Perchlorate Contamination in the Mather Air Force Base Water Service Area
RANCHO CORDOVA, SACRAMENTO COUNTY, CALIFORNIA
Based upon the information reviewed, there was a completed exposure pathway to perchlorate-contaminated water in the Main Base Water System at Mather Air Force Base. This exposure may have occurred to patients at the base hospital, employees, customers, and visitors in the Main Base Area of the base before it was closed in 1993; however, the levels of perchlorate in the well water at that time are not known. Thus, it is was not possible in this health consultation to evaluate the health impact of those exposures.
Since the closing of the base in 1993, there has been a mixed use of the base. The area that is served by the Main Base area has been developed by Sacramento County to be an air cargo field with commercial and light industrial areas. McClellan Air Force Base is now operating the hospital at Mather and the county has a transitional housing unit located in the area served by the Main Base water system. Using the recent Main Base well sampling results for perchlorate, CDHS evaluated exposures to employees, adult customers/visitors, temporary adult residents and adult patients. There are no permanent residences located in the area served by the Main Base water system.
It is difficult to predict when the perchlorate first contaminated the Mather Main Base wells but it may have been as early as 1987. As of August 1997, when the upgraded intertie with the Family Housing unit went on-line, exposure to perchlorate contaminated water probably is no longer occurring in the Mather Main Base area because the wells contaminated with perchlorate have either been taken off-line or are only used for emergency purposes.
The perchlorate concentration in two Mather Main Base drinking water wells (Main Base wells #1 and 2) exceeds a concentration (4 to 18 ppb) suggested by the USEPA provisional reference dose based on a 70 kg individual consuming two liters of water a day. Since the uncertainty factors are supposed to account for the somewhat limited toxicological information, it is conceivable that as more toxicological data becomes available, a change in the (provisional) reference dose may occur.
The estimated dose for a Mather Main Base worker, temporary adult resident at the transitional housing unit, and adult patient at the hospital in the Main Base Area exposed to water from well #1, #2 or an average of the four Main Base wells exceeds the provisional reference dose range (0.0001 to 0.0005 mg/kg/day) which means that noncancer (thyroid depression) health effects may have occurred when the workers, temporary adult resident, and adult patients were exposed to water from the Main Base wells. However, because there is a very large uncertainty factor associated with the provisional reference dose and the estimated doses do not approach the NOAEL, it is unlikely that these exposures did cause any noncancer health effects to the workers and temporary Adult residents. Since a patient's health is probably already compromised, the large uncertainty factor built into the provisional reference dose may not necessarily ensure that a health impact did not occur.
The estimated dose for the frequent adult resident/visitor exposed to water from well #1, #2 or an average of the four Main Base wells does not exceed the provisional reference dose range. This means that noncancer (thyroid depression) health effects would not have occurred to the frequent adult resident/visitor drinking or washing with water at the Main Base area.
Based upon the information available at the time this health consultation was written, CDHS concludes that well water from Main Base wells #1, #2, and a combination of those wells may pose a health threat to the users of that water.
The Public Health Recommendations and Actions Plan (PHRAP) for this site contains a description of actions taken, to be taken, or under consideration by ATSDR and CDHS at and near the site. The purpose of the PHRAP is to ensure that this health consultation not only identifies public health hazards, but also provides a plan of action designed to mitigate and prevent adverse human health effects resulting from exposure to hazardous substances in the environment. The CDHS and ATSDR will follow-up on this plan to ensure that actions are carried out.
- Mather Air Force Base Conversion Agency provided an alternative, and perchlorate-free water supply to the Main Base Water System.
- CDHS prepared a fact sheet about perchlorate and health. CDHS made this fact sheet available to the affected water purveyors including the Mather Air Force Base Conversion Agency.
- Mather Air Force Base Conversion Agency communicated with the Mather Air Force Base site mailing list on one occasion ragarding perchlorate level in affected wells, and mentioned in this communication that the perchlorate fact sheet developed by CDHS cooperative agreement staff was available upon request.
- The Air Force and the Perchlorate Study Group (a number of manufacturers and users of perchlorate) are sponsoring an investigation into fate and transport questions regarding perchlorate. For instance, they will investigate if is perchlorate is taken up and bioconcentrated by vegetable crops and the skin permeability of perchlorate.
- The Air Force and the Perchlorate Study Group are also sponsoring a series of animal studies to address some of the information lacking in understanding perchlorate toxicology. CDHS cooperative agreement staff along with other state and federal scientists, were asked by the Air Force to recommend and oversee the planning of the animal studies. As of August 1997, the study protocols have been finalized and the process of choosing a laboratory to conduct the studies is underway. A report on the studies is expected in mid-summer 1998.
- Use Mather Main Base wells #1, 2, and 3 for fire protection only until perchlorate levels fall below 18 ppb.
- Continue communicating with the Mather Main Base water customers about the perchlorate issue.
- Continue monitoring drinking water wells for perchlorate, and discontinue using wells that have levels that exceed the safe level for perchlorate (currently 18 ppb).
- If indicated based on new toxicological information, review toxicological evaluation of past and current perchlorate exposures in the Main Base area.
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ENVIRONMENTAL AND HEALTH EFFECTS ASSESSORS:
Marilyn C. Underwood, Ph.D.
Environmental Health Investigation Branch
California Department of Health Services
COMMUNITY RELATIONS COORDINATOR:
Jane Riggan, M.S.W.
Public Health Social Work Consultant II
Environmental Health Investigations Branch
California Department of Health Services
ATSDR REGIONAL REPRESENTATIVES
Regional Representatives, Region IX
Agency for Toxic Substances and Disease Registry
ATSDR TECHNICAL PROJECT OFFICER:
William Greim, M.S., MPH
Environmental Health Scientist
Division of Health Assessment and Consultation
Superfund Site Assessment Branch, State Programs Section
The Perchlorate Contamination in the Mather Air Force Water Service Area, Aerojet-General Corporation Health Consultation was prepared by the California Department of Health Services under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was begun.
Technical Project Officer, SPS, SSAB, DHAC
The Division of Health Assessment and Consultation, ATSDR, has reviewed this health consultation, and concurs with its findings.
Chief, SPS, SSAB, DHAC, ATSDR