Use of Advanced Analytical Tools to Identify Dry Weather MS4 Flow Sources in South Orange County
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Orange County Public Works (OCPW) on behalf of the South Orange County Watershed Management Area (SOC WMA) Permittees led a first-of-its-kind study at 20 major storm drain outfalls to assess sources of dry weather flow. These studies include collection of real-time flow monitoring data, analysis of water usage data, and testing of advanced analytical monitoring tools.

Results are being used to guide and prioritize strategies related to water conservation, water recycling, and human waste reduction as part of SOC WMA Water Quality Improvement Plan (WQIP) implementation.

One of the key technical objectives of these studies was to evaluate the effectiveness of advanced analytical tools for the identification of dry weather flow sources at priority outfalls. Advanced tools are needed because flow monitoring and analysis of conventional analytes are not capable of conclusively identifying flow sources (such as recycled water versus wastewater). Tools being tested include isotopic analyses (water and nitrate isotopes), human DNA markers (HF183 and HF183 treated with propidium monoazide [PMA] to remove non-viable cells), pharmaceuticals and personal care products (PPCPs), and next generation DNA sequencing (NGS) to distinguish between groundwater, potable water, sewage, and recycled water sources of dry weather flow.

Source water samples were collected from representative areas to provide control samples for known sources. Outfall samples were collected, including sampling timed near minimum and maximum diurnal flowrates. Multiple lines of evidence were formed from the analytical results to characterize flow sources to each outfall, including how they change over time (i.e., diurnally and seasonally). The results of these studies will inform management actions and provide a template to guide future studies across the watershed management area.

This presentation will highlight the advanced flow source identification tools being used to support WQIP implementation in South Orange County, which is the first to employ a source control-based approach to address bacteria and unnatural water balance issues. Results from sampling and analysis will be shared, including the limitations of these tools and recommendations for the most useful tools for flow source identification. The audience will be invited to participate through a Q&A session on the utility of these tools for other watersheds across California, as this represents a toolbox approach that other agencies could follow to identify flow sources in their MS4. This presentation is directly related to the conference's theme "envision the future" as it incorporates emerging scientific tools to reduce human impacts and restore a natural flow balance to surface waters through sustainable management actions.

Publication Summary

  • Geosyntec Authors: Jared Ervin
  • All Authors: Jared Ervin, Geosyntec Consultants; Cindy Rivers, County of Orange
  • Title: California Stormwater Quality Association (CASQA) 2020 Virtual Conference
  • Event or Publication: Event
  • Practice Areas: Urban Stormwater Management Planning and Design, Water and Natural Resources
  • Citation: Several Geosyntec staff members will present at the California Stormwater Quality Association (CASQA) 2020 Virtual Conference on September 15 and 16, 2020.
  • Date: September 16, 2020
  • Location: Online
  • Publication Type: Platform Presentation