The Times carries a weekly question-and-answer column on the
perchlorate issue. If you have a question, lease e-mail it to us at
ed******@*************es.com or fax to 779-3886.
The Times carries a weekly question-and-answer column on the perchlorate issue. If you have a question, lease e-mail it to us at ed******@*************es.com or fax to 779-3886.
Q. Given current ground and surface water conditions, how many decades can perchlorate persist?
A. According to experts at the Santa Clara Valley Water District, perchlorate is very stable in groundwater. It does not biodegrade unless there is an absence of available, dissolved oxygen. Groundwater has naturally occurring dissolved oxygen, which microbes will use first before turning to other sources, so natural biodegradation of perchlorate is unlikely.
In the Olin Corp. case, perchlorate may have started slowly entering the soil as many as 48 years ago until, over time, there is so much perchlorate that a plume nearly eight miles long results. Perchlorate may disperse in the aquifer as it flows downstream underground – to the extent that it may not be detectable using available analytical methods, but it won’t disappear.
Introduction of clean water through streams and recharge operations may further dilute the perchlorate to levels.
Q. What maximum level of perchlorate in water (in parts per billion) is the Department of Defense lobbying the Environmental Protection Agency to establish?
A. Kevin Mayer, regional perchlorate coordinator for the EPA, responds: “Defense Department and aerospace industry experts have suggested that human clinical trials show no adverse effects at approximately 200 ppb. There have also been a number of studies of large populations exposed to perchlorate that do not show a pattern of thyroid-related health problems.
Some of these experts suggest that a partial uncertainty factor might be appropriate to protect sensitive subpopulations, since the 37 subjects of the human clinical study were all healthy adults. This would bring the level down to 70 ppb. Both U.S. EPA and the State of California have suggested additional uncertainty factors should be applied to this study, which would bring the level to below 10 ppb.”
