Building and Applying a Modeling Tool to Develop and Inform the District of Columbia’s Consolidated MS4

TMDL Implementation Plan

Benjamin Crary

LimnoTech

04/08/2016

Overview

1. The District’s stormwater permit requirements

2. Modeling of stormwater runoff and pollutant reductions

3. Implementation Plan Modeling Tool built for the

Department of Environment and Energy (DOEE)

4. Overall Implementation Plan actions

The District’s Stormwater Landscape

Three stormwater conveyance systems in the District:

*Runoff entering the Combined Sewer System is treated at the Blue Plains Treatment Plant.

Conveyance Total Area

Municipal Separate Storm Sewer System (MS4) 19,750 acres

Direct Drainage 7,230 acres

Combined Sewer System 12,220 acres

The District’s MS4 permit requirements

• MS4 Permit Requirement Includes: • WLAs that cover daily, seasonal, and annual time scales

• 500+ numeric MS4 WLAs

• 23 waterbodies

• 45 regulated drainage areas (“TMDL Segments”)

• 18 total pollutants

Conventional Metals Organics Other

Total Nitrogen Arsenic Chlordane Bacteria

Total Phosphorus Copper Heptachlor Epoxide BOD

Total Suspended Solids Lead Dieldrin PCBs

Mercury DDD, DDE, DDT Trash

Zinc PAH1, PAH2, PAH3 Oil and Grease

The District’s MS4 permit requirements

**The permit requires a consolidated TMDL Implementation Plan for all MS4 WLAs

The District’s MS4 permit requirements

Create a consolidated TMDL Implementation Plan for all MS4 WLAs

• Schedule for attainment of all 500+ WLAs

• Demonstration through modeling how attainment will be achieved

• Narrative for schedule and controls

Implementation Plan Modeling Approach

• Runoff and pollutant calculations based on Revised Simple Method

• Runoff is a function of precipitation, area, and the runoff coefficient

• Pollutant load is a function of EMC and runoff

• BMP pollutant removal is a function of BMP volume and load efficiency

BMP Module - Overview

• Reductions driven largely by DOEE’s stormwaterregulations for private development

• Most BMPs now designed to regulatory standards

• Steps to quantify BMP load reductions:• 1. Consolidate and curate an inventory of all BMPs in the

MS4• Bioretention, permeable pavement, trees, etc.

• 2. Establish BMP efficiencies for all BMP types • Known Design Specs: used SWMM-based efficiency curves• Unknown Design Specs: used literature based load efficiencies

• 3. Locate each BMP geographically and assign to appropriate TMDL segments

Program Annual Area Projection

Compliance with Stormwater Regulations

187 acres/yr

Direct investment inBMP implementation and programmatic and source control efforts

21 acres/yr

BMP Module – BMP Efficiency Comparison BMP Type Efficiency at 1.2” Design

Enhanced Permeable Pavement

92%

Enhanced Bioretention

90%

EnhancedBioretentionwith Underdrain

83%

Standard Bioretention

58%

Green Roof 50%

Standard Permeable Pavement

0%

SWMM-based BMP Volume Reduction Efficiency Curves (retention-based BMPs)

*1.2” Design Regulation for Major Land Disturbances

Design Specifications Known: Retention Curves

Design Specifications Unknown: Literature-based efficiency matrix

BMP Module - Efficiencies

Green Roof

Rainwater

Harvesting

Impervious

Surface

Disconnect

Permeable

Pavement

Systems Bioretention

Filtering

Systems Infiltration

Open

Channel

Systems Ponds Wetland

Storage

Practices

Proprietary

Practices

Arsenic 17 8 9 38 41 43 52 36 33 33 19 5

BOD 0 0 0 0 0 40 51 30 0 63 27 0

Chlordane 6 3 3 12 13 14 17 12 11 11 6 2

Copper 20 10 10 45 48 51 61 43 38 38 22 6

DDD 20 10 10 46 49 52 62 44 39 39 23 7

DDE 24 12 13 55 59 63 75 53 47 47 28 8

DDT 22 11 12 51 54 58 69 48 43 43 25 7

Dieldrin 0 0 0 0 0 0 0 0 0 0 0 0

Fecal Coliform Bacteria 23 11 12 52 56 60 71 50 45 45 26 7

Heptachlor Epoxide 0 0 0 0 0 0 0 0 0 0 0 0

Lead 27 13 14 60 64 68 81 57 51 51 30 9

Mercury 17 8 9 38 41 43 52 36 33 33 19 5

Oil and Grease 0 0 0 0 0 0 0 0 0 0 0 62

PAH1 1 0 0 1 1 1 2 1 1 1 1 0

PAH2 9 5 5 21 23 24 29 21 18 18 11 3

PAH3 29 14 15 66 71 76 90 63 57 57 33 9

TN 43 40 13 47 58 40 83 42 20 20 13 5

TP 45 40 13 50 68 60 85 43 45 45 15 10

TPCB 18 9 9 40 43 46 54 38 34 34 20 6

TSS 31 15 16 70 75 80 95 67 60 60 35 10

Zinc 23 11 12 52 56 60 71 50 45 45 26 7

*Runoff and load into practice based on drainage area to BMP

BMP Module - Recap

• Assign an efficiency for each BMP based on design specifications

• Credit efficiency towards meeting appropriate WLA based on its geographic location

• Automate process using the database-driven Implementation Plan Modeling Tool

IPMT Framework

• No proprietary software or licensing requirements except for Windows

• Can be installed locally on any computer that has Windows

• Databases are in MS Access

• Calculator is coded using .Net

• GUI/mapping provided by DotSpatial (Open source GIS)

What does the IPMT do?

• Provide a geospatial display of stormwater related inventories

• Query and display specific TMDL information

• Display BMP implementation spatially and through a detailed inventory

• Calculate runoff, pollutant loads, and load reductions

• Track progress towards WLAs (required by permit)

• Generate report and graphics

Presents complex modeling results in an easy-to-use interface

Geospatial display of stormwater related inventories

Query TMDL Inventory

Display BMP implementation

Track progress towards WLAs

Query detailed results:

Overview of all WLAs:

IPMT Summary

• Power is in the integrated databases • (TMDL inventory, BMP inventory, etc.)

• Great automated tracking and reporting tools• Graphics and tables that feed into reports to EPA

• Framework for continually adding more information

Only one component of a larger Implementation Plan

•Meeting WLA attainment schedules•Milestones and benchmarks•Ultimate attainment of WLAs

•Monitoring•Measures WQ improvements• Feedback for model adjustments

•Other programmatic approaches

Other Implementation Plan Components

Ben CraryLimnoTech

(202) 864-6827bcrary@limno.com

Jonathan ChampionDC Department of Energy and

EnvironmentStormwater Management Division

(202) 535 1722jonathan.champion@dc.gov

www.dcstormwaterplan.org