NYC Green Infrastructure R&D – Setting the Standard for the City’s Storm Runoff Management Plan
Under a SPDES permit, the NYC Department of Environmental Protection (DEP) is working to quantify the benefits achieved from implementing green infrastructure in MS4 drainage areas. Boomi assisted this effort and led the task on lot size soil disturbance threshold study and a cost-benefit analysis to help DEP make informed decisions on construction and post-construction stormwater control requirements in MS4 areas.
We conducted a literature study and utility survey to capture the construction and post-construction stormwater control measures (SCMs) at new development and redevelopment projects used by other urban cities. A hierarchical approach was developed for cost estimation and also as guidance for the public and private property owners, as shown in the graphic below. Extensive watershed delineations and reconciliations were performed in GIS to develop a single subcatchment layer of MS4 areas.
Development and redevelopment data for 15 years and Pluto landuses were used to cluster disturbed impervious acres for different threshold sizes. Groundwater and bedrock depths were used to segregate these disturbed acres into soil or space or soil/space constrained and unconstrained portions to assign appropriate SCMs and develop the associated costs and benefits. All the analyses were performed at the LTCP waterbody scale, except for the East River and Open Waters that were divided into four borough-specific groups.
InfoWorks CS model was used to develop the baseline (without SCMs) flows into various waterbodies. Event mean concentrations (EMCs) were used for the five water quality parameters (total nitrogen and phosphorus, total suspended solids, fecal coliforms and enterococci) to estimate baseline pollutant loads.
Removal efficiencies for SCMs were used to assess the pollutant load reductions for each threshold size for comparison with costs and develop the benefit-cost curves. These curves, along with the inputs gathered from stakeholders during public meetings, are being used by DEP to establish the construction and post-construction stormwater control requirements in MS4 areas.