MOSES LAKE WELLFIELD CONTAMINATION
(a/k/a SKYLINE WATER SYSTEM)
MOSES LAKE, GRANT COUNTY, WASHINGTON
No data is available on TCE levels in the tap water of residents served by Skyline water. Since each well provides water to the distribution system separately, the effect of mixing these two sources on the TCE levels at individual taps is difficult to estimate. Therefore, a worst-case scenario will be evaluated that assumes exposure to the maximum level of TCE in Well #1 (11.5 ppb) for 8 months/year and Well #2 (32.2 ppb) for 4 months/year. This approach is intended to evaluate the highest possible exposure with the understanding that most residents are likely to have been exposed at lower levels.
TCE in drinking water can get into the body through drinking, skin contact and breathing of vapors that come off the water during household use (e.g. cooking, dish/clothes washing, showering/bathing). Although bottled drinking water has been made available since March 1994, it is not clear that all residents are using it. Therefore, the following discussion of potential cancer and non-cancer health effects assumes that exposure to contaminated water includes drinking as well as skin contact and breathing of vapors. The significance of drinking bottled water relative to exposure and health is also discussed.
Current exposure to TCE in Skyline drinking water is not expected to result in any non-cancerous health problems for most residents. This is because studies of humans and animals have shown that non-cancerous adverse health effects related to TCE exposure occur only at higher levels than what was estimated for Skyline residents. There is some concern, however, for developmental effects in children born to women who use Skyline water while pregnant.
Most of the health effects attributed to TCE exposure have come from studies in animals. Animals given much higher amounts of TCE than what would result
Developmental Health Effects
The developing fetus is often more sensitive to toxic chemicals than children or adults. Exposure to toxic chemicals prior to birth can cause adverse effects on development that include physical birth defects as well as impaired learning and behavior. Developmental health effects can also include adverse birth outcomes such as low birth weight, early delivery spontaneous abortion and stillbirth.
Although this comparison suggests that it would take considerably higher levels of TCE in the Skyline water system to result in such birth defects, it is important to consider the human studies that have associated birth defects in children with exposure to TCE in drinking water prior to birth. The birth defects identified included heart malformations, neural tube defects and oral clefts. Other adverse birth outcomes reported include low birth weight and increased fetal death.[4, 5, 6, 7] Speech and hearing impairment has also been associated with TCE exposure in young children.[8, 9] The levels of exposure in these studies are not well defined and in some cases included other contaminants. Some of the studies appear to have involved substantially higher levels of TCE in drinking water than those measured in the Skyline water system while others are similar. One of these studies looked at exposure below the MCL for TCE and did not find a statistically significant association with adverse birth outcomes.  There is no evidence that TCE levels below the MCL can cause any non-cancer health effects.
These studies are suggestive of an association between TCE exposure and developmental effects but are not sufficient to allow an accurate estimate of what the risk might be for Skyline residents. Further study may show no association between the levels of TCE in Skyline wells and this type of health effect. The EPA is currently reviewing all available data on the health effects of TCE in order to provide updated and reliable health effects information. Until new data are available, it should be assumed that some risk exists for children born to mothers who are exposed while pregnant to current levels of TCE in Skyline drinking water. Exposure during the first three months of pregnancy is of particular concern. It is likely that this risk is very low based on the data currently available.
Use of Well # 2 (the well with higher TCE levels) has been restricted to emergency situations (i.e., failure of Well #1). Available data indicate that the removal of Well #2 from the water system will reduce the risk for adverse developmental effects provided that levels of TCE in Well #1 do not increase. It is important to note, however, that short term use of Well #2 could still pose a health concern for pregnant women.
A slight increase in cancer risk is expected for residents exposed to TCE in Skyline water for many years. This slight increase in cancer risk was calculated for a 30-year period of a child growing to adulthood exposed to maximum levels of TCE in drinking water via drinking, skin contact and inhalation. Shorter periods of exposure will lower this cancer risk such that residents living at Skyline for only a few years are not expected to have a significant increase in cancer risk. The cancer risk estimated from exposure to TCE at levels below the MCL is not considered to be significant.
TCE was previously classified by EPA as a Group B2 probable human carcinogen based on adequate animal data and insufficient human data. This
The relevance of cancer caused in laboratory animals at high doses of any chemical is questionable for humans exposed to much lower levels found in the environment. Such animal data are considered to be much stronger when supported by evidence of cancer in humans. There is no clear evidence that any type of cancer has resulted from exposure of humans to TCE. Suggestive evidence indicates that workers exposed to TCE from dry cleaning operations showed an increase in lung, cervical and skin cancer. Dry cleaners also use other chemicals, however, including tetrachloroethylene (PCE) which could be responsible for this increase. Increases in leukemia were detected in two populations exposed to TCE in drinking water. Both of these populations, one located in Woburn, MA and the other in New Jersey, were also exposed to other chemicals found in the drinking water.
There is much uncertainty in assessing the cancer risk related to the low levels of TCE found in Skyline drinking water. In order to be protective of health, this assessment of cancer risk makes assumptions that may well be over protective. For example, it is likely that long-term exposure is less than that assumed under the worst-case scenario discussed above since TCE levels in Well #2 were lower in past years. Also, it is assumed that TCE can cause cancer in humans at these low levels which has not been definitively established. However, the potential exists for continued exposure of some residents to levels of TCE that, if continued over many years, would result in a slight increase in cancer risk.
Bottled drinking water has been made available to all Skyline residents since March 1994. However, not all residents are using bottled water. The above assessment assumed that exposure includes drinking as well as skin contact and breathing vapors. The amount of TCE that gets into the body through skin contact and breathing vapors is assumed to be equal to the amount received through drinking. Therefore, residents who use bottled water for drinking could be reducing their exposure by as much as 50 percent. However, some studies indicate that the amount of TCE breathed after showering and other household water use is larger than the amount received by either drinking or skin contact. Any exposure through the air or skin will depend on water use habits, ventilation, water temperature and other factors.