Monterey Peninsula Water Supply Project (MPWSP)

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A watershed-related topic examined by the ENVS 560/L Watershed Systems class at CSUMB.

Project Summary

The Monterey Peninsula Water Supply Project (MPWSP) was designed to meet water consumption needs of the Monterey Peninsula. The original project design consisted of a 9.6 million gallon per day (mgd) desalination plant, slant intake wells, pipelines for brackish water and brine disposal, production water delivery pipes, and improvements to the existing Seaside Groundwater Basin Aquifer Storage and Recovery (ASR) system [1]. The final Environmental Impact Review [2] forthe MPWSP was submitted for public review on March 23, 2018.

In 2009, a cease and desist order from State Water Resources Control Board (SWRCB) was enacted to prevent the Peninsula's water purveyor, California American Water Company (CalAm), from illegally diverting water from the Carmel River by December 31, 2016[3]. The order requires a 70% reduction in water pumped from the Carmel River by the end of 2016[4]. Due to this order, an alternative water source became necessary to fulfill the demand of the 40,000 customers in CalAm's Monterey District service area[1]. In 2012, CalAm proposed the MPWSP to fill the growing need for water following the failure of the Regional Water Project (RWP). Additionally, the Monterey Regional Water Pollution Control Agency (MRWPCA) proposed the 3,500 acre foot per year Monterey Peninsula Groundwater Replenishment Project (MPGRP), which would reduce the desalination plant's water output from 9.6 mgd to 6.4 mgd [5]. Despite setbacks the MPWSP continues to move forward, laying the foundation required to began construction.


The MPWSP has an estimated cost of $322 million[6]. Estimated cost is based on a 6.4 mgd desalination facility including cost associated pre-construction. These costs will be allocated to following portions of the project:

Aspect of MPWP Estimated Cost Spent to Date
Surface Intake Systems and Supply Return Facilities $79M 27%
Desalination Plant $115M 18%
Pipeline Facilities $128M 37%
Pre-Construction Cost $8M 100%

Rate Changes

Monterey Peninsula rate payers can expect significant bill increases with the progression and completion of the Monterey Peninsula Water Supply Project, including an annual, increasing surcharge [7]. Additionally, Peninsula water customers will experience bill increases between 58.5% and 79% in March 2017 to make up for CalAm's lost revenue from drought conservation efforts [8].

These impending rate increases have caused the formation of several groups who want to buy out, or privatize, the region's water company. Privatization, groups like Public Water Now argue, would reduce costs to customers by cutting out CalAm's profit gains [9].

Current Status

Alt text
Figure 1. MPWSP project area and preliminary facilities map[1].

CalAm purchased a 46 acre property northwest of the MRWPCA's wastewater treatment plant for the location of the desalination plant[5], and is testing nine novel, subsurface slant intake wells at the CEMEX active mining area north of Marina [1].

In December 2014, CalAm began work on a test slant intake well located at the CEMEX sand mining facility in North Marina[10]. After several setbacks, CalAm received a permit from the California Coastal Commission to operate the test slant wells until February 2018. Slant wells are being tested as an alternative to vertical wells to reduce their amount of marine organism impingement and other environmental effects. Slant wells are a new technology, and are therefore controversial. As a test technology, they did not require a CEQA review, and if they are approved following testing will remain permanently in place. The subsurface wells intake from groundwater aquifers that have been intruded with saltwater, drawing in brackish water [1].

Construction has begun on the the 7-mile water delivery pipeline running from Seaside to Pacific Grove. This pipeline will deliver water from the Seaside basin to the Peninsula, as part of the overall water supply plan [11].

On November 20, 2015, CalAm filed for a petition to modify the cease and desist order and allow more time to find alternative water sources[12]. This would extend the deadline to December 31, 2020 and set reductions to the amount of water CalAm could pump from the Carmel River. In December 2015, the test slant wells reached 92% salinity, an increase from 75% when it was first installed [13] .

The DEIR closed for public comment on March 29, 2017. The final EIR is scheduled to be released in September 2017 followed by possible approval by the CCC. The Monterey pipeline and ASR pump station is projected to be completed by December 2017, and the desalination plant is has a projected start time of 2020 [14].


  • October 20 2009
    • Cease and desist order from SWRCB enacted which prevents CalAm from illegally diverting water and requires a 70% reduction in water taken from the Carmel River by December 31, 2016[3]
  • April 12, 2011
    • Investigation begins into the RWP, ultimately leading to a project shut-down
  • April 23, 2012
    • CalAm filed an application with the California Public Utilities Commission leading to the creation of the MPWP
  • October 10, 2012
    • Notice of Preparition of the project's EIR was released[1]
  • September 2014
  • December 2014
    • Drilling of a test slant intake well began at the CEMEX sand mining facility in Marina
  • January 30, 2015
    • Reached the final depth of the slant well, testing its feasibility for the MPWSP water source[16]
  • March 30, 2015
    • Completed test slant well successfully and began pumping and returning water to the ocean[17].
  • December 2015
    • Contractors selected for source wells and pipelines [18]
  • September 2016
    • California Public Utilities Commission approves pipeline component
  • December 2016
    • EIR Draft Completion
    • SWRCB CDO milestone
  • January 2017
    • Draft EIR/EIS dispersed for public comment; pipeline installation begins [19]
  • March 2017
    • End of EIR draft public review
  • September 2017
    • Approval to start construction on the Monterey pipeline
  • November 2017
    • EIR Draft Approval
  • First Quarter 2018
    • Estimation of CPUC's final decision
  • Jan-March 2018
    • Coastal Commission final decision [6]
  • March 23, 2018
    • Final EIR was released [2]
  • March-August 2018
    • Construction of desalination plant and related facilities begins [6]
  • June 2018
    • End of Final EIR Public Review
  • September 2018
    • Certificate of Public Convenience and Necessity (CPCN) approval of MPWSP
  • December 2018
  • September 2019
    • Construction of the desalination plant begins



  1. 1.0 1.1 1.2 1.3 1.4 1.5 State of California Public Utilities Commission
  2. 2.0 2.1 Environmental Impact Review,
  3. 3.0 3.1 Office of Ratepayer Advocates: Background - Monterey Peninsula Water Supply Project
  4. MPWSP, Home Page
  5. 5.0 5.1 California American Water. 2013. Monterey Peninsula Water Supply Project: Desalination Infrastructure-Request for Qualifications. []
  6. 6.0 6.1 6.2
  7. California American Water. 2012. Cost workshops on Monterey Peninsula Water Supply Project.[1]
  8. Johnson J. 2017. Cal Am water bills to rise as much as 79% in March; more increases pending. Monterey Herald.[2]
  9. Public Water Now
  10. Cook I. 2014. Monterey Peninsulat Water Supply Project: Presentation to MPWSP Governance Committee. California American Water.
  11. Johnson J. 2016. Celebrating water milestones: CalAm pipeline groundbreaking, recycled water purchase agreement signing.
  12. California American Water. 2016. Monterey Peninsula Water Supply Project: Progress Report. [3]
  13. California American Water. 2015. MPWSP Anticipated Schedule.
  14. California Water Association, CalAm Awarded $1 Million Grant for Desalination Slant Test Well
  15. Crooks I. 2015. Ian Crooks: Cal Am test slant well to deliver key data. Monterey Herald.Monterey Herald Article: Cal Am test slant well to deliver key data
  16. Conrad C. 2015. Cal-Am desalination well now pumping water. KSBW8. [4]
  18. Monterey Peninsula Water Management District. 2016. Water supply for the Monterey Peninsula: Update on Development of Water Supply Projects.[5]


This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.