The objective of this project was to demonstrate a novel vessel design and operating practice that can fully utilize the capacity of highly perchlorate-selective ion exchange resin while mitigating other operational problems that often result in premature resin replacement. This was done at three municipalities in Southern California (City of Rialto, City of Colton, and West Valley Water District) at full-scale (1,250 gpm). In addition to minimizing cost, this vessel design is both small in footprint and low in profile, which is beneficial for aesthetics as many of the wells are located in residential areas.

Technology Description

Three demonstrations of the utilization of a novel vessel design and operating practice combined with a highly perchlorate-selective ion exchange resin were undertaken at three municipalities, the West Valley Water District, City of Colton, and City of Rialto, in Southern California. The vessel design combined a lead vessel operated in up-flow mode followed by a polishing vessel operated in down-flow mode. The design provided the capability to remove contaminated resin from the bottom of the lead vessel with replacement of the exhausted resin by uncontaminated resin remaining at the top of the lead vessel and addition of fresh media at the top of the lead vessel. Three operational cycles were completed at the West Valley Water District. Flow balancing issues limited the City of Colton demonstration to two cycles, while several different operational setbacks allowed only one cycle at Rialto.

Demonstration Results

Each demonstration site had a high volume well (>1,000 gpm) on a groundwater source that had shown persistent perchlorate contamination. Each city had perchlorate in the groundwater at levels between 6-60 ppb. The recommended regulatory level for the state of California was 6 ppb. A brief summary of the performance of the system at each site is provided below:

  • West Valley Water District achieved the required <6 ppb perchlorate in the treated water over the entire three cycles of operation.
  • City of Colton achieved the required <6 ppb perchlorate in the treated water over two cycles of operation.
  • City of Rialto achieved the required <6 ppb perchlorate in the treated water during one cycle of operation.
  • Cycle throughput ranged from 200-320 MM gallons (~6 months) and was not directly correlated to influent perchlorate concentration.
  • Resin compaction during the cycle time compromised resin removal from the subsurface lateral and disturbed the natural chromatographic profile of the resin bed.
  • Overall performances of each unit were compromised by resin compaction and effective removal, but the economic benefit was not lost.
  • Capital costs and site preparation are quite low and very affordable at approximately $275,000 per unit. Additional costs are likely based on individual site requirements.

Implementation Issues

While operational and equipment difficulties compromised effective contaminant removal to some degree, they did not obviate the economic benefit of the technology. Capital and site preparation costs of approximately $275,000/unit should prove very affordable. Average total annual operating costs were estimated at approximately $77,000/unit with total resin replacement costs of about $110,000 recommended once every three years.