Leadership in the Beneficial Use of Stormwater From Urban Areas

In its broadest interpretation, stormwater capture and use (SCU) represents the practice of collecting and beneficially using stormwater (i.e., water from precipitation runoff that reaches the ground, streets, and other impervious surfaces) and rainwater (i.e., precipitation that falls on roofs and is collected before reaching the ground).

With appropriate treatment and storage, this captured water can serve various potable uses, including: aquifer recharge, blend water for potable reuse projects, as well as a wide range of non-potable purposes, such as irrigation, industrial supply, toilet flushing, washing, dust suppression, firefighting, and evaporative cooling. Figure 1 shows different types of SCU, with their complexity and contamination potential plotted against their size and scale.

Recognizing the flexibility and merits of SCU, the WateReuse Association is currently supporting the implementation of the Environmental Protection Agency’s (EPA) Water Reuse Action Plan (WRAP), namely Action 3.3, which aims to “convene experts to address opportunities and challenges related to urban SCU.” To directly inform activities associated with this action, Carollo’s experts are supporting two notable projects being pursued by the Water Research Foundation (WRF), which will not only expand our knowledge and research of SCU practices, but also inform regulatory actions that responsibly hold those practices to high standards of reliability and safety.

WRF 4841: Assessing the State of Knowledge and Research Needs for Stormwater Harvesting
Carollo’s Jim Rasmus and Elisa Garvey serve as the Principal Investigator and Water Supply Expert, respectively, for WRF 4841, which aims to set a new baseline for the level of current knowledge surrounding SCU and to identify critical, nationwide research objectives. By meeting these goals, the team hopes to understand priorities for, and differences in, SCU practices across various regions of the US. One key outcome of this project to date is an SCU decision tree that enables agencies and utilities to develop a robust SCU program by assessing geographically-driven opportunities,
such as:

• How much water is available?
• When will water be needed the most?
• What are the most optimal ways to reuse this water?
• Where can it be stored?

WRF 5034: Assessing the Microbial Risks and Potential Impacts from Stormwater Collection and Use
Jim Rasmus and Principal Technologist Amos Branch are on a project team led by Colorado State University’s Professor Sybil Sharvelle to execute WRF 5034, an effort that strives to establish best management practices for SCU. The team is currently synthesizing existing research on stormwater’s microbial risks, associated impacts, and viable treatment processes to develop a Stormwater Use Roadmap that offers pragmatic guidance on the design and operation of stormwater use systems.The guidance will address the selection of appropriate log-reduction targets according to stormwater quality and intended end-use in a manner consistent with approaches used for the non-potable reuse of sewage as well as methodologies for tracking stormwater’s microbial quality and continuously monitoring operational systems.The study has determined the following outcomes to date:

• Proposed a log sewage-dilution approach that adjusts sewage-reuse targets derived from quantitative microbial risk assessments to appropriate values that specifically serve the beneficial use of stormwater.
• Investigated novel bacteriophage HF183 and quantified its ability to determine sewage-contamination levels in stormwater between dilutions of 10:1 to 10:4.
• Investigated likely chemical source trackers and estimated their abilities to determine potential sewage contamination
  in stormwater between dilutions of 10:1 to 10:3.

WRF 5034’s findings are being used to directly inform progressive regulations created to expand SCU practices. In California, SB 966 (2018) requires the State to establish uniform, risk-based water-quality standards for the on-site treatment and use of non-potable water. The State Water Resources Control Board is expected to publish its standards in December 2022, while the State has until December 2023 to develop any corresponding updates to building standards

Read more of this issue of Currents: Currents: Volume 2, 2022