Green Streets Amendment

GREEN STREETS AMENDMENT

for the

MONTGOMERY COUNTY ROAD CODE BILL

MontgomeryCounty Stormwater Partners[*]

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Contents:

Purpose…………………..….Page 1

Technical Proposal………….Page 2

Toolbox of Techniques….…..Page 6

Endnotes…………………… Page 18

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PURPOSE

Of a Green Streets Amendment

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The Road Code bill should be amended to mandate that a minimum quantity of stormwater be retained and treated on-site, within the road right-of-way, preferably using vegetation-based stormwater management techniques.

This should be achieved using the following principles of roadway design:

• Incorporate bioretention features to the maximum extent practicable, particularly by utilizing landscaping units for this purpose[†].
• Utilize evolving design standards to ensure that MontgomeryCounty’s roadway stormwater management techniques keep pace with the national and international state of the art.
• Minimize impervious surfaces to the maximum extent practicable, once all transportation modes, particularly pedestrian and bicycling needs, are considered.[i]
• Utilize “open section” roads instead of “curb and gutter” roads wherever practicable.
• Preserve existing rural and rustic roads/

1

TECHNICAL PROPOSAL

Basic Description: Each category of road is required to retain a certain volume of stormwater on-site, within the road right-of-way. Roadway designers would use a prioritized “toolbox” of stormwater retention techniques to meet or exceed the stormwater retention requirements. Vegetative infiltration techniquesare preferred, due to their superior performance. Although road designers are free to choose from all the tools included in the law’s stormwater toolbox, specific combinations are suggested for different categories of roadways, based on the particular needs and challenges of that road category.

The Preferred Tools listed for each roadway category are further explained in the Toolbox section, and are documented with technical, web-based references.[‡]

Technical Proposal:

RULE: All roadways must be designed to meet or exceed the following standards for on-site stormwater retention, using one or more of the on-site techniquesspecified by this law:

Stormwater Performance Standards, by Roadway Category:

• ULTRA-URBAN[§]
• Road Code street categories included:

Business District Streets

Priniciple Secondary Residential Streets

(w/ curbs, & 1- or 2-sided parking)

Secondary Residential Streets

(w/curbs, 1-,2-, or no-sided parking)

Tertiary Residential Street

• Minimum stormwater retention: ½ ”

Basis: The Silver Spring Central Business District Sector Plan (2001) calls for stormwater quality treatment on-site for redevelopment projects, but allows for waiver payments into a stream restoration fund in lieu of stormwater quantity volume treatment. The State of Maryland stormwater design manual requires redevelopment projects of 5000 sq. ft. or larger to treat a portion of their stormwater on-site.[ii]

Preferred tools:

• Stormwater planters

Street Trees with Structural Cells (or other Proven Stormwater Retention ability)

Bioretention Medians

Permeable/ pervious pavements

(Note: Underdrains and impermeable liners will be required, as well as overflow drainage/ conveyance; the latter for all categories.)

• Other Options:Underground SW treatment devices

• URBAN
• Road Code street categories included:

Arterials

Industrial Streets

Primary Residential Streets

Secondary Residential Streets

Tertiary Residential Streets

• Minimum stormwater retention: 1”

Example of a similar standard: the Anacostia Waterfront Corporation proposed stormwater standard is on-site retention with beneficial reuse of 1” of rain over 24 hours with a 48-hour antecedent dry period.[iii] This standard applies to all projects including streets and sidewalks as well as buildings and parking lots.

• Preferred tools: Stormwater planters

Street Trees with Structural Cells

Bioretention Medians

Bioretention Swales (Bioswales)

(Underdrains will be necessary, but there may be a few cases where greater infiltration can be achieved e.g. where impermeable liners will not be necessary, as appropriate given soiltype, etc.)

• SUBURBAN
• Road Code street categories included:

Minor Arterials

Primary Residential Streets (with curbs)

Principle Secondary Residential Streets

Secondary Residential Streets

Tertiary Residential Streets

• Minimum stormwater retention: 2”

Example of a similar standard: The Seattle Public Utilities Natural Drainage System Program (that has now completed five major projects) uses a multi-faceted set of goals that includes maximizing on-site retention so as to protect streams from the one to two-year storm event.[iv] The one-year, 24-hour storm size for MontgomeryCounty is 2.6”.

• Preferred tools: Bioretention Cul-de-Sacs

Bioretention Medians

Bioretention Swales (Bioswales)

Bioretention curb extensions

Open Section Roads

Permeable Pavements (for sidewalks)

(Underdrains will be necessary, but there may be cases where greater infiltration can be achieved e.g. where impermeable liners will not be necessary.)

• RURAL
• Road Code street categories included:

Country Roads

Primary Residential Streets (no curbs)

Principle Secondary Residential Streets

Secondary Residential Streets (no curbs, no parking)

• Minimum stormwater retention: 3”

Example: open section roads are applied by the Montgomery Planning Board for rural developments,[v] and these inherently involve the use of swales. The Pembroke development in Frederick County, MD utilized open section roads with bioretention swales and incorporated a design standard of 3” (the two-year storm).[vi]

• Preferred tools: Bioretention Swales

Bioretention Medians

Open Section Roads

Sheet flow to forested areas

• HIGHWAYS/ PARKWAYS
• Road Code street categories included:

Freeways

Controlled Major Highways

Major Highways

Parkways

• Minimum stormwater retention: 3”

Examples: The Prince George’s County highway LID project yielded an average of 35% runoff volume reduction over pre-existing levels for this highway – bioretention retrofit project.[vii]

• Preferred tools: Bioretention Swales

Bioretention Medians

Toolbox of Techniques for On-site Stormwater Retention:

Stormwater Planters

Stormwater Planters in the Portland OR Green Streets Program. from:

Description: These planters, when subjected to a flow test, absorbed 70% of the 25-year storm. This “SW 12th Avenue Green Street Project” project won high honors from the American Society of Landscape Architects.(2006 ASLA General Design Award of Honor for Portland designer Kevin Robert Perry.)

Stormwater Planter Cross Section: go to:

Street Trees As Stormwater Managers

Example: Street Trees with Structural Cells

; this is the design of Jim Urban, ASLA, and it conforms to AASHTO H-20 standards. (Provided as an example, not an endorsement.) See also:

• Description: This is a new technology with thirty projects on the drawing boards and scheduled for implementation in 2007 – 2008. The Street Tree Structural Cell is a modular hard plastic unit designed to hold engineered soil mixes for street trees; provide root controls and sidewalk support, and to collect and retain stormwater either from sidewalk runoff or from roadway runoff entering through specially-designed inlets. Depending upon ultimate tree size and root requirements, each installation requires between 10 and 100 cells.[viii]
• Technical Specifications / Design Standards: The patent with detailed technical specifications is available at:

Bioretention Medians

Highway bioretention features (right-hand picture) through a highway LID project of Prince George’s County, Maryland, as reported in December 2006.[ix] .

Diagram of highway bioretention facility including cross section. From: The US EPA/ US DOT “Green Highways” program web site at

Bioretention Curb Extensions.

Portland Oregon’s Green Streets Program, plan-view diagram of bioretention curb extensions. From:

Detail of curb cut enabling excess stormwater to overflow into the street and the sewer system. Portland green street program – NE Siskiyou St. Project.

Bioretention Cul de Sacs

Source: Boston MAPC: Metropolitan Area Planning Council, at:

• Description: The circular design of existing cul de sac centers is an easy location for a bowl-shaped rain garden. Road grading will need to create at least a 2% slope toward the center in order to effectively collect and treat runoff.

• Technical Specifications / Design Standards: See the Center for Watershed Protection’s fact sheet on alternative turnarounds at: See also the Virginia Beach Green Ribbon Committee recommendations at: which recommend reducing from a 40-foot radius to a 30-foot radius.

Bioswales/ Vegetated Swales

The award-winning Seattle “SEA Street” prototype (Street Edge Alternatives.)

Source: Boston MAPC: Metropolitan Area Planning Council, at:

Bioswales: Construction cost information from Seattle SEA Street Program[x]

Bioswales (continued).

Both Portland, Oregon and Seattle, Washington now have extensive design and construction experience with right-of-way bioswales for road redevelopment projects.

• Technical Specifications / Design Standards:

Example from the Seattle SEA Street program:

.

Open Section Roads

• Description: This green street technique overlaps with the bioswale technique. One definition of an open section road is that it is a road without curbs and gutters. Thus, the road is designed to sheet-flow stormwater into absorptive zones within the right of way that typically are vegetated (grassy) swales or fully-engineered linear bioretention units.

Center For Watershed Protection,

Example of a successful subdivision in MontgomeryCounty that utilized open section roads:

Winchester Homes’ Auburn Village at Sandy Spring in Olney, Maryland, which incorporated open section roads as part of its stormwater management strategy (this subdivision is no longer included on Winchester’s web site.)

Underground Stormwater Treatment devices:

Description: Underground stormwater treatment devices range from

plastic storage/ infiltration pipes, to stainless steel underground storage and solids settling tanks. There is a wide range of vendors selling these technologies, which can work for road cross-sections and other urban, highly-impervious settings where vegetated landscaping-based stormwater management simply won’t work. As a few prominent examples, Vortechnics, StormFilter, and StormCeptor are some of the major underground stormwater treatment devices on the market.

Montgomery County DEP stormwater maintenance managers have testified that on average, underground stormwater devices cost $3000 per year to maintain.[xi]

Stormwater magazine, published by Forester Communications, contains many articles and ads from vendors selling these underground devices; this link is for an article reviewing the maintenance needs of these devices. The illustration is from this article, and depicts a vacuum truck cleaning out an underground unit.

Permeable Pavement

Porous Pavement

From: City of Seattle Flow Control Technical Guidance Manual 2000

Permeable Pavement at Northwood H.S., Silver Spring, MD. From: .

Description: A wide range of choices in permeable/ porous pavements is available for many different applications, ranging from porous concrete and asphalt to permeable interlocking paver blocks.

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Endnotes

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[*] Anacostia Riverkeeper at Earth Conservation Corps, Anacostia Watershed Citizens Advisory Committee,

Anacostia Watershed Society, Audubon Naturalist Society, Chesapeake Bay Foundation, Clean Water

Action, Eyes of Paint Branch, Friends of Cabin John Creek Watershed, Friends of Hillmead Park, Friends of Rock Creek’s Environment, Friends of Sligo Creek, Friends of the Earth, Greater Goshen Civic Association, Montgomery County Civic Federation, Natural Resources Defense Council, Neighbors of Northwest Branch, Northwood-Four Corners Civic Association, Potomac Conservancy, RiverSides, Sierra Club, and the West Montgomery County Citizens Association.

[†]Bioretention definition: Bioretention combines engineered soils and vegetation in a dug-out, trenched, or depressed area to collect, treat, store, filter, and/or infiltrate stormwater runoff. Bioretention may be incorporated into normally-landscaped roadway features such as medians, cul de sacs, traffic circles, curb extensions, planters, street tree containers, and swales.

[‡]Detailed design drawings and specifications for roughly ten green street techniques or technique components, including bioswales; tree boxes; planters; curb extensions, and concrete inlets are presented on Portland’s Green Streets web page at:

[§]Ultra-Urban: refers to “downtown” and Central Business District neighborhoods with high densities of buildings, typically mixtures of retail, residential, and other adjacent uses, buildings fronting on the street/ sidewalk; and high overall imperviousness.

[i] The City of Seattle Pinehurst Green Grid Project, completed in October 2006, reported a 22% reduction in impervious surface as a result of this “green” street redevelopment project – the roadway imperviousness dropped from 74% down to 55%. (see the Seattle Public Utilities’ “Environmental Checklist,” part B.g., at:

[ii]Maryland-NationalCapitolPark and Planning Commission, Silver Spring Central Business District Sector Plan (2001)

[iii] Anacostia Waterfront Corporation, Environmental Standards Development Committee, Draft Environmental Standards, February 2007.

[iv]Seattle Public Utilities, Natural Drainage Systems Program. Program Goals & Overview at:.

[v] See, for instance, the table on p. 6 of the Planning Board memo of Nov. 19, 2003, regarding a proposed development in the Upper Rock Creek master plan area. Open Section Roads are listed as a design element for two rural zones.

[vi] Michael Clar, Ecosite Inc. Pembroke Woods Low Impact Development (LID) Residential Subdivision, Emmittsburg, Maryland. At:

[vii]Prince George’s County Department of Environmental Resources, Final Report – Pilot Projects for Urban LID Retrofit Program in the Anacostia River Watershed Phase III. December 2006. .

[viii] Structural Cell designer Jim Urban, personal communication 3/7/07. ; ;

[ix]Prince George’s County op. cit

10Source: Powerpoint presentation of Tracy Tackett, Seattle SEA Street LID manager, at:

[xi] Keith Levchenko, Montgomery County Council, October 26, 2004 memo on Montgomery County Public Schools Stormwater Management Facility Maintenance to the Education and Transportation & Environment Committees, page 3.