California Water News Daily Your Source For Water News in California
The city of Delano, in California’s Central Valley, is working in conjunction with the State Water Resources Control Board on a unique pilot plan to remove nitrate from groundwater to be used as a drinking water source.
A 2013 report to California’s legislature indicated that more than 680 of 3,037 community water systems within the state had used a polluted groundwater source affected by one or more “principal contaminants” such as nitrate or arsenic. Nitrate detections were found in 207 water systems such as Delano’s and have required blending the water, or using another treatment, to mitigate the nitrate effects before it could be used as a safe drinking water source. The report also found that nearly 21 million residents, statewide, were reliant on a pouted groundwater source.
Nitrate is the second most common contaminant in groundwater aquifers that are used by more than 75 percent of the state’s regulated public water systems. It is especially widespread in the Tulare Lake and Salinas basins.
However, Delano’s three-year pilot program, funded by a $5 million state grant, could serve as a model for addressing nitrate contamination in groundwater sources. The project is funded by the California Department of Water Resources (DWR) under Proposition 50, Chapter 6(b) for pilot and demonstration projects for treatment or removal of the specific contaminants. Delano, identified as a disadvantaged community, was eligible to receive this $5 million grant for the nitrate demonstration project.
“Until now, public water systems have had to make a hard choice – either don’t use the water, provide treatment or blend water contaminated with nitrate with clean water from another location,” said the State Water Board’s Division of Drinking Water Deputy Director Cindy Forbes. “If successful, this pilot program could clear the way for an innovative treatment and provide another option for communities that want to treat their existing groundwater for potable use by residents.”
Currently, nitrate mitigation includes ion exchange, reverse osmosis and electrodialysis. Producing safe drinking water for public consumption in California is typically done through blending of water sources, ion exchange treatment and reverse osmosis.
The Delano groundwater pilot project will be using a wastewater treatment approach called biological denitrification – using bacteria to reduce nitrate and converting the common groundwater contaminant into nitrogen gas. By turning the nitrate into nitrogen gas, the process avoids generating a waste stream of nitrates that would have to be discarded safely somewhere else.
The city of Delano will treat water from one of their 14 wells, identified as Well 35. Well 35 is not currently used for drinking water for residential use; the well is being used for the pilot project because it is a source of future water supply.
Denitrifying bacteria are naturally present in groundwater, and the treatment plant where the process is occurring was specifically designed to create an optimal environment for the biological process. A portion of the water is treated biologically. Following the biological denitrification process, additional steps including filtration, disinfection and blending are taken to produce safe drinking water that meets the nitrate drinking water standard.
According to the State Water Resources Control Board, the biological denitrification treatment used in Delano’s groundwater pilot program is not intended to replace existing approaches. It may serve as a cost effective alternative for a public water system to use when considering local factors and economics related to providing safe drinking water.
Delano city staff will be monitoring the treatment system both on-site and remotely as part of the pilot program. Laboratory samples will be collected regularly; the results are reported to the State Water Board’s Division of Drinking Water on a monthly basis. To ensure optimum treatment, multiple continuous monitoring instruments and sensors are used to track the system’s performance. Multiple alarms and automatic shutdowns will be included, and the facility is programmed to shut down the treatment system should any problem arise.
