New Crediting Approaches:Impervious Cover Disconnection and CMAC

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Today’s Speakers

Jeremy HansonVirginia Tech

jchanson@vt.edu

Reid ChristiansonCenter for Watershed Protection

rdc@cwp.org

Jamie LefkowitzOpti

jlefkowitz@optirtc.com

Today’s Agenda

• Impervious Cover Disconnection to Amended Soils

• Continuous Monitoring and Adaptive Control

• Audience Questions/Feedback

Recommendations of the Expert Panel to Define Removal Rates for Disconnecting

Runoff from Impervious Areas onto Amended Soils or Treatment in the Stormwater

Conveyance System

CSN Webcast

March 30, 2017

Bill Stack, Center for Watershed Protection, Panel ChairJeremy Hanson, Virginia Tech, Panel Coordinator

Reid Christianson, P.E, PhD, CWP Staff supportLisa Fraley-McNeal, CWP Staff support

Background

• Urban Stormwater Workgroup asked panel to evaluate the nutrient and sediment removal and runoff reduction benefits associated with disconnecting existing acres of impervious cover through several engineering and/or field assessment methods defined in their Charge.

• Met 9 times from July, 2015 through April 2016.

• Final approval of report in December 2016.

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Our esteemed panel of expertsName Role AffiliationBill Stack Panel Chair Center for Watershed Protection

Greg Evanylo Panel Member Virginia Tech

Jason Papacosma Panel Member Arlington County, Dept. of Environmental Services

Ryan Winston Panel Member North Carolina State

David Sample Panel Member Virginia Tech

Franco Montalto Panel Member Drexel University

Justin Shafer Panel Member City of Norfolk (VA)

Panel support

Jeremy Hanson Panel and VT

Coordinator

Virginia Tech, CBPO

Brian Benham VT Project Lead Virginia Tech

Greg Sandi WTWG Representative MDE

Jeff Sweeney CBP Modeling Team

Representative

EPA, CBPO

Liz Ottinger Regulatory Support EPA Region 3

Reid Christianson CWP Staff Support CWP

Lisa Fraley-McNeal CWP Staff Support CWP

Steve Stewart Former Panel Member Baltimore County, Dept. of Environmental Protection and

Sustainability 12

Protocol Units1 Pollutant Removal

Impervious area disconnection to

amended HSG A or B soils that are

not compacted

Pounds per year

TN, TP, and TSS removal calculated as simple impervious disconnection following recommendations of the Expert Panel to Define Removal Rates for Urban Filter Strips (UFS EP, 2014).

Impervious area disconnection to

amended HSG C or D soils or

compacted A and B soils

Pounds per year

TN, TP, and TSS removal calculated based on the runoff reduction from a 1.0 inch rain event, which is used as the water quality volume treated and the RR pollutant removal curves in SRP EP (2013).

Treatment in the conveyance systemPounds per year

TN, TP, and TSS removal calculated based on the water quality volume treated and the RR and ST pollutant removal curves in SRP EP (2013).

1Note that relative reductions from the SRP EP (2013) curves must be multiplied by location specific TN, TP, and TSS yields (i.e. 50% reduction of 10 pounds per acre per year for one acre gives 5 pounds per year reduction).

Table E - 1. Recommended nutrient and sediment removal for the disconnection of existing impervious area runoff from stormwater drainage systems.

Description of Protocols*

Results expressed in inches of runoff treated per acre of impervious cover to be compatible with runoff adjuster curves

*For Maryland sites, refer to Appendix G of the panel report. More on this at the end. 13

Default rate

Assumptions used to calculate the rate (these are conservative assumptions, not qualifying conditions):

• impervious to pervious ratio (I:P) of 1 or lower

• adding at least 1 inch of compost (@50% OM)

• incorporated 3 inches into native soil

A “default rate” is for planning purposes and “non-conforming” projects. Non-conforming projects are defined as planned or implemented projects where more detailed information is not available or not applied using the panel’s simplified or computational methods described in following slides.

TN TP TSS

12.3% 14.6% 15.6%

Default rates are from the RR curves in the Retrofit Expert Panel recommended protocols,

using a value of 0.1 inches per impervious acre treated.

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Qualifying Conditions

Qualifying conditions are important criteria for viability and performance of the practice, such as--

• How IC is directed to amended soil

• Tillage specifications

• Nutrient testing for soils

• Soil testing for parameters used in computational approach

• Compost specifications

• Fertilization specifications for groundcover

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Simplified Method for Impervious Area Disconnection Coupled with Soil Amendments

Table 8. Soil types grouped by a sites existing organic matter and loose, medium, and tight existing soil conditions.

Initial Soil Condition

Organic

Matter

Loose Medium Tight

1% or less

Loam Silt

Silt loam

Sandy clay loam

Silty clay loam

greater

than 1%

Loam

Silt

Silt loam

Sandy clay loam

Silty clay loam

Clay loam

Silty clay

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Curves or table for simplified method

Table 9 Initial Organic Matter =

1.0

Initial Organic Matter =

2.0

Initial Organic Matter =

3.0I:P* Loose Medium Tight Loose Medium Tight Loose Medium Tight

15 0.022 0.005 0.002 0.029 0.004 0.002 0.066 0.008 0.002

14 0.024 0.005 0.002 0.032 0.004 0.002 0.071 0.009 0.002

5 0.088 0.028 0.006 0.108 0.019 0.006 0.201 0.040 0.010

4 0.117 0.041 0.007 0.142 0.029 0.007 0.249 0.056 0.017

3 0.171 0.067 0.008 0.203 0.049 0.008 0.326 0.087 0.032

2 0.287 0.134 0.010 0.331 0.100 0.010 0.466 0.161 0.072

1 0.659 0.428 0.034 0.723 0.323 0.102 0.793 0.447 0.262

0.5 1.039 0.765 0.054 1.106 0.580 0.182 1.067 0.775 0.477

0.25 1.737 1.409 0.091 1.805 1.070 0.335 1.542 1.395 0.890

Water treated (in) per impervious acre based on initial soil conditions

*1 inch of compost incorporated 3 inches

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Example Problem: Simplified Method• Impervious surface disconnection

(public building) to an amended pervious area.

• I:P ratio = 2:1• 0.5 acres of roof disconnected to

• 0.25 acres of pervious

• SSURGO soil data• Leonardtown silt loam

• 3% organic matter

• “Loose” initial soil conditions

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Simplified Method Example (cont.)

• 0.466 inches of water treated per impervious acre

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Simplified Method Example (cont.)

• Using the retrofit curves in Section 5.3• 43% TN red.

• 50% TP red.

• 54% TSS red.

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Step 1. Estimate Impact of Soil Amendments and Decompaction on Hydraulic Properties of Soils before and after amendments.

Computational method

What are sand, clay, organic matter, bulk

density?

Sand + clay + OM + Bulk density

Saxton and Rawls

equations=

Saturated hydraulic

conductivity (Ksat)

21

Computational Method

Step 2: Adjust Ksat to account for the hydraulic loading based on the ratio of impervious area being introduced to the amended soils.

𝐾𝑆𝑎𝑡𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 =𝐿𝑓

𝐷𝐶𝑜𝑛𝑑𝐾𝑆𝑎𝑡𝐶𝑜𝑛𝑑

+𝐿𝑓 − 𝐷𝐶𝑜𝑛𝑑𝐾𝑆𝑎𝑡𝑁𝑎𝑡𝑖𝑣𝑒

22

Computational method

Step 3. Convert Saturated Hydraulic Conductivity to a Curve Number

Step 4. Estimate Curve Number and Water Treated Due to Amended Pervious Area and Disconnected Impervious Area

Post Amendment:

Pre Amendment:Q-site from 1.0” precipitation and existing RCN

Q-(site + Disconnected IC area) from 1.0” using weighted RCN- _______________________________________________

Runoff reduction due to amendments23

Example Problem: Computational Method• Same Conditions

• I:P ratio = 2:1

• Silt loam• 20% sand (by mass)

• 20% clay (by mass)

• 3% organic matter

• Bulk density = 1.46 g/cm3 (CF = 1.1)

• KSat_Initial = 0.27 in/hr (Saxton & Rawls, 2006 or SPAW)

• CNInitial = 91.7 (Chong & Teng, 1986)

• Overall site CN = 95.3

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Computational Method Example (cont.)• Same amendment as simplified method

• 1 inch compost (@50% OM)• 3 inch incorporation

• I:P = 2 Lf = 8 inches

• Silt loam• Organic matter increases to 6%• Bulk density decreases to = 1.08 g/cm3 (CF = 1.0)• KSat_Conditioned = 1.39 in/hr (Saxton & Rawls, 2006 or SPAW)

• KSat_Effective = 0.64 in/hr

• CNConditioned = 79.7 (Chong & Teng, 1986)

• Overall site CN = 89.7

25

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Computational Method Example (cont.)• Runoff Reduction = 40%

• 0.521 inches per impervious acre

• Retrofit curves• 46% TN red.

• 53% TP red.

• 57% TSS red.

Simplified

Computational

More than 1” of Compost?• 2 inches of compost

• 6 inch incorporation

Simplified

Computational

Computational 2” Compost & 6” Incorporation

27

Treatment in the Conveyance System

Stormwater Treatment• Installation of Weirs or Check Dams to Provide

Storage (Stormwater Treatment)• Conversion of a Ditch into a Wet

Swale/Wetland (Stormwater Treatment)

Runoff Reduction• Conversion of a Ditch into a Dry Swale• Creation of Linear Bioretention Treatment

Cells within a Ditch

28

Basic Design Process

• Estimate the water quality volume available.

• Verify that the channel has adequate hydraulic capacity to safely pass the design storm.

• Ensure that minimum residence time is achieved for the design storm.

• Compute the runoff depth treated per impervious acre.

• Use the Retrofit Curves to determine TN, TP, and TSS reductions.

29

Stormwater Treatment (ST)In the Conveyance System

Example

The existing 150’ grass swale at the northern end of the school site will be retrofit with 5 check dams spaced 30’ apart.

Maximum ponding depth = 3”

Water Quality Volume = 450 ft3

5% Impervious = 0.25 ac impervious

450ft3/0.25 ac = 0.5” treated per impervious acre

30

TN, TP, and TSS Reduction Associated with Stormwater Treatment

Recommendations of the Expert Panel to Define Removal Rates for Urban Stormwater Retrofit Projects

26% TNRemoval

31

Data Reporting

32

• For impervious area disconnections directed over HSG D soils or areas that are compacted by construction equipment. To calculate runoff depth treated, use BMP Design Manual methods, Chapter 5 for Disconnection of Rooftop and Non-Rooftop Runoff (Tables 5.6 and 5.7)

In Maryland:

Table 1. Removal Rates for ESD/Runoff Reduction (RR) Practices1

Runoff Depth

Treated (inches)

TSS TP TN

0.1 20.4% 18.9% 16.6%

0.2 35.5% 33.0% 28.6%

0.25 40.4% 37.6% 32.5%

0.3 44.4% 41.3% 35.6%

0.4 50.7% 47.2% 40.6%

0.5 55.6% 51.8% 44.5%

0.6 59.6% 55.5% 47.7%

0.7 62.9% 58.6% 50.3%

0.75 64.4% 60.1% 51.5%

0.8 65.9% 61.4% 52.6%

0.9 68.4% 63.8% 54.7%

1.0 70.7% 65.9% 56.5%

1. Values based on the CBP approved publication, Recommendations of the Expert Panel to Define

Removal Rates for New State Stormwater Performance Standards (Schueler and Lane, 2012)

33

Q&A Break

Continuous Monitoring and Adaptive Control

New Crediting Approach forStormwater Pond Retrofits

Chesapeake Stormwater NetworkMarch 30, 2017

36

Outline

• What is CMAC?• Where to use it and how• Retrofit case studies

◦ Wet ponds◦ Dry Ponds

• Operations and Maintenance

37

What is CMAC?

Solar Power

Opti Control Panel Actuated

Valve

Water Level

Sensor

Existing Outlet

Structure

38

How CMAC works

1. Read forecast2. Prepare for incoming runoff3. Manage discharge during wet weather4. Meet retention goals5. Manage discharge to return to dry weather level

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

15-Aug 16-Aug 17-Aug 18-Aug 19-Aug 20-Aug

flow

rate

(cfs

)

vo

lum

e (

cu

bic

fe

et)

Pond Volume Inflow Discharge

1

2

3

4

5

0.97”

rainfall

39

Where to use CMAC

• Pre-1990s flood control facilities• No water quality volume• Undersized wet ponds• Highly constrained sites

40

New crediting approach

Adaptively controlled volume

→ Water quality treatment volume

→ Treated acres and percent removal

41

Example design requirements

24-hour retention of the water

quality volume within the

adaptive pool

Full drainage of the adaptive pool

through the actuated valve within 24 hours

Safe conveyance of the 100-year 24-hour storm,

using local jurisdictional

requirements for low flow orifice

clogging conditions and

freeboard

Conveyance of the 1-year 24-hour

storm while actively

controlling the valve to not

exceed the pre-development peak

runoff flow rate

Contingent on local regulations

Case Study #1: Wet Pond Enhancement

42

43

University Blvd Wet Pond – Montgomery County, MD

• Anacostia River Watershed• 15 ac-ft wet pond• 440 acre drainage; 36% imp.• In line on Sligo Creek• Retrofit November 2015

44

University Blvd Wet Pond – Hardware

45

University Blvd Wet Pond – Hydraulic Monitoring

0

1

2

3

4

5

6

7

8

9

1/1/16 1/16/16 1/31/16 2/15/16 3/1/16 3/16/16 3/31/16 4/15/16 4/30/16 5/15/16

Wat

er E

leva

tio

n (

ft)

Elevation (ft)

Overflow into Riser

PASSIVE

BASELINE

ACTIVE

CONTROL

46

University Blvd Pond – Web Dashboard

Case Study #2: Dry Pond Conversion

47

48

Regional Dry Pond 1468DP – Fairfax County, VA

• Difficult Run Watershed• 11.5 ac-ft dry pond• 284 acre watershed; 40% impervious• Retrofit January 2017

49

1468DP – Hardware

50

1468DP – Hardware

51

1468DP – Retaining runoff

52

1468DP – Web dashboard

53

Fairfax County CMAC pilot sites

54

Watershed scale deployment

55

Operation and maintenance

O&M Manual Regular Maintenance

Email Alerts

56

Register here

Join us on April 20th to learn more about CMAC

57

Questions & Contact

Jamie Lefkowitz, P.E.Director of Project Developmentjlefkowitz@optirtc.com

Hari VasupuramMarketing Managerhvasupuram@optirtc.com National Fish and Wildlife Foundation

Metro Washington Council of GovernmentsMontgomery County, MDFairfax County, VA

ACKNOWLEDGEMENTS

Webcast Resourceswww.chesapeakestormwater.net

• Archived Webcast and Presentation Slides

• CMAC Sample Conceptual Design

• CMAC Chesapeake Bay Program Approval Overview

• IC Disconnection Panel Report

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