Stormwater Retrofitting and Nutrient Accounting in the Chesapeake Bay Watershed

Transcription

1 Stormwater Retrofitting and Nutrient Accounting in the Chesapeake Bay Watershed

2 Welcome to the Webcast To Ask a Question Submit your question in the chat box located to the left of the slides. We will answer as many as possible during Q&A. To Answer a Poll Question Simply select the preferred option. For those viewing this session alongside several colleagues, respond in a manner that represents your organization as a whole. We ARE Recording this Session All comments and questions will be recorded and included in the archives. We will notify you as soon as the recording and related resources are loaded on the web. We Appreciate Your Feedback Fill out our evaluations our funders need to hear it!

3 Speaker Info Tom Schueler & Cecilia Lane Chesapeake Stormwater Network Ellicott City, MD

4 Chesapeake Bay Stormwater Training Partnership Visit: To learn how you can have access to: Discounted Webcasts Free One-day design workshops Intensive master stormwater design seminars Direct On-site technical assistance Self guided web-based learning modules

5 CSN Updates College of Stormwater Knowledge! New LID Maintenance Resources under development 6 New Expert Panels - ongoing Fall 2012 Network Survey Fall Webcast Series October 4: Estimating Nutrient Reduction at New and Redevelopment Sites in the Chesapeake Bay Watershed

6 Webcast Agenda 1. Retrofit Basics 1. Why Retrofit? 2. Best Opportunities for Retrofitting in Urban Landscape 3. The Stormwater Retrofit Process 2. Calculating Retrofit Nutrient Reduction 3. Costs of Retrofitting

7 Webcast Caveats & Ground Rules Please ask questions or make comments using the chat box The proposed retrofit nutrient reduction protocols are currently undergoing the approval process by the Chesapeake Bay Program

8 POLL Question 1 I am interested in retrofitting because I: work for a local government am a private consultant work for a state or federal regulatory agency work for a watershed or advocacy group other

9 POLL Question 2 I would characterize my retrofit experience as being: Not much Limited Decent Good, but have some technical questions Strong, I should be giving this webcast

10 Part 1. Retrofit Basics Part 1. Retrofit Basics

11 Why Retrofit? Local watershed restoration Meet IC Treatment Targets in MD Comply with Bay-wide TMDLs (and local ones too) Improve local stream habitat and diversity Fix old mistakes/drainage problems Improve performance of existing stormwater infrastructure

12 The Changing Stormwater Landscape Under New MS4 Permits and the Chesapeake Bay TMDL ~ 10 to 30% TP and TN load reductions needed from existing development Massive Increase in Retrofitting 15 Years to Get It Done

13 The Retrofit Story in the Chesapeake Bay PA: retrofit activity to expand as part of their new PAG-13 MS4 permits VA: Phase 1 MS4 permits requiring 40% pollutant reduction for existing development MD: treat 20% of IC in each 5-year permit cycle; possible Phase 2 permit requirements

14 The Retrofit Story in the Chesapeake Bay DC: on-site LID residential and business incentive programs; extensive green street retrofit program DE, WV, NY: not as significant of a restoration technique focusing on other pollutant source sectors Federal Facilities: federal agencies required to lead by example

15 Why Retrofits Are Different Urban Retrofit Practices Construction costs are 1.5 to 4 times greater Assessment and design costs are higher Sized to meet watershed restoration objectives Typically installed on public land Urban soils often cannot support infiltration Fingerprinted around existing development New Stormwater Practices Designers seek least costly options Focus on low cost design and construction Sized to meet local stormwater design standards Installed at new development projects Soils may support infiltration More flexibility on where to locate practices

16 Why Retrofits Are Different Urban Retrofit Practices Must be acceptable to adjacent neighbors Most are publicly maintained Not all candidate sites are feasible Tied into existing conveyance system Integrated with other restoration practices Public investment in watershed infrastructure New Stormwater Practices Aesthetics are not always a major design factor Most require private maintenance Nearly all sites are made to work Usually creates new conveyance system Stand-alone practice Private investment in stormwater infrastructure

17 Best Opportunities for Retrofitting in the Urban Landscape

18 Retrofit Categories 1. Near Existing Stormwater Outfalls 2. Within the Conveyance System 3. Adjacent to Large Parking Lots 4. Green street retrofits 5. On-site LID retrofits 1. BMP Conversions 2. BMP Enhancements 3. BMP Restoration

19 NEW RETROFITS Near Existing Stormwater Outfalls Source: CWP

20 NEW RETROFITS Within the Existing Conveyance System Source: CWP

21 NEW RETROFITS Adjacent to Large Parking Lots Source: CWP Wet Pond Bioretention

22 NEW RETROFITS Green Street Retrofits

23 NEW RETROFITS On-Site LID Retrofits

24 Retrofit Categories 1. BMP Conversions 2. BMP Enhancements 3. BMP Restoration

25 EXISTING RETROFITS BMP CONVERSION DRY POND CONSTRUCTED WETLAND

26 BMP CONVERSIONS Rehabilitating Failed Infiltration Practices

27 BMP CONVERSIONS Adding Bioretention/Filtering to Ponds

28 EXISTING RETROFITS BMP ENHANCEMENT INCREASE IN HYDRAULIC RETENTION TIME

29 EXISTING RETROFITS BMP RESTORATION MAJOR REPAIRS OR UPGRADES TO EXISTING BMPs THAT HAVE FAILED OR LOST ORIGINAL TREATMENT CAPACITY

30 BMP RESTORATION - Qualifying Conditions - Only 4 types of restoration allowed: a) Major Sediment Cleanouts Removal of sediment, debris equal to or grater than 1/10 of the volume of the facility b) Vegetative Harvesting Removal of excessive growth with off-site sequestration c) Filter Media Enhancements Removal and sequestration of contaminated material and replacement with superior media d) Complete BMP Rehab Only applies to older BMPs not previously reported

31 BMP RESTORATION CAVEATS No credit given for routine maintenance Restoration activities must restore original capacity of the BMP at a minimum

32 The Stormwater Retrofit Process

33 Step 1 Retrofit Scoping Consult with stakeholders Understand watershed conditions and develop restoration objectives Select subwatersheds Identify targeted land use for treatment Identify typical locations where retrofitting may be most successful

34 Step 2 Desktop Analysis Analyze mapping and metrics to find prospective sites Aerial photos Topography Hydrology Ownership Land cover Storm sewers Existing BMPs Outfalls Road Crossings

35 Step 3 Field Investigation Characterize drainage patterns and retrofit potential at each parcel

36 Develop Conceptual Design Develop conceptual designs

37 Step 4 Compile Retrofit Inventory

38 Step 5 Evaluation and Ranking Assign weights to ranking factors Nutrient reduction Community Benefits Permitting Environmental Site Constraints Costs Category Ranking Factor Potential Score Potential for Treatment 40 Total drainage area treated 15 Impervious area treated 15 Land use treated 10 Potential for Greater Ecological and Community Benefits 25 Potential education / demonstration project AND/OR public accessibility Treatment of area(s) of concern 5 Potential to support other planned or on-going watershed restoration projects and activities Site Constraints 35 Access for construction and maintenance 15 Potential for conflict with existing utilities 5 Potential ecological conflicts 10 Project for further consideration (yes/maybe) 5 Total Potential Score

39 Step 6 Subwatershed Analysis

40 Step 7: Retrofit Design Convert concept to a construction drawing Requires site analysis and construction plan More realistic construction costs come to light Copyright 2000, CWP

41 Step 8. Inspection, Maintenance and Evaluation

42 Manual 3: Urban Stormwater Retrofit Practices Contains extensive guidance on different retrofits and the process for finding them in the urban landscape Free download at

43 Questions and Answers

44 POLL Question 3 What is the major driver for stormwater retrofits in your community? Local watershed restoration plans Bay-wide TMDL (or local TMDL) MS4 Stormwater permit requirements Demonstration grants Not really doing much retrofitting yet

45 Part 2. Computation of Sediment and Nutrient Reductions associated with Retrofits

46 The CBP Process Outlined in the WQGIT BMP Review Protocol (WQGIT, 2010) BMP Expert Panel reviews existing research set of recommendations Recommendations used to derive methods and/or protocols to derive nutrient removal rates for the proposed BMP

47 The Status Approved by USWG in April Conditionally approved by WTWG in May USWG response in June Technical memo resubmitted to WTWG in July Conditionally approved by WTWG in August Currently seeking Final approval from WQGIT BMP EXPERT PANEL URBAN STORMWATER WORKGROUP WATERSHED TECHNICAL WORKGROUP WATER QUALITY GIT

48 The Expert Panel Panelist Ray Bahr Ted Brown LJ Hansen Joe Kelly Jason Papacosma Virginia Snead Bill Stack Rebecca Stack Steve Stewart Affiliation Maryland Department of the Environment Biohabitats, Inc. City of Suffolk, VA Pennsylvania Department of Environmental Protection Arlington, VA Virginia Department of Conservation and Recreation Center for Watershed Protection District Department of the Environment Baltimore County

49 Key panel outcomes More retrofit options = more opportunities to get credit! Simple to use method for determining pollutant removal! Reporting and verification procedures are flexible and can be adapted to align with existing state reporting requirements. Not a one size fits all approach: Each retrofit has its own unique removal rate based on the amount of runoff it treats and the degree of runoff reduction it provides

50 Evolution of Stormwater BMP Removal Rates Stormwater is an evolving science At least 10 different sets of studies in the last 25 years alone! The need for numbers NOW versus the variability (or limited availability) of data With so many conflicting removal rates how to come up with generic removal rates that localities can use??

51 Protocol for determining retrofit removal rates Extensive review of current BMP performance research Developed a table of different classes of retrofits Determined composite Anchor Rates Developed a series of retrofit removal rate adjustor curves

52 All practices sorted into 2 categories: Runoff Reduction (RR) & Stormwater Treatment (ST) Classification of Retrofits Runoff Reduction Practices (RR) Stormwater Treatment Practices (ST) Bioretention Dry Swale Infiltration Permeable Pavement Green Roof Achieve at least 25% reduction of annual runoff volume Constructed Wetlands Filtering Practices Proprietary Practices Wet Swale Wet Ponds Traditional Practices

53 Anchor 1 Table A-3 Composite Approach to Derive Nutrient Mass Load Reductions for RR ad ST Runoff Reduction Practices 1, PRACTICE TP Mass Reduction (%) TN Mass Reduction (%) Bioretention Dry Swale Infiltration Permeable Pavers Green Roof/Rain Tank Average RR Wet Ponds Const. Wetlands Filtering Practice Wet Swale Average ST Source: Table A-5, nutrient rates computed using the average mass reduction for both Design Level 1 and Level 2. 2 This value was subsequently discounted by 18% to reflect the impact of nitrate migration from runoff reduction practices described later in this appendix.

54 Total Phosphorus Removal (%) 100% 95% 90% 85% 80% 75% 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% Total Phosphorus Removal for RR and ST Stormwater Retrofit Practices ST RR Runoff Depth Treated per Impervious Acre (inches)

55 Retrofit Removal Adjustor Curves Use of Rainfall Frequency Analysis to determine the amount of bypass and pollutant removal above and below 1.0 Converted to series of Retrofit Removal Adjustor Curves

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57 The N curve was reduced based on WTWG feedback on groundwater nitrate loss from runoff reduction practices

58 Retrofit Removal Adjustor Curves To determine the amount of runoff depth treated at a site: 1. Estimate the Runoff Storage volume (RS) available at the site in acre-feet. 2. Impervious Area (IA) in acres 3. Input into Standard Retrofit Equation: = RS (12) IA

59 Local Reporting Check with your State stormwater agency first! Panel Recommends: Retrofit class (i.e., new retrofit facility or existing BMP retrofit) GPS coordinates Year of installation 12 digit watershed in which it is located Total drainage area and impervious cover area treated Runoff volume treated and identify type of BMP (RR or ST) Projected sediment, nitrogen and phosphorus removal rates

60 Design Examples

61 Design Examples New Retrofit Facility Constructed Wetland A constructed wetland is built in parkland as a retrofit, classified as a ST practice The retrofit storage is estimated to be 1.67 acre-feet Treats runoff from 50 acre residential neighborhood with 40% impervious cover

62 Design Examples New Retrofit Facility Constructed Wetland Using the Standard Retrofit Equation: RS (12) = IA RS = Retrofit Storage 1.67 ac-ft IA = Impervious Area = 20 acres 1.67 (12) 20 = 1.0 inch

63 Design Examples New Retrofit Facility Constructed Wetland Pollutant Removal Efficiencies of the practice TP TN TSS 52% 33% 66%

64 Determining the Baseline Load Only necessary for locals that want to compare retrofit options! Can calculate the baseline load using the generic state-wide CBWM (version 5.3.2) urban unit loading rates from MDE guidance document: Calculate the number of pervious and impervious acres in the DA, Multiply by the unit loading rates:

65 Retrofit Example 1 Constructed Wetland Total Nitrogen Total Phosphorus Suspended Sediment Pounds/acre/year Tons/acre/year IMPERV PERV IMPERV PERV IMPERV PERV MDE Loading Rates Area (acres) Baseline Load Removal Rate Load Removed ac 30 ac 20 ac 30 ac 20 ac 30 ac 500 lbs/yr 57.9 lbs/yr 11.3 tons/yr 33% 52% 66% 164 lbs/yr 30.1 lbs/yr 7.46 tons/yr

66 BMP Conversion Example Dry pond conversion Create new water quality storage using a combination of a forebay with a permanent pool, a submerged gravel wetland cell and a final bioretention polishing cell New facility now provides a runoff storage volume of 1.3 acrefeet Treats a site area of 65 40% impervious Classified as a RR practice

67 Design Examples BMP Conversion Using the Standard Retrofit Equation: RS (12) = IA RS = Retrofit Storage 1.3 ac-ft IA = Impervious Area = 26 acres 1.3 (12) 26 = 0.6 inches Pollutant Removal Efficiencies of the practice TP TN TSS 55% 47% 59%

68 Design Examples BMP Conversion Pollutant Removal Efficiencies of the practice TP TN TSS 55% 47% 59%

69 Design Examples BMP Enhancement Dry Extended Detention pond sized to capture 0.3 of runoff 10 acre commercial drainage 100% impervious Short-circuiting of pond led to half of original storage volume 0.15

70 Design Examples BMP Enhancement Pond enhanced to: Increase hydraulic retention time (prevent shortcircuiting) Provide pretreatment Wetland cells added to bottom of pond in order to provide better treatment Enhancements created additional 0.3 of storage for a combined new storage of: 0.6 per impervious acre

71 Design Examples BMP Enhancement Enhancements are slightly different New removal rates found as the difference between the original rates and the enhanced rates Original and enhanced rates from the curves Increase in both runoff volume captured AND runoff reduction capabilities TP TN TSS Enhanced Rate 44% 28% 55% Original Rate 22% 14% 28% Incremental Removal Rate 22% 14% 27%

72 Design Example BMP Restoration Captures 0.5 of runoff from the impervious cover of contributing watershed: 40 50% impervious Previously reported to the State Sedimentation and invasive plant growth decreased storage volume by 60% Only actually provides 0.2 of runoff capture City conducts major sediment dredging, invasive plant removal, replants pond with natives Recovers 0.3 of storage to original design volume of 0.5

73 Design Examples BMP Restoration How the pollutant removal is calculated depends on whether or not the BMP has previously been reported to the state. If the BMP has previously reported to the state: the existing removal rate is calculated and reported the first year. in subsequent years the restored rate is reported to the State. TP TN TSS Restored Rate (0.5 ) 40% 25% 48% Existing Rate (0.2 ) 26% 16% 33% If the BMP has not been reported to the state, it is considered a new retrofit

74 Accountability 1. Duration of Retrofit Removal Rate: 10 yrs MAX Can be renewed based on field performance inspection: still exists, is maintained and operates as designed 5 yrs for on-site LID Can be renewed upon visual inspection 2. No Double Counting! Rate cannot be used if retrofit is an offset for new development 3. Initial Verification of Performance Post-construction certification that retrofit installed to design standards, functioning properly

75 Accountability 4. Local Reporting Check with your state stormwater agency! Expert panel recommendations 5. Local Recordkeeping More extensive record keeping (i.e., construction drawings, as-builts etc.) For the lifetime of the retrofit 6. Ongoing Field Verification Inspection every 10 years If facility not performing to original design, will have up to 1 year to take corrective maintenance Renewal of removal rates if corrective maintenance occurs

76 Q & A

77 Part 3 The Costs of Retrofitting

78 Retrofit Construction Costs for Existing BMPs (per impervious acre treated) BMP Conversions: BMP Enhancements: BMP Restoration: 5 to 15 K 5 to 10 K 2 to 5 K Less excavation, modify plumbing, own or control land, strong neighborhood support

79 We Love These Guys!

80 Dealing with the Local BMP Legacy Thirty Years of BMPs. The BMP Inventory in a Maryland County (2006) Potentially High Performers Known Low Performers Bioretention/Dry Swales 49 Underground 270 Detention Sand Filters 279 Dry Ponds 528 Wet pond 212 Oil Grit Separators 805 Pond Wetland 98 Proprietary Practices 239 Infiltration Basin 58 Flow Splitter 321 Infiltration Trench 459 Other (plunge pools) 30 Grand Total 3350

81 Breakdown of Retrofit Costs 1. Discovery Costs 2. Project Evaluation Costs 3. Design, Engineering and Permitting 4. Contracting

82 Comparative New Retrofit Construction Costs * (per impervious acre treated) New Retrofits: 12 to 30 K Non-residential LID: 40 to 80 K * Residential LID: 80 to 120 K * Green Streets: 100 to 150 K * * Demonstration project phase, should drop

83 Caveats on Retrofit Cost Numbers Enormous variation within each retrofit category depending on site conditions These estimates represent the 25% easiest Major influence of the prototype effect CSN to do retrofit cost survey in to get better estimates

84 Discovery Costs Cost to identify candidate sites for potential retrofits Involves desktop GIS analysis and subsequent field investigation Two options: 1. Comprehensive subwatershed evaluation 2. Limited assessment of existing BMP inventory

85 Discovery Costs Usually done by consultant, but can be done in house For a ten square mile subwatershed, plan on: 200 hours for comp subwatershed eval. 40 hours for BMP inventory assessment

86 Project Evaluation Costs Cost to evaluate project feasibility, develop concept design and compute reductions Rule of Thumb: 10 to 20 hours per site Based on Recent CWP fieldwork Requires some engineering review and neighborhood consultation

87 Retrofit Cost Inflators What is Fixed Wetland permitting Off-site haul of excavated materials Sewer or utility relocation Need easements or contested ROW Complicated plumbing (flow splitters) Parking, maintenance of traffic Amenity landscaping Others? Take care in the stream corridor!

88 Design, Engineering and Permitting Costs Typically run be 30 to 50% of retrofit construction cost High end: demonstration projects, refiguring plumbing, unfamiliar practices Low end: Conversion, enhancement or restoration of existing BMPs

89 Contract Administration Costs Assume that 1 FTE is needed for every 1 to 2 million contracted in retrofit capital budget Project bundling, design/build, call contracts, bid incentives and other project management tools can reduce costs and improve quality

90 Session Resources Visit our Stormwater Retrofits page in the College of Stormwater Knowledge:

91 Thanks! Please take a minute to answer a multiple choice evaluation survey to improve future webcasts Or your comments directly to watershedgal@hotmail.com