PUBLIC HEALTH ASSESSMENT
COMMENCEMENT BAY - SOUTH TACOMA CHANNEL
(a/k/a TACOMA LANDFILL)
TACOMA, PIERCE COUNTY, WASHINGTON
The Tacoma Landfill is a 190-acre landfill in the City of Tacoma, Washington. The landfill is currently operating on about 18 acres. Since 1960, the area has accepted garbage and municipal wastes, as well as some industrial wastes, which have since been designated as hazardous. The site is closely surrounded by numerous apartment complexes, small homes, and businesses. Groundwater contaminated primarily with volatile organic compounds (VOC's) was detected southwest of the site in residential wells in 1983. Residences affected by the contaminated groundwater were connected to the municipal water system, and quarterly monitoring of residential wells continues. Subsurface soil samples and some surface water samples from the site were contaminated. A gas extraction system was installed because of high levels of methane gas found in indoor air in small businesses surrounding the site. The site is unlikely to pose a current health threat. However, the predicted migration pattern of contaminated groundwater could result in a threat to municipal and private well water supplies in the future if no remedial action is taken.
The Tacoma Landfill is a National Priorities List site which is located in South Tacoma, Washington. The disposal site is located in a hilly area and is surrounded by residential and commercial areas. The primary active fill area is approximately 18 acres in size and is below ground level. Some filling is also occurring in other areas for the purpose of bringing these areas up to final grade before capping. The inactive parts of the site are covered with grasses. The disposal site is currently owned and operated by the City of Tacoma.
Since 1960, the city has accepted municipal and industrial wastes at the landfill. Current investigations into the contributors of hazardous materials to the site may elucidate the types, amounts, and locations of hazardous wastes dumped at the site. However, it is likely that chlorinated phenols, other chlorinated organic compounds, heavy metals, waste oils, and paint sludges were deposited at the site during the 1960's and 1970's.
Remedial actions have included the placement of a chain link fence with barbed wire around the entire site and the installation of a gas extraction system. The Final Remedial Investigation (RI) was issued in December 1987. A Record of Decision (ROD) was issued in March 1988. The ROD specifies that contaminated groundwater will be extracted and treated. In addition, the landfill will be capped, except for the active portion in the central area, which will be capped when filled.
A site visit was conducted on July 11, 1988, by Regional and Headquarters Agency for Toxic Substances and Disease Registry (ATSDR) staff. The information in this Health Assessment is based on this visit, on the December 1987 RI, and on the ROD of March 1988.
Public access to the Tacoma Landfill site is prevented by a fence. However during working hours, the back gate is left open and unguarded, which would allow unauthorized entry. The inactive sections of the landfill are covered by grasses, and the road is covered with pebble-sized gravel to suppress dust formation. However, dust formation can occur with vehicular traffic. During the ATSDR site visit, there was no evidence of surface water runoff. However, personnel from the Washington Department of Ecology have recently (April 1988) observed surface water runoff from the site just south of the central pit.
The currently operating section of the landfill is a lined pit of approximately 18 acres with constant daily traffic. The landfill office and the gas extraction flare station are located on a paved road approximately one-eighth of a mile from the front gate. Vehicles carrying refuse are stopped at a small booth before entering the site and driving down to the pit area.
Data on the principal water, air, and soil contaminants were obtained from the RI Reports. The major contamination both on-site and off-site consists of VOC's.
The following table lists the contaminants of concern found in the landfill site area, the media that are contaminated, and the range of concentrations found.
|Groundwater (ug/l)||Benzene |
|ND - 19 |
ND - 31
ND - 140
ND - 5
ND - 1300
ND - 36
ND - 190
ND - 80
ND - 170
ND - 63
ND - 1200
|Sewers/ Below Surface Leachate (ug/l)||Benzyl Alcohol |
|ND - 84 |
ND - 49
ND - 260
ND - 600
30 - 220
|Surface Water (ug/l)||Nickel |
|ND - 209 |
ND - 56
|Sediment (ug/kg)||Methylene Chloride |
|TR - 10 |
7 - 23
TR - 10
|Subsurface Soil (ug/kg)||Acetone |
|ND - 520 |
ND - 2400
ND - 40
ND - 21
|Landfill Gas (mg/m3)||Benzene |
|ND - 4.8 |
ND - 17
ND - 120
ND - 240
ND - 32
5.3 - 860
ND - 5.8
ND - 25
TR - 124
TR = trace amount found
ND = contaminant not detectable
The following table lists the contaminants of concern found off-site, the media contaminated, and the range of concentrations found.
|Groundwater (ug/l)||2-Butanone |
|ND - 80 |
ND - 15
ND - 9
ND - 0.6
ND - 34
ND - 150
ND - 17
ND - 200
|Sewers/Leachate (ug/l)||Cadmium |
|ND - 15.5 |
ND - 209
ND - 2,957
|Surface Water (ug/l)||Cadmium |
|ND - 1.1 |
10 - 56
ND - 56
|Sediments (ug/kg)||Acetone |
|ND - 140 |
ND - 364,500
ND - 900
ND - 37
ND - 10
ND - 23
ND - 45
TR = trace amount found
ND = contaminant not detectable
Physical hazards on the site are limited to those resulting from the daily operation of a municipal landfill. Unauthorized access to the site after working hours is restricted by a fence with barbed wire; however, a back gate allows unrestricted access during operating hours.
The landfill serves a population of approximately 212,000. The site is located in an area of Tacoma bordering on the municipality of Fircrest. Several large apartment complexes and small industries surround the site. On the west side of the site, the yards of the housing developments abut the site fence, and on the south, small homes on South 48th Street also have yards bordering on the site. East of the site, a large apartment complex sits on a cliff overlooking the landfill. Information was not provided on the numbers of residences or people located near the site or the numbers of on-site workers or individuals who use the landfill daily.
On-site contamination was sufficiently characterized by groundwater, sanitary sewer, and subsurface soil sampling. Off-site groundwater contamination was characterized by sampling of private wells and monitoring wells around the site. There is a lack of groundwater data from southeast of the site in the residential area. Although the RI indicates that it is unlikely that groundwater from the site will flow to the southeast, this possibility cannot be conclusively dismissed without sampling data.
Neither on-site nor off-site surface soil sampling was done. However, clean fill has been placed on the site for several years, and it is not likely that surface soil is contaminated at this time.
Off-site gas probe sampling is regularly performed by the City of Tacoma to detect soil gas accumulation. The results of this monitoring were not provided in the RI.
Tests conducted by the U.S. Environmental Protection Agency (EPA) on the landfill gas flares indicated that over 99 percent of the VOC's detected in significant concentrations in the inlet to the flares were combusted. However, data were not provided for the actual concentrations of VOC's in the gas flare emissions. Without this information, the air quality around the flares cannot be evaluated.
The Tacoma Landfill is currently active, and it is operated by the City of Tacoma. The City plans to operate the existing fill area for at least 4 or 5 years and may expand the life of the landfill by extending the fill area in the future. The City is actively working with the EPA and the Washington Department of Ecology on remediation of the site. Data on the current population living and working at the site were not provided; however, further residential development of surrounding land is expected to continue. The data provided were not sufficient to determine the numbers of individuals exposed to landfill gas in structures off-site, nor to determine any ambient air quality impacts.
Conclusions contained in this Health Assessment are based on the information received by ATSDR. The accuracy of these conclusions is dependent on the validity and reliability of the data provided.
Surface water flows towards Leach Creek which has a drainage basin area of 7 square miles. This includes runoff from portions of the City of Tacoma and the Town of Fircrest, and from local industries. From information presented in the RI, it appears that Leach Creek is also the discharge zone for groundwater flowing under the landfill to the west. The concentrations of contaminants in water from Leach Creek were not of health concern. An elevated concentration of arsenic was detected in one sediment sample from a tributary of Leach Creek. However, sediment samples from other locations did not contain significant concentrations of contaminants.
Surface water runoff from the south of the site drains into the Flett Creek drainage basin. No data were presented for this drainage basin. Drainage from the north of the site runs into a pond, which has been contaminated with toluene. Pond sediments contain cadmium, copper, lead, mercury, silver, and zinc above background levels.
Off-site storm sewers which discharge to Leach Creek receive runoff from the landfill. However, the off-site storm sewers, where high levels of metals were found, were located downstream of the industrial area. The metals found at concentrations higher than expected were cadmium and nickel.
Storm water runoff from the major portion of the landfill discharges to the sanitary sewer that crosses the site and is treated at Tacoma's treatment plant #1 (primary treatment). Levels of contaminants found in sanitary sewers were not likely to be of concern.
The Tacoma Landfill lies within a groundwater recharge area for the two primary potable water aquifers, Colvos Sand and Older Gravel. These unconsolidated aquifers are approximately 100 feet below the surface, hydraulically connected, and generally flow toward the southwest. Leach Creek is a surface discharge point for these two aquifers. A densely packed silty aquitard, Older Till, separates the two aquifers from the lower aquifer systems (Older Outwash, Older Sand, and Older Lacustrine).
The Colvos Sand and Older Gravel aquifers are the only source for potable water for the Town of Fircrest. The Town withdraws water from the aquifers through six wells west of the Tacoma Landfill, three of which are 0.2 mile from the edge of the landfill (see Appendix Figure I). These wells appear to only affect the groundwater flow pattern at the northwest boundaries of the Tacoma Landfill.
During the months of June through September, the City of Tacoma supplements its Green River water supply with nine wells east of the Tacoma Landfill. The closest of these wells is located approximately 1 mile from the landfill boundary. When the City of Tacoma wells are operating, the groundwater beneath the Tacoma Landfill flows towards the southeast. The groundwater returns to its natural flow pattern when the Tacoma City wells are not operating. Appendix Figures II and III depict the groundwater flow patterns and indicate how the Tacoma City wells influence the direction of flow.
Chemical contaminants have leached out of the waste material found in the Tacoma Landfill and migrated into the two upper aquifers, Colvos Sand, and Older Gravel. These contaminants have migrated with the groundwater and have entered private potable wells southwest of the Tacoma Landfill. Appendix Figure IV delineates the extent of migration of the contaminants. These contaminants will continue to migrate with the groundwater and eventually discharge to Leach Creek. Potable water wells to the southwest of the Tacoma Landfill and east of Leach Creek are likely to become contaminated. The wells providing potable water for the City of Tacoma and the Town of Fircrest could become contaminated during periods of severe drought, or if the Tacoma City wells were operated more frequently. Under the present conditions, however, it does not appear likely that the Tacoma City wells will become contaminated. The Fircrest Town wells could become contaminated, under present conditions, if large quantities of contaminants were to leach out of the northern parts of the Tacoma Landfill. Fircrest Town wells numbers two, four, and five tend to withdraw groundwater from the northern portion of the Tacoma Landfill (see Appendix Figure II).
Monitoring well TL-008 had the highest concentration of chemical contaminants. It is located in the west-central part of the landfill. Residential wells southwest of the site have been contaminated with VOC's; however, these wells are no longer in use.
Numerous VOC's were detected in both on-site and off-site groundwater samples. Under anaerobic conditions, trichloroethylene and other VOC's may be degraded by microbes to dichlorethylene and vinyl chloride. Therefore, the presence of these latter compounds in groundwater may be because of microbial degradation rather than disposal of these compounds in the landfill.
Since data were not provided on levels of contaminants in the ambient air surrounding the site, this environmental pathway cannot be evaluated, even though a 99 percent combustion efficiency for the gas flares is stated. In the RI, air quality modeling of the gas emissions from the landfill gas flares and diffuse emissions from the landfill surface suggested that a current public health threat because of ambient air quality is unlikely. Air flow directions, as characterized by this modeling, predict the highest concentrations of contaminants immediately west of the two landfill flares near the landfill boundary.
Monitoring by off-site probes of shallow wells has shown a decrease in gas pressure and concentration of methane since the installation of the gas extraction system. Deeper gas probes have shown little decrease in methane concentrations. Benzene, tetrachloroethene, trichloroethene, toluene, and vinyl chloride appear at high levels prior to combustion. However, after combustion, the levels are much diminished. According to the RI Report, off-site gas monitoring has shown less than 100 ppm by volume of hydrocarbons in ambient air.
Surface soil was not tested for contaminants; therefore, this pathway cannot be fully addressed. However, landfill records show that municipal and other clean fill has been placed on the closed areas of the landfill. Subsurface soils were found to be contaminated. VOC's contaminants may volatilize from the soils or be adsorbed to dust particles if the subsurface soil is exposed in the future.
- On-site workers and remedial workers could be exposed to subsurface soils and wastes by dermal contact and possible ingestion. This would mainly be a problem if subsurface soils were exposed by expansion of the active fill area or future remedial activities.
- On-site workers and residents living in close proximity to the site may be exposed to gases and volatile compounds from the site. With the continued efficient operation of the gas extraction and combustion system, and monitoring of homes and businesses for gas infiltration, this will not be a pathway of concern. However, if the gas extraction system failed, workers and other individuals near the flares could potentially be exposed to high levels of contaminants. Methane gas may cause explosions if the concentrations became very high in nearby homes or businesses.
- Municipal and private potable water supplies may be impacted by contaminated groundwater from the site in the absence of appropriate remedial activity.
- Inhalation exposures to VOC's in water could occur from non-consumption household water use such as showering, bathing, house cleaning, running dishwashers and washing machines, flushing toilets, etc. Dermal contact with water containing certain VOC's could result in additional exposure.
- Leach Creek is located in an urban area, and it is probable that neighborhood children play in and around the creek. However, occasional recreational use of the creek would not be expected to result in adverse health effects from the concentrations of chemicals detected in creek water and sediments.
- Leach Creek is not used a potable water source, and there is no known use of the creek for the irrigation of agricultural crops or livestock. Although Leach Creek may support salmonid runs in the lower part of the stream, fishing in the vicinity of the landfill is unlikely. Because the landfill is located in an urban area, the hunting of game animals is unlikely. Therefore, exposure to contamination by the consumption of biota from the area is not expected to be an exposure pathway of concern.
Since off-site soil sampling was not done, human exposure to possibly contaminated off-site soil cannot be evaluated, but this is a potential pathway. Exposure to contaminated soil can occur via ingestion of soil (especially by children), inhalation of reentrained contaminated soil and contaminants volatilized from soil, or from dermal contact.
The public health implications resulting from human exposure to contaminants at the Tacoma Landfill will be discussed via exposure to specific environmental media.
The principal contaminants of concern detected in off-site groundwater include vinyl chloride, methylene chloride, and 1,1,1-trichlorethane (TCA). On-site groundwater contamination also included benzene, tetrachloroethene, trans-1,2-dichloroethene and trichloroethene. In 1985, 1986, and 1987, the affected households were connected to the municipal water supply thereby eliminating exposures. However, migration of the contaminated groundwater could have a future impact on other wells in the area. Because of the potential for the off-site migration of contaminants, this Health Assessment will also address contaminants found at high concentrations on-site.
The presence of VOC's in groundwater could result in exposure by ingestion, dermal contact, and the inhalation of VOC's released to indoor air from water used in the home.
Occupational exposure to vinyl chloride has been associated with an increased incidence of angiosarcomas of the liver as well as tumors at other sites. Other non-carcinogenic toxic effects that may occur upon exposure to high concentrations of vinyl chloride include hepatotoxicity and central nervous system (CNS) disturbances. Epidemiological studies have suggested an association between exposure to vinyl chloride and an increased incidence of fetal loss and birth malformations. Both on-site and off-site wells contained vinyl chloride at concentrations that are above acceptable health-based values.
In animal experiments, inhalation exposures to methylene chloride have induced tumors of the liver, lung, and other organs. Noncarcinogenic toxic effects on the liver and kidneys have also been observed in animals exposed to high concentrations of methylene chloride.
In laboratory studies, mice that had been exposed to high concentrations of TCA by inhalation exhibited signs of liver toxicity. Acute human exposure to high concentrations of TCA can cause alterations of CNS function. However, the concentrations of TCA detected in water from on-site and off-site wells were below the EPA drinking water Maximum Contaminant Level (MCL)
Epidemiological studies have demonstrated that exposure to benzene can cause bone marrow toxicity. Occupational exposure to benzene in the rubber coating, leather working, rotograuve printing, and other industries has been correlated with an increased incidence of blood dyscrasias, aplastic anemia, and leukemia. High level exposures to benzene have also been associated with cytogenic aberrations in bone marrow and peripheral blood cells Although benzene was not detected in off-site wells, water from some on-site wells contained benzene concentrations in excess of the EPA drinking water MCL.
Although on-site subsurface soil is contaminated with VOC's, no significant current exposure is likely. However, during excavation or remediation activities, inhalation could be an exposure pathway of concern, since soil disturbing activities may lead to an increase in the quantities of VOC's in the ambient air. In this case, it may be necessary to provide workers with respirators and protective clothing and ensure that they follow all applicable National Institute for Occupational Safety and Health Administration regulations, guidelines, and recommendations.
Off-site soil sampling was not done, thus the potential health impact from exposure to off-site soils cannot be evaluated.
Landfill gas was found to be contaminated with methane and VOC's. The potential exposure of workers to high levels of methane, vinyl chloride, toluene, and other VOC's in the landfill gas is likely to be of concern only if there is a failure of the gas extraction system. Individuals occupying buildings previously found to have gas infiltration could also potentially be exposed to these gases if the extraction system failed.
Although exposure to methane does not pose a high toxic risk, the infiltration of methane into enclosed buildings can pose a risk of explosion and fire. As previously discussed, chronic exposure to vinyl chloride is of concern because of its potential carcinogenic and non-carcinogenic toxic effects. Human inhalation exposure to high concentrations of toluene can cause CNS toxicity. Chronic exposure to high concentrations of toluene may also affect liver function.
Based on the information reviewed, ATSDR has concluded that this site is of potential public health concern because of the potential risk to human health resulting from possible exposure to hazardous substances at concentrations that may result in adverse health effects. As noted in the Human Exposure Pathways Section, human exposure to VOC's may occur via groundwater ingestion, as well as by inhalation exposure from non-ingestion household water use.
Under the present site conditions, groundwater contamination is the primary potential human exposure pathway of concern. With implementation of the remedial alternative outlined in the March 1988 ROD, that is, capping of the inactive areas of the landfill and construction of a pump and treat system, the flow of contaminated groundwater from the site will be controlled. Also, continued testing of drinking and monitoring wells will characterize future contaminant migration and will assist EPA in preventing exposures of public health concern. As suggested in the RI, additional monitoring wells may be necessary between the landfill and Fircrest wells to ensure the safety of the town's drinking water supply. All potable private and public wells possibly subject to site-related contamination should be regularly monitored for contaminants of concern.
Continuation of air quality monitoring will be necessary to assess the ambient air quality impacts, if any, of the gas extraction system. In addition, monitoring of homes and buildings previously impacted by gas infiltration should be continued. Data on concentrations of VOC's in off-site structures and in ambient air on-site should be provided in order to assess the current air quality situation. The planned expansion of the system to capture deep well gas to prevent off-site migration of methane and other hazardous compounds in landfill gas will further reduce the potential for off-site exposures. In the event of a shut-down of the gas extraction system, immediate monitoring of the landfill office and flare area, as well as buildings previously impacted by gas infiltration, should be implemented. Individuals working on the system during a shut-down should be properly protected.
In the case of remedial activities or expansion of the landfill, workers should be protected from inhalation or direct contact with contaminated subsurface soils.
In accordance with the Comprehensive Environmental Response, Compensation, and Liability Act as amended, the Tacoma Landfill Site/Commencement Bay, Tacoma, Washington, has been evaluated for appropriate follow-up with respect to health effects studies. Although there are indications that human exposure to contaminated water may have possibly occurred, this site is not being considered for follow-up health studies at this time because no current exposure pathway can be defined, and no test is available to evaluate possible past exposures.
Sven E. Rodenbeck, P.E.,
Environmental Health Engineer
Environmental Engineering Branch
Health Effects Reviewers:
Environmental Health Intern
Health Sciences Branch
Kenneth G. Orloff, Ph.D.
Health Sciences Branch
Greg Thomas, Public Health Advisor,
Field Operations Branch
- Remedial Investigation Report, Tacoma Landfill, Tacoma, Washington, December, 1987. Prepared by Black & Veatch, Engineers-Architects, Overland Park, Kansas.
- Record of Decision, Decision Summary, and Responsiveness Summary for Final Remedial Action, Commencement Bay - South Tacoma Channel, Tacoma Landfill Site, Tacoma, Washington, March 1988. U.S. Environmental Protection Agency, Region 10, Seattle, Washington.
- Robert D. Kleopfer, Diane M. Easley, Bernard B. Haas, Jr., and Trudy G. Delhi; Anaerobic Degradation of Trichlorethylene in Soil; Environmental Science and Technology 19; 277-280 (1985).