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Site History

Previous Key Actions for the Site

All of the following information is derived from reports of the Groundwater Division of the Rhode Island Department of Environmental Management.

1980 The Dry Bridge Road Landfill was licensed by the Rhode Island Department of Environmental Management (RIDEM) to accept railroad ties on 6.9 acres of a former gravel pit site. The license was later expanded to allow for disposal of demolition debris and shredded automobile waste. The license was renewed annually for the 6.9 acre site.

1986 Hometown Properties, Incorporated, (the owners of Dry Bridge Road Landfill) filed a preliminary application to expand the landfill to use an additional 14.1 acres of the site for disposal of construction and demolition debris.

1987 The RIDEM Groundwater Section completed a hydrogeological assessment of Hometown Properties' expansion request and recommended the application be denied in order to protect the underlying aquifer. The assessment noted that the site is located 6,000-8,000 feet upgradient of four North Kingstown municipal wells and that groundwater flowing beneath the landfill would be expected to flow toward and reach the wellfield.

1988 RIDEM issued a Notice of Violation to Hometown Properties regarding odors and fire (underground burning) at the landfill. The Notice of Violation was resolved after corrective actions were taken at the site.

1988 The administrative hearing officer upheld RIDEM's denial of the expansion. RIDEM's director endorsed the decision, and Hometown Properties appealed to the Superior Court in September of 1988.

1989 The Superior Court reversed the hearing officer's decision and ordered the Dry Bridge Road Landfill license application be granted. RIDEM and the Town of North Kingstown appealed to the Supreme Court.

1990 The Rhode Island Supreme Court denied a RIDEM motion for a stay on the issuance of a license to Hometown Properties.

1990 The town of North Kingstown requested that RIDEM review the adequacy of groundwater monitoring at the site.

1990 RIDEM issued a license to Hometown Properties with 17 conditions for Dry Bridge Road Landfill. RIDEM required the installation of new monitoring wells and quarterly sampling of groundwater for metals and volatile organic chemicals.

1991 RIDEM renewed the Hometown Properties license for a 3-year period.

1992 Hometown Properties installed a new monitoring well network at the site.

1992 Under a new zoning ordinance in North Kingstown, the Dry Bridge Road Landfill was designated as within the wellhead protection area for the Annaquatucket wellfield.

1992 Hometown Properties began a feasibility project recycling railroad ties.

1994 In response to finding elevated metals and di-2-ethyl-hexylphthalate (DEHP) in monitoring wells, RIDEM requested a modification plan to better characterize groundwater conditions. Hometown Properties proposed additional sampling and installation of a new non-PVC monitoring well.

1994 Hometown Properties filed a request to amend their operating plan in order to partially cap the site and increase the height, volume, and length of operation of the facility.

1996 Residents registered complaints about landfill odors and truck traffic.

1997 Hometown Properties applied for approval of plans to construct, install, or modify air pollution control equipment relating to the landfill gas flares. RIDEM required that a system be installed to reduce sulfur dioxide emissions produced from the burning of gas containing hydrogen sulfide.

1997 Hometown Properties implemented a sulfur pretreatment control program, began daily application of a landfill cap called Posi-Shell, and installed two landfill gas flares to remove hydrogen sulfide.



Evaluation of Environmental Contamination and Potential Exposure Pathways Methodology

Quality Assurance

In preparing this report, ATSDR staff members relied on the information provided in the referenced documents and by representatives of the Rhode Island Department of Environmental Management (RIDEM) and the U.S. Environmental Protection Agency (EPA). ATSDR assumes that adequate quality assurance and control measures were taken during chain-of-custody, laboratory procedures, and data reporting. The validity of the analyses and conclusions drawn in this document are determined by the availability and reliability of the information.

Human Exposure Pathway Evaluation and the use of ATSDR Comparison Values

ATSDR assesses a site by evaluating the level of exposure in potential or completed exposure pathways. An exposure pathway is the way chemicals may enter a person's body to cause a health effect. An exposure pathway must include all the steps between the release of a chemical and the population exposed: (1) a chemical release source, (2) chemical movement, (3) a place where people can come into contact with the chemical, (4) a route of human exposure, and (5) a population that could be exposed . In this consultation, ATSDR evaluates the pathways of air and water for people living in nearby neighborhoods, to determine whether there is a potential for inhalation or consumption of substances that might expose them to chemical compounds from the landfill.

Data evaluators use comparison values as screening tools to evaluate environmental data relevant to exposure pathways. Comparison values are concentrations of contaminants that are considered to be safe levels of exposure. Comparison values used in this document include ATSDR's environmental media evaluation guide, or EMEG, and ATSDR's cancer risk evaluation guide, or CREG. Comparison values are derived from available health guidelines, such as ATSDR's minimal risk levels and EPA's cancer slope factor (a method EPA uses to determine carcinogenicity).

The derivation of a comparison value uses conservative exposure assumptions, resulting in values that are much lower than exposure concentrations that have been observed to cause adverse health effects. These comparison values are therefore protective of public health in essentially all exposure situations. That is, if the concentrations in the exposure medium are less than the comparison values, the exposures are not of health concern and no further analysis of the pathway is required. While concentrations below the comparison value are not expected to lead to any observable health effect, it should not be inferred that a concentration greater than the comparison value will necessarily lead to adverse effects. Depending on site-specific environmental exposure factors (for example, duration of exposure) and human activities that result in exposure (time spent in area of contamination), exposure to levels above the comparison value may or may not lead to a health effect. ATSDR's comparison values, therefore, are not used to predict the occurrence of adverse health effects.

The comparison values used in this evaluation are defined as follows. The CREG is a concentration at which excess cancer risk is not likely to exceed one case of cancer in a million persons exposed over a lifetime. The CREG is a very conservative comparison value that is used to estimate cancer risk. Exposure to a concentration equal to or less than the CREG is defined as an insignificant risk and is an acceptable level of exposure over a lifetime. The risk from exposure is not considered as a significant risk unless the exposure concentration is approximately 10 times the CREG and exposure occurs over several years. The EMEG is a concentration at which daily exposure for a lifetime is unlikely to result in adverse noncancerous effects.

Selecting Contaminants of Concern

Contaminants of concern (COCs) are the site-specific chemical substances that the health assessor selects for further evaluation of potential health effects. Identifying contaminants of concern is a process that requires the assessor to examine contaminant concentrations at the site, the quality of environmental sampling data, and the potential for human exposure. A thorough review of each of these issues is required to accurately select COCs in the site-specific human exposure pathway. The following text describes the selection process.

In the first step of the COC selection process, the maximum contaminant concentrations are compared directly to health comparison values. ATSDR considers site-specific exposure factors to ensure selection of appropriate health comparison values. If the maximum concentration reported for a chemical was less than the health comparison value, ATSDR would conclude that exposure to that chemical was not of public health concern; therefore, no further data review would be required for that chemical. However, if the maximum concentration was greater than the health comparison value, the chemical would be selected for additional data review. In addition, any chemicals detected that did not have relevant health comparison values would also be selected for additional data review.

Comparison values have not been developed for some contaminants, and, based on new scientific information, other comparison values may be determined to be inappropriate for the specific type of exposure. In those cases, the contaminants are included as contaminants of concern if current scientific information indicates exposure to those contaminants may be of public health concern.

The next step of the process requires a more in-depth review of data for each of the contaminants selected. Factors used in the selection of the COCs include the number of samples with levels above the minimum detection limit, the number of samples with detections above an acute or chronic health comparison value, and the potential for exposure at the monitoring location.



Ambient Air Sampling Results

Toxicological Evaluation

Based on available data, there are no completed off-site exposure pathways of public health concern. Below is a description of the exposure pathways outlined in the accompanying tables.

Table 1.

On-Site Ambient Air Sampling Data for Dry Bridge Road Landfill
Compound Concentration Range (ppb) Sampling Date Location of Max. Value Comparison Value (ppb) Source
Benzene 0.15-0.83 9/96-12/96 Working face 0.031 Chronic CREG
Carbon Tetrachloride 0.08-0.12 9/96-6/97 Working face 0.011 Chronic CREG
Chloroform 0.09 3/97 Working face 20 Chronic EMEG

Chronic CREG


Inter EMEG

1,1-Dichloroethylene* ** 0.06-0.43 9/96-12/96 Working face 0.005 Chronic CREG


Inter EMEG

Hydrogen Sulfide 50.0-100.0 6/96-12/96 Working face 0.7 Inter RMEG
Methylene Chloride 0.12-2.93 9/96-3/97 Working face 0.85


Chronic CREG

Inter EMEG

*Method Blank: 1,1-Dichloroethylene (9/96)-0.004 g,
**Trip Blank: 1,1-Dichloroethylene (9/96)-0.004 g; 1,1-Dichloroethylene (12/96)-0.006 g; Chloroform (6/96)-0.009 g;

Table 2.

Off-Site Ambient Air Sampling Data for Dry Bridge Road Landfill
Compound Concentration Range (ppb) Sampling Date Location of Max. Value Comparison Value (ppb) Source
Benzene 0.05-1.51 9/96-3/97 Downwind perimeter 0.031 Chronic CREG
Carbon Tetrachloride 0.05-0.33 12/95- 6/97 House 0.011 Chronic CREG
Chloroform 0.10-0.65 6/96 Downwind perimeter 20 Chronic EMEG

Chronic CREG

50 Inter EMEG
1,1-Dichloroethylene* ** 0.10-0.39 9/96-12/96 Downwind perimeter 0.005 Chronic CREG


Inter EMEG

Hydrogen Sulfide 3.0-400.0 3/97-12/95 Downwind perimeter 0.7 Inter RMEG
Methylene Chloride 0.09-27.16 9/96-12/96 House 0.85 Chronic CREG


Inter EMEG

Sulfur Dioxide 1.0-465.0 10/97-5/97 Dry Bridge Rd. 139 NAAQS

*Method Blank: 1,1-Dichloroethylene (9/96)-0.004 g
**Trip Blank: 1,1-Dichloroethylene (9/96)-0.004 g; 1,1-Dichloroethylene (12/96)-0.006 g; Chloroform (6/96)-0.009 g
CREG = Cancer Risk Evaluation Guide
EMEG = Environmental Media Evaluation Guide
RMEG = Reference Dose Media Evaluation Guide
NAAQS = Environmental Protection Agency's National Ambient Air Quality Standard
OSHA TWA = Occupational Safety and Health Administration Time Weighted Average
ppm = part per million
ppb = part per billion
Working Face = the work day's disposal area

Table 3.

On-Site Ambient Air Sampling Chemicals Above ATSDR's Comparison Values Compared to NIOSH and OSHA Comparison Values for Dry Bridge Road Landfill
Compound Maximum Concentration (ppb) ATSDR Comparison Value(ppb) NIOSH Comparison Value (ppb) OSHA Comparison Value (ppb)
Benzene 0.83 Chronic CREG = 0.031 TWA = 100 TWA = 1,000

STEL = 1,000

STEL = 5,000

Carbon Tetrachloride 0.12 Chronic CREG = 0.011 STEL = 2,000 TWA = 10,000

Ceiling = 25,000

Chloroform 0.09 Chronic CREG = 0.008 STEL = 2,000/60 min. Ceiling = 50,000
1,1-Dichloroethylene 0.43 Chronic CREG = 0.005 Ca None
Methylene Chloride 2.93 Chronic CREG = 0.85 None TWA = 500,000

Ceiling = 1,000,000

TWA = Time Weighted Average
STEL = Short-Term Exposure Limit
Ceiling = Highest permissible exposure limit
Ca = Potential occupational carcinogen where a threshold has not been identified



ATSDR's Response to Public Comments

This appendix contains both the comments received during the public comment period for the Dry Bridge Road Landfill and ATSDR's response to those comments. The comments have been numbered and are in italic with the response directly below each comment.

1 It is still unclear whether or not the health effects being described by the residents surrounding this facility are related to landfill odors. Is it the opinion of ATSDR that the symptoms are unrelated to the landfill or could these general respiratory symptoms be due to landfill gases but not cause any long term or permanent health impact??

The continued health complaints mentioned by residents in the vicinity of Dry Bridge Road Landfill are predominantly respiratory-related: pneumonia, asthma, and difficulty breathing. ATSDR concludes that these health complaints are currently not related to landfill odors. Landfill odors are primarily made up of hydrogen sulfide and sulfur dioxide. These gases can be detected by the human nose at very low concentrations. The highest concentration of hydrogen sulfide (rotten egg smell) detected in residential areas surrounding the landfill was 1000 times less than concentrations known to cause respiratory discomfort [21]. The highest sulfur dioxide concentration (burnt smell) detected at the landfill boundary was approximately 35 times less than the concentration shown to cause a sore throat in enclosed areas [22]. This sulfur dioxide reading was taken at the boundary of the landfill and was a peak concentration that did not exceed regulatory or health guidelines. Sulfur dioxide concentrations in the ambient air on-site have been consistently 350 times less than concentrations shown to cause respiratory irritation. Concentrations are expected to be lower in the residential areas; however, infrequent landfill emission releases may result in nuisance odors.

Annoyance-type symptoms (such as nausea and headaches) have been documented by residents surrounding Dry Bridge Road Landfill. Although the available ambient air data do not indicate a toxicological reason for these symptoms, bad smells can trigger headache and nausea (even at low levels). Some suggested readings are listed below on similar symptoms in relation to odor prevelance (24) (25) (26) (27).

2 Specific Request: The town of North Kingstown requested ATSDR to perform an independent evaluation of health related health complaints of individuals living in the vicinity of Dry Bridge Road Landfill.

ATSDR's Exposure Investigation Section evaluated North Kingstown's request for a health complaint evaluation. ATSDR investigates health effects based on measured environmental contamination and the possibility of human exposure to contaminants. The contaminants in the ambient air around Dry Bridge Road Landfill were not at levels known to cause respiratory distress. ATSDR received approximately 54 health complaint surveys from North Kingstown residents that were documented before landfill emission controls were fully operating. Of these varied health complaints, asthma and pneumonia are frequently mentioned. Asthma and pneumonia are common respiratory ailments throughout the United States, however, they are not annually reported or tracked diseases in the state of Rhode Island. Due to this limited information, a comparison population is not available and a comparison using these health complaints would not provide accurate results.

ATSDR is not able to facilitate a comparative evaluation based on health complaints, however, ATSDR will provide a small group availability session in July. This session will entail informational one-on-one meetings for concerned community members wishing to discuss health problems thought to be attributed to landfill emissions with an ATSDR medical doctor, environmental health scientist, and community involvement specialist. Details of this meeting will be made available through the local newspaper and town hall in the near future.

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

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