NYCDEP’s Water-Energy Study: Streamlining Greenhouse Gas Assessments for City-wide Initiatives


  • Elaine Labate, Paul Knowles, and Sandeep Mehrotra - Hazen and Sawyer

Green infrastructure such as this right of way bioswale reduces the amount of stormwater entering the combined sewer system and provides direct carbon sequestration from plants, trees, and soil.

An important component of the study was to understand and model, for the first time, the relationship between program activities and resultant GHG co-benefits for green infrastructure, water demand management and conservation, wetland restoration, and forested conservation. For the green infrastructure program in particular, this relationship involved an advanced approach to understanding how the program fits within NYC’s complex combined sewer system.

The study follows the Global Protocol for Community Scale GHG Emissions, which requires derivation of activity data and emissions factors for modeled programs. Deriving these parameters for DEP’s programs so that calculated values were representative of true performance was a complex task. Sewersheds, defined as the geographic areas contributing stormwater and/or sanitary flow to each of the City’s 14 wastewater treatment plants, were used as the modeling boundaries.

The input, calculations and results for the study were formulated into DEP’s Water-Energy-Nexus Tool: a Dashboard style, Excel-based calculator that allows rapid and convenient estimation of GHG co-benefits from dissimilar programs. The modular format of the tool facilitates expansion to other programs and City agencies.

The study assessed the GHG reduction benefits of NYC’s 95,000 acre water supply forestlands. The forestlands are vital to the quality of NYC’s drinking water supply and sequester GHG equivalent to 53,000 cars. The ongoing protection of the forestlands from unsustainable development will assist NYC’s pursuit of GHG reduction targets.

The Water-Energy-Nexus Tool outputs customized results to provide DEP convenient and rapid reporting of GHG co-benefits for a variety of uses. The tool will guide DEP’s decision making regarding how future water and wastewater related sustainability programs can best support the City’s GHG reduction goals.

With the current focus on energy efficiency and the need to reduce Greenhouse Gas (GHG) emissions, it is critical for cities and agencies to be able to understand the energy and GHG implications of their planned initiatives. The Excel-based tool developed as part of this project allows cities and agencies to quantify the GHG implications of “softer” stormwater and water initiatives, and provides them with the means to evaluate the implications in terms of City-wide GHG “costs” and benefits”.

This tool was developed for New York City Department of Environmental Protection (DEP) to inform which of their current and planned programs could provide the greatest GHG and energy reductions, in addition to their functional benefits, in terms of the relevant city-wide compartments for GHG assessment, such as reductions from altered treatment at both water and wastewater facilities, and carbon sequestration, as well as the increase associated with operation and maintenance activities. The tool is available for free download on the DEP website.

DEP has been aggressively working to reduce Greenhouse Gas (GHG) emissions from all aspects of its infrastructure and programs, with the ultimate goal of a 40% reduction by 2030, relative to the 2006 fiscal year baseline. As of 2015, DEP had developed GHG inventories for the majority of its traditional facilities, including water and wastewater treatment plants, but wanted to quantify the impacts associated with stormwater and water conservation initiatives, and to understand them in the context of the agency’s GHG goals.

The Water-Energy Nexus Study and the development of this tool focused on three of DEP’s programs: green infrastructure, water demand management and conservation, and wetland restoration. DEP owns and operates 14 wastewater treatment plants (WWTPs) within NYC; both the green infrastructure and water demand management and conservation analyses focused on net GHG impacts within the sewershed tributaries of each WWTP. This tool allows the user to produce green infrastructure and water demand management and conservation GHG estimates on a sewershed level; considering the “cost” associated with operation and maintenance, as well as the “benefits” of altered treatment volume at the WWTP and of a reduction in non-revenue water losses through leak detection and repair, and, when applicable, carbon sequestration. The wetland analysis considered the “benefits” associated with carbon sequestration and the “costs” of methanogensis, when applicable based on wetland classification.

This presentation will walk through a case study of stormwater and water initiatives for one DEP sewershed in NYC, and discuss the methodology behind the tool, as well as the general costs and benefits that are most important for cities and agencies to understand when considering the implementation of these types of initiatives.

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Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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