Dudek to study Rainbow Municipal Water District groundwater recovery potential

Dudek will be studying the possibility of the Rainbow Municipal Water District obtaining some of its water supply from the Bonsall Groundwater Basin of the San Luis Rey River.

The board voted 5-0 to approve a $572,903 contract with Dudek, Oct. 24, to provide engineering services for studies which would bring a Bonsall Groundwater Basin desalter project closer to implementation.

“This project is to evaluate what water rights we have in the Bonsall basin and the feasibility of extracting that,” Rainbow general manager Tom Kennedy said.

Rainbow, which currently has approximately 7,800 meter accounts, has no groundwater supply at this time and purchases the entirety of the district’s supply from the San Diego County Water Authority. The SDCWA purchases much of its water from the Metropolitan Water District of Southern California, so Rainbow’s supply rates are vulnerable to increases in MWD and SDCWA rates.

The district is currently in the feasibility and planning stages of a brackish groundwater desalination project which would provide a local supply and decrease Rainbow’s dependence on imported water.

“This is a long-term project,” Kennedy said. “We’ve been working on this for a number of years.”

In August, the Rainbow board approved a grant application to the state Department of Water Resources for funding to offset the cost of a feasibility study for brackish groundwater desalination.

Rainbow staff completed a technical memorandum in May 2017 which compared a baseline groundwater extraction and desalination project with three indirect potable reuse alternatives. The technical memorandum recommended that the baseline groundwater desalination project should be implemented and that the indirect potable reuse alternatives should be considered for possible implementation in the future. The technical memorandum also recommended subsequent actions to advance the implementation of brackish groundwater desalination.

District staff then prepared a request for proposals to update and validate the 2016 groundwater model, calibrate that model, use the model to verify production well yields in the Bonsall basin, conform imported return flow water rights and regulatory structures, collect groundwater quality data, undertake exploratory borings for production well sites, assist the district with property acquisition and with contracts and agreements and revise and refine the desalter project alternatives and the costs including brine disposal options.

The request for proposals was issued July 25. Dudek was the only firm which responded by the deadline, Aug. 30. The proposal and Dudek’s past work were evaluated, and it was determined that Dudek had the necessary expertise in groundwater modeling, water rights, water quality, borings and well construction, pump testing of wells, desalination plant planning, siting, alternatives, costs and brine management. The district staff evaluation also determined that Dudek’s past performance made the company qualified to undertake the studies for the Bonsall Groundwater Basin desalter project.

The total estimated cost for the project is $602,903, which includes $30,000 for project management and administration to be conducted by Rainbow staff. Rainbow may also refine the scope of the project if the district’s needs are better served by such changes.

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