Phase 3 - Extended Pumping and Pilot Plant Testing Feasibility ...

Dana Point Ocean Desalination Project: Phase 3 - Extended Pumping and
Pilot Plant Testing Feasibility Investigation
By Richard Bell, MWDOC Principal Engineer
Since 2002, the Municipal Water District of Orange County (MWDOC) has been
investigating the technical, environmental, economic, and institutional feasibility
for the planned Dana Point Ocean Desalination Project. This project is part of an
overall water supply reliability program for Orange County and the region. It is
part of Metropolitan Water District of Southern California’s Integrated Resources
Plan and Seawater Desalination Program.
The proposed project location, which is adjacent to San Juan Creek, was
determined to be the best desalination site in south Orange County. An ocean
desalination plant will enhance water supply and system reliability to an area that
is over 95% dependent on imported water supply. One of the major project
challenges is to find an appropriate, cost-effective, and environmentally
acceptable means to supply the desalination plant with ocean water.
Over the past four years, MWDOC has been investigating the use of state-of-theart
slant beach well technology for production of ocean water from sands and
gravels that underlie the ocean in this location. The offshore marine aquifer was
formed by processes of erosion and sedimentation within the continental shelf
during the ice ages when sea level was over 350 feet lower than today. The
hydrogeology work conducted to date indicates that the aquifer in this location is
highly permeable and extends well out under the ocean. Producing ocean water
from the marine aquifer would completely avoid entrainment and impingement
impacts that occur from conventional intakes.
Since the entire width of the sand and gravel deposits underlying San Juan
Creek is fully located within Doheny State Beach, the Test Slant Well was sited
near the Lifeguard Tower just north of San Juan Creek. It was successfully
constructed in spring 2006. A short-term aquifer and water quality pumping test
was conducted, indicating a productive aquifer. Due to the very wet 2004/05
water year, the saltwater interface in the marine aquifer was located about 1,100
feet offshore at the time of the initial short-term testing work. An extended
pumping test is required to pull in ocean water and perform various more
intensive water quality and pilot process treatment testing.
The Test Slant Well is the first slant beach well constructed under the ocean for
ocean water desalination feed water supply. Advanced dual rotary water well
drilling technology was utilized in constructing the Test Slant Well. For this
location, this technology was found to have the least environmental impact on the
ocean compared to other subsurface technologies while providing very good
yield and excellent feed water quality.
This approach has been well received by the California Coastal Commission and
the environmental community. Where feasible, subsurface intakes can offer cost
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savings and environmental benefits compared to conventional open intake
systems. Since the fall of 2004, MWDOC’s Phase 1 and 2 feasibility
investigations received State Parks’ approval and support, a State Lands
Commission Lease, a Regional Board NPDES Permit and 401 Certification, a
USACOE Nationwide Permit and Jurisdiction Determination, and California
Coastal Commission Coastal Development Permits.
To date, MWDOC has received letters of support from the Surfrider Foundation
and Orange County Coastkeeper for investigating this approach to providing
feedwater supply for this project.
In support of this investigation work, grants have been received from the U.S.
Environmental Protection Agency, U.S. Bureau of Reclamation, California
Department of Water Resources, and local and regional water agencies.
Phase 3 Extended Pumping and Pilot Plant Testing
Over the last several months, MWDOC has been working with several agencies
in south Orange County on forming a project participation committee to direct the
Phase 3 Extended Pumping and Pilot Plant Testing work, which will complete the
feasibility investigation work previously undertaken in Phase 1 and 2. To date,
South Coast Water District, Laguna Beach County Water District, and Moulton
Niguel Water District have agreed to participate in Phase 3. Other agencies are
also considering participation.
Key elements of the Phase 3 investigation include confirmation of filtration
capability of the aquifer and well, evaluation of biofouling and mineral scaling
potential and control options, testing of candidate reverse osmosis membranes,
completion of the hydrogeology investigation work, validation/refinement of the
groundwater model, and updating the overall project engineering feasibility study.
Phase 3 Extended Pumping and Pilot Plant Testing will require up to two years of
continuous pumping to pull in ocean water and to conduct the necessary water
quality testing and treatment process studies. The Phase 3 work includes
installation of a submersible pump in the Test Slant Well, a fully buried wellhead,
a short 12-inch diameter pipeline, a mobile test facility, and a discharge pipe and
diffuser assembly. Currently discussions are being held with State Parks to
permit the temporary mobile test facility to be situated adjacent to the rear
parking lot near San Juan Creek. The produced and aerated Test Slant Well
water is planned to be discharged to ocean at the surf zone in a safe area
adjacent to the west San Juan Creek concrete levee structure (groin).
Discussions are now underway with the permitting agencies, and environmental
documentation work has been initiated.
The purpose of the membrane pilot testing is to evaluate whether any special
pretreatment would be required to control biofouling and mineral scaling,
including low levels of dissolved iron and manganese that are anticipated to be
present in the water. The extended pumping data would then be used to validate
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and refine the groundwater model. The model would then be used to finalize the
recommended project capacity and to assess groundwater levels and related
effects under a range of upstream pumping patterns and groundwater level
conditions.
The Phase 3 schedule is looking to obtain all permits and approvals later this fall
in order to allow the installation of the Phase 3 test facilities by mid-May 2009.
All construction work on the State Beach needs to be completed prior to the busy
summer beach season.
Exhibit 1. Phase 3 Extended Pumping and Pilot Plant Testing Facilities, Doheny
State Beach
Feasibility Investigation, Dana Point Ocean Desalination Project
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