Como 3 subwatershed analysis (draft)

Como 3 Subwatershed Analysis

July 21, 2010

Changes from previous draft noted in yellow

Prepared For:

Capitol Region Watershed District

Prepared By:

TABLE OF CONTENTS A. Executive Summary.................................................................................................. 1 B. Introduction............................................................................................................... 1 C. Project Goals ............................................................................................................ 2 D. Data Inventory and Subwatershed Delineation...................................................... 2 E. Baseline Modeling .................................................................................................... 9

E.1. XPSWMM Modeling..................................................................................... 9 E.2. P8 Modeling ............................................................................................... 12

F. Preliminary BMP Identification .............................................................................. 14 G. BMP Evaluations .................................................................................................... 17

G.1. High Priority BMP Opportunities............................................................. 17 G.2. Low Priority BMP Opportunities.............................................................. 36 G.3. Future BMP Opportunities ....................................................................... 41 G.4. Results....................................................................................................... 44

H. Recommendations.................................................................................................. 45 Figures Figure 1 – Subwatershed Boundary Delineation (10-ft Contours) Figure 2 – Impervious Areas Figure 3 – Soil Types Figure 4 – Land Use Figure 5 – Subwatershed Boundary Delineation (1-ft Contours) Figure 6 – Storm Sewer Network Figure 7 – Potential BMP Locations Figure 8 – Site 2 - Underground Infiltration at Orchard Recreation Center Figure 9 – Site 4 – Median Rain Garden Figure 10 – Site 5 – Pool Reconstruction – Underground Storage/Reuse Basin Figure 11 – Site 7 – Pervious Parking Lot near Como Lake Pavilion Figure 12 – Site 8 – Intersection Realignment and Boulevard Rain Gardens Figure 13 – Site 9 – Pervious Parking Lot at Como Park Senior High School Figure 14 – Site 10 – Street Reconstruction with Bump-out Rain Gardens Figure 15 – Site 15 – Underground Filtration at Chatsworth and Como Tables Table 1 – Trunk Line/Subcatchment Drainage Areas Table 2 – Subcatchment Areas Table 3 – Subcatchment Runoff Volumes for 5-yr, 24-hr Event Table 4 – Surcharged Manholes (5-Year Storm) Table 5 – Phosphorus Loading Limits from CLSP Table 6 -- Phosphorus Loading Como 3 Study Table 7 – Potential BMP Sites Table 8 – High Priority BMP Sites Table 9 – Summary of High Priority Site Phosphorus Removal Table 10 – Low Priority BMP Sites Table 11 – Future BMP Opportunities Appendix Appendix A – Engineer’s Opinion of Probable Cost Appendix B – Soil Borings Appendix C – Hydrologic Soil Information

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A. Executive Summary

The purpose of this study was to identify potential Best Management Practice (BMP) facilities within the Como 3 Subwatershed to efficiently reduce the phosphorus loading into Como Lake by 107-lbs/year. Reduction of phosphorus loading into the lake is expected to improve the water quality of the lake for both wildlife and residents visiting the lake and surrounding park.

Preliminary BMP sites were identified based on criteria established by the study team. Existing information was gathered from various sources and a stormwater runoff model was created using XP Engineering Stormwater Wastewater Software (XPSWMM). A Program for Predicting Polluting Particle Passage thru Pits, Puddles, and Ponds (P8) model was developed to evaluate water quality, specifically phosphorus loading. These models set a baseline for stormwater volume and phosphorus loading that was later used to identify and evaluate selected high priority BMP locations. A calculated phosphorus loading reduction of 124.5-lbs/yr was estimated for the eight high priority sites. The established yearly reduction goal of 107-lbs/yr is expected to be surpassed by these sites. Capitol Region Watershed District (CRWD), through its permitting process of construction activities will continue to require volume reduction measures on developments. CRWD also will continue to encourage water quality improvement by residents and other governing bodies. B. Introduction

In 2002, CRWD completed the Como Lake Strategic Plan (CLSP). Its purpose was to identify important Como Lake management issues through input from key stakeholder groups, prioritize the issues and associated goals, and identify implementation activities including institutional and public roles, time frame, and funding. The planning process identified stakeholder concerns and issues with the lake, developed goals and expectations for the future of the lake and then developed strategies and implementation activities to meet the desired goals.

In 2003, CRWD completed a more detailed analysis of Como Lake 7 Subwatershed. That study led to improvement projects within the Como 7 Subwatershed and since then, CRWD has turned its attention to the study of the Como 3 Subwatershed. The initiation of this study was the next step in CRWD’s pursuit of implementation of the CLSP.

This study required coordination between CRWD, City of St. Paul Public Works, and City of St. Paul Parks and Recreation to fully evaluate existing data and formulate a plan to achieve the expectations defined in the CLSP. The following report is supported by each aforementioned entity and utilized the experience and findings of the previous studies.

The CLSP established a goal of 60% reduction of phosphorus loading for Como Lake. This goal was based on input and general guidance from the plan’s Advisory Committee to reduce, to the maximum extent possible the loadings to the Lake. After gathering watershed information from various sources, this study identified fifteen specific BMP locations and evaluated them to varying degrees for potential phosphorus removal. Through discussions with CRWD and other entities, eight sites were classified as high priority sites and were evaluated further through modeling and preliminary design. This study reflects the CLSP goal of phosphorus reduction of 107-lbs/yr or 60% of the calculated current phosphorus loading within the Como 3 Subwatershed. This study’s evaluations indicate that the eight priority sites provide an initial annual reduction of 124.5-lbs/yr. All together these selected sites surpass the goal. It is

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anticipated that the other lower priority sites, when implemented, will provide further reduction as City of St. Paul and project partners continues to implement projects to improve the water quality of Como Lake. In addition to implementing the BMP projects described in this report, activities such as street sweeping, reduction of pervious areas during reconstruction and use of non-phosphorus fertilizer will allow City of St. Paul and project partners to achieve loading reduction goals in Como Lake.

C. Project Goals

The primary work product for this study was to develop stormwater runoff and water quality models to enable the identification and evaluation of BMP’s capable of effectively removing phosphorus and reducing stormwater volume. To achieve this goal, the following tasks were completed:

1. Evaluate existing information 2. Develop a detailed stormwater runoff and water quality model 3. Evaluate the water quality impacts and opportunities to implement the CRWD’s

target pollutant reduction goal of 107-lbs/yr 4. Develop an implementation plan including costs and proposed schedule

These four steps led the study team to assemble data from field visits, previous studies and modeling activities, and other governing agencies. The study team then used two separate computer models to evaluate the subwatershed. XPSWMM was utilized to model the hydrology and hydraulics of the existing storm sewer trunk lines while P8 modeled phosphorus load concentrations. The P8 software was utilized to evaluate the effectiveness of various BMP facilities, calculate the phosphorus load reduction, and estimate stormwater runoff volume reduction within the Como 3 Subwatershed.

D. Data Inventory and Subwatershed Delineation

The City of St. Paul provided the study team AutoCAD data containing 1-foot contour elevations, storm sewer locations and characteristics, and street mapping. CRWD provided GIS shapefiles showing general watershed delineation (Figure 1), impervious areas (Figure 2), soil infiltration potential (Figure 3), and land use (Figure 4). All available information was first combined and organized in an ArcMap GIS document. ArcMap was used to extract information about the storm sewers and aided in calculation of hydrologic characteristics (time of concentration and runoff coefficients) of the Como 3 Subwatershed. The resulting databases were then imported into XPSWMM for analysis.

The Como 3 Subwatershed boundary, which was initially developed by CRWD based on 10-foot contour data, was refined utilizing 1-foot contour data (Figure 5). The computed subwatershed area measured 516.5 acres utilizing the 10-foot contours and 458.2 acres utilizing the 1-foot contours. The use of the 1-foot contours to refine the subwatershed boundaries resulted in a subwatershed covering an area 88.7% of the initial size. Section E.2 of this report indicates how this area reduction was incorporated into the study’s phosphorus loading.

During field investigations, two areas were identified that likely do not drain to Como Lake. The Bandana Square parking lot, between Energy Park Drive and the railroad tracks to the north,

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discharges to storm sewer catchbasin manholes nearly 16-feet deep. Considering their location in the watershed, such deep storm sewers suggest that the outfall location is likely west into the St. Anthony Park subwatershed. The property management was contacted and plans for the sewer network were reviewed. The Bandana Square storm sewer network flows to the northeastern corner, but the exact outfall is yet unknown as the Bandana Square network appears to discharge into the adjacent property’s storm sewer.

Another area, southeast of 1200 Energy Park, adjacent to Lexington and the railroad to the south, appears to drain to a basin without an outlet. Information regarding this drainage system has been requested from the Port Authority. As of the date of this report, information is still pending regarding these locations; therefore, this study removes these two drainage areas from the contributing area to Como Lake and the associated loading of the area is zero-lbs/yr.

The subwatershed was divided into smaller subcatchments representing drainage areas associated with storm sewer trunk lines that discharge to Como Lake. Figure 5 and the following Table 1 provide descriptions of the subcatchment areas.

Table 1 – Trunk Line/Subcatchment Drainage Areas

Trunk Line/ Subcatchment

Drainage Area (acres)

1 21.8 2 47.5 3 83.8 4 224.5 (1) 5 51.4 6 15.1

(1) Excludes 14.1-ac of Bandana Square and 1200 Energy Park

These storm sewer trunk line subcatchments were then divided into subcatchments at logical points to model the hydraulics of the existing system. The subcatchment labeled “San_Sewer” at the Como Swimming Pool drains to the sanitary sewer and is therefore excluded from the Como 3 Subwatershed. Subcatchment 6_2 drains to the Como 7 Subwatershed 60-inch trunk line (Figure 5) and was therefore not modeled as part of this analysis. Subcatchment 6_1 partially drains through storm sewer and overland flow into Como Lake. Since the conveyance is not part of a major trunk line it was not included in the hydraulic model. Subcatchment 4_5 flows were added to subcatchment 4_1 in the model. It was delineated separately due to the existence of Lily Pond and the need to analyze the pond in the P8 model.

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Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 5

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Table 2 - Subcatchment Areas

Subcatchments Drainage Area (acres)

Percent of Como 3 Subwatershed

1_1 21.8 4.7% 2_1 7.9 1.7% 2_2 21.1 4.6% 2_3 18.5 4.0% 3_1 42.5 9.3% 3_2 41.3 9.0% 4_1 61.9 13.5% 4_2 77.2 16.8% 4_3 22.7 4.9% 4_4 50.9 (1) 11.1% 4_5 4.7 1.0% 4_6 7.2 1.6% 5_1 8.6 1.9% 5_2 5.1 1.1% 5_3 11.0 2.4% 5_4 26.6 5.8% 6_1 13.3 2.9% 6_2 1.8 0.4%

San_Sewer 1.0 0.2% (1) Excludes 14.1-ac (3.1%) of Bandana Square and 1200 Energy Park

With the collection of various data, the study team was able to begin the process of establishing baseline modeling for both hydraulic computations and phosphorus loading.

E. Baseline Modeling E.1. XPSWMM Modeling

Two methodologies were utilized to estimate the flows from the subcatchments. The first methodology employed composite runoff curve numbers (CNs), which were generated for each subcatchment by dividing the subcatchments into pervious and impervious areas then calculating a weighted average based on area. Pervious areas were treated as “open-space” with “good” (>75%) cover. The pervious area was given a CN of 62 based on likely soil conditions. This also conformed to the XPSWMM model used in the Como 7 Subwatershed Analysis and Natural Resources Conservation Service (NRCS) TR-55 documentation. All impervious areas were assigned a CN of 98.

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The second methodology kept the pervious and impervious areas distinct within the hydrology calculations. This methodology resulted in 18% to 20% higher flows in the system. Based on previous experience with similar systems in urban watersheds, the higher flows more accurately represent anticipated runoff rates. Consequently, the second methodology was utilized for all hydraulic and volume reduction calculations for the subwatershed study.

Runoff volumes and peak flows were calculated for the one-inch, 5-year (3.6 inch) and 100-year (5.9 inch) 24-hour storm events using the Soil Conservation Service (SCS) Type II Distribution hydrograph. The one-inch storm, often referred to as the “first flush” event, typically includes the greatest concentration of pollutants. The 5-year storm is used to evaluate storm sewer conveyance systems, since it matches the design standard of the City of St. Paul. The 100-year storm is generally considered the event to be evaluated for severe flooding. During this study however, a limited effort was spent on the 100-year event since evaluation of that event would require modeling of all street sections to include overland routing of stormwater. The overland evaluation was outside the scope of the present study.

Representation of the pipe network was imported to XPSWMM from ArcMap Geographic Information Systems (GIS). The model includes the location, elevations, and physical characteristics of the five major trunk lines discharging into Como Lake within the subwatershed. The GIS information was checked against as-built sewer strip maps provided by the City of St. Paul and suspected errors were documented and corrected based on engineering judgment. Further field reconnaissance by HR Green staff revealed other discrepancies which were noted and corrected in the model. This corrected information was reviewed and approved by City Public Works staff. Figure 6 displays the storm sewer network evaluated. Included in the model network are storm sewer locations within park property which was provided by St. Paul Parks and Recreation.

Runoff generated by the storm events in the runoff layer were applied to the pipe network at the most downstream manhole/catch basin in each subcatchment. Flows from subcatchment 4_1 and 4_5 were both applied at the same location: MH 119200. Although all manhole and lateral storm sewer pipe data are included in the XPSWMM model, flows were only applied to the main trunk lines. The following table shows the runoff volumes produced in each subcatchment for the 5-year, 24-hour storm and the volume not conveyed by the storm sewer trunk lines due to modeled surcharge of stormwater to the surface.

Table 3 -- Subcatchment Runoff Volumes for 5-yr, 24-hr Event

Trunk Line/ Subcatchment

Total Runoff Volume (cf)

Volume in Excess of Pipe Capacity (cf)

1 139,410 0 2 266,920 0 3 486,290 8,540 4 1,166,780 51,380 5 98,530 0 6 65,670 0

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Figure 6

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The following table shows the ID number and location of surcharged manholes during the 5-year, 24-hour storm.

Table 4 -- Flooded Manholes (5-Year Storm)

ID Number Location Subcatchment

116704 Chatsworth St. and Jessamine Ave. 3 116703 Chatsworth St. and Jessamine Ave. 3 116711 Chatsworth St. half block south of Como Ave 3 116595 West of Gateway Dr. 3 116270 Lexington Pkwy. and Energy Dr. 4 116375 Lexington Pkwy. and Jessamine Ave. 4 116374 Lexington Pkwy. and Jessamine Ave. 4 116373 Lexington Pkwy. and Como Ave. 4 119183 Lexington Pkwy. and Horton Ave. 4 119169 Lexington Pkwy. and Horton Ave. 4 119200 Horton Ave. and Como Blvd. 4 119188 Horton Ave. and Church Hill St. 4

Surcharge at these manholes indicates insufficient downstream pipe capacity during the 5-year event and the excess water is conveyed by the street. While outlet structures to Como Lake for subcatchments 1, 2, and 3 appeared functional and consistent with the provided information, the outlet structure for subcatchment 4 appeared smaller than the provided size and was changed in the model to reflect the field verified size. This may explain the prevalent manhole surcharge shown in the model results. The outlet for subcatchment 5 was observed to be 75% filled with sediment at the outfall. As a result, the model was adjusted to reflect the reduced conveyance.

The XPSWMM model was provided to City of St. Paul staff for review of the City’s storm sewer system. The study team’s review of the data was useful to the City as they continue to develop their city-wide storm sewer database. E.2. P8 Modeling

The P8 model was used to estimate the phosphorus load from each subcatchment. Existing models for the entire district were provided by CRWD. The Como 7 Subwatershed Analysis used a modified version of this existing P8 model. The methodology and assumptions used to build the P8 model in the Como 7 study were followed to modify the Como 3 model. The study team included the following information to develop the Como 3 model:

• Daily precipitation and temperature data files from the Minneapolis/St. Paul Airport

• The period from September 30th, 1994 through October 1st, 1995 was chosen as the one-year runtime

• A pollutant particle distribution file which was calibrated to observed stormwater quality outputs in the District was provided by CRWD

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• The P8 model was modified to include only the subcatchments delineated in the Como 3 Subwatershed.

The total yearly phosphorus load was calculated by adding the modeled output of subcatchments that discharge out of the Como 3 subwatershed (i.e. the most downstream subcatchments.) All subcatchments eventually output to Como Lake except those previously described: 6_2 (outputs to Como 7 subwatershed) and 4_6 (outputs to ephemeral pond north of Como Avenue). The phosphorus load from 4_6 was included in the baseline P8 model to reflect the possibility of treatment. Subcatchment 4_5 is treated by the existing Lily Pond, which removes an estimated 93.6% of the total 0.9 pounds of phosphorus produced per year. The remaining phosphorus is discharged to subcatchment 4_1.

A comparison of flow rates and volumes was made between the P8 model and the XPSWMM model in an effort to establish confidence in the results. Each software model was run with a 24-hour 5-year event with Type II rainfall distribution. The total runoff volume each model produced was within 3% of each other: 54.2 ac-ft (P8) versus 52.9 ac-ft (XPSWMM). Consequently, the design team believes the P8 model adequately reflects the hydrologic conditions within the watershed.

The previous CLSP P8 model of the greater Como Lake watershed predicted the existing phosphorus output from the Como 3 subwatershed to be 233 pounds per year. The Como 3 P8 model predicted the phosphorus output to be 156 pounds per year. This result is 67% of the previous CRWD P8 model. The lower calculated phosphorus loading is attributed to refinement of the Como 3 subwatershed area using more precise topography (1-foot contours verses 10-foot contours) and refined CN values for the pervious areas in each subcatchment. The modeled particle distribution matched what was used in the previous study of Como 7 Subwatershed and would not affect the difference in calculated loading. Discussions with CRWD indicated the desire to follow the previously determined phosphorus load reduction target of 107-lbs/yr, versus the relative percentage reduction. Therefore the study team used the previously established loading reduction target as the reduction goal.

Table 5 provides the calculated target phosphorous load reduction based on the methodology used in the Como Lake Strategic Management Plan. Table 5 -- Phosphorus Loading Limits from CLSP

Initial

P Load Target 60% Reduction

Weighting Factor

Weighted Reduction

Initial 20% Reduction

Final Reduction Target

(lb/yr) (lb/yr) (lb/yr) (lb/yr) (lb/yr) 233 140 1.1 154 47 107

The CLSP specifies an initial target phosphorus reduction of 60%. The target reduction is weighted based on the priority assigned in the Plan. The Final Reduction Target is the Weighted Reduction minus a 20% reduction in the Initial Phosphorus Load as a result of redevelopment and good housekeeping procedures already met. A final phosphorus load discharge of 49 pounds per year is expected after water quality BMPs are fully implemented. This is the difference between the calculated Como 3 P8 existing model loading (156 lb/yr) minus the final target reduction (107 lb/yr).

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The study revised the phosphorus loading target more by reducing the loading rate relative to the reduction in drainage area as determined by subwatershed boundary redelineation. A loading rate was calculated by dividing the initial Como 3 boundary by the CLSP final reduction target. This rate (0.207-lbs/yr/ac) was then multiplied by the revised boundary area. Two further reductions were made based on the two field identified areas likely not contributing to the subwatershed. As a result, the final Study BMP Target Reduction is 92.0-lbs/yr. Table 6 below summarizes the calculations. Table 6 -- Phosphorus Loading Como 3 Study

Description Area (ac)

Total Phosphorus Reduction

(lbs/yr) Rate

(lbs/yr/ac) Initial Como 3 Subwatershed Boundary 516.5 107.0 0.207 Subwatershed Boundary Revision, area reduction 58.3 -12.1 0.207 Bandana Square Drainage Area (removed) 9.3 -1.9 0.207 1200 Energy Park Infiltration Drainage Area (removed) 4.8 -1.0 0.207

Study BMP Target Reduction: 92.0

With the target reduction identified, the study team worked to identify possible BMP locations. F. Preliminary BMP Identification

Using the study data, the study team identified several locations that had the potential to be suitable BMP location sites. The criteria used to select the sites included:

• Open space available • Proximity to existing storm sewer trunk lines • Upstream or contributing drainage area • Locations within or near areas of known future construction projects • Opportunities for cooperation between stakeholders • Flooding locations indicated by XPSWMM • Flooding areas indicated by residents and other stakeholders • Soil infiltration suitability

Upon further field reconnaissance with CRWD, the list of sites was modified with the addition, as well as disqualification of others. Lastly, the City of St. Paul reviewed the locations independently and identified an additional site that was added as Site 15. Table 7 on the following page lists the identified preliminary BMP locations (see Figure 7). Land access was not determined as part of this analysis. Projects identified in this report would only move forward to final design and construction after formal written agreement with the landowner is secured allowing access to the property.

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Table 7 -- Potential BMP Sites

Preliminary Site ID BMP Opportunity Description

1 Small demonstration project at east end of parking lot, curb cut with a shaded rain garden; relocate catchbasin to rain garden. Highly visible location with community education opportunity

2 Existing ball field in poor condition adjacent to major storm trunk line. Underground infiltration system installation with new ball field above. Great potential for community support.

3 Outfall trunk line into step, micro ponds between trails. Maintenance may be issue, lower priority site.

4 Open median along trunk line could provide for a rain garden location.

5 Swimming pool/parking facility to be redesigned by Parks. Future BMP project to be coordinated with development plans. Possible underground storage/reuse.

6 Heavy impervious percentage from roof top and pavement. Potential to work with property owner for water quality improvements.

7 Parking lot with potential for pervious pavement along eastern side as well as rain garden development between trail and parking lot. Highly visible location with community education opportunity.

8 Realignment of the existing intersection could provide rain garden and/or infiltration strip locations.

9 The high school parking lot in poor condition could be fully/partially reconstructed utilizing pervious pavers and an underground infiltration system tying into adjacent trunk line.

10 Street reconstruction may provide berms for infiltration strips and/or rain gardens. Work closely with City staff to evaluate BMP potential.

11 Rehabilitation of an existing depression for infiltration including curb cuts to provide runoff routing.

12 Existing parking lot curbed islands could be depressed to allow rain garden opportunity. Existing catch basins could be extended a short distance for incorporation.

13 Small rain garden demonstration project near Como Lake Pavilion to provide education opportunities. Low performance likely; lower priority site.

14 The abandonment or realignment of Como Ave west of Lexington could provide a variety of BMP opportunity to be incorporated with the expansion of the McMurray Field Park

15 An open area within the wooded park land located mid block of Como Avenue near Chatsworth provides a potential location for an underground infiltration basin or filtration basin.

During the preliminary BMP site reconnaissance, an infiltration basin at the southern extent of the Como 3 subwatershed was identified in subcatchment 4_4. Its drainage area is likely that of the adjacent parking lot and industrial building. Further detailed evaluation of the area was not performed as utility plans were not available. It is likely, however, that this infiltration basin does provide loading reduction to the Como 3 subwatershed.

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Figure 7

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G. BMP Evaluations

With the established list of potential BMP sites, the study team discussed the sites with input from CRWD and grouped them into three categories:

• High Priority Opportunities • Low Priority Opportunities • Future Opportunities

The intent of the ranking was not to discount any of the sites since each site was considered a viable and potentially beneficial opportunity to reduce phosphorus loading. The groupings instead provided focus for the study team to achieve a more efficient and effective course towards achieving loading reductions. The following provides further details of each site and how the identified BMP locations may be useful to meet the desired reduction goals.

G.1. High Priority BMP Opportunities

Review of the identified opportunities established the following sites as the highest priority due to their perceived constructability and potential for the greatest cost to benefit ratio. Each site is described in greater detail below.

Table 8 -- High Priority BMP Sites

High Priority Site ID BMP Opportunity Description

2 Underground Infiltration at Orchard Recreation Center 4 Median Rain Garden 5 Pool Reconstruction – Underground reuse/infiltration basin 7 Pervious Parking Lot near Como Lake Pavilion 8 Intersection Realignment and Boulevard Rain Gardens 9 Pervious Parking Lot at Como Park Senior High School 10 Street Reconstruction with Bump-out Rain Gardens 15 Underground Filtration at Chatsworth and Como

Site 2 – Underground Infiltration at Orchard Recreation Center

The Orchard Recreation Center contains open areas used for soccer and baseball by the neighboring community. The open flat area as well as its close proximity to the subcatchment 2_2 trunkline made the site a high priority possibility for an underground infiltration basin. A depressed dry basin at the site would also provide benefit, but an underground basin would provide continued recreation opportunities without the possibility of flooded or soggy fields. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Depending on final design, a diversion structure would likely be incorporated at the corner manhole located at the intersection of Jessamine Avenue and Victoria Street or mid block along Victoria. The trunkline along Jessamine is approximately five feet lower than that along Victoria and may require additional excavation to establish a flowline into the basin.

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The diversion would direct the first 1.0-inch rainfall into a high void ratio underground treatment facility. Once filled with the first flush, additional flow would bypass the diversion and continue towards Como Lake. The first flush volume containing the most pollutants would gradually infiltrate through the rock media into the subsoil and recharge the groundwater table. The pollutants would be filtered in the rock media and native soil. Figure 8 provides a schematic sketch of the proposed facility.

Considering the current land use, the study team suggests focusing on the water quality treatment volume of 1 inch of runoff and utilizing the underground option. However, during final design the underground storage could be reevaluated and sized larger to accommodate greater event storm flows and possibly reduce street flooding.

Modeling of this BMP with P8 indicated an annual reduction of 22.1-lbs/yr. This result included a treatment volume of 0.81 ac-ft or 35,065-cf. The filtration media was modeled as 1.2 feet high with a footprint of 19,200-sf. The infiltration basin could consist of a cast in place structure (top and sides) with a high void rock bottom. But a more economical design may be to use structural plastic arches designed specifically for such an application. The top of the storage area would be approximately 4 to 8 feet below the surface, providing ample opportunities for vegetative growth or even baseball backstop installations. The required footprint area would easily fit in the open area and provide the opportunity for improvements to the ball fields themselves. Soil borings obtained at the site indicate an SW/SP soil which has an approximate infiltration rate of 0.8-in/hr, consistent with the CRWD Rules.

The StormTech system (plastic arches) was used in this study as one example of an underground storage/infiltration system and is not meant to be an endorsement by this study or CRWD. The use of the system allows for consistency and comparison between BMPs. During final design, it is anticipated that various alternatives for underground storage/infiltration will be evaluated for effectiveness and cost.

The estimated probable cost for the Site 2 BMP totaled $314,750. This estimate, as well as other estimates of probable costs presented throughout this report, is provided assuming the associated project is a stand alone endeavor. It is anticipated that the actual BMP construction will be performed as part of a larger project, thereby reducing the project costs of each BMP. A breakdown summary of the costs as well as a soil boring log is included in the appendix.

Site 2

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Figure 8

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Site 4 – Median Rain Garden

The intersection of Horton Avenue and Van Slyke Avenue currently includes a mix of medians and lane separations for traffic control. One such triangular median is currently grass covered and of sufficient area that a rain garden may be a possible BMP. The use of curb cuts, valley gutters and/or street gradient adjustment may direct runoff to enter a depressed median rain garden arrangement. Figure 9 provides a schematic sketch of Site 4. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Evaluations of the adjacent trunk storm sewer under Horton Avenue indicate that it is too deep (10-feet) to allow a diversion into the proposed rain garden. The median is too small to allow the necessary depth for such a connection and only local runoff traveling overland is treated at the site. A surface inlet through a curb cut is a preferred design to direct stormwater to the rain garden.

Modeling of the site indicated an entrapment of 1.4-lbs/yr of phosphorus. The 0.026 ac-ft, or 1242-cf treatment volume requires a 1656-sf footprint. The stormwater of the first flush would be contained in the rain garden soil and infiltrate, evaporate, or transpire through the plantings preventing the runoff pollutants from entering Como Lake. The pollutants would be trapped in the soil or taken up by the plantings.

The estimated probable cost for the Site 4 BMP totaled $20,780. A breakdown summary of the costs as well as soil boring log of the site is included in the appendix.

Site 4

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Figure 9

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Site 5 – Pool Reconstruction- Underground Storage/Reuse Basin

The St. Paul Park and Recreation Department is considering a major expansion project of the Como Park swimming pool. A project of this type will require CRWD permitting. It is expected that the St. Paul Park and Recreation Department will work closely with CRWD during planning of the project to implement stormwater treatment BMPs within the site. Surface BMPs likely applicable to the site include rain gardens, depressed parking medians, and pervious pavement filtration. Additionally, St. Paul Public Works identified this location as a prime location to treat the largest stormwater subcatchment area due to the large trunk line under Lexington. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Underground infiltration was initially considered, but a hand augured soil boring indicated lean clay soils between 8 and 12-ft below grade (limit of auger). However, significant pollutant removal could still be achieved utilizing an underground storage reservoir for irrigation use on the pool site as well as the adjacent McMurray Field. A concept similar to that used at the St. Anthony Water Reuse Facility could be evaluated further and provide both volume and nutrient loading reduction. During the design phase of the site, the study team recommends obtaining additional soil borings to further evaluate the site for infiltration as well as determine the water table location. Also, during the design phase, the irrigation requirements of the area need to be evaluated for reservoir sizing. Soil type aside, the opportunity for significant volume reduction is possible due to the site’s location adjacent to the major stormwater trunk line along Lexington Avenue and open ground cover. The trunk storm sewer under Lexington is nearly 11 feet deep and the St. Anthony facility utilizes an inflow invert at a similar depth. The difference, however is that the St. Anthony site had a constrained footprint. The open area of Site 5 may provide for shallower construction and cost savings in comparison. For purposes of this study, three underground basin sizes were evaluated in P8. Capturing the first 0.5-in runoff (115,870-cf) produced a phosphorus reduction of nearly 78-lbs/yr. Capturing the first 1.0-in runoff (231,740-cf) produced a slightly larger reduction of 87.0-lbs/yr. Since these volumes are quite large and the associated costs would be significant, the study team ran a P8 model of a 500,000 gallon reservoir as used in St. Anthony (66,840-cf). The result was a phosphorus reduction of 60.8-lbs/yr. If infiltration is not feasible, pumping the respective volume for irrigation purposes as was done in St. Anthony may be an attractive alternative. A cast in place reservoir as constructed in St. Anthony in 2008 cost approximately $1,177,000 for the storage facility and the associated irrigation system and utility work. Adding 15% for legal, administrative and engineering fees and 10% contingency suggests an estimated project cost of $1,471,250.

Site 5

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Figure 10

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Site 7—Pervious Parking Lot near Como Lake Pavilion

The expansive parking lot located south of the Como Lake Pavilion slopes towards the lake. The BMP envisioned for the parking lot consists of using pervious pavers or other porous pavement along the eastern parking stalls with an underdrain system discharging into the existing storm sewer outfalls. Runoff from the parking lot, as well as drainage from the hill to the west, would drain into the pervious surface, through a rock media, and be collected by the underdrain system. Particles with associated nutrients and pollutants would be trapped in the rock media, preventing their discharge into Como Lake. Figure 10 provides a schematic sketch of Site 7. An underdrain system would only be needed if the soil was determined during final design to be poor for infiltration or if the water table was found to be too shallow. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

The modeled BMP produced an anticipated annual phosphorus reduction of 2.3-lbs/year utilizing a pervious parking lot footprint of 0.49 acres or 21,470 square feet. A treated volume of 0.123 ac-ft or 5,357-cf was calculated and a probable cost of $232,040 was estimated for the BMP construction. A breakdown summary of the costs as well as a schematic drawing of the site is included in the appendix.

Site 7

7/21/10 25

Figure 11

7/21/10 26

Site 8 – Intersection Realignment and Boulevard Rain Gardens

Similar to Site 4, Site 8 is located at a non-traditional intersection. Argyle Street intersects Van Slyke Avenue in a “Y” pattern leaving a large triangle median and an expanse of pavement. The proposed BMP at this location would include realigning the intersection into a traditional “T” and using the resulting berm areas for rain garden development. The rain garden to the west would treat surface flows collected at the curb line from rooftops, yards and sidewalk from the west and south while an additional rain garden on the east side of the intersection would treat curbline flows traveling from the south. Curb inlets would be installed downstream of the curb openings into the rain garden to accept excess flows once the first 1.0-inch of runoff is captured in rain gardens. Figure 11 provides a sketch of the realigned intersection and the proposed rain garden locations. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Modeling of the two rain gardens at this site indicates an annual phosphorus capture of 3.9-lbs/yr. The treatment volume of 0.053 ac-ft or 2304-cf would be contained in two garden footprints of 2664-sf and 408-sf. A breakdown summary of the estimated $85,910 construction cost is located in the appendix.

Site 8

7/21/10 27

Figure 12

7/21/10 28

Site 9 –Pervious Parking Lot at Como Park Senior High School

Similar to Site 7, the expansive parking lot located on the campus of Como Park Senior High School provides the opportunity to construct a pervious pavement system. Since Site 9 appears to be at a higher elevation than Site 7, the additional use of infiltration is possible under the pervious pavement and subgrade rock. The BMP envisioned for the 1.85 acre parking lot consists of using pervious pavers or another porous surface (concrete or asphalt) in the vicinity of the existing storm drain inlet located in the western end of the parking lot. Runoff from the parking lot would drain through pervious surface, through a rock media and would be held in void space below ground. It is expected that the soils below the rock media will allow infiltration back into the groundwater thereby reducing storm sewer water quantity as well as improving the water quality. Due to the pavement at the site, borings were not taken at this location. During final design, a boring is recommended to confirm the ability to infiltrate. Excess stormwater would be collected by a catchbasin and conveyed via the existing storm sewer collection system. Particles, nutrients, and pollutants will be collected in the rock media, preventing their ultimate discharge into Como Lake. Figure 12 provides a sketch of the proposed BMP. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

The modeled BMP produced an annual phosphorus reduction of 2.6-lbs/year utilizing a parking lot footprint of 0.62 acres or 26,870-sf to treat 6,708-cf of storm volume. A probable cost of $326,510 was estimated for the BMP construction. A breakdown summary of the costs is included in the appendix. Additionally, the parking lot is currently in very poor condition and in need of complete reconstruction. Due to its size, such a reconstruction will require a CRWD permit and it is expected that such a BMP as described above can be implementable to meet permit requirements.

Site 9

7/21/10 29

Figure 13

7/21/10 30

Site 10 – Street Reconstruction with Bump-out Rain Gardens

The existing streets south of the railroad in subcatchments 3_2, 2_2, and 2_3 were visited to determine their potential for BMP implementation as this area is scheduled for improvement by the City of St. Paul. This area is in the City’s 2010 RSVP (Residential Street Vitality Program). Most of the streets include boulevards containing both sidewalks and mature trees, limiting the potential for implementation of typical linear treatment facilities such as rain gardens or filter strips. One street, Orchard Avenue, however, was identified since it is without sidewalks and has fewer trees. The option of creating relatively small bump-outs at the street intersections was considered. The bump-outs would provide a depressed area where runoff containing the first flush would enter via curb openings and either infiltrate, evaporate or be taken up by plantings. Engineered soil with an infiltration rate of 1.0-in/hr is required due to the small footprint to maximize treatment. Runoff that is greater than the garden volume would bypass the depression and travel to a traditional curb inlet. Figure 13 provides a sketch of a typical bump-out rain garden. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

A typical site with a 50-sf footprint could reduce phosphorus loading by 0.1-lbs/yr by treating 37.5-cf of volume. Considering the easterly slope of Orchard Avenue east of Ryde Street, the study team suggests that a total of 10 bump-out locations could be created, totaling a yearly phosphorus loading reduction of 1-lbs/yr. The rather small load reduction potential of the bump-outs compared with the larger treatment option identified nearby at Site 2 may suggest that the load reduction benefit may not fully justify the bump-out rain gardens. However, the bump-outs would provide visual enhancements to the street as well as traffic calming benefits if implemented. A break down of the estimated $83,650 construction cost is provided in the appendix. As with each proposed BMP, the estimated costs presented are for stand alone projects. Anticipated cost reduction can be foreseen when projects are combined with other construction activities such as a road reconstruction.

Site 10

7/21/10 31

Figure 14

7/21/10 32

Site 15 – Underground Filtration at Chatsworth and Como

An open grassed area located near the Chatsworth Street storm trunk line provides the opportunity for an underground infiltration or filtration basin. For purposes of this study, the BMP was anticipated to treat flow from the subcatchment 3_1 trunkline along Chatsworth Street, utilizing a 12-inch storm pipe to divert flows. This solution will require trenching pipe through the existing stands of trees in the park. Alternatively, if the Chatsworth diversion is not feasible, a diversion from the smaller adjacent storm sewer under Como Avenue is possible, but a smaller benefit would be achieved. Figure 14 provides a layout sketch of Site 15 where both storm sewer lines can be seen. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

A soil boring log taken at the site is included in the appendix. The boring at the location only reached a depth of 6-ft. At that depth the soil is considered Type D. Soils of that time generally do not infiltrate well, if at all. The flowline of the diversion structure to be used is five feet below grade. Considering a depth of filter media of 42 inches, the bottom of the basin would be 8.5-ft below grade, below that of the boring. For the purposes of this study, the design team computed removal rates using a filtration system. An infiltration rate was not used for sizing of the volume, but during final design, additional deeper borings are suggested to further evaluate the soils and infiltration ability.

Due to space limitations and tree proximity, the basin was sized to hold only the 0.5-inch runoff volume. The modeled BMP produced an annual phosphorus reduction of 30.4-lbs/year utilizing a footprint of 0.53 acres or 22,880-sf treating 42,907-cf. A probable cost of $394,270 was estimated for the BMP construction. A breakdown summary of the costs is also included in the appendix.

If trees were not limiting the footprint of the site, a 1.0-inch runoff volume would require an 88% larger footprint (42,632-sf) to treat 1.97 ac-ft. The resultant phosphorus reduction would be 35.8-lbs/yr. The incremental increase in loading reduction would not seem to justify nearly doubling the footprint and eliminating the adjacent mature trees.

Alternatively, an open air retention basin is also possible at the site to provide greater volume attenuation of flood flows. This option however would alter the current feel of the wooded park area and is not recommended by the study team.

Site 15

7/21/10 33

Figure 15

7/21/10 34

Summary of High Priority sites

The following table provides a summary of the high priority sites. It includes the relative removal efficiency of each device on its contributing drainage area as determined by P8 modeling. The total phosphorus loading removal of these sites is 137% of the targeted 92.0-lbs/yr BMP reduction goal for the Como 3 subwatershed. It should be noted that three of the sites (Site 2, 5, and 15) achieve over 112.3 lb/yr total phosphorus removed. Potential partnerships are identified for each BMP that may likely lead to the implementation of the BMP.

See Table 9 on page 35.

Table 9 Footnotes:

(1) Project costs shown were estimated as stand alone project. Construction in conjunction with other work will likely result in lower costs per BMP project. (2) Equals 500,000 gallons. The St. Anthony Water Reuse Facility is includes a 500,000 gallon storage tank. (3) Represents St. Anthony’s actual costs for a concrete cast in place facility constructed in 2008 plus: 15% for administrative, legal and engineering cost; 10% contingency.

9/11/08 35

Table 9-- Summary of High Priority Site Phosphorus Removal

High Priority Site ID

BMP Description Phosphorus

Load Removal Efficiency

Calculated Phosphorus

removal (lbs/year)

Treatment Volume

(cf)

Estimate of Probable

Cost(1)

Estimated Phosphorus removal cost

($/lb)

Project Partners

Implementation

Schedule

2

Underground infiltration at Orchard Recreation Center

93.8% 22.1 35,065 $314,750 $14,242

CRWD, Public

Works/Park and Rec.

In conjunction with 2010 RSVP Project

4 Median rain garden 87.6% 1.4 1,242 $20,780 $14,843 CRWD, Public Works

In conjunction with intersection reconstruction

5

Pool Reconstruction – Underground storage/re-use basin

66.0% 60.8 66,840 (2) $1,471,250(3) $24,198

CRWD, Public

Works/Park and Rec.

In conjunction with Pool rehabilitation, McMurray Field reconstruction, and/or Como Ave realignment

7 Pervious parking lot/rain garden 96.9% 2.3 5,358 $232,040 $100,887

CRWD, Parks and

Rec.

In conjunction with parking lot rehabilitation

8 Median rain gardens 69.2% / 67.3% 3.9 total 2,304 $85,910 $22,028

CRWD, Public Works

In conjunction with intersection reconstruction

9 Pervious parking lot 96.9% 2.6 6,708 $326,510 $125,581

CRWD, School District

In conjunction with parking lot reconstruction

10 Rain gardens 28.2% 1.0 total

(0.1 per site, 10 sites)

375 $83,650 $83,650 CRWD, Public Works


15

Underground Filtration at Chatsworth and Como Ave.

79.0% 30.4 85,813 $394,270 $12,969

CRWD, Public

Works/Park and Rec.


Total: 124.5 203,705 $2,929,160 $23,527

9/11/08 36

G.2. Low Priority BMP Opportunities

Of the 15 sites identified in this study, five have been classified as low priority. Although each site is anticipated to achieve stormwater treatment benefits, these sites have associated aspects that lead the team to believe they would likely be implemented further into the future. Two sites exist on private property and their implementation schedule will likely be determined by the needs of the land owners and less influenced directly by CRWD or the City of St. Paul.

The table below provides a list of these low priority sites. Following the table, each site is described in greater detail. These sites were not modeled in P8 software nor were cost estimates established for the sites. It should be noted that three of the sites may provide a significant community education benefit considering their incorporation into heavily visited park facilities. These projects would not be implemented without first gaining City (or other landowner) approval and a formal agreement. Table 10 - Low Priority BMP Sites

Low Priority Site ID BMP Description

1 Rain Garden Education Site 3 Step Micro Ponds between Trails 6 Commercial Retrofit - Stormceptor 12 Commercial Retrofit – Sunken Parking Lot Islands 13 Rain Garden Education Site near Como Lake Pavilion

7/21/10 37

Site 1- Rain Garden Education Site

This location provides an opportunity to create a rain garden in a high foot traffic location. The rain garden would treat runoff from the small parking lot serving the walking/bike trail and fishing pier located there. Since the parking lot contains only 10 spaces and a minimal drainage area, the treatment volume is considered small and therefore a lower priority site. Field observations discovered silt and sediment accumulation at the far eastern end of the parking lot along the curb. An existing catchbasin was also identified near the deposition site, suggesting that some sediment and therefore nutrient loading may be entering the lake at this location. Routing the storm drainage into a rain garden behind the curb at this location would reduce such loading. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

A more significant benefit of the rain garden may be its use as an education site. Considering the high traffic location on the walking/bike trail and fishing pier, the public will be given an opportunity to read about and observe how rain gardens work. This opportunity may create additional interest in BMPs and potentially interest in the use of BMPs elsewhere, including residential properties.

Site 1

7/21/10 38

Site 3- Step Micro Ponds between Trails

The substantial Lexington Avenue storm sewer trunk line serving subcatchment 4 discharges into Como Lake at this location. The outfall has been found to be protruding from the ground to the extent that the crown of the pipe has become exposed. The BMP opportunity is to shorten the outfall pipe, daylight the storm sewer, and create a series of pools that could cascade between the various hike and bike trails. Due to large drainage area, a bypass sewer would be required to prevent the high flows from washing out the pools. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

A significant drawback to this site may be the required maintenance and potential impact to the trial system. Significant cost may be experienced to provide the various trail crossings and the treatment level may be limited due to the available space. Therefore, this site is considered a low priority opportunity even though it may provide a certain level of stormwater treatment. However, as with Site 1 described above, its proximity to the heavily used trail system would provide excellent education and unique landscape beautification benefits.

Site 3

7/21/10 39

Site 6 – Commercial Retrofit - Stormceptor

This location is a large sized industrial site with expansive impervious areas comprised of rooftop and parking and truck delivery facilities. Nearly the entire site is considered impervious. Therefore, a method of stormwater treatment would be beneficial to the watershed. During site visits, the pavement was recognized as recently constructed. Contact with the property owner has not occurred, but it is believed that a structural retrofit to the onsite storm sewer collection system may be possible. Given the lack of green space available, a hydrodynamic stormwater device may be the best opportunity, although pollutant reduction achieved may not warrant the construction costs. This site is considered a low priority because it is on private property and the site does not appear that it will be undergoing any construction activities soon. If reconstruction does occur in the future, a CRWD permit may provide the avenue to proceed with a stormwater BMP opportunity. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Site 6

7/21/10 40

Site 12—Commercial Retrofit – Sunken Parking Lot Islands

During the watershed evaluation, the large parking lot of Bandana Square on the north side of Energy Park Drive was identified as an expansive location of untreated stormwater. Furthermore, existing catchbasins were found to be located near the east end side of the parking lot, near existing parking lot islands. Increased stormwater management is possible by utilizing sunken islands with curb cuts to accumulate parking lot runoff. Vegetated islands with appropriate plantings would provide uptake of the rainwater and nutrients along with minimal stormwater volume reduction. The BMP would provide an infiltration location to allow the water to seep into the ground. Both actions will reduce downstream transportation of pollutants. The site is considered a low priority because it is private property and based on conversation with the building owners, unlikely for a quick development time table.

The study team did perform a site meeting with the management of the Bandana Square complex and stormwater treatment options were discussed. The management company is very interested in such opportunities and future renovations will consider stormwater issues. In fact, the site is currently experiencing stormwater catchbasin failures due to seepage and management is replacing them. Continued discussions are expected with the management company and their contracting vendor to evaluate the replacement process and possibly incorporate stormwater treatment opportunities. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Site 12

7/21/10 41

Site 13—Rain Garden Education Site near Como Lake Pavilion

As discussed regarding Site 1 above, this site would provide a limited nutrient removal effectiveness given its small direct watershed. Considering its location near the Como Lake Pavilion and the various events being held there, the site may provide a great public education site. The site would treat localized runoff from a portion of the parking lot as well as the green space and walkways adjacent to it. Providing a rain garden with natural plantings and educational signs would encourage public interest and support for stormwater management techniques. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Site 13

7/21/10 42

G.3. Future BMP Opportunities

Lastly, the list of identified BMP opportunities includes three sites classified for future development. These sites include areas of future planned improvements by the City of St. Paul Public Works and Parks and Recreation department. This study anticipates that the CRWD will be included in the planning process for these improvements. The sites are summarized below and described further in the following pages. These projects would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Table 11 - Future BMP Opportunities

Future Opportunities

Site ID BMP Description

11 Woodland Wetland Restoration 14 Como Avenue Realignment / McMurray Field Park Expansion

7/21/10 43

Site 11—Woodland Wetland Restoration

Currently, trail improvements are under way in the location next to the existing wooded wetland. This is the ephemeral wetland mentioned previously in the study. Further improvement plans include addressing the quality of the wetland. Only a small 12-in storm sewer conveyed stormwater from the entire subcatchment. This aspect led the study team to classify this site as a future opportunity as stormwater conveyance to Como Lake is likely limited in volume through the storm sewer. Greater volume likely accumulates at the wetland itself and infiltrates. Improvements performed by the St. Paul Parks and Recreation department should be coordinated with CRWD to address the stormwater treatment improvement options. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Site 11

7/21/10 44

Site 14 – Como Avenue Realignment / McMurray Field Park Expansion

The City of St. Paul is currently considering alternatives for the realignment of Como Avenue between the existing Como Park swimming pool and McMurray Field. The City is discussing options with St. Paul Parks and Recreation for realignment to provide opportunities of expansion of the McMurray Field softball diamonds to the north. Such expansion would require CRWD permitting. Similar to Site 5, CRWD can expect to be involved during the planning phase. Underground infiltration and/or volume detention may be viable options considering its location adjacent to the Lexington storm sewer trunk line and the identified surcharged manholes associated with it. This project would not be implemented without first gaining City (or other landowner) approval and a formal agreement.

Site 14

G.4. Results

Calculated phosphorus loading reductions of approximately 124.5-lbs/yr was estimated for the eight high priority sites identified by the study team. To achieve the established yearly reduction goal, the study team recommends implementation of the high priority sites, as outlined above. CRWD, through its permitting process of construction activities will continue to require and should encourage additional water quality improvement measures with residents, St. Paul Parks and Recreation, City of St. Paul Public Works and others.

7/21/10 45

H. Recommendations

The study team recommends implementation of the high priority BMPs to achieve phosphorus loading reductions to the greatest extent possible. Low priority and future BMP sites should be closely monitored through ongoing communication with the city and site owners to ensure that appropriate BMPs are included in any reconstruction activities. Focus on areas adjacent to the Lexington Avenue trunkline will provide the greatest opportunity to achieve pollutant loading reduction goals because of the large subwatershed area, existing land uses, and available open.

In summary, the study team recommends that following actions be taken by CRWD in continued pursuit of watershed improvement.

1. Begin detailed planning and designing of the eight identified high priority BMP sites.

2. Continue discussions with City of St. Paul and St. Paul Parks and Recreation concerning future improvement projects.

3. Continue the established permitting procedure and work with private land owners during their redevelopment planning process to promote stormwater volume reduction and water quality improvement.

COMO3

COMO7

920

930

940

5

910

900

890

10

950

880

8

70

15

86 0960

880

940

930

930

9 20

920

940

910

910

930

890

910

910

910

920

940

930

920

880

920

9 40

930

870

93 0

940

87

0

910

920

940

910

900

910

930

890

920

920

910

930

910

910

900920

900

890

9

4 0

930

890

910

940 910

940

910

930

9 20

910

930

910

890

920

920

920

8 90

930

930

890

880

930

930

910

890

910

890

920

900

930

91 0

910

920

940

900

940

920

940

910

930

910

880

910

930

9 10

930

88 0

940

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920

92

0

900

910

940

920

920

940

890

910

920

93 0

91 0

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15

920

910

880

910

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920920

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950

930

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910

920

940

900

940

920

92 0

9 2092

0

910

910

930

930

910

940

910

920

9 0 0

880

Como 3Subwatershed Analysis

Prepared For:Capitol Region Watershed District

Figure 1Subwatershed Boundary

Delineation(10-ft. Contours)

®0 500 1,000 Feet

Map LegendSubwatersheds

10-ft. Contour

Note: From 2000 CRWD Watershed Management Plan

Map LegendComo 3 Subwatershed

Subwatersheds

Impervious Surface



Figure 2Impervious Areas

®0 500 1,000 Feet


Como LakeMap LegendComo 3 Subwatershed

Hydrologic Soil Group

A

A/D

B

No Rating



Figure 3Soil Types

®0 500 1,000 Feet


Map LegendComo 3 Subwatershed

Subwatersheds



Figure 4Land Use

®0 480 960 Feet

LegendLand UseLUSE2005.UseDesc

<Null>

Agricultural

Airport

Extractive

Farmstead

Golf Course

Industrial and Utility

Institutional

Major Highway

Manufactured Housing Parks

Mixed Use Commercial and Other

Mixed Use Industrial

Mixed Use Residential

Multifamily

Office

Park, Recreational, or Preserve

Railway

Retail and Other Commercial

Seasonal/Vacation

Single Family Attached

Single Family Detached

Undeveloped

Water


Area to Be Investigated

Likely Drains to

Infiltration Basin

Area to Be Investigated

Likely Drains to west into

St. Anthony Park Watershed

9.3 Ac

4.3 Ac

Map Legend

Catchment

Subcatchments

Investigation_Area



Figure 5Subwatershed Boundary

Delineation

®

6

5

4

32

1

0 500 1,000 Feet

1_1

2_1

2_2

2_3

3_1

3_2

4_4

4_3

4_2

San_Sewer

4_64_1

5_3

5_2

5_1

6_2

6_1

4_5

Note: Delineation based on 1-foot topographic data and revised sewer data.

id604265 pdfMachine by Broadgun Software - a great PDF writer! - a great PDF creator! - http://www.pdfmachine.com http://www.broadgun.com

#*

#*

#*

#*

#*

Map Legend

Subcatchments

#* Outfall

Modeled Flow Point MH

Modeled Pipe

Trunk Line MH

Trunk Line Pipe



Figure 6Storm Sewer Network

®

5

4

32

1

0 470 940 Feet

4_6

4_1

4_5

5_3

4_2

6_1

6_2

5_2

5_1

4_4

3_1

3_2

4_3

1_1

2_2

2_3

2_1

119169

16383

119188

MH 119200

116595

116711

116703

116704

116375

116374

116373

116270

116374 Surcharged Manholes(5-yr Storm)


Existing Infiltration Basin

15

5

7

14

26

10

3

911

12

1

4

13

8

Map LegendComo 3 Subwateshed

Potential_BMP_Locations

Existing Infiltration Basin



Figure 7Potential BMP

Locations

®0 500 1,000 Feet

12" Inlet

12" Inlet

A

1

2

Scenario

1Approximate Area Required: 116' X 235'Number of Units Required: 726(22 Columns X 33 Rows)

2 Approximate Area Required: 100' X 192'Number of Units Required: 513(19 Columns X 27 Rows)

Natural GroundSurface

A Typical Cross-Section

Clean, Washed Stone~40% Void Space

StormTech SC-740System

Varies

42" Minimum

BARR

ETT S

T

VICTO

RIA

ST N

JESSAMINE AVE W

MILT

ON S

T N

Burlington Northern Santa Fe Railway

Map LegendRailroad

Modeled Pipe

Trunk Line MH

Trunk Line Pipe



Figure 8Site 2

®Not to scale.

Orchard Recreation Center

Underground Infiltration at Orchard Recreation Center

HORTON AVE

CHUR

CHILL

STVAN SLYKE AVE

COMO BLVD W

GATEWAY DR

COMO BLVD W

Map LegendModeled Pipe

Trunk Line MH

Trunk Line Pipe



Figure 9Site 4

®Not to scale.

Curb Cut

A

Maximum 3:1 Slopes

Rain Gardenw/ 1,656 Square Foot Floor

2

Median Rain Garden

A Typical Cross-Section9" Maximum

3' Amended SoilOverflow

Structure Gravelw/ Drain Tile(if needed)

COMO AVE

HORTON AVE

LE

XIN

GT

ON

PK

WY

N

CH

UR

CH

ILL

ST

VAN SLYKE AVE

OX

FO

RD

ST

N

Map Legend

Modeled Pipe

Trunk Line MH

Trunk Line Pipe



Figure 10Site 5

®

Not to scale.

Pool ReconstructionUnderground Storage/Reuse

Basin

48" RCP Inlet

48" RCP Outlet

Concrete Wall Footings

Concrete FacilityFloor

48" RCP48" RCP

Minimum 12"Aggregate

Compacted Subgrade

Minimum 500,000 Gallon CapacityStorage Volume (66,840 Cubic Feet)

Alternate 1: Storage Facility with Concrete Walls & Top or Concrete Arch.Alternate 2: Storage Facility with Metal Walls & Top or Metal Arch.Alternate 3: Storage Facility Using Plastic or Alternate Materials for Walls & Top.

Natural Ground Surface

7'11'

Variable

Submersible Vertical Turbine Pump Booster Station to IrrigationSystem

Submersible SolidsHandling Pumps to Sanitary

Variable

Existing Pool Facility

McMurray Field

A




Trunk Line MH

Trunk Line Pipe



Figure 11Site 7

®Not to scale.

Area Required: 0.49 acreof Pervious Pavers or PorousPavement

A

Porous P.C.CSand/Gravel

4"

6"

Curb

ExistingSub-Base

Lake Como

Lake ComoPavilion

Pervious Parking Lot near Lake Como Pavilion

Flow Direction

A Typical Cross-Section2

COMO AVE

ARGY

LE S

T

VAN SLYKE AVE

COMO BLVD W

CHAT

SWOR

TH S

T N

GATEWAY DR


Trunk Line MH

Trunk Line Pipe



Figure 12Site 8

®Not to scale.

New StreetAlignment

2

13' Amended Soil

Gravelw/ Drain Tile(if needed)

OverflowStructure

2 A

A

1 Rain Garden w/2,664 Square Foot Floor2 Rain Garden w/408 Square Foot Floor

Intersection Realignment and Boulevard Rain Gradens

9" MaximumA Typical Cross-Section

ROSE AVE W

COMO BLVD E


Trunk Line MH

Trunk Line Pipe



Figure 13Site 9

®Not to scale.

Area Required: 0.62 acreof Pervious Pavers or PorousPavement

A


4"

6"

Porous P.C.CSand/Gravel Existing

Sub-Base

Lake Como

Como Park Senior High School

Pervious Parking Lot atComo Park High School

_̂

_̂

_̂ _̂_̂_̂

_̂

_̂

_̂

_̂

HATCH AVE

COMO

PL

ORCHARD AVE

AVON

ST N

COLN

E ST

BARR

ETT S

T

VICTO

RIA

ST N

JESSAMINE AVE W

COMO AVE

MILT

ON S

T N

COLN

E ST

MILT

ON S

T N


Trunk Line MH

Trunk Line Pipe



Figure 14Site 10

®Not to scale.

Street Reconstructionwith Bump-out Rain Gardens

COMO

PL

ORCHARD AVE

New Sidewalk

New Curbw/Cut Inlet

Infiltration'Bump-Out'

Conventional Intakefor Overflow/Bypass Flow

Note:Typical Design can beused in Multiple Locations.

_̂ Potential Bump-Out Rain Garden

Varies

42" Minimum

Natural GroundSurface


1

1Approximate Area Required: 20' X 110'Number of Units Required: 580(29 Columns X 20 Rows)

A

Lake Como

!!2

Diversion Structure

COMO AVE

GATEWAY DR

CHAT

SWOR

TH S

T N

RYDE

ST

COMO BLVD W

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Trunk Line MH

Trunk Line Pipe



Figure 15Site 15

®Not to scale.

12" RCP Inlet

StormTech SC-740System

Clean, Washed Stone~40% Void Space

Underground Filtrationat Chatsworth and Como

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Drain Tile Line

Como 3 subwatershed analysis (draft)

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Transcript of Como 3 subwatershed analysis (draft)