KITSAP COUNTY - BAINBRIDGE ISLAND DUMP
BAINBRIDGE, KITSAP COUNTY, WASHINGTON
The Washington State Department of Ecology (Ecology) asked the Washington State Department of Health (DOH) to evaluate potential short-term health threats from vinyl chloride and other contaminants detected in domestic water supply wells in the vicinity of the Bainbridge Island Landfill in Kitsap County, Washington. This health consultation summarizes our evaluation of the public health implications resulting from actual or potential exposure to these contaminants, but does not attempt to identify the source(s) of contamination. Although Ecology is evaluating the Bainbridge Island Landfill (site) as a potential source of contamination, in this health consultation, the landfill is cited as a reference point only.
Ecology is currently overseeing a Remedial Investigation and Feasibility Study (RI/FS) for the site pursuant to the Model Toxics Control Act (MTCA). The site is located west of Eagle Harbor on Bainbridge Island and covers 40 acres, of which approximately 7 acres were used for refuse disposal. The landfill stopped accepting waste in 1975. The site comprises the northeast quarter of the northwest quarter of Section 33, Township 25 North, Range 2 East. Approximately 1,200 people live within 1 mile of the site and approximately 56,000 people live within 5 miles of the site (1990 census data).
As part of the Bainbridge Island Landfill RI/FS, Kitsap County is conducting quarterly sampling of 16 monitoring wells at the landfill and approximately 20 domestic water supply wells located in the vicinity of the landfill to evaluate water quality. DOH has been asked to review these data. This health consultation presents our findings.
How DOH/OTS Evaluates Data
All monitoring well and domestic well sampling data were evaluated without regard to the source of contamination. Contaminants detected in drinking water wells exceeding a cancer and/or non-cancer health-based screening value were further evaluated in this health consultation. Screening values are media-specific concentrations used to select environmental contaminants for further evaluation. Contaminant concentrations at or below screening values are unlikely to pose a health threat. Contaminant concentrations exceeding screening values do not necessarily pose a health threat, but are further evaluated to determine whether they are at levels observed to cause toxic effects (referred to as toxic effect levels) in human population and/or laboratory animal studies. Exposure assumptions used in this health consultation are listed in Appendix A. Definitions are listed in Appendix B.
Evaluating non-cancer risk:
To evaluate the potential for non-cancer adverse health effects as a result of exposure to contaminated environmental media (i.e, drinking water), a dose was estimated for each contaminant exceeding a health-based screening value. The doses were calculated for a scenario in which residents were assumed to be exposed to the maximum detected chemical concentrations in their drinking water. The estimated dose for an adult and child through adulthood for each contaminant was then compared to ATSDR's minimal risk level (MRL) or EPA's oral reference dose (RfD). MRLs and RfDs are estimates of daily exposure of a human to a chemical that is likely to be without an appreciable non-cancer risk over a specified duration of exposure. They are derived from toxic effect levels obtained from human and laboratory animal studies. These toxic effect levels are expressed as either the lowest adverse effect level (LOAEL) or the no-observed adverse effect level (NOAEL). In human or animal studies, the LOAEL is the lowest dose at which an adverse effect is seen, while the NOAEL is the highest dose that did not result in any adverse health effects.
Because of the uncertainty associated with these data, the toxic effect levels are divided by safety factors (usually 100 or 1,000) to provide the more protective MRL or RfD. If a dose exceeds the MRL or RfD, the potential exists for adverse health effects. Thus, a dose only slightly exceeding the MRL or RfD would fall well below the toxic effect level. The higher the estimated dose is above the MRL or RfD, the closer it will be to the toxic effect level.
Evaluating cancer risk:
For screening of chemicals which are known or expected to cause cancer, it is assumed that no "safe" level exists, and EPA cancer slope factors are used to calculate an "estimated" cancer risk. An exposure which results in an estimated cancer risk of one additional cancer in a population of one million people exposed over a 70 year lifetime, is considered an acceptable risk, and is thus used as the screening value. In a population of one million men in the U.S., 500,000 are expected to develop cancer from all causes in their lifetime. For U.S. woman, the figure is 333,000. The additional estimated cancer risk means that if those one million men are exposed for 70 years to this level of the chemical, 500,001 will develop cancer. For those one million woman exposed, 333,001 will develop cancer.
How DOH Office of Toxic Substances evaluation methods differ from DOH Office of Drinking Water
Kitsap County Department of Public Works and the Bremerton/Kitsap County Health District have raised questions concerning the difference between the DOH Office of Toxic Substances (OTS) and DOH Office of Drinking Water (DW) in evaluating contaminants in drinking water supplies. Within the Environmental Health Division of DOH, both the DW office and OTS have roles in evaluating contaminants in domestic drinking water supplies. To assist the reader in understanding the differences between our respective roles and the criteria each of our offices use to evaluate exposure to contaminants (i.e., MCLs vs. ATSDR criteria), it is necessary to explain our respective mandates and authorities.
The DOH/DW Office regulates public water systems. In Kitsap County, responsibility for public systems serving 25 or fewer connections is delegated to the Bremerton-Kitsap County Health District. Federal and State drinking water standards, called maximum contaminant levels (MCLs) are used by the DOH/DW Office and Kitsap County Health District in regulating these systems, and are legally enforceable standards. Although generally protective of public health, other non health-based considerations were made when developing MCLs, such as technological feasibility, implementation costs, and analytical limitations. In setting the MCL for vinyl chloride, for example, the Environmental Protection Agency has adopted a value which corresponds to the higher end of their acceptable risk range (one additional cancer per 10,000 people exposed, averaged over a lifetime). Also, the MCL does not consider routes of exposure other than ingestion (i.e., inhalation and dermal contact). For these reasons, DOH/OTS does not rely on MCL values alone as an indicator of potential health risk. As a result, DOH/OTS can, and sometimes does, recommend actions at levels below that which the DOH/DW Office may require of public water systems.
DOH/OTS's role is to provide technical assistance to agencies, groups, or individuals on actual or potential health risks from exposure to hazardous substances in the environment, such as contaminants in drinking water supplies. We evaluate data and draw conclusions about potential health risks based on site-specific exposure scenarios and by utilizing current chemical toxicity information and standard risk assessment methodologies to estimate exposures. In doing so, DOH/OTS goes a step further (beyond simply comparing the contaminant concentration to the numerical MCL value) in assessing potential health risk. Our conclusions can result in recommendations for actions to protect public health. However, our recommendations are just that, and are not legally enforceable.
Four of the domestic wells tested by Kitsap County are Group B wells (a public water system that serves more than one family but less than 25 people or 15 connections) and one is a Group A well (a public water system with 15 or more service connections or an average of 25 or more people per day for 60 or more days within a calendar year). The Group A well serves 1 residence and a school/day care facility. The remaining domestic wells are private wells serving individual residences.
Domestic supply wells and monitoring wells were initially analyzed for volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), pesticides, herbicides, polychlorinated biphenyls (PCBs), total petroleum hydrocarbons (TPH), inorganics (metals), cyanide, and conventionals, such as total organic carbon, temperature, conductivity, etc. In later sampling rounds, fewer chemicals were tested, although VOCs continued to be analyzed. Domestic well sample analysis currently includes VOCs and conventional parameters (conductivity, nitrate, pH, alkalinity, chloride, total dissolved solids, dissolved oxygen, sulfate).
Some VOCs and SVOCs have been and continue to be detected at low levels in domestic wells (except for vinyl chloride, all VOCs and SVOCs are below ATSDR health-based screening values). Those compounds below ATSDR screening values do not pose a public health threat and will not be discussed in the remainder of the health consultation. Several inorganic compounds were also detected above comparison values in several of the domestic wells. Table 1 lists the domestic wells with the single highest chemical detections, and the range of detections for that chemical in the well. The Table also lists each chemical's health-based screening value, the well types, well IDs, and approximate number of residences served by the well.