced sand filter (IESF) While the filter itself can take many forms, the basic principle is that iron filings are mixed with sand to make a porous medium. As stormwater filters through, phosphates and other dissolved constituents bind with the iron, and are thus removed from the water. This is a successful technique for reducing dissolved phosphorus levels, but it requires maintenance and must not be submerged underwater for long periods of time. Shoreline stabilization This is appropriate along degraded lake shorelines. The process consists of structural reinforcement of the shoreline using rip-rap and/or establishment of a native vegetation buffer along the shoreline to filter runoff, prevent sheet erosion, and reduce wave erosion. Vegetated swales This practice consists of a vegetation-filled drainage course with gently sloping sides, often accompanied by check dams and/or rain gardens to assist the vegetation in slowing flow, increasing infiltration, and improving removal of pollutants from stormwater. Bioretention This type of retrofit is effective at intercepting stormwater runoff for treatment before it would enter stormwater conveyance systems. A bioretention basin, also referred to as a rain garden, consists of a depression utilizing native soils or engineered soils (depending on the infiltrative capacity of the soil), along with native vegetation. An underdrain with connection to the existing storm sewer system is recommended if infiltration capability is limited by underlying soils or soil compaction. It is important to properly design and install the engineered soils so that the bioretention basins take no less than 24 hours to drain but no more than 48 hours. The underdrain can be installed with a plug that can be removed in the event of poor drainage. The bioretention basins in this study fall within the categories listed below: Simple Bioretention Includes engineered soils, native vegetation, and an underdrain. No concrete work necessary. Moderate Bioretention - Includes engineered soils, native vegetation, engineered soils, an underdrain, a curb cut, and a forebay. No retaining wall necessary. Complex Bioretention Includes engineered soils, native vegetation, underdrain, a curb cut, a forebay, a retaining wall with sand/rock columns. A schematic of a bioretention basin and example modeling parameters used within WinSLAMM can be seen in Appendix B. Stormwater pond In this structure, stormwater runoff is directed to a basin that allows the water sufficient time for suspended solids to settle out, thus providing both retention and treatment of stormwater runoff, also reducing downstream runoff volume and erosion potential.

15 16 Native Buffer Along water bodies, a native vegetation buffer is recommended both to protect the shoreline from erosion from wave action and to protect the water from runoff from streets and lawns. Lawn clippings, fertilizers, and other runoff from lawns are high in phosphorus, which can trigger algal blooms in the water. Permeable Pavement Parking lots are generally paved with an impervious surface, creating a large surface area of polluted stormwater runoff. As an alternative, permeable pavement is designed to allow infiltration of stormwater into the soil below for local treatment without the need to remove parking spaces. Underground Stormwater Storage System The underground storage option is generally employed when there is not available surface space for a bioretention basin, stormwater pond, or other surface feature. Stormwater is directed to underground chambers for immediate storage and gradual infiltration into the soils below. SAFL Baffle The SAFL Baffle is a device developed by the St. Anthony Laboratory at the University of Minnesota that fits into sumped manholes or catch basins to filter stormwater in underground infrastructure. In this study, these devices were proposed in locations just before the stormwater outlets into Bald Eagle Lake in order to settle out sediment. This devices needs to be cleaned out periodically. An alternate model is the Preserver, from Momentum Environmental. Streambank stabilization Streambanks without sufficient stabilization erode and degrade the bank, causing potentially large volumes of sediment to enter the ditch or stream, and ultimately, the lake. Depending on the force of flow and the level of bank erosion, stabilization may consist of native plug or live stake planting of shrubs, trees, or other vegetation with strong roots. In cases with higher flows and severe undercutting, regrading, riprap, and other reinforcement may be needed in conjunction with vegetation. Tree trenches This BMP consists of a series of tree pits in a sidewalk with an underground trench to collect and infiltrate stormwater. Underneath the sidewalk, the runoff from surrounding impervious surfaces waters the trees, with excess water slowly infiltrating below the surface. Retrofit Cost Estimates Each retrofit was assigned an estimated materials, design, and installation cost of implementation, as well as an annual maintenance cost (Table 2). Most cost estimates were derived from recent installation costs provided by design and construction professionals, as well as estimates from manufacturers. A cost-perlb of TP removed was then calculated for the 30-year life cycle of each retrofit, using the following equation: (total 1 st year cost + 29 years * annual maintenance) / (30 year * TP removed ()). This value was used for the cost-benefit ranking of the retrofits. Actual implementation and maintenance costs will vary depending on contractor, selected materials, slope, soil type, and other variables.

16 Table 2. Average BMP Cost Estimates, revised May BMP BMP Installation and Maintenance Cost Estimates Cost of Installation: includes design, materials, installation, and 1st year of maintenance Annual Maintenance Cost Simple Bioretention (Rain Garden) $14-$17.50 $0.75/ft² Moderate Bioretention (Rain Garden) $17.50-$23 $0.75/ft² Complex Bioretention (Rain Garden) $23-$37.5 $0.75/ft² Stormwater Pond $0.70-$1.40/ft³ volume 6% of initial cost/year Streambank Stabilization $245/linear foot $950 Shoreline Stabilization $130/linear foot $950 Iron Enhanced Sand Filter - RCD11 project estimate $250,000 $5,000 Vegetated Swales $13/linear foot $225 SAFL Baffle - includes sump installation $10,000/unit $240 for 3 cleanings per year Underground Pipe - total cost for 4-8 site $25,000 n/a Underground Stormwater Storage System $30,000 (site-specific estimate) $425 Tree Trench $135/lf + $650/tree $500 Permeable Pavement $15.13/ft² $0.75/ft² Native Buffer $6.68/ft² $275-$380

17 18 Results Catchment Comparison The seven catchments and their total modeled TP and TSS base loads from surface runoff (including reductions from pre-existing best management practices) are listed in Table 3 below. This information was used in prioritizing catchments for retrofit installation. Table 3. Base loads for Bald Eagle Lake subwatershed catchments, as modeled in WinSLAMM Existing Contaminant Load Summary Catchment TP () TSS () Runoff (ft³/yr) Area (acres) ** **Values are for surface runoff only and do not include estimated JD-1 nutrient loads Figure 7 shows the TP load from surface runoff in the 7 catchments. Catchment 4 stands out as a principal contributor of nutrients to Bald Eagle Lake, largely through the highway and commercial runoff, which are diverted to RCD-11 before entering Bald Eagle Lake. For this reason, retrofits are proposed both at the areas where pollutants collect (parking lots and highway runoff) as well as the ditch itself. Modeled TP (lb) Base load by Catchment lb TP/year Catchment # Figure 7. Annual base loads of Total Phosphorus, in pounds, for each catchment within the south Bald Eagle Lake Subwatershed, as modeled by RCD staff using WinSLAMM software.

18 19 When the Total Phosphorus values are adjusted to include the average annual phosphorus load of Judicial Ditch 1 (using TMDL 2012 values), Catchment 3 clearly stands out as the highest contributor of phosphorus to the lake (Figure 8), although the vast majority of the load is entering from east of the study area. Most of the suggested retrofits in Catchment 3 are close to this ditch, and it is recommended to continue to install retrofits in Washington County where this ditch originates as well as to explore treatment options in the stormwater ponds where the ditch water collects before entering Bald Eagle Lake. lb TP/year TP (lb) Base load including JD Catchment # Figure 8. Annual base loads of Total Phosphorus, in pounds, for each catchment within the south Bald Eagle Lake Subwatershed, including Judicial Ditch 1 s TP load (from the 2012 TMDL report) in Catchment 3. After Catchments 3 and 4, the catchment with the highest level of pollutants (by mass) is Catchment 1, which is divided by the railroad into east and west lobes. The runoff from the industrial east half of the catchment passes by culvert under the railroad tracks to the ditch on the west side of the tracks, where it follows the ditch south before discharging into the lake. Catchment 2 does not have proposed retrofits, despite the model s estimated annual contribution of lbs of TP. Catchment 2 is mostly composed of undeveloped wetland, which WinSLAMM, designed for urban catchments, does not accurately model. It is assumed that the actual nutrient output of this catchment is lower than modeled, especially since each residential development in this area has runoff pre-treatment in stormwater ponds, whose overflow would have to pass over a half mile of wetland before discharging into a pond which outlets into Bald Eagle Lake. This catchment has at least twice the number of pre-existing stormwater BMPs as any other catchment in the study. Catchments 5, 6, and 7 are smaller in acreage and contribute fewer pounds of pollutants per year to Bald Eagle Lake. Nonetheless, their concentrations (TP/acre) are nearly as high as Catchment 4 s nutrient contribution (Figure 9), and therefore retrofits have been proposed in these catchments as well. These retrofits consist primarily of shoreline stabilization, native buffers, rain gardens, and SAFL baffles. Catchment 7 is mostly composed of low-density residential land cover with a great deal of wetlands. For lakeshore homes, the retrofit proposed in Catchment 7 is the installation of lb TP/acre/year TP (lb)/acre (concentration) Catchment # Figure 9. Annual base load concentration of Total Phosphorus, in pounds per acre, for each catchment within the south Bald Eagle Lake Subwatershed, as modeled by RCD staff using WinSLAMM software.

19 20 native vegetation buffers in areas where short-rooted, erosion-prone turf-grass extends all the way to the shoreline, making it vulnerable to wave erosion. Catchment Results The following section shows results per catchment, including maps and tables showing retrofit locations and the TP and TSS reduction per retrofit. Maps include detailed retrofit locations as well as an overview map (Figure 10) to show all proposed retrofits within the subwatershed area. Figure 10. Proposed Stormwater Retrofit Locations in the south Bald Eagle Lake subwatershed

20 21 Table 4. Ranked results for the proposed retrofits in the South Bald Eagle Lake subwatershed. ID Catchment BMP Rain Garden Complexity TSS removed lb/year TP BMP area removed ft2 Total Initial Cost Annual O&M Cost/lb P removed/yr (30 yr) Stormwater pond $ 53,970 $ 3,238 $ Streambank Stabilization $ 9,800 $ 950 $ Shoreline Stabilization $ 2,600 $ 950 $ Iron Enhanced Sand Filter $ 250,000 $ 5,000 $ Rain garden simple $ 9,800 $ 525 $ Vegetated Swale $ 5,850 $ 225 $ Shoreline Stabilization $ 26,000 $ 9,500 $ Rain garden moderate $ 8,750 $ 375 $ SAFL Baffle n/a $ 10,000 $ 240 $ SAFL Baffle n/a $ 10,000 $ 240 $ Rain garden complex $ 11,500 $ 375 $ Rain garden moderate $ 8,750 $ 375 $ Shoreline Stabilization $ 2,600 $ 950 $ Rain garden simple $ 5,250 $ 225 $ Rain garden simple $ 5,250 $ 225 $ Rain garden simple $ 6,125 $ 263 $ 1, Rain garden simple $ 7,000 $ 375 $ 1, Rain garden moderate $ 7,500 $ 225 $ 1, Rain garden simple $ 5,250 $ 225 $ 1, Rain garden moderate $ 17,500 $ 750 $ 1, Rain garden simple $ 5,250 $ 225 $ 1, Underground Storage System $ 30,000 $ 425 $ 1, Underground pipe n/a $ 25,000 $ - $ 1, Stormwater pond $ 8,711 $ 523 $ 1, Rain garden moderate $ 31,500 $ 1,350 $ 1, Tree trench $ 29,450 $ 500 $ 2, Rain garden complex $ 17,250 $ 563 $ 2, Permeable Pavement $ 11,196 $ 555 $ 2, Rain garden moderate $ 8,750 $ 375 $ 2, Rain garden simple $ 5,250 $ 225 $ 2, Rain garden simple $ 10,500 $ 563 $ 2, Rain garden simple $ 3,063 $ 131 $ 2, Rain garden moderate $ 7,500 $ 225 $ 2, Rain garden complex $ 15,000 $ 300 $ 3, Native Buffer $ 8,016 $ 380 $ 6, Native Buffer $ 5,344 $ 275 $ 7, Native Buffer $ 6,680 $ 380 $ 7, Native Buffer $ 5,344 $ 275 $ 9,061 Below is a guide to the column headings for Table 4 s retrofit summary: ID a unique site ID number per proposed retrofit Catchment hydrologic division of land whose water flows in toward the lake BMP Type of best management practice retrofit Rain garden Complexity Simple, Moderate, or Complex rain garden designs TSS Removed the Total Suspended Solids removed by the retrofit (lb/year) TP Removed the Total Phosphorus removed by the retrofit (lb/year) BMP area proposed size of modeled retrofit (square feet) Total Initial cost cost estimates of materials, labor, and design for 1 st year implementation Annual O & M estimated Operation & Maintenance cost per year (30 year term) Cost/lb P Removed/yr Cost per pound of TP removed in the 30 year life span.

21 22 Catchment 1 DESCRIPTION Catchment 1, totaling 329 acres, is largely composed of undeveloped or park land, with some industrial, institutional, and commercial land in subcatchments 1-B, 1-C, and 1-D (see pie chart in Figure 11 and map in Figure 12). Residential areas include subcatchment 1-E and the southwest shoreline of 1-A. Though subcatchments 1-B through 1-E have basic stormwater treatment via stormwater ponds, a modeled 67 pounds of TP and 31,900 pounds of TSS pass from east to west of the railroad tracks through a culvert, at which point the runoff follows a ditch southward until its ultimate discharge into Bald Eagle Lake. Lakeshore residences, including a small recreational park with a baseball field, are in the southwest corner of subcatchment 1-A, and the southeast corner contains a boat launch, parking lots, and a recreational area for the Bald Eagle-Otter Lake Regional Park. Figure 11. Catchment 1 Land Cover, by percentage Table 5. Catchment 1 Base load for total phosphorus, total suspended sediments, and runoff volume, after subtracting modeled reductions from existing best management practices. Catchment 1 - Existing Contaminant Loading Base Load Treatment Net Treatment % Existing Load Number of BMPs 5 1 Swale, 3 Stormwater Ponds, Street BMP types Sweeping TP () % TSS () % Volume (ft³/yr) %

22 23 RETROFIT RECOMMENDATION Figure 12. Proposed Stormwater Retrofit Locations in Catchment 1

23 24 1-1, Stormwater Pond In Catchment 1, the most effective modeled retrofit to treat the runoff from subcatchments 1- B through 1-E is a ½-acre stormwater pond (retrofit 1-1) in the prairie restoration area west of Hugo Rd and south of Leibel Rd. This is a strategic location about 100 ft west of the point where the runoff passes underneath the railroad tracks and discharging into a north-south ditch (Figure 13). Currently this water flows about a half mile south along the ditch before discharging directly into Bald Eagle Lake. The water could pass via culvert under Hugo Rd for treatment. Cost estimate below reflects stormwater pond construction costs only. Figure 13. North-South ditch on the west side of the railroad tracks containing runoff from 1-B, 1-C, 1-D, and 1-E southward toward Bald Eagle Lake. 1-6, Stormwater Pond The boat launch in subcatchment 1-A currently has water accumulating in the southwest corner of the parking lot before overflowing ultimately into the lake, together with contaminants from vehicular traffic. Ramsey County Parks and Recreation has proposed plans to reconstruct this parking lot using best management practices such as a stormwater pond and an iron-enhanced sand filter. Though the appropriateness and effectiveness of retrofits depend on the future reconstruction of the parking lot, a stormwater pond (retrofit 1-6) was modeled in the location of current ponding in the lot (Figure 14), for a reduction of about 50% of both TP and TSS of runoff from the neighborshed. Figure 14. Retrofit 1-6 location, where water currently pools in the existing parking lot of the Bald Eagle Lake boat launch. 1-2, 1-3, 1-4, 1-5, Rain Gardens The remaining of the recommended retrofits for Catchment 1 are for the residential area in the southwest corner of subcatchment 1-A, including three rain gardens on private property and one crescent-shaped rain garden between the Birch Park baseball field and the culvert leading to Bald Eagle Lake, on Ramsey County property. Rain garden retrofits in Catchment 1 are all located in High or Moderately High Infiltration Potential areas, as identified by the 2012 TMDL study (Figure 15).

24 Figure 15. (top left): Baseball park location of 1-2 rain garden. (top right): Residential location of 1-4 rain garden. (bottom left): High Infiltration Potential map from 2012 TMDL. (bottom right): locations of 4 rain gardens. If all 6 proposed retrofits are implemented in this catchment, it is modeled that 39.6 lbs of TP and 22,286 lbs of TSS would be filtered or settled out per year, resulting in a 28% and 49% decrease, respectively, from the base load at total project cost of $88,231, not including annual maintenance. See table below for project-specific results, and table 18 for overall catchment results. Table 6. Summary of modeled TSS and TP reductions and estimated costs for proposed retrofits, Catchment 1 ID BMP Rain garden complexity TSS before TSS after TSS removed TP before TP after TP removed % of Catchment TP reduced BMP area ft2 Total Initial Cost Annual O&M Cost/lb P removed/yr (30 yr) 1-1 Stormwater pond % $ 53,970 $ 3,238 $ Raingarden simple % 700 $ 9,800 $ 525 $ Raingarden simple % 300 $ 5,250 $ 225 $ 1, Raingarden simple % 300 $ 5,250 $ 225 $ 1, Raingarden simple % 300 $ 5,250 $ 225 $ Stormwater pond % $ 8,711 $ 523 $ 1,741

25 26 Catchment 2 DESCRIPTION Catchment 2, measuring 346 acres, consists of 50% residential land use branching mostly from Portland Avenue in the east, 44% undeveloped wetland in the center and 6% highway/road cover in the west (see pie chart in Figure 16 and map in Figure 18). For the relatively new housing developments, each drainage area (subdivided into sub-catchments) diverts runoff to its respective stormwater pond. In heavy rains, these ponds overflow into over 100 acres of wetlands which slowly drain westward. The wetlands outlet into a stormwater pond in the southwest corner of Catchment 2. Overflow from this stormwater pond is directed by culvert westward under the railroad tracks and into Bald Eagle Lake, swept by the current of Judicial Ditch 1, which feeds into a stormwater pond directly south of the adjacent pond and follows the same route to discharge into Bald Eagle Lake (Figure 17). Figure 16. Catchment 2 Land Cover Figure 17. Existing stormwater ponds and direction of drainage from Judicial Ditch 1 and the wetland area westward to Bald Eagle Lake Table 7. Catchment 2 Base load for total phosphorus, total suspended sediments, and runoff volume, after subtracting modeled reductions from existing best management practices. Catchment 2 - Existing Contaminant Loading Base Load Treatment Net Treatment % Existing Load Number of BMPs 10 1 Swale, 8 Stormwater Ponds, Street BMP types Sweeping TP () % TSS () % Volume (ft³/yr) %

26 27 RETROFIT RECOMMENDATION Due to the high number of existing best management practices in place (twice as many as the next highest catchment) and the wetland providing additional buffer for stormwater runoff, there are no recommended BMPs for Catchment 2. Figure 18. Catchment 2 Subcatchments with Stormwater ponds in residential areas

27 28 Catchment 3 DESCRIPTION Catchment 3, which has 241 acres, is two thirds residential, with the majority of remaining land cover undeveloped or park (see pie chart in Figure 19 and map in Figure 20). Judicial Ditch 1 passes through Catchment 3, carrying a great deal of water and nutrient load from the east, passing through two sequential stormwater ponds along Hwy 61 before entering Bald Eagle Lake. Runoff from residential subcatchments 3-D and 3-E drains into stormwater ponds before overflowing into JD-1. Subcatchment 3- A lies to the west of Highway 61, and its stormwater flows directly into the lake or into a ditch, flowing north along the railroad tracks before joining the remaining Catchment 3 water in the canal depositing to Bald Eagle Lake. Figure 19. Catchment 3 Land Cover Table 8. Catchment 3 Base load for total phosphorus, total suspended sediments, and runoff volume, after subtracting modeled reductions from existing best management practices. Catchment 3 - Existing Contaminant Loading Base Load Treatment Net Treatment % Existing Load Number of BMPs 5 BMP types 4 Stormwater Ponds, Street Sweeping TP () % 74.7 TSS () % Volume (ft³/yr) %

28 29 RETROFIT RECOMMENDATION Figure 20. Proposed Stormwater Retrofit Locations in Catchment 3 Eagle Brook Church (3-1, 3-2, 3-3, 3-4), Tree Trenches and Rain Gardens The Eagle Brook Church s proximity to JD-1 and Bald Eagle Lake, its public visibility and regular grounds maintenance, and its large area of impervious surface made it an excellent candidate for stormwater BMP retrofits. Rain gardens were found to be most appropriate for the grassy areas between the north parking lot and the stormwater pond, while the central parking lot s existing sidewalk divider provides a nice opportunity to install tree trenches (3-4) for underground stormwater treatment. Most of the parking lot

29 30 area, as well as a portion of nearby Hwy 61, drains to the stormwater pond in the north, which in turn overflows to Judicial Ditch 1. The stormwater pond can be evaluated to see if dredging, alum treatment, or another BMP would be beneficial to improve water treatment for this large area of impervious runoff. 3-7, Streambank Stabilization Figure 21. Eagle Brook parking lot proposed retrofits Where JD-1 crosses under Portland Ave, there is erosion and undercutting of both the north and south banks of the ditch to the west of Portland Ave due to the bottleneck effect where the narrowing of the channel accelerates water, creating greater erosive force. This scoured area loses large amounts of sediment into the stream, as estimated by the BWSR Pollution Reduction Estimator for Stream and Ditch Bank Stabilization (BWSR, 2010). In Figure 22, erosion and considerable soil loss is visible from exposed roots. Bank stabilization is suggested here to reduce the amount of soil and nutrients directly entering the system. Figure 22. Judicial Ditch 1 bank erosion and proposed site of stabilization (Retrofit 3-7)

30 31 Buffalo St (3-5, 3-6, 3-8) Rain Gardens Three additional locations were found to be well-suited for rain gardens, especially retrofits 3-5 and 3-6 which would intercept a great deal of stormwater just before entering JD-1. Retrofit 3-5, on public land, would intercept street runoff from Portland Avenue for about 650 feet before treatment in the east side of Garden Creek Park while Retrofit 3-6, on private land, would treat water from Buffalo St for about 500 feet west of JD-1 as well as some residential runoff before discharge into JD-1. Retrofit 3-8 is a rain garden catching runoff from the parking lot of the Kingdom Hall of Jehovah s Witnesses. Figure 23. Retrofit area 3-5, viewed from Portland Ave (left) and Retrofit area 3-6, seen from Buffalo St (right) Although no formal recommendation is made in this document regarding treatment of the large stormwater ponds east of Hwy 61, north and south of Meehan Drive, further study is recommended for this specific area, since most of the contamination of Bald Eagle Lake, according to the 2012 TMDL, passes through these stormwater ponds. An ironenhanced sand filter bench, an oxygenation system, and alum treatments were discussed options, but water passes swiftly though this area, from southeast to northwest through large culverts, which does not allow time for treatment involving settling out or chemical reactions. Also, the large culverts do not permit for bounce with rain events, which is Figure 24. JD-1 Stormwater ponds North and South of Meehan Dr. (JD-1 goes from southeast to northwest)

31 32 necessary for an IESF treatment. Possible dredging or alternative treatments should be considered to reduce overall nutrient load to Bald Eagle Lake. If all 8 proposed retrofits are implemented in this catchment, it is modeled that 6.5 lbs of TP and 5,865 lbs of TSS would be prevented from entering the lake per year, resulting in a 9% and 35% decrease, respectively, from the base load at total project cost of $86,063, not including annual maintenance. See table 9 below for project-specific results, and table 18 for overall catchment results. Table 9. Summary of modeled TSS and TP reductions and estimated costs for proposed retrofits, Catchment 3 ID BMP Rain garden complexity TSS before TSS after TSS removed TP before TP after TP removed % of Catchment TP reduced BMP area ft2 Total Initial Cost Annual O&M Cost/lb P removed/yr (30 yr) 3-1 Raingarden moderate % 500 $ 8,750 $ 375 $ 2, Raingarden simple % 175 $ 3,063 $ 131 $ 2, raingarden church moderate % 1000 $ 17,500 $ 750 $ 1, Tree trench % 3400 $ 29,450 $ 500 $ 2, Raingarden simple % 500 $ 7,000 $ 375 $ 1, Raingarden simple % 300 $ 5,250 $ 225 $ Streambank Stabilization % 150 $ 9,800 $ 950 $ Raingarden simple % 300 $ 5,250 $ 225 $ 2,617

32 33 Catchment 4 DESCRIPTION The largest catchment by area (455 acres), Catchment 4 is the most significant land contributor of both TP and TSS to Bald Eagle Lake, by pounds as well as concentration (pounds per square mile). Railroad tracks passing southwest to northeast separate the catchment into White Bear Township (north of the tracks) and White Bear Lake (south of the tracks). Slightly less than half the land cover of the catchment is residential (Figure 25). About 1.5 miles of Hwy 61 passes north-south through the catchment, dividing it into an eastern half, which is composed mostly of wetland, and a western half, which is mostly residential (Figure 26). The southernmost lobe, reaching almost to White Bear Lake City Hall, is largely commercial and institutional. A culvert under Hwy 61 brings runoff from the eastern section (subcatchment 4-B) downhill toward the western section (subcatchment 4-A), where RCD-11 conveys this water, as well as runoff collected from the south and surrounding areas, to Bald Eagle Lake. Though some water enters the lake through outfalls in Catchment 4, the vast majority of the water courses through RCD-11, which is a strategic location for stormwater treatment. Figure 25. Catchment 4 Land Cover Table 10. Catchment 4 Base load for total phosphorus, total suspended sediments, and runoff volume, after subtracting modeled reductions from existing best management practices. Catchment 4 - Existing Contaminant Loading Base Load Treatment Net Treatment % Existing Load Number of BMPs 2 BMP types 1 Stormwater Pond, Street Sweeping TP () % TSS () % Volume (ft³/yr) %

33 34 RETROFIT RECOMMENDATION With the exception of street-sweeping and a stormwater pond in a small residential subcatchment (4-C), there are few BMPs currently in place for this area, so there is a great deal of room for improvement for retrofits. Figure 26. Proposed Stormwater Retrofit Locations in Catchment 4

34 35 4-3, Iron-Enhanced Sand Filter The most significant proposed retrofit for this catchment is an iron-enhanced sand filter pump and basin system (4-3) to treat water from Ramsey County Ditch 11, through which the majority of the catchment s runoff passes. The proposed site is on White Bear Township land south of Park Avenue between East Street and Eagle Street (Figure 27). This publically-owned land has about 600 linear feet of ditch coursing through it and ample space to install a system to pump water out for treatment and subsequent return to the system. An estimated 29 lbs of TP and 5,878 lbs of TSS would be removed from RCD-11 annually with the implementation of this retrofit, based on MPCA s median pollutant removal percentages for IESFs and an estimated 10% of ditch water being pumped and treated (MPCA, 2016). Figure 27. Location for Retrofit 4-3 (Park & Eagle) 4-1 and 4-2, Swale and Rain Garden The home at 5422 Bald Eagle Blvd is the lowest point for about 2.3 acres of runoff, collecting first in the home s back yard and coursing westward to the front yard along a residential ditch that turns into a river during rains according to the resident, before crossing underneath Bald Eagle Blvd and draining into the lake. Two proposed retrofits for this area are (4-1), the installation of a vegetated swale for the residential ditch just south of the home and (4-2), a rain garden in the back yard of the home, where it meets the north end of East Street (Figure 28). Figure 28. Location for proposed swale (4-1) (left) and aerial view of 4-1 and 4-2 over a topographic map (right)

35 36 Of all the outfalls along the south and east shores of Bald Eagle Lake, this ditch outfall appeared to carry the most runoff during March rains as indicated by area of liquid water around the outfall in the frozen lake during an early March field reconnaissance trip. Together, the swale and rain garden could remove 1.1 lbs of TP and 323 lbs of TSS annually. For on-site treatment, many bioretention basins (rain gardens) are proposed for this catchment in residential, commercial, and institutional land. Most of the remaining proposed retrofits are in one of three clusters: White Bear High School, the Best Western/McDonald s complex on Hwy 61, and the White Bear Chamber of Commerce/LeeAnn Chin parking lot area. 4-4, Rain Gardens The White Bear High School proposed retrofit is a series of rectangular rain gardens with curb cuts to catch runoff from the school s parking lot, which drains to the east. Collectively, these rain gardens (4-4) are modeled to remove 1.4 lbs of TP and 813 lbs of TSS annually from this high-activity lot. This part of the high school is in a high to medium-high infiltration potential area (TMDL-IP, 2012). Figure 29. Location for proposed rain gardens for Retrofit 4-4 at White Bear High School. 4-5, 4-6, 4-7, 4-8, 4-9, Rain Gardens, Pipe The Best Western/McDonald s complex east of Hwy 61, between 8 th St and 10 th St, has numerous proposed retrofits to the site due to its large area of impervious surface and its ample green space for treatment between the parking lots and Highway 61 (Figure 30).

36 37 Sites 4-5 and 4-7 are proposed curb-cut rain gardens to treat runoff from Hwy is classified as moderate, but 4-7 is classified as complex because the water would need to pass underneath the existing sidewalk to enter the rain garden (Figure 31). Site 4-8 is a proposed underground pipe to connect the parking lot s stormwater runoff to the proposed bioretention basin, since curbline and storm drains in the lot currently prevent runoff from entering the ditch. The east side of the proposed pipe would be located in the existing manhole where runoff collects. 4-6 is a proposed rain garden around the existing Best Western sign and an adjoining parking lot space, where another storm drain is currently collecting runoff (Figure 32). Finally, 4-9 is a proposed rain garden collecting runoff from parking lots east and west of the depression. Curb cuts are already in place, so it is classified as simple. Figure 30. Best Western Retrofits, aerial view Figure 31. Location for Rain garden 4-5 (left), Rain garden 4-7 (right), and conveyance pipe (4-8)

37 Figure 32. Location for rain garden 4-6 (left) and rain garden 4-9 (right) 4-10 and 4-11 Permeable Pavement, Underground Stormwater System The White Bear Chamber of Commerce/LeeAnn Chin parking lot area is a highly frequented series of parking lots with a large amount of impervious surface whose runoff currently enters the stormwater system directly without treatment. The lot was split into three sections, corresponding to drainage areas. The northernmost drainage area closest to Caribou Coffee has a proposed retrofit of permeable pavement (4-10) replacing the current paved surface in strategically located parking spaces with in the area shown in Figure 33 to allow stormwater to infiltrate locally. The underground stormwater storage system (Retrofit 4-11) is located underground near the junction of the southern two drainage areas, where stormwater can drain to the system, and ultimately infiltrate into the sandy soils below. The cost estimate was derived from site-specific estimates requested from two companies using the Minimal Impact Design Standard of 1.1 of runoff treatment from impervious surfaces in their design. Due to Figure 33. Locations for 4-10 and 4-11, aerial view the heavy use of these areas, removal of parking spots for rain gardens was not considered in order to preserve the current number of parking spots. If all 11 proposed retrofits are implemented in this catchment, it is modeled that 34.3 lbs of TP and 8,025 lbs of TSS would be filtered out per year, resulting in a 15% and 12% decrease, respectively, from the base load at total project cost of $405,421, not including annual maintenance.

38 39 See table below for project-specific results, and table 18 for overall catchment results. Table 11. Summary of modeled TSS and TP reductions and estimated costs for proposed retrofits, Catchment 4

39 40 Catchment 5 DESCRIPTION Like Catchment 4, Catchment 5 (101 acres) is divided by the railroad tracks into White Bear Township (north of the tracks) and White Bear Lake (south of the tracks). The runoff from the fields of White Bear Lake High School (the catchment s 6% institutional land) pass into a wetland and stormwater pond, under the railroad tracks via culvert, and through a small stream in a wooded area (part of the catchment s 29% undeveloped land) until Stillwater Street. The remaining 65% of land cover is single-family residential land (Figure 34). Figure 34. Catchment 5 Land Cover Drainage is generally toward the north, with most streets lacking curbs. Bald Eagle Avenue, however, has curbs and catch basins north of Stillwater Street, where two rain gardens are proposed to divert and treat stormwater before entering the lake. On the east side of the Catchment, water enters the lake through an outfall to the west of the end of Park Avenue. A great deal of shoreline erosion has occurred along this part of the Bald Eagle lakeshore due to minimal reinforcement, the action of waves, and the annual erosive force of ice heaving as the frozen lake pushes against the shore (MNDNR, 2012). Table 12. Catchment 5 Base load for total phosphorus, total suspended sediments, and runoff volume, after subtracting modeled reductions from existing best management practices. Catchment 5 - Existing Contaminant Loading Base Load Treatment Net Treatment % Existing Load Number of BMPs 2 BMP types 1 Stormwater Pond, Street Sweeping TP () % TSS () % Volume (ft³/yr) %

40 41 RETROFIT RECOMMENDATION The recommended retrofits are curb-cut rain gardens along Bald Eagle Ave, a shoreline stabilization to the ice-damaged shoreline east and west of Bald Eagle Avenue, and a SAFL Baffle at the intersection of Park Ave and Bald Eagle Blvd E. Figure 35. Proposed Stormwater Retrofit Locations in Catchment 5

41 and 5-2, Rain Gardens Of the two rain gardens in this catchment, 5-1 has a far greater pollution reduction benefit because its neighborshed extends considerably further south than 5-2, whose neighborshed only extends mid-way between Bald Eagle Blvd and Stillwater St, where another catch basin intercepts water from further south (Figure 36). Figure 36. Neighborsheds for 5-1 and , Shoreline Stabilization In Retrofit 5-4, the length of shoreline modeled for stabilization in this area measures 200 linear feet, though actual stabilization length can vary, depending on priority and feasibility of work in individual sections of shoreline. In the area pictured below, soil slumping is visible (left) as well as erosion from ice pushing against the shoreline (right). These areas correspond to shorelines just west and east of where Bald Eagle Avenue meets Bald Eagle Blvd. Figure 37. Erosion and damage from ice-heaving along the southeast lakeshore of Bald Eagle Lake 5-3, SAFL Baffle Retrofit 5-3, a SAFL Baffle, is proposed on Bald Eagle Blvd just west of Park Avenue. The sewershed for this outfall extends east along Park Avenue and southward. The manhole indicated in Figure 38 corresponding to retrofit 5-3 is seen near the end of the stormwater infrastructure east-west line leading to Bald Eagle Lake. Further study should be connected to ensure proper depth and connectivity to the outfall. Included in the price of the SAFL Baffle estimate in this study is the price of adding a sump to a manhole, if it does not currently have a sump. The Preserver by Momentum Environmental is a similar sediment-settling structure made to fit into manholes and is an alternative to the SAFL Baffle.

42 43 Park Ave Figure 38. Location of manhole (left) and stormwater infrastructure (right) for Retrofit 5-3. If all 4 proposed retrofits are implemented in this catchment, it is modeled that 17.0 lbs of TP and 19,483 lbs of TSS would be prevented from entering the lake per year, resulting in a 35% and 149% decrease, respectively, from the base load at total project cost of $52,250, not including annual maintenance. The TSS decrease is so high relative to the base load because the existing conditions model did not take into account the hundreds of feet of eroding shoreline in this area, but rather the general land use type (recreational/undeveloped). See table below for project-specific results, and table 18 for overall catchment results. Table 13. Summary of modeled TSS and TP reductions and estimated costs for proposed retrofits, Catchment 5 ID BMP Rain garden complexity TSS before TSS after TSS removed TP before TP after TP removed % of Catchment TP reduced BMP area ft2 Total Initial Cost Annual O&M Cost/lb P removed/yr (30 yr) 5-1 Raingarden moderate % 500 $ 8,750 $ 375 $ Raingarden moderate % 300 $ 7,500 $ 225 $ 2, SAFL Baffle % n/a $ 10,000 $ 240 $ Shoreline Stabilization % 600 $ 26,000 $ 9,500 $ 666

43 44 Catchment 6 DESCRIPTION Catchment 6 (106 acres) has 84% residential land cover (Figure 39). The remaining 16% undeveloped or park land consists of Mead Park in the southwest corner as well as wooded areas, such as the area beside the railroad tracks along the southern edge of the catchment (see map in Figure 40). Similar to Catchment 5, the only existing BMPs counted in the model are biannual street sweeping and one stormwater pond, located in 6-B. Acreage, land use, and nutrient loading is very similar to Catchment 5, and similar retrofits are proposed in this section. Saint Anthony Avenue has stormwater infrastructure outletting directly into Bald Eagle Lake, affording an opportunity for stormwater treatment in the area of concentrated flow. Some areas of the shoreline show signs of erosion and would benefit from stabilization. Figure 39. Catchment 6 Land Cover Table 14. Catchment 6 Base load for total phosphorus, total suspended sediments, and runoff volume, after subtracting modeled reductions from existing best management practices. Catchment 6 - Existing Contaminant Loading Base Load Treatment Net Treatment % Existing Load Number of BMPs 2 BMP types 1 Stormwater Pond, Street Sweeping TP () % 50.4 TSS () % Volume (ft³/yr) %

44 45 RETROFIT RECOMMENDATION The highest-ranked retrofits for Catchment 6 are a shoreline stabilization (6-4) and a SAFL Baffle (6-5) at the intersection of St Anthony Ave and W Bald Eagle Ave. From the early March reconnaissance trip to view outfalls, this outfall was one of few that showed considerable liquid water where the outfall met the lake, indicating a relatively large drainage area. Also visible was sediment, which could have been from a combination of the crumbling shoreline and the runoff conveyed through stormwater infrastructure. Figure 40. Proposed Stormwater Retrofit Locations in Catchment 6

45 and 6-5, Shoreline Stabilization & SAFL Baffle Pictured below is the degraded shoreline at the point of the outfall (left), which is recommended for stabilization (Retrofit 6-4) as well as the catch basin (right) where the SAFL Baffle (Retrofit 6-5) is proposed. SAFL Baffles are intended for placement in sumps of either manholes or catch basins, and from initial review, the catch basin pictured below is the best location to install the SAFL Baffle, though it may be necessary to first create a sump, which is included in the price estimate. Both 6-4 and 6-5 are on right-ofway land. Figure 41. Locations for Retrofit 6-4 (left) and Retrofit 6-5 (right) 6-1, 6-2, 6-3, Rain Gardens and Shoreline Stabilization The remaining 3 retrofits suggested for Catchment 6 are clustered around the intersection of West Avenue and W Bald Eagle Blvd. West Avenue conveys runoff from approximately 500 ft southward downhill to an abandoned boat launch (left), where runoff enters the lake. This right-of-way property was chosen for a rain garden (6-3) due to its high volume of polluted water and its vulnerable position adjacent to the lake. Just west of the launch, slumped land and shoreline degradation (pictured below to the right) is the site of Retrofit 6-2 for Shoreline Stabilization. Figure 42. Location for Retrofits 6-3 (left) and 6-2 (right)

46 47 Finally, Retrofit 6-1 is a proposed rain garden on private land just south of W Bald Eagle Blvd, where runoff from the street as well as residential lots drain. The rain garden would intercept and filter pollutants destined for the existing beehive storm drain structure (Figure 43). Figure 43. Location for Retrofit 6-1 If all 5 proposed retrofits are implemented in this catchment, it is modeled that 5.0 lbs of TP and 4,775 lbs of TSS would be prevented from entering the lake per year, resulting in a 10% and 33% decrease, respectively, from the base load at total project cost of $39,950, not including annual maintenance. See table below for project-specific results, and table 18 for overall catchment results. Table 15. Summary of modeled TSS and TP reductions and estimated costs for proposed retrofits, Catchment 6 ID BMP Rain garden complexity TSS before TSS after TSS removed TP before TP after TP removed % of Catchment TP reduced BMP area ft2 Total Initial Cost Annual O&M Cost/lb P removed/yr (30 yr) 6-1 Raingarden moderate % 300 $ 7,500 $ 225 $ 1, Shoreline Stabilization % 60 $ 2,600 $ 950 $ Raingarden complex % 750 $ 17,250 $ 563 $ 2, Shoreline Stabilization % 60 $ 2,600 $ 950 $ SAFL Baffle % n/a $ 10,000 $ 240 $ 774

47 48 Catchment 7 DESCRIPTION Catchment 7, consisting of 90 acres along the west shore of Bald Eagle Lake, is the smallest catchment with the least amount of modeled pollution. 62% of the land cover is residential, with the remaining 38% of land undeveloped, such as wetlands in the lowland areas between Otter Lake and Bald Eagle Lake. Few retrofits were proposed in this area because of the low contaminant load and because the topography and lack of stormwater infrastructure are not conducive to intercepting large amounts of storm water. With a narrow band of land draining directly into the lake, drainage areas are quite small for any particular BMP. Furthermore, much of the residential land drains to wetlands for pre-treatment before entering Bald Eagle Lake. Figure 44. Catchment 7 Land Cover Table 16. Catchment 7 Base load for total phosphorus, total suspended sediments, and runoff volume, after subtracting modeled reductions from existing best management practices. Catchment 7 - Existing Contaminant Loading Base Load Treatment Net Treatment % Existing Load Number of BMPs 1 BMP types Street Sweeping TP () % TSS () % 9302 Volume (ft³/yr) %

48 49 RETROFIT RECOMMENDATION Retrofits for Catchment 7 consist of establishing native vegetation buffers along shores of properties which currently have turf lawns lacking a buffer before runoff potentially containing fertilizers, lawn clippings, or other pollutants enters the lake. For the privacy of homeowners, private shorelines (not visible from the street) were not visited. Catchment 7 sites identified in this study were selected from viewing aerial imagery. A physical shoreline assessment is recommended to determine the most urgent areas requiring shoreline restoration and/or native vegetation buffer establishment. Figure 45. Proposed Stormwater Retrofit Locations in Catchment 7

49 50 7-1, 7-2, 7-3, 7-4, Native Buffers Modeled benefits for these native buffers are quite low, yielding high costs per pound of phosphorus removed and occupying the lowest priority projects of the ranked list. Actual benefits may be much higher, depending on the status of the shorelines. If shorelines are eroding, a combination of native buffer/shoreline stabilization would be the best choice, for a much higher reduction in nutrients entering the lake. If all 4 proposed retrofits are implemented in this catchment, it is modeled that 0.3 lbs of TP and 42.6 lbs of TSS would be prevented from entering the lake per year, resulting in a 1% and 0.5% decrease, respectively, from the base load at total project cost of $39,950, not including annual maintenance. Figure 46. Locations of Retrofits 7-1 and 7-2. See table below for project-specific results, and table 18 for overall catchment results. Table 17. Summary of modeled TSS and TP reductions and estimated costs for proposed retrofits, Catchment 7 ID BMP Rain garden complexity TSS before TSS after TSS removed TP before TP after TP removed % of Catchment TP reduced BMP area ft2 Total Initial Cost Annual O&M Cost/lb P removed/yr (30 yr) 7-1 Native Buffer % 800 $ 5,344 $ 275 $ 7, Native Buffer % 1200 $ 8,016 $ 380 $ 6, Native Buffer % 1000 $ 6,680 $ 380 $ 7, Native Buffer % 800 $ 5,344 $ 275 $ 9,061

50 51 Conclusions and Recommendations The objective of this study was to present a detailed review of the drainage area within the south Bald Eagle Lake subwatershed in order to identify the most cost-effective retrofits to existing stormwater conveyance practices that could be implemented to improve water quality, reduce runoff, reduce TP and TSS, and enhance groundwater recharge. A variety of retrofits were recommended, including an iron enhanced sand filter, bioretention basins, permeable pavement, shoreline stabilization, bank stabilization, SAFL Baffles, native vegetation buffers, stormwater ponds, a vegetated swale, an underground storage system, and a tree trench system. These practices require further study prior to implementation to generate functional designs and more accurate cost estimates. Only general estimates are provided in this report due to the broad scope of the study and time restrictions. If all of the proposed retrofits were implemented, models indicate an annual reduction of 15% TP and 32% TSS in the entire subwatershed s runoff (Table 18). Table 18. Total estimated annual reduction of total phosphorus and total suspended solids if all proposed retrofits are implemented in the south Bald Eagle Lake subwatershed Catchment Contaminant Load Potential Reduction TP Base Load () TP pot. Reduction () TSS Base Load () TSS pot. Reduction (lb/year) * TOTAL % Reduction 15% 32% * Values do not include Judicial Ditch 1 nutrient load Of the proposed retrofits, three stand out as high-ranking, large projects that together account for 78% of the proposed TP reduction and 75% of the proposed TSS reduction: 1-1, the Stormwater Pond in Catchment 1 4-3, the Iron Enhanced Sand Filter pump system for RCD-11 in Catchment 4 5-4, the Shoreline Stabilization project along Bald Eagle Blvd in Catchment 5

51 52 Since the internal loading of Bald Eagle Lake has recently been treated with aluminum sulfate, the next largest contributor of phosphorus to Bald Eagle Lake is Judicial Ditch 1. Although it is the most crucial water body to treat, it presents many challenges due to its high flow, high percentage of dissolved phosphorus, and its tremendous drainage area, mostly in Washington County. Oxygenation of the ditch has been attempted, with unsatisfactory results. An Iron Enhanced Sand Filter bench was considered in one of the stormwater ponds near the end of the ditch, but the bounce of the pond would not be high enough to treat a large amount of water and to thoroughly dry the sand filter between rains. Dredging, oxygenation, and alum treatment of the ponds are other possible projects to consider to reduce the phosphorus content of the ditch. Although no individual project was chosen and priced out in this analysis, it is recommended that a study be completed to determine the most effective practice to treat water from Judicial Ditch 1. In commercial areas near Highway 61 in Catchment 4, it is recommended to sweep streets with more frequency, such as monthly, to achieve the same beneficial effect as the twice-annual sweeping of residential streets. Another suggestion is to conduct studies of ditch banks for RCD-11 and JD-1 to identify bank degradation sites for stabilization projects. Likewise, a more thorough investigation of the shoreline would highlight the shoreline areas in greatest need of stabilization to reduce direct sediment and nutrient contact with Bald Eagle Lake. Homeowners can also do their part by following best practices such as infrequent mowing of ditches, the use of phosphorus-free lawn fertilizers, and collecting grass clippings and leaves before lawn waste enters stormwater conveyance systems to Bald Eagle Lake, where the nutrient load can lead to algal blooms. Lakeshore homeowners should implement a shoreline restoration where needed to have a native plant buffer between turf lawns and the lake to reduce erosion and capture direct runoff. Rice Creek Watershed District has a Clean Water cost-share program that would help home-owners finance such beneficial projects on their land. For Washington County s golf courses and agricultural fields, best management practices such as stormwater collection and reuse, establishment of buffer zones, bio-infiltration, and fertilizer management are recommended to reduce nutrient loading to Judicial Ditch 1 and Bald Eagle Lake. These BMPS are meant to slow the rate of stormwater conveyance, reduce or filter pollutants, and promote stormwater infiltration. Design, modeling, and placement for these BMPs require individual study to assure the maximum benefit. This analysis represents one of many components of a comprehensive watershed restoration plan other important components include: educational outreach, buffer zone management, discharge prevention, upland native plant community restoration, and pollutant source control. The implementation of the retrofits described in this analysis would be a significant step to reducing the harmful impact of polluted surface runoff to the impaired Bald Eagle Lake system.

52 53 Appendix A. WinSLAMM Modeling Parameters and Land Use Codes WinSLAMM modeling parameters and files used in the analysis File Name Date Created/ Last Modified Created By Description CPZ: These files contain the sediment particle size distributions developed from monitored data. The files area used in the evaluation of control practices that rely upon particle settling for pollution control. NURP.CPZ 5/16/88 Pitt/UA Summarizes NURP outfall particle size data PPD (Pollutant Probability Distribution) files describe the pollutant concentrations found in source areas. USGS/DNR pollutant probability distribution file from Wisconsin WI_GEO01.ppd 11/26/02 Horwatich/USGS monitoring data. PRR (Particulate Residue Reduction) files describe the fraction of total particulates that remains in the drainage system (curbs and gutters, grass swales, and storm drainage) after rain events end due to deposition. This fraction of the total particulates does not reach the outfall, so the outfall values are reduced by the fraction indicated in the.prr file. USGS/DNR particulate residue reduction file for the delivery WI_DLV01.prr 7/8/01 Horwatich/USGS system from Wisconsin monitoring data. RSV (Runoff coefficient file). These coefficients, when multiplied by rain depths, land use source areas, and a conversion factor, determine the runoff volumes needed by WinSLAMM. WI_SL06 Dec06.rsv 12/18/06 Horwatich/USGS USGS/DNR runoff volumetric coefficient file from Wisconsin monitoring data. Use for all versions of WinSLAMM starting from v STD (Street Delivery File): These files describe the fraction of total particulates that are washed from the streets during rains, but are subsequently redeposited due to lack of energy in the flowing water. WI_Com Inst Indust Dec06.std WI_Res and Other Urban Dec06.std Freeway Dec06.std 12/12/06 Horwatich/USGS 12/07/06 Horwatich/USGS 7/12/05 Pitt/UA USGS/DNR street delivery file from Wisconsin monitoring data. Use for all versions of WinSLAMM starting from v for Industrial, Commercial and Institutional land uses. USGS/DNR street delivery file from Wisconsin monitoring data. Use for all versions of WinSLAMM starting from v for Residential and Other Urban land uses. Street delivery file developed to account for TSS reductions due to losses in a freeway delivery system based upon early USDOT research. Renamed Freeway.std PSC (Particulate Solids Concentration): Values in this file, when multiplied by source area runoff volumes and a conversion factor, calculate particulate solids loadings (lbs). WI_AVG01.psc 11/26/02 Horwatich/USGS MN Minneapolis 59.RAN Parameter Start/End Date Winter Season Range Drainage System NA NA RAN (Rain Files): USGS/DNR particulate solids concentration file from Wisconsin monitoring data. A n event-record of rainfall for the year 1959, considered as an average year, in the form of Start Date, Start Time, End Date, End Time and Rainfall (in inches). Settings Description Defines the modeling period in reference to the rain file data. In this case, the entire one year period was selected (i.e., 01/02/59-12/28/59). Set to begin on November 7 th and end on March 17 th. Set to Curb and gutter, valleys, or sealed swales in fair condition. Appendices South

53 54 WinSLAMM Standard Land Use Codes: RESIDENTIAL LAND USES Medium Density Residential without Alleys (MDRNA): 2-6 units/acre. Low Density Residential (LDR): Same as HDRNA except the density is 0.7 to 2 units/acre. High Density Residential without Alleys (HDRNA): Urban single family housing at a density of greater than 6 units/acre. Includes house, driveway, yards, sidewalks, and streets. Multiple Family Residential (MFRNA): Housing for three or more families, from 1-3 stories in height. Units may be adjoined up-and-down, side-by-side; or front-and-rear. Includes building, yard, parking lot, and driveways. Does not include alleys. Suburban (SUB): Same as HDRNA except the density is between 0.2 and 0.6 units/acre. INDUSTRIAL LAND USES Medium Industrial (MI): This category includes businesses such as lumber yards, auto salvage yards, junk yards, grain elevators, agricultural coops, oil tank farms, coal and salt storage areas, slaughter houses, and areas for bulk storage of fertilizers. Light industrial (LI): Those buildings that are used for the storage and/or distribution of goods waiting further processing or sale to retailers. This category mostly includes warehouses, and wholesalers where all operations are conducted indoors, but with truck loading and transfer operations conducted outside. INSTITUTIONAL LAND USES Education (SCH): Includes any public or private primary, secondary, or college educational institutional grounds. Includes buildings, playgrounds, athletic fields, roads, parking lots, and lawn areas. Miscellaneous Institutional (INST): Churches and large areas of institutional property not part of CST and CDT. OTHER URBAN LAND USES Parks (PARK): Outdoor recreational areas including municipal playgrounds, botanical gardens, arboretums, golf courses, and natural areas. Open Space or Undeveloped (OSUD): Lands that are private or publicly owned with no structures and have a complete vegetative cover. This includes vacant lots, urban fringe areas slated for development, greenways, and forest areas. FREEWAY LAND USES Freeways (FREE): Limited access highways and the interchange areas, including any vegetated rights-of-ways. The freeway standard land use files require the typical cross section type, the average daily traffic (ADT) level, and the slope. Appendices South

54 55 Appendix B. Bioretention design Curb cut rain garden, with 1.5-2ft perimeter wall, in a residential area. Bioretention design WinSLAMM Bioinfiltration Control Device parameters Graphic courtesy of Charles River Watershed Association, Weston, MA. Appendices South

55 56 Biotention design example in WinSLAMM Appendices South