FINAL REPORT Evaluation of Seawater Desalination Projects ...

EVALUATION OF SEAWATER DESALINATION PROJECTS
PROPOSED FOR THE MONTEREY PENINSULA
Environmental Impacts or Environmental Documentation
The proposed CWP desalination plant would receive raw seawater from the MLPP cooling
water return system. The MLPP is currently permitted for up to 1.226 billion gallons per day
of seawater intake. Units 1 and 2 of MLPP currently utilize a seawater intake within the
northern portion of Moss Landing Harbor. The MLPP utilizes modified traveling screens at
its intakes. This intake screening system includes vertical screen panels mounted on a
continuous belt. The screen mechanism consists of 3/8-inch (0.9 cm) mesh, a drive
mechanism, and a spray cleaning system. A key feature of the CWP is that the source water
would come through the Units 1 and 2, which have recently been modernized and operate at
a more consistent and higher volume. Seawater is collected at the disengaging basin after it
has been pumped through Units 1 and 2. A weir within the disengaging basin controls the
water depth and cooling water outflow to the discharge pipelines. Source water for the
desalination plant would be diverted from the disengaging basin (which receives water only
from Units 1 and 2) prior to discharge into the ocean. 54
The most recent 316(b) resource assessment of proposed modernization plans for the MLPP
concluded that the long-term impact of impingement and entrainment on the populations of
marine and estuarine fish, fish larvae, and cancer crab larvae would be relatively minor. 55
Duke Energy modified the intake system to reduce entrainment and impingement. In
addition to the intake modifications, the Regional Water Quality Control Board, the
California Energy Commission, and Duke Energy developed a habitat enhancement program
called the Elkhorn Slough Enhancement Program. This program is designed to minimize the
adverse environmental effects of the intake system on the Elkhorn Slough watershed
resources and allow Duke Energy to comply with Section 316(b) of the CWA. The
objectives of the Elkhorn Slough Enhancement Program are to implement a conservation
acquisition program for Elkhorn Slough and restore wetlands.
The CWP desalination facility would not alter the operations of the MLPP. The volume and
velocity of water entering the MLPP intakes would remain unchanged. The proposed
desalination facility would not have a separate direct ocean water intake and would use only
cooling water that is already screened by the MLPP. Although the desalination facility
would have its own screening system (three-millimeter screens), the system would convey
any screened organisms back to the MLPP outfall. Thus, there would be no impacts due to
impingement as a result of Desalination Facility implementation.
54 This description is taken from the CWP Conceptual Design Report (Draft) prepared for California American
Water, September 2005.
55 This conclusion is taken from the Proponent’s Environmental Assessment for the Coastal Water Project,
CPUC Proceeding A.04-09-019 page 5.7-9.
Monterey Peninsula Water Management District 7-10