It's been in the works for a decade now, but the result of California's ban on the use of seawater to cool a series of mostly natural gas-fired coastal electric generation plants is expected to have an impact on the state's carbon footprint in the decade to come.

Since a 2010 decision by the Water Resources Control Board, energy agencies have been coordinating the elimination of so-called once-through-cooling (OTC) in 19 coastal plants. The plants were ordered to phase out OTC nearly a decade ago.

Eight years ago the gas-fired generation facilities submitted plans indicating whether they would follow one of two state options for repowering or closing their plants. All but three Los Angeles Department of Water and Power OTC gas-fired plants were included, collectively holding 17,500 MW of capacity.

According to the California Energy Commission (CEC), most of the gas-fired plants have been retired with a handful to be added by the end of 2020. Nearly 10,000 MW of gas-fired units at 11 different coastal locations are now retired, according to the CEC. Statistics show nearly 5,000 MW will be retiring by the end of 2020.

The CEC indicated that NRG Energy Inc. built a gas-fired generation facility adjacent to its Marsh Landing project in Northern California, and it has five gas-fired peaking units operating on part of the shuttered Encina site in Carlsbad.

A state science advisory team last year outlined a blueprint for ocean water restoration in the offshore areas once used to cool the power plants with seawater.