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3 Lake Riley/Rice marsh Lake Water Quality Improvement Proj. CITY OF CHANHASSEN 7700 Market Boulevard PO Box 147 Chanhassen, MN 55317 Administration Phone 952.227.1100 Fax 952.227.1110 Building Inspections Phone 952.227.1180 Fax 952.227.1190 Engineering Phone 952.227.1160 Fax 952.227.1170 Finance Phone 952.227.1140 Fax 952.227.1110 Park & Recreation Phone 952.227.1120 Fax 952.227.1110 Recreation Center 2310 Coulter Boulevard Phone 952.227.1400 Fax 952.227.1404 Planning & Natural Resources Phone 952.227.1130 Fax 952.227.1110 Public Works 1591 Park Road Phone 952.227.1300 Fax 952.227.1310 Senior Center Phone 952.227.1125 Fax 952.227.1110 Web Site www.ci.chanhassen.mn.us 8 MEMORANDUM TO: Park and Recreation Commission Todd Hoffman, Park & Recreation Director-4 FROM: DA TE: February 14, 2006 SUBJ: Lake Riley/Rice Marsh Lake Water Quality Improvement Project; Riley-Purgatory-Bluff Creek Watershed District The Riley-Purgatory-Bluff Creek Watershed District is sponsoring the Lake Riley/Rice Marsh Lake Water Quality Improvement Project. The District was established by the Minnesota Water Resources Board in 1969, acting under authority of the Watershed Law. The District is governed by a five member board with one manager being appointed by the Carver County Commissioners and the other four by the Hennepin County Commissioners. The District works with various government bodies to help regulate storm water run-off, improve water quality, and provide recreation. This project will significantly improve five separate storm water basins in the City of Chanhassen, three of which lie wholly within the borders of Rice Marsh Lake Park. Attached is a copy of a letter from Robert Obermeyer, the District's consulting engineer, dated January 27, 2006, and addressed to Lori Haak, Water Resources Coordinator for the City of Chanhassen. Mr. Obermeyer's letter introduces the construction documents, speaks to the construction timeline, and solicits comments about the project. Selected staff members met on February 2, 2006, to review the District's proposal. Upon conclusion of our meeting, Ms. Haak forwarded the following comments to the District's Engineer. . All neighbors in the immediate vicinity of the projects (especially the three ponds adjacent to Rice Marsh Lake) should be notified of the project via U.S. mail. . The restoration of trails damaged by the construction activity should be included as part of the bid package. . Trail closures should be thoroughly reviewed and addressed as necessary. . The proposed timing of the projects (which projects get constructed when) should be conveyed to the City and the project neighbors. . The Market Boulevard pond is a highly visible site with high traffic volumes (pedestrian and vehicular) on Market Boulevard. Keeping the truck drivers alert and the streets free of tracked dirt and mud are certainly important for all the projects, but will be even more essential in this location. The City of Chanhassen . A growing community with clean lakes, Quality schools, a charming downtown, thriving businesses, winding trails, and beautiful parks. A great place to live, work, and play. Park & Recreation Commission February 14, 2006 Page 2 In a follow up conversation with Mr. Obermeyer, it was ascertained that the District has already addressed the majority of these issues. In regard to the neighborhood communication request, it has been agreed that the City will provide mailing labels to the District. The District will in turn mail the appropriate notification letters. Trail closures will be coordinated with the District and contractor with appropriate on-site notifications being posted. Staff is pleased that the District is sponsoring these important water quality projects within the City. This report is intended to raise your awareness to the projects. Your comments, questions and/or recommendations will be forwarded to the city's Water Resources Coordinator for inclusion in her report to the City Council. ATTACHMENT 1. Letter from Robert Obermeyer, Riley Purgatory Bluff Creek Watershed District Consulting Engineer 2. Introduction to Riley Purgatory Bluff Creek Watershed District 3. Project Description 4. Project Plans Barr Engineering Company 4700 West 77th Street . Minneapolis. MN 55435-4803 Phone: 952-832-2600 . Fax: 952-832-2601 . www.barr.com An EEO Employer BARR Minneapolis, MN . Hibbing, MN . Duluth, MN . Ann Arbor, MI . Jefferson City, MO January 27, 2006 Ms. Lori Haak City of Chanhassen 7700 Market Boulevard P.O. Box 147 Chanhassen, MN 55317 Re: Lake Riley/Rice Marsh Lake Water Quality Improvement Project Dear Ms. Haak: Enclosed for your review and comment is a set of construction documents for the Lake Riley/Rice Marsh Lake Water Quality Improvement Project. It is my intention to proceed with the bidding process as soon as possible with the construction schedule being weather dependent. I would anticipate that the upper basins could be constructed yet this construction season but the basins within Rice Marsh Lake likely will not be constructed until the 2006-2007 winter months. If you have any questions, please give me a call at 952-832-2857. bert . Obermeyer Barr Engineering Comp n~ Engineers for the District C: Board of Managers Paul Haik Riley Purgatory Bluff Creek Watershed District: General Page 1 of 2 .(:?;'General . 'Lakes & Creeks .,: Regulatory Program .~JNews .' :~Municipalities . Citizens Advisory . Construction Permits .:"Home .,. http://www.rileypurgatorybluffcreek.org/general.htm Riley Purgatory Bluff Creek" Watershed District r& General What does the RPBC Watershed do? The RPBCWD works with other government bodies to regulate stormwater runoff, improve water quality, and provide recreation. The District also works with developers on any project that proposes to alter floodplains, wetlands or streams. The RPBCWD requires permits for such projects to ensure that land use changes do not negatively impact water quality and flood protection. District review of permits provides an opportunity for citizen input on water related issues. The District has worked with municipalities to construct water quality and flood control projects such as the Chain of Lakes and the Purgatory Recreation Area Staring Lake Outlet. With the newly approved Water Management Plan, the District now may pursue projects that improve water quality. These projects, like past flood control projects, will be conducted in full cooperation with municipalities. How is the RPBCWD governed? A five member Board of Managers governs the RPBCWD. One is appointed by the Carver County Commission, the other four by the Hennepin County Commission. Each serves a three year term. Vice President Conrad Fiskness 8033 Cheyenne Ave. Chanhassen, MN 55317 952-934-5581 Term expires: 7/30/06 Manager Mark Dillon 3411 Fairlawn Drive Minnetonka, MN 55345 952-476-2709 Term expires: 7/30/08 Treasurer Philip Wright 9484 Painters Ridge Eden Prairie, MN 55347 952-942-0424 Manager Erin Ahola 19080 Broadmoore Drive Eden Prairie, MN 55346 952-934-5449 2/1012006 Riley Purgatory Bluff Creek Watershed District: General Page 2 of 2 Term expires: 07/30/07 Term expires: 7/30/08 Secretary Howard L. Peterson 7021 Duck Lake Road, Eden Prairie, MN 55346, 952-934-2050. Term expires: 7/30/06 Manager Michael J. Casanova 18559 Kristie Lane Eden Prairie, MN 55346 952-937-2322 A Citizens' Advisory Committee meets the first Tuesday of every month to advise the Board of Managers on citizen concerns relative to water issues. For more information, contact: Jennifer Olim, Chair (W) 952-949-6768 John Howe, Vice Chair (H) 952-975-0953 (W) 952-595-8888 view meeting schedule If you have any questions, or difficulties, using this website please call 952-832-2862. h Up:/ /www.rileypurgatorybluffcreek.org/general.htm 2/10/2006 ,...... Riley-Purgatory-Bluff Creek Watershed District's Lake Riley and Rice Marsh Lake: Water Quality Improvement Project Wetland Replacement Plan ,..., Prepared for the City of Chanhassen, the City of Eden Prairie, The Riley-Purgatory-Bluff Creek Watershed District February 2006 ,..., BARR 4700 West 77th Street Minneapolis, MN 55435 Phone: (952) 832-2600 Fax: (952) 832-2601 ,.... Riley-Purgatory-Bluff Creek Watershed District's Lake Riley and Rice Marsh Lake: Water Quality Improvement Project Wetland Replacement Plan Table of Contents 1.0 Introduction ........... ........ ...... .......................... ........ ........... ... ....... ........... .................. ....... ........... ....... ......1 2.0 Background........................................................................................................................... .................3 3.0 Proj ect Description........................................................................................................................... ......5 3.1 Project Need .. .... ....................................... ............................. ............... ........ ......... ..... .................5 3.2 Proj ect Plan ....... ... ... ..... .................................... ........ ................ .......... ........................ ..... ..... ....... 7 3.2.1 Rice Marsh Lake ......... .............. ........... ....... ...... ....... ........ ..... .... ............... ........... ...........7 4.0 Sequencing Analysis............................................................................................................................ ..8 4.1 No Build Alternative.. ......... .... ................................... ..... ...... ........ .................. ........... ............ ..... 8 4.2 Wetland Avoidance Alternative ............. ............ ....... ............ ........ .......... ........... ............. ............ 8 4.3 Proposed Alternative................................................................................................................... 9 5.0 General Environmental Setting ................ .............. ................. ...... ..................... ...................... ..... .......12 ,..... 6.0 Wetland Delineation....... ..... ... ......... ...... ................... ........................... ........... .... .... ......... ...... ... ........ ....13 6.1 Wetland Delineation and Classification Methods .....................................................................13 6.2 Wetland Descriptions ...... .................................. ............ ................ ...... ............. ......... ...... ...... ... .14 7 .0 Wetland Impacts and Mitigation.. ......... ................... ............... ...... ................................ ..... ........... .......20 8.0 Post-Construction Maintenance and Inspection ... ....... ................... .......... ....... ....... .............. ..... ........ ...23 ,.... i ,... 1.0 Introduction On behalf of the City of Chanhassen, the City of Eden Prairie, and the Riley-Purgatory-Bluff Creek Watershed District (District), Barr Engineering Company is submitting a Wetland Replacement Plan Application for the alteration of existing stormwater management basins and conveyance systems in Chanhassen, Minnesota and the expansion of an existing stormwater management basin into the City of Eden Prairie. The Riley-Purgatory-Bluff Creek Watershed District's Lake Riley and Rice Marsh Lake: Water Quality Improvement Project was recommended in the May 2004 Engineer's Report Lake Riley Water Quality Improvement Project and is the outcome of Use Attainability Analyses (UAAs) prescribed by the J 996 Riley-Purgatory-Bluff Creek Watershed District Water Management Plan. The recommended improvements for Lake Riley and Rice Marsh Lake are based on historical water quality data, the results of an intensive 1997 through 1998 lake and watershed runoff water quality monitoring program, and computer simulations of watershed runoff, calibrated to the 1997 through 1998 data set. Computer simulations estimated watershed runoff under existing and proposed future land use conditions and under varying climatic conditions. Maintaining the quality of Lake Riley and Rice Marsh Lake is important to the cities of Chanhassen, Eden Prairie, and the '" District and improvements to the existing stormwater treatment system in a cost-effective manner is needed to sustain existing water quality levels. Existing stormwater management basins within the watershed to Lake Riley and Rice Marsh Lake are inadequate to meet water quality management goals of the District. The project site is located in Township 116 and parts of: Section 13, Range 23 (Carver County); the southeast quarter of Section 12 (Carver County) and the southwest quarter of Section 7, Range 23 (Hennepin County); Section 18, Range 22 (Hennepin County); and Section 23, Range 23 (Carver County), Minnesota as shown in Figure 1. This Riley-Purgatory-Bluff Creek Watershed District UAA: Water Quality Improvement Project Replacement Plan (plan) has been prepared in accordance with the requirements of the 1991 Wetland Conservation Act (WCA) as administered by the city of Chanhassen and Section 404 of the Clean Water Act administered by the U.S. Army Corps of Engineers (Corps). The Minnesota Department of Natural Resources (MnDNR) has indicated that a Work in Protected Waters Permit is required for the proposed excavation below the ordinary high water level (OHWL) of Rice Marsh Lake, within water quality basin RM -1.1 and RM-2.6. In addition, the MnDNR has determined that the remaining DNR jurisdictional work, outlet repair/alteration for water quality basin 2.6, will not require a MnDNR permit, as this work falls under the District's MnDNR General Permit (97-6113). The MnDNR "... 1 ,.., 2.0 Background The Riley-Purgatory-Bluff Creek Watershed District (District) was established by the Minnesota Water Resources Board in 1969, acting under authority of the Watershed Law. As charged by the law and the order establishing the District, the general purpose of the District is to protect public health and welfare and to provide for the provident use of natural resources. The District carries out these purposes through planning, permit issuance, flood control, and conservation projects. ,..... The District is located in the southwestern portion of the Twin Cities Metropolitan Area, encompassing an area of 47.3 square miles. There are three major subwatersheds within the District-Riley Creek, with a watershed area of 10.0 square miles; Purgatory Creek, with a water area of 31.4 square miles; and Bluff Creek, with a watershed area of 5.9 square miles. All three creeks discharge to the Minnesota River. Stormwater management within the urbanizing watershed was guided initially by the District's Overall Plan dated 1973. The 1973 Overall Plan guided development within District until it was revised in May 1996, Water Management Plan, in accordance with the Metropolitan Surface Water Management Act and Watershed Law: Minnesota Statutes Chapters 103B and 103D, respectively. The water quality improvement projects recommended in the Engineer's Report for Lake Riley and Rice Marsh Lake, revised November 9, 2004, are the outcome of Use Attainability Analvses (UAA) prescribed by the 1996 Riley-Purgatory- Bluff Creek Watershed District Water Management Plan (see Appendix C). The UAA for Lake Riley and Rice Marsh Lake (Figure 1) were completed to provide the scientific foundation for lake-specific management plans that will preserve existing--or achieve potential- beneficial uses of the lakes. The UAA is a structured, scientific assessment of the factors affecting attainment of a beneficial use, both currently and under ultimate watershed development conditions. "Use Attainment" refers to achievement of water quality conditions suitable to support lake-specific beneficial uses such as swimming, fishing, wildlife habitat, and aesthetic viewing among others, as designated in the 1996 Water Management Plan. Lake Riley is designated as a Level I "swimming lake" by the District (see Table 1) and, as such, its water quality condition should score 53, or less, on the Carlson's Trophic State Index (Secchi disc basis, TSIsn) rating system. This index score is calculated from the interrelationships between summer Secchi disc transparencies and epilimnetic concentrations of chlorophyll a and total phosphorus. (The index results in scoring generally between zero and one hundred; lower score being indicative of better lake water quality.) A TSIsn score of 53 corresponds to a total phosphorus ,.... P:\23\27\E61IWetland ReplacementlRPBCWD_ WQ_lmprov_ WRP.doc 3 ,..... 3.0 Project Description The Lake Riley and Rice Marsh Lake UAA: Water Quality Improvement Project involves the alteration of five existing stormwater ponds and conveyance systems in Chanhassen, Minnesota. The project is proposed to be conducted on approximately 9 acres of land, on five separate sites in the cities of Chanhassen and Eden Prairie (Figure 2). 3.1 Project Need The current summer average total phosphorous concentration of Rice Marsh Lake is approximately 150 JLgfL, down from an observed peak of710 JLg/L: in 1972 (see Figure 3), shortly after the cessation of domestic wastewater discharges to the lake. Prior to that date, the lake was the receiving water for wastewater effluents from the Chanhassen municipal-and Lakeview Hills Apartment- wastewater treatment plants. Consequently, Rice Marsh Lake sediments are rich in phosphorus subject to release into the overlying lake water during summer periods of sediment anoxia. Data contained in the Lake Riley UAA demonstrate that the phosphorous concentrations of Riley Creek waters increase by a factor of approximately 3 as the creek passes through Rice Marsh Lake. This ,..... indicates that the lake sediments are acting as a "nutrient pump", resulting in an increased phosphorus load to Lake Riley. This phenomenon was also observed and reported in an earlier study conducted by the Metropolitan Council (R.A. Osgood. 1983. Diagnostic-Feasibility Study of Lake Rilev, Pub!. No. 10-83-095E). The summer average total phosphorus concentration of Rice Marsh Lake has declined exponentially over the past 33 years as the deposited phosphorus in its sediment have been released and flushed through the system, and as new, less fertile sediments have buried the phosphorus-rich deposits (see Figure 2). This has resulted in a generally declining phosphorus load to Lake Riley and its water quality has improved somewhat as a result. Trend analyses indicate Lake Riley total phosphorus concentrations have steadily declined over a 30-year period, from about 80 ILg/L in the early-1970s to about 40 JLg/L in the late-1990s. However, more recent data suggest phosphorus concentrations may now be rising as the lake's watershed is urbanizing. Figures 4 and 5 contrast the existing and predicted future watershed land uses within the portion of the Lake Riley watershed downstream from Rice Marsh Lake. As is clearly evident in Figure 5, much of the currently natural, open space will be developed into suburban residential land uses. Similarly, all agricultural lands will be converted to residential land use, or lost to construction of ."... P:\23\27\E61\Wetland ReplacemenllRPBCWD_ WQ_Improv_ WRP.doc 5 ",-.. 3.2 Project Plan The project plan includes the in-pond management actions within Rice Marsh Lake watershed. However, stormwater treatments within the Rice Marsh Lake watershed will also benefit the downstream watershed, Riley Lake (Sheet G2, Appendix E). 3.2.1 Rice Marsh Lake Five improvements are proposed in the Rice Marsh Lake watershed (Figure 2), including: . Upgrade an existing water quality basin (RM-1.1) on the northwest side of Rice Marsh Lake, located within Rice Marsh Lake Park, south of Dakota Lane (Drawing W -01, Appendix F). This stormwater management basin/wetland currently receives untreated stormwater and is hydraulically linked to Rice Marsh Lake. . Upgrade an existing water quality basin (RM-2.2) on the north side of 78th Street West, south of Twilight Trail, and west of 187th Avenue (Drawing W -02, Appendix F). This stormwater management basin/wetland presently receives untreated stormwater. . Upgrade an existing water quality basin (RM-2.5) on the north side of Rice Marsh Lake, located within Rice Marsh lake Park, southwest of Poplar Circle and southeast of Cheyenne Avenue (Drawing W-03, Appendix F). This stormwater management basin/wetland ",-.. presently receives untreated stormwater and is hydraulically linked to Rice Marsh Lake. . Upgrade an existing water quality basin (RM-2.6) on the north side of Rice Marsh Lake, located within Rice Marsh lake Park, directly downstream of water quality basin RM-2.5, southwest of Poplar Circle and southeast of Cheyenne Avenue (Drawing W -04, Appendix F). This stormwater management basin/wetland presently receives untreated stormwater and is hydraulically linked to Rice Marsh Lake. . Upgrade an existing water quality basin (RM-6.5) located northwest of the intersection of Highway 5 and Market Boulevard (Drawing W -05, Appendix F). This stormwater management basin/wetland presently receives untreated stormwater. ,.... P:123\27\E6I\Wetland ReplacementlRPBCWD_ WQ_lmprov_ WRP.doc 7 ".... management goals of the District. In addition, the city of Chanhassen has plans to develop/utilize these areas for purposes other than stormwater treatment. Briefly, the idea of purchasing upland areas, where homes currently exist near the northern portion of Rice Marsh Lake, to construct water quality treatment areas was discussed, but was immediately ruled-out due to the very high purchase price and likely objections from landowners. Storm water enters Rice Marsh Lake in specific locations and those inflows in need of additional treatment were identified by the UAA. In order to treat those inflows to meet the Cities and District water quality goals for the downstream water bodies; upland and existing stormwater management locations, and alternative best management practices (BMPs) were the first areas explored. Due to many factors, wetland impacts cannot be avoided in all locations where water quality treatment is needed. ,..., After considering all factors including: the location of the existing storm-sewer infrastructure, the water quality treatment currently provided by existing storm water management basins, existing topography, upland areas the City of Chanhassen or the City of Eden Prairie may be willing/able to purchase for water quality treatment, and objections from landowners, it was not feasible or prudent to stay completely outside of jurisdictional wetlands. 4.3 Proposed Alternative The proposed alternative described in Section 3.0 is the only feasible and prudent alternative to achieve the water quality goals of the District. The proposed alternative avoids and minimizes regulated wetland impacts to the greatest extent practicable. ,.... For over two years, the District and the city of Chanhassen have worked with the property owners to inform them of the project and determine acceptable areas suitable for stormwater management basins. As was historically common practice, stormwater basins and ditches were placed in low- lying wetland areas. The alteration of these wetlands to improve stormwater treatment occurred before the passing of the WCA. These existing stormwater management areas typically represent the most prudent location for improving stormwater treatment. After suitable water quality treatment areas were located, the District, with input from city of Chanhassen staff, designed the stormwater management basins to meet the water quality goals of the project, while avoiding/minimizing wetland impacts. Completion of the project as proposed will have minimal impacts to wetland resources and will improve the water quality of the two strategic water bodies, Lake Riley and P:\23\27IE611 Wetland ReplacementlRPBCWD _ WQ_lmprov _ WRP.doc 9 " ,...., ,.... . Water quality basin 2.2: The amount of Type 3 and 4 wetland excavation was minimized to the extent practical. The approximate reduction in regulated wetland impacts was 3.000 square feet. . Water quality basin 2.6: The western extent of the proposed pond was altered to minimize wetland excavation in the Type 3 wetland. In addition, the proposed pond was extended to the east, utilizing existing upland. The approximate reduction in regulated wetland impacts was 15.000 square feet. P:\23\27\E61IWclland RcplaccmcnllRPBCWD_ WQ_Improv_ WRP.doc 11 ,.... 6.0 Wetland Delineation 6.1 Wetland Delineation and Classification Methods The wetlands within the project area (Figure 2) were originally identified from aerial photographs and were field delineated on May 2 through May 5,2005. The field investigation resulted in the delineation of eleven wetlands within the initial project area (Figures 4-9, Appendix H). The wetland boundaries were surveyed using a Global Positioning System with sub-meter accuracy. On June 23, 2005, the wetland borders were field verified by the City of Chanhassen, the local government unit administering the Wetland Conservation Act (Appendix I). ,..... The wetland delineations were established according to the Routine On-Site Determination Method specified in the U.S. Army Corps of Engineers Wetland Delineation Manual (1987 Edition). The wetland were classified in accordance with the U.S. Fish and Wildlife Service Circular 39 System (Types 1,2,3, etc.), and the U.S. Fish and Wildlife Service Cowardin System (PEMB, PSSC, PFOB, etc.). The wetland boundaries were delineated with pin flags that were numbered and placed at intervals of approximately 20 to 50 feet. A summary of the delineated wetlands can be found in Table 2, Appendix H. Information on soil types within the evaluation area was obtained from the Soil Conservation Service (SCS) Soil Survey for Hennepin County and Carver County (Figure 2, Appendix H). The National Wetlands Inventory map (Figure 3, Appendix H) shows seven wetlands within the initial project area. The Minnesota Department of Natural Resources (MnDNR) Public Waters or Wetlands map (Figure 4, Appendix H) shows the presence of one public water (Rice Marsh Lake, PW 10-IP) within or immediately adjacent to the project. Numerous soil borings were placed in and around the wetlands, to a depth of at least 18 inches below the ground surface whenever possible. Representative soil samples from each boring were examined for hydric soil indicators. Soil colors (e.g., 7.5YR 4/2, etc.) were determined with the aid ofa Munsell~ soil color chart and noted on the Wetland Data Forms (Appendix D). The hydrologic conditions were evaluated at each soil boring and are also noted on the Wetland Data Forms. ,..... The dominant plant species in each wetland were identified, and the corresponding wetland indicator status of each plant species was determined and noted on the Wetland Data Forms. A summary of the wetland classifications and wetland areas are provided in the following descriptions. P:\23127\E61IWelland ReplacemenllRPBCWD_ WQ_lmprov_ WRP.doc 13 """" . Site RM-2.2: Wetland 1 is a 1.8 acre, Type 4/3/6 (PEMF/C/SSB) deep marsh/shrub-carr (Figure 7), which receives directed stormwater from inlets located at the north, west and east edges of the wetland. The wetland is bordered by railroad tracks to the north, business parking lots to the east and south, and is located northwest of wetland RM -2.1. A nursery is also located along the southern edge of the wetland. The wetland is dominated by cattail, reed canary grass, box elder, cottonwood, willow species (Salix lucida and Salix nigra), red-osier dogwood, aspen, goldenrod (Solidago spp.) and Canada thistle (Cirsium arvense). Upland vegetation includes cottonwood, oak (Quercus spp.), box elder, goldenrod, Kentucky bluegrass, clover (Trifolium spp.), arborvitae (Thuja occidentalis), birdsfoot trefoil, red-osier dogwood, maple (Acer spp.), and sumac (Rhus spp.). The soil profile near the edge of the wetland consists of 5 inches of black (IOYR 2/1) loam, above at least 11 inches of black (lOYR 2/1) loam with mottling. The wetland was inundated with 6 inches to 2 feet during the May site visit. ,..... . Site RM-2.4: Wetland 1 is a 0.27 acre, Type 3/4 (pEMFIPABF) shallow marsh/deep marsh (Figure 8), which receives directed stormwater from Lake Dr. to the south and business parking lots and driveways along the north, west and east borders. A car wash is located north of the wetland. The wetland is dominated by cattail, duckweed, sandbar willow (Salix exigua) and box elder. The upland vegetation includes mowed and maintained Kentucky bluegrass and planted blue spruce, red pine and green ash. Impervious surfaces surround the wetland. The soil profile at the edge of the wetland consists of at least 12 inches of black (10YR 2/1) muck with numerous greenish gray (5G 5/1) mottles and inclusions of peat. Thirty percent of the wetland is Type 4 (P ABG) and inundated with as much as 2 feet of water. Seventy percent of the wetland is Type 3 (PEMF) and inundated with approximately 6 inches of water during the May site visit. ,..... . Site RM-2.5: Wetland 1 is a 0.08 acre, Type 4/6 (PABGIPSSB) deep marsh/shrub-carr (Figure 9). The wetland receives stormwater from surrounding residential lots. A weir separates the north P:\231271E611Wctland RcplaccmcntlRPBCWD_ WQ_Improv_ WRP.doc 15 ,..... ~ ,.... . Site RM-2.8: Wetland 1 is a 0.035 acre, Type 1 (PEMA) seasonally flooded ditch along the south side of the railroad tracks (Figure 10). This ditch receives stormwater from the railroad to the north and surrounding uplands in the south. The wetland is dominated by reed canary grass, cottonwood, boxelder and red-osier dogwood. Approximately 50% of the wetland is unvegetated. Upland vegetation includes leafy spurge, reed canary grass, goldenrod and cottonwood. The soil profile in the center of the wetland consists of24 inches of black (10YR 3/1) sandy clay with many distinct yellow (10YR 7/6) mottles. The soil was damp at the surface and water was observed at a depth of 3 inches during the May site visit. . Site RM-2.8: Wetland 2 is a 0.003 acre, Type 1 (PEMA) seasonally flooded ditch, which receives directed stormwater from an inlet west of Highway 101 (Figure 10). This small wetland is located in the northeast corner of the evaluation area south of the railroad tracks and west of Highway 101. The wetland is dominated by fowl bluegrass, switchgrass (Panicum virgatum), and cottonwood. Upland vegetation includes switchgrass and brome grass (Bromus inermus). The soil profile within the wetland consists of 6 inches of very dark brown (10YR 2/2) loamy clay with some yellowish brown (10YR 5/6) mottles, above 7 inches of gray (lOYR 5/1) loamy clay with numerous yellowish brown (10YR 5/6) mottles and organic streaking. The underlying 11 inches is a light brownish gray (10YR 6/2) clay with numerous brownish yellow (lOYR 6/8) mottles. The wetland was saturated to the surface and water was observed at a depth of 14 inches during the May site visit. No wetlands were found within the vicinity of the proposed pond at the center of the evaluation area for Site RM-2.8. . Site RM-6.5: Wetland 1 is a 3.4 acre, 4/3/2/6 (PABG/PEMF/PEMC/PSSB) shallow/deep marsh/shrub-carr (Figure 11), which receives directed stormwater from Highway 5 to the south P:123\27\E61IWctland ReplacementlRPBCWD_ WQ_Improv_ WRP.doc 17 ,.... ,.... ,.... The wetland is dominated by reed canary grass, hybrid cattail (Typha glauca), black willow, peachleafwillow (Salix amygdaloides), and cottonwood. Upland vegetation includes reed canary grass and brome grass. The soil profile at the edge ofthe wetland consists of at 14 inches of black (1 OYR 2/1) muck above 10 inches of black (10YR 2/1) loamy clay with sand and few large yellowish brown (10YR 5/6) mottles. Thirty percent of the wetland was saturated to the surface during the May site visit. P:\23\27\E61\Wetland Replaccment\RPBCWD_ WQ_lmprov_WRP.doc 19 ,..... wetland bank is one of four existing wetland banks located within the major watershed, Minnesota River -Shakopee, with sufficient credits available for sale to the public, and that has been approved by the Corps. The Corps has preliminarily indicated that all proposed project-related fill and excavation, within the existing/proposed five stormwater treatment areas will likely be regulated by the Corps, requiring compensation under the Clean Water Act. A total of 362,384 square feet (8.32 acres) of Corps- regulated wetland impacts is associated with the project (Table 2). If wetland compensation is "in- place", "in-kind", and "in-advance", the Corps's minimum compensation ratio of 1: 1 is acceptable. However, impacts proposed within Type 4 (71,909 square feet) and Type 6 (17,411 square feet) are planned to replaced "out-of-kind" (replaced with a different wetland type) with a replacement ratio is 1.5:1. Corps Impacts and Proposed Compensation ,..., Wetland Type Type 2 Type 3 Type 4 Type 6 Impacts Required Impacts Required Impacts Required Impacts Required Compensation Compensation Compensation Compensation (I:l ratio) (1:1 ratio) (1.5:1 ratio) (1.5:1 ratio) Totals (sq. ft.) 107,864 26, II 7 86,968 86,968 186,097 186,097 71,909 (7 I ,909 · 1.5) 17,411 (17,41 I · 1.5) Grand 362,384 406,995 Totals (sq. ft.) The mitigation for impacts under the Clean Water Act will be accomplished through a combination of wetland re-establishment/vegetation enhancement activities, and the purchase of wetland banking credits. A total of 295,419 square feet of stormwater management basins will be created/altered in five locations as part of the project. The Corps has indicated that a 50 percent credit for a total of 147,710 square feet (295,419 square feet./2 - see Table 2) may be allowed. The remaining minimum mitigation requirement, 5.95 acres (259,335 square feet), is to be provided by the purchase of new wetland credits from the Mueller wetland bank, Account #1114. A draft Application for Withdrawal of Wetland Credits form is provided in Appendix B. Mitigation for the proposed 3.28 acres of I"""'" unavoidable WCA wetland impacts will include the purchase of 5.95 acres of new wetland credits P:\23127\E61IWctland RcplaccmcnllRPBCWD_ WQ_lmprov_ WRP.doc 21 .~ 8.0 Post-Construction Maintenance and Inspection The City of Chanhassen will inspect each of the five altered/enhanced water quality basins every five years and will remove accumulated sediment as needed. 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