Tracking urban contaminant fate and transport: An application of PySWMM and the USEPA SWMM5 API

The US Environmental Protection Agency’s National Homeland Security Research Center (NHSRC) aims to enhance communities’ abilities to respond to intentional or unintentional chemical, biological, and radiological (CBR) releases. Effective emergency response actions in the face of these manmade and natural disasters necessitates a comprehensive knowledge of the fate and transport processes that spread CBR agents (e.g., spores that cause anthrax, radionuclides) in urban landscapes. Precipitation or decontamination strategies that involve applying liquids to roads or other surfaces may further spread contaminants, potentially to stormwater and/or sewage networks. Modeling tools that can help predict the extent and magnitude of both surface and subsurface contamination will allow for more efficient allocation of resources and more effective sampling and remediation. After a broad survey of potential modeling tools for simulating the fate and transport of CBR agents in urban stormwater, the USEPA Stormwater Management Model (SWMM5) computational engine was selected to meet NHSRC’s research needs. Working with the OpenWaterAnalytics open source initiative, we have begun expanding the pollutant capabilities of the SWMM5 application programming interface (API) and PySWMM, a Python interfacing wrapper for the SWMM5 API functions. Newly-developed functionality includes the ability to track the pollutant loading on the surface of subcatchments during simulations. In remediation activities, this allows for mapping and monitoring of contaminated zones after precipitation events of various sizes and may help decision makers in the allocation of resources for surface sampling and decontamination.  This presentation will demonstrate how to use the python wrapper with several simple examples. Additionally, it will discuss how further expansion and development of the SWMM5 pollutant API functions will benefit not only the NHSRC research program, but also a wide range of other pollutant and water quality applications (e.g., optimization of water quality treatment; quantifying the extent of agricultural, airborne, or other urban pollutants). We will also provide an update on the various related projects underway at the NHSRC, which includes both lab and field-scale studies seeking to elucidate contaminant washoff mechanisms (e.g., spore washoff experiments with a rainfall simulator, pressure washer, and garden hose). This research further constrains the appropriate equations and coefficient values necessary for effective modeling of CBR agent fate and transport.