Water Resources

Water Resources

Water resources at the DCPP include both the natural waters of the marina and intertidal area, as well as the fresh water produced through the desalination plant.  Protection of marine resources and the ability to have fresh water on-site are two very important issues when looking at the potential for repurposing facilities for new uses and allowing public access to the Diablo Canyon lands, including the coastal areas.

Public Meeting on Water Resources

On October 28, 2020, a public meeting covering the topic of DCPP Water Resources was held by the DCDEP.  The topics covered were:

  • Existing Breakwaters and Marina
  • Marine and Intertidal Resources
  • Seawater Desalination

Presentations were made by the California State Lands Commission (CSLC) about the public trust doctrine and how this affects use of sovereign lands defined as extending from the high watermark to three nautical miles into the ocean, by biologists on the special undisturbed nature of the marine resources in the area of DCPP and about the desalinization facility currently located on-site.  Presentations by the speakers can be found here:

2020 Panel Meetings – Diablo Canyon Decommissioning Engagement Panel (diablocanyonpanel.org)

Existing Breakwaters and Marina

There are two breakwaters, which are known as the east and west breakwaters.  The breakwaters were constructed to protect the large water pumps and intake structure from excessive water surges.  They also created a protective cove for small boats and the ability to use barges to bring materials and equipment in and out of the DCPP site.  PG&E and the Department of Fish and Game have studied the marine resources in the marina area since the construction of the breakwaters.

The California State Lands Commission (CSLC) is responsible for managing California sovereign tide and submerged lands and the beds of navigable waterways on behalf of the public, acting as trustee under the public trust doctrine.  For the DCPP, this includes the west and east breakwaters, boat dock, water intake facilities, cooling water discharge channel and office, maintenance, electrical and storage facilities.

The CSLC approved a lease with PG&E (Lease No. PRC 9347.1) on June 28, 2016 that expires on August 26, 2025, unless terminated sooner (as allowed under the lease).   The current lease modifies the original lease with provisions specific to the termination of the operation of the DCPP.  The current lease was issued with the understanding that PG&E will not continue operation of the DCPP past August 26, 2025.

The CSLC is aware that PG&E is exploring options for the reuse of the leased premises. and staff is open to discussing and exploring new opportunities to, and concepts for, repurposing the existing lease facilities at DCPP.  These include the potential to transfer of the lease to a new user, PG&E maintaining the lease and subletting to a new user or multiple new users, or a combination of these options over the duration of the decommissioning project.

Marine and Intertidal Resources

The intertidal area or zone is anywhere where the ocean meets the land, from steep rocky ledges to sloping, sandy beaches.  Intertidal zones have high biodiversity and can host a plethora of rare and fragile species, which have been threatened and destroyed by coastal development and over-exposure to human activity.

The DCPP lies adjacent to fourteen miles of the intertidal zone.  The dominant feature of Diablo’s intertidal zone are the healthy and unusually biodiverse tide pools, which have been the subject of extensive study by PG&E and its consultants.  The tide pools have remained largely undisturbed and intact because of the absence of significant human activity during PG&E’s operation of the plant and by prior owners/inhabitants (including 10,000+ years by the Chumash).

After decommissioning, there should be mechanisms in place that would continue to protect these natural resources.

Seawater Desalination

DCPP currently uses a desalination plant to provide water for dust suppression, fire protection, plant operations and drinking water.  The desalination plant was initially commissioned to provide a source of fresh water to the power plant, independent of any local available groundwater resource.  A reliable specialized filtered water source is needed on-site to provide fresh, deionized water of  high purity to top-off two loops of the reactor.

The decommissioning of DCPP poses two immediate problems for the future of the desalination plant.  First, the loss of the power plant’s once-through cooling loop currently used to dilute the desalination plant brine outflow close to shore means that a new, separate pipe system would need to be installed to discharge the brine far from shore.  This will likely require a separate environmental impact assessment, and incur new cost.  Furthermore, the 2015 California Ocean Plan recommends that for desalination plants: “The preferred technology is to commingle brine with wastewater that would otherwise be discharged to the ocean”.

Second, the loss of ‘free’ electrical power from DCPP to support the desalination plant means that either a new source of cheap electrical energy must be found to continue its operation, or that the cost of the water produced will have to reflect this additional expense.

The water resource requirements of San Luis Obispo County need to be recognized as an ongoing concern that will only be exacerbated in the coming years, because of global warming and intermittent drought conditions.  Long term solutions to the county’s water needs must take into account both the environmental and economic impact of the solutions proposed.  The maintenance of the desalination plant beyond decommissioning would not only provide a potential solution to long term county-wide water supply issues, but would also provide a reliable source of water to allow for repurposing on the DCPP site.

Vision Statements

  • The conservation of the breakwaters and associated harbor area and the intake and discharge coves and associated marine terraces should be considered to assure the protection of the ecological resources of the area, limit the amount of demolition debris, reduce the impact to neighboring communities and create opportunities for repurposing
  • The Diablo Canyon Lands and coastline, and in particular the intertidal zone of the Diablo Coast, are a precious community and ecological treasure and should warrant the strongest of protection efforts to ensure their conservation in-perpetuity
  • The desalination plant represents a proven facility that has been in operation for over 40 years, and its potential capacity for supplying the Central Coast, as well as the DCPP site, with a significant and reliable source of fresh water should be considered fully and not disposed of lightly


  1. Breakwaters and Marina
    1. The breakwaters and associated harbor should remain in place in order to provide opportunities for repurposing and to limit demolition debris and its need to be transported off-site
    2. The harbor and breakwater areas should be managed and repurposed in a manner consistent with the protection of habitat and wildlife
    3. The harbor should be considered for use as a protected area for boaters during inclement weather
    4. The lease with CSLC should be modified as necessary to allow the breakwaters and harbor areas to remain in place beyond decommissioning
    5. The facilities associated with the harbor located on the land should be preserved where appropriate to allow for repurposing as a public marina or educational/research marina facility, consistent with the long-term protection of marine resources
  1. Intertidal Zone/Marine Resources
    1. The discharge cove and intertidal areas should be studied by qualified individuals during and after decommissioning in order to continue to monitor the health of the marine resources
    2. The management of the Diablo Canyon Lands, including the fragile intertidal zone, should be undertaken by a successor entity in a manner that will protect the areas from “trampling” and other human activity that could irreparably damage the resource
    3. The public should be ensured access to the Diablo Canyon Lands to the greatest extent possible, while assuring that such access will not threaten the biodiversity and health of the intertidal zone and other fragile marine resources
    4. The impact that public access has had on other tidepool regions of the state should be carefully considered to understand how negative impacts have occurred and how it can be prevented along the Diablo Coast
  1. Desalination Facility
    1. The installation of the latest in high efficiency polymer membranes should be considered by PG&E as part of its future regular maintenance in order to retrofit the existing plant, bring it to the forefront of desalination technology, and reduce its operational costs significantly
    2. The County of San Luis Obispo should engage in and where possible actively participate in, the permitting for potential windfarms being considered near DCPP in order to obtain preferential rates for the energy required to operate the desalination plant
    3. The potential for optimizing the location of the desalination plant closer to Avila Beach and the existing Port San Luis Harbor should be evaluated as a way to reduce the length of pipeline necessary to, connect to an existing local and/or regional water purveyor
    4. The DCPP desalination plant should be marketed nationally to potential investors and operators in order to gauge interest in continued operation beyond decommissioning
    5. The potential of partnering the DCPP desalination plant with other water purveyors in the area should be evaluated


  1. Breakwaters and Marina
    1. Recommend that PG&E pursue retention of the breakwaters and associated harbor with the CSLC, CPUC and the California Coastal Commission in order to provide opportunities for repurposing the harbor and other on shore marina facilities
    2. Recommend PG&E work with the CSLC to modify the existing lease as necessary to allow for retention of the breakwaters and other on shore facilities specified in the lease
    3. Recommend that PG&E require that future management of the breakwaters and harbor be accomplished in a manner that preserves the natural habitat, allows for long term maintenance and creates a safe harbour for boaters in distress
    4. Recommend that PG&E use barging as the primary method of removal of materials if the breakwaters are required to be demolished
    5. Recommend that PG&E continue to monitor and study the harbor and other coastal areas throughout the decommissioning process to ensure the sensitive marine habitat is undamaged and preserved in perpetuity
  1. Intertidal Zone / Marine Resources
    1. Recommend that any studies already undertaken by PG&E and its consultants regarding the Diablo Canyon Lands and its fragile intertidal zone be used to craft future management plans for the region by PG&E or a successor conservation entity or entities
    2. Recommend that the lessons learned through the establishment, placement, and operation of the Point Buchon Trail on the North Ranch and the Pecho Coast Trail on the South Ranch, be taken into consideration in the development of future land use and management plans
    3. Recommend that governmental permitting entities require transfer of the Diablo Canyon Lands to a conservation entity or entities only after a full assessment of that entity’s ability to protect the land and water resources, from a practical, scientific, and financial perspective to ensure the appropriate protection of natural and cultural resources in perpetuity
    4. Recommend that PG&E and governmental permitting entities work to provide permanent endowment monies for the continued protection and management of the marine and terrestrial resources
    5. Recommend that public access to coastal trails along the Diablo Canyon Lands be specifically sited and managed to ensure no degradation of the intertidal zone and other cultural and ecological resources
    6. Recommend that PG&E temporarily cease any existing public uses on the Diablo Canyon Lands that result in degradation of the intertidal zone (and any ecological or cultural resources of the lands) to allow for the regeneration of any impacted resources and where necessary, perform active restoration
  1. Desalination Facilities
    1. Recommend that PG&E as part of its future regular maintenance of the desalination plant retrofit the plant with the latest in high efficiency polymer membranes in order to increase efficiency and reduce operational costs
    2. Recommend that the County take part in the permitting of offshore windfarms as appropriate in order to negotiate better rates for the energy required to operate a desalination plant
    3. Recommend that PG&E conduct a nationwide marketing effort to highlight the availability of the desalination plant to investors and operators
    4. Recommend that PG&E conduct a detailed cost-benefit study of the possibility of relocating the existing plant to the south side of the Diablo Canyon Lands (near the security gate and Port San Luis) and an alternative method to carry the brine effluent offshore
    5. Recommend that the County consider the possibility of partnering the operation of the desalination plant with other water purveyors in the greater area, including those outside of San Luis Obispo County
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