PUBLIC HEALTH ASSESSMENT
SEATTLE MUNICIPAL LANDFILL/KENT HIGHLANDS
KENT, KING COUNTY, WASHINGTON
The tables in this section list the contaminants of concern for the Kent Highlands landfill site. DOHand the Agency for Toxic Substances and Disease Registry (ATSDR) evaluate these contaminantsin subsequent sections of the public health assessment and determine whether exposure to them haspublic health significance. ATSDR and DOH select and discuss these contaminants based upon the following factors:
- Concentrations of contaminants on and off the site.
- Field data quality, laboratory data quality, and sample design.
- Comparison of on-site and off-site concentrations with background concentrations, if available.
- Comparison of on-site and off-site concentrations with public health assessment comparison values for non-carcinogenic and carcinogenic endpoints. These comparison values are Environmental Media Evaluation Guides (EMEGs), Cancer Risk Evaluation Guides (CREGs), Reference Dose Media Evaluation Guides (RMEGs), Maximum Contaminant Levels (MCLs), and other relevant health based guides.
- Community health concerns.
The fact that compounds are listed here does not necessarily imply that a human health threat exists. Instead, it only indicates which contaminants will be evaluated further.
The tables contain the following abbreviations:
- ug/L = microgram of contaminant per liter of sample (parts per billion or ppb)
- ug/m3= microgram of contaminant per cubic meter of sample
EMEGs are estimated contaminant concentrations in particular media at which daily exposure wouldbe unlikely to result in non-cancer health effects. An EMEG is calculated using an assumed bodyweight, and ingestion rate, and an ATSDR Minimal Risk Level (MRL). The tables showcomparison values for adult and child exposure. ATSDR developed MRLs to evaluate health effectsof contaminants commonly found at hazardous waste sites. MRLs are estimates of daily exposurein mg/kg/day to contaminants below which non-cancer, adverse health effects are unlikely to occur. If no MRL exists for a contaminant, a comparison value is calculated from an EPA Reference Dose(RfD), another estimate of the daily exposure to a contaminant that is unlikely to cause non-cancer,adverse health effects. The resulting value is called an RMEG.
CREGs are estimated contaminant concentrations at which exposure would be unlikely to result inmore than one excess cancer in one million persons exposed for a lifetime of 70 years. A CREGis calculated from EPA cancer slope factors, an adult body weight of 70 kg, an accepted ingestionrate, and a risk of 1 X 10-6, which is 1 additional cancer case in a population of 1,000,000 exposedfor a lifetime of 70 years.
To identify possible facilities that could contribute to contamination of the Kent Highlands Landfillsite, DOH searched the Toxic Chemical Release Inventory (TRI) Database by city and zip code forall available years (1987, 1988, 1989, 1990, 1991). TRI was developed by EPA from informationregarding chemical releases into air, water, and soil, as provided according to law by certainindustries. TRI contained information for 323 documented instances of chemical releases into theenvironment (air) in the city of Kent, some of which were within one mile of the landfill site.
During the Remedial Investigation on-site investigations were conducted for ground water, surfacewater, subsurface gas, and ambient air to characterize the contaminants in each media. Soils werenot considered a potential for exposure because they were imported for fill cover or not associatedwith the waste materials. Effects on plants and wildlife were also studied.(5) Contaminants havemigrated to ground water, surface waters, and air. However, site remediation efforts for leachateand gas collection have reduced concentrations to very low levels.(5)
Ground Water Contamination
Several ground water aquifers are found under the landfill, but the two which seem the mostimportant for possible exposure were the Sand Aquifer and the Recent Alluvium Aquifer becausethey extend beyond the physical boundaries of the fill and could be used for domestic watersupplies. The Sand Aquifer has 12 monitoring wells, of which, 3 are upgradient and are thought toshow background levels. The Recent Alluvium Aquifer is below the eastern portion of the landfilland the Green River. Three of the wells tested for the Recent Alluvium were privately owned wellsin the valley east of the site. One of those wells, which is used for irrigation, displayedconcentrations higher than background levels for iron and manganese. All other parameters werebelow background levels.(5)
|Contaminant|| Maximum Concentrations|
|Benzene||<1 - 3.6||1||CREG|
|Contaminant|| Maximum Concentrations|
|Antimony|| 43.8 (up-gradient)|
Surface Water Contamination
There were two settling ponds (a north pond and a south pond) at the east portion of the landfillwhich collected surface run-off from the site and some adjoining property. There is a third pondwhich collects and pre-treats leachate before it is pumped to the municipal sewage treatment plant. The north pond also collected leachate from seeps, and therefore, was automatically pumped out tothe leachate pond. A gated overflow line from the north pond to Midway Creek has been closed andnot used since discovery of the seeps. As mentioned earlier, the north pond has been eliminated byfilling and covering. Midway creek flows through part of the landfill property and empties into theGreen River. Upgradient samples indicate there are contaminants entering Midway Creek from roadrunoff prior to flowing into the landfill site.
|Contaminant|| Maximum Concentration|
|Arsenic||29.2 - 54||3|
|Manganese||2,975 - 8,190||50|
|Contaminant|| Maximum Concentration|
|Arsenic||1.4 - 13.2||3|
|Manganese||83.4 - 1,340||50|
|Vanadium||5.2 - 38.1||30|
|Contaminant|| Maximum Concentration|
|Arsenic||0.9 - 1.0||3|
|Manganese||165 - 287||50|
Subsurface Gas Contamination
Early monitoring found levels of soil gas at or near explosive levels in one location. Informationcollected indicated there had been very little migration of gas from the site and concentrations wereinsignificant. Also, it appears that since the landfill closed and the control systems were installed,the amount of gas being produced is decreasing.(5)(6)
Ambient Air Contamination
Samples were taken from the extractive flare and 12 passive gas flares to obtain concentrations of12 compounds in raw, uncombusted landfill gas. Approximately 90 percent of the flares were litduring site investigations. A complicated air contaminant modeling system was conducted whichestimated contaminant levels on and off the site. The model set up a total of 403 ground-level, off-site receptor locations for evaluation, including 357 locations on a grid system around the landfill,36 boundary receptors, and 10 "sensitive" receptor locations. The model also factored informationfor gasses released from the surface of the fill. The estimated concentrations at the boundaryreceptor points were all below ATSDR comparison values for each of the 12 compounds.(5)
DOH personnel did not find information in the Remedial Investigation regarding past exposure togasses for site workers. Since approximately 10 percent of the flares were unlit at any time thereappears to be a possibility of exposure to the raw gasses. However, the fact that some torches wereunlit was probably due to either low flow of gas or concentrations too low to support combustion. See Table 6 for concentrations for concentrations documented in the final Remedial Investigationreport and ATSDR comparison values.
|Contaminant|| Maximum Concentration|
The Remedial Investigation examined off-site ground water, surface water, and ambient air.
Ground Water Contaminants
Literature searches revealed there are 17 private wells within a two mile radius of the landfill, mostof which are upgradient. Three existing, privately owned wells, in the Valley Aquifer,downgradient from the landfill(part of the Recent Alluvium Aquifer) were sampled for all theparameters found in the other monitoring wells. None of the contaminants were above ATSDRcomparison levels.
Surface Water Contaminants
Midway Creek and the Green River were sampled at points upstream and downstream from thelandfill. Midway Creek flows from above the landfill, under SR 516, through the east toe of thelandfill property, and then a short distance to the Green River. Sampling appears to show there iscontamination entering the stream prior to entering the landfill site. Indeed, some concentrationswere lower in the downstream samples. Concentrations in samples from the Green River were belowcomparison values.
Ambient Air Contaminants
The air sampling model established a total of 403 ground-level, off-site receptor locations forevaluation, including 357 locations on a grid system around the landfill, 36 boundary receptors, and10 "sensitive" monitoring points to establish what concentrations would be possible at areas suchas residences, parking lots, and traffic intersections. All of the off-site modeled results for each ofthe 12 contaminants were below ATSDR comparison levels.
In preparing this Public Health Assessment, DOH relies on the information provided in thereferenced documents and assumes that adequate quality assurance and quality control measureswere followed with regard to chain-of-custody, laboratory procedures, and data reporting. Thevalidity of the analysis and conclusions drawn for this Public Health Assessment are determined bythe completeness, relevance, and reliability of the referenced information.
DOH personnel did not notice any particular physical hazards on the site.
To determine whether site workers or area residents are exposed to contaminants from the site, DOHand ATSDR evaluate the environmental and human activities that lead to human exposure. Thispathway analysis evaluates five elements: The source of contamination, transport of contaminantsthrough environmental media (soil, ground water, etc.), points of human exposure, routes of humanexposure (inhalation, ingestion, etc.), and the exposed population.
ATSDR categorizes an exposure pathway as completed or potential if it cannot be eliminated. Anexposure pathway can be eliminated if at least one of the five elements is missing and will never bepresent. Completed pathways have all five elements and indicate that exposure to a contaminanthas occurred in the past, is currently occurring, or will occur in the future. Potential pathwaysindicate that all five elements could exist and that exposure to a contaminant could have occurredin the past, could be occurring now, or could occur in the future.
|Pathway||Exposure Pathway Elements||Time|
|Source||Media|| Point of|
| Route of|
Midway Creek flows through the site at the east fringe. It collects contaminants from road run-offprior to entering the site and has picked up contaminants on-site from the south and north ponds. After leaving the site the creek flows into the Green River. At that location there was evidence thatchildren have played in the water.
|Pathway||Exposed Pathway Elements||Time|
Soil Gas/Air Pathway
Past site workers had opportunity to become exposed to gasses from the landfill. An ambient airmodel was conducted in the RI which showed a possibility of small concentrations of contaminantson-site and migrating off-site. The gasses produced in the fill material were able to escape throughthe cover soil and through unlit torches. Past site workers could have been exposed to soil gassesfrom unlit torches, since approximately 10 percent of them were unlit during site inspections. Present gas control systems have reduced exposure to the point that there is no present or future pathway.
Ground Water Pathway
Ground water under the landfill has received contaminants through infiltration. There may be asmany as 17 private wells within a two mile radius of the site. None of the 3 private wells whichwere tested during the RI had contaminant levels exceeding ATSDR comparison levels. Given thepresent circumstances, it seems highly unlikely that a well could or would be constructed near thelandfill because of poor natural water quality and low yield in the upper zone of the Recent AlluvianAquifer, prevailing regulatory constraints, and the availability of water from the City of Kent water system.
Surface Water Pathway
There is, or was, a potential of exposure for site workers or trespassers from contaminants in surfacewater from the north pond, south pond, and the leachate pond. Trespassers, and workers whomaintained the pond pumping equipment, could have been be exposed to contaminants by dermalcontact and incidental ingestion of the water. However, the chance of either exposure is extremelyremote because the pond areas are secured by fencing and dense vegetation, and site workers usedprotective clothing. For those reasons this potential pathway is eliminated.
There is a potential for exposure for people who use the Green River for recreation. Fishermen andswimmers in the area where Midway Creek enters the river could be exposed to contaminants bydermal contact and incidental ingestion. Since there were no contaminant concentrations in theGreen River that exceeded ATSDR comparison values it appears that there is no source element and therefore we have eliminated this pathway.
In this section of the public health assessment we will discuss the health effects in persons exposedto specific contaminants, evaluate state and local health outcome databases, and address specificcommunity health concerns.
We use MRL and RfD values, in conjunction with estimated human exposure doses, to evaluatecontaminants for non-carcinogenic adverse health effects. MRLs are developed for each route ofexposure, such as ingestion and inhalation, and for length of exposure, such as acute(less than 14days), intermediate(15 to 364 days), and chronic(greater than 364 days). Chronic MRLs are usedin this public health assessment whenever possible. ATSDR presents these MRLs in ToxicologicalProfiles. These chemical-specific profiles provide information on health effects, environmentaltransport, human exposure, and regulatory status. For compounds that have been classified ascarcinogenic (cancer causing), EPA has developed cancer slope factors for calculation of thepotential risk. In order to perform the calculation, adequate data must be available for dose level,frequency, and length of exposure. The calculated cancer risk is an estimate of the excess cancerrisk in an exposed population. The following discussions regarding specific compounds and thecalculated exposure doses are based upon maximum contaminant levels and a "worst case scenario". The reader should recognize that the use of the maximum detected concentration of a contaminantto calculate the exposure dose may result in an overestimate of actual exposure. Child exposureswere estimated for off-site incidental ingestion of surface water and adult exposures were estimatedfor inhalation of on-site gas.
For a conservative analysis of the possible exposures, the authors used the following assumptions:
- Adult Body Weight = 70 kilograms (kg)
- Child Body Weight = 16 kg
- Child Ingestion Rate(water) = 4 milliliters/exposure(incidental)
- Adult Inhalation Rate = 9600 liters/work day
- Exposure period = 5 days/week for 5 years (site worker air)
= 1 day/week for 10 years (child in Midway Creek)
An exposure dose is calculated and then compared to the MRL or RfD, or a cancer risk is calculated. When calculating the exposure dose you must have a contaminant concentration, ingestion rate orinhalation rate, and a body weight. Where exposure is intermittent, you must also have an exposurefactor which will average the total time. Cancer risk values are factored for a 5 year exposure forair and a 10 year exposure for surface water over a lifetime of 70 years.
Where estimated daily exposure doses exceed MRLs or RfDs, we further compare with values calledNo Observed Adverse Effect Level (NOAEL) and Lowest Observed Adverse Effect Level(LOAEL). Data from human studies are used preferentially, but animal studies can be used toindicate possible human health effects. It should be noted that there are uncertainties when usingthese estimated doses and NOAELs, and in some cases the exposure may be above or below by asmall margin. That small difference may or may not be protective for sensitive individuals orpopulations.
Midway Creek The authors estimated exposure doses for a "worst case scenario" for a child playingin Midway Creek one day per week for 10 years. The chemicals of concern were Arsenic andManganese, since they exceeded the comparison values in table 5.
|The estimated exposure dose was 4 orders of magnitude lower than the oral RfD. Cancer risk was estimated to represent no increased risk of cancer.|
|The estimated exposure dose was 2 orders of magnitude lower than the oral RfD.|
Based upon these estimates, exposure to these media is not likely to result in adverse human health effects.
Non-Combusted Soil Gas From Table 6 there are 2 chemicals of concern (benzene and 1,2-dibromoethane) where past site workers could have been exposed to gas from flares. A "worst casescenario" of a site worker being exposed to maximum levels sampled from flares for five days perweek for five years was examined. Estimated doses for both of the chemicals were below chronicnon-cancer health guidelines. Cancer risk was estimated for all 8 chemicals combined andrepresented no increased risk of cancer.
Please refer to the previous discussion in the Health Outcome Data section for health outcome databases available in Washington State. We were not able to find any specific information for the localarea around the Kent Highlands Landfill site. Therefore, health outcome data cannot be evaluated at this time.
As mentioned earlier, public comments regarding the site have been minimal. Residents south ofthe site were concerned about air contamination and odor from landfill gasses. The investigationsconducted for ambient air and the exposure scenarios examined in this section did not reveal a significant exposure.
The public was officially invited to review and comment on this draft health assessment during theperiod of July 15, 1994 to August 30, 1994. The document was made available at the Kent PublicLibrary. A news release was distributed to 3 newspapers in the area of Kent and Seattle. As ofSeptember 15, 1994, the Department of Health did not receive comments from the public regarding this public health assessment draft.