CWA committee given presentation on planned update for state desalination regulations

On March 20, the State Water Resources Control Board released a proposed plan to address seawater desalination facility intake and discharge systems. San Diego County Water Authority (SDCWA) water resources manager Bob Yamada, whose responsibilities include SDCWA desalination programs, addressed the SWRCB proposal during the April 23 meeting of the CWA's Water Planning Committee.

"The main goal here is to provide statewide guidance and consistency with regard to regulations," Yamada said.

The Ocean Plan establishes water quality objectives for California's ocean waters and thus provides the basis for regulation of discharges into California coastal waters. The Ocean Plan is typically implemented through National Pollutant Discharge Elimination System (NPDES) permits issued by regional water quality control boards. While NPDES permits for desalination facilities are considered on a regional basis, the Ocean Plan provides statewide guidance and consistency regarding the permitting of intakes and discharges.

The process to update the Ocean Plan began in 2007 and was deferred before resuming in 2011. The process included expert panels to address intake and brine discharge impacts along with mitigation. The CWA has contracted with Poseidon Water on the Carlsbad seawater desalination plant, and both the CWA and Poseidon participated in stakeholder meetings, public workshops, and the submission of written comments.

"Many of the Water Authority's and Poseidon's concerns related to the Carlsbad project have been addressed," Yamada said.

The concerns involved the recognition of site-specific conditions and the allowance of flexibility for compliance with the new regulations. "The regulations need to take into account the fact that these sites are different," Yamada said.

The Regional Water Quality Control Board has already permitted the Carlsbad desalination plant, although the renewal of the permit will require compliance with the new regulations. The current permit also includes conditions regarding the Encina Power Station which will cease operations in 2017, including associated cooling flows from that station, so the transition to stand-alone operation for the desalination plant will require upgrades to the intake system which will be regulated by the new discharge standards.

The long-term plans of the SDCWA include constructing a seawater desalination plant on Camp Pendleton. On March 26, the SDCWA board approved a testing program to determine whether an open ocean intake and discharge system or subsurface intake and multi-port diffuser discharge technologies would best meet the CWA goals for the project; that testing program will take approximately two years to complete.

The revision from the draft updated Ocean Plan addressed CWA concerns including consideration of specific conditions and alternative approaches for compliance with intake and discharge requirements, the inclusion of the California Environmental Quality Act (CEQA) definition of feasibility which was used by the state's Fourth Circuit Court of Appeals in finding the Carlsbad project compliant with CEQA requirements, a provision to account for previously-approved mitigation projects, and an adjustment from 36 months to a more reasonable 12 months for empirical studies such as entrainment or flow augmentation.

"There are a couple of remaining concerns that need to be addressed," Yamada said.

Although the proposed final amendment provided for alternative brine disposal methods such as the flow augmentation method used in Carlsbad, the definitions of "brine mixing zone" and "natural background salinity" could hinder proof that alternative methods could provide protection comparable to other methods such as wastewater dilution and multi-port diffusers.

The definition of "brine mixing zone" includes a limit of 100 meters laterally from the points of discharge which would render flow augmentation impractical due to the amount of dilution water required to meet the receiving water salinity limitation.

"Natural background salinity" is defined as the 20-year mean monthly salinity at the project location. The proposed amendment limits brine discharges to no more than 2.0 parts per thousand above the natural background salinity, but the data for the Carlsbad project shows monthly means ranging from 33.4 to 33.7 parts per thousand.

"The discharge salinity regulations at this point don't allow for the natural variations in the Pacific Ocean salinity," Yamada said.