Monterey Peninsula Water Supply Project (MPWSP), California, United States of America


Monterey plant

The Monterey Peninsula Water Supply Project (MPWSP) is an under construction water supply project in the Monterey Peninsula region, in the central California coast in the US.



The City Council of Santa Barbara is planning to reactivate and operate the Charles E. Meyer seawater desalination plant in the city.


The project is managed by California American Water (CAL AM), a subsidiary of American Water Works Company, which will own and operate the plant and related facilities upon completion.

The MPWSP is designed to solve the water supply crisis in the Peninsula region, which comprises the cities of Monterey, Carmel, Pacific Grove and unincorporated areas of Monterey County.

The project encompasses the construction of a desalination plant, expansion of existing aquifer storage and recovery (ASR) system and upgrades to groundwater replenishment (GWR) system. Construction is scheduled to begin in the second quarter of 2017 and the plant will become operational in early 2019.

The total investment on the project is estimated to be $277m, $51m of which will be for subsurface intake and return facilities, $131m for pipeline facilities and $95m for the construction of the desalination plant.

Monterey Peninsula Water Supply Project background

Water from the Carmel River is the primary source of water to the Peninsula region. Considering the possible threat to water species caused due to the excessive use of water from the river, the State Water Resources Control Board (SWRCB) has ordered California American Water to significantly reduce the water supply from the river.

The order, along with other supply restrictions in other parts of the county, has resulted in the 70% cut down of the water supply to the region, which necessitated an alternative source of water to meet the water needs.

California American Water has been trying to find out an efficient and environmentally sustainable water supply system since 2004. In 2011, after examining 11 potential solutions, it finally filed an application with the California Public Utilities Commission (CPUC) for the MPWS project.

MPWS project construction and infrastructure details

The scope of the MPWS project includes construction of slant wells, a new desalination plant, improvements to the existing seaside groundwater basin ASR system, and expansion of current aquifer storage and recovery project.

A desalination facility, with a capacity of either 9.6 million gallons per day (mgd) or 6.4mgd, is proposed to be constructed on a 46-acre site near Charles Benson Road, northwest of the Monterey Regional Water Pollution Control Agency's (MRWPCA) regional wastewater treatment plant.

Other facilities of the plant will include pre-treatment systems, reverse osmosis (RO) and post treatment systems, chemical feed and storage facilities, a brine storage basin and an administrative building.

The existing seaside groundwater basin ASR system will be upgraded to secure water supply for approximately 40,000 customers. The system is required to serve 3,500 acres a year, based on which the capacity of the desalination plant will be decided.

A series of slant wells will be constructed in a 376-acre coastal property located north of the city of Marina to draw seawater into the desalination plant. The seawater intake system will comprise ten 750ft-long subsurface slant wells extending offshore into the Monterey Bay and other facilities. The seawater from the slant wells will be transported to the desalination plant through new pipelines.

Treated water from the plant will be transferred to the California American Water distribution system at the metering station through a ten-mile (16.1km) pipeline. Resultant brine from the plant will be discharged to the ocean through an existing outfall.

"The project is managed by California American Water (CAL AM), a subsidiary of American Water Works Company."

The existing aquifer and recovery project, which collects excess winter-flows from the Carmel river and stores for reuse during the warmer dry months, will be expanded. Three new ASR wells will be constructed, adding 900 acre-feet of annual capacity to the system.

Contractors involved

The contract, valued at $2.8m per slant well, to construct seven to nine source water slant wells was awarded to Boart Longyear Company in November 2015.

Before awarding the contract, CAL AM along with Boart Longyear conducted a feasibility study to test the slant well's performance. The results exceeded the expectations in terms of water quality levels and production capabilities.

The design and build contract of the desalination plant was awarded to CDM Constructors, a wholly owned subsidiary of CDM Smith, in February 2014. The $87m contract includes design, construction and commissioning of the desalination plant.