PUBLIC HEALTH ASSESSMENT
SEATTLE MUNICIPAL LANDFILL/KENT HIGHLANDS
KENT, KING COUNTY, WASHINGTON
ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS
The tables in this section list the contaminants of concern for the Kent Highlands landfill site. DOH and the Agency for Toxic Substances and Disease Registry (ATSDR) evaluate these contaminants in subsequent sections of the public health assessment and determine whether exposure to them has public health significance. ATSDR and DOH select and discuss these contaminants based upon the following factors:
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:
EMEGs are estimated contaminant concentrations in particular media at which daily exposure would be unlikely to result in non-cancer health effects. An EMEG is calculated using an assumed body weight, and ingestion rate, and an ATSDR Minimal Risk Level (MRL). The tables show comparison values for adult and child exposure. ATSDR developed MRLs to evaluate health effects of contaminants commonly found at hazardous waste sites. MRLs are estimates of daily exposure in 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 in more than one excess cancer in one million persons exposed for a lifetime of 70 years. A CREG is calculated from EPA cancer slope factors, an adult body weight of 70 kg, an accepted ingestion rate, and a risk of 1 X 10-6, which is 1 additional cancer case in a population of 1,000,000 exposed for a lifetime of 70 years.
To identify possible facilities that could contribute to contamination of the Kent Highlands Landfill site, DOH searched the Toxic Chemical Release Inventory (TRI) Database by city and zip code for all available years (1987, 1988, 1989, 1990, 1991). TRI was developed by EPA from information regarding chemical releases into air, water, and soil, as provided according to law by certain industries. TRI contained information for 323 documented instances of chemical releases into the environment (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, surface water, subsurface gas, and ambient air to characterize the contaminants in each media. Soils were not considered a potential for exposure because they were imported for fill cover or not associated with the waste materials. Effects on plants and wildlife were also studied.(5) Contaminants have migrated to ground water, surface waters, and air. However, site remediation efforts for leachate and 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 most important for possible exposure were the Sand Aquifer and the Recent Alluvium Aquifer because they extend beyond the physical boundaries of the fill and could be used for domestic water supplies. The Sand Aquifer has 12 monitoring wells, of which, 3 are upgradient and are thought to show background levels. The Recent Alluvium Aquifer is below the eastern portion of the landfill and the Green River. Three of the wells tested for the Recent Alluvium were privately owned wells in the valley east of the site. One of those wells, which is used for irrigation, displayed concentrations higher than background levels for iron and manganese. All other parameters were below background levels.(5)
Table 1. Range of Concentrations in On-Site Ground Water in the Sand Aquifer(5)
| Contaminant | Maximum Concentrations ug/L (ppb) |
Comparison Values | |
| ug/L | Source | ||
| Benzene | <1 - 3.6 | 1 | CREG |
| Aluminum | 100 | none | none |
| Antimony | 25.8 | 4 10 |
RMEG (child) RMEG (adult) |
| Arsenic | 17 | 3 10 0.02 |
EMEG (child) EMEG (adult) CREG |
| Manganese | 21,500 | 50 200 |
RMEG (child) RMEG (adult) |
Table 2. Range of Concentrations in On-Site Ground Water in the Recent Alluvium Aquifer (5)
| Contaminant | Maximum Concentrations ug/L (ppb) |
Comparison Values | |
| ug/L | Source | ||
| Antimony | 43.8 (up-gradient) 24.9 (on-site) |
4 10 |
RMEG (child) RMEG (adult) |
| Arsenic | 91 | 3 10 0.02 |
EMEG (child) EMEG (adult) CREG |
| Nickel | 135 | 100 | MCL |
| Manganese | 12,900 | 50 200 |
RMEG (child) RMEG (adult) |
Surface Water Contamination
There were two settling ponds (a north pond and a south pond) at the east portion of the landfill which collected surface run-off from the site and some adjoining property. There is a third pond which 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 to the leachate pond. A gated overflow line from the north pond to Midway Creek has been closed and not used since discovery of the seeps. As mentioned earlier, the north pond has been eliminated by filling and covering. Midway creek flows through part of the landfill property and empties into the Green River. Upgradient samples indicate there are contaminants entering Midway Creek from road runoff prior to flowing into the landfill site.
Table 3. North Pond Surface Water(5)
| Contaminant | Maximum Concentration (ug/L) |
Comparison Values | |
| ug/L | Source | ||
| Arsenic | 29.2 - 54 | 3 10 0.02 |
EMEG (Child) EMEG (Adult) CREG |
| Manganese | 2,975 - 8,190 | 50 200 |
RMEG (Child) RMEG (Adult) |
Table 4. South Pond Surface Water(5)
| Contaminant | Maximum Concentration (ug/L) |
Comparison Values | |
| ug/L | Source | ||
| Arsenic | 1.4 - 13.2 | 3 10 0.02 |
EMEG (Child) EMEG (Adult) CREG |
| Manganese | 83.4 - 1,340 | 50 200 |
RMEG (Child) RMEG (Adult) |
| Vanadium | 5.2 - 38.1 | 30 100 |
EMEG (Child) EMEG (Adult) |
Table 5. Midway Creek Surface Water (5)
| Contaminant | Maximum Concentration (ug/L) |
Comparison Values | |
| ug/L | Source | ||
| Arsenic | 0.9 - 1.0 | 3 10 0.02 |
EMEG (Child) EMEG (Adult) CREG |
| Manganese | 165 - 287 | 50 200 |
RMEG (Child) RMEG (Adult) |
Subsurface Gas Contamination
Early monitoring found levels of soil gas at or near explosive levels in one location. Information collected indicated there had been very little migration of gas from the site and concentrations were insignificant. 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 of 12 compounds in raw, uncombusted landfill gas. Approximately 90 percent of the flares were lit during site investigations. A complicated air contaminant modeling system was conducted which estimated 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 information for gasses released from the surface of the fill. The estimated concentrations at the boundary receptor 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 to
gasses for site workers. Since approximately 10 percent of the flares were unlit at any time there
appears to be a possibility of exposure to the raw gasses. However, the fact that some torches were
unlit 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 Investigation
report and ATSDR comparison values.
Table 6. Non-Combusted Gas Contamination(5)
| Contaminant | Maximum Concentration ug/m3 |
Comparison Value | |
| ug/m3 | Source | ||
| Methylene chloride | 0.22 | 2 | CREG |
| Chloroform | 0.018 | 0.04 | CREG |
| 1,2-dichloroethane | 0.016 | 0.04 | CREG |
| Benzene | 0.49 | 0.1 | CREG |
| Carbon tetrachloride | 0.02 | 0.07 | CREG |
| Trichloroethylene | 0.21 | 0.6 | CREG |
| Perchloroethylene | 0.36 | 2 | CREG |
| 1,2-dibromoethane | 0.018 | 0.005 | CREG |
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, most of 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 the parameters found in the other monitoring wells. None of the contaminants were above ATSDR comparison levels.
Surface Water Contaminants
Midway Creek and the Green River were sampled at points upstream and downstream from the landfill. Midway Creek flows from above the landfill, under SR 516, through the east toe of the landfill property, and then a short distance to the Green River. Sampling appears to show there is contamination entering the stream prior to entering the landfill site. Indeed, some concentrations were lower in the downstream samples. Concentrations in samples from the Green River were below comparison values.
Ambient Air Contaminants
The air sampling model established 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" monitoring points to establish what concentrations would be possible at areas such as residences, parking lots, and traffic intersections. All of the off-site modeled results for each of the 12 contaminants were below ATSDR comparison levels.
C. QUALITY ASSURANCE AND QUALITY CONTROL
In preparing this Public Health Assessment, DOH relies on the information provided in the referenced documents and assumes that adequate quality assurance and quality control measures were followed with regard to chain-of-custody, laboratory procedures, and data reporting. The validity of the analysis and conclusions drawn for this Public Health Assessment are determined by the 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, DOH and ATSDR evaluate the environmental and human activities that lead to human exposure. This pathway analysis evaluates five elements: The source of contamination, transport of contaminants through environmental media (soil, ground water, etc.), points of human exposure, routes of human exposure (inhalation, ingestion, etc.), and the exposed population.
ATSDR categorizes an exposure pathway as completed or potential if it cannot be eliminated. An exposure pathway can be eliminated if at least one of the five elements is missing and will never be present. Completed pathways have all five elements and indicate that exposure to a contaminant has occurred in the past, is currently occurring, or will occur in the future. Potential pathways indicate that all five elements could exist and that exposure to a contaminant could have occurred in the past, could be occurring now, or could occur in the future.
A. COMPLETED EXPOSURE PATHWAYS
Table 7. Completed Pathways
| Pathway | Exposure Pathway Elements | Time | ||||
| Source | Media | Point of Exposure |
Route of Exposure |
Exposed Population |
||
| Surface Water |
Midway Creek |
Water | Midway Creek |
Ingestion & Dermal Absorption |
Recreationists | Past Present Future |
Surface Water
Midway Creek flows through the site at the east fringe. It collects contaminants from road run-off prior 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 that children have played in the water.
B. POTENTIAL EXPOSURE PATHWAYS
Table 8. Potential Pathways
| Pathway | Exposed Pathway Elements | Time | ||||
| Source | Media | Point of Exposure |
Route of Exposure |
Exposed Population |
||
| Soil Gas | Unlit Torches |
Air | Torch | Inhalation | Site Workers | Past |
| Ground Water | Alluvium Aquifer |
Water | Wells | Ingestion | Residents | Future |
Soil Gas/Air Pathway
Past site workers had opportunity to become exposed to gasses from the landfill. An ambient air model was conducted in the RI which showed a possibility of small concentrations of contaminants on-site and migrating off-site. The gasses produced in the fill material were able to escape through the cover soil and through unlit torches. Past site workers could have been exposed to soil gasses from 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 as many as 17 private wells within a two mile radius of the site. None of the 3 private wells which were tested during the RI had contaminant levels exceeding ATSDR comparison levels. Given the present circumstances, it seems highly unlikely that a well could or would be constructed near the landfill because of poor natural water quality and low yield in the upper zone of the Recent Alluvian Aquifer, prevailing regulatory constraints, and the availability of water from the City of Kent water system.
C. ELIMINATED EXPOSURE PATHWAYS
Surface Water Pathway
There is, or was, a potential of exposure for site workers or trespassers from contaminants in surface water from the north pond, south pond, and the leachate pond. Trespassers, and workers who maintained the pond pumping equipment, could have been be exposed to contaminants by dermal contact and incidental ingestion of the water. However, the chance of either exposure is extremely remote because the pond areas are secured by fencing and dense vegetation, and site workers used protective 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 and
swimmers in the area where Midway Creek enters the river could be exposed to contaminants by
dermal contact and incidental ingestion. Since there were no contaminant concentrations in the
Green River that exceeded ATSDR comparison values it appears that there is no source element and therefore we have eliminated this pathway.
Introduction
In this section of the public health assessment we will discuss the health effects in persons exposed to specific contaminants, evaluate state and local health outcome databases, and address specific community health concerns.
We use MRL and RfD values, in conjunction with estimated human exposure doses, to evaluate contaminants for non-carcinogenic adverse health effects. MRLs are developed for each route of exposure, such as ingestion and inhalation, and for length of exposure, such as acute(less than 14 days), intermediate(15 to 364 days), and chronic(greater than 364 days). Chronic MRLs are used in this public health assessment whenever possible. ATSDR presents these MRLs in Toxicological Profiles. These chemical-specific profiles provide information on health effects, environmental transport, human exposure, and regulatory status. For compounds that have been classified as carcinogenic (cancer causing), EPA has developed cancer slope factors for calculation of the potential 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 cancer risk in an exposed population. The following discussions regarding specific compounds and the calculated 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 contaminant to calculate the exposure dose may result in an overestimate of actual exposure. Child exposures were estimated for off-site incidental ingestion of surface water and adult exposures were estimated for inhalation of on-site gas.
For a conservative analysis of the possible exposures, the authors used the following assumptions:
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 or inhalation rate, and a body weight. Where exposure is intermittent, you must also have an exposure factor which will average the total time. Cancer risk values are factored for a 5 year exposure for air 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 called No 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 to indicate possible human health effects. It should be noted that there are uncertainties when using these estimated doses and NOAELs, and in some cases the exposure may be above or below by a small margin. That small difference may or may not be protective for sensitive individuals or populations.
Midway Creek The authors estimated exposure doses for a "worst case scenario" for a child playing
in Midway Creek one day per week for 10 years. The chemicals of concern were Arsenic and
Manganese, 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 case scenario" of a site worker being exposed to maximum levels sampled from flares for five days per week for five years was examined. Estimated doses for both of the chemicals were below chronic non-cancer health guidelines. Cancer risk was estimated for all 8 chemicals combined and represented no increased risk of cancer.
B. HEALTH OUTCOME DATA EVALUATION
Please refer to the previous discussion in the Health Outcome Data section for health outcome data bases available in Washington State. We were not able to find any specific information for the local area around the Kent Highlands Landfill site. Therefore, health outcome data cannot be evaluated at this time.
C. COMMUNITY HEALTH CONCERNS EVALUATION
As mentioned earlier, public comments regarding the site have been minimal. Residents south of the site were concerned about air contamination and odor from landfill gasses. The investigations conducted 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 the period of July 15, 1994 to August 30, 1994. The document was made available at the Kent Public Library. A news release was distributed to 3 newspapers in the area of Kent and Seattle. As of September 15, 1994, the Department of Health did not receive comments from the public regarding this public health assessment draft.
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