A Case Study in Developing an Accurate and Defensible Collection-System Model

As the New York City (NYC) Department of Environmental Protection (DEP) finds wider uses for its collection-system models, it is also finding a need for these models to be more accurate and defensible than ever before. This case study describes how DEP applied peer-reviewed (WERF 2015) methods for collection-system monitoring and modeling to develop a robust and demonstrably accurate collection-system model. The resulting model is now being used for multiple purposes, such as evaluating existing collection-system performance for annual permit compliance, assessing proposed alternatives as part of DEP’s combined-sewer overflow (CSO) Long-Term Control Plan (LTCP), establishing stormwater discharges for DEP’s Municipal Separate Storm Sewer System (MS4) project, and supporting the City’s position in a legal case. The significance of this work is that it demonstrates that DEP’s peer-reviewed methodology is sound, implementable, and can be used by other municipalities to produce robust and defensible collection-system model results.