In 2010, California enacted a new policy intended to address the water and marine environmental protection problems posed by the antiquated Once Through Cooling (OTC) systems of power plants up and down the California coast. As of mid-2015, the Diablo Canyon nuclear plant is the only remaining facility out of compliance


Called the Policy on the Use of Coastal and Estuarine Waters for Power Plant Cooling, this mandate required that by 2015, all coastal power plants must have in place replacement cooling systems that conserve water and protect the marine environment.

The nuclear industry lobbied to have until 2015 to provide arguments for if and how they could comply with the policy. San Onofre was shut down in 2013, so that leaves only Diablo in question.

Unless the State Water Resources Control Board, which oversees OTC policy, accepts a permanent exclusion from the policy to Diablo owner PG&E, the power plant is by law to have cooling towers in place by 2024 (the date at which the first of the two reactors reaches it current license limit).

Reasons for enforcing the Policy to stop OTC

Diablo Canyon alone is responsible for nearly 80% of coastal power plant OTC ocean withdrawals (Diablo Canyon: 78 Percent of California Coastal Power Plant Once-Through Cooling  Water Withdrawals by  Bill Powers, P.E., November 23, 2013).

Diablo Canyon’s antiquated cooling system draws in an estimated 2.5 billion gallons of water per day and discharges that water back into the ocean some 20 degrees F hotter.  In the course of this intake and outflow, it is estimated that annually the reactors’ cooling system sucks in more than a billion fish in early life stages, most of which die. Additionally, more than 700 pounds of adult fish are destroyed every year.

Cooling towers could be built on the current site at the parking lot, which would have minimal land impact, and could use salt water, which would make desalination unnecessary. The construction costs would not exceed $ 2 billion.

Mesh screens would be ineffective at protecting sea life. (Even Bechtel, consultant to PG&E, admitted mesh screen technology would not significantly decrease the fish kills caused by intake and outflow.

Simply put, defense of the OTC policy and the inclusion of Diablo in the adhering to the policy is one of the most important, most effective, and most obvious things that anyone concerned about the marine environment can do in these next few months. PG&E’s Diablo Canyon power plant ought to be treated just like the other coastal power plants, and profits ought not win out over protection of the environment and public health.

Individuals or organizations interested in joining with San Luis Obispo Mothers for Peace and allied organizations in a grass roots campaign to urge the Water Board to hold PG&E accountable for compliance with state policy are encouraged to request to be added to the OTC email list by contacting mothers.for.peace.slo@gmail.com