Nitrate Contamination in a Public Drinking Water Supply

Fresno uses anion resin to reduce nitrate levels in well water and meet California regulations

Challenge

The City of Fresno, CA was forced to seek a solution to return previously contaminated and closed drinking well sites online in order to answer it's population increases and possible summer drought conditions, These wells had been removed from service due to nitrate levels above the State of California maximum contamination level.

The well sites are located in former farm areas or rural residential areas that were not connected to the City's publicly owned treatment works. Contamination is believed to be the result of a combination of septic system failures and/or agricultural runoff. A single source of contamination was not identified.

 

Solution

Evoqua Water Technologies provided the City with two solutions to meet the different needs of particular levels.

Two of the sites required low-flow systems that could not be generated on-site, since there were no sewer connections. Mobile equipment trailers loaded with anion resin in chloride form were used, and the resin regenerated off-site.

The other sites had significantly higher flow rates and were connected to the City's publicly owned treatment works. On-site regeneration of the anion resin provided the City with the most economical solution for these sites.

All sites included blending pumps and nitrate monitors with fail-safe alarm shutdown.

Results

Within three weeks of contract initiation, the first well was operating. The remaining three wells were operating and meeting specifications within four weeks of award.

The City was able to operate the four wells making an additional 3,850 gpm of potable water during peak usage hours and an additional 2,100 gpm during all other hours. In 2003, the City operated two wells making an additional 2,100 gpm, 24 hours per day, 7 days per week.