Statewide Drywell Guidance Update: Results and Recommendations Moving Forward
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The State Water Resources Control Board (SWRCB) is working with Geosyntec Consultants to develop statewide guidance for the siting, design, and implementation of drywells.

Drywells continue to be an attractive approach to stormwater management and groundwater supply augmentation, especially for space-limited applications. While drywells do represent a cost-effective means for managing stormwater and replenishing water supply, the increased use of drywells and deep injection of stormwater requires careful planning to protect groundwater and surface water resources. During last year's conference, the SWRCB presented on the overall plan for this project and described the priorities and concerns of the technical advisory committee (TAC). The purpose of this presentation will be to provide an update on the project, including summarizing results from a groundwater contamination risk analysis of landuse-specific stormwater runoff parameters and a summary of pretreatment best management practice (BMP) type effectiveness for specific pollutants of concern (POCs).

To identify the studied parameters in stormwater runoff from specific regional landuses that are expected to frequently exceed applicable groundwater quality objectives (GWQOs), stormwater runoff data collected from locations with dominant landuses were downloaded from multiple databases including the Southern California Coastal Water Research Project (SCCWRP) stormwater landuse database, the Stormwater Multiple Application and Reporting and Tracking System (SMARTS), and other City and County landuse-based stormwater datasets. The distribution of results from these databases were compared to applicable drinking water Maximum Contaminant Levels [MCLs] (representing the typical GWQOs for municipally designated groundwater basins) and the landuse-pollutant combinations presenting the highest potential risk to groundwater contamination were identified. These higher risk landuse-pollutant combinations will be presented as they may be used to tailor drywell siting and design guidance to specific landuses in the future. In addition, BMP influent and effluent data from the International Stormwater BMP Database, a publicly available database of over 700 BMP studies and performance analysis results, has been summarized to demonstrate the specific BMP pretreatment types capable of reducing POC concentrations to below applicable MCLs. This information will be presented as it may be used in the future to guide the selection of pretreatment BMPs to target high groundwater contamination risk POCs. The results of these analyses and previous literature reviews including studies on emerging contaminants that may pose a greater risk to contamination compared to typically studied and understood pollutants, will be used to develop a risk-based framework for future drywell guidance. This presentation will conclude with an overview of how these research results and lessons learned from drywell case studies will be used to develop the future drywell siting and design guidance, anticipated to be complete in early 2020. In addition, the SWRCB will provide an update on how the technical guidance may be used in the future to regulate and/or encourage drywell implementation.

The audience will be invited to participate through a Q&A session to clarify how this guidance may relate to their past, ongoing, or future drywell projects. This presentation is directly related to the conference's theme of "Stormwater… Why We Do What We do: Looking back and Looking forward" as the presentation will address lessons learned from previous drywell implementations and monitoring data collected during previous stormwater studies, which will be used to inform future guidance that promotes drywell implementation as a beneficial tool for stormwater quality and quantity management but is also sufficiently protective of groundwater and surface water resources.

Publication Summary

  • Geosyntec Authors: Adam Questad, Brandon Steets
  • All Authors: Adam Questad, Brandon Steets, Geosyntec Consultants; Matthew Freese, SWRCB
  • Title: 2019 CASQA Annual Conference
  • Event or Publication: Event
  • Practice Areas: Groundwater Assessment and Remediation, Urban Stormwater Management Planning and Design
  • Citation: Geosyntec will make substantial technical contributions at the California Stormwater Quality Association (CASQA) Annual Conference at the Monterey Conference Center in Monterey, California on October 7-9, 2019.
  • Date: October 7-9, 2019
  • Location: Monterey, California
  • Publication Type: Platform Presentation