Contaminated Groundwater in the San Gabriel Valley, California Stephen Hinds and James Mackcracken

The San Gabriel Groundwater Basin covers an area of more than 160 square miles just east of Los Angeles The Basin is the primary source of drinking water for over a million people Over time, hundreds of individual facilities have contributed to the contamination of the groundwater Basic Facts Los Angeles County

Basic Facts In 1979 the water was found to contain volatile organic compounds (VOC’s) It also contained the solid rocket fuel Perchlorate (causes hypothyroidism) and Nitrosodimethylamine (NDMA) (a carcinogen) Sources of contamination were identified and isolated. Nineteen companies were charged $200 million to assist the clean up operation

In 1984, 24 shallow wells were dug to assess extent of the problem Installation of a 450 m monitoring well Model of groundwater flow produced Clean up found to be essential to prevent further contamination of drinking water over the whole of Los Angeles Engineering Solutions

Four separate pumping stations constructed across the valley to extract and purify groundwater 22,000 gallons/min Ion exchange (removes prochlorate and nitrates) Ultra violet treatment and hydrogen peroxide (removes NDMA and dioxanes and VOC’s) Water air stripped (removes VOC’s) and off gas captured and sent to the granular activated carbon system for final abatement. Engineering Solutions

Charged atoms pass through ion exchange resins Contaminants displace similarly charged ions from the resin into the water In the San Gabriel valley perchlorate ions in the groundwater were replaced by chloride ions Ion Exchange

Advantages Only method for extracting perchlorate ions Disadvantages Expensive as ion exchange resins have to be replaced and disposed of Ion Exchange

Uses UV rays to kill VOC’s Kills micro-organisms by rearranging DNA and blocking reproduction UV passes through Quartz or Teflon barriers Mercury lamps at 2573 Angstroms Ultra-Violet Treatment

Advantages No chemical consumption- reduced cost No by-products Low energy requirements No moving parts (reliable) Disadvantages Doesn’t remove carcinogens Cleaning apparatus can prove difficult Can’t be used underground Ultra-Violet Treatment

Expensive clean up operation costing $350 million (£200 million) Long-term solution – total clean up will take years Action was needed due to legal requirements for drinking water standards Conclusion