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FPUD to replace GAC filter media at Santa Margarita treatment plant

The Fallbrook Public Utility District has awarded a contract to replace the filter media in the granular activated carbon vessels at the Santa Margarita Groundwater Treatment Plant.

FPUD’s board voted 5-0 May 29 to award a $680,777 contract to Calgon Carbon Corporation for the replacement of Filtrasorb 400 carbon media over the next three years, and the contract allows for annual price increases based on costs but not to exceed 10% annually. The filters are part of the granular activated carbon system which removes per and polyfluoroalkyl substances (PFAS) contaminants from water.

The water FPUD obtains from the Santa Margarita River Conjunctive Use Project is delivered from Camp Pendleton to the boundary of the Naval Weapons Station and Fallbrook behind the FPUD solar facility site on Alturas Road. The water is treated at the Alturas Road plant and delivered into FPUD's distribution system.

In addition to treating PFAS contaminants from the treated water with a combination of granular activated carbon and reverse osmosis, the groundwater treatment plant utilizes greensand filters for iron and manganese removal followed by reverse osmosis and chlorination.

Reverse osmosis removes more than 99% of salts which pass through the process, so some flow bypasses the reverse osmosis process to meet the district's overall salt target.

The granular activated carbon treatment system includes three pairs of large vessels, with each pair consisting of a lead vessel and a lag vessel, with a 12 foot diameter and a height of approximately 20 feet.

In December 2020, the FPUD board awarded Calgon Carbon Corporation a $1,260,493 contract to provide granular activated carbon treatment system equipment.

The Santa Margarita Groundwater Treatment Plant has been operating since December 2021. The amount of water FPUD will obtain under the Conjunctive Use Project agreement is dependent upon weather conditions.

In a normal hydrological year, based on the average over the past 50 years, FPUD will receive 3,100 acre-feet. FPUD will receive 5,120 acre-feet for an above-normal year and 6,320 acre-feet for a very wet year. The design of the treatment plant was based on an average flow of 3,100 acre-feet, and based on that average flow the life of the granular activated carbon material was estimated to be about five years.

The first few months of the treatment plant’s operation occurred during a below-normal water year. The 2022-23 water year was considered a very wet water year, and the flow was four times more than the below-normal flow. The 2023-24 water year is also an above-normal water year with flow three times more than the below-normal flow.

The media which stratifies the contaminants is sampled quarterly. The higher-than-expected flow levels have caused bleed-through on all three lead filters. Sampling in late 2023, detected certain contaminants in the later stages of the lead filters, and the most recent sampling indicated that the contaminants seem to be moving through the filter media faster than anticipated.

FPUD will likely move to monthly sampling after the next quarter, and the requirement to change out the filter media will likely be met soon after that. At that point the lag vessels will be moved to the lead position and new lag vessels will be installed.

Author Bio

Joe Naiman, Writer

Joe Naiman has been writing for the Village News since 2001


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