Green Roofs and CSO Mitigation:

Green Roofs and CSO Mitigation: Evaluating green infrastructure expansion in partnership with Newtown Creek Alliance Kingsland Wildflowers Green Roof Brooklyn, NYC Sulekha Gangopadhyay Capstone Presentation Fall 2017

Introduction: Pollution in Newtown Creek Newtown Creek is a designated Superfund waterway in New York City, located along the border of Queens and Brooklyn counties, and connected to the East River. Contaminants include industrial waste, raw sewage, oil, and street trash. The sewage problem is due to the number of combined stormwater sewage outfalls emptying into the Creek. Newtown Creek Alliance (NCA) is a local environmental organization working on remediation of the Creek and facilitating public environmental education and community engagement with local waterways. [NYS Department of Health] [Newtown Creek Alliance]

CSO and Urban Systems [NYC DEP] In older cities like New York, water from storm events exceed sewer system capacity, and due to the combined stormwater and sewage system, flow untreated into city waterways. Green Infrastructure (rain gardens, bioswales, green roofs, porous streets and sidewalks, etc) may be utilized to mitigate combined sewer outflow (CSO).

Combined Sewer Overflow Diagram [CUNY Graduate Center Academic Commons]

Sewage Outfalls and Water Quality [NYC DEC] [Newtown Creek Alliance]

Algal blooms in Newtown Creek due to CSO [Newtown Creek Alliance] Organisms from Newtown Creek (Ecological Restoration Project)

NYC DEP Green Infrastructure Typology Recommendations [NYC DEP]

Visual Representation of Forms of Green Infrastructure [Philadelphia Water Department]

Green Infrastructure Section of NYC DEP Long Term Control Plan: 83 million gallons per year (MGY) reduction from GI planned or implemented in the Newtown Creek Long Term Control Plan (LTCP) Program implementation through 2030 However, NC077 as 1 outfall alone produces about 300 MGY per year (NYC DEP LTCP).

NYC DEP Outfall Map

Area of Interest: Maspeth Combined Sewer Outfall sewer shed on Maspeth side of Newtown Creek Maspeth area outfall NC077 (1 of the top 3 outfalls with high volume of discharges) CSO outfall NC077 in the Maspeth section of Newtown Creek has roughly 41 CSO events and about 300 million gallons of stormwater discharge per year Outfall NC077 [Open Sewer Atlas]

Zoning Category: Industrial [Oasis NYC]

Project Introduction: Developing building selection framework for implementation of industrial green roofs in Maspeth, Queens region in order to supplement the green infrastructure projects in the NYC DEP Long Term Control Plan Calculation of total stormwater diversion from CSO through green roof implementation Policy recommendations [Newtown Creek Alliance]

Benefits of Green Roofs Insulation Energy savings Habitat Provide cooling Reduce smog Absorb rainwater [Hazen and Sawyer Environmental Engineers]

Existing Industrial Green Roof Example in Brooklyn Kingsland Wildflowers Benefits: Absorbs stormwater Provides habitat for native flora and fauna Provides a venue for educational and community events

Financing NYC Green Roof Tax Abatement (GRTA) fiscal incentive NYC DEP Green Infrastructure Grant Program upfront cost can be a disincentive, as the grant is dispensed through reimbursement [Newtown Creek Alliance]

Drainage Typology [NYC DEP]]

Potential Industrial Green Roof Areas Maspeth Region [Newtown Creek Alliance] Recreated GIS figure of Maspeth lot areas containing rooftops identified via NYC

How Much Stormwater Diversion is Possible? Mapping prospective rooftop locations to supplement DEP Long Term Control Plan GI projects requires identifying sewer system boundaries in the area. Calculations involve water retention figures based on lightweight soil medium depth, selected according to building roof load bearing and cost, and total area of green roof surface. [Google Maps]

Precipitation Patterns Climate models indicate that annual average precipitation in New York State will increase by 18% by 2020, and the number of heavy rainfall events will increase as well. The number of days over 1 inch of rainfall in New York City is expected to be roughly 13 in the 2020s, and roughly 3 for rainfall over 2 inches (ClimAID, NYSERDA).

Absorption Capacity of Soil Medium 1 cubic foot of lightweight green roof medium could potentially hold 0.33 cubic feet or 2.4 gallons of water (Professor Paul Mankiewicz, 12/7/17) Therefore, 10,000 square feet of medium at this thickness could capture a maximum of 24,000 gallons of stormwater. A 2inch rain event would create 1,667 cubic feet or 12,470 gallons of rainwater per 10,000 square foot of green roof (1/6 of a foot of rain multiplied by 10,000 feet of area = 1,667 cubic feet). This is roughly half of total soil capacity. Since 1 cubic foot of soil material can absorb up to an almost 4" storm, 6 inches of this medium is adequate for approximately a 2 rain event.

Stormwater Diversion from Green Roof Implementation in Maspeth CSO outfall NC077 in the Maspeth section of Newtown Creek has roughly 41 CSO events per year, and an outflow of roughly 300 million gallons per year, averaging out to about 7,317,073 million gallons per event. The total amount of available roof space in Maspeth is roughly 5,893,077 square feet (NYC MapPLUTO). A twoinch rain event would produce about 982,180 gallons (1/6 foot of rain multiplied by 2,893,077 square feet) of water total across this area, which would then be easily accommodated by 612 of the growing medium and diverted from the combined sewer outfall. This amount of capture would amount to about 13.4% diversion. However, an additional consideration is space limitations on some roofs due to other uses, and NCA will focus on industrial roof spaces above 10,000 square feet in Maspeth.

Conclusion and Recommendations Accompanying strategies to achieve greater stormwater diversion include: Increasing outreach and public engagement in order to facilitate greater participation in green roof implementation projects Changing the reimbursement method of delivering the GI grant in order to incentivize property owners Implementation of a stormwater fee based on level of runoff created by impermeable surfaces on individual properties, and refining standards for new construction. [Newtown Creek Alliance]

Thank You [Newtown Creek Alliance]

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NYC Dept. of Planning (2017). North Brooklyn Industry Plan. Retrieved from: https://www1.nyc.gov/site/planning/plans/northbrooklynvisionplan/northbrooklynvisionplanupdates.page NYC Dept. of Planning (2017). NYC MapPLUTO. Retrieved from: https://www1.nyc.gov/site/planning/datamaps/opendata.page NYC Parks (2013). Green Roofs. Retrieved from: https://www.nycgovparks.org/pagefiles/53/citywideservicesgreenroof_2.pdf Northeast Regional Climate Center. (2017). Cornell. Retrieved from: http://www.nrcc.cornell.edu/ City of New York. (2017). NYC Open Data. Retrieved from: https://opendata.cityofnewyork.us/ Open Sewer Atlas NYC. (2017). Retrieved from www.openseweratlas.tumblr.com Philadelphia Water Department. (2017). Stormwater. Retrieved from: http://www.phila.gov/water/wu/stormwater/pages/default.aspx Smith, P. (2013) The Toxins Lurking in Newtown Creek. New York Magazine. Retrieved from: http://nymag.com/news/intelligencer/newtowncreek201312/ Stein, J. and Kuz, Z. (2016). Fluid Frontiers: Stormwater management research in the Red Hook Sewershed, Brooklyn. Pratt Institute. Valderrama, A., Lochner, J., Koval, M. (2017). Catalyzing Green Infrastructure on Private Property: Recommendations for a Green, Equitable, and Sustainable New York City. NRDC. Retrieved from https://www.nrdc.org/sites/default/files/greeninfrastructurerecommendationsataglance.pdf Wilson, W. (2016). Stormwater. University of Chicago Press.

[Newtown Creek Alliance]