“This was a very important issue that needed to be dealt with and needed a high level of effort early on,” explained Todd Croft, supervisor for the Remediation Branch in the Nevada environmental division’s Bureau of Corrective Action. “Rather than take an enforcement posture, we put our effort into remediation and not litigation.”
What followed was a sit-down with agencies to craft a plan both for mitigative measures and later, remedial measures.
“When perchlorate was detected in the Colorado River in 1997 and traced back to our site in Henderson, Nev., we immediately began meeting with the NDEP and EPA to discuss remediation plans,” said Pat Corbett, Tronox vice president of Safety and Environmental Affairs. “Tronox is committed to being a good environmental steward.”
“The focus was on rolling up our shirt sleeves and getting the work done,” Croft added.
Capturing the contamination
Tronox’s initial strategy was to capture and treat perchlorate at three locations: on-site at the chemical plant where the perchlorate was most concentrated; at an Athens Road location midway between Tronox and the Las Vegas Wash; and near the Las Vegas Wash.
“In 1998, we elected to stop commercial production of ammonium perchlorate and began interim remediation efforts under the oversight of the NDEP and EPA, while we developed and installed a remediation system,” Corbett said.
Today, the system is treating at full capacity and has resulted in a 90 percent reduction in perchlorate entering the Las Vegas Wash from the Tronox site, according to Corbett. Total expenditures for Tronox through 2005 for the Henderson perchlorate remediation were $124 million, he added.
Remediation steps were based on modeling done by the Nevada state environmental division and an MWD contractor, according to Croft. “We did a lot of modeling to figure out how long the perchlorate would remain in the system and to help determine the clean up schedules,” he said.
Croft explained that it takes time for ground and surface water to travel, and that even after a source of perchlorate is reduced, it takes some time for the clean water to flush out the contaminated water in the distribution system.
A Metropolitan contractor investigated flushing times and issued a report in 2004 that estimated how long it would take Colorado River perchlorate concentrations to reach target levels with various control methods in place. The estimates for perchlorate levels for mid-2004 and late 2005 were right on target with concentrations of 4 and 2 parts per billion, respectively.
California Adopts a Perchlorate Standard
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On Oct. 18, 2007, the California Department of Public Health adopted a drinking water standard for perchlorate of 6 parts per billion. As part of the rule-making process, the proposed standard was made available for public comment from Aug. 28 through Nov. 3, 2006. The adopted standard mirrors the one used as an “advisory” level until a maximum contaminant level or MCL was finalized. After further revisions, another 15-day comment period, and administrative law review, DPH adopted the new standard.
The level was based on a public health goal set by the state Office of Environmental Health Hazard Assessment in March 2004. The PHG established 6 ppb as the concentration of the contaminant in drinking water that did not pose any significant risk to health.
The U.S. Environmental Protection Agency has not yet decided if it will regulate perchlorate at a national level. The contaminant is on the “candidate contaminant list” and will be evaluated along with other contaminants of concern for a possible drinking water standard in the future.
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There is more good news now related to monitoring, according to Bart Koch, Metropolitan’s Chemistry Unit Manager: In 2005, all 12 monthly samples from water drawn at the Colorado River near Parker Dam were less than 4 parts per billion, below the recently adopted California standard of 6 parts per billion. At one time, groundwater obtained from some of the monitoring wells on the Tronox site near the former perchlorate production area had perchlorate concentrations as high as 3,700 parts per million, which would be more than 600,000 times the proposed California standard.
While remediation technology is typically of interest, in the case of perchlorate removal, the remediation strategy was of equal importance, and interest. It worked without litigation, making it somewhat unique, Croft said.
The reaction by American Pacific Corporation was focused. According to AMPAC’s Jeff Gibson, Director, Environmental Services, Nevada Operations, the company began to study the site after being notified of contamination, to “determine where the perchlorate was located and to assess what the best course of action would be.”
“We spent about $12 million studying the site, including more than 80 monitoring wells and the evaluation of technologies,” Gibson said.
After studying several technologies and ruling some out for various reasons, American Pacific Corporation decided on a method that extracted perchlorate contaminated groundwater from highly concentrated areas and conveyed it to a downstream location where it would be treated using a biological in-situ treatment method. This strategy was successfully piloted during 2002-03.
This type of treatment (discussed in more detail in the sidebar) is proving so successful at removing perchlorate, that other companies, including Tronox, are considering its use. By the end of 2006, AMPAC spent about $8.5 million on the biological treatment plant to remediate perchlorate.
In resolving the problem, Gibson mentioned that other agencies provided consideration and support aside from the Nevada Division of Environmental Protection. They included the city of Henderson and Clark County —both agencies were involved in permitting and leasing land to accommodate pipelines in public streets, construction of their treatment facility and re-injection of the treatment water in public land.
Tronox Vice President Corbett said that Tronox was able to recover some of its $124 million investment in remediation from the U.S. government, which originally owned the site and was the recipient of a majority of the perchlorate produced. Tronox was paid $20.5 million in February 2006 for clean up, and starting Jan. 1, 2011, the government will pay 21 percent of remaining costs tied to perchlorate cleanup in Henderson.
Stewart said that Metropolitan periodically consults with other agencies facing perchlorate issues in a “technical exchange” and continues to support agencies applying for grants for perchlorate cleanup. With perchlorate being handled effectively, Metropolitan is able to concentrate on other water quality concerns and improvements, including an $856 million program to retrofit its five water treatment plants with ozone technology, Stewart said.
It’s a welcome, if not unexpected outcome, which plays into Mark Twain’s advice to “Always do right. This will gratify some people and astonish the rest.”
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