HEALTH CONSULTATION
GRIGGS AND WALNUT GROUNDWATER SITE
(a/k/a GRIGGS AND WALNUT GROUND WATER PLUME)
LAS CRUCES, DOÑA AÑA COUNTY, NEW MEXICO
SUMMARY AND STATEMENT OF ISSUES
The State of New Mexico Environment Department (NMED) requested an evaluation of the potential risk posed by evaporative cooler use associated with the Griggs and Walnut Groundwater Site, Las Cruces, New Mexico, by the Agency for Toxic Substances and Disease Registry's (ATSDR) in January 2003 (1). The water used by the evaporative coolers in homes and businesses in the City of Las Cruces is provided by the public water supply and contains low-level detections of tetrachloroethene (PCE). PCE concentrations detected in the public water supply in Las Cruces have not been found to exceed the Environmental Protection Agency's (EPA's) Maximum Contaminant Level (MCL) of 5 micrograms per liter (µg/L). ATSDR has prepared this Health Consultation in response to the NMED request.
The Griggs and Walnut Groundwater Site is a contaminated groundwater plume centered near the intersection of Griggs Avenue and Walnut Street in Las Cruces, Doña Aña County, New Mexico. The area of contamination is approximately 2,500 feet by 4,000 feet. The impacted wells in this area range in depth from 576 to 730 feet. The exact extent of the groundwater contaminant plume has yet to be defined. Five municipal drinking water wells have been impacted by contamination associated with the site. Only one of the municipal wells (Well #18) contains concentrations of PCE above the MCL. The City of Las Cruces supplies water to the community from 28 municipal wells, which are monitored periodically in accordance with EPA's Safe Drinking Water Act (2). Based on the available data, no water with PCE concentrations greater than the MCL of 5 µg/L has entered the distribution system that provides drinking water to the community. Well #18 was off-line when PCE concentrations greater than 5 µg/L were measured. Residential tap water samples collected from April 2000 to April 2002 indicated the presence of low-level concentrations of PCE (up to 3.5 µg/L) in the water supply used for domestic purposes, including use in evaporative coolers for cooling air in homes and businesses (1).
Evaporative coolers (also referred to as swamp coolers) are used by many homeowners to cool indoor air in areas with hot and dry climates, such as Las Cruces, New Mexico. Although evaporative coolers may have different features, they operate in a very similar manner. The coolers draw in warm outside air into the unit and through wet filter (paper or fiber) pads. The water used to wet the filter pads is from the home's water supply. Water collects in a basin at the base of the unit, is then pumped to the top of the filters, where it trickles down the filter pad. As the hot air moves through the wet filter pads, the air is cooled and humidified. The cooled air enters the heating, ventilation, and air conditioning system and is distributed throughout the home through vents. Cooler air exits the indoor environment through open windows and doors (3).
NMED provided the following information for consideration in the evaporative cooler exposure evaluation (1):
The following reference materials were also provided to ATSDR from NMED for consideration in the swamp cooler investigation:
.To estimate potential exposure to public water users in the City of Las Cruces, ATSDR utilized an approach used by the Arizona Department of Health Services to evaluate evaporative cooler use in Tucson, Arizona (4). The approach estimates the concentrations of contaminants present in air resulting from the use of water with detectable concentrations of contaminants in evaporative coolers.
ATSDR used the following calculation and conservative assumptions (derived from the resources provided by NMED) to calculate the PCE concentration in air:
C = (CW) (WU)
CFM
| C= concentration in air (milligrams per cubic meter [mg/m3]) CW= concentration in water (µg/L) WU= water used by the evaporative cooler per minute (liters per minute [L/min]) CFM = cooler air volume per minute (cubic meters per minute [m3/min]) |
ATSDR considered the maximum concentrations of PCE in water to be 5 µg/L (1). The estimated water use was assumed to be 0.16 L/min (2). An estimated air volume of 100 m3/min (3) was assumed for a house of approximately 1,500 to 2,000 square feet.
Public Health Implications
A review of the scientific literature indicates that exposure to high levels of PCE via inhalation has been associated with neurological, liver, and kidney effects among humans and animals. Leukemia and liver cancer has also been observed among study animals exposed to high concentrations of PCE via inhalation (5). Cancer and non-cancer health effects were considered as part of the evaluation of PCE exposure in indoor air as a result of evaporative cooler use associated with the Griggs and Walnut Groundwater Site. Non-cancer health effects and cancer are discussed in the following sections.
Non-cancer health effects
To evaluate the potential for non-cancer health effects, the calculated concentration of PCE of 0.0080 µg/m3 was compared with ATSDR's chronic inhalation Minimal Risk Level (MRL) of 275 µg/m3 (5). ATSDR's inhalation MRL is derived for continuous inhalation exposure over a 7-day per week, 24-hour exposure period, for conservatism. Many individuals may go to work or school and, therefore, may be exposed to potential contaminants for shorter periods of time. The chronic inhalation MRL for PCE is based on neurological effects observed among humans exposed to concentrations many thousands of times greater than the concentrations calculated for PCE in indoor air for the Griggs and Walnut Groundwater Site (5). Therefore, non-cancer health effects are not expected among individuals exposed to PCE in indoor air resulting from the use of water in evaporative coolers that contains low-level PCE concentrations in Las Cruces.
Cancer
Exposure to a cancer-causing compound, even at low concentrations, is assumed to be associated with some increased risk for evaluation purposes. The estimated excess risk of developing cancer from exposure to PCE associated with evaporative cooler use in the vicinity of the Griggs and Walnut Groundwater Site was calculated with consideration of several factors, such as contaminant concentration (estimated by the approach previously discussed), inhalation rate (20 cubic meters per day [m3/day]), exposure duration (365 days per year), exposure frequency (30 years), and body weight (70 kilograms). The calculation of risk is not a specific estimate of expected cancers. Rather, it is a theoretical estimate of the increase in the probability that a person may develop cancer sometime during his or her lifetime following exposure to a particular contaminant. Therefore, exposure is averaged over the lifetime of an individual (365 days/year for 70 years). ATSDR also incorporated EPA's chemical-specific inhalation Cancer Slope Factor (CSFs or cancer potency estimates) to calculate the increased excess lifetime cancer risk from exposure to PCE present in indoor air from evaporative cooler use. EPA's inhalation CSF of 1.0 x 10-2 (milligrams per kilogram per day-1) mg/kg/day-1, is currently under review.
There are varying suggestions among the scientific community regarding an acceptable excess lifetime cancer risk, due to the uncertainties regarding the mechanism of cancer. The recommendations of many scientists and EPA have been in the risk range of 1 in 1,000,000 to 1 in 10,000 (also referred to as 1 x 10-6 to 1 x 10-4) excess cancer cases. An increased lifetime cancer risk of 1 in 1,000,000 (or 1 x 10-6) or less is generally considered an insignificant increase in cancer risk.
The theoretical excess lifetime cancer risk associated with inhalation exposure to PCE from evaporative cooler use in Las Cruces is 1.0 x 10-8, which indicates a very low excess cancer risk. The available scientific literature indicates cancerous effects (leukemia and liver) among animals exposed to concentrations of PCE via inhalation that were many thousands of times greater than the concentrations of PCE expected to be present in indoor air from evaporative cooler use (5). Therefore, cancer is very unlikely to occur among individuals exposed to PCE in indoor air resulting from the use of water in evaporative coolers that contain low-level PCE concentrations in Las Cruces.
To ensure that the health of the nation's children is protected, ATSDR has implemented an initiative to protect children from exposure to hazardous substances. ATSDR recognizes that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of their water, soil, air, or food. Infants and children may be more susceptible to toxic substances than adults due to their immature and developing organs. Children are smaller, which results in higher doses when compared with adults. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care. ATSDR's evaluation contained within this document considered children as a susceptible subpopulation.
ATSDR considered exposure to children as part of the evaluation of inhalation of PCE in indoor air resulting from evaporative cooler use. The concentrations at which harmful effects have been observed among individuals exposed to PCE is many thousands of times greater than those associated with evaporative cooler use in the vicinity of the Griggs and Walnut Groundwater Site (5). Based on the available information and the scientific literature, health impacts are not expected among children exposed to low-level concentrations of PCE in indoor air in Las Cruces.
Based on the information provided by NMED and the available scientific literature, cancer and non-cancer health effects are not expected to occur among individuals (adults and children) exposed to low concentrations of PCE in indoor air as a result of evaporative cooler use in Las Cruces, New Mexico. Therefore, ATSDR concludes No Apparent Public Health Hazard exists for inhalation exposure evaluated in this Health Consultation. ATSDR's No Apparent Public Health Hazard category refers to sites where human exposure to contaminated media might be occurring, might have occurred in the past, or might occur in the future, but where the exposure is not expected to cause any harmful health effects (6).
ATSDR recommends continued monitoring of the Las Cruces public water supply, in accordance with the Safe Drinking Water Act, to ensure levels of PCE in drinking water do not exceed the MCL of 5 µg/L. If levels of PCE in drinking water are found to exceed the MCL, ATSDR recommends a re-evaluation of the potential risk posed by evaporative cooler use in the vicinity of the Griggs and Walnut Groundwater Site.
A Public Health Action Plan describes the actions designed to mitigate or prevent adverse human health effects that might result from exposure to hazardous substances associated with site contamination. This Health Consultation, which focuses specifically on the evaporative cooler exposure pathway, was prepared by ATSDR in response to a request from NMED. Based on the findings of this Health Consultation, no specific public health actions are warranted at the site at this time. A summary of the public health actions that have been taken and those to be completed for the Griggs and Walnut Groundwater Site is provided below.
Actions Taken
Actions to Be Completed
Robert Knowles, MS, REHS
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
Annmarie DePasquale, MPH
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
Reviewed By:
Gregory Zarus, Atmospheric Scientist
Division of Health Assessment and Consultation
Exposure Investigations Branch
..
