Retrofitting Revisited: A Post-Expert Panel...

Retrofitting Revisited:A Post-Expert Panel Perspective

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Poll Question #1

How many people are watching with you today?

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Poll Question #2

Tell us a little about yourselves…who are you representing today?

• Local government

• Private sector

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• Non-profit

• Academia

• Other…tell us in the chat box

Poll Question #3

Tell us what YOUR role in retrofitting is:

• I design them

• I construct them

• I record/track/account for them to meet my permit/restoration/TMDL requirements

• I conduct retrofit/watershed assessments

• What is a retrofit?

Tom SchuelerChesapeake Stormwater

Networkwatershedguy@hotmail.com

Cecilia LaneChesapeake Stormwater

Networkwatershedgal@hotmail.com

Speaker Info

1964

My Early Retrofitting Years

Wiggle-tail

Today’s Agenda

1. Retrofit Classification

2. Envisioning Restoration

3. The Retrofit Discovery Process

4. Tom’s Short Cut Process

5. Retrofit Evaluation: Removal and Costs

6. Some FAQs for Retrofits

7. Some Other Options

8. Discussion

Why Retrofit?

~ 10 to 30% TP and TN load reductions needed from existing development

Massive Increase in Retrofitting

15 Years to Get It Done

Stormwater Retrofit Classification

Category 1

RETROFIT EXISTING BMPS

1. BMP Conversions

2. BMP Enhancements

3. BMP Restoration

Can be the most cost effective type of retrofit since it represents existing stormwater infrastructure that you already own or control

EXISTING RETROFITS

BMP CONVERSION

DRY POND

CONSTRUCTEDWETLAND

Retrofit Existing Stormwater Basins

1. Excavate Storage

– Wet pool

– Sand filter

2. Raise Embankment

Retrofit Existing Stormwater Basins

3. Modify Riser

Retrofit Existing Stormwater Basins

4. Trade Storage

OTHER BMP CONVERSIONSAdding Bioretention or Sand Filters to Dry Ponds

EXISTING RETROFITS

BMP ENHANCEMENT

Increase treatment volume, hydraulic residence time or other design elements to improve pollutant removal *

* Expert panel did not provide a lot of specifics

EXISTING RETROFITS

BMP RESTORATION

DREDGING AN UNDERPERFORMING POND TO RESTORE FULL PERFORMANCE

Retrofit Category 2: NEW BMPs

Near Existing Stormwater Outfalls

Source: CWP

NEW BMPs

Within the Existing Conveyance System *

Source: CWP

* Impervious Cover Disconnection EP provides new design methods for this kind of retrofit

Wet Pond

Bioretention

NEW BMPs

Adjacent to Large Parking Lots

Source: CWP

NEW BMPs

Green Streets

NEW BMPs

Residential Stewardship Practices

A lot of resources, design tools, tracking systems and incentive programs have been developed for this class of

retrofits in recent years

Questions ?

Envisioning Restoration

Retrofitting requires:

Sleuthing skills to determine what can work at highly constrained sites

Simultaneously envisioning restoration possibilities and anticipating potential

problems

What would you do here?

Activity

The Retrofit Discovery Process

Source: USRM 3, CWP

Step 1. Retrofit Scoping

• Purpose

– Define a retrofit strategy to meet local restoration objectives

• Key tasks

– Review local stormwater management infrastructure and practices

– Define restoration objectives

– Define preferred retrofit practices and locations

Step 1. Retrofit Scoping

•Consult with stakeholders

•Understand watershed conditions and develop restoration objectives

•Select subwatersheds

•Identify target land usesto treat

Step 2. Desktop Retrofit Analysis

• Purpose

– Rapidly search for and identify potential retrofit sites across the subwatershed

– Save time in the field

• Key tasks

– Secure GIS layers and other mapping data

– Conduct a structured desktop search for retrofit sites

– Prepare base maps for field investigation

Step 2. Desktop AnalysisAnalyze mapping and metrics to find prospective sites

• Aerial photos

• Topography

• Hydrology

• Ownership

• Land cover

• Storm sewers

• Existing BMPs

• Outfalls

• Road

Good Desktop Search Targets

• Publicly owned property

• Institutional property

• Existing stormwater ponds

• Stormwater outfalls

• Large impervious cover with adjacent open land

• Conveyance system intersected with open space

• Where roads cross ditches

• Streets that meet width and slope criteria and include a nearby storm drain.

Step 3. Field InvestigationCharacterize drainage patterns and retrofit potential at each parcel

• Take photos, measurements, notes

• Sketch retrofit and drainage area.

Look at Existing Stormwater Infrastructure & Feasibility Factors

Understand the Plumbing at the Site

Rooftop Connections

Follow the Runoff

Weep Hole Drainage Chute

Eroded Conveyance Grass Channel

Storm Drain

Pipe Invert

Available Hydraulic Head

Detention Areas

2-year

10-year100-year

Storm drain Storm drain Manholes

Curb Drop Inlet

GAS

Sanitary Sewer

Utilities!Cable

Water line

Stream Impacts

Our friend the beaver….

Forest Buffers

Trees in general

High quality wetlands Low quality wetlands

Soil Indicators

Soil Depth

Saturated Soils

Compacted Soils

Develop Conceptual DesignDevelop conceptual designs

Step 4. Compile Retrofit Inventory

Retrofit Inventory CompilationUpdate parcel-based database with field data

• Input into master database –spreadsheet or similar format

Step 5. Evaluation and Ranking

• Consult with stakeholders

• Use ranking factors based on predetermined subwatershed objectives

• Assign weights to ranking factors

• Develop system to assign scores to individual sites

• Create a prioritized list

Step 6. Subwatershed Analysis

Step 7. Final Design and Construction

• More realistic

construction costs

come to light

• Convert concept to a

construction drawing

• Requires site analysis

and construction plan

Step 8. Inspection, Maintenance and Verification

Questions ?

Initial Verification of Retrofit Installation

• Localities to verify that retrofits:– Installed properly– Meets/exceeds design

standards– Functions hydrologically as

designed

• Initial verification should be provided by the designer or inspector as condition of project completion

Retrofit Verification

• CBP emphasizing verification of BMPs installed for the TMDL

• The Retrofit Removal Rate is not perpetual

• Good for 10 years, and can be renewed based on field inspections (5 years for on-site LID retrofits)

• Use of simple visual indicators

Performance Verification

Ensure BMP still exists and is providing the

pollutant removal it was designed to achieve or if

it requires major restoration

MS-4 Permit/Bay TMDL

Once every 9 -10 years

Trained evaluator

Facility BMP

Inventory

State BMP

Reporting for Bay TMDL

73

Retrofit Tracking

Tom’s Short Cut Method

• Evaluate the condition of your legacy stormwater ponds to optimize the nutrient reduction, safety and habitat value of your existing stormwater infrastructure

Retrofit Evaluation

• Defining Retrofit Pollutant Removal

• Evaluating Retrofit Cost

– Individual Retrofits

– Administering a Local Retrofit Program

Retrofit Removal Rates

BMP removal rates are a function of runoff depth captured and the amount ofstormwater treatment (ST) or runoff reduction (RR) achieved by the practice

Classification of BMPsRunoff Reduction Practices

(RR)

Stormwater

Treatment Practices

(ST)

Bioretention Constructed Wetlands

Dry Swale Filtering Practices

Infiltration Wet Swale

Permeable PavementWet Ponds

Green Roof

All practices sorted into 2 categories: Runoff Reduction (RR) &

Stormwater Treatment (ST)

Achieve at least 25% reduction of annual runoff volume

Traditional Practices

Design Examples – New Retrofit Facility Constructed Wetland

• A constructed wetland is built on a federal facility 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

Design Examples – New Retrofit Facility Constructed Wetland

• Using the Standard Retrofit Equation:

• RS = Retrofit Storage ≈ 1.67 ac-ft

• IA = Impervious Area = 20 acres

X = (RS x 12) / IA

(1.67 x 12) / 20 = 1.0 inch

TP TN TSS

55% 35% 70%

Design Examples – New Retrofit Facility Constructed Wetland

Pollutant Removal Efficienciesof the practice

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

10.85 9.43 2.04 0.57 0.46 0.07

Area

(acres)20 ac 30 ac 20 ac 30 ac 20 ac 30 ac

Baseline

Load500 lbs/yr 57.9 lbs/yr 11.3 tons/yr

Removal

Rate35% 55% 66%

Load

Removed175 lbs/yr 31.85 lbs/yr 7.91 tons/yr

* Example using MDE guidance loading rates

Questions ?

The Costs of Retrofitting

Retrofit Construction Costs for Existing BMPs (per impervious acre treated)

BMP Conversions: 5 to 15 K

BMP Enhancements: 5 to 10 K

BMP Restoration: 2 to 5 K

Less excavation, modify plumbing, own or control land, strong neighborhood support

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

• Enormous variation within each retrofit category depending on site conditions

• These estimates represent the “25% easiest”

• Major influence of the “prototype effect”

Caveats on Retrofit Cost Numbers

1. Discovery Costs2. Project Evaluation Costs 3. Design, Engineering and Permitting4. Contracting5. Construction6. Retrofit Maintenance

Breakdown of Retrofit 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

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

Discovery Costs

• Cost to: • evaluate project feasibility• develop concept design • compute reductions and

cost • Rule of Thumb: 10 to 20

hours per site• May requires some

engineering review and neighborhood consultation

Project Evaluation Costs

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

Take care in the stream corridor !

Retrofit Cost Inflators

• 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

Design, Engineering and Permitting Costs

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

Tip 1. Develop multiple revenue streams and delivery mechanisms

• Capital Improvement Budget

• Stormwater Offset Fees

• Stormwater Utility Discounts

• Stormwater Maintenance Budgets

• Maintenance Enforcement

• Street Reconstruction

• Piggyback on Municipal Construction Projects

• Public/Private Partnerships

Another slice of restoration

A slice of restoration

Frequently Asked Questions

Q: Are Regenerative Stormwater Conveyance practices considered retrofits?

• Yes! Dry RSC practices can be treated as an upland BMP or as a retrofit for treating stormwater runoff

• Use the “RR” curve for determining removal rates

• Wet channel RSC practices are considered to be a stream restoration practice

Cabin Branch RSC project

Q: What about a Floating Treatment Wetland in an existing Wet Pond?

• Good question!

• Currently the focus of a CBP Urban BMP Review Panel

Floating Treatment WetlandPhoto credit: Sarah White, Clemson University

Q: What happens if my project has a mix of runoff reduction and stormwater treatment

practices ?

Answer: Use the curve associated with the practices that provide a majority of the runoff capture or storage volume for the site as a whole

For example, Site C has RR practices providing 60% of the runoff capture volume and ST practices provide the rest. Use the RR curve

Q: I have trouble reading the curves…can you provide the actual equations for them so I can plug them into a spreadsheet and calculate the removal

rates directly?

• A brilliant idea! While they are shown here, they are also in the FAQ document.

TPRR y = 0.0304x5 - 0.2619x4 + 0.9161x3 - 1.6837x2 + 1.7072x - 0.0091

ST y = 0.0239x5 - 0.2058x4 + 0.7198x3 - 1.3229x2 + 1.3414x - 0.0072

TNRR y = 0.0308x5 - 0.2562x4 + 0.8634x3 - 1.5285x2 + 1.501x - 0.013

ST y = 0.0152x5 - 0.131x4 + 0.4581x3 - 0.8418x2 + 0.8536x - 0.0046

TSSRR y = 0.0326x5 - 0.2806x4 + 0.9816x3 - 1.8039x2 + 1.8292x - 0.0098

ST y = 0.0304x5 - 0.2619x4 + 0.9161x3 - 1.6837x2 + 1.7072x - 0.0091

Q: What if I want to use a retrofit practice that is does not fall into the current retrofit

classification ?

• Good question!

• Two possibilities:– Determined by future

expert panels based on the priority assigned by the USWG

– Practice can be mapped into existing urban BMP credit

CMAC Outfall RetrofitPhoto credit: Marcus Quigley, OptiRTC

Prerequisites

• Cannot be a proprietary practice

• Represents a real change on the ground that occurs in the present day (e.g., no historic BMP finds)

• Have verification procedures that are as stringent or more stringent than their “parent” BMP

Process

• Proposer provides supporting documentation for consideration by USWG

• USWG can accept, accept w/ modification, reject or require a full blown expert panel

• States can individually opt out if they are not comfortable with the technical basis for the decision, reporting requirements and/or verification protocols

• Modelers will be consulted prior to any decision

Other CBP-Approved Urban BMPs to Meet the Bay Pollution Diet

1. New State Performance Standards

2. Redevelopment Credits

3. Residential Stewardship Practices

4. Urban Nutrient Management

5. Stream Restoration

6. Enhanced Erosion and Sediment Control

7. Illicit Discharge Removal

8. Street and Storm Drain Cleaning

9. Shoreline Management

10. Septic System Upgrades

11. FTWs and UTC (this summer)

Resources

• U-1 Urban Stormwater Retrofits Fact Sheet

• USRM 3: Urban Stormwater Retrofit Practices

• CWP Stormwater Retrofitting Reconnaissance Videos:

– Part 1: https://youtu.be/tHvuzReiDHQ

– Part 2: https://youtu.be/Q-9j2RgLW3I

– Part 3: https://youtu.be/vmjyskDxzuU

• Retrofit Expert Panel Report

• Retrofit FAQ Document

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