Recycled Water Feasibility Study

EKI prepared a Recycled Water Feasibility Study that evaluated alternatives for use of recycled water produced by Ironhouse Sanitary District’s (ISD’s) Water Recycling Facility. The evaluated recycled water projects were aimed at diversifying Diablo Water District’s (DWD’s) water supply portfolio to make it more drought resilient. For this study, EKI prepared a recycled water market evaluation identifying and quantifying potential recycled water users within the study area, then prepared a screening assessment of 16 conceptual alternatives against five screening criteria developed during meetings with DWD and ISD staff. Based on the results of the screening assessment, six alternatives were retained for detailed analysis.

The detailed analysis conducted by EKI included an evaluation of regulatory and permitting requirements, water quality impacts, achievement of recycled water goals, costs, and energy use. The alternatives evaluated as part of this detailed analysis included park irrigation, groundwater infiltration using a spreading basin, indirect potable reuse (IPR) via deep well injection of advanced-treated recycled water, and direct potable reuse (DPR) of advanced-treated recycled water by blending with groundwater. As part of the IPR evaluation, EKI used a MODFLOW-based groundwater flow model previously developed by EKI team members to identify appropriate sites for injection wells that would result in greater than 12 months of retention time prior to the recycled water being extracted by DWD’s water supply wells. EKI interacted directly with the agency boards and other key stakeholders and the public to communicate the results of the study and to plan for next steps in implementation.  The Study, which recommended IPR via deep well injection, was approved by the State Water Resources Control Board with no substantive comments.

Outcome

EKI is currently preparing an addendum to the Recycle Water Feasibility Study to account for recent updates to regulations, costs, and public acceptability levels of the IPR and DPR options, also incorporating results from public survey of current attitudes toward IPR and DPR. EKI will be assisting with implementation of the recommended alternative, which is expected to be either IPR via deep-well injection or DPR via blending with groundwater.