Constructing Wetlands for Wastewater Treatment: Design Considerations & Strategies for Success

Transcription

1 Constructing Wetlands for Wastewater Treatment: Design Considerations & Strategies for Success Metropolitan Water Reclamation District of Greater Chicago and V3 Companies Introductions Jennifer Maercklein, P.E., CFM Water Resources Project Manager V3 Companies Tom Slowinski Director of Wetland/Ecology Group V3 Companies Joseph Schuessler, P.E. Principal Civil Engineer Metropolitan Water Reclamation District Presentation Overview Treatment Wetlands: What Are They? MWRD Background MWRD s Perspective Case Study Background Site Selection Criteria Site Design Criteria Construction Success Questions 1

2 Treatment Wetlands: What Are They? Constructed wetlands to treat effluent to achieve further reductions in nutrient removal Series of treatment cells with hydraulic controls Nutrient Cycling Benefits include: q Significant O&M Cost Savings q Can Help Gain Buy-in From Environmental Community MWRD Background Organized in 1889 q Direct response to typhoid and cholera epidemic q Reversed flow of Chicago and Calumet Rivers Serves most of Cook County (including City of Chicago) MWRD Background 7 WRPs and 23 pumping stations q 1.5 BGD avg DWF, 5.25M people, 10.35M equivalent World s largest WRP q 1.2 BGD design capacity, 2.38M people, 260 sq mi Controls 76 miles of navigable waters 2

3 MWRD s Perspective Pending nutrient standards q Gulf of Mexico Hypoxia Considering alternatives to supplement conventional biological and chemical WRP nutrient removal. 2004: Dr. Robert Kadlec report on Lake Calumet treatment wetland concept 2005: WERF Report on nutrient farming and traditional farming economic comparison MWRD s Perspective 2005 WERF Report: q Two possible effluent standards: 3.0 mg/l TN and 1.0 mg/l TP 2.18 mg/l TN and 0.5 mg/l TP q 189, ,000 acres of treatment wetlands q Present value cost for: Treatment wetlands: $870M - $1.4B Conventional removal: $2.4B - $2.9B q Annual O&M Savings: 51% 63% MWRD s Perspective 2006: Potential nutrient farm site near Hennepin, Illinois. 2007: Pilot studies at two sites between Des Plaines River & Chicago Sanitary and Ship Canal. Treatment wetland considerations: q Must provide a least-cost life-cycle alternative q Supplement to conventional nutrient removal q Additional benefits: Sustainable Reduced energy and chemical use Overall positive environmental impacts. 3

4 Case Study Background Project Location Case Study Background Centennial Trail Site Powerhouse Site Case Study Background Centennial Trail Prairie-Marsh q 175 acres q Approximately two miles long q Between Des Plaines River and Sanitary and Ship Canal q Railroad berm/bike trail on west q Highly disturbed on east side 4

5 Case Study Background Powerhouse Marsh q 65 acres q Between Des Plaines River and Sanitary and Ship Canal q Downstream of Lock & Dam q Elevation drop in Canal q Highly disturbed on east side q Future Caton Farm Rd Xing q Also considered property west of River and east of Canal Site Selection Criteria Location Topography Floodplain Wetlands Soils Public Use Photo: Robert H. Kadlec, Ph.D. Site Selection Criteria: Location Distance from Treatment Plant q Locate Treatment Wetlands at WRP Pipe effluent from WRP to wetland q Locate Treatment Wetlands downstream from WRP Nutrient Farming or Trading Compute regulatory requirements at WRP Demonstrate that equivalent load reductions occur at wetland 5

6 Site Selection Criteria: Location Adequate Source of Hydrology q Direct effluent q Other hydrologic source MWRD Projects q Chicago Sanitary and Ship Canal q Centennial Trail: Pump Station q Powerhouse: Gravity System Photo: MWRD Site Selection Criteria: Topography General Considerations Include: Sufficient Topographic Relief for Gravity Flow Between Cells? Earthwork q Grading Necessary to Create Terraced Cells q Associated Cost Consider Stormwater Runoff from Onsite & Offsite q Bypass offsite flow around wetland, or q Consider in flow calculations and nutrient removal calculations Site Selection Criteria: Topography Centennial Trail q Generally flat q Gentle slope from north to south q Abrupt rise in grade at southern end q Little offsite flow Powerhouse q Two plateaus q Each slopes from north to south q No offsite flow 6

7 Site Selection Criteria: Floodplains Is floodplain located on site? General Considerations: q Rule of Thumb: 25-year Protection to Wetlands q Higher levels of protection more costly; wetland plants can withstand flooding q Lower levels of protection may result in frequent dilution of waters to be treated q Consider regulatory criteria for floodplains Compensatory Storage Floodway Regulations Site Selection Criteria: Floodplains Centennial Trail q No riverine floodplain q Zone A in canal q Zone A in depressional area onsite q Needed to establish BFE q Design includes compensatory storage Site Selection Criteria: Floodplains Powerhouse q Floodplain from Des Plaines River q Floodway q Zone A in canal q Design includes compensatory storage 7

8 Site Selection Criteria: Wetlands Are regulatory wetlands present? Consider quality of existing wetlands Site Selection Criteria: Wetlands Detailed wetland delineation Determine extent and quality of wetlands Determine wetland permitting issues or constraints Identify potential threatened & endangered species issues Site Selection Criteria: Wetlands Centennial Trail Wetland Delineation q 83.5 Acres (48 %) q Area 1: 80.4 Acres q Areas 2-10: Ac. High Quality (Area 1) q FQI = 53.7 q 169 Native Species Need to avoid high quality wetland Impacts not permittable? 8

9 Site Selection Criteria: Wetlands Powerhouse Marsh Wetland Delineation q Acres (33%) q Area 1: Acres q Areas 2-7: Ac. High Quality (Area 1) q FQI = 23.1 q HQAR by definition Minimize wetland impacts Mitigate for impacted functions Site Selection Criteria: Soils Permeability q If permeable, groundwater aquifer may warrant liner Environmental Condition q Nutrients present in soil? q Soil contamination? Suitable as Growing Substrate? Centennial & Powerhouse q Bedrock q Poor, thin overlying soils q Topsoil import Site Selection Criteria: Public Use Is Site Currently Used by Public? Is Public Use Desired? q Boardwalks, Trails, etc. for Recreation q Educational Opportunities q Security Considerations Photos: Robert H. Kadlec, Ph.D. 9

10 Site Design Criteria Nutrient Removal Goals Cell Geometry Internal Flow Controls Wetland Permitting Photos: Robert H. Kadlec, Ph.D. Site Design Criteria: Nutrient Removal Establish Nutrient Removal Goals Which Nutrients to Target? q Phosphorus q Nitrogen Concentration Reduction or Load Reduction? q Centennial Trail: Concentration Reduction q Powerhouse: Load Reduction Site Design Criteria: Nutrient Removal Concentration Reduction Goal q Optimize flow to achieve target effluent limits q Often results in lower flow rate through system than a load reduction system q Achieve lower reduction in total nutrient load, but higher reduction in concentration Load Reduction Goal q Maximize flow rate through system q Achieve high reduction in total pollutant loading q Achieve lower reduction in effluent concentrations 10

11 Site Design Criteria: Cell Geometry General Design Considerations: Layout for optimum length:width ratio of 4:1 Elevation drop between cells based on head loss through system Minimize dry zones and short circuiting q Water to pass through as much vegetation as possible q Achieve greatest reduction in nutrient loading Optimize footprint given any physical constraint Site Design Criteria: Cell Geometry Powerhouse q Two parallel flow paths 5 cells in series 3 cells in series q Gravity-fed system q 8.96 MGD q 29.6 acres q Avoid ComEd power poles Site Design Criteria: Cell Geometry Centennial Trail q Three cells q Operate independently q Pump station and transmission pipe q 1.74 MGD q 28.6 acres q Avoid gas line q Operational flexibility 11

12 Site Design Criteria: Internal Flow Controls Keep Flow Distributed to Minimize Dry Zones and Short-Circuiting Distribution System at Upstream End q Distribution Ditches q Level Spreaders q Wire Mesh Gabions q Rock Fill Trenches Internal Mixing Collection System at Downstream End Site Design Criteria: Wetland Permitting U. S. Army Corps of Engineers, Chicago District Regional Permit 5, Wetland and Stream Restoration and Enhancement Authorizes the restoration, creation or enhancement of wetlands Site Design Criteria: Wetland Permitting Has flexible wetland impact limits, mitigation requirements, performance standards, and buffers Requires net gain in aquatic resource functions & values Proposed treatment wetlands will increase wetland acreage and provide water quality and wildlife habitat benefits 12

13 Site Design Criteria: Wetland Permitting Centennial Trail q 1.8 acres of impact q 28.6 acres of treatment wetlands q Mitigation ratio = 15:1 Powerhouse Marsh q 10.8 acres of impact q 29.6 acres of treatment wetlands q Mitigation ratio = 2.74:1 Site Design Criteria: How to Establish Wetland Plant Communities? Corps permit and mitigation requirements q Provide functional wetland restoration or mitigation q Meet wetland restoration performance standards q Treatment wetlands are not generally wetland mitigation Treatment Goals q How soon will effective treatment occur? Options evaluated: Natural revegetation, native seeding or native planting Will a design precedent be set? Site Design Criteria: How to Establish Wetland Plant Communities? Natural vegetation establishment q Lower cost (no material or labor cost) q 2-3 years to establish 80% coverage q Delay in achieving designed treatment level q Low quality vegetation (Cattails & Common Reed) 13

14 Site Design Criteria: How to Establish Wetland Plant Communities? Native plant seeding only q Higher cost ($3,500/acre) q Allows species selection q Slow plant community development (3-4 years) q Minimize water levels to allow seed germination q Delay in achieving design treatment level q Increased management and monitoring costs to meet mitigation performance standards Site Design Criteria: How to Establish Wetland Plant Communities? Native Planting (Recommended) q Higher cost ($20,000 per acre) q 5,000 plants per acre (standard V3 rate) q Allows species selection q Quick plant community development (1-2 years) q Achieve treatment levels (2-3 years) q Higher quality wetland (tolerant emergent plants) q Performance standards modified for treatment wetlands q Modified management & monitoring requirements Construction Success V3 s Design-Build-Manage Approach to Successful Wetland Mitigation Construction (MWRDGC projects are design only) 14

15 What is Design-Build-Manage? Engineering & Ecological Design Build q Earthwork, Erosion Control q Water Control Structures q Native Plant & Seed Installation Manage q Weed Control (mowing, herbicide) q Burn Management q Replanting q Vegetation and Hydrology Monitoring q Annual Reporting V3 Design-Build-Manage Goals Improve success of V3 design projects. Provide professional management of plant installations Planting contractors lack long-term commitment and do not provide professional supervision Increase knowledge base of naturalized designs and implementation Expand V3 design/build capabilities 15

16 April 2003 August 2003 April 2003 August 2003 Benefits of Design-Build-Manage Respond to unforeseen field conditions q Hydrology & grading q Optimal plant material placement Contractor flexibility q Design & Budget Modifications q Erosion Control Modifications q Schedule Control (Planting timing) Control all ecological management activities Shared objectives = project success q Designer, contractor, plant installer 16

17 Conclusions With proper location and design, Treatment Wetlands can provide a means to remove nutrients from WTP effluent Can be a cost-effective, sustainable solution toward meeting regulatory requirements Can provide ancillary benefits q Increased wetland acreage q Wildlife habitat q Recreational uses & educational opportunities Design-Build-Manage can improve project success Questions? 17