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Revised National Pollutant Discharge Elimination System (NPDES) permit
The NPDES permit for an existing ocean intake/outfall must be revised and approved if it is to be used as an intake for a desalination facility�
The CSLC, which leases coastal and off-shore lands, recently expanded their mission to include the biological review of entrainment, impingement, and discharge effects of shoreline and off-shore seawater intake and discharge facilities operating on state-leased lands� The CSLC has indicated that after 2026 the CSLC will no longer renew leases for once-through-cooling water intakes� The CSLC's earlier position has been modified in deference to the regulatory authority granted to California's State and Regional Water Quality Control Boards under federal CWA and state water codes� The CSLC recognizes that a once-through cooling water intake with a NPDES permit that is in compliance with Section 316(b) will be qualified for lease approval or renewal�
In the case of a desalination facility proposing to withdraw feed water from an existing seawater intake with a valid NPDES permit, the altered permitted use (e�g�, changed from cooling water to process feed water) of the facility's intake or discharge flow requires a new and separate facility NPDES permit� Such was the case in California's most recently issued NPDES permit for a co-located desalination facility's feed water intake (100-mgd Carlsbad desalination facility)� In this case, the San Diego Regional Water Quality Board required the applicant to assess the facili- ty's potential entrainment, impingement, and hypersaline discharge effects, assuming that the site's existing cooling water intake and discharge were no longer permitted� Under such a scenario, the desalination facility would be required to withdraw an additional 200 mgd (757,000 m3/d) of sea- water to maintain discharge salinity no greater than 40 g/L� The analyses assessed the resulting impingement and entrainment effects of feed water withdrawal associated with desalination-only operations� The impact analyses also took into account the entrainment and impingement effects associated with the need to increase seawater flows to meet the facility's discharge limits for salin- ity� The analyses also assumed that the entrainment and impingement effects and any associated requirement to minimize or mitigate these effects to meet future regulations would become the sole
The use of a seawater intake or discharge from an existing facility to supply feed water to the desalination facility would require a separate NPDES permit for the desalination facility's new purpose for the use of intake flow and discharge� However, if the desalination facility is only diverting power plant discharge water for feed water, there is a case to be made that in circum- stances when the entrainment mortality is nearly 100 percent prior to reaching the desalination facility's withdrawal point, any additional entrainment effects resulting from the desalination oper- ation are of a de mininus nature� From the standpoint of entrainment and impingement effects, the use of a primary host facility's discharged seawater represents a high level of recycling technology, as well as avoiding new entrainment and impingement impacts associated with a new seawater intake�
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