3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 1 

## Chapter 3. Technical Guidance on Controlling Urban Runoff 1 

## in the Chesapeake Bay 2



## Contents 3 

### 1 Introduction.....................................

................................................... ........................................6 4 

### 1.1 Need for Urban Runoff Guidance Update ..........

................................................... ...........6 5 

### 1.1.1 Purpose

................................................... ................................................... .............6 6 

### 1.1.2 Intended Audience ..................................

................................................... ...........10 7 

### 1.1.3 Water Quality Significance of Urban Runoff in the Chesapeake Bay 8 

### Watershed ..........................................

................................................... .................11 9 

### 1.1.4 Managing Urban Runoff to Reduce Nutrients and Sediment Loss........................15 10 

### 1.2 Overview of the Urban Runoff Chapter...........

................................................... ............23 11 

### 1.2.1 Management Practices and Management Practices Scale s...................................24 12 

### 1.2.2 Implementation Measures for Urban Runoff in the Che sapeake Bay 13 

### Watershed to Control Nonpoint Source Nutrient and S ediment Pollution............26 14 

### 1.3 References.....................................

................................................... ...............................30 15 

### 2 Implementation Measures for Reducing Urban Runoff Volume............................................ .33 16 

### 2.1 Maximize Infiltration, Evapotranspiration, and Harvest and Use ................................. 2.1 Maintain or Restore Predevelopment Hydrology 17 

### 2.2 Implement Policies to Preserve and Restore Rede velopment Hydrology .................. 2.1.1 Estab lishing Performance Design Objectives 18 

### 2.3 Use Planning and Development Techniques ........

................................................... ...... 2.2 Select Approaches to Achieve Performance Goals Base d on Scale of Implementatio 19 

### 2. 3 2 .1 The Impacts of Land Use on Hydrology and Geomorp hology..............................43 20 

### 2.3 .2 Use Appropriate Designs as Part of a Comprehensive Watershed Plan................45 21 

### 2.3. 3 1 New Development and Redevelopment Strategies : Smart Growth, 22 

### Cons ervation Design, and LID

................................................... ...........................48 23 

### 2.4 Use Conservation Design and LID Techniques.....

................................................... .. 2.3.2 For Existing Urban Areas (i.e., Retrofits) 24 

### 2.5 Evaluate Codes and Ordinances..................

................................................... ................ 2.4 Costs of Green Infrastructure/LID Practices 25 

### 2.6 Evaluate Transportation-related Standards......

................................................... ........ 2.4.1 Potential Ancillary Benefits of LID/Green Infrastru cture 26 

### 2.7 Minimize directly connected impervious areas ...

................................................... .... 2.4.2 Potential Cost Savings of LID/Gre 27 

### 2.8 Implement Restoration..........................

................................................... ................... 2.4.3 Costs of Water Quality and Coastal Impairments 28 

### 2.8.1 Urban Tree Canopy............................

................................................... ............. 2.4.4 Costs of Individual Practices 29 

### 2.8.2 Streams, Floodways, and Riparian Areas .......

................................................... ... 2.5 References 30 

### 2.9 Reduce Impacts of Existing Urban Areas.........

................................................... ........... 65 31 

### 2.9.1 Retrofits....................................

................................................... ........................... 65 32 

### 2.10.2 Redevelopment ...............................

................................................... .................... 67 333/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 2 

### 2.10 Costs of Green Infrastructure/LID Practices...

................................................... ............. 68 1 

### 2.10.1 Potential Ancillary Benefits of LID/Green In frastructure ..................................... 69 2 

### 2.10.2 Potential Cost Savings of LID/Green Infrastr ucture.............................................

. 70 3 

### 2.10.3 Costs of Water Quality and Coastal Impairmen ts.................................................

. 72 4 

### 2.10.4 Costs of Individual Practices ...............

................................................... ............... 72 5 

### 2.11 References....................................

................................................... ................................ 82 6 

### 3 Implementation Measures for Reducing Pollutant Co ncentrations with Source Controls 7 

### and Treatment ......................................

................................................... ............................. 3-82 8 

### 233 9 

### 3.1 Source Control/Pollution Prevention ............

................................................... ........... 3-83 10 

### 3.1 .1 Identify Pollutants of Concern....................

................................................... .... 3-83 11 

### 234 12 

### 3 .1 .2 Implement Pollution-Prevention and Source-Reduct ion Practices and Policies... 3-88 13 

### 239 14 

### 3.1.3 Source Controls..............................

................................................... ................. 3-89 15 

### 3.1.4 Public Outreach..............................

................................................... ................. 3-91 16 

### 3.1.4 Downspout Disconnection......................

................................................... ........ 3-93 17 

### 3.1.5 Inspections of Commercial/Industrial Faciliti es ................................................ 3 -93 18 

### 3.2 Runoff Treatment...............................

................................................... ...................... 3-95 19 

### 3.2.1 Identify Pollutants of Concern...............

................................................... ......... 3-95 20 

### 3.2.2 Select 3.3

........................... Impleme nt Treatment Practices Appropriate to the POC 3-95 21 

### 244 22 

### 3.3 References.....................................

................................................... ......................... 3-102 23 

### 4 3.3.1

....... Use New Approaches in Assessing Treatment Technolog y Effectiveness 247 24 

### 3.3.2 Estimating Effectiveness of Stormwater Treatment Pr actices

............................. 248 25 

### 3.4 Consider Long

- term Mainten ance

................................................... ............................. 250 26 

### 3.5 Address Physical Site Limitations

................................................... ............................. 251 27 

### 3.6 Address Aesthetics and Safety

................................................... ................................... 251 28 

### 4. Urban Runoff Management for the Redevelopment Secto r ................................................ 3-110 29 

### 252 30 

### 4.1 Establish Stormwater Performance Standards for the Redevelopment Sector 31 

### Consistent with the Goal of Restoring Predevelopmen t Hydrology ........................ 3-113 32 

### Introduction

................................................... ................................................... ...................... 252 33 

### 4.2 Challenges and Opportunities in the Redevelopment S ector

........................................ 252 34 

### 4.3 Stormwater Performance Goals for the Redevelopment Sector

................................... 255 353/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 3 

### 4.4 Stormwater Management Practices for Redevelopment..

......................................... 3-114 1 

### 255 2 

### 4. 2.1 5

................................................... .......... Practice Integration and Assessment Tools 3-118 3 

### 259 4 

### 4.3 Site Evaluations ...............................

................................................... ...................... 3-119 5 

### 4.4 Codes and Ordinance Review.....................

................................................... ........... 3-120 6 

### 4.5 Demonstration Projects.........................

................................................... ................. 3-120 7 

### 4.6 Incentives Programmatic Practices for Early Adopters..................................... ........ 3-120 8 

### the Redevelopment Sector

................................................... .................................................. 260 9 

### 4.7 Maximize Urban Forest Canopy.......................

................................................... ..... 3-121 10 

### 4.8 Amend Compacted Urban Soils....................

................................................... ......... 3-121 11 

### 4.9 References.........................................

................................................... ............... 3-121 262 12 

### 5 Turf Management..................................

................................................... .......................... 3-125 13 

### 265 14 

### 5.1 Turf Management Implementation Measures

................................................... ............ 265 15 

### 5.2 Background

................................................... ................................................... ......... 3-126 16 

### : Turf Impacts

................................................... ................................................... ................... 267 17 

### 5. 2 3

................................................... ................................................... .. Turf-Related Impacts 3-128 18 

### 268 19 

### 5. 2 3 .1 Soil Compaction.................................

................................................... ........... 3-128 20 

### 268 21 

### 5. 3. 2 .2 Irrigation

................................................... ................................................... ........ 269 22 

### 5.3.3 Fertilizer Applications ...........................

................................................... ....... 3-128 23 

### 269 24 

### 5. 2. 3 .4 Pesticide Applications............................

................................................... ....... 3-129 25 

### 270 26 

### 5.2.4 Irrigation ...................................

................................................... .................... 3-130 27 

### 5.2.7 Energy and Air Quality.......................

................................................... .......... 3-130 28 

### 5. 3 4 Turf Management Strategies, Practices, Resources a nd Examples .......................... 3-131 29 

### 271 30 

### 5. 3 4 .1 Fertilizer Management.............................

................................................... ..... 3-131 31 

### 5.3.2 Pesticide Management .........................

................................................... ......... 3-135 32 

### 5.3.3 Mowing.......................................

................................................... .................. 3-135 33 

### 5.3.4 Soil Amendments..............................

................................................... ............ 3-135 343/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 4 

### 5.3.5 Water Management.............................

................................................... .......... 3-136 1 

### 5.3.6 Grass Species Selection ......................

................................................... .......... 3-138 2 

### 5.3.7 Turf Assessments..................................

................................................... ........ 3-140 3 

### 271 4 

### 5. 4.2 Low Input Turf and Lawns

................................................... ............................... 272 5 

### 5. 4. 3 .8 Turf Restrictions .................................

................................................... .......... 3-143 6 

### 274 7 

### 5. 3.9 4.4

................................................... ................ Incentives for Landscape Conversion 3-144 8 

### 274 9 

### 5. 3.10 4.5

............................................ Environmentally Friendly Landscape Requirements 3-145 10 

### 275 11 

### 5. 3.11 4.6

................................................... ................................. Xeriscaping Requirements 3-146 12 

### 276 13 

### 5.4 .7 Fertilizer Prohibitions

................................................... ....................................... 277 14 

### 5.4.8 Local Effor ts to Regulate Home

- based Fertilizer Application

............................ 278 15 

### 5.4.9 Effectiveness of Fertilizer Bans

................................................... ........................ 279 16 

### 5.4.10 Soil amendments, composting and microbial and funga l innoculation

............... 280 17 

### 5.5 References........................................

................................................... ................ 3-147 281 18 

### 6

. BMP Fact Sheets...................................

................................................... .......................... 3-153 19 

### 283 20 

### 6.1 Introduction...................................

................................................... ......................... 3-153 21 

### 283 22 

### 6.1.1 Additional BMP fact sheets ...................

................................................... ....... 3-153 23 

### 283 24 

### 6.1.2 Performance estimate summaries for Infiltrati on Practices ............................. 3-153 25 

### 284 26 

### 6.2 Rainwater Harvesting...........................

................................................... .................. 3-156 27 

### 286 28 

### 6.3 Green roofs....................................

................................................... ......................... 3-162 29 

### 293 30 

### 6.4 Blue Roofs .....................................

................................................... ........................ 3-168 31 

### 299 32 

### 6.5 Bioretention/Biofiltration.....................

................................................... .................. 3 -174 33 

### 05 343/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 5 

### 6.6 Soil Restoration...............................

................................................... ....................... 3 -188 1 

### 19 2 

### 6.7 Reforestation, Urban Forestry..................

................................................... .............. 3 -194 3 

### 25 4 

### 6.8 Street Sweeping ................................

................................................... ..................... 3 -203 5 

### 34 6 

### 6.9 Constructed Wetlands ...........................

................................................... ................. 3 -208 7 

### 39 8 

### Appendix 1 A : Methods and Tools for Controlling Stormwater Runo ff 9 

### (Quantity and Quality) .............................

................................................... .................. 3 -217 48 10 

### 1 A .1 Methods and Manuals.............................

................................................... ........... 3 -217 48 11 

### 1 A .2 Complex, LID-capable Models.....................

................................................... ..... 3 -219 50 12 

### 1 A .3 Simpler Models..................................

................................................... .................... 3 -223 13 

### 54 14 

### Appendix 2 B : Procedures and Case Studies from the Section 438 Guidance..................... 3 -226 57 153/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 6 

## 1 Introduction 1 

## 1.1 Need for Urban Runoff Guidance Update 2



### 1.1.1 Purpose 3 

### Technical Guidance on Controlling Urban Runoff in t he Chesapeake Bay was developed to 4 

### provide guidance on the most up-to-date, proven, an d cost-effective practices for controlling 5 

### urban runoff for federal land management in the Che sapeake Bay region, as required by 6 

### Executive Order 13508. Federal agencies in the Ches apeake Bay watershed will find this 7 

### guidance useful in managing urban runoff from the d evelopment and redevelopment of federal 8 

### facilities and other land areas owned or managed by the federal government. 9 

### At the same time, EPA recognizes that the great maj ority of land in the Chesapeake Bay 10 

### watershed is nonfederal land and is managed by priv ate landowners, states, and local 11 

### governments. Indeed, the vast majority of actions t o restore the Chesapeake Bay will need to 12 

### take place on nonfederal lands and will need to be implemented by nonfederal actors. From the 13 

### perspective of land management and water quality re storation/protection, f ederal and non f

ederal 14 

### land managers will need to employ the same set of “proven cost-effective tools and pr actices that 15 

### reduce water pollution” are appropriate for both federal and nonfederal lan d managers to restore 16 

### and protect the Chesapeake Bay. 17 

### Therefore, EPA has written this document to be equa lly applicable to federal and nonfederal land 18 

### management. It is EPA’s hope that all states, local governments, conservation districts, 19 

### watershed groups, and citizens in the Chesapeake Ba y watershed will find this document to be a 20 

### useful guide to implementing the most effective and cost-effective practices available to restore 21 

### and protect the Chesapeake Bay. 22 

### Finally, many of the nutrient and sediment sources in the Chesapeake Bay watershed are similar 23 

### to sources in other watersheds around the country, and many of the practices needed to protect 24 

### and restore the Chesapeake Bay are the same as or v ery similar to those used in those other 25 

### watersheds. Indeed, while EPA has made great effort s to assure that all relevant data for the 26 

### Chesapeake Bay watershed has been considered and us ed as appropriate in preparing and 27 

### publishing this guidance, EPA has also employed dat a from outside the Chesapeake Bay 28 

### watershed when it was deemed to be relevant and app licable to the Chesapeake Bay. By the 29 

### same token, for that reason, much of the informatio n provided in this document is relevant to 30 

### other areas of the United States, and EPA strongly recommends that practitioners outside the 31 

### Chesapeake Bay watershed consider this document (in cluding especially next generation tools 32 

### and actions ) in developing and implementing their own watershe d plans and strategies to address 33 

### nutrient and sediment pollution from nonpoint sourc es. 34 

### The primary approaches approach recommended in this guidance to protect the Chesape ake Bay 35 

### and its tributaries—as well as waters in much of th e rest of the United States—from the effects 36 

### of development are is to use green infrastructure/low impact development (LID) approaches and 37 

### planning and development techniques, such as smart growth, that minimize the detrimental 38 

### effects of development on the environment . Section 2 of this chapter focuses on such approac hes. 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 7 

### The objective of green infrastructure/LID is to mai ntain or restore the predevelopment site 1 

### hydrology in regard to the temperature, rate, volume, and dur ation of flow. This can be 2 

### accomplished during development, redevelopment, or retrofit. In some cases, achieving more 3 

### runoff retention might be necessary for water quali ty protection, and this document does not 4 

### preclude setting that performance objective. More specifically, this approach it is intended and 5 

### designed to maintain or restore stream flows such that recei ving waters , and stream channels, are 6 

### not negatively affected by changes in runoff . This temperature, volumes, durations , and rates

. 7 

### Th at approach protects predevelopment hydrology and pro vides significant reductions in 8 

### pollutant runoff. However, in some circumstances, s pecific pollutant control practices, (e.g., 9 

### source controls) will need to be implemented to add ress pollutant runoff, and Section 3 of this 10 

### chapter addresses those practices. 11 

### Planning can help guide development to areas that m inimize effects on sensitive resources and 12 

### natural areas. Planning can help ensure that new an d redevelopment sites are designed to reduce 13 

### runoff volume through on-site stormwater retention. 14

This document 15



### • Emphasizes replicating predevelopment hydrology as a more reliable and effective 16 

### stormwater management practice than traditional app roaches that focus on pollutants 17 

### without addressing hydrology. That emphasis is alre ady expressed in a number of recent 18 

### EPA documents and numerous states, cities, and expe rt groups, including the National 19 

### Academy of Sciences (http://epa.gov/greeninfrastructure) 20

•



### . 21



### • Incorporates by reference the Technical Guidance on Implementing the Stormwater 22 

### Runoff Requirements for Federal Projects under Sect ion 438 of the Energy Independence 23 

### and Security Act , EPA 841-B-09-001, December 2009, which provides t he hydrologic 24 

### analysis for this approach. Elements of that docume nt are referenced here, but it is not 25 

### repeated in its entirety ; it is provided at http://www.epa.gov/owow/nps/lid /section438/

. 26



### • Builds on that technical guidance by providing user s with sources to the newest research 27 

### on key management practices and approaches and refe rs the reader to other resources 28 

### where appropriate 29



### • Emphasizes those practices that can be most cost-ef fective—some, in fact, less costly 30 

### than the conventional stormwater management alterna tive. 31 

### This document addresses technical management practi ces for restoring and maintaining surface 32 

### water quality. Green infrastructure/LID is generall y used for managing smaller storm events that 33 

### compose the bulk of annual rainfall and therefore c ontribute s the most to both pollutant loading 34 

### and stream degradation. This document does not addr ess other stormwater issues, primarily 35 

### flood-control or stormwater program management. How ever, those issues are addressed at length 36 

### in documents referenced here. 37 

### Such an approach of maintaining predevelopment hydr ology is already required for federal 38 

### facilities by the Energy Independence and Security Act (EISA) of 2007 (P.L. 110-140, H.R. 6) 39 

### section 438 . Subsequent , subsequent EPA guidance (EPA 841-B-09-001) provides advice on 40 

### how to implement this at federal facilities. 413/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 8 

### EISA that mandates certain federal facilities to comply with the following: 1 

### Stormwater runoff requirements for federal developm ent projects. The 2 

### sponsor of any development or redevelopment project involving a Federal facility 3 

### with a footprint that exceeds 5,000 square feet sha ll use site planning, design, 4 

### construction, and maintenance strategies for the pr operty to maintain or restore, to 5 

### the maximum extent technically feasible, the predev elopment hydrology of the 6 

### property with regard to the temperature, rate, volu me, and duration of flow. 7 

### State and local stormwater programs established und er the Clean Water Act Amendments of 8 

### 1987 were traditionally established to control poll utants that are associated with municipal and 9 

### industrial discharges, e.g., nutrients, sediment, a nd metals. Increases in runoff volume and peak 10 

### discharge rates have been regulated through state a nd local flood control programs but in many 11 

### states have not been significantly addressed with r egard to their role in water quality and habitat 12 

### protection. Knowledge accumulated during the past 2 0 years has led to the conclusion that 13 

### conventional approaches to control runoff have not resulted in adequate protection of the nations 14 

### water resources, and, in fact, have had detrimental effects associated with increased volumes 15 

### runoff (National Research Council 2008). An example of that detrimental effect is referenced in 16 

### Figure 3-1. 17

A Maryland Department of Natural Resources (DNR) st udy highlights the detrimental impact that development, loss of forest and temperature changes has had on brook tro ut, Maryland’s only native trout species, based on thre e decades of study. For every one percent increase in impervi ous land cover in a stream’s watershed, the odds of brook tr out survival decreased by nearly 60 percent (Stranko, e t.al. 2008).
Figure 3-1. Maryland Department of Natural Resource s study 18 

### This document emphasizes site-specific management p ractices from green infrastructure/LID 19 

### that are driven by locally applicable performance o bjectives. Each site or watershed has its own 20 

### unique circumstances—a combination of land uses, wa ter resource needs, environmental 21 

### conditions, regulatory drivers, and community attri butes—that will affect which approaches are 22 

### most successful in terms of effectiveness and commu nity acceptance. The means selected will 23 

### vary depending on the development setting and site- specific opportunities and constraints; 24 

### however, designing to replicate predevelopment hydr ology is the overall goal that best ensures 25 

### achieving full designated uses of the waters. In ca ses where green infrastructure/LID is not 26 

### feasible on-site or is otherwise inadequate to meet water quality objectives, additional measures 27 

### should would be considered required , as discussed in Section 3 of this chapter. 28 

### The past decade has brought significant growth in t he use of approaches that seek to control 29 

### runoff volume at the site scale using a variety of decentralized stormwater controls and runoff 30 

### retention methods that have the objective of replic ating the predevelopment hydrology as much 31 

### as technically feasible. That type of holistic, hyd rology-based approach to urban runoff 32 

### management is termed low impact development or LID (also referred to variously as better site 33 

### design, environmentally sensitive design, sustainab le stormwater management, and green 343/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 9 

### infrastructure , among others). The approach has been proven to be technically achievable and 1 

### cost-effective; examples demonstrating this are pro vided in Figures 3-2 and 3-3 that describe 2 

### projects in Portland, Oregon, and in coastal North Carolina. 3 

### The purpose of this document is to present an overv iew of the practices and resources available 4 

### for federal facilities and others to achieve water quality goals in the most cost-effective and 5 

### potentially successful manner, with the overall obj ective of improving water quality, habitat, and 6 

### the environmental and economic resources of the Che sapeake Bay and its tributaries. 7

Portland Bureau of Environmental Services (BES) com pleted the first design in what was to become the Tabor to the River

program in 2007, solving drainage and watershed pr oblems with LID, along with new combined sewer pipes. These facilities not only provide sewer capacity, but also watershed health benefits such as groundwater recharge and ad ded vegetation that improves urban habitat conditions. The 1,472-acre basin is high-density residential de velopment, with commercial land use, and approximately 37% impervious. Sewer capacity solutions Capacity Solutions , in addition to new piping and rehabilitation, inc lude LID Facilities:

• 500 LID facilities in the public right-of-way (cur b extensions, vegetated planters, and flow restrictors)

• Runoff from 8 acres of parking and rooftops on pri vate property controlled by LID facilities (e.g., vegetated planters, rain gardens, eco-roofs) Watershed Management Solutions:

• Two revegetation projects to remove invasive speci es

• 3,500 trees planted in the city’s right-of-way

• Neighborhood education and project outreach

• Improved access to the Willamette River from an ad jacent neighborhood The success of that first project encouraged BES to expand to a larger, basin-wide program named Tabor to the River. Beginning its third year of implementation, the pro gram strives to create a healthy urban watershed by integrating sewer rehabilitation , green stormwater management, tree planting and other watershed projects to improve sewer syste m reliability, stop sewer backups in basements and street flooding, control combined sewer overflo ws (CSOs), and restore watershed health. Sources: Portland BES Web site for Tabor to the Riv er: www.portlandonline.com/bes/index.cfm?c=47591; Tsurumi, Naomi and Bill Owen Painting it Green—Replacing an All-Pipe Solution wi th an Integrated Solution Emphasizing Low Impact Development; American Society of Civil Engineers (ASCE), Low Impact Development Conference Proceedings, 2008
Figure 3-2. LID Green Streets save Portland, Oregon, nearly $60 million while re storing water 8 quality. 93/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 10 1

Using LID on a development project in Middlesound N orth Carolina, where LID is encouraged to protect shellfish beds and coastal recreational wat ers, the developer saved money and realized marketing advantages compared to tradition stormwat er design:

• Gained 3 to 4 additional lots (from 56 to 59)

• Reduced stormwater pipe by 89%

• Decreased road widths 9%

• Eliminated 9,000-ft curb and gutter

• Eliminated 5 infiltration basins $ in construction and maintenance

• Eliminated 5 monitoring wells $ in construction and monitoring fees

• Eliminated 10,000 linear feet of stormwater force main

• Saved $1.5 million in fill

• Increased localized stormwater infiltration

• Eliminated 3 Tsurumi stormwater pumps

• Increased functional and recreation open space

• Minimized wetlands intrusion and wildlife impacts

• Buyers prefer green real estate

• Promotes good neighbor

• Decreased construction traffic

“ Your ideas and preliminary plans for incorporating LID for Ridgefield Ridge Field are proving invaluable. After having it approved for a conventi onal stormwater system, we were concerned with the extreme costs of the system and developmen t’s financial feasibility. However, with the utilization of an LID stormwater system we can dram atically reduce the costs and make the project viable again. In our estimates we are proje cting a savings up to $1.5 million and adding 4 lots. In addition, we will be saving many of the na tural features and topography resulting in a ‘greener,’ more conservation oriented neighborhood. ” —Ridgefield Property Developer, February 2009
Source: Todd Miller North Carolina Coastal Federati on; Heather Burkert, and H.K Burkert & Co.
Figure 3-3. Developer realizes savings and marketin g value with LID while better protecting 2 coastal waters. 3



### 1.1.2 Intended Audience 4 

### The primary audience for this document is stormwate r managers in federal agencies and at the 5 

### local, state, and federal levels who are responsibl e for meeting water quality goals and 6 

### implementing water quality programs in developing a nd developed areas. Another key audience 7 

### is the development community and their multidiscipl ine designers, because new and 8 

### redevelopment projects offer the best opportunity t o implement stormwater controls to mitigate 9 

### development’s affects on water resources. Others wh o might benefit from this information are 10 

### local public officials responsible for land use and water quality decision making, academia and 11 

### research groups, environmental and community organi zations, and the business community. 123/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 11 

### 1.1.3 Water Quality Significance of Urban Runoff in the Chesapeake Bay 1 

### Watershed 2 

### This section discusses the water quality significan ce of urban runoff. Urban stormwater runoff is 3 

### responsible for a significant portion of the nitrog en (N) , phosphorus (P) , and sediment loading to 4 

### the Chesapeake Bay and the loading has been continu ing to increase over time because of 5 

### development. Understanding the core cause of this p roblem is essential to reducing this source. 6 

### This section contains background on the causes and consequences of stormwater discharges, i.e. 7 

### the alterations to natural hydrology and the result ing impacts, and solutions that can be used to 8 

### address the causes and consequences of stormwater d ischarges, and how to implement those 9 

### solutions such that they will be applicable to all areas of the country and comply with section 10 

### 438 of EISA. 11 

### In the natural, undisturbed environment, rainfall i s quickly absorbed by trees, and other 12 

### vegetation. Rainfall that is not intercepted by lea ves infiltrates into the ground or is returned to 13 

### the atmosphere by the process of evapotranspiration . Very little rainfall becomes stormwater 14 

### runoff, and runoff generally occurs only with large r precipitation events. Traditional 15 

### development practices cover large areas of the grou nd with impervious surfaces such as roads, 16 

### driveways, sidewalks, and buildings. Once such deve lopment occurs, rainwater cannot infiltrate 17 

### into the ground and as a result, runs off the site at rates and volumes that are much higher than 18 

### would naturally occur. Under developed conditions, runoff occurs even during small 19 

### precipitation events that would normally be absorbe d by the soil and vegetation. The collective 20 

### force of the increased runoff scours streambeds, er odes stream banks, and causes large quantities 21 

### of sediment and other entrained pollutants to enter the waterbody each time it rains (Shaver et al. 22 

### 2007; Booth testimony 2008). 23 

### As watersheds are developed and impervious surfaces increase in area, the hydrology of the 24 

### watersheds fundamentally changes over time, which r esults in degraded aquatic ecosystems. In 25 

### recognition of those problems, stormwater managers employed extended detention approaches to 26 

### mitigate the effects of increased runoff peak runof f rates. However, wet ponds and similar 27 

### practices inadequately protect downstream hydrology because of the following inherent 28 

### limitations of the conventional practices (National Research Council 2008; Shaver et al. 2007): 29



### • Poor peak control for small, frequently occurring s torms 30



### • Negligible volume reduction 31



### • Increased duration of peak flow 32 

### Detention storage targets relatively large, infrequ ent storms, such as the 2- and 10-year/24-hour 33 

### storms for peak flow rate control. As a result of t hat design limitation, flow rates from smaller, 34 

### frequently occurring storms typically exceed those that existed on-site before land development 35 

### occurred and these increases in runoff volumes and velocities typically result in flows erosive to 36 

### stream channel stability (Shaver et al. 2007). Sect ion 438 of EISA is intended to address the 37 

### inadequacies of the historical detention approach t o managing stormwater and promote more 38 

### sustainable practices that have been selected to ma intain or restore predevelopment site 39 

### hydrology. 403/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 12 

### A 2008 National Research Council report on urban st ormwater confirmed the shortcomings 1 

### of current stormwater control efforts. Three of the report’s findings on stormwater 2 

### management approaches are particularly relevant (Na tional Research Council 2008). 3 

### 1. Individual controls on stormwater discharges are in adequate as the sole solution to 4 

### stormwater in urban watersheds. 5 

### 2. Stormwater control measures such as product substit ution, better site design, downspout 6 

### disconnection, conservation of natural areas, and w atershed and land-use planning can 7 

### dramatically reduce the volume of runoff and pollut ant load from new development. 8 

### 3. Stormwater control measures that harvest, infiltrat e, and evapotranspire stormwater are 9 

### critical to reducing the volume and pollutant loadi ng of small storms. 10

11

Courtesy of C. May, University of Washington.

Predevelopment hydrology. Courtesy of C. May, University of Washington. Post-development hydrology.

Figure 3-4. Predevelopment and post-development hyd rology (USDA).



### Land cover changes that result from site developmen t include increased imperviousness, soil 12 

### compaction, loss of vegetation, and loss of natural drainage patterns result in increased runoff 13 

### volumes and peak runoff rates. The cumulative effec ts of the land cover changes result in 143/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 13 

### alterations of the natural hydrology of a site, whi ch disrupts the natural water balance and 1 

### changes water flow paths. The consequences of these impacts include the following: 2
1. 

### Increased volume of runoff. With decreased area for infiltration and evapotran spiration 3 

### due to development, a greater amount of rainfall is converted to overland runoff which 4 

### results in larger stormwater discharges. 5
2. 

### Increased peak flow of runoff . Increased impervious surface area and higher conn ectivity 6 

### of impervious surfaces and stormwater conveyance sy stems increase the flow rate of 7 

### stormwater discharges and increase the energy and v elocity of discharges into the stream 8 

### channel. 9
3. 

### Increased duration of discharge . Detention systems generate greater flow volumes f or 10 

### extended periods. Those prolonged, higher discharge rates can undermine the stability of 11 

### the stream channel and induce erosion, channel inci sion and bank cutting. 12
4. 

### Baseflow and sediment loading changes. Changes to baseflow are caused by alternations 13 

### to the hydrologic cycle created by land cover chang es and increased imperviousness, 14 

### which prevents rain from recharging groundwater, wh ere it serves as baseflow for 15 

### streams. Such changes increase the flashiness of streams, resulting in elevated flows 16 

### during or after storm events, and greatly diminishe d baseflows in between storms. Higher 17 

### peak flows erode streambeds and stream banks. 18
5. 

### Increased pollutant loadings . Impervious areas are a collection site for pollut ants. When 19 

### rainfall occurs, the pollutants are mobilized and t ransported directly to stormwater 20 

### conveyances and receiving streams via the imperviou s surfaces. 21
6. 

### Increased temperature of runoff . Impervious surfaces absorb and store heat and tra nsfer it 22 

### to stormwater runoff. Higher runoff temperatures ca n have deleterious effects on 23 

### receiving streams. Detention basins magnify this pr oblem by trapping and discharging 24 

### runoff that is heated by solar radiation (Galli 199 1; Schueler and Helfrich 1988). 25
7. 

### Habitat modifications and stream morphology changes

. Increased runoff rate and volume 26 

### alter stream morphology. Highly erosive stormwater can wash out in-stream structures 27 

### that serve as habitat. Large storms deepen, widen, and straighten channels, disconnecting 28 

### streams from their floodplains and destroying meand ers that serve to dissipate hydraulic 29 

### energy. 30 

### The resulting increases in volume, peak flow, and d uration are illustrated in the hydrograph in 31 

### Figure 3-5, which is a representation of a site’s s tormwater discharge with respect to time. The 32 

### hydrograph illustrates the effects of development o n runoff volume and timing of the runoff. 33 

### Individual points on the curve represent the rate o f stormwater discharge at a given time. The 34 

### graph illustrates that development and correspondin g changes in land cover result in greater 35 

### discharge rates, greater volumes, and shorter disch arge periods. In a natural condition, runoff 36 

### rates are slower than those on developed sites, and the discharges occur over a longer period. The 37 

### predevelopment peak discharge rate is also much low er than the post-development peak 38 

### discharge rate because of attenuation and absorptio n by soils and vegetation. In the post39 

### development condition, there is generally a much sh orter time before runoff begins because of 40 

### increased impervious surface area, a higher degree of connectivity of those areas, and the loss of 41 

### soils and vegetative cover that slow or reduce runo ff. 423/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 14 1



### t Q Post-Development Condition

Pre-Development Condition

2 Note: Q = volumetric flow rate; t = time 3 Figure 3-5. Post-development hydrograph. 4

5

6 Figure 3-6. Stream displaying the effects of stormw ater runoff and channel downcutting. 73/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 15 

### 1.1.4 Managing Urban Runoff to Reduce Nutrients and Sediment Loss 1

1.1.4.1 Preserving and Restoring Hydrology 2 

### A new approach has evolved in recent years to 3 

### eliminate or reduce the amount of water and 4 

### pollutants that run off a site and ultimately are 5 

### discharged into adjacent waterbodies. 6 

### The fundamental principle is to employ systems and 7 

### practices that use or mimic natural processes to do 8 

### any of the following: (1) infiltrate and recharge, 9 

### (2 ) ) evapotranspire, or (3) harvest and use 10 

### precipitation near where it falls. 11 

### Green infrastructure practices include a wide varie ty 12 

### of practices that use such mechanisms. They can be 13 

### used at the site, neighborhood, and 14 

### watershed/regional scales. In this document, the 15 

### focus is on site-level practices, such as bioretent ion 16 

### and water harvesting, but it also addresses the lan d 17 

### management scales of planning (i.e., planning 18 

### techniques such as smart growth), and site design 19 

### (i.e., site design techniques such as conservation 20 

### development). 21 

### Although the performance objective of “restoring or 22 

### maintaining predevelopment hydrology” applies at 23 

### the site

- level, flexibility exists to u s e nearby areas or 24 

### areas directly adjacent to the facility to manage t he runoff, i.e., evapotranspirate, infiltrate , or 25 

### harvest and use

. Where justifiable, it also m ight be appropriate to evapotranspirate, infiltrate or 26 

### harvest and use an equivalent or greater amount of runoff offsite as long as the runoff is 27 

### discharged or used in the same receiving subwaters hed or watershed. 28 

### The objective of stormwater management should be to replicate predevelopment hydrology to 29 

### protect and preserve both the water resources on

- site and those downstream

. For example, if 30 

### before development, 25 percent of the annual rainfall ru ns directly into the stream and the 31 

### remainder infiltrates into the ground or is evapotr anspired into the air, the post

- development goal 32 

### should be to limit runoff to 25 percent of the annu al precipitation while maintaining the correct 33 

### aquifer recharge rate

. Th at has the benefit, in most cases, of delivering wate r to the stream at 34 

### approximately the same rate, volume, duration and t emperature as the stream had naturally 35 

### evolved before development. The result will be to eliminate or mi nimize the erosion of 36 

### stre ambeds and streambanks, significantly reduce the de livery of many pollutants to waterbod ies, 37 

### and retain historical in

- stream temperatures. 38 

### Restoring or maintaining predevelopment hydrology h as emerged as a control approach for 39 

### several reasons. Most importantly, the approach is intended to directly address the root cause of 40 

### impairment. Current control approaches have been se lected in an attempt to control the 41 Figure 3-7. Parking lot bioswale and permeable pavers in Chicago.3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 16 

### symptoms (peak flow, and excess pollutants), but th e strategy is largely ineffectual because of 1 

### the scale of the problem, the cumulative effects of multiple developments and the need to 2 

### manage both site and watershed level effects. With current approaches, it is also difficult to 3 

### adequately protect and improve water quality becaus e the measures employed are not addressing 4 

### the main problem, which is a hydrologic imbalance. 5 

### Designing facilities on the basis of the goal of ma intaining or restoring predevelopment 6 

### hydrology provides a site-specific basis and an obj ective methodology with which to determine 7 

### appropriate practices to protect the receiving envi ronment. 8 

### Using predevelopment hydrology as the guiding contr ol principal also allows the designer to 9 

### consider climatic and geologic variability and tail or the solutions to the project location. Thus, 10 

### the need for a one–size-fits-all approach is render ed unnecessary because the design objective is 11 

### dictated by the predevelopment site conditions and other technicalities of the project site and 12 

### facility use . Site and , thus , is not merely a solution based 13 

### on the ease of administration

. Instead of p rescribed 14 

### approaches dictating discharge volumes or flow rate s, 15 

### site assessments of historical infiltration and runoff rates 16 

### will inform the designer and provide the basis for a 17 

### suitable design. The use of this approach will mini mize 18 

### compliance complications that can arise from 19 

### prescriptive design approaches that do not account for 20 

### the variability of precipitation frequencies, rainf all 21 

### intensities, and land cover and soil conditions tha t 22 

### influence infiltration and runoff. 23 

### More information on addressing hydromodification an d 24 

### riparian buffers are provided in separate volumes o f this 25 

### document. 26

1.1.4.2 Defining Green Infrastructure/LID 27 

### LID i 

### is a stormwater management strategy that many 28 

### localities across the country have adopted. It is a 29 

### stormwater management approach and set of practices 30 

### that can be used to reduce runoff and pollutant loa dings 31 

### by managing the runoff as close to its source(s) as 32 

### possible. A set or system of small-scale practices, linked 33 

### together on the site, is often used. LID approaches can be 34

i The term LID is one of many used to describe the practices and techniques employed to provide advanced stormwater management; green infrastructure , conservation design , and sustainable stormwater management are other common terms. However labeled, each of the id entified practices seeks to maintain and use vegeta tion and open space, optimize natural hydrologic processes t o reduce stormwater volumes and discharge rates, an d use multiple treatment mechanisms to remove a large ran ge of pollutants. In the context of this report, ca se studies ascribing to one of the above, or similar, labels w ere evaluated, and those terms are used interchange ably throughout the document. Figure 3
- 7

. Parking lot bioswale and permeable pavers in Chicago.3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 17 

### used to reduce the effects of development and redev elopment activities on water resources. In the 1 

### case of new development, LID is typically used to a chieve or pursue the goal of maintaining or 2 

### closely replicating the predevelopment hydrology of the site. In areas where development has 3 

### already occurred, LID can be used as a retrofit pra ctice to reduce runoff volumes, pollutant 4 

### loadings, and the overall effects of existing devel opment on the affected receiving waters. 5 

### In general, implementing integrated LID practices c an result in enhanced environmental 6 

### performance while at the same time reduce developme nt costs when compared to traditional 7 

### stormwater management approaches. LID techniques pr omote the use of natural systems, which 8 

### can effectively reduce remove nutrients, pathogens, and 9 

### metals from stormwater through runoff volume reduction, 10 

### filtration, and other processes . These same systems can be 11 

### designed to accommodate or bypass larger flows when 12 

### large rain event s occur, when the LID practice is sized for 13 

### small rain events. 14 

### Cost savings can be achieved in reduced infrastruct ure, 15 

### particularly in new development where land is avail able for 16 

### surface practices, because the total volume of runo ff to be 17 

### managed is minimized through infiltration and 18 

### evapotranspiration. By working to mimic the natural water 19 

### cycle, LID practices protect downstream resources f rom 20 

### pollutants and adverse hydrologic impacts that can degrade 21 

### stream channels and harm aquatic life. 22 

### It is important to note that typical, real

- world LID designs usually incorporate more than one 23 

### type of practice or technique to provide integrated treatment of runoff from a site. For example, 24 

### in lieu of a treatment pond serving a new subdivisi on, planners might incorporate a bioretention 25 

### area in each yard, disconnect downspouts from drive way surfaces, remove curbs or cut out 26 

### drainage slots into curbs, and install grassed swal es in common areas. Integrating small practices 27 

### throughout a site instead of using extended detenti on wet ponds for treatment purposes to control 28


### ru noff from a subdivision is the basis of the LID approach. 29 

### Planning techniques such as Smart Growth minimize 30 

### runoff by approaches techniques such as enhancing density 31 

### along existing transportation and other infrastruct ure 32 

### corridors, to reduce Greenfield development. 33 

### Conservation designs minimize runoff by conserving 34 

### undeveloped land and reducing the amount of impervi ous 35 

### surface, which can cause increased runoff volumes. Open 36 

### space can be used to treat the increased runoff fro m the 37 

### built environment through infiltration or 38 

### evapotranspiration. For example, developers can use 39 

### conservation designs to preserve important features on the 40 

### site such as wetland and riparian areas, forested t racts, and 41 

### areas of pervious soils. Development plans that out line 42 

### the smallest site disturbance minimize stripping to psoil 43 Runoff Storage Practices

• Parking lot, street, and sidewalk storage in underground infiltrating vaults

• Rain barrels and cisterns

• Depressional storage in landscape islands and in tree, shrub, or turf depressions Green roofs Examples of Conservation Design

• Cluster development

• Undeveloped land conservation Examples of Conservation Design

• Cluster development

• Undeveloped land conservation

• Reduced pavement widths (streets, sidewalks)

• Shared driveways

• Reduced setbacks (shorter driveways)

• Site fingerprinting during construction

Examples of LID Practices

• Infiltration basins and trenches

• Permeable pavement

• Disconnected downspouts

• Rain gardens and other vegetated treatment systems3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 18 

### and compacting subsoil. Such simplistic, nonstructu ral 1 

### methods reduce the need to build large runoff controls 2 

### like retention ponds for treatment and larger stormwater 3 

### conveyance systems, thereby decreasing the overall 4 

### project cost. Reducing the total area of impervious 5 

### surface by limiting road widths and parking areas a lso 6 

### reduces the volume of runoff that must be treated. 7 

### Conservation designs benefit residents and their qu ality 8 

### of life because of increased access and proximity t o 9 

### communal open space, a greater sense of community, and 10 

### expanded recreational opportunities. 11 

### LID practices are engineered structures or landscape 12 

### features designed to capture and infiltrate, store, convey, or 13 

### filter runoff in a manner that attempts to replicat e 14 

### predevelopment hydrology. 15 

### Infiltration practices can also be used to achieve a goal of recharging g roundwater while at the 16 

### same time reducing runoff. Recharging groundwater i s especially important in areas where 17 

### maintaining drinking water supplies and stream base flow is of special concern because of limited 18 

### precipitation or a high withdrawal demands. Infiltr ation of runoff can also help to maintain 19 

### stream temperatures because the infiltrated water t hat moves laterally to replenish stream 20 

### baseflow typically has a lower temperature than ove rland 21 

### flows, which might be subject to solar radiation. A nother 22 

### advantage of infiltration practices is that they ca n be 23 

### integrated into landscape features in a site-disper sed 24 

### manner. This feature can result in aesthetic benefi ts and, 25 

### in some cases, recreational opportunities; for exam ple, 26 

### some infiltration areas can be used as playing fiel ds 27 

### during dry periods. 28 

### Runoff storage practices reduce the volume and peak rate 29 

### of runoff to protect streams from the erosive force s of 30 

### high flows, and irrigate landscaping to providing 31 

### aesthetic benefits such as more sustainable (i.e., more 32 

### self-watering) landscape islands, tree boxes, and r ain gardens. Designers can take advantage of 33 

### the space beneath paved areas like parking lots and sidewalks to provide additional storage. For 34 

### example, underground vaults can be used to store ru noff in both urban and rural areas, and street 35 

### tree designs have been developed to better enable u se of that space for root growth to enable 36 

### establishment of healthy urban tree canopy. 37 

### Runoff conveyance practices can be used to slow flow 38 

### velocities, lengthen the runoff time of concentrati on, and 39 

### delay peak flows that are discharged off-site. LID 40 

### conveyance practices can be used as an alternative to 41 

### curb-and-gutter systems. LID conveyance practices o ften 42 

### have rough vegetative surfaces that reduce runoff 43 

### velocities and allow settling of solids. They promo te 44 Filtration Practices

• Infiltration basins and trenches

• Porous pavement

• Disconnected downspouts

• Rain gardens and other vegetated treatment systems Runoff Storage Practices

• Parking lot, street, and sidewalk storage in underground infiltrating vaults

• Rain barrels and cisterns

• Depressional storage in landscape islands and in tree, shrub, or turf depressions

• Green roofs

Runoff Conveyance Practices

• Eliminating curbs and gutters

• Creating grassed swales and grass-lined channels

• Roughening surfaces

• Creating long flow paths over landscaped areas

• Installing smaller culverts, pipes, and inlets

• Creating terraces and check dams Filtration Practices

• Bioretention/rain gardens

• Vegetated swales

• Vegetated filter strips/buffers Runoff Conveyance Practices

• Eliminating curbs and gutters

• Creating grassed swales and grass-lined channels

• Roughening surfaces

• Creating long flow paths over landscaped areas

• Installing smaller culverts, pipes, and inlets

• Creating terraces and check dams

Filtration Practices

• Bioretention/rain gardens

• Vegetated swales

• Vegetated filter strips/buffers3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 19 

### infiltration, filtration, and some biological uptak e of 1 

### pollutants. LID conveyance practices also can perfo rm 2 

### functions similar to those of conventional curbs, 3 

### channels, and gutters. For example, they can be use d to 4 

### reduce flooding around structures by routing runoff to 5 

### landscaped areas for treatment, infiltration, and 6 

### evapotranspiration. 7 

### Filtration practices capture pollutants by physical 8 

### filtration of solids or cation exchange of dissolve d 9 

### pollutants. They also reduce runoff volume, recharg e 10 

### groundwater, increase stream baseflow, and reduce 11 

### thermal impacts. Pollutant buildup can be of concer n, 12 

### pollutants are typically captured in the upper soil horizon 13 

### and can be removed by replacing the topsoil, and li fe can 14 

### be extended by selecting plants that also provide p hytoremediation. 15 

### Conservation landscaping reduces labor, watering, and chemical use. Properly preparing soils 16 

### and selecting species adapted to the site increases the success of plant growth, stabilizing soils 17 

### and allowing for biological uptake of pollutants. P est resistance (reducing the need for 18 

### pesticides) and improved soil infiltration from roo t growth are among the goals. Conservation 19 

### landscaping is promoted by many entities in the 20 

### Chesapeake Bay area and elsewhere. 21

1.1.4.3 Ancillary Benefits of Designing to Restore 22 and Preserve Predevelopment Hydrology 23 

### Unlike traditional stormwater management, an approa ch 24 

### to maintain or restore predevelopment hydrology mee ts 25 

### multiple performance objectives and can offer ancil lary 26 

### benefits, including the following: 27


### Pollution abatement. LID practices more reliably reduce 28 

### pollutant loadings by reducing the runoff volume. L ID 29 

### practices, to a lesser degree, can reduce pollutant s by 30 

### settling, filtering, adsorption, and biological upt ake. Th at 31 

### improves habitat and enhances recreational uses. 32 

### Protection of downstream water resources

. LID practices help to prevent or reduce hydrologic 33 

### effects on receiving waters, reduce stream channel degradation from erosion and sedimentation, 34 

### improve water quality, increase water supply, and e nhance the recreational and aesthetic value of 35 

### our natural resources. LID pract ices can be used to protect water resources that ar e downstream 36 

### in the watershed. Other potential benefits include reduced incidence of illness from swimming 37 

### and wading, more robust and safer seafood supplies. 38 Conservation Landscaping

• Planting native, drought-tolerant plants

• Converting turf areas to shrubs and trees

• Reforestation

• Encouraging longer grass length

• Planting wildflower meadows rather than turf along medians and in open space

• Amending soil to improve infiltration

• Integrated pest management

Conservation Landscaping

• Planting native, drought-tolerant plants

• Converting turf areas to shrubs and trees

• Reforestation

• Encouraging longer grass length

• Planting wildflower meadows rather than turf along medians and in open space

• Amending soil to improve infiltration

• Integrated pest management3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 20 

### Protect integrity of streams and floodplains to pre serve ecological functions. Costs of 1 

### streambank restoration can be reduced or avoided al together. Using LID techniques also can help 2 

### protect or restore floodplains, which can be used a s park space or wildlife habitat. ii 3 

### Groundwater recharge and stream baseflow

. Growing water shortages nationwide increasingly 4 

### indicate the need for holistic water resource management strategies to integrate stormwater, 5 

### drinking water, and wastewater programs . Development increases impervious surfaces and 6 

### runoff. Infiltration practices replenish groundwate r and increase stream baseflow. Adequate 7 

### groundwater recharge baseflow to streams during dry weather is important because low 8 

### groundwater levels can lead to low baseflows in dry weather. Greater greater fluctuations in 9 

### stream flows and temperatures occur when rainfall does not infiltrate , to the detriment of aquatic 10 

### life. 11 

### Water quality improvements/reduced treatment costs

. Keeping It is almost always less expensive 12 

### to keep water clean can prevent the costs for cleaning than it i s to clean it up. The Trust for Public 13 

### Land iii 

### notes that Atlanta’s tree cover has saved more tha n $883 million by preventing the need 14 

### for stormwater facilities. A study by the Trust for Public Land and the American Water Works 15 

### Association iv 

### of 27 water suppliers found higher forest cover in a watershed reduced water 16 

### treatment costs. According to the study, approximat ely 50 percent of the variation in treatment 17 

### costs can be tied to the percentage of forest cover . It also found that for every 10 percent increase 18 

### in forest cover, treatment and chemical costs decre ased approximately 20 percent, up to about 60 19 

### percent forest cover. 20 

### Reduced incidence of combined sewer overflow (CSOs)

. Many municipalities with older sewer 21 

### systems have CSOs, i.e. sewers that discharge sanitary wastewater during st orms. LID 22 

### techniques, by retaining and infiltrating runoff, r educe the frequency and amount of CSOs. Past 23 

### efforts typically have solely concentrated on approaches focused on treating the sanitary waste 24 

### together with the runoff

. For the past several years, communities such as Por tland (Oregon), 25 

### Chicago, and the District of Columbia have been pil oting and implementing LID approaches 26 

### aimed at reducing runoff generated to the combined system. 27 

### Habitat improvements. Innovative stormwater management techniques like L ID or conservation 28 

### design can be used to improve natural resources and wildlife habitat, maintain or increase land 29 

### value, or avoid expensive mitigation costs. 30 

### Reduced downstream flooding and property damage

. LID practices , when applied throughout a 31 

### watershed, can reduce flash flooding, and reduce property dam age or risk during small storm 32 

### events. 33

ii Trust for Public Land. 1999. The Economic Benefits of Open Space

. title?

. Trust for Public Land, San Francisco, CA.

iii Trust for Public Land. 1999. The Economic Benefits of Open Space

. <http://www.tpl.org/tier3_cd.cfm?content_item_id=11 95&folder_id=727>. Accessed March 29, 2006.

iv Trust for Public Land and American Water Works Asso ciation. 2004. Protecting the Source

. Trust for Public Land, San Francisco, CA.3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 21 

### Reduce erosion and sediment loss . Designs that manage runoff on-site or as close as possible to 1 

### its point of generation reduce erosion and sediment transport, as well as stream erosion. 2 

### Real estate value/property tax revenue

. Property owners will pay a premium to be near 3 

### amenities like water features, open space, trails, and clustered subdivisions. EPA’s early 4 

### Economic Benefits of Runoff Controls v 

### described many examples, and the trend will likely 5 

### increase as urbanization makes natural areas more s carce and precious. 6 

### Lot yield . In cases where LID practices are incorporated on individual house lots and along 7 

### roadsides as part of the landscaping, land that wou ld normally be dedicated for a stormwater 8 

### pond or other large structural control can be devel oped with additional housing lots. 9


### Aesthetic value. LID designs can enhance a property’s aesthetics us ing trees, shrubs, and 10 

### flowering plants that complement other landscaping features, resulting in a perceived value of 11 

### extra landscaping. 12 

### Public spaces/quality of life/public participation. Placing water quality practices on individual 13 

### lots provides opportunities to enhance public aware ness of their natural environment. 14 

### Homeowners often consider An American Lives, Inc., real estate study found th at 77.7 percent of 15 

### potential homeowners rated natural open space as to be essential or very important in planned 16 

### communities. 17 

### Reduce air pollution through uptake by trees. Trees remove gaseous air pollution primarily by 18 

### uptake via leaf stomata, though some gases are remo ved by the plant surface . Once inside the 19 

### leaf, gases diffuse into intercellular spaces and can be absorbed by water films to form acids or 20 

### react with inner

- leaf surfaces (Smith 1990). In 1994 the U.S. Forest Service esti mated that trees 21 

### in Baltimore removed an estimated 499 metric tons o f air pollution at an estimated value to 22 

### society of $2.7 million (Nowak and Crane 2000) 23 

### Reducing urban heat island effect through evapotran spiration

. For trees over grass, mid-day 24 

### temperatures have been reported to be are 0.7 degree Celsius ( o 

### C) to 1.3 o 

### C cooler than in an 25 

### open area. Reduced air temperature can improve air quality because the emission of many 26 

### pollutants or ozone-forming chemicals are temperatu re dependent. Lower air temperature can 27 

### reduce ozone formation (Souch and Souch 1993; Nowak at www.ufore.org 

### ) 28 

### Reduced energy costs. Improve insulation against summer heat is provided with green roofs. 29 

### Mature, shady, deciduous trees can reduce air condi tioning costs up to 30 percent, while a wind 30 

### break of evergreens can save 10–50 percent off heat ing costs in the winter 31 

### ( www.dnr.state.md.us/forests/publications/urban5.htm l ). 32 

### Saving money on drainage infrastructure. Curb, gutter, storm drain pipes, and runoff detenti on 33 

### practices can be reduced by reducing the volume of runoff to be conveyed (WERF 2008; USEPA 34 

### 2007). 35

v USEPA (U.S. Environmental Protection Agency). 1995. Economic Benefits of Runoff Controls

. ( U.S. Environmental Protection Agency, Office of Water, W ashington, DC.3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 22 

### Example Green Infrastructure Benefits Analysis by Philadelphia

. An example of the wide 1 

### array of benefits achievable is presented in Philad elphia’s Green City, Clean Water report 2 

### summarizing the vision of using LID to mitigate sto rmwater overflows. Philadelphia has, like 3 

### many older cities, a legacy of combined sanitary an d storm sewers , and recently compared the 4 

### costs and benefits of using green infrastructure to help mitigate the CSOs. Figure 3-8 presents an 5 

### overview of the benefits the city envisions from a plan to implement green stormwater 6 

### management. 7

Economic Benefits About 250 people would be employed in green jobs pe r year

Increase of more than 1 million recreational user-d ays per year would be enjoyed Reduction of approximately 140 fatalities cause by excessive heat over the next 40 years Social Benefits

Increase in property values of 2%–5% in greened nei ghborhoods

1.5 billion pounds of carbon dioxide emissions avoi ded [partially through reduced heavy equipment requirements for alternative stormw ater management] or absorbed Air quality benefits on average leading annually to : 1-2 avoided premature deaths, 20 avoided asthma attacks, and 250 missed days of work or school Water quality and habitat improvements including : 5-8 billion gallons of CSO avoided per year; 190 acres of wetlands restored or created , 11 miles of stream restored. Environmental Benefits

Reduction in electricity and fuel use [partially th rough reduced construction of

alternative stormwater management infrastructure]. Source: Green City, Clean Waters: Philadelphia’s Pr ogram for Combined Sewer Overflow Control, A Long-T erm 8 Control Plan Update, Summary Report, 2009. http://planphilly.com/node/9842 9 Figure 3-8. Projected ancillary benefits of using L ID and green infrastructure stormwater practices 10 in Philadelphia to help achieve CSO mitigation. 11 

### Figure 3-9 shows the benefits (and external costs) estimated for a 40 year period of two of the 12 

### options Philadelphia compared for CSO solutions. Th e 50 percent LID, or green infrastructure 13 

### option, is a scenario in which 50 percent of the im pervious surface in the CSO area is managed 14 

### through green infrastructure, and the remainder thr ough conventional storage tunnels. The 30’ 15 

### Tunnel option represents a scenario where large tun nels would be used to manage the CSO. 16 

### Philadelphia selected these options for analysis pu rposes, and they do not represent 17 

### implementation decisions by the City. This table de monstrates only the value of the ancillary 18 

### benefits of using green infrastructure for CSO miti gation compared to the lack of ancillary 19 

### benefits of traditional CSO management. The cost es timates for construction and maintenance 20 

### can be found in the Long-Term Control Plan at http://www.phillywatersheds.org/ltcpu/

. 21 

### Estimated capital and O&M costs of individual green infrastructure elements considered by 22 

### Philadelphia are provided in Section 2 3 of this chapter. 23

243/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 23 1 Source: Summary of Triple Bottom Line Analysis, City of Phi ladelphia Long-Term Control Plan, 2 http://www.phillywatersheds.org/ltcpu/Vol02_TBL.pdf 3 http://www.phillywatersheds.org/ltcpu/Vol02_TBL.pdf 4 Figure 3-9. Summary of Philadelphia’s analysis of g reen infrastructure to help mitigate CSOs: 5 Present present value benefits of two options studied (Cumulative estimated through 2049 in 2009 6 million USD ISD ) 7 

### A broad overview of the ancillary benefits that can be realized from LID is provided by the 8 

### Center for Neighborhood Technology in its Green Val ues Calculator ( www.cnt.org/natural9 

### resources/green-values ). 10


## 1.2 Overview of the Urban Runoff Chapter 11 

### This chapter provides recommendations for the appro aches recommended for restoring or 12 

### maintaining predevelopment hydrology for urban runo ff to maintain or restore, to the maximum 13 

### extent technically feasible, the predevelopment hyd rology of the property with regard to the 14 

### temperature, rate, volume, and duration of flow. 15 

### Maintaining or restoring predevelopment hydrology i s the stormwater management goal 16 

### recommended in this document, as required by Congre ss in section 438 of EISA. A number of 17 

### technical resources, guidance, and design manuals a re available that review in detail the key 18 

### techniques and topics pertinent to urban runoff con trol. Several of these documents are listed as 19 

### the subject areas are addressed. The technical mate rial that is available in these existing sources 20 

### will not be repeated here. 213/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 24 

### 1.2.1 Management Practices and Management Practices Scale s 1 

### The following presents an overview of the approach presented in this chapter to achieve this goal 2 

### by implementing strategies at the regional and wate rshed scale down to the site scale, as follows: 3



### • At the regional or watershed scale, planning techni ques such as smart growth and policies 4 

### to allow conservation development, as part of water shed planning, can be used to lay the 5 

### groundwork for ensuring that development has minimu m impacts on water resources, 6 

### including no net increase in stormwater runoff. Thi s is important for both developed areas 7 

### and for yet undeveloped areas. 8



### • At the site scale, using green infrastructure/LID p ractices, along with source control and 9 

### pollution prevention, are necessary to achieve the goals of protecting and restoring the 10 

### Chesapeake Bay. 11 

### Applying LID practices at the site scale is recomme nded for new development, redevelopment, 12 

### and retrofit. LID practices are flexible in design, so are widely applicable. LID practices such as 13 

### functional conservation landscaping, bioretention, and swales require only a minimum 14 

### modification from traditional landscaping design, o ften at no additional cost and potentially 15 

### provide long-term reductions in cost

. Many jurisdictions across the United States have a dopted 16 

### policies and design guides for such practices, incl uding many in the Chesapeake Bay area. 17 

### LID practices such as minimizing impervious surface s, porous pavement, green alleys, green 18 

### streets, cisterns and rain barrels, and green roofs have become widely accepted in cities that have 19 

### needed to manage excess pollutant runoff, water sho rtages, or flash flooding. The technology is 20 

### now well-proven and shown to be adaptable for imple mentation at new development, 21 

### redevelopment, and retrofit sites. Relatively small -scale LID practices can be dispersed 22 

### throughout a site, capturing runoff from small drai nage areas for infiltration, evapotranspiration, 23 

### or capture and use. A site can be designed based on a rooftop-to-stream treatment train approach 24 

### that includes both source-control practices and run off treatment practices. The treatment train 25 

### approach allows site designers and stormwater manag ers to take advantage of every opportunity 26 

### to prevent runoff pollution and reduce runoff volum e close to its source, thereby protecting 27 

### headwater streams, municipal drainage systems, and downstream receiving waters, as follows: 28



### • Minimize runoff generation by limiting the amount o f directly connected impervious 29 

### surface 30



### • Capture runoff for evaporation or reuse 31



### • Naturally infiltrate and filter runoff through land scaped areas 32



### • Direct surplus runoff to engineered practices such as bioretention and other infiltration 33 

### devices 34



### • Prevent contamination of runoff using pollution pre vention techniques 35



### • Manage off-site runoff using regional stormwater pr actices, if necessary 36 

### This guidance provides an overview of the implement ation measures recommended for 37 

### managing urban stormwater to protect and restore th e Chesapeake Bay or other waters affected 38 

### by development. The implementation measures are act ion-oriented and, when considered 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 25 

### together, from watershed

- scale to site scale, form a step-wise approach to a ddressing runoff 1 

### volume and pollutant concentrations and for selecti ng management practices. 2



### Sections 

### 1. 2 

### .2 Implementation Measures for Urban Runoff in the 3 

### Chesapeake Bay Watershed to Control Nonpoint Source Nutrient and 4 

### 3 

### Sediment Pollution 5 

### Maintain or restore, to the maximum extent technica lly feasible, the 6 

### predevelopment hydrology of this chapter summarize key elements of this approac h: the 7 

### property with regard to the temperature, rate, volume reduction , and duration of flow. 8


### The implementation measure is : 9

• 

### Reduc e u rban r unoff v olume by understanding local land use

- hydrology relationships and 10


### a pplying performance standards that protect or resto re hydrology to predevelopment 11 

### levels. Section 2 presents an approach of l and use and growth management measures that 12 

### guide development to areas that minimize effe cts o n sensitive resources and open space 13 

### and ensur e that new and redevelopment sites are designed to re duce runoff volume 14 

### through on

- site stormwater retention. 15

• 16

• 

### Reduce Pollutant Concentrations with Source Control s and Treatment 17

• 

### The implementation measure is : 18

• 

### Reduce pollutant reduction through co ncentrations by implementing source 19 

### control controls and by treatment

. practices as necessary to meet water quality goals. 20 

### Section 3 addresses pollutant source controls that prevent po llutants from coming into 21 

### contact with rainwater and runoff, as well as treatment controls that help to ensure that 22 

### polluted runoff does not enter waterways. 23

• 24

• 

### Sectors of urban development with particular import ance for in the Chesapeake Bay 25 

### watershed are redevelopment and turf management. Se ctions 4 and 5 summarize 26 

### considerations associated with these two important sources of pollutants contributed by 27 

### urban areas to the Chesapeake Bay. The subset of specific implementation measures for 28 

### turf management are presented. 29
30


### Section 6 consists of a series of fact sheets that briefly describe some of the key practices for 31 

### which new research and guidance is available and in clude applicability, unit processes, 32 

### feasibility constraints and limitations, runoff vol ume and pollutant load removal estimates as 33 

### applicable, design and maintenance considerations, costs and factors that affect cost, and key 34 

### references and resources. Photos and diagrams of ty pical applications are provided, as well. The 35 

### fact sheets are intended to highlight new research and as well as seminal resources with the most 36 

### up-to-date approach on thinking about each management practice. Those practices that which are 37 

### adequately covered by other publicly available reso urces have links to existing sources. 383/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 26 

### 1.2.2 Implementation Measures for Urban Runoff in t he Chesapeake Bay 1 

### Watershed to Control Nonpoint Source Nutrient and S ediment 2 

### Pollution 3 

### Development or redevelopment projects with a footpr int that exceeds 5,000 square feet 4 

### should use site planning, design, construction, and maintenance strategies for the property 5 

### to maintain or restore, to the maximum extent techn ically feasible, the predevelopment 6 

### hydrology of the watershed and site with regard to the temperature, rate, volume, and 7 

### duration of flow. (Note: That is based on the approach adopted by Co ngress for federal facilities 8 

### in section 438 of the Energy Independence and Secur ity Act, 2007) 9 

### Implementation Measures:

• Maximize infiltration, evapotranspiration, and harv est and use practices on-site, to the extent feasible. Examples of these practices includ e:

− Bioretention cells or raingardens

− Green streets, right-of-way and parking lot designs and retrofits

− Cisterns and interior and exterior use of runoff

− Green roofs

− Tree planting and urban forestry

− Soil amendments and turf management

• Design and implement policies to preserve or restor e predevelopment hydrology with regard to the temperature, rate, volume and duratio n of flow, or more restrictive if needed for site-specific water quality protection. Impleme nt at the regional, watershed and site scales, as appropriate. Consider the following fact ors: land use, hydrology, geomorphology, and climate. Use Options 1 or 2 or s imilar performance based approaches to achieve the desired hydrological goal s:

− Option 1: Retain the 95 th 

### Percentile Rainfall Event (simplified method)

− Option 2: Conduct site-specific hydrologic analysis

• Use development and planning techniques to direct d evelopment to areas where development will:

− Have fewer impacts on water quality

− Preserve the integrity of healthy watersheds

− Achieve local objectives for infrastructure managem ent and sustainability

• Use conservation design and LID techniques to

− Minimize the hydrologic impacts of the development and preserve natural drainage ways to the extent feasible

− Integrate green infrastructure/low impact developme nt (LID) practices into the design and construction of the development, to the extent feasible and preferably at the neighborhood scale

• Evaluate and revise local codes and ordinances, as necessary, to promote implementation3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 27 

### of green infrastructure/LID designs and practices a nd examine the following policies and mechanisms to identify opportunities, incentives an d barriers to promote GI/LID:

− Zoning ordinances

− Subdivision codes

− Street standards and road design guidelines

− Parking requirements

− Setbacks (requirements for long driveways, etc.)

− Height limitations (encourage density where appropr iate)

− Open space or natural resource plans

− Comprehensive plans

− Funding mechanisms and other fiscal policies to enc ourage the use of green infrastructure/LID practices

• Examine and revise transportation, public right of way and parking lot policies, guidance and standards to reduce impervious areas and water resource impacts

• Minimize directly connected impervious areas by:

− Disconnection of downspouts

− Infiltration of runoff onsite (preferably through b ioretention practices

− Product substitution, e.g., use of permeable paving materials

− Harvest and use of runoff onsite

− Construction of green roofs

• Restore streams, floodways, and riparian areas to m itigate channel erosion and sedimentation and enhance the pollutant removal cap acity of these areas

• Reduce the impacts of existing impervious areas thr ough redevelopment and infill policies and strategies and identify and implement incentives for redevelopment that encourage the use of green infrastructure/LID desig ns and practices.

− Retrofit existing urban areas to achieve the desire d performance goals

− Assess candidate sites, prioritize, and implement p ractices based on expected cumulative benefit to the subwatershed or watershed

− Assess retrofit potential of significant runoff sou rces such as streets, highways, parking lots and rooftops.

− Develop and implement redevelopment programs that i dentify opportunities for a range of types and sizes of redevelopment projects to mitigate water resource impacts that:

o establish appropriate redevelopment stormwater perf ormance standards consistent with the goal of restoring predevelopmen t hydrology with regard to the temperature, rate, volume and duration of flow, or more restrictive if needed for site-specific water quality protection

o include development of an inventory of appropriate mitigation practices (e.g.3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 28



### permeable pavement, infiltration practices, green r oofs) that will be encouraged or required for implementation at redeve lopment sites that are smaller than the applicability threshold

o include site assessment to determine appropriate GI /LID practices

o review codes and ordinances and modify as appropria te to allow and encourage GI/LID practices

o implement GI/LID demonstration projects

o incentivize early adopters of GI/LID practices

o maximize urban forest canopy to reduce runoff

o conduct soil analyses and amend compacted urban soi ls to promote infiltration

1 

### Reduce Pollutant Concentrations by implementing sou rce control measures and by 2 

### treatment practices as necessary to meet water qual ity goals 3 

### Source Control/Pollution Prevention 4 

### Implementation Measures:

• Identify the pollutants of concern (POCs) to help t arget the selection of pollution prevention/source control that are most appropriate , for example, nutrients and sediment

• Implement pollution prevention/source control pract ices, i.e. nonstructural, programmatic efforts as basic, routine land management practices to target specific pollutants

• Require source controls on

− New and redevelopment site plans for commercial/ind ustrial facilities

− Commercial industrial facilities through developmen t of a Stormwater Pollution Prevention Plan (SWPPP)

− Municipal facilities through development of SWPPPs

• Develop and implement ongoing outreach programs aim ed at behavior change to prevent pollution and control it at its source. Methods for impact and effectiveness evaluation should be incorporated into these outreach and educ ation programs.

• Implement residential downspout disconnection progr am

• Conduct inspections of commercial/industrial facili ties to provide compliance assistance or to ensure implementation of controls3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 29 

### Runoff Treatment 1


### Implementation Measures:

• Identify the pollutants of concern (POCs) to help t arget the section of treatment approaches that are most appropriate

• Select treatment practices based on applicability t o the POCs

− Use practices to reduce of runoff volume as the pre ferred and most reliable approach to reducing pollutant loading to receiving waters

− Use treatment practices as needed if reduction of r unoff is not feasible

− Base the selection of treatment practice on

o treatment effectiveness for the POC to ensure disch arge quality

o long-term maintenance considerations to ensure cont inued adequate maintenance and recognition of life-cycle costs

o site limitations to ensure appropriateness of pract ice to the site

o aesthetics and safety to ensure public acceptance
Turf Management Implementation Measures 2 

### Implementation Measures:

• Reduce turf management inputs (nutrients, pesticide s, irrigation water)

• Reduce total turf area cultivated through initial d esign or redesign of existing landscapes

• Reduce total area maintained under high input presc ription management programs

• Convert nonessential turf to low or lower maintenan ce vegetated areas such as naturalized forest, meadow, native plantings, xeris capes or turf cultivars that require little or no inputs

• Increase infiltrative and retention capacity of mai ntained turf

• Reduce sediment loadings from turf areas

• Examine municipal codes and ordinances and/or other facility, corporate or agency policy directives and guidance for opportunities to

− Adopt or revise policy or guidance to reduce total turf area, nonessential turf area and high input turf areas through requirements and/ or incentive programs

− Employ management practices that have a decreased p otential impact on water

resources

• Conduct a municipal or facility wide assessment of turf area within the jurisdiction or facility property. This assessment should include

− a map of the jurisdiction or facility and include t he identification of all turf areas

− an inventory or calculation of the total turf area in acres or hectares using GIS techniques or other methods3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 30



### − an evaluation to determine essential and nonessential turf areas

− identification and delineation of all high and low input turf areas

− an evaluation of all turf management activities an d inputs preferably by turf category or significant turf area within the jurisd iction or facility

− assessments of turf health and infiltrative capacit y and opportunities to increase soil health to promote the infiltrative capacity of turf areas

• Develop a management plan that contains

− an analysis of options to reduce or eliminate nonessential turf or convert essential turf to low input turf

− stated goals and objectives regarding the reduction of turf related inputs (water, fertilizers, pesticides, fossil fuels) on a municip al or facility wide basis

− an analysis of options to reduce potable water use through the use of hardy cultivars or the use of recycled water or harvested runoff

− an identification of areas where soil amendments be used to enhance soil health and the infiltration capacity of the soils

− areas of turf that could be used to manage runoff

− areas of turf that could be replaced by lower maint enance cultivars or other grasses such as switch grass

− a training program for landscaping personnel

− an implementation schedule

• Develop and implement ongoing public education and outreach programs on turf reduction and Bay-friendly lawn and turf management. Programs should target b ehavior change and promote the adoption of water resource f riendly practices by increasing awareness, promoting appropriate behaviors and acti ons, providing training and incentives. Impact and effectiveness evaluation sho uld be incorporated into these outreach and education programs.

• Conduct a life-cycle cost benefit analysis to reduc e inputs and maintenance burden of managed turf areas.
1



## 1.3 References 2 

### Allmendinger, Nicholas E., James E. Pizzuto, Glenn E. Moglen, and Mikolaj Lewicki. 2007. A 3 

### sediment budget for a sediment budget for an urbani zing watershed, 1951-1996, 4 

### Montgomery County, Maryland, U.S.A. Paper No. J0505 1 of the Journal of the American 5 

### Water Resources Association. Received April 25, 2005; accepted March 29, 2007. 6 

### CNT (Center for Neighborhood Technology). No date. Green Values Stormwater Toolbox

. 7 

### Center for Neighborhood Technology, Chicago, IL. <w ww.cnt.org/natural-resources/green8 

### values>. Accessed February 23, 2010. 93/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 31 

### Maryland Department of Natural Resources. No date. Trees Save Energy . DNR, Annapolis, MD. 1 

### <http://www.dnr.state.md.us/forests/publications/ur ban5.html>. Accessed February 23, 2 

### 2010. 3


### National Research Council. 2008. Urban Stormwater Management in the United States. The 4 

### National Academies Press and the Committee on Reducing Stormwater Discharge 5 

### Contributions to Water Pollution , Washington, DC. 6 

### Nowak, D.J., and Crane, D.E. 2000 1998 . The Urban Forest Effects (UFORE) Model: quantifyi ng 7 

### urban forest structure and functions. In Hansen, M. and T. Burk (eds.) Resources 8 

### Inventories in the 21st Century . U.S. Department of Agriculture Forest Service Gen eral 9 

### Technical Report NC-212: 714–72). St. Paul, MN. 10 

### <http://www.ufore.org/about/files/NowakCrane_UFORE. pdf>. Integrated Tools 11 

### Proceedings. < http://www.ufore.org/about/files/NowakCrane_UFORE. pdf > Accessed 12 

### February 22, 2010. 13 

### Philadelphia Water Department. No date. Green City, Clean Water. Office of Watersheds. 14 

### Philadelphia, PA. <http://www.phillywatersheds.org/ ltcpu/>. Accessed February 23, 2010. 15 

### Philadelphia Water Department. 2009. Summary of Triple Bottom Line Analysis, City of 16 

### Philadelphia Long-Term Control Plan . Office of Watersheds, Philadelphia PA. 17 

### <http://www.phillywatersheds.org/ltcpu/Vol02_TBL.pd f> Accessed February 23, 2010. 18 

### Plan Philly. 2009. Green City, Clean Waters: Philad elphia’s Program for Combined Sewer 19 

### Overflow Control, A Long-Term Control Plan Update, Summary Report, 2009. University 20 

### of Pennsylvania School of Design, Philadelphia, PA. <http://planphilly.com/node/9842>. 21 

### Accessed February 23, 2010. 22 

### Reese, A. 2009. Volume-based hydrology: Examining t he shift in focus from peak flows and 23 

### pollution treatment to mimicking predevelopment vol umes . Stormwater 10(6). 24 

### < http://www.stormh2o.com/september-2009/volume-based

25 

### hydrology.aspx http:// www.stormh2o.com/september

- 2009/volume

- based

- hydrology.aspx >. 26 

### Accessed January 15, 2010. 27 

### Smith, W.H. 1990. Air Pollution and Forests. Springer-Verlag, New York, NY. 28 

### Souch, C.A., and C. Souch. 1993. The effect of tree s on summertime below canopy urban 29 

### climates: a case study, Bloomington, Indiana. J. Arboric. 19(5):303–312. 30 

### Stranko, S.A., R.H. Hilderbrand, R.P. Morgan II, M. W. Staley, A.J. Becker, A. Roseberry31 

### Lincoln, E.S. Perry, and P.T. Jacobson. 2008. Brook Trout Declines with Land Cover and 32 

### Temperature Changes in Maryland. North American Journal of Fisheries Management 33 

### 28:1223–1232 doi: 10.1577/M07-032.1 < http://afsjournals.org/doi/abs/10.1577/M07- 34 

### 032.1 http://afsjournals.org/doi/abs/10.1577/M07

- 032.1 > and 35 

### <http://www.dnr.state.md.us/dnrnews/pressrelease200 8/100308.html 36 

### <http:// www.dnr.state.md.us/dnrnews/pressrelease2008/100308 .html >. Accessed February 37 

### 22, 2010. 383/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 32 

### Trust for Public Land. 1999. The Economic Benefits of Open Space . San Francisco, CA. 1 

### <http://www.tpl.org/tier3_cd.cfm?content_item_id=11 95&folder_id=727>. Accessed 2 

### March 29, 2006. 3


### Trust for Public Land and American Water Works Asso ciation. 2004. Protecting the Source

. 4 

### Trust for Public Land, San Francisco, CA and Americ an Water Works Association, 5 

### Denver, CO. 6 

### U.S. Department of Agriculture. 2000. Resources Inv entories in the 21 st 

### Century. U.S. 7 

### Department of Agriculture Forest Service General Te chnical Report NC-212 (pp. 714– 8 

### 720). U.S. Department of Agriculture, St. Paul, MN. 9 

### <http://www.nrs.fs.fed.us/pubs/276>. < http://www.nrs.fs.fed.us/pubs/276 > Accessed 10 

### February 22, 2010. 11 

### USEPA (U.S. Environmental Protection Agency). 1995. Economic Benefits of Runoff Controls 12 

### (U.S. Environmental Protection Agency, Office of Wa ter, Washington, DC. 13 

### USEPA (U.S. Environmental Protection Agency). 2009. Technical Guidance on Implementing 14 

### the Stormwater Runoff Requirements for Federal Proj ects under Section 438 of the Energy 15 

### Independence and Security Act. 16 

### < http://www.epa.gov/owow/NPS/lid/section438/pdf/fina l_sec438_eisa.pdf http:// www.epa. 17 

### gov/owow/NPS/lid/section438/pdf/final_sec438_eisa.p df >. Accessed January 15, 2010. 18 

### Weinstein, N. C. Glass, J.P. Heaney, J. Lee, W. Hub er, P. Jones, C, Kloss, M. Quigley, E. 19 

### Strecker, and K. Stephens. 2005. Decentralized Stormwater Controls for Urban Retrofi t 20 

### and Combined Sewer Overflow Reduction. Water Environment Research Foundation, 21 

### Alexandria, VA. 22 

### WERF (Water Environment Research Foundation). 2008. Using Rainwater to Grow Livable 23 

### Communities: Benefits of Green Development. 24 

### < http://www.werf.org/livablecommunities/pdf/benefits .pdf http:// www.werf.org/livablecom 25 

### munities/pdf/benefits.pdf >. Accessed January 15, 2010. 263/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 33 

## 2 Implementation Measures for Reducing Urban Runoff 1 

## Volume 2 

### The shortcomings of traditional, detention-based st ormwater control efforts, and the need to use 3 

### approaches to reduce runoff volume to protect water quality, have been well-documented (NRC 4 

### 2008; USEPA 2009). 5 

### This section presents an approach of land use and g rowth management measures that guide 6 

### development to areas that minimize effects on sensi tive resources and open space and ensure that 7 

### new and redevelopment sites are designed to reduce runoff volume through on-site stormwater 8 

### retention. 9 

### Development or redevelopment projects with a footpr int that exceeds 5,000 square feet 10 

### should use site planning, design, construction, and maintenance strategies for the property 11 

### to maintain or restore, to the maximum extent techn ically feasible, the predevelopment 12 

### hydrology of the watershed and site with regard to the temperature, rate, volume, and 13 

### duration of flow. (Note: Based on the approach adopted by Congress f or Federal facilities in 14 

### Section 438 of the Energy Independence and Security Act, 2007) 15 

### Implementation Measures:

• Maximize infiltration, evapotranspiration, and harv est and use practices on-site, to the extent feasible. Examples of these practices includ e

− Bioretention cells or raingardens

− Green streets, row of way and parking lot designs a nd retrofits

− Cisterns and interior and exterior use of runoff

− Green roofs

− Tree planting and urban forestry

− Soil amendments and turf management

• Design and implement policies to preserve or restor e predevelopment hydrology with regard to the temperature, rate, volume and duratio n of flow, or more restrictive if needed for site-specific water quality protection. Impleme nt at the regional, watershed and site scales, as appropriate. Consider the following fact ors: land use, hydrology, geomorphology, and climate. Use Options 1 or 2 or s imilar performance based approaches to achieve the desired hydrological goal s

− Option 1: Retain the 95 th 

### Percentile Rainfall Event (simplified method)

− Option 2: Conduct site-specific hydrologic analysis

• Use development and planning techniques to direct d evelopment to areas where development will

− Have fewer impacts on water quality

− Preserve the integrity of healthy watersheds

− Achieve local objectives for infrastructure managem ent and sustainability3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 34 

### • Use conservation design and LID techniques to

− Minimize the hydrologic impacts of the development and preserve natural drainageways to the extent feasible

− Integrate green infrastructure/low impact developme nt (LID) practices into the design and construction of the development, to the extent feasible and preferably at the neighborhood scale

• Evaluate and revise local codes and ordinances, as necessary, to promote implementation of green infrastructure/LID designs and practices a nd examine the following policies and mechanisms to identify opportunities, incentives an d barriers to promote GI/LID

− Zoning ordinances

− Subdivision codes

− Street standards and road design guidelines

− Parking requirements

− Setbacks (requirements for long driveways, etc.)

− Height limitations (encourage density where appropr iate)

− Open space or natural resource plans

− Comprehensive plans

− Funding mechanisms and other fiscal policies to enc ourage the use of green infrastructure/LID practices

• Examine and revise transportation, public right of way and parking lot policies, guidance and standards to reduce impervious areas and water resource impacts

• Minimize directly connected impervious areas by

− Disconnection of downspouts

− Infiltration of runoff onsite (preferably through b ioretention practices

− Product substitution ,e.g., use of permeable paving materials

− Harvest and use of runoff onsite

− Construction of green roofs

• Restore streams, floodways, and riparian areas to m itigate channel erosion and sedimentation and enhance the pollutant removal cap acity of these areas

• Reduce the impacts of existing impervious areas thr ough redevelopment and infill policies and strategies and identify and implement incentives for redevelopment that encourage the use of green infrastructure/LID desig ns and practices.

− Retrofit existing urban areas to achieve the desire d performance goals

− Assess candidate sites, prioritize, and implement p ractices based on expected cumulative benefit to the subwatershed or watershed

− Assess retrofit potential of significant runoff sou rces such as streets, highways, parking lots and rooftops.

− Develop and implement redevelopment programs that i dentify opportunities for a3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 35



### range of types and sizes of redevelopment projects to mitigate water resource impacts that

o establish appropriate redevelopment stormwater perf ormance standards consistent with the goal of restoring predevelopmen t hydrology

o include development of an inventory of appropriate mitigation practices (e.g. permeable pavement, infiltration practices, green r oofs) that will be encouraged or required for implementation at redeve lopment sites that are smaller than the applicability threshold

o include site assessment to determine appropriate GI /LID practices

o review codes and ordinances and modify as appropria te to allow and encourage GI/LID practices

o implement GI/LID demonstration projects

o incentivize early adopters of GI/LID practices

o maximize urban forest canopy to reduce runoff

o conduct soil analyses and amend compacted urban soi ls to promote infiltration
1 

## 2.1 Maximize Infiltration, Evapotranspiration, and Harvest and Use 2


### T he shortcomings of traditional, detention

- based stormwater control efforts , and the need to use 3 

### approaches to reduce runof f volume to protect water quality , have been well

- documented (NRC 4 

### 2008, EPA 2009). 5 

### The implementation measure is: 6


### Reduce urban runoff volume by understanding local land use

- hydrology relationships and 7 

### applying performance standards that protect or rest ore hydrology to predevelopment 8 

### levels

. 9


### This section presents an approach of l and use and growth management measures that guide 10 

### development to areas that minimize effe cts o n sensitive resources and open space and ensur e that 11 

### new and redevelopment sites are de signed to reduce runoff volume through on

- site stormwater 12 

### retention 13


### The recommended approaches for reducing runoff volume are the following : 14

• 

### M aintain or restore predevelopment hydrology, at lea st with regard to the temperature, 15 

### rate, volume, and duration o f flow

. 16



### − Maximize infiltration, evapotranspiration, and harv est and use practices on

- site 17

• 

### Select the approach for achieving this performance goal on the basis of the scale being 18 

### addressed (i.e., regional, watershed, site) and on an understanding of the la nd use, 19 

### hydrology, geomorphology, and climate type for the site or watershed 20

• 

### Use appropriate design s a s part of a comprehensive watershed plan 21



### − For n ew development and redevelopment 223/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 36



###  Use development planning techniques such as smart growth to determine 1 

### where to d evelop to 2



### o Have minimum impact on water quality 3



### o Protect existing healthy watersheds 4



### o Achieve local objectives for infrastructure management 5



###  Use c onservation d esign techniques to 6



### o Minimize the hydrologic modifications of the developments 7



### o Enable the effect ive integration and placement of Green 8 

### Infrastructure/ LID practices 9



###  Use Green Infrastructure/ LID practices to manage stormwater on

- site for 10 

### smaller storm events for protection of water qualit y (in addition to meeting 11 

### local regulations for flood control) 12



###  Mi nimize impervious areas by using techniques such as reducing street widths 13 

### or parking lot sizes 14



###  Minimize directly connected impervious areas, such as downspout 15 

### disconnection 16



###  Use LID Practices: Maximize infiltration, evapotran spiration , and harvest and 17


### use practices 18



###  Restore streams, floodways, and riparian areas to m itigate channel erosion that 19 

### contributes to sediment pollution, and restore the natural pollutant removal 20 

### capability of these ecosystems 21



### − For e xisting urban areas (i.e., retrofits) : 22



###  Use designs a ppropriate to new development and redevelopment (ab ove) 23



###  Redevelop existing impervious areas through infill strategies , including 24 

### incentives for redevelopment 25


## 2.1 Maintain or R estore Predevelopment H ydrology 26 

### Restoring or maintaining predevelopment hydrology h as emerged as the generally preferred 27 

### approach for controlling urban runoff and protectin g water quality for several reasons. Most 28 

### importantly, this approach addresses the root cause of impairment. Traditional control 29 

### approaches attempt to control the symptoms (e.g., p eak flow, excess pollutants), but that is 30 

### largely ineffectual in protecting streams and water quality because of the scale of the problem, 31 

### the cumulative effects of multiple developments, an d the need to manage both site- and 32 

### watershed-level effects. The problems associated wi th traditional control approaches in 33 

### protecting water quality are presented in the Intro duction to this chapter. This section presents 34 

### the approaches for obtaining the goal of restoring or maintaining predevelopment hydrology. 35 

### To maintain or restore site or watershed hydrology, the watershed should must function 36 

### hydrologically after development as it did before h uman induced land alterations. In the 37 

### Chesapeake Bay, most areas before development were forested with mature trees, and the bulk of 38 

### the rainfall was intercepted, infiltrated, or evapo transpired. 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 37 

### To mimic the natural behavior of the landscape the stormwater management system should be 1 

### designed to manage runoff through the following: 2



### • Infiltration and groundwater recharge 3



### • Evapotranspiration 4



### • Harvest or rainfall and use of captured rainfall on -site 5 

### On sites where inadequate area or the intended use of the development precludes managing the 6 

### desired volume on-site, off-site mitigation should be considered within the same subwatershed. 7 

### The intent of maintaining or restoring site and wat ershed hydrology is to preserve or restore 8 

### stream and groundwater hydrology so that the system is stable and resilient enough to support 9 

### aquatic biota, stream channel stability, and histor ical aquifer recharge rates. That will help ensure 10 

### that receiving waters are not negatively affected b y changes in runoff temperature, volumes, 11 

### durations, and rates. 12



### 2. 2 Implement Policies 1.1 Establishing Performance Design 13 

### Objectives 14 

## The performance

- based app roached described in the following 15 

## paragraphs is intended to Preserve and Restore Redevelopment 16 

## Hydrology 17 

### provide designers the option of selecting either a simplified method or a more site

- specific 18 

### methodology that allows the designer to factor in s ite co nditions. Both options give the designer 19 

### flexibility in selecting appropriate, technically feasible practices to redu ce the volume of 20 

### stormwater discharged to the maximum extent technic ally feasible (METF). In the simplified 21 

### option, the performance standar d has already been determined. In the second option, the 22 

### performance standard will be determined by site eva luation and subsequent continuous 23 

### simulation modeling methods. 24 

### This guidance provides two options that site design ers can use to establish appropriate 25 

### performance goals toward achieving the goal of main taining or restoring predevelopment 26 

### hydrology ; however, it is noted that in many situations it m ight be feasible and beneficial to 27 

### design to have no runoff from a site. The discussio n of the two options does not preclude the use 28 

### of more protective performance goals . Option 1, the methodology based on retention of t he 95 th 29 

### percentile rainfall event, is a simple way to estab lish the performance goal and does not require 30 

### detailed analysis of the site conditions or a conti nuous simulation modeling approach. It is 31 

### assumed that using that performance standard will g enerally result in designs that protect or 32 

### restore site hydrology. However, there could be sit uations where Option 1 (retaining the 95 th 33 

### percentile rainfall event) is not protective enough to maintain or restore the predevelopment 34 

### hydrology of the project (for example, in some head water streams) or is overprotective (in the 35 

### case of naturally impermeable surfaces). In such ca ses, Option 2 (site-specific hydrologic 36 

### analysis) could be used to determine the performanc e design objective necessary to preserve 37 

### predevelopment runoff conditions. The expectation i s that Option 2 can be used in situations 38 

### where the designer has the requisite data and resou rces to analyze site infiltration, 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 38 

### evapotranspiration, interception, and potential har vest and use scenarios to establish these design 1 

### objectives and to design the runoff management syst em to meet the goals of maintaining and 2 

### restoring site hydrology. More detailed description s of the two options follow. 3

Option 1: Retain the 95 th Percentile Rainfall Event 4 

### Under Option 1, managers design, construct, and mai ntain stormwater management practices that 5 

### manage rainfall on-site, and prevent the off-site d ischarge of the precipitation from all rainfall 6 

### events less than or equal to the 95 th 

### percentile rainfall event to the METF. The 95 th 

### percentile 7 

### rainfall event is the event whose precipitation tot al is greater than or equal to 95 percent of all 8 

### storm events over a given period of record. For exa mple, to determine what the 95 th 

### percentile 9 

### storm event is in a specific location, all 24-hour storms that have recorded values over a 30-year 10 

### period would be tabulated, and a 95 th 

### percentile storm would be determined from that rec ord, i.e., 11 

### 5 percent of the storms would be greater than the n umber determined to be the 95 th 

### percentile 12 

### storm. Thus the 95 th 

### percentile storm would be represented by a number such as 1.5 inches, and 13 

### that would be the design storm. The designer select s a system of practices, to the METF, that 14 

### infiltrate, evapotranspire, or harvest and reuse th at volume multiplied by the total area of the 15 

### facility/project footprint. Methods and data used t o estimate the 95 th 

### percentile event are 16 

### discussed in the appendix 2 of this document. 17 

### For the purposes of this document, retaining all st orms up to and including the 95 th 

### percentile 18 

### storm event is analogous to maintaining or restorin g the predevelopment hydrology with respect 19 

### to the volume, flow rate, duration, and temperature of the runoff for most sites. 20 

### Where technically feasible, the goal of Option 1 is that 100 percent of the volume of water from 21 

### storms less than or equal to the 95 th 

### percentile event over the footprint of the project should must 22 

### not be discharged to surface waters. In some cases, runoff can be harvested and re used and 23 

### ultimately can be discharged to surface waters or a sanitary treatment system; such direct or 24 

### indirect discharges must be authorized. For example if runoff is captured for nonpotable uses 25 

### such as toilet flushing or other uses that are not irrigation related, the waters could be discharged 26 

### into the sanitary sewer system or other appropriate system depending on local requirements. 27


### Runoff volumes that exceed the 95 th 

### percentile event can be managed by using overflow or 28 

### diversion strategies and practices as well as the d etention practices used for flood control. 29 

### Designers should also account for potential thermal effects of structures such as roofs and paved 30 

### surfaces that can increase the temperature of storm water runoff. Designers should select 31 

### materials that minimize temperature increases (cons ider material such as concrete versus asphalt; 32 

### vegetated roofs. and the like and use them as appro priate). 33 

### Rationale for Selecting Option 1. Option 1 was selected because retention of 100 per cent of all 34 

### rainfall events equal to or less than the 95 th 

### percentile rainfall event was estimated to be a 35 

### conservative and protective representation of the natural hydrology on most sit es. On most sites, 36 

### little or no runoff occurs from small, frequently o ccurring storms, and such storms account for a 37 

### large proportion of the annual precipitation volume . When development occurs, the hydrologic 38 

### balance of the site is disturbed and as a result ru noff occurs from both small and large storms. 39 

### There is an increase in the number of runoff events , and an increase in the runoff volume, 403/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 39 

### duration, rate, and temperature. Receiving water de gradation and habitat loss occur from this 1 

### changed hydrologic regime. 2 

### Table 3-1 contains representative 95 th 

### percentile storm event volumes in inches from sele cted 3 

### U.S. cities. Figure 3-10 contains a plot representi ng storm event frequency for Washington, DC. 4 

### In Figure 3-10, the 95 th 

### percentile storm event has been identified and is approximately 1.5 5 

### inches. 6

Calculating the 95 th Percentile Rainfall Event 7 

### This document’s appendix 2 contains information on how to calculate the 95 th 

### percentile rainfall 8 

### event for a specific area. A long-term record of da ily rainfall amounts (ideally, at least 30 years) 9 

### is needed to calculate the 95 th 

### percentile rainfall. 10 

### Designers opting to use Option 1 would need to do t he following: 11
1. 

### Calculate or verify the precipitation amount from t he 95 th 

### percentile storm event (that 12 

### number would be typically expressed in inches, e.g. , 1.5 inches) 13
2. 

### Employ on-site stormwater management controls to th e METF that infiltrate, 14 

### evapotranspire, or harvest and use the appropriate design volume 153/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 40 Table 3-1. Example 95 th percentile storm events for select U.S. cities 1

City 95 th percentile event rainfall total (in) City 95 th percentile event rainfall total (in) Atlanta, GA 1.8 Kansas City, MO 1.7 Baltimore, MD 1.6 Knoxville, TN 1.5 Boston, MA 1.5 Louisville, KY 1.5 Buffalo, NY 1.1 Minneapolis, MN 1.4 Burlington, VT 1.1 New York, NY 1.7 Charleston, WV 1.2 Salt Lake City, UT 0.8 Coeur D’Alene, ID 0.7 Phoenix, AZ 1.0 Cincinnati, OH 1.5 Portland, OR 1.0 Columbus, OH 1.3 Seattle, WA 1.6 Concord, NH 1.3 Washington, DC 1.5 Denver, CO 1.1 Adapted adapted from Hirschman and Kosco 2008 2

3 Figure 3-10. Rainfall frequency spectrum showing th e 95 th percentile rainfall event for Washington, 4 DC (Reagan National Airport ~1.5 inches) 53/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 41 

### • The 95 th 

### percentile event can be calculated by using the fo llowing procedures below 1 

### (summarized from Hirschman and Kosco. 2008. Managing Stormwater in Your 2 

### Community: A Guide for Building an Effective Post-C onstruction Program, Center for 3 

### Watershed Protection):Obtain a long-term rainfall r ecord from a nearby weather station 4 

### (daily precipitation is fine, but try to obtain at least 30 years of daily record). Long-term 5 

### rainfall records can be obtained from many sources, including NOAA at 6 

### www.nesdis.noaa.gov 7



### • Remove from the data set all data for small rainfal l events that are 0.1 inch or less and 8 

### snowfall events that do not immediately melt. Such events should be deleted because they 9 

### do not typically cause runoff and could cause the a nalyses of the 95 th 

### percentile storm 10 

### runoff volume to be inaccurate. 11



### • Use a spreadsheet or simple statistical package to sort the rainfall events from highest to 12 

### lowest. In the next column, calculate the percentag e of rainfall events that are less than 13 

### each ranked event (event number / total number of e vents). For example, if there were 14 

### 1,000 rainfall events and the highest rainfall even t was a 4-inch event, 999 events are less 15 

### than the 4-inch rainfall event (or a percentile of 999 / 1,000, or 99.9 percent). 16



### • Use the rainfall event at 95 percent as the 95 th 

### percentile storm event. 17

Option 2: Site-Specific Hydrologic Analysis 18 

### Under Option 2, the predevelopment hydrology would be determined on the basis of site-specific 19 

### conditions and local meteorology by using continuou s simulation modeling techniques, 20 

### published data, studies, or other established tools . The designer would then identify the 21 

### predevelopment condition of the site and quantify t hat the post-development runoff volume and 22 

### peak flow discharges are equivalent to predevelopme nt conditions. The post-construction rate, 23 

### volume, duration and temperature of runoff should must not exceed the predevelopment 24 

### conditions rates , and the predevelopment hydrology should be replic ated through site design and 25 

### other appropriate practices to the METF. Additional discussions of appropriate methodologies to 26 

### use in assessing site hydrology have been included in this document’s appendix 2

. 27 

### The predevelopment hydrologic condition of the site is the combination of runoff, infiltration, 28 

### and evapotranspiration rates and volumes that typic ally existed on the facility site before 29 

### development

on a greenfields site (meaning any construction of infrastructure on undeveloped 30 

### land such as meadows or forests). In practice, dete rmining the predevelopment hydrology of a 31 

### site can be difficult if no suitable reference site is available. As a result, reference conditions fo r 32 

### typical land cover types in the locality often are used to approximate what fraction of the 33 

### precipitation ran off, soaked into the ground, or w as evaporated from the landscape. Using 34 

### reference conditions can be problematic if suitable data are not available or unique site 35 

### conditions exist that do not fit within a typical l and use cover type for the area, e.g., meadow or 36 

### forest. The intent is not to restore the site to pr e-Columbian conditions but to develop or 37 

### redevelop the site to ensure that a stable hydrolog ic regime is in place to protect groundwater, 38 

### surface water, and receiving stream channel stabili ty. 39 

### For redevelopment sites, existing site conditions a nd uses of the site can influence the amount of 40 

### runoff that can be managed on-site through infiltra tion, evapotranspiration, and harvest and use 41 

### and, thus, affect the achievement of the performanc e design objective. In the context of some 423/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 42 

### redevelopment projects, fully restoring predevelopm ent hydrology can be difficult to achieve. In 1 

### such cases, EPA recommends using a systematic analy sis to determine what practices can be 2 

### implemented. The Technical Guidance on Implementing the Stormwater R unoff Requirements 3 

### for Federal Projects under Section 438 of the Energ y Independence and Security Act, EPA 841- 4 B-09-001 

### , December 2009, (http://www.epa.gov/owow/nps/lid/section438) provides 5 

### methodology for federal facilities in determining M ETF. Examples of conditions that could 6 

### prevent a fully restored predevelopment hydrology a re a combination of the following: 7



### • The 1) t he presence of shallow bedrock; 2) contaminated soils, near-surface groundwater; 8


### or 3) other factors such as underground facilities or uti lities. 9



### • The design of the site precludes the use of soil am endments, plantings of vegetation or 10 

### other designs that can be used to infiltrate and ev apotranspirate runoff. 11



### • Water harvesting and reuse are not practical or pos sible because the volume of water used 12 

### for irrigation, toilet flushing, industrial make-up water, wash-waters, and the like, is not 13 

### significant enough to warrant designing and using w ater harvesting and reuse systems 14



### • Modifications to an existing building to manage sto rmwater are not feasible because of 15 

### structural or plumbing constraints or other factors as identified by the facility 16 

### owner/operator. 17



### • Small project sites where the lot is too small to a ccommodate infiltration practices 18 

### adequately sized to infiltrate the volume of runoff from impervious surfaces. 19



### • Soils that cannot be sufficiently amended to provid e for the requisite infiltration rates. 20



### • Situations where site use is inconsistent with the capture and reuse of stormwater or other 21 

### physical conditions on-site that preclude the use o f plants for evapotranspiration or 22 

### bioinfiltration. 23



### • Retention or use of stormwater on-site or discharge of stormwater on-site via infiltration 24 

### has a significant adverse effect on the site or the downgradient water balance of surface 25 

### waters, groundwaters or receiving watershed ecologi cal processes. 26



### • State and local requirements or permit requirements that prohibit water collection or 27 

### make it technically infeasible to use certain green infrastructure/LID techniques. 28



### • Retention or use of stormwater on the site would ca use an adverse water balance to either 29 

### or both the receiving surface waterbody or groundwa ter. 30

31 

### In cases where a technical infeasibility exists tha t precludes full implementation of the 32 

### performance design goal, stormwater practices to in filtrate, evapotranspire, or harvest and use 33 

### on-site the maximum amount of stormwater technicall y feasible should be implemented. 343/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 43 

## 2. 3 Use Planning

2 Select

Approaches to Achieve Performance 1 

## Goals Based on Scale of Implementation and Development 2 

## Techniques 3


## Site

- Specific Conditions 4



### 2. 3 2 .1 The Impacts of Land Use on Hydrology and Geomorp hology 5 

### An evaluation of the land use and hydrology/geomorp hology of a watershed or site is an 6 

### important first step in designing to maintain or re store predevelopment hydrology and mitigate 7 

### pollutant loading. 8 

### One of the key strategies to reduce runoff is to ch ange the pattern of land development to one 9 

### that is less destructive to water quality. Land use is the largest driver of changes in stormwater 10 

### runoff, and developed and urbanized lands contribut e the largest volumes of increased runoff. 11 

### The progression of development has led to the incre ased urbanization of the population. The 12 

### urbanization of land, however, has outpaced the urb anization of the population, indicative of 13 

### sprawl -type development. Between 1975 and 1995 the amount of urbanized land more than 14 

### doubled in the Baltimore-Washington Metropolitan ar ea. That trend has been witnessed 15 

### nationally. Table 3-2 shows how land development in the United States outpaced population 16 

### growth from 1970 to 1990. 17

Table 3-2. A comparison of population growth rates of U.S. cities versus 18 corresponding 19 urbanized land growth rates shows the pattern of gr owth 20 Sprawl, 1970—1990 (NRC 2008) 21 % Increase city population Average % increase in city urbanized land < 10% 38% 11%–30% 54% 31%–50% 72% > 50% 112%
22 

### These urbanization patterns have significant effect s on land use as the predeveloped conditions 23 

### of forests, meadows, and agricultural lands are rep laced by hardened landscapes. Impervious 24 

### surfaces, such as roads and roofs are the predomina te land cover in urban areas. For example 25



### • Roads and parking lots are as much as 70 percent of total impervious cover in ultra-urban 26 

### areas (National Research Council 2008) 27



### • Roads tend to capture and export more stormwater po llutants than other land covers in 28 

### highly impervious areas, especially for small rainf all events (National Research Council 29 

### 2008) 30 

### Even urban land cover that is not hardscape does no t infiltrate rainfall as it would before 31 

### development. Urban soils have much higher bulk dens ity (the mass of dry soil divided by its 32 

### volume, which serves as a predictor of porosity) th an undisturbed soils because of soil 333/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 44 

### compaction typical of construction practices and ur ban uses. As shown in Table 3-3 the bulk 1 

### density of urban soils is closer to concrete than t o undisturbed soils. The ability of soils with such 2 

### levels of compaction to infiltrate and retain storm water is greatly diminished and results in 3 

### greater quantities of runoff. The lack of an absorp tive humus layer, and active soil biota, can also 4 

### play a role in reducing infiltration rates. 5 

### As a result of such compaction, the runoff from urb an soils often resembles that of impervious 6 

### surfaces, especially for larger storm events. 7

Table 3-3. Bulk Density of Urban Soils is Closer to Concrete than to 8 Undisturbed Soils (Schueler and Holland 2000) 9

Material Bulk density (grams per cubic centimeter) Undisturbed Soil 1.1 to 1.4 Urban Lawn 1.5 to 1.9 Fill Soil 1.8 to 2.0 Soil Adjacent to Buildings and Roadways 1.5 to 2.1 Concrete 2.2 Source: Schueler and Holland 2000 10 

### An understanding of such effects is essential to ef fectively mitigate them. Watershed and site 11 

### assessments enable a better understanding of the fa ctors contributing to hydromodification, so 12 

### that appropriate mitigation techniques can be selec ted. The site assessment process should 13 

### evaluate the hydrology, topography, soils, vegetati on, and water features (i.e., wetlands, riparian 14 

### areas, and floodplains) to identify how stormwater moves through the site before development. 15 

### Additional information on the site assessment proce ss is provided in Section 3 of this document. 16 

### In addition, to protect stream channels from increa sed erosion, it is necessary to control the total 17 

### time—the duration—stream channels are subject to ge omorphically significant flows. The flows 18 

### can result in channel erosion caused by the additio nal energy imparted to the stream channel by 19 

### the increases in runoff velocities and volumes. The extended high flows typically lead to stream 20 

### channel destabilization because the stream did not evolve under those conditions and lacks the 21 

### capacity to dissipate this increased energy without scouring the stream bed. In response, both the 22 

### channel and banks are incised, creating increased s ediment transport. Those problems are 23 

### aggravated as the flow travels downstream, with oth er altered watersheds contributing their 24 

### increased volumes. 25 

### The traditional stormwater management approach was based on primarily on flood protection, 26 

### and often focused on not exceeding a predevelopment flow rate, but it did not take into account 27 

### additional volume. When there is greater volume to be discharged, the duration of the peak flow 28 

### rate is longer than under predevelopment condition. When multiple discharges of this type enter 29 

### a receiving stream, the flow peaks that once were s equential become additive, creating much 30 

### higher peak flows in the stream than existed in pre development conditions. The relationships 31 

### between hydrologic and geomorphic changes and biolo gical parameters can be analyzed using 32 

### protocols such as that laid out in WERF’s Protocols for Studying Wet Weather Impacts and 33 

### Urbanization Patterns (WERF 2008). 343/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 45 

### To achieve the goal of overall waterbody health, ot her jurisdictions have established various 1 

### performance objectives. The following are examples of state and local performance criteria 2 

### developed to address the goal of restoring or maint aining predevelopment hydrology: 3



### • Santa Clara Valley, California. The hydromodification control limits post-construct ion 4 

### runoff to pre-construction rates or durations. Perf ormance criteria to demonstrate 5 

### compliance include (1) the project must use stormwa ter controls to maintain pre6 

### construction stream erosion potential and (2) post- construction stormwater discharge 7 

### rates and flow durations must be equivalent to pre- construction values for flows from 8 

### 10 10 percent of the 2-year peak flow up to the full, 10- year peak flow (Santa Clara 9 

### Valley 2005). 10



### • Western Washington. Stormwater discharges must match developed dischar ge durations 11 

### to predeveloped durations for the range of predevel oped discharge rates from 50 percent 12 

### of the 2-year peak flow up to the full, 50-year pea k flow (Western Washington 13 

### Stormwater Management Manual 2005). 14

• 

### Coastal areas of North Carolina

. A ny development over 12 percent imperious must 15 

### control approximately 3.6 inches of rainfal l, or the one

- year, 24

- hour storm, if the project 16 

### is within a half mile of shellfishing waters. For areas outside the boundary, the trigger for 17 

### stormwater controls is 25 percent impervious with a requirement to control 1.5 inches of 18 

### rainfall. 19



### 2.3 .2 Use Appropriate Designs as Part of a Comprehensive Watershed 20 

### Plan 21 

### This section contains an overview of example strate gies, policies, and practices that land 22 

### managers on different scales (federal, state, local ) have used to reduce the effects of development 23 

### and redevelopment on receiving water hydrology. Sec tion 3 contains a description of strategies 24 

### and practices that can be used to protect water qua lity and reduce pollutant loading from 25 

### developed areas. 26 

### The strategies and approaches used to achieve a com munity’s hydrologic stormwater goals will 27 

### depend on the scale at which the approach is be app lied—regional, local jurisdiction, watershed, 28 

### subdivision/facility campus, building lot. Issues a nd potential tools for different scales of 29 

### implementation are provided in Table 3-4. 30 

### Such strategies should be included as part of a com prehensive watershed plan to protect the 31 

### resources in the watershed and downstream. Developm ent approaches should be viewed across a 32 

### watershed or region, down to the local scale, to he lp achieve communities’ desired goals for 33 

### water resources while avoiding unintended consequen ces, such as flooding or inadequate base 34 

### stream flow. Comprehensive planning is an effective nonstructural tool to reduce the amount of 35 

### impervious surface in a watershed and to guide futu re development in a manner that best protects 36 

### water quality. Resources for preparing watershed pl ans are provided in Table 3-5. 37

Table 3-4: Strategies and tools for implementing st ormwater protection goals at different scales 38

Scale Example strategies at different scales Example programs and initiatives3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 46 Scale Example strategies at

different scales Example programs and initiatives National Association of Regional Councils Promotes information exchange to help regional orga nizations achieve goals. National

EPA’s Green Infrastructure

and LID websites, U.S. Department of Defense LID Policy Provide national-level guidance

Regional Commissions facilitate cooperation (such as similar ordinances for development equity) and leverage funds for outreach, etc. Northern Virginia Regional Commission: Example prog ram www.onlyrain.org. Washington Metropolitan Council of Governments: Exa mple Symposium—Innovative Stormwater Controls on Roads & Highways, November 2009
Interstate, multijurisdictional partnerships Chesapeake Bay Program: state, federal, academic an d nonprofit partnership. www.chesapeakebay.net/partnerorganizations.aspx Public-Private Partnerships (any scale) The Healthy Lawn and Clean Water Initiative, Chesapeake Bay Executive Council and the fertilizer industry a gree on voluntary P phosphorus reductions in fertilizer http://archive.chesapeakebay.net/pubs/Lawn_Care_MOU .pdf The Growing Home Campaign. Provides incentives for homeowners to increase urban canopy with cost share d by landscape industry. www.baltimorecountymd.gov/Agencies/environment/grow inghome Regional

University-Public-Private

Partnerships Designing and monitoring pilot or demonstration fac ilities. Outreach with university and extension programs. Stormwater programs at Villanova, University of Mar yland, and North Carolina State University working together in partnership Ordinances that allow LID, fees to enable programs, fines, technical assistance D.C.’s Impervious Area Fee Spotsylvania, Virginia, Ordinance Lycoming County, Pennsylvania (Draft), prepared und er PA Act 167 Smart Growth policies Baltimore County, Maryland, designates land managem ent areas; www.baltimorecountymd.gov/Agencies/planning/ masterplanning/smartgrowth.html%20 The Philadelphia Green program revitalizes and maintain abandoned land and public spaces by partnering with government, businesses, and the community Local Jurisdiction

Green Street policies The Port Towns’ (Maryland) 2010 Legislative Priorit ies include Fund at least one Green Street in each of the Port Towns

. http://porttowns.org Watershed Urban Pollutant trading a :

Support development of program a ,b Region states are evaluating programs c . EPA Region 3 is evaluating the use of urban stormwater trading for the Chesapeake Bay. Virginia Soil and Water Conservation Board Guidance Document on Stormwater Nonpoint Nutrient Offsets, A pproved July 23, 2009. http://townhall.virginia.gov/L/GDocs.cfm3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 47 Scale Example strategies at

different scales Example programs and initiatives Use watershed-scale hydraulic and pollutant models to optimize control type and location Models such as BMP-DSS (BMP Decision Support System ) have been used in Maryland as planning tools

Inter-jurisdictional cooperation for purposes of load management and TMDL application Chesapeake Bay Program

Local Watershed Groups where Volunteers lead projects; form or engage EPA’s Watershed Central provides blog and information: http://wiki.epa.gov/watershed/index.php Anne Arundel County, Maryland Master Watershed Stew ards Academy Fee-in-lieu or off-site mitigation when compliance on-site is not feasible Washington, DC, Proposed Off-Site Stormwater Mitiga tion Fee

Total Maximum Daily Load (TMDL) provides framework for prioritizing efforts Restoring the Legendary Lynnhaven Oysters: Coordinated Actions Lower Bacteria Levels and Reope n Shellfish Areas in the Lynnhaven River Watershed, www.epa.gov/owow/TMDL/tmdlsatwork/pdf/lynnhaven_riv er_s ound_byte.pdf; and www.epa.gov/owow/nps/Success319/state/va_3bays.htm Subdivision or facility campus Smart Growth, Conservation

Development Arlington, Virginia’s MetroRail Corridor Lancaster County, Pennsylvania Downtown Silver Spring, Maryland Sussex County, Delaware Building Lot LID Practices Design guides for LID prepared by federal, state, a nd, local entities
Notes 1 a. Lal, Harbans, Nutrient Credit Trading: A Market-based Approach fo r Improving Water Quality 2 NTSC/NRCS/USDA; www.wsi.nrcs.usda.gov/products/w2q/mkt_based/docs/n itrogen_credit_trading.pdf 3
b. EPA. 2003 Fact Sheet: Water Quality Trading Policy

. www.epa.gov/owow/watershed/trading/2003factsheet.pd f; 4 and Water Quality Trading Policy , www.epa.gov/owow/watershed/trading/finalpolicy2003 .pdf 5 c. Chesapeake Bay Foundation, Facts About Nutrient Trading from the Chesapeake Ba y Foundation, 6 www.cbf.org/Document.Doc?id=141 7

Table 3-5. Resources for preparing watershed plans 8 Reference Information provided National Management Measures to Control Nonpoint Source Pollution from Urban Areas. EPA-841-B-05-004. USEPA 2005. Provides overview of elements in developing and implementing watershed protection plans
Handbook for Developing Watershed Plans to Restore and Protect our Waters. EPA 841B-08- 002. USEPA 2008. Describes processes and tools used to quantify existing pollutant loads, develop estimates of load reductions needed, identify appropriate management measures, and track progress 93/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 48 

### The strategy selected for protecting and restoring watershed hydrology depends on the existing 1 

### condition of the landscape: new development strateg ies have a different focus than retrofit 2 

### activities in an existing urban landscape. Where re development or infill development occurs, 3 

### measures and practices to restore the predevelopmen t hydrology should be used, but because that 4 

### will likely be constrained by existing development features, a different suite of approaches might 5 

### be more suitable than those recommended for new dev elopment. 6



### 2.3. 3 1 New Development and Redevelopment Strategies : Smart Growth, 7 

### Conservatio n Design, and LID 8 

### The objective in new development is preventing addi tional runoff, pollutant loading, and the 9 

### corresponding degradation in the watershed. Control measures focus first on Smart Growth, 10 

### Conservation Design, and the use of LID practices. 11

Development Planning Techniques such as Smart Growt h 12 

### New development creates extensive areas of impervio us cover, and increased runoff volumes. 13 

### The developments are necessarily supported by addit ional roads and other associated 14 

### infrastructure, compounding the effects. Communitie s should consider the cumulative impact of 15 

### large scale development, including the loss of natu ral areas and degraded streams and rivers. 16 

### Decisions about where and how to develop affect wat er quality perhaps more than any other 17 

### factor. Preserving and restoring natural landscape features (such as forests, floodplains, and 18 

### wetlands) is an integral part of green infrastructu re. Efficient land use such as redevelopment of 19 

### already degraded sites can also serve to protect ec ologically sensitive areas from development. 20 

### Underused shopping centers or excess parking lot ar ea can be targeted for development cost 21 

### effectively when considering that the supporting in frastructure is likely already in place. 22 

### Development planning techniques such as Smart Growt h should be used to accomplish the 23 

### multiple goals of sound community development with minimum detrimental effects on water 24 

### quality. Sound principles of both smart growth and water quality protection can achieved by a 25 

### using these approaches for new development, redevel opment, and retrofit. To achieve the 26 

### common goals of smart growth and water quality prot ection, new development should be within 27 

### or adjacent to existing development when possible. Examples of guidance to be used in planning 28 

### development are provided in Table 3-6. Those docume nts also contain information on the water 29 

### quality benefits that the pollution-avoidance strat egies provide. 30

Table 3-6. Existing guidance on smart growth approa ches 31 Document Highlights Using Smart Growth Techniques as Stormwater Best Management Practices
, www.epa.gov/dced/stormwater.htm Detail policies and techniques that are integral non-structural stormwater practices
Smart Growth for Clean Water: Helping Communities Address the Water Quality Impacts of Sprawl , National Association of Local Governmental Environmental Professionals, Trust for Public Land, ERG www.nalgep.org/publications/PublicationsDetail.cfm? Li Identifies approaches that can improve water quality, profiles successful local partnerships, and identifies barriers and solutions to implement smart growth for clean water programs.3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 49 nkAdvID=42157 Protecting Water Resources with Higher-Density Development, www.epa.gov/dced/water_density.htm Provides research and example scenarios of how higher densities may better protect water quality—especially at the lot and watershed levels. Water Quality Scorecard: Incorporating Green Infrastructure Practices at the Municipal, Neighborhood, and Site Scales www.epa.gov/dced/water_scorecard.htm Provides policy guidance and case studies for protecting open space, promoting infill, designing better streets and parking lots, and adopting site-level green infrastructure practices.
1 

### The Smart Growth Network has established the 10 pri mary principles of Smart Growth, which 2 

### are listed in Figure 3-11. Many of these principles indirectly mitigate the impacts of growth on 3 

### water resources, but the three listed in bold font, in particular, can be used to reduce or avoid the 4 

### stormwater related impacts of both new development and redevelopment. 5

• Create Range of Housing Opportunities and Choices : Providing quality housing for people of all

income levels is an integral component in any smart growth strategy.

• Create Walkable Neighborhoods : Walkable communities are desirable places to live , work, learn, worship, and play and, therefore, are a key compone nt of smart growth.

• Encourage Community and Stakeholder Collaboration : Growth can create great places to live, work and play—if it responds to a community’s own sense of how and where it wants to grow.

• Foster Distinctive, Attractive Communities with a S trong Sense of Place : Smart growth encourages communities to craft a vision and set standards for development and construction that respond to community values of architectural beauty and distin ctiveness, as well as expanded choices in housing and transportation.

• Make Development Decisions Predictable, Fair and Co st Effective : For a community to be successful in implementing smart growth, the private sector mu st embrace it.

• Mix Land Uses : Smart growth supports the integration of mixed la nd uses into communities as a critical component of achieving better places to li ve.

• Preserve Open Space, Farmland, Natural Beauty and C ritical Environmental Areas : Open space preservation supports smart growth goals by bolster ing local economies, preserving critical environmental areas, improving our communities qual ity of life, and guiding new growth into existing communities.

• Provide a Variety of Transportation Choices : Providing people with more choices in housing, shopping, communities, and transportation is a key aim of smart growth.

• Strengthen and Direct Development Toward Existing C ommunities : Smart growth directs development toward existing communities already ser ved by infrastructure, seeking to use the resources that existing neighborhoods offer, and co nserve open space and irreplaceable natural resources on the urban fringe.

• Take Advantage of Compact Building Design : Smart growth provides a means for communities to incorporate more compact building design as an alte rnative to conventional, land-consumptive development.
Source: The Smart Growth Network: www.smartgrowth.org/about/principles/default.asp?re s=1024#top 6 Figure 3-11. The 10 primary principles of smart gro wth 73/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 50 

### The primary smart growth principles that can be use d to reduce the hydrological impacts of 1 

### development and redevelopment activities are as fol lows: 2



### • Conserve Undeveloped Land to preserving critical environmental areas. This ma intains 3 

### natural riparian buffers, floodplains, natural drai nage ways, predevelopment hydrology, 4 

### and watershed functions. Protecting natural areas s uch as forests, grasslands, and 5 

### wetlands, and other open spaces that serve to filte r, infiltrate, and evapotranspirate 6 

### rainfall and snowmelt help maintain the stability o f the watershed. 7



### • Use Compact Site Design to reduce the extent of land disturbance, minimize 8 

### infrastructure requirements to service the communit y, and reduce the overall impervious 9 

### footprint (also see Conservation Design below). 10



### • Direct Development to Existing Communities and Infr astructure to reduce the 11 

### development of greenfields. This makes use of exist ing transportation networks, and 12 

### reduces sprawl and the addition of new impervious s urfaces. Redevelopment of existing 13 

### communities and Brownfields can result in positive water quality impacts and limits the 14 

### changes in land cover in undeveloped areas that res ult in stormwater volume increases 15 

### (Refer to Redevelopment Management Sector for addit ional detail). 16



## 2.4 Use Conservation Design and LID Techniques 17 

### While planning techniques such as smart growth focu s on where to locate development and 18 

### redevelopment, techniques such as conservation desi gn promote the best practices to mitigate the 19 

### impacts of properly sited development. The design g oal is to mitigate the overall hydrologic 20 

### modifications by protection of natural areas and ec osystem functions. Conservation design 21 

### methods include (City of Portland 2004) : 22



### • Fitting development to the terrain to minimize land disturbance 23



### • Confining construction activities to the least area necessary and away from critical areas 24



### • Preserving areas with natural vegetation (especiall y forested areas) as much as possible 25



### • On sites with a mix of soil types, locating impervi ous areas over less permeable soil (e.g., 26 

### till), and trying to restrict development over more porous soils (e.g., outwash) 27



### • Clustering buildings together 28



### • Minimizing impervious areas 29



### • Maintaining and using the natural drainage patterns 30 

### Existing guidance on Conservation Design is provide d in Table 3-7 31 

### Implementing these methods often requires an evalua tion of institutional issues that influence 32 

### growth and development. Using policies requiring co mpacting development, conserving 33 

### open space, and protecting environmental assets is often impeded by zoning requirements 34 

### (Arendt 1999). When considering using conservation design policies to protect water 35 

### resources, the following zoning issues should exami ned both to determine if existing policies 36 

### are promoting sprawl and to identify impediments th at could preclude adoption or 37 

### implementation of more environmentally sound design s. 383/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 51 Table 3-7. Existing guidance on conservation design approaches 1 Document Highlights Conservation Design for Stormwater Management: A De sign Approach To Reduce Stormwater Impacts from Land Dev elopment and Achieve Multiple Objectives, Delaware Departmen t of Natural Resources and Environmental Control and The Environ mental Management Center of the Brandywine Conservancy, 19 97 www.dnrec.state.de.us/DNREC2000/Divisions/Soil/Stor mwater/New/D elaware_CD_Manual.pdf Approaches, design procedures, and case studies.

Randall Arendt, Growing Greener: Putting Conservati on into Local Plans and Ordinances, National Lands Trust-American Planning Association-American Society of Landscape Architect s, 1999. Evaluates the regulatory and zoning issues for implementing conservation design strategies Site Planning for Urban Stream Protection, Tom Schu eler/ Metropolitan Washington Council of Governments, 199 5, www.mwcog.org/store/item.asp?PUBLICATION_ID=56 Reduce pollutants and protect aquatic resources through improved construction site planning. Center for Watershed Protection www.cwp.org/Resource_Library/Better_Site_Design/ind ex.htm Library of References

2



### • Separate Lot Size from Density. Avoid specifying minimum lot sizes, where 3 

### appropriate, because it can promote sprawl and disp ersed development patterns, thereby 4 

### leading to increased impervious surfaces. Instead, consider specifying the maximum 5 

### number of dwellings permitted on the buildable acre age involved or the maximum 6 

### buildable acres on a given size parcel to promote c luster development and common, 7 

### undivided conservation land

. 8



### • Account for Environmental Constraints in Density Ca lculations. Land that is 9 

### unbuildable because of environmental constraints sh ould be discounted from the total 10 

### land area used in density calculations. Including o nly usable land as the basis for density 11 

### calculations ensures that intended densities are me t and not skewed when developments 12 

### satisfy set-aside provisions with inherently unbuil dable land. 13



### • Establish Minimum Permitted Lot Sizes. The amount of land conserved through 14 

### subdivisions is directly related to the permitted d ifference between maximum density and 15 

### the minimum lot size. For example, in a one-acre di strict where the minimum permitted 16 

### lot size is one-half acre of unconstrained land, th e remaining unconstrained land plus the 17 

### constrained land would compose the open space. 18



### • Design Complete, Smart Streets that Minimize Imperv iousness. Street design 19 

### standards and engineering practices should encourag e streets to be no wider than is 20 

### necessary to move traffic (cars, pedestrians, bicyc les, as is appropriate for the 21 

### community) effectively. Shared driveways, reduced d riveway widths, two-track 22 

### driveways, and rear garages and alleys should be en couraged for all single-family 23 

### developments to reduce total impervious area. Encou rage designers to use alternative 24 

### designs that reduce curb and gutter, or allow curb cuts to enable street drainage into 25 

### swales or bioretention. 26



### • Encourage Efficient Provision of Parking. Alternative and flexible parking 27 

### requirements (shared parking, off-site parking, etc ) should be allowed to reduce parking 283/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 52 

### surface area and flexibility and incentives should be provided to developers to induce a 1 

### reduction in parking area. 2



### • Minimize Frontages and Setbacks. Reducing frontages and setbacks conserves land, 3 

### reduces impervious surfaces, and helps to promote t he creation of more walkable 4 

### neighborhoods by bringing buildings closer together to walkable distances. 5



### • Establish Minimum Required Open Space. Minimum requirements for open space 6 

### help to promote conservation designs, reduce imperv ious surface area, and can help 7 

### enhance the quality and the total amount of land to be preserved. 8

Green Infrastructure/LID Practices 9 

### LID is a term used to describe land planning and en gineering strategies that are used to manage 10 

### stormwater or runoff to preserve or restore the pre development hydrologic condition of the site 11 

### or development. When LID practices are implemented on a site, significantly less runoff occurs; 12 

### therefore, pollutant loading is reduced. 13 

### A primary goal is the protection or restoration of water quality and aquatic habitat. EPA and 14 

### others also refer to LID as green infrastructure fo r wet-weather control. Many design guides have 15 

### been developed that provide detailed design informa tion on LID practices. Several of those are 16 

### listed in the appendix 1 as design tools. The recognized initial leading pub lication is Low-impact 17 

### Development Strategies, An Integrated Design Approa ch, by Prince George’s County, Maryland, 18 

### and EPA, Document Number EPA 841-B-00-003, June 199 9. 19 

### This approach uses engineered, small-scale hydrolog ic controls or practices distributed across, 20 

### and integrated with, the site or development. A gre en infrastructure/LID design functions to 21 

### replicate the natural hydrology through storage, de tention, infiltration, evapotranspiration, or 22 

### harvest and use. The objectives are to reduce runof f volume, attenuate peak runoff rates, or filter 23 

### and remove pollutants from runoff. By incorporating controls specifically into upland areas, 24 

### effects on wetlands and other sensitive areas can b e reduced or eliminated. 25 

### Many types of LID practices exist, with many variat ions of each practice. Projects are most 26 

### successful when practitioners integrate them into a site design and use them in a treatment train 27 

### approach. In such an approach, the overflow from on e practice flows into a second or third 28 

### practice, such as a green roof followed by a cister n, with the overflow to a planter box with its 29 

### own overflow and underdrain. Site conditions, appli cable performance requirements, and cost 30 

### typically influence the selection of appropriate LI D practices. Table 3-8 lists some of the major 31 

### types of practices, and a fact sheet or link for ea ch is provided in Section 6 5

. 32

Table 3-8. Typical LID practices (Fact s heets, or links to fact sheets, 33 are provided in Section 5) 34 LID BMPs for site plans

Alternative Turnarounds a Bioretention/Bio

infiltration Permeable Pavement and Pavers

Rainwater Harvesting Conservation Easements a Infiltration Trenches and Basins Development Districts a Blue Roofs with Water Eliminating Curbs and Gutters a Green Roofs (Eco3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 53 H arvesting roofs) Green Design Strategies a Infrastructure Planning a Narrower Residential Streets a Open Space Design a Protection of Natural Features a Riparian/Forested Buffer a Street Design and Patterns a Urban Forestry a,b Site Scale LID Practices Bioretention (Rain Gardens) a,b Rainwater Harvesting b Green Roofs (Eco roofs) a,b Blue Roofs with Water Harvesting b Green Parking a Grassed Swales a Infiltration Trench a Infiltration Basin a Permeable Interlocking Concrete Pavement a Pervious Concrete Pavement a Porous Asphalt Pavement a Vegetated Filter Strip a Soil restoration b Constructed wetlands b Compost Blankets a
Notes 1 a. Fact sheet provided at 2 http://cfpub.epa.gov/npdes/stormwater/menuofbmps/in dex.cfm?action=min_measure&min_measure_id=5 3 b. Fact sheet provided in Section 6 of this chapter 4 

### The performance of LID practices in reducing the an nual volume of runoff varies significantly 5 

### according to the specific design of the practice an d the regional climate. Depending on the site 6 

### design and area rainfall patterns, runoff can be ca n be maintained at predevelopment conditions 7 

### by careful site planning and design. Several design guides have been developed that detail the 8 

### procedures for site analysis and LID practice sizin g. Some of the best design guides for LID are 9 

### provided in Table 3-9. Additional resources are lis ted in the appendix 1 and in the fact sheets in 10 

### Section 6

. 11

Table 3-9. Example nationally applicable LID design methods and manuals 12 Prince George’s County, Maryland, Low-Impact Development Design Strategies: An Integr ated Design Approach , EPA 841-B-00-003, 2000. Prince George’s County, Maryland, Low-Impact Development Hydrologic Analysis , EPA 841-B-00-002, 2000. www.epa.gov/nps/lid/ USEPA, Stormwater Best Management Practices Design Guide , Office of Research and Development, EPA/600/R-04/121, Volumes 1-3 (121, 121A, 121B), Se ptember 2004. http://www.epa.gov/nrmrl/pubs/600r04121/600r04121.h tm Center for Watershed Protection Urban Subwatershed Restoration Manual Series ( http://www.cwp.org/Store/usrm.htm ) Center for Watershed Protection Managing Stormwater in Your Community: A Guide for Building an Effective Post-Construction Program ( http://www.cwp.org/Resource_Library/Center_Docs/SW/ pcguidance/Manual/ PostConstructionManual.pdf ) U.S. Naval Facilities Engineering Command, Low Impact Development, Draft, Unified Design Crite ria, UFC 3-210-10, October 2004. http://www.wbdg.org/ccb/DOD/UFC/ufc_3_210_10.pdf U.S. Army Corps of Engineers. Low Impact Development for Sustainable Installation s: Stormwater Design and Planning Guidance for Development within Army Training Areas . Public Works Technical Bulletin 200-1-62. October 2008.3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 54 Geosyntec Consultants and Wright Water Engineers. Urban Stormwater BMP Performance Monitoring

. 2009. http://www.bmpdatabase.org/MonitoringEval.htm The Low-Impact Development Center, http://www.lowimpactdevelopment.org/ ; several LID manuals 1 

### Specific to the Chesapeake Bay area, a literature r eview and assessment of the reported 2 

### performance of many LID practices was recently cond ucted for the region to estimate the 3 

### capability of the practices for volume control and pollutant reduction. The Mid-Atlantic Water 4 

### Program housed at the University of Maryland review ed and compiled effectiveness estimates 5 

### for BMPs implemented and reported by the Chesapeake Bay watershed jurisdictions ( Developing 6 

### Best Management Practice Definitions and Effectiven ess Estimates for Nitrogen, Phosphorus, 7 

### and Sediment in the Chesapeake Bay, December 2009 8 

### ( www.chesapeakebay.net/websitesearchresults.aspx?men uitem=19557 ). The report estimates 9 

### that the performance of the infiltration practices such as bioretention, as des igned and with safety 10 

### factor considerations, could reduce runoff from the first 1 - inch to 1.5 inch of runoff up to 80 11 

### percent, for the purposes of conservatively estimat ing wide-scale effectiveness in the region. 12 

### That equate s to about the 85 th 

### to 95 th 

### percentile storm event in the region. Additional information 13 

### on these findings are provided in Section 6.1.2 Performance estimate summaries for Infiltration 14 

### Practices, and in the Bioretention fact sheet in Section 6. 15 

### By using design procedures outlined in the LID manu als such as those in Table 3-9 and in 16 

### appendix 1 of this document , practices can achieve runoff reduction to restore or maintain 17 

### predevelopment hydrology. 18 

### The effectiveness of conservation design with LID i n reducing runoff is demonstrated in 19 

### subdivision-wide results recently reported. Sources for information on existing LID subdivisions 20 

### are provided in Table 3-10. 21

Table 3-10. Sources of information on existing LID subdivisions 22 Name, location, and reference Performance summary Meadow on the Hybelos, 8.27-acres Puget Sound area in Pierce County, Washington. www.sldtonline.com/content/view/344/75 2007 to 2008: LID subdivision designs performed better than design objectives, and exceeded the local requirement that post-development discharge volume not exceed predevelopment discharge volume. The researchers also reported that that underdrains significantly impair hydrologic performance (WERF 2009). Cross Plains, WI; Burnsville, MN; Somerset, MD: Jordon Cove, CT (ASCE/WERF/EPA International Stormwater BMP Database, Urban Stormwater BMP Performance Monitoring— Geosyntec Consultants and Wright Water Engineers 2009). www.bmpdatabase.org Annual runoff reductions from 40% to 90% over the monitoring period were observed, with significantly reduced performance when rain events occurred under already saturated conditions.

233/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 55 

## 2.5 Evaluate Codes and Ordinances 1 

### LID approaches and practices, smart growth and cons ervation development strategies can all be 2 

### hindered by existing codes and ordinances often bec ause of the lack of understanding of the 3 

### practices that in some cases differ from the tradit ional stormwater management approaches used 4 

### in land management. Resources that planners, munici pal officials, and designers can use to 5 

### evaluate codes and ordinances for revision to accom modate these approaches are provided in 6 

### Table 3-11. 7

Table 3-11. Resources for evaluating codes and ordi nances 8 Water Quality Scorecard: Incorporating Green Infrastructure Practices at the Municipal, Neighbor hood, and Site Scales
, www.epa.gov/dced/water_scorecard.htm%20%20 Provides policy guidance and case studies for protecting open space, promoting infill, designing better streets and parking lots, and adopting site-level green infrastructure practices. Out of the Gutter, National Resources Defense Counc il, July 2002 http://www.nrdc.org/water/pollution/gutter/gutter.p df NRDC recommends LID, for Washington, DC, including specific observation and recommendations for revisions to existing codes and ordinances. A Catalyst for Community Land Use Change , National NEMO Network 2008 Progress Report: http://nemonet.uconn.edu/about_network/publications /2 008_report.htm Examples of local regulations for water quality protection

Puget Sound Partnership Low Impact Development Local Regulation Assistance www.psp.wa.gov/Project Assistance to help local governments integrate LID into their development standards and regulations.

Better Site Design: A Handbook for Changing Development Rules in Your Community, Center for Watershed Protection, 1998 www.cwp.org/Store/bsd.htm Examples and case studies for changing development regulations to promote better site design, also referred to as environmentally sensitive design or LID Plan Review checklist and flow chart, Office of Watersheds, Philadelphia Water Department: www.phillyriverinfo.org/WICLibrary/%20DevelopmentPr ocess_Final.pdf Example of how to prioritize stormwater planning early in the overall plan review process for development projects.
Audit of Pavement Standards for the Saluda-Reedy Watershed, Mitigating the Impacts of Impervious Surfaces in Greenville and Pickens Counties, South Carolina, Saluda-Reedy Watershed Consortium c/o Upstate Forever, 2006. www.upstateforever.org Identifies opportunities for flexibility in street width, parking ratios, sidewalk and driveway, and other aspects of paving.

9 

### The following list contains the most common element s of local codes and ordinances that can 10 

### cause unnecessary construction of impervious surfac e areas (CWP 1998 Water Quality 11 

### Scorecard; USEPA 2009). Communities should carefully review ex isting policy mechanisms to 12 

### determine opportunities to revise codes and ordinan ces to reduce water resource effects that can 13 

### result from creating impervious surfaces: 143/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 56 

### • Zoning ordinances can be used to specify the type and intensity of la nd uses allowed on a 1 

### parcel. Some zoning ordinances are used to dictate single-use, low-density uses such as 2 

### residential. Dispersing low-density development acr oss the watershed can negatively 3 

### affect receiving waters by constructing significant ly more impervious surfaces. 4



### • Subdivision codes or ordinances can be used to specify development re quirements for a 5 

### parcel. Housing footprint minimums, setback distanc es from the street, road width, street 6 

### configuration, open space requirements, and lot siz e are all often specified in subdivision 7 

### codes and often inadvertently require constructing unnecessary impervious cover. 8



### • Street standards or road design guidelines are used to dictate the width of the road, 9 

### turning radius, street connectivity, and intersecti on design requirements. Communities 10 

### should review street and road standards to determin e if road designs can be changed to 11 

### reduce impervious surface cover and still meet tran sportation and safety requirements. 12



### • Parking requirements are generally set to the minimum, not the maximum, number of 13 

### parking spaces required for retail and office parki ng. Setting minimums often leads to 14 

### designing parking lots with enough peak demand peri ods, such as the day after 15 

### Thanksgiving, which can create acres of unused pave ment during the rest of the year. 16



### • Setbacks are used to define the required distance between a building and the right-of-way 17 

### or lot line. Many setback requirements specify the use of long driveways especially when 18 

### large lots are a requirement for development. Estab lishing maximum setback lines for 19 

### residential and retail developments can reduce the creation of unnecessary impervious 20 

### surface areas by bringing buildings closer to the s treet. 21



### • Height limitations are used to limit the number of floors in a buildin g. Limiting height 22 

### can spread development out if square footage is unm et by vertical density. 23



### • Open space or natural resource plans are used to identify land parcels that are or will be 24 

### set aside for recreation, habitat corridors, or pre servation. Such plans help communities 25 

### prioritize their conservation, parks, and recreatio n goals and protect important areas from 26 

### development. 27



### • Comprehensive plans might be required by state law, and many cities, to wns, and 28 

### counties prepare comprehensive plans to support zon ing codes. Most comprehensive 29 

### plans include elements that are intended to address land use, open space protection or 30 

### creation, natural resource protection, transportati on, economic development, and housing. 31 

### These elements are important facets of a comprehens ive watershed protection approach. 32 

### Increasingly, local governments are identifying are as of existing green infrastructure and 33 

### outlining opportunities to add new green infrastruc ture throughout the community to 34 

### protect water resources. 35


## 2.6 Evaluate Transportation-related Standards 36
Minimize/reduce impervious areas by using technique s such as reduced street widths 37 and parking areas 38 

### One direct method of addressing impervious area is to physically limit the size of the impervious 39 

### area. These strategies are most often applied when designing road widths and parking areas

. 40 

### Many urban and suburban streets are sized to meet c ode requirements for emergency service 413/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 57 

### vehicles, on-street parking, and free flow of traff ic. Such code requirements often result in streets 1 

### being oversized for their typical everyday function s. The Uniform Fire Code requires that streets 2 

### have a minimum 20 feet of unobstructed width; a str eet with parking on both sides would require 3 

### a width of at least 34 feet. In practice, many subu rban and urban streets can be much wider than 4 

### that as local design practices have increased stree t widths to 40 and 50 feet. Those designs result 5 

### in increased runoff and associated pollutant loadin gs. 6 

### Many communities have adopted narrower street width standards while also accommodating 7 

### emergency vehicles by developing alternative street -parking configurations, designing adequate 8 

### turnarounds, prohibiting parking near intersections , providing vehicle pullout space, and using 9 

### smaller block lengths. Examples are provided in Tab le 3-12. A key to identifying and 10 

### successfully codifying narrow street widths is coor dination among departments, including fire, 11 

### transportation, and public works. 12

Table 3-12. Examples of adopted narrow street width s 13

Jurisdiction Street width (feet) Parking condition Phoenix, AZ 28 parking both sides Santa Rosa, CA 30 26

– 28 20 20 parking both sides, < 1 , 000ADT

parking one side no parking neck downs @ intersection Orlando, FL 28 22 parking both sides, res. Lots < 55 feet wide

parking both sides, res. Lots > 55 feet wide Birmingham, MI 26 20 parking both sides

parking one side Howard County, MD 24 parking unregulated Kirkland, WA 12 20 24 28 alley

parking one side parking both sides—low-density only parking both sides Madison, WI 27 28 parking both sides, <3DU/AC

parking both sides, 3-10 DU/AC ADT: Average Daily Traffic; DU/AC: dwelling units p er acre Source: Adapted from Cohen 2000, and CWP 1998. http://www.stormwatercenter.net/Assorted%20Fact%20S heets/Tool4_Site_Design/narrow_streets.htm


### The same principles apply to parking areas. Zoning requirements often require that parking be 14 

### provided for the maximum business day, resulting in unused parking and impervious area for the 15 

### majority of the year. Reassessing the actual needed parking area can minimize impervious area. 16 

### Green street and highway design is necessary to hel p mitigate the effects of stormwater runoff 17 

### from those surfaces. A proven example of a green st reet is Seattle’s pilot Street Edge 18 

### Alternatives Project (SEA Streets), completed in 20 01. It is an LID design that provides drainage 19 

### that more closely mimics the natural landscape befo re development .Seattle Public Utilities 20 

### accomplished this by reducing impervious surfaces t o 11 percent less than a traditional street, by 213/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 58 

### providing surface detention in swales, and adding m ore than 100 evergreen trees and 1,100 1 

### shrubs. Monitoring shows that the design has succes sfully reduced the volume of stormwater 2 

### runoff by 99 percent. http://www.seattle.gov/util/About_SPU/Drainage_&_Se wer_System/ 3 

### GreenStormwaterInfrastructure/NaturalDrainageProjec ts/StreetEdgeAlternatives/index.htm

. 4


### Resources for additional information on street and highway design for LID is provided in 5 

### Table Table 3-13. 6

Table 3-13. Resources for information on street and highway design for LID 7 Document Highlights Green Highway Partnership (GHP), with weekly electronic newsletter, www.greenhighways.org Tracks practices for green highways and green infrastructure, including innovative storm water management, LID and transportation legislation. Project 25-20(01): Evaluation of Best Management Practices for Highway Runoff Control, Low Impact Development Highway Manual, National Cooperative Highway Research Program, http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rp t_56 5.pdf Provides scientific and economic information for selection and design of best management practices (BMPs) to control highway runoff, including BMPs to treat: nutrients, TPH, PAH, metals, pathogens, pesticides, temperature, TSS, trash Anacostia Waterfront Transportation Architecture Design Standards http://ddot.dc.gov/ddot/cwp/view,a,1249,q,627063,dd otN av_GID,1744,ddotNav,|33960|.asp Guidelines for transportation design to support the economic and environmental health of the region, incorporating LID design practices.
Portland Green Street Program , Portland, Oregon, Bureau of Environmental Services (BES) www.portlandonline.com/BES/index.cfm?c=44407 Design information, project reports, technical guides, newsletter

Tabor to the River, Portland BES www.portlandonline.com/bes/index.cfm?c=47591 Comprehensive, 500-street, watershed retrofit program detailed. Natural Drainage Projects, Seattle, Washington, Seattle Public Utilities (SPU), www.seattle.gov/util/naturalsystems Design information and details on LID street design and elements, porous pavement specification, project reports 

### 2.7 8 

## Minimize directly connected impervious areas 9 

### Not all impervious areas are created equal. Impervi ous areas that are directly connected to the 10 

### storm sewer system convey excess stormwater volumes more rapidly and with greater impact 11 

### than impervious areas that do not have a direct con nection (i.e., disconnected). The term effective 12 

### impervious area (EIA) is used to describe this concept. EIA is the measure of how much 13 

### impervious surface is directly connected to the con veyance system. One of the first steps to 14 

### mitigating the effects of imperviousness is evaluat ing the opportunities to disconnect it so the 15 

### rain can be infiltrated, evapotranspired, or harves ted and used. 16



### • Downspout Disconnection. Downspout disconnection is the process of separati ng roof 17 

### downspouts from the sewer system and redirecting ro of runoff onto pervious surfaces, 18 

### most commonly a lawn, or to a stormwater management practices such as a bioretention 19 

### cell or cistern. 203/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 59 

### • Product Substitution. Using permeable pavements can reduce directly conn ected 1 

### impervious area because pervious materials are subs tituted for impervious materials 2 

### while maintaining the intended function. Permeable pavements can be used to infiltrate 3 

### stormwater, making areas that were once a source of stormwater a means of reducing the 4 

### volume of runoff. Similarly, green roof retrofits r educe the imperviousness of rooftops by 5 

### using engineered soil media and vegetation to lower the runoff potential. 6



### • Maximizing Opportunities to Infiltrate, Evapotransp irate, and Harvest and Use. 7 

### Infiltration and evapotranspiration is often accomp lished by incorporating bioretention 8 

### into street designs. Bioretention offers an effecti ve multipurpose stormwater management 9 

### strategy. Bioretention features can be tree boxes t hat collect stormwater runoff from the 10 

### street (similar to conventional tree boxes), plante r boxes, curb extensions, or bioswales. 11 

### To adapt to street configurations, grades, soil con ditions, and space availability, a range 12 

### of shapes, sizes, and layouts can be used. Using ex isting rights-of-way and using 13 

### techniques such as curb cuts to facilitate stormwat er movement are common practices. 14 

### Rainwater harvesting has recently become recognized as a stormwater management tool because 15 

### of its ability to reduce stormwater runoff volumes from impervious surfaces. It also serves as a 16 

### source substitute for potable water and can enhance water supplies and decrease the cost and 17 

### impacts of supplying water to urban areas. Collecte d rainwater is ideal for nonpotable 18 

### applications, such as landscape irrigation, toilet and urinal flushing, cooling system make-up, and 19 

### vehicle washing. Such collection and use is a key c omponent of an integrated water resources 20 

### management approach. Performance of rainwater harve sting systems depends on the volume of 21 

### water stored and the demand for the stored water. 22 

### Rainwater harvesting has been practiced by civiliza tions for centuries, and is now actively used 23 

### in many countries that experience chronic or season al water shortages. In this country, though, 24 

### rainwater harvesting has been primarily used for fl ash flooding control, or otherwise managing 25 

### drainage problems. Now, in states such as Georgia, Virginia, and Texas, government-supported 26 

### organizations have prepared manuals and guidelines for residential and commercial water 27 

### harvesting for drought preparedness. In the Northwe st, residential and commercial rainwater 28 

### harvesting is used for stormwater management. In we stern cities, rainwater harvesting is 29 

### becoming more common—Los Angeles County and Tucson, Arizona, for example—but water 30 

### rights issues could restrict its use in some states

. 31 

### Design and installation manuals relevant to the Che sapeake Bay area, references to example city 32 

### ordinances, and other information on rainwater harv esting is provided in the fact sheet in 33 

### Section 6. 34


## 2.8 Implement Restoration 35


### 2.8.1 Urban Tree Canopy 36

Use LID Practices : Infiltration/ev apotranspiration with increased u rban t ree c a nopy 37 

### Significant potential exists to reduce runoff volum es on an annual basis using increased urban 38 

### tree canopy (UTC). Interception in the tree canopy provides some capture in small events, but 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 60 

### trees can evapotranspirate significant amounts—up t o 200 to 800 gallons per day for some 1 

### mature tree species (ITRC 2009). Each deciduous tre e in the Baltimore area in the 2009 weather 2 

### pattern evapotranspired (in leaf-on period) approxi mately (personal communication, David 3 

### Nowak, U.S. Forest Service) : 4



### • 2.6 gallons/day for a small tree (1 m radius crown) 5



### • 260 gallons/day for a large tree (10 m radius crown ) 6 

### For dense urban environments—and where utility conf licts can be managed—new technologies 7 

### include 8



### • Structures or structural soils that allow root grow th under sidewalks and vehicle areas. 9



### • Permeable pavements that enable stormwater to flow to roots while supporting loads; 10



### • Flexible sidewalk material (example: Belleview, Was hington, 11 

### http://www.ci.bellevue.wa.us/rubber_sidewalk.htm, 12



### • Large-diameter soaking hoses or vaults built into t ree pits that collect and infiltrate a first 13 

### portion of runoff for evapotranspiration. 14 

### Using those technologies, little or no additional l and is consumed in managing stormwater

. 15


### Conver ting paved areas or compacted turf to functional conser vation landscaping can also 16 

### improve infiltration and some street tree maintenance issues can be better m anaged reduce runoff. 17 

### Native grasses and shrubs wit h deep roots and more leaf area evapotranspirate mo re than turf and 18 

### help keep the soil from compacting, allowing more i nfiltration

. 19 

### To estimate the effectiveness of adding urban tree canopy and green roofs at reducing the 20 

### stormwater runoff volumes in a dense urban environm ent, Casey Trees and LimnoTech 21 

### developed the Green Build-out Model to quantify the stormwater benefits of trees and green 22 

### roofs for different coverage scenarios in Washingto n, DC. The model was applied to an intensive 23 

### greening scenario and a moderate greening scenario. Nearly all the waters in Washington, DC, 24 

### are seriously polluted by urban stormwater runoff a nd the sewage overflows it causes. The Green 25 

### Build-out Model demonstrates that trees and green r oofs—just a portion of the types of 26 

### infrastructure practices available—can be used to a chieve substantial reductions in stormwater 27 

### runoff and sewage discharges to the rivers. Key fin dings show for an average year 28



### • The intensive greening scenario eliminates more tha n 1.2 billion gallons of stormwater 29



### • Reductions in stormwater runoff volume of up to 10 percent across the city, with up to 27 30 

### percent reductions in individual sewersheds under t he most intensive greening scenario 31



### • The DC Water and Sewer Authority could realize betw een $1.4 and $5.1 million per year 32 

### in annual operational savings in the area because o f reduced pumping and treatment 33 

### costs. 34



### • General hydrological relationships, including unit area planning factors, and modeling 35 

### methodologies that are transferable to other munici palities. 363/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 61 

### Using trees to help managing stormwater and protect water quality is becoming accepted by 1 

### some engineers and land managers as sustainability becomes more important in land design. A 2 

### statement by the Chesapeake Bay Executive Council i n 2006 emphasizes the point. 3 

### Forests are the most beneficial land use for protec ting water quality, due to their 4 

### ability to capture, filter, and retain water, as we ll as air pollution from the air. 5 

### Forests are also essential to the provision of clea n drinking water to over 10 6 

### million residents of the watershed and provide valu able ecological services and 7 

### economic benefits including carbon sequestration, f lood control, wildlife habitat, 8 

### and forest products. 9 

### A summary of resources for estimating stormwater ma nagement benefits of tree canopy are 10 

### provided in Table 3-14. Additional information is p rovided in the Reforestation/Urban Forestry 11 

### and Bioretention Fact Sheets in Section 6. 12

Table 3-14. Resources for estimating stormwater ben efits of tree canopy and vegetation 13 Citygreen software by American Forests www.americanforests.org/productsandpubs/citygreen Trees Reduce Stormwater website by American Forests www.americanforests.org/graytogreen/stormwater Analyzes the ecological and economic benefits of tree canopy and other green space

i-Tree suite of software Tools from USDA Forest Ser vice www.itreetools.org Tools enable quantification on a per tree basis or on a watershed scale Phytotechnology Technical and Regulatory Guidance, The Interstate Technology & Regulatory Council, 200 9 Provides guidance on using vegetation for soil remediation, and estimates of transpiration rates. Casey Trees, Washington, D.C. Green Build-out Modelwww.caseytrees.org/planning/greenerdevelopment/gbo/index.php The Green Build-out Model demonstrated that trees and green roofs can be used to achieve substantial reductions in stormwater runoff and sewage discharges to the rivers. 14


### 2.8.2 Streams, Floodways, and Riparian Areas 15

Use LID Practices: Rainwater Harvesting 16 

### Rainwater harvesting has recen tly become recognized as a stormwater management to ol because 17 

### of its ability to reduce stormwater runoff volumes from impervious surfaces. It also serves as a 18 

### source substitute for potable water and can enhance water supplies and decrease the cost and 19 

### impa cts of supplying water to urban areas. Collected ra inwater is ideal for nonpotable 20 

### applications, such as landscape irrigation, toilet and urinal flushing, cooling system make

- up, and 21 

### vehicle washing. Such collection and use is a key component of an in tegra ted water resources 22 

### management approach. Performance of rainwater harvesting systems depend s on the volume of 23 

### water stored and the demand for the stored water. 24 

### Rainwater harvesting has, of course ( 1) been practiced by civilizations for centuries, a nd ( 2) i s 25 

### now actively used in many countries that experience chronic or seasonal water shortages. In this 26 

### country, though, rainwater harvesting has been prim arily used for flash flooding control, or 273/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 62 

### otherwise managing drainage problems. Now, in state s such as Geo rgia, Virginia, and Texas, 1 

### government

- supported organizations have prepared manuals and g uidelines for residential and 2 

### commercial water harvesting for drought preparednes s. In the Northwest, residential and 3 

### commercial rainwater harvesting is used for storm water management. In western cities, 4 

### rainwater harvesting i s becoming more common

— Los Angeles County and Tucson, Arizona, for 5 

### example

— but water rights issues could restrict its use in some states. 6 

### Design and installation manuals relevant to the Che sapeake Bay area, references to example city 7 

### ordinances, and other information on rainwater harv esting is provided in the f act s heet in 8 

### Section 6

. 9

Restor e s tream s, floodways, and riparian areas 10 

### Using stream and floodplain restoration, managers a ttempt to restore the ecological and 11 

### hydrological functions and processes of a stream an d its floodplain. The stream corridor is 12 

### typically considered to consist of the stream chann el, riparian zone, and flood plains (level areas 13 

### near the channel, formed by the stream and flooded during moderate-to-high flow events). 14 

### Stream corridors are influenced by the cumulative e ffects of upland and upstream activities and 15 

### practices, including agricultural production, fores try, recreation, other land uses, or urban 16 

### development. Specific restoration goals can include flood control, sediment control, improving 17 

### drainage, stabilizing banks, and improving habitat. Figure 3-12 shows the effect of increasing 18 

### urbanization on stream channel erosion and floodpla in disconnection. Correcting stream damage 19 

### using stream restoration techniques is a costly und ertaking with uncertain rewards; preventing 20 

### the damage by using the techniques described in thi s guidance is a more reliable approach. 21

223/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 63 1 Figure 3-12. Impacts of urbanization on stream chan nel erosion and floodplain disconnection. 2 

### Restoring impaired waterways is important to restor ing predevelopment hydrology and reducing 3 

### loading from larger and scouring flows. Degraded st reams can themselves become a source of 4 

### downstream pollution, such as when P phosp horus -laden sediments are mobilized during high5 

### flow events. In such cases, stream restoration can be a useful strategy to improve downstream 6 

### water quality. However, it is important to keep in mind that the elevated flows causing sediment 7 

### mobilization must also be addressed. Stream stabili zation requires restoration of the stream’s 8 

### energy signature. The predevelopment hydrology of t he watershed should must be restored to 9 

### regain the predevelopment character of the stream; however, in existing urban areas that might 10 

### be a longer-term goal. 11 

### A summary of existing information of the effects of stream hydromodification on the quality of 12 

### the Chesapeake Bay is provided in Table 3-15. The s tudies demonstrate the importance of stream 133/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 64 

### restoration and protection in achieving pollutant r eduction in the Chesapeake Bay, particularly 1 

### for sediment and the P phosphorus that accompanies sediment loading. 2

Table 3-15. Studies quantifying the impact of sedim ent loading stream hydromodification on 3 Chesapeake Bay water quality 4 Study Findings A Summary Report of Sediment Processes in Chesapeake Bay and Watershed, U.S. Geological Survey, Water-Resources Investigations Report 03-41 23, 2003 Summarizes the impacts and sources of sediment and notes that sediment yield from urbanized areas can remain high after active construction is complete because of increased stream corridor erosion from altered hydrology Schueler, Thomas, et.al, The Practice of Watershed Protection, Technical Note #119 from Watershed Protection Techniques 3(3):729–734 , Center for Watershed Protection, 2000. Stream enlargement, and the resulting transport of excess sediment, is caused by urban development
U.S. Environmental Protection Agency. 2001. Protecting and Restoring America’s Watershed’s: Status, Trends
, and Initiatives in Watershed Management, EPA 840-R00-001. www.epa.gov/owow/nps/urbanm/pdf/urban_guidance.pdf. Straightened and channelized streams carry more sediments and other pollutants to their receiving waters. Up to 75% of the transported sediment from the Pocomoke watershed on the Eastern Shore of Maryland was found to be erosion from within the stream corridor Gellis, Allen C., et. al. Synthesis of U.S. Geological Survey Science for the Chesapeake Bay Ecosystem and Implications for Environmental Management, Chapter 6: Sources and Transport of Sediment in the Watershed

. 2007, U.S. Geological Survey Circular 1316. Sediment sources are throughout the Chesapeake Bay watershed, with more in developed and steep areas

Gellis, A.C., et al, 2009, Sources, transport, and storage of sediment in the Chesapeake Bay Watershed . U.S. Geological Survey Scientific Investigations Report 2008– 5186 In the Piedmont region, streambank erosion was a major source of sediment in developed Little Conestoga Creek; 30% of sediment from the Mattawoman Watershed on the Coastal Plain (flat land) is from streambanks Devereux, Olivia H., et al., Suspended-sediment sources in an urban watershed

, Northeast Branch Anacostia River, Maryland. Hydrological Processes, Accepted 2009. Streambank erosion was the primary source of sediment in the Northeast Branch Anacostia River

5 

### Stream restoration can help to restore the natural ecosystem function of N nitrogen removal that 6 

### occurs in streams. Studies that evaluate the N nitrogen removal ability of restored streams are 7 

### summarized in Table 3-16. 8 

### In addition to the water quality improvements that can be achieved through stream restoration, 9 

### the flood management community has become increasin gly aware of the benefits of restoration 10 

### in preventing flood damages. The Association of Sta te Floodplain Managers has prepared a 11 

### white paper called Natural and Beneficial Floodplain Functions: Floodp lain Management— 12 

### More than Flood Loss Reduction ( www.floods.org ) , which emphasizes the multiple benefits of 13 

### protecting and restoring streams and their associat ed floodplains. 14

153/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 65 Table 3-16. Studies evaluating the N nitrogen removal ability of restored streams in the 1 Chesapeake Bay watershed 2 Study Finding Kausal, Sujay S., et.al. Effects of Stream Restoration on Denitrification in an Urbanizing Watershed

. Ecological Applications, 18(3), 2008, pp. 789-804. Streams with ecological functions intact remove N nitrogen at a much higher rate than degraded urban streams, and stream restoration practices can restore this N nitrogen removal function. Klocker, Carolyn A, et. al. Nitrogen uptake and denitrification in restored and unrestored streams in urban Maryland

, USA. Aquatic Sciences, Accepted October 2009. Degraded urban streams, deeply eroded and disconnected from their floodplain have substantially lower rates of N nitrogen removal that than streams hydraulically connected to their riparian banks via low slopes, and reconnecting the stream to the floodplain can increase. 3 

### Techniques for stream and floodplain restoration ar e described in the Hydromodification section 4 

### of this document. Example references for stream res toration, and for information on the effects 5 

### of urban runoff on stream ecosystems, are provided in Table 3-17. 6

Table 3-17. References on urban stormwater effects on streams with emphasis on restoration and 7 habitat 8 USDA Natural Resources Conservation Service, Part 654 Stream Restoration Design National Engineering Handbook, 210–VI–NEH, August 2007 Federal Interagency Stream Restoration Working Grou p (FISRWG) (1998 ). Stream Corridor Restoration: Principles, Processes, and Practices, ISBN-0-934213-60-7, Distributed by the National Te chnical Information Service at 1-800-533-6847. Infiltration vs. Surface Water Discharge: Guidance for Stormwater Managers, Final Report . 03-SW-4, Water Environment Research Federation (WERF 2006) A ppendix B. Assessment of Existing Watershed Conditions: Effects on Habitat. 9



## 2. 9 Reduce Impacts of 3.2 For Existing Urban Areas 10



### 2.9.1 (i.e. , Retrofits ) 11 

### Many urban areas were developed without any or with few stormwater controls designed to 12 

### protect water quality and prevent stream channel de gradation. This section of the document 13 

### contains recommendations for practices that can be used in such areas to try to reverse 14 

### degradation that has already occurred in the past b y reducing the volume, rates, and duration of 15 

### runoff. Specifically, the recommended control measu res on existing urban land focus on retrofits 16 

### to roof downspouts, roads, parking lots, and areas of compacted soils. 17 

### An effective retrofit strategy for urbanized areas combines planning techniques such as smart 18 

### growth and green infrastructure/LID techniques. A c omprehensive guide on retrofits for existing 19 

### urban areas is the Center for Watershed Protection’ s Urban Stormwater Retrofit Practices (CWP 20 

### 2007). 213/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 66 

### The CWP Urban Stormwater Retrofit Practices manual focuses on stormwater retrofit practices 1 

### that can capture and treat stormwater runoff before it is delivered to the stream. The manual 2 

### describes both off-site storage and on-site retrofi t techniques that can be used to remove 3 

### stormwater pollutants, minimize channel erosion, an d help restore stream hydrology. Guidance 4 

### on choosing the best locations in a subwatershed fo r retrofitting is provided in a series of 13 5 

### profile sheets. The manual then presents a method t o assess retrofit potential at the subwatershed 6 

### level, including methods to conduct a retrofit inve ntory, assess candidate sites, screen for priority 7 

### projects, and evaluate their expected cumulative be nefit. The manual concludes by offering tips 8 

### on retrofit design, permitting, construction, and m aintenance considerations. 9 

### Table 3-18 presents common locations where addition al storage and infiltration for stormwater 10 

### can be provided in a subwatershed, and also common locations for on-site retrofits. 11

Table 3-18. Common locations for additional stormwa ter storage and infiltration and on-site 12 retrofits 13 Common on-site retrofit locations in a subwatershed Common Storage Retrofit Locations Common On

- Site Retrofit Locations in a Subwatershed Where How Road Right of Ways Direct runoff to a depression or excavated stormwat er bioretention/infiltration treatment

area within the right-of-way of a road, highway, tr ansport or power line corridor. Prominent examples include highway cloverleaf, medi an and wide right-of-way areas. Near Large Parking Lots Provide stormwater infiltration treatment in open s paces near the downgradient outfall

of large parking lots (5 acres plus). Conveyance Systems Investigate the upper portions of the existing stor mwater conveyance systems (such as

ditches) to look for opportunities to improve the p erformance. That can be done either by creating in-line storage cells (small dams with overflows) that allow infiltration or by splitting flows to off-line infiltration/treatment areas in the drainage corridor Hotspot Operations Install filtering or bioretention treatment to remo ve pollutants from confirmed or severe

stormwater hotspots discovered during field investi gation Small Parking Lots Insert stormwater treatment, preferably depressed b ioretention or expanded tree boxes,

in or on the margins of small parking lots (less th an 5 acres). In many cases, the parking lot is delineated into a series of smaller, on-site treatment units. Individual Streets Look for opportunities with the street, its right-o f-way, cul-de-sacs and traffic calming

devices to infiltrate and treat stormwater runoff b efore it gets into the street storm drain network Individual Rooftops Disconnect downspouts from storm drains, store and use the rainwater, and infiltrate

excess stormwater runoff close to the source Little Retrofits Convert or disconnect isolated areas of impervious cover to infiltration and bioretention,

and treat excess runoff in an adjacent pervious are a using low tech approaches such as a filter strip Hardscapes Landscapes Reconfigure the drainage of high-visibility urban l andscapes, plazas, and public spaces

to capture and use, infiltrate and evapotranspirate , and treat excess stormwater runoff with landscaping and other urban design features. Underground Provide stormwater infiltration or treatment in an underground location when no surface

land is available for surface treatment. Use this a s a last resort at dense, ultra-urban sites. 143/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 67 

### Examples of LID road retrofits in the Chesapeake Ba y watershed are included in Table 3-19. 1

Table 3-19. Examples of Maryland LID road retrofits 2 Site Reference Knollbrook Drive and Talbert Lane median and the Ray Road stormdrain outfall in the Takoma Branch subwatershed Final Technical Report, Pilot Projects for LID Urba n Retrofit Program, In the Anacostia River Watershed, Phase IV , USEPA: Prince Georges County, Maryland, 2007
U.S. Route 1 and Maryland Route 201 at I-95 (Bioretention) www.princegeorgescountymd.gov/Government/AgencyInde x/DER/ESG/ pdf/Final Technical Report Phase III.pd Decatur Street Improvement, Edmonston, MD (holistic green street—multiple LID retrofits) www.lowimpactdevelopment.org/greenstreets/projects. htm; http://edmonston.us.com/GreenStreetGroundbreaking.h tml

Route 202 Median (Bioretention) www.co.pg.md.us/Government/AgencyIndex/GoingGreen/p df/2009- annual-green-report.pdf Route 201 Median (Bioretention) www.co.pg.md.us/Government/AgencyIndex/GoingGreen/p df/2009- annual-green-report.pdf Peace Cross Green Highway Project—NW Prince George’s County, adjacent to the Anacostia River. Network:

• Baltimore Avenue

• Bladensburg Road

• Annapolis Road www.princegeorgescountymd.gov/Government/AgencyInde x/DER/ESG/ pdf/Final%20Technical%20Report_Phase%20III.pdf
www.springerlink.com/content/l682122767u41k7x/fullt ext.pdf

Route 202/I-495 interchange (Bioretention) www.co.pg.md.us/Government/AgencyIndex/GoingGreen/p df/2009- annual-green-report.pdf 3


### 2.10.2 Redevelopment 4 

### Implementation of an effective redevelopment progra m is essential to restoring water quality, as 5 

### discussed previously in this document. Section 4 of this guidance provides information on 6 

### important issues that should be addressed in redeve lopment policies, and example practices that 7 

### are appropriate for redevelopment. Figure 3-13 lists the stormwater retrofit and redev elopment 8 

### programs that several cities have adopted or are pi loting using green infrastructure/LID 9 

### approaches. Implementation measures for redevelopment programs include establishing 10 

### appropriate redevelopment performance standards, cr eating an inventory of appropriate 11 

### mitigation practices for a range of project sizes, conducting site assessments as part of practice 12 

### selection, review of codes and ordinances, implemen ting demonstration projects, providing It 13 

### also lists information on incentives , maximizing forest canopy, and mitigating compacte d soils

. 143/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 68 1

2 Figure 3-13. Municipal stormwater retrofit/redevelo pment programs. 3



## 2. 10 4 Costs of Green Infrastructure/LID Practices 4 

### Cost is a primary factor in selecting stormwater ma nagement practices. The most important LID 5 

### practices, i.e., good development planning practice s that minimize effects, do not cost more and 6 

### provide multiple other benefits in addition to wate r quality. When selecting stormwater 7 

### management practices or implementing policy decisio ns, consider factors beyond capital, O&M, 8 

### and life cycle cost such as the following: 9



### • Understanding the ancillary benefits that can be as sociated with LID/green infrastructure 10 

### practices 11



### • Understanding the potential cost savings of using d istributed LID practices compared to 12 

### conventional stormwater controls; this has been dem onstrated in cities evaluating 13 

### combined sewer overflow solutions (PWD 2009), and i n the construction of new 14 

### residential subdivisions (USEPA 2007) 15



### • Flexibility inherent in these practices allows them to be integrated into the urban 16 

### environment in many cases (NRDC 2006), such as wate r harvesting, or under-sidewalk 17 

### supported elevated pavement systems (such as infiltrating storage vau lts or tree root 18 

### vaults, as in the Minneapolis downtown MARQ2 street redesign that included load19 

### bearing structurally supported space for street tree roots under the sidewalk and adjacent 20 

### areas, http://www.stormh20.com/march-april-2010/reshaping- minneapolis21 

### project.aspx h ttp://www.ci.minneapolis.mn.us/public

- works/Marq2/about.asp ) 22 Some Municipal Highlights for Retrofit and Redevelopment Approaches and Practices: Portland, Oregon, Bureau of Environmental Services: “A Sustainable Approach to Stormwater Management”, http://www.portlandonline.com/bes/index.cfm?c=34598 Seattle, Washington, Seattle Public Utilities “Natu ral Drainage Systems: Green Stormwater Infrastructure”, http://www.seattle.gov/util/About_SPU/Drainage_&_Se wer_System/GreenStormwaterInfrastructure/i ndex.htm Kansas City, Missouri, “10,000 Raingardens” Program
, www.rainkc.gov Philadelphia, Pennsylvania, “Greenworks Philadelphi a”, www.phila.gov/green EPA’s Green Infrastructure website: Case Studies o f Green Municipalities
, http://cfpub.epa.gov/npdes/greeninfrastructure/gica sestudies.cfm#Municipal

Some Municipal Highlights for Retrofit and Redevelopment Approaches and Practices: Portland, Oregon, Bureau of Environmental Services: A Sustainable Approach to Stormwater Management, http://www.portlandonline.com/bes/index.cfm?c=34598 Seattle, Washington, SPU/Natural Drainage Systems: Green Stormwater Infrastructure, http://www.seattle.gov/util/About_SPU/Drainage_&_Se wer_System/GreenStormwaterInfrastructure/i ndex.htm Kansas City, Missouri, www.rainkc.gov Philadelphia, Pennsylvania, www.phila.gov/green www.lowimpactdevelopment.org/recognition/categories .htm3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 69 

### • Costs are expected to decrease as the practices bec ome more standard, for example, the 1 

### costs of permeable pavement and of green roofs have been reported to have decreased in 2 

### regions where they have been used on a larger scale . That is quantified in estimates by 3 

### PWD reported in this section. 4



### • Jurisdictions have found costs to be equivalent or less than conventional stormwater 5 

### management practices. An example is Spotsylvania Co unty, Virginia, described in Figure 6 

### 3-14. 7
Spotsylvania County has allowed LID for several yea rs. The development community has realized cost savings from LID, after initial skepticism. The cou nty gives examples of just a few of the many successful LID projects:

• Mt. Zion Baptist Church—Historical Church in devel oped area. Needed to add-on to the church but could not afford the land for a basin, instead used grass-paver type system GrassTrac TM for parking lot instead of pavement and stone in the travel way . An underground tank captures and infiltrates rainwater. Originally, a 42” diameter outlet was pl anned, now a 6” PVC pipe works, with minimal runoff. Used a landscaping rain garden before the d rainage inlets. The net savings was approximately 45 percent from estimated costs in 2008.

• Patriot Park—This development had no outlet as a r esult of 1930’s development design. Evapotranspiration rates were used to establish a p otential water uptake per plant. By using the required buffer and landscaping features the tradit ional SWM basin was eliminated and there would be no downstream impact because rain is retai ned onsite for up to a 100 yr storm event.

• Fence Company—The project was to have bioretention with an underground stormwater storage system. Once installed, the owner found that the bi o-retention with underground storage cost approximately 30 percent less than a traditional ba sin with riser and land needed. Positives noted

o More land for storage of his material

o Lower costs for installation,

o Easier to access and maintain. Spotsylvania has standardized agreements for BMP in stallation, inspection, and maintenance

.

- When it comes to the economics of LID practices for the most part you will not get an accurate figure until you show your applicants how to do it right. I have had farmers, homeowner, developers and many other say that after going through proper training courses they have found LID to be much easier then they have seen in the books and have be en led to believe. —Richard Street, Spotsylvania County, Virginia, Dep artment of Code Compliance, January 2010 Figure 3-14. LID cost savings realized in Spotsylva nia County, Virginia 8



### 2. 10 4 .1 Potential Ancillary Benefits of LID/Green Infras tructure 9 

### Ancillary benefits are often achieved using LID, an d they should be factored into managers’ 10 

### consideration of project cost. For example, signifi cant ancillary benefits have been quantified for 11 

### green roofs in Cost Benefit Evaluation of Ecoroofs 2008, City of P ortland Bureau of 12 

### Environmental Services. These benefits are summarized in Figure 3-15. 13

14 Benefits to the public

• Reduced public costs to manage stormwater

• Avoided public stormwater infrastructure needs and O&M costs

• Reduced carbon emissions3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 70 • Improved air quality

• Increased habitat areas Benefits to private interests include the following :

• Reduced stormwater fees

• Reduced private infrastructure and O&M costs

• Reduced energy demand and costs

• Increased roof longevity

• Increased Floor Area Ratio density bonus potential The calculated benefits of a hypothetical 40,000 sf green roof include the following:

• $404,000: the net benefit to the property owner by year 40.

• $191,421: the net benefit to the public by year 40. There is an immediate and long term public benefit. By year five, the benefit is already $101,660. Source: City of Portland Bureau of Environmental Se rvices 1 Figure 3-15. Benefits are quantified for green roof s in Cost Benefit Evaluation of Ecoroofs 2008 2 

### Also, a broad range of societal benefits are descri bed in PWD’s A Triple Bottom Line Assessment 3 

### of Traditional and Green Infrastructure, Options fo r Controlling CSO Events in Philadelphia's 4 

### Watersheds Final Report, 2009. The categories of benefit accrual resulting from us ing green 5 

### infrastructure stormwater management approaches are the following: 6



### • Recreational Use and Values 7



### • Property Values, as Enhanced by the LID Options 8



### • Heat Stress and Related Premature Fatalities Avoide d 9



### • Water Quality and Aquatic Habitat Enhancements and Values 10



### • Wetland Enhancement and Creation 11



### • Poverty Reduction Benefits of Local Green Infrastru cture Jobs 12



### • Energy Usage and Related Changes in Carbon and Othe r Emissions 13



### • Air Quality Pollutant Removal from Added Vegetation 14



### 2. 10 4 .2 Potential Cost Savings of LID/Green Infrastructu re 15 

### EPA’s report, Reducing Stormwater Costs through Low Impact Develo pment (LID) Strategies 16 

### and Practices ( EPA 841-F-07-006 

### ) compares the projected or known costs of LID prac tices with 17 

### those of conventional development approaches. Tradi tional approaches to stormwater 18 

### management typically use curbs, gutters, and piping . LID-based designs, in contrast, are 19 

### designed to use natural drainage features or engine ered swales and vegetated contours for runoff 20 

### conveyance and treatment. In terms of costs, LID te chniques can reduce the amount of materials 21 

### needed for paving roads and driveways and for insta lling curbs and gutters. Other LID 22 

### techniques can eliminate or reduce the need for cur bs and gutters, thereby reducing infrastructure 23 

### costs. Note that in some circumstances LID techniqu es might result in higher costs because of 24 

### more expensive plant material, site preparation, so il amendments, as well as increased project 25 

### management costs. Other considerations include land required to implement a management 26 

### practice and differences in maintenance requirement s

. 273/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 71 

### Seventeen case studies were evaluated. In general, the case studies demonstrate that LID can 1 

### reduce project costs and improve environmental perf ormance. Although not all the benefits of 2 

### the projects were monetized, with a few exceptions, LID practices were shown to be fiscally and 3 

### environmentally beneficial. In some cases, initial material costs were higher; in most cases, 4 

### however, significant savings were realized because of reduced costs for site grading and 5 

### preparation, stormwater infrastructure, site paving , and landscaping. Total capital cost savings 6 

### ranged from 15 to 80 percent when LID methods were used (Table 3-20). The full report is at 7 

### www.epa.gov/nps/lid

. 8

Table 3-20. Cost comparisons between conventional a nd LID approaches 9

Project a Conventional development cost LID cost Cost difference b Percent

difference b 2nd Avenue SEA Street $868,803 $651,548 $217,255 25% Auburn Hills $2,360,385 $1,598,989 $761,396 32% Bellingham City Hall $27,600 $5,600 $22,000 80% Bellingham Bloedel Donovan Park $52,800 $12,800 $40,000 76% Gap Creek $4,620,600 $3,942,100 $678,500 15% Garden Valley $324,400 $260,700 $63,700 20% Kensington Estates $765,700 $1,502,900 –$737,200 -96% Laurel Springs $1,654,021 $1,149,552 $504,469 30% Mill Creek c $12,510 $9,099 $3,411 27% Prairie Glen $1,004,848 $599,536 $405,312 40% Somerset $2,456,843 $1,671,461 $785,382 32% Tellabs Corporate Campus $3,162,160 $2,700,650 $461,510 15%
Source : Reducing Stormwater Costs through Low Impact Develo pment (LID) Strategies and Practices, EPA 841-F-07-006 Notes: a. Some of the case study results do not lend thems elves to display in the format of this table (Centr al Park Commercial Redesigns, Crown Street, Poplar Street A partments, Prairie Crossing, Portland Downspout Disconnection, and Toronto Green Roofs). b. Negative values denote increased cost for the LI D design over conventional development costs. c Mil l Creek costs are reported on a per-lot basis.



### For CSO communities like Philadelphia that need to reduce stormwater volumes into sewers in 10 

### dense, urban areas, LID has been shown to help lowe r estimated long-term costs of compliance 11 

### by reducing the size of the storage tunnels that ar e built 12 

### ( http://www.phillywatersheds.org/ltcpu/LTCPU_Complet e.pdf http: //www.phillywatersheds.org/l 13 

### tcpu/LTCPU_Complete.pdf ). That can be made a redevelopment requirement (as in 14 

### Philadelphia), to enable implementing the controls over a development horizon time frame. An 15 

### additional cost benefit is that there is less need for bond revenue, and less debt service if less 16 

### corrective infrastructure can be used. 173/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 72 

### 2. 10 4 .3 Costs of Water Quality and Coastal Impairments 1 

### This guidance document does not provide a literatur e review of estimated costs of water quality 2 

### impairments, but communities should evaluate the da mages from such impairments when 3 

### determining the true cost of stormwater management. For example, beach closures and shellfish 4 

### bed contamination, and loss of fisheries represent significant economic costs to society. An 5 

### overview of some of these issues is provided in EPA ’s 2000 report Liquid Assets 6 

### ( http://www.epa.gov/water/liquidassets/execsumm.html ). 7



### 2. 10 4 .4 Costs of Individual Practices 8 

### Given the considerations described above, it is cle ar that comparing the costs of LID practices to 9 

### each other, or just to other stormwater management practices, is not the best way to show to the 10 

### value of LID practices. In addition to not accounti ng for these benefits, just stating practice cost 11 

### does not show how costs can be optimized by integra ting LID features into the landscape, or by 12 

### selecting rooftop-to-stream incremental features to filter, treat, retain, capture and use runoff. A 13 

### green roof might appear a high cost practice, but i n a densely urbanized area it could be the most 14 

### economical solution for stormwater management, and given the potential benefits shown in 15 

### Figure 3-15, could be a very worthwhile investment in the long term. 16 

### Issues that should be considered when estimating ca pital and O&M costs are the following: 17



### • Because LID practices are relatively new, few examp les of comprehensive, full-scale 18 

### project costs are readily available. 19



### • Limited literature values for costs often do not pr ovide complete information needed, 20 

### such as design/construction/startup information, or level of water quality treatment to be 21 

### provided 22



### • Costs are highly site specific, such as if area con tractors are familiar with the practices, 23 

### and therefore vary considerably. 24



### • O&M will account for much of the ownership cost, so managers should consider the 25 

### expected reliability and ease of maintenance when s electing a practice, not just the capital 26 

### cost. 27



### • O&M costs attributed to LID practices were found to primarily be for aesthetics (WERF 28 

### 2005). Many of the activities that would have occur red in regular nonfunctional 29 

### landscaping (weed control, litter removal) are repo rted as LID maintenance. That can 30 

### make it difficult to determine how much of the repo rted cost is actually an additional cost 31 

### incurred to ensure that the practice functions. 32



### • O&M costs for maintaining bioretention might not be any different from the current 33 

### maintenance costs for nonfunctional landscaping, in fact, they could be lower because 34 

### bioretention would receive more rainwater and requi re less watering 35



### • LID practices are primarily uses of conventional co nstruction techniques that can be 36 

### readily estimated using local contractor quotes and industry guides such as Reed 37 

### Construction Data (R.S. Means), as is done for conv entional construction. 38



### • A wide range of potential cost outcomes is reported , such as 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 73 

### − Cost savings using LID is widely reported from mini mizing conventional piped 1 

### infrastructure and ponds, and simply using land and landscaping functionally 2



### − Higher cost in dense, urban environments where cist ern systems or green roofs might 3 

### be costly, but necessary because of land limitation s. 4



### − Limited cost savings or additional costs because th e local codes require installing 5 

### minimum-sized piped systems regardless of LID desig n. This could be from an 6 

### archa ic code or for ensuring flood control or other site-specific issues. 7



### • LID approaches often have other cost benefits that should be included in a consideration 8 

### of the total value of a practice , such as : reduced downstream piping/culvert costs, or 9 

### potentially lower O&M costs. 10 

### Estimates of stormwater management practice costs h ave been prepared by several entities and 11 

### reflect the variability that is inherent in site-sp ecific design and construction. 12 

### The determination of the most cost-effective practi ce is site-specific, depending on the 13 

### availability of land, the local costs of labor and materials, and level of treatment required. The 14 

### costs of individual practices are provided in the p ractice Fact Sheets in Section 6. General cost 15 

### ranges and cost estimating approaches for LID and o ther stormwater management practices have 16 

### been documented in the literature and are repeated here. References are provided in Table 3-21. 17

Table 3-21. Sources of general cost ranges and cost estimating approaches for LID practices 18 USEPA. Stormwater Best Management Practices Design Guide , Office of Research and Development, EPA/600/R-04/121, Volumes 1-3 (121, 121A, 121B), Se ptember 2004. USEPA. The Use of Best Management Practices (BMPs) in Urba n Watersheds, Office of Research and Development, EPA/600/R-04/184, September 2004. Center for Watershed Protection. Urban Subwatershed Restoration Manual Series, 2007 ( http://www.cwp.org/Store/usrm.htm ) Water Environment Research Federation. Performance and Whole-Life Costs of Sustainable Urb an Drainage Systems, 01-CTS-21T, 2005 Water Environment Research Federation. Decentralized Stormwater Controls for Urban Retrofi t and Combined Sewer Overflow Reduction, Phase II, 2009. Wiess, Peter T., et al. The Cost and Effectiveness of Stormwater Management Practices, Minnesota Department of Transportation, MN/RC – 2005-23
19 

### However, to supplement existing information sources , some recent examples are summarized in 20 

### Table 3-22, and some specific recent cost informati on from those sources is provided here. 21

Table 3-22. Sources of recent cost information for LID practices—capital, O&M, life cycle 22 Source Key items USEPA. Reducing Stormwater Costs through Low-Impact Development, Publication Number EPA 841-F-07-006, December 2007 Savings of 15% to 80% found for LID subdivisions compared to conventional subdivision drainage practices. ECONorthwest. T he Economics of Low-Impact Development: A Literature Review, November 2007 Case studies of LID costs and economic benefits3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 74 Source Key items Natural Resources Defense Council. Rooftops to Rivers: Green Strategies for Controlling Stormwater and Combined Sewer Overflows ; NRDC 2006. www.nrdc.org/water/pollution/rooftops/contents.asp Policy guide for decision makers for LID; nine case studies of successfully used green techniques Fact Sheets in Section 6 Cost considerations associated with each practice presented. City of Portland, Oregon, Bureau of Environmental S ervices, Sustainable Stormwater Management Pages, www.portlandonline.com/bes/index.cfm?c=34598 Extensive examples of green roofs and green streets, as well as other sustainable stormwater practices Water Environment Research Federation. WERF Cost Tool , 2009. Free spreadsheet tool developed as part of Performance and Whole Life Cost of Best Management Practices and Su stainable Urban Drainage Systems (2005). Water Environment Research Federation. www.werf.org/AM/Template.cfm?Section=Stormwater3 Provides estimates based on literature values. Intended for modification as needed for user project data. Calculates life cycle cost. Contains literature review by practice. City of Philadelphia. Long Term Control Plan Update, Supplemental Documentation, Volume 3, Basis of Cost Opinions
, September 2009; www.phillywatersheds.org/ltcpu/Vol03_Cost.pdf Full range of LID costs for new, redevelopment, and retrofit. O&M costs. Anticipated cost reduction as practices become more widely used. Retrofit focus. North Carolina Coastal Federation. Low Impact Development Pilot Study to Reduce Fecal Coliform into Core Sound, Fin al Report, Sea Grant Project Number: 07-EP-03, November 2008 Detailed costs for rain gardens, cisterns, conservation landscaping and other LID practices. Six implemented and 9 planned. North Carolina State University (NCSU). Bill Hunt e t al. Evaluating LID for a Engineering Development in the Lockwood F olly Watershed

, North Carolina. www.nhcgov.com/AgnAndDpt/PLNG/Documents/BrunswickLI D.pdf Demonstrates the cost savings achievable using LID in place of conventional stormwater treatment.
New York City, Plan NYC, Appendix C, 2008, www.nyc.gov/html/planyc2030/html/stormwater/stormwa ter.shtml For controls that are high-priority for retrofit. City of Portland, Bureau of Environmental Services. Cost Benefit Evaluation of Ecoroofs 2008. www.portlandonline.com/bes/index.cfm?c=50818&a=2610 53 Quantifies the benefits to owner and public of installing green roofs
PWD. A Triple Bottom Line Assessment of Traditional and Green Infrastructure. Options for Controlling CSO Events in Philadelphia's Watersheds Final Report, 2009. www.phillywatersheds.org/ltcpu/Vol02_TBL.pdf LID-based, green infrastructure approaches provide a wide array of important environmental and social benefits to the community, and that these benefits are not generally provided by the more traditional alternatives. 1 

### Sources of cost data for urban stormwater retrofits , especially roadway retrofits, include the 2 

### following: 3



### • Portland, Oregon’s Bureau of Environmental Services ; and Seattle, Washington. For 4 

### example, Portland notes in its description of its T abor to the River watershed green5 

### streets retrofit that resolving the drainage proble ms it faces using only pipe solutions 6 

### would have cost an estimated $144 million, while ad ding sustainable, green stormwater 7 

### management systems reduced the estimated cost to $8 6 million and enhanced water 83/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 75 

### quality and watershed health 1 

### ( www.portlandonline.com/bes/index.cfm?c=50500&a=2300 66 ). 2



### • Seattle, Washington’s utilities department, Seattle Public Utilities (SPU), has developed 3 

### and adopted a green streets design and retrofit app roach it calls Natural Drainage Systems 4 

### (NDS), started with the completion of the successfu l SEA Street project in 2001 5



### • ( www.seattle.gov/util/About_SPU/Drainage_&_Sewer_Sys tem/GreenStormwaterInfrastr 6 

### ucture/NaturalDrainageProjects/index.htm ). As part of the program’s adoption, SPU 7 

### conducted a benefit/cost comparison in 2003 between traditional designs and the NDS 8 

### design. A summary is provided in Figure 3-16 9

10 113/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 76 1 Source: www.seattle.gov/util/About_SPU/Drainage_&_Sewer_Sy stem/GreenStormwaterInfrastructure/index.htm 2 Figure 3-16. Comparison by Seattle Public Utilities shows lower construction costs for Natural 3 Drainage Systems than traditional street design 4 

### Local governments in the Mid-Atlantic area with cos t data include the following: 5



### • Philadelphia, Pennsylvania, Retrofits 6



### • Montgomery County, Maryland, Retrofits 7



### • North Carolina Division of Soil and Water’s Community Conservation Assistance 8 

### Program (CCAP ) 9 

### Philadelphia Water Department (PWD). PWD conducted a cost analysis of wet-weather 10 

### management approaches as part of its effort to scre en and compare green-to-gray technologies in 11 

### its Long-Term CSO Control Plan Update (LTCPU). The costs for several of those technologies 12 

### are provided here; for additional information and a ssumptions, see the LTCPU. In general, these 13 

### are planning-level estimates, expected to fall in t he range of –30 percent to +50 percent for the 14 

### Philadelphia area. 15 

### These costs were used as the basis for estimating t he cost-to-benefits comparison of PWD’s 16 

### report A Triple Bottom Line Assessment of Tra ditional and Green Infrastructure Options for 17 

### Controlling CSO Events in Philadelphia's Watersheds . The report indicates that the benefits from 18 

### green infrastructure stormwater management are sign ificant; those findings on benefit valuations 19 

### are applicable even to non-CSO communities. To comp are the costs of traditional versus green 20 

### infrastructure, PWD assessed the capital, O&M, and life cycle costs for several stormwater 21 

### management practices. It is important to note that the estimated costs were for facilities that 22 

### would theoretically meet Philadelphia’s stormwater ordinance, shown in Figure 3-17, to manage 233/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 77 

### the first inch of runoff from directly connected im pervious area, by infiltration possible, unless a 1 

### waiver is obtained. 2

Source: Philadelphia’s Stormwater Manual; http://www.phillyriverinfo.org/WICLibrary/chapter%2 01.pdf 3 Figure 3-17. Philadelphia Stormwater Manual v2.0—Se ction 1.1.1 Stormwater Ordinance and 4 Regulations 5 

### Cost estimate ranges from PWD’s Long-Term Control P lan for planning purposes are provided 6 

### in Table 3-23 for redevelopment and for retrofit. I n the LTCPU, PWD addresses many of the 7 

### considerations in evaluating costs, including O&M s chedules and costs, and replacement costs. 8

Table 3-23. Summary of direct construction cost est imates from PWD’s Long-Term Control Plan 9 Supplemental Documentation, Volume 3 [ENRCCI 7966; RSMEAN 115.2] 10

Control Type Minimum cost ($ / impervious acre) Median cost

($/impervious acre) Mean cost

($ / impervious acre) Max cost

($ / impervious acre) Retrofit $65,000 $120,000 $160,000 $410,000 Bioretention Redevelopment $44,000 $90,000 $110,000 $200,000

Retrofit $65,000 $120,000 $160,000 $410,000 Subsurface Infiltration Redevelopment $44,000 $90,000 $110,000 $200,000

Retrofit $430,000 $500,000 $500,000 $570,000 Green Roof Redevelopment $200,000 $250,000 $250,000 $290,000

Retrofit $65,000 $160,000 $160,000 $410,000 Porous Pavement Redevelopment $44,000 $110,000 $110,000 $200,000

Retrofit $18,000 $18,000 $18,000 $18,000 Street Trees Redevelopment $15,000 $15,000 $15,000 $15,000 Source: Philadelphia LTCP

* From Philadelphia LTCP: Other cities have been experiencing costs in the ra nge of $7–16 per square foot ($305,000–$700,000 per impervious acre), with a typ ical range of $10–14 per square foot ($435,000–$610 ,000 per impervious acre). A recent green roof at Temple-Amb ler campus was approximately $11 per square foot ($ 480,000 per impervious acre). The least expensive green roo fs in Chicago, which has the largest-scale program in the U.S., are on the order of $6–7 per square foot ($285,000 per impervious acre), and this could be a reasonabl e estimate of what can be achieved in the future with a large

- 0 scale program in Philadelphia. The Water Quality requirement stipulates management of the first one inch of runoff from all Directly Connected Impervious Areas (DCIA) within the limits of earth disturbance. The Water Quality requirement is established to (1) recharge the grou ndwater table and increase stream base flows; (2) restore more natural site hydrology; (3) reduce pollution in runoff; and (4) reduce combined sewer overflows (CSO) from the city’s combined sewer syst ems. The requirement is similar to water quality requirements in surrounding states and in other maj or cities.

• The requirement must be met by infiltrating the wa ter quality volume unless infiltration is determined to be infeasible (because of contaminati on, high groundwater table, shallow bed rock, poor infiltration rates, etc.) or where it can be d emonstrated that infiltration would cause property or environmental damage.

• A waiver from the infiltration requirement must be submitted and approved if infiltration is not feasible... (continues)3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 78 1 

### In addition to capital cost, PWD estimates the cost decrease that can occur as LID practices 2 

### become more of a standard practice. PWD LTCPU estim ates that costs will decrease for the 3 

### following reasons (PWD 2009): 4



### • Improved site designs will result as designers lear n to incorporate the new stormwater 5 

### requirements into designs from the beginning. Now, such features are added to a site plan 6 

### as an afterthought, resulting in higher design cost s. Leaving more functional open space 7 

### in the site design for stormwater management is ass umed to occur over time, and 8 

### designers will learn how to work with the expected site conditions. 9



### • Lower material costs are expected over time as the practices become more standard. The 10 

### materials that at a premium now because they are a specialty item will become routine. 11 

### For example, PWD estimates that in the future, poro us pavement costs will be 12 

### comparable to traditional pavement costs. 13



### • Reduced design costs are expected as more designers become familiar with LID 14 

### practices. PWD estimates that designs for LID proje cts will be on par with more standard 15 

### designs. 16



### • Reduced perception of risk will result in a lower c ontingency being applied to cost 17 

### estimates. 18 

### The ranges of cost reduction expected by PWD over t ime from improved site design and lower 19 

### material costs is approximately 20 percent up to ab out 25 percent. 20 

### LID Green Street Programs. Green street projects have been implemented for the past several 21 

### years in Portland, Oregon, and Seattle, Washington, and other locations. Montgomery County, 22 

### Maryland , . Montgomery County has undertaken several green streets projects, and recently 23 

### compared the costs of its projects, both estimated and completed, with reported costs from other 24 

### jurisdictions, as well as could be interpreted from the literature information provided. There is 25 

### limited data available to date, and many factors co ntribute to the differences in costs reported, so 26 

### this data might not be widely applicable. Table 3-2 4 presents a recent summary of the 27 

### Montgomery County evaluation, with information adde d from Portland on its Portland’s 28 

### estimates. 29

Table 3-24. Summary of green streets cost Montgomery County , Mary land , evaluation 30 Estimated level of WQ control Total DA Cost per acre DA (in $1,000s) Cost per sf BMP SA (in $/sf) Cost per impervious acre DA (in $1,000s) (acres) design construction design construction design construction Bioretention retrofit projects Montgomery County 100% 1.1 a $17 $112 $17 $113 $20 $131

100% 0.17 b $41 $214 $26 $136 $41 $214 Portland (Areas reported as impervious only) 100% 0.21 c $10 $79 $8 $29 $10 $79

Prince 66% 13.4 d $14 $104 $19 $139 $32 $2333/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 79

Estimated level of WQ control Total DA Cost per acre DA (in $1,000s) Cost per sf BMP SA (in $/sf) Cost per impervious acre DA (in $1,000s) (acres) design construction design construction design construction George’s County 86% 1.5 e $72 $92 $99 $126 $217 $276

Swales and Filter Strip Retrofit Projects Montgomery County 16% to 50% 1.1 to 3.7 f $33 to $75 $26 to $84 $35 to $86 $39 to $44 $96 to

$128 $40 to $143

Caltrans Swales 56% 0.20 to 2.4 g,i NR $31 to $121 NR $12 to $58 NR $35 to $128

Caltrans Filter Strips 100% 0.49 to 2.42 h,j NR $23 to $120 NR $12 to $43 NR $35 to $128

Burnsville, MN (less urbanized) NR 5.3 j $12 $24 NR NR NR NR

Notes: 1 Source: Montgomery County, Maryland, and Portland, Oregon 2 NR = Not Reported; DA = Drainage Area; SA = Surface Area; sf = square foot; Estimated Level of Control = 3 a. Dennis Ave. Health Center 4 b. 12 th & Montgomery Ave. ; , Portland, OR, Report - only planter & pavers; 5 ttp://asla.org/awards/2006/06winners/341.html ttp://asla.org/awards/2006/06winners/341.html 6 c. Green-Siskiyou, OR - curb planters, no subdrain, assume total DA (total impervious DA in report); 7 http://www.asla.org/awards/2007/07winners/506_nna.h tml http://www.asla.org/awards/2007/07winners/506_nna.h tml 8 d. Route 201 Gateway - roadway median retrofit 9 e. US Rt. 1 at I-95 Interchange 10 f. Various projects, combination of completed costs and costs estimated for projects yet to be built 11 g. Various 2004 projects; include factors that incr eased the cost for dense urban retrofit (traffic co ntrol, etc.) 12 h. Various 2004 projects; include factors that incr eased the cost for dense urban retrofit (traffic co ntrol, etc.) 13 i. BMP Retrofit Pilot Program, Final Report, Report ID CTSW - RT - 01 – 050, California Department of 14 Transportation, January 2004 15 j. Roadside swales and rain gardens; suburban commu nity retrofits 16
17 

### Coastal North Carolina, Community Conservation Assi stance Program (CCAP). Striving to 18 

### protect its shellfish resources, LID has requirements have been encouraged in place in North 19 

### Carolina since 1986

. but were strengthened in 2009 including a requirement for new and 20 

### redeveloped projects to 21

• 

### Retain and contro l approximately 3.6 inches of rainfall, or the one

- year, 24

- hour storm, 22 

### for projects within one

- half mile of shellfishing waters. 23



### • Retain and control 1.5 inches for project s with gre ater than 25 percent impervious cover, 24 

### for areas outside the one

- half mile area 25 

### As a result, North Carolina has implemented a cost- share program to help start the adoption of 26 

### new LID technologies. They developed cost informati on that they use in the CCAP to estimate 27 

### cost-sharing amounts. Table 3-25 provides a summary costs for coastal North Carolina for 2009. 283/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 80 Table 3-25. LID costs used by the North Carolina Di vision of Water Quality’s Community Cost 1 Share Program 2

BMP Components Unit type All areas unit cost Abandoned well closure Each Backyard rain garden SqFt Bioretention excavation SqFt $5.00 Bioretention soil amendment -sand SqFt $0.50 Bioretention mulch SqFt $0.75 Bioretention plants (installed) SqFt $1.50 Backyard wetland SqFt Wetland excavation SqFt $5.50 Wetland plants (installed) SqFt $2.30 Wetland outlet structure Each $50.00 Cisterns Each Cistern 250-1,000 gallons installed Gallon $1.75 Cistern 1,000-3,000 galons installed Gallon $1.00 Cistern 3,000 gallons installed Gallon Accessories package Each $700.00 Cistern foundation SqFt $1.40 Concrete pad for cistern SqFt $3.60 Shipping charge Each Critical area planting SqFt Grading - minimum Job $25.00 Grading - light, 1" - 3" avg 100 SqFt $3.90 Grading - medium, 3" - 6" avg 100 SqFt $4.82 Grading - heavy, 6" - 9" avg 100 SqFt $5.74 Grading - extra heavy, 9" - 12" avg 100 SqFt $6.66 Grading - maximum heavy, more than 12" avg 100 SqFt $7.58 Vegetation (grass) - minimum Job $15.00 Vegetation (grass) 100 SqFt $0.75 Vegetation (trees/shrubs) SqFt Vegetation - mulch, netting 100 SqFt Vegetation - mulch, small grain straw 100 SqFt $1.28 Matting - excelsior, installed SqYd $0.95 Diversion Feet Excavation SqFt $5.00 Vegetation (grass) 100 SqFt $0.75 Filter cloth-geotextile fabric SqYd $2.25 Filter cloth-pins, metal anchor Each $2.00 Vegetation - mulch, netting 100 SqFt Vegetation - mulch, small grain straw 100 SqFt $1.26 Matting - excelsior, installed SqYd $0.953/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 81 1 

### Amesbury, Massachusetts Cost Comparison of LID Parking Lot and Conventional Parking 2 

### Lot. When evaluating the costs of LID, it is important t o do it in comparison to the costs of 3 

### alternative stormwater management. The economies of subdivision development with LID 4 

### practices have been documented (USEPA 2007). As an example, Table 3-26 presents a detailed 5 

### breakdown of a cost comparison for two parking area s estimated in for a project in 6 

### Massachusetts , indicating that the LID construction cost was not higher than conventional costs. 7 

### For this project, design costs were reported as hig her because it was a relatively new type of 8 

### design, but lower maintenance costs were reported t o be anticipated. 9

Table 3-26. Comparison of conventional design vs. b ioretention in two parking areas in Amesbury, 10 Massachusetts 11
Bioretention Area 1 Bioretention Area 2
Island = 51,155 SF (4,867 SF landscape) Adjacent to clubhouse = 77,90 SF (19,584 SF landscape)
Quantity Unit

cost Total cost Quantity Unit cost Total cost Item LID Standard LID Standard LID Standard LID Stan dard Loam (4" depth) (CY) NA 59.6 $40 NA $2,384 179 239.4 $40 $7,160 $9,576 Bioretention soil mix (24" depth) (CY) 360.5 NA $40 $14,421 NA 363 NA $40 $14,520 NA Seed (SY) 240 541 $4 $960 $2,164 1360.8 1941 $4 $5,443 $7,764 Composted, double shredded hardwood mulch (3" depth) (CY) 25 0 $28 $700 $0 68 20 $28 $1,904 $560 Trees (EA) 18 18 $518 $9,315 $9,315 45 45 $518 $23,288 $23,288 Shrubs (EA) 61 30 $32 $1,922 $945 216 108 $32 $6,804 $3,402 Perennials and grasses (EA) 1450 0 $2 $2,900 $0 2068 0 $2 $4,136 $0Landscape

total $30,217 $14,808 total $63,255 $44,590 HDPE Drain pipe (12" dia) (LF) NA 55.4 $12 NA $648 NA 148 $12 NA $1,732 Catch Basins (EA) NA 2 $3,07 5 NA $6,150 NA 4 $3,075 NA $12,300 Water Quality Units (Stormcepto r STC 900) (EA) NA 1 $8,00 0 NA $8,000 NA 1 $8,000 NA $8,000 Curb (Extruded Concrete) Straight (LF) NA 506.8 $6 NA $2,914 NA 655.5 $6 NA $3,769Sitework

Curb (Extruded Concrete) Radius (LF) NA 45.7 $8 NA $356 NA 78.5 $8 NA $6123/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 82 Bioretention Area 1 Bioretention Area 2
Island = 51,155 SF (4,867 SF landscape) Adjacent to clubhouse = 77,90 SF (19,584 SF landscape)
Quantity Unit

cost Total cost Quantity Unit cost Total cost Item LID Standard LID Standard LID Standard LID Stan dard Wheel Stops (EA) 43 NA $66 $2,838 NA 49 NA $66 $3,234 NA Drain Manholes (EA) NA NA $3,32 5 NA NA NA 1 $3,325 NA $3,325 Earthwork (CY) NA 183 $5 NA $860 NA 493 $5 NA $2,317 Pipe Bedding (CY) NA 15.3 $2 NA $36 NA 41.1 $2 NA $96
total $2,838 $18,964 total $3,234 $32,151
Bioretention Area 1 Bioretention Area 2
total $33,055 $33,772 total $66,489 $76,740 Source: Eisenburg, Bethany, Design, Engineering, In stallation, and O&M Considerations for Incorporatin g 1 Stormwater Low Impact Development (LID) in Urban, S uburban, Rural, and Brownfields Sites, American Soc iety of 2 Civil Engineers (ASCE), Low Impact Development Conf erence Proceedings, 2008 3

4



## 2. 11 5

References 5


### American Forests. CITYgreen . American Forests, Washington, 6 

### DC.<http://www.americanforests.org/productsandpubs/ citygreen>. Accessed February 23, 7 

### 2010. 8


### American Forests. Trees Reduce Stormwater . American Forests, Washington, 9 

### DC.<http://www.americanforests.org/graytogreen/stor mwater>. Accessed February 23, 10 

### 2010. 11 

### Arendt, R. 1999. Growing Greener: Putting Conservation into Local Pl ans and Ordinances

. 12 

### National Lands Trust-American Planning Association- American Society of Landscape 13 

### Architects, Island Press, Washington, DC. 14


### ASFPM

. 2010. Natural and Beneficial Floodplain Functions: Flood plain Management—More 15 

### than Flood Loss Reduction. Association of State Floodplain Managers, Madison, WI. 16 

### <http://www.floods.org>. Accessed February 23, 2010

. 17 

### Casey Trees. 2008. Green Build-out Model . Casey Trees, Washington, D.C. 18 

### <http://www.caseytrees.org/planning/greener-develop ment/gbo/index.php>. Accessed 19 

### February 23, 2010. 20


### Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing 21 

### Development Rules in Your Community . Center for Watershed Protection, Ellicott, MD. 22 

### <http://www.cwp.org/Store/bsd.htm>. Accessed Februa ry 23, 2010. 233/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 83 

### Center for Watershed Protection. 2003-2008. Urban Subwatershed Restoration Manual Series

. 1 

### Center for Watershed Protection, Ellicott City, MD. 2 

### <http://www.cwp.org/Store/usrm.htm>. Accessed Febru ary 23, 2010 ST

. 3


### Center for Watershed Protection. 2008. Managing Stormwater in Your Community: A Guide for 4 

### Building an Effective Post-Construction Program . Center for Watershed Protection, 5 

### Ellicott City, MD. 6 

### <http://www.cwp.org/Resource_Library/Center_Docs/SW /pcguidance/Manual/PostConstr 7 

### uctionManual.pdf>. Accessed February 23, 2010. 8


### Center for Watershed Protection. 2008. Better Site Design Resources . Center for Watershed 9 

### Protection, Ellicott City, MD. 10 

### <http://www.cwp.org/Resource_Library/Better_Site_De sign/index.htm>. Accessed 11 

### February 23, 2010. 12 

### Cheng, M.S., C.A. Akinbobola, J. Zhen, J. Riverson, K. Alvi and L. Shoemaker. 2009. BMP 13 

### decision support system for evaluating stormwater m anagement alternatives. Frontieers of 14 

### Environmental Science & Engineering in China. 3(4): 453-463. 15 

### <http://www.springerlink.com/content/l682122767u41k 7x/fulltext.pdf>. Accessed 16 

### February 23, 2010. 17 

### Chesapeake Bay Foundation. No date. Facts About Nutrient Trading from the Chesapeake Ba y 18 

### Foundation . Chesapeake Bay Foundation, Annapolis, MD. 19 

### < http://www.cbf.org/Document.Doc?id=141>. Accessed F ebruary 23, 2010. 20 

### Chesapeake Bay Program. 2009. Developing Best Management Practice Definitions and 21 

### Effectiveness Estimates for Nitrogen, Phosphorus, a nd Sediment in the Chesapeake Bay, 22 

### December 2009 . Chesapeake Bay Program, Annapolis, MD. 23 

### < http://www.chesapeakebay.net/websitesearchresults.a spx?menuitem=19557>. Accessed 24 

### February 23, 2010. 25 

### City of New York. 2008. Plan NYC, Appendix C . City of New York, New York, NY. 26 

### <http://www.nyc.gov/html/planyc2030/html/stormwater /stormwater.shtml>. Accessed 27 

### February 24, 2010. 28 

### City of Philadelphia. 2010. Philadelphia Going Green . City of Philadelphia, Philadelphia, PA. 29 

### <http://www.phila.gov/green>. Accessed February 23, 2010. 30 

### City of Philadelphia. 2009. Long Term Control Plan Update, Supplemental Documen tation, 31 

### Volume 3, Basis of Cost Opinions . City of Philadelphia, Philadelphia, PA. 32 

### <http://www.phillywatersheds.org/ltcpu/Vol03_Cost.p df>. Accessed February 24, 2010. 33 

### City of Philadelphia. No date. Philadelphia’s Stormwater Manual . Philadelphia Water 34 

### Department, Philadelphia, PA. 35 

### <http://www.phillyriverinfo.org/WICLibrary/chapter% 201.pdf>. Accessed February 24, 36 

### 2010. 373/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 84 

### City of Portland. 2008. Cost Benefit Evaluation of Ecoroofs 2008. City of Portland Bureau of 1 

### Environmental Services, Portland, OR. 2 

### <http://www.portlandonline.com/BES/index.cfm?a=2610 53&c=50818>. Accessed 3 

### February 23, 2010. 4 

### City of Portland. 2004. City of Portland Stormwater Manual. Environmental Services, City of 5 

### Portland, Clean River Works, Portland, OR. 6 

### < http:// www.portlandonline.com/BES/index.cfm?c=35122 >. Accessed February 22, 2010. 7 

### City of Seattle. 2010. Green Stormwater Infrastructure . Seattle Public Utilities. Seattle, WA. 8 

### <http://www.seattle.gov/util/About_SPU/Drainage_&_S ewer_System/GreenStormwaterInf 9 

### rastructure/index.htm>. Accessed February 23, 2010. 10 

### City of Seattle. 2010. Natural Drainage Projects . Seattle Public Utilities. Seattle, WA. 11 

### <http://www.seattle.gov/util/naturalsystems>. Acces sed February 23, 2010. 12 

### City of Seattle. 2010. Street Edge Alternatives . Seattle Public Utilities, Seattle, WA. 13 

### <http://www.seattle.gov/util/About_SPU/Drainage_&_S ewer_System/GreenStormwaterInf 14 

### rastructure/NaturalDrainageProjects/StreetEdgeAlter natives/index.htm>. Accessed 15 

### February 23, 2010. 16 

### Cohen, A. 2006 Narrow Streets Database. Congress for the New Urbanism. 17 

### <http://lists.cacities.org/pipermail/hced/attachmen ts/20031030/91bd1be8/NARROWSTRE 18 

### ETSDATABASE-0003.doc>. Accessed March 5, 2009. 19 

### DDOT (District Department of Transportation). Anaco stia Waterfront Transportation 20 

### Architecture Design Standards. District Department of Transportation, Washington, DC. 21 

### <http://ddot.dc.gov/ddot/cwp/view,a,1249,q,627063,d dotNav_GID,1744,ddotNav,|33960|.a 22 

### sp>. Accessed February 23, 2010. 23 

### Delaware DNREC (Department of Natural Resources and Environmental Control). 1997. 24 

### Conservation Design for Stormwater Management: A De sign Approach To Reduce 25 

### Stormwater Impacts from Land Development and Achiev e Multiple Objectives Related to 26 

### Land Use . Delaware Department of Natural Resources and Envi ronmental Control and The 27 

### Environmental Management Center of the Brandywine C onservancy, Dover, DE. 28 

### <http://www.dnrec.state.de.us/DNREC2000/Divisions/S oil/Stormwater/New/Delaware_C 29 

### D_Manual.pdf>. Accessed February 23, 2010. 30 

### Devereux, Olivia H., Karen L. Prestegaard, Brian A. Needelman and Allen C. Gellis. 2010. 31 

### Suspended-sediment sources in an urban watershed , Northeast Branch Anacostia River, 32 

### Maryland

. Hydrological Processes , Accepted 2009. 33


### ECONorthwest. 2007. The Economics of Low-Impact Development: A Literatu re Review

. 34 

### EcoNorthwest, Eugene, OR. 35 

### Eisenburg, Bethany. 2008. Design, Engineering, Installation, and O&M Consider ations for 36 

### Incorporating Stormwater Low Impact Development (LI D) in Urban, Suburban, Rural, and 37 

### Brownfields Sites. American Society of Civil Engineers (ASCE), Low Im pact Development 38 

### Conference Proceedings, 2008. 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 85 

### Federal Interagency Stream Restoration Working Grou p (FISRWG.) 1998 . Stream Corridor 1 

### Restoration: Principles, Processes, and Practices. National Technical Information Service, 2 

### Alexandria, VA. 3 

### Gellis, Allen C., Cliff R. Hupp, Jurate M. Landwehr and Milan J. Pavich. 2007. Synthesis of U.S. 4 

### Geological Survey Science for the Chesapeake Bay Ec osystem and Implications for 5 

### Environmental Management, Chapter 6: Sources and Tr ansport of Sediment in the 6 

### Watershed . U.S. Geological Survey Circular 1316. U.S. Geolog ical Survey, Reston, VA. 7 

### Gellis, A.C., Cliff R. Hupp, Milan J. Pavich, Jurat e M. Landwehr, William S.L. Banks, Bernard 8 

### E. Hubbard, Michael J. Langland, Jerry C. Ritchie a nd Joanna M. Reuter. 2009. Sources, 9 

### transport, and storage of sediment in the Chesapeak e Bay Watershed . U.S. Geological 10 

### Survey Scientific Investigations Report 2008–5186. U.S. Geological Survey, Reston, VA. 11 

### Geosyntec Consultants and Wright Water Engineers. 2 009. Urban Stormwater BMP 12 

### Performance Monitoring . International Stormwater BMP Database. 13 

### <http://www.bmpdatabase.org/MonitoringEval.htm>. Ac cessed February 23, 2010. 14 

### Hinman, C. 2005. Low Impact Development Manual—Technical Guidance Ma nual for Puget 15 

### Sound . Puget Sound Action Team, Washington State Univers ity Pierce County Extension, 16 

### Tacoma, WA. <http://www.psp.wa.gov/downloads/LID/LI D_manual2005.pdf>. Accessed 17 

### February 22, 2010. 18 

### Hunt, Bill, Jason Wright and Dwane Jones. No date. Evaluating LID for an Engineering 19 

### Development in the Lockwood Folly Watershed, North Carolina . North Carolina State 20 

### University (NCSU), Raleigh, NC. 21 

### <http://www.nhcgov.com/AgnAndDpt/PLNG/Documents/Bru nswickLID.pdf>. Accessed 22 

### February 24, 2010. 23


### i-Tree. 2010. What Is i-Tree? USDA Forest Service, Washington, 24 

### DC.<http://www.itreetools.org>. Accessed February 2 3, 2010. 25 

### The Interstate Technology & Regulatory Council . 20 09. Phytotechnology Technical and 26 

### Regulatory Guidance . The Interstate Technology & Regulatory Council, W ashington, DC. 27 

### Kaushal, Sujay S., Peter M. Groffman, Paul M. Mayer , Elise Striz and Arthur J. Gold. 2008. 28 

### Effects of Stream Restoration on Denitrification in an Urba nizing Watershed. Ecological 29 

### Applications , 18(3): 789-804. 30 

### Klocker, Carolyn A., Sujay S. Kaushal, Peter M. Gro ffman, Paul M. Mayer and Raymond P. 31 

### Morgan. 2009. Nitrogen uptake and denitrification i n restored and unrestored streams in 32 

### urban Maryland, USA. Aquatic Sciences , 71(4): 411-424. 33 

### Lal, Harbans. Nutrient Credit Trading: A Market-based Approach fo r Improving Water Quality

. 34 

### WNTSC/NRCS/USDA, Portland, OR. 35 

### <http://www.wsi.nrcs.usda.gov/products/w2q/mkt_base d/docs/nitrogen_credit_trading.pdf>. 36 

### Accessed February 23, 2010. 373/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 86 

### The Low-Impact Development Center. 2008. Low Impact Development . The Low-Impact 1 

### Development Center, Beltsville, MD. <http://www.low impactdevelopment.org/>. Accessed 2 

### February 23, 2010. 3


### National Association of Local Government Environmen tal Professionals, Trust for Public Land, 4 

### and ERG. 2003. Smart Growth for Clean Water: Helping Communities A ddress the Water 5 

### Quality Impacts of Sprawl . National Association of Local Government Environm ental 6 

### Professionals, Washington DC City, ST , Trust for Public Land, San Francisco, CA City, ST , 7 

### and ERG, Boston, MA City, ST

. 8 

### National Cooperative Highway Research Program. 2006

. Project 25-20(01): Evaluation of Best 9 

### Management Practices for Highway Runoff Control, Puget Sound Action Team. 2005. Low 10 

### Impact Development Highway Manual
, Oregon State University, Corvallis, OR.

— 11 

### Technical Guidance Manual for Puget Sound

. 12 

### < http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rp t_565.pdfwww.psp.wa.gov/download 13 

### s/LID/LID_manual2005.pdf >. Accessed February 23, 2010. 14


### Natural Resources Defense Council. 2006. Rooftops to Rivers: Green Strategies for Controllin g 15 

### Stormwater and Combined Sewer Overflows ; NRDC, New York, NY. 16 

### <http://www.nrdc.org/water/pollution/rooftops/conte nts.asp>. Accessed February 24, 2010. 17


### NEMO. 2008. A Catalyst for Community Land Use Change , 2008 Progress Report . National 18 

### NEMO Network, Haddam, CT. 19 

### <http://nemonet.uconn.edu/about_network/publication s/2008_report.htm>. Accessed 20 

### February 23, 2010. 21


### North Carolina Coastal Federation. 2008. Low Impact Development Pilot Study to Reduce Fecal 22 

### Coliform into Core Sound, Final Report . North Carolina Coastal Federation, Newport, NC. 23


### PBES

. 2010 . Portland Green Street Program . Portland Bureau of Environmental Services, 24 

### Portland, OR. <http://www.portlandonline.com/BES/in dex.cfm?c=44407>. Accessed 25 

### February 23, 2010. 26


### PBES

. 2010 . Tabor to the River . Portland Bureau of Environmental Services, Portla nd, OR. 27 

### <http://www.portlandonline.com/bes/index.cfm?c=4759 1>. Accessed February 23, 2010. 28


### Portland Bureau of Environmental Services. 2010. A Sustainable Approach to Stormwater 29 

### Management . City of Portland, OR. 30 

### <http://www.portlandonline.com/bes/index.cfm?c=3459 8>. Accessed February 23, 2010. 31 

### Prince George’s County, Maryland. 2009. Annual Repo rt. Prince George’s County, MD. 32 

### <http://www.co.pg.md.us/Government/AgencyIndex/Goin gGreen/pdf/2009-annual-green33 

### report.pdf>. Accessed February 23, 2010. 34 

### Saluda-Reedy Watershed Consortium. 2006. Audit of Pavement Standards for the Saluda-Reedy 35 

### Watershed, Mitigating the Impacts of Impervious Sur faces in Greenville and Pickens 36 

### Counties, South Carolina . Upstate Forever, SC. <http://www.upstateforever.o rg>. 37 

### Accessed February 23 22 , 2010. 383/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 87 

### Santa Clara Valley Urban Runoff Pollution Preventio n Program. 2005. Hydromodification 1 

### Management Plan—Final Report

. Sunnyvale, CA. 2 

### <http://www.eoainc.com/hmp_final_draft>. < http://www.eoainc.com/hmp_final_draft >

. 3 

### Accessed February 22, 2010. 4 

### Schueler, Tom. 1995. Site Planning for Urban Stream Protection. Metropolitan Washington 5 

### Council of Governments, Washington, DC. 6 

### <http://www.mwcog.org/store/item.asp?PUBLICATION_ID =56>. Accessed February 23, 7 

### 2010. 8 

### Schueler, T.R., and H.K. Holland. 2000. The Practice of Watershed Protection: Article 36—Th e 9 

### Compaction of Urban Soils

. Technical Note #107 from Watershed Protection Techniques , 10 

### 3(2): 661-665. The Center for Watershed Protection , . Ellicott City, MD. 11


### Smart Growth Network. 2010. Principles of Smart Growth . National Center for Appropriate 12 

### Technology, Butte, MT. 13 

### <http://www.smartgrowth.org/about/principles/defaul t.asp?res=1024#top>. Accessed 14 

### February 23, 2010. 15 

### Stratus Consulting. 2009. A Triple Bottom Line Assessment of Traditional and Green 16 

### Infrastructure, Options for Controlling CSO Events in Philadelphia's Watersheds Final 17 

### Report . Stratus Consulting, Inc, Boulder, CO. 18 

### <http://www.michigan.gov/documents/dnr/TBL.Assessme ntGreenVsTraditionalStormwate 19 

### rMgt_293337_7.pdf>. Accessed February 23, 2010. 20


### Town of Edmonston. No date. Project Green Street . Town of Edmonston, MD. 21 

### <http://edmonston.us.com/GreenStreetGroundbreaking. html>. Accessed February 23, 22 

### 2010. 23 

### U.S. Army Corps of Engineers. 2008. Low Impact Development for Sustainable Installation s: 24 

### Stormwater Design and Planning Guidance for Develop ment within Army Training Areas

. 25 

### Public Works Technical Bulletin 200-1-62. U.S. Army Corps of Engineers, Washington, 26 

### DC. 27 

### USDA (U.S. Department of Agriculture) Natural Resou rces Conservation Service. 2007. Part 28 

### 654 Stream Restoration Design National Engineering Handbook . U.S. Department of 29 

### Agriculture, Washington, DC. 30 

### USEPA (U.S. Environmental Protection Agency) and Pr ince George’s County, Maryland. 1999. 31 

### Low-impact Development Strategies, An Integrated De sign Approach, U.S. Environmental 32 

### Protection Agency, Washington, DC, and Prince Georg e’s County, MD. 33 

### USEPA (U.S. Environmental Protection Agency) and Pr ince George’s County, Maryland. 2000. 34 

### Low-impact Development Strategies, An Integrated De sign Approach, U.S. Environmental 35 

### Protection Agency, Washington, DC, and Prince Georg e’s County, MD. 363/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 88 

### USEPA (U.S. Environmental Protection Agency) and Pr ince George’s County, Maryland. 2000. 1 

### Low-Impact Development Hydrologic Analysis . U.S. Environmental Protection Agency, 2 

### Washington, DC, and Prince George’s County, MD. <ht tp://www.epa.gov/nps/lid/>. 3 

### Accessed February 23, 2010. 4 

### USEPA (U.S. Environmental Protection Agency) and Pr ince George’s County, Maryland. 2006. 5 

### Final Technical Report Phase III. U.S. Environmenta l Protection Agency, Washington, DC 6 

### and Prince George’s County, MD. 7 

### <http://www.princegeorgescountymd.gov/Government/Ag encyIndex/DER/ESG/pdf/Final 8 

### %20Technical%20Report_Phase%20III.pdf>. Accessed Fe bruary 23, 2010. 9 

### USEPA (U.S. Environmental Protection Agency) and Pr ince George’s County, Maryland. 2007. 10 

### Final Technical Report, Pilot Projects for LID Urba n Retrofit Program, In the Anacostia 11 

### River Watershed, Phase IV . U.S. Environmental Protection Agency, Washington, DC and 12 

### Prince Georges County, Maryland. 13 

### <http://www.princegeorgescountymd.gov/Government/Ag encyIndex/DER/ESG/pdf/Final 14 

### Technical Report Phase III.pdf>. Accessed February 23, 010. 15 

### USEPA (U.S. Environmental Protection Agency). 2001. Protecting and Restoring America’s 16 

### Watershed’s: Status, Trends, and Initiatives in Wat ershed Management . U.S. 17 

### Environmental Protection Agency, Washington, DC. 18 

### <http://www.epa.gov/owow/nps/urbanm/pdf/urban_guida nce.pdf>. Accessed February 23, 19 

### 2010. 20 

### USEPA (U.S. Environmental Protection Agency). 2003. Fact Sheet: Water Quality Trading 21 

### Policy . U.S. Environmental Protection Agency, Washington DC. 22 

### <http://www.epa.gov/owow/watershed/trading/2003fact sheet.pdf>. Accessed February 23, 23 

### 2010. 24 

### USEPA (U.S. Environmental Protection Agency). 2003. Water Quality Trading Policy . U.S. 25 

### Environmental Protection Agency, Washington, DC. 26 

### <http://www.epa.gov/owow/watershed/trading/finalpol icy2003.pdf>. Accessed February 27 

### 23, 2010. 28 

### USEPA (U.S. Environmental Protection Agency). 2004. Stormwater Best Management Practices 29 

### Design Guide , Volumes 1-3 (121, 121A, 121B) . U.S. Environmental Protection Agency, 30 

### Office of Research and Development, Washington, DC. 31 

### <http://www.epa.gov/nrmrl/pubs/600r04121/600r04121. htm>. Accessed February 23, 32 

### 2010. 33 

### USEPA (U.S. Environmental Protection Agency). 2004. Stormwater Best Management Practices 34 

### Design Guide, Office of Research and Development , Volumes 1-3 (121, 121A, 121B). U.S. 35 

### Environmental Protection Agency, Washington, DC. 36 

### USEPA (U.S. Environmental Protection Agency). 2004. The Use of Best Management Practices 37 

### (BMPs) in Urban Watersheds , U.S. Environmental Protection Agency, Office of R esearch 38 

### and Development, Washington, DC. 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 89 

### USEPA (U.S. Environmental Protection Agency). 2005. National Management Measures to 1 

### Control Nonpoint Source Pollution from Urban Areas . U.S. Environmental Protection 2 

### Agency, Washington, DC. 3 

### USEPA (U.S. Environmental Protection Agency). 2005

. Using Smart Growth Techniques as 4 

### Stormwater Best Management Practices . U.S. Environmental Protection Agency, 5 

### Washington, DC. 6 

### USEPA (U.S. Environmental Protection Agency). 2008. Handbook for Developing Watershed 7 

### Plans to Restore and Protect our Waters . U.S. Environmental Protection Agency, 8 

### Washington, DC. 9 

### USEPA (U.S. Environmental Protection Agency). 2009. Technical Guidance on Implementing 10 

### the Stormwater Runoff Requirements for Federal Proj ects under Section 438 of the Energy 11 

### Independence and Security Act . U.S. Environmental Protection Agency, Washington, DC. 12 

### <http://www.epa.gov/owow/NPS/lid/section438/pdf/fin al_sec438_eisa.pdf < 13 

### http://www.epa.gov/owow/NPS/lid/section438/pdf/fina l_sec438_eisa.pdf > Accessed 14 

### February 22, 2010. 15 

### USEPA (U.S. Environmental Protection Agency). 2010. Liquid Assets

. 2005. Using Smart 16 

### Growth Techniques as Stormwater Best Management Pra ctices

. U.S. Environmental 17 

### Protection Agency, Washington, DC. 18 

### <http://www.epa.gov/water/liquidassets/execsumm.htm l>. Accessed February 23, 2010. 19 

### USEPA (U.S. Environmental Protection Agency). 2010. Protecting Water Resources with 20 

### Higher-Density Development . U.S. Environmental Protection Agency, Washington, DC. 21 

### <http://www.epa.gov/dced/water_density.htm>. Access ed February 23, 2010. 22 

### USEPA (U.S. Environmental Protection Agency). 2010. Reducing Stormwater Costs through 23 

### Low Impact Development (LID) Strategies and Practic es . U.S. Environmental Protection 24 

### Agency, Washington, DC. <http://www.epa.gov/nps/lid >. Accessed February 23, 2010. 25 

### USEPA (U.S. Environmental Protection Agency). 2010. Water Quality Scorecard: 26 

### Incorporating Green Infrastructure Practices at the Municipal, Neighborhood, and Site 27 

### Scale . U.S. Environmental Protection Agency, Washington, DC. 28 

### <http://www.epa.gov/dced/water_scorecard.htm>. Acce ssed February 23, 2010. 29 

### USEPA (U.S. Environmental Protection Agency). 2010. Water Quality Scorecard: 30 

### Incorporating Green Infrastructure Practices at the Municipal, Neighborhood, and Site 31 

### Scales . <http://www.epa.gov/dced/water_scorecard.htm>. 32 

### USGS (U.S. Geological Survey). 2003. A Summary Report of Sediment Processes in Chesapeak e 33 

### Bay and Watershed

. U.S. Geological Survey, Reston, VA. 34 

### U.S. Naval Facilities Engineering Command. 2004. Low Impact Development, Draft, Unified 35 

### Design Criteria. U.S. Department of Defense, Washington, DC. 36 

### < http://www.wbdg.org/ccb/DOD/UFC/ufc_3_210_10.pdf>. Accessed February 23, 2010. 373/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 90 

### WERF (Water Environment Research Federation). 2005. Performance and Whole-Life Costs of 1 

### Sustainable Urban Drainage Systems . Water Environment Research Federation, 2 

### Alexandria, VA. 3 

### WERF (Water Environment Research Federation). 2006. Infiltration vs. Surface Water 4 

### Discharge: Guidance for Stormwater Managers, Final Report . Appendix B. Assessment of 5 

### Existing Watershed Conditions: Effects on Habitat. Water Environment Research 6 

### Federation, Alexandria, VA. 7 

### WERF (Water Environment Research Federation). Foundation )

. 2008. Protocol for Studying Wet 8 

### Weather Impacts and Urbanization Patterns . Water Environment Research Foundation, 9 

### Alexandria, VA City, ST

. 10 

### WERF (Water Environment Research Federation). 2009. WERF Cost Tool , 2009. Free 11 

### spreadsheet tool developed as part of Performance and Whole Life Cost of Best 12 

### Management Practices and Sustainable Urban Drainage Systems (2005). Water 13 

### Environment Research Federation. 14 

### www.werf.org/AM/Template.cfm?Section=Stormwater3 15 

### Washington State Department of Ecology. 2005. Western Washington Stormwater Management 16 

### Manual

. Olympia, WA. < www.ecy.wa.gov/programs/wq/stormwater/manual.html >. 17 

### Accessed February 22, 2010. 18 

### Weinstein, Neil, Jennifer Cotting, Dan Nees, Sara D owning, Jeff Lee, Benjamin Tauber, Ann 19 

### English, Christopher Kloss, Charles Glass, Wayne C. Huber and Tracy Morgan. 2009. 20 

### Decentralized Stormwater Controls for Urban Retrofi t and Combined Sewer Overflow 21 

### Reduction, Phase II . Water Environment Research Federation, Alexandria , VA. 22 

### Wiess, P.T., J.S. Gulliver, and A.J. Erickson. 2005

. The Cost and Effectiveness of Stormwater 23 

### Management Practices . Minnesota Department of Transportation, Minneapol is, MN. 24 

### Woodworth, J.W. Jr. 2002. Out of the Gutter . National Resources Defense Council, New York, 25 

### NY. <http://www.nrdc.org/water/pollution/gutter/gut ter.pdf>. Accessed February 23, 2010. 26