7.
Land and Soil Health Risks
Authors
The information in this chapter was prepared by the following individuals:
Description of health risks from the Superfund sites and from Resource Conservation and Recovery Act sites:
o Will Humble, R.S., M.P.H., Risk Assessment and Environmental Epidemiology Section, Arizona Department of Health
Description of health risks from leaking underground storage tanks (USTs):
o Mason Bolitho, Arizona Department of Water Resources
o Michael Jorden, Arizona Dry Cleaners and Launderers Association
o Lance Shea, J.D., formerly of Streich Lang Law Associates
CERCLA and WQARF Superfund Sites
Introduction
This section explores the potential health risks that may be presented to Arizonans from exposure to chemical contaminants at federal and state superfund sites in Arizona.
Available information about the federal EPA Superfund (CERCLA), the State of Arizona Water Quality Assurance Revolving Fund (WQARF), and the United States Department of Defense (DOD) sites were collected and evaluated to determine the potential routes of exposure and types of contaminants at these sites (ADEQ, 1993). Estimates of population risk were then made based on an analysis of this information. The analysis and conclusions reflect potential future risks rather than risks that may have been posed by exposures at these sites in the past.
Many of the Superfund, WQARF and DOD sites in Arizona have not yet been fully characterized. Additionally, formal quantitative health risk assessments have not yet been completed at most of the sites. Therefore, there is uncertainty about the types and magnitude of risks that may be posed by these sites, and the risk assessment conducted here should be interpreted as a cursory analysis.
Number and Types of Sites
As of fiscal year 1994, there were 63 Superfund, WQARF or DOD sites in Arizona. Their distribution is as follows:
o 31 in the Phoenix area
o 12 in the Tucson area
o 20 in other areas of Arizona
The 63 sites are affected primarily by groundwater contamination, although some sites have surface soil and surface water contamination.
The primary contaminants affecting the groundwater at these sites are solvents such as tetrachloroethylene (PCE), trichloroethylene (TCE), and their degradation products.
Contaminated media at these sites include surface soils, subsurface soils, surface water, and groundwater. In addition, air may become contaminated at some sites through wind erosion of contaminated surface soils or diffusion of organic contaminants from surface soils. Table 7.1 presents the number and percentage of the sites with demonstrated contamination of each media.
Table 7.1 Contaminated Media at Arizona Waste Sites
-------------------------------------------------- | Media | Number of | Percent | | | Sites | | | | | (%) | ================================================== | Groundwater | 42 | 64 | -------------------------------------------------- | Off-Site Groundwater | 21 | 32 | -------------------------------------------------- | Surface Water | 5 | 7 | -------------------------------------------------- | Surface Soil | 15 | 23 | --------------------------------------------------
Groundwater is the medium most frequently contaminated at sites in Arizona. A few sites contain surface contamination such as dross sites. Table 7.2 displays the number and percentage of Arizona sites in 1993 by category (ADEQ, 1993).
Table 7.2 Arizona Hazardous Waste Sites by Category
---------------------------------------------------- | Category | Number of | Percent of Total | | | Sites | | | | | (%) | ==================================================== | Industrial | 20 | 32 | ---------------------------------------------------- | Military | 14 | 22 | ---------------------------------------------------- | Landfills | 10 | 16 | ---------------------------------------------------- | Airports | 8 | 13 | ---------------------------------------------------- | Mining | 5 | 8 | ---------------------------------------------------- | International | 11 | | ---------------------------------------------------- | Unknown/Misc. | 58 | | ----------------------------------------------------
Exposure Assessment
Current Land Use
Land uses at Arizona sites include residential, industrial, military, rangeland and no current use.
Land use is important in determining the magnitude of the population exposed to the contaminants of concern. This exposure assessment focuses on sites located in residential and industrial settings since there is greater potential for human exposure in these areas.
Exposure Pathway Identification
A potentially complete human exposure pathway describes the route a chemical may take from the source to a population or receptor. A complete exposure pathway includes the following components:
o A source and a mechanism of release to the environment
o A medium for the transport of the released chemical in the environment
o A point of potential human contact with a contaminated medium (exposure point)
o An exposure route at the exposure point (ingestion, inhalation, dermal contact).
An exposure point may occur on-site or at a distance from the site, depending on transport mechanisms influencing the chemical(s).
Source and Receiving Media
The source of chemicals in the groundwater are primarily attributed to waste handling procedures.
For most of the waste disposal methods, soil serves as the receiving media, releasing the chemicals to groundwater. Unlike most volatile organic compounds, inorganic constituents occur naturally in groundwater requiring the identification, evaluation, and estimation of inorganic chemicals in relation to background concentrations.
Groundwater
Both organics and inorganics have been detected in the groundwater plumes emanating from waste sites in Arizona. Observed groundwater contaminants also include degradation products. Table 7.3 lists the most frequently detected chemicals of concern in groundwater at listed Arizona waste sites.
Table 7.3 Frequent Contaminants in Groundwater at Arizona Hazardous Waste Sites
-------------------------------------------------------- | Organic Contaminants | Inorganic Contaminants | ======================================================== | Tetrachloroethylene (PCE) | Arsenic | -------------------------------------------------------- | Trichloroethylene (TCE) | Nitrate | -------------------------------------------------------- | Chloroform | Sulfate | -------------------------------------------------------- | Methylene Chloride | Boron | -------------------------------------------------------- | Benzene | Lead | -------------------------------------------------------- | Bromodichloromethane | Chromium | -------------------------------------------------------- | 1,1 Dichloroethylene | Manganese | -------------------------------------------------------- | Toluene | | -------------------------------------------------------- | 1,1,1 Trichloroethane | | -------------------------------------------------------- | Vinyl Chloride | | --------------------------------------------------------
Arsenic frequently presents a majority of the cancer and non-cancer health risks at Arizona waste sites.
Surface Water
Natural surface waters are documented to be contaminated at five waste sites in Arizona. Most of these sites contain inorganic contaminants.
Air
Some chemicals may be released into the air through volatilization or erosion from soils. No documentation of substantial airborne contamination at Arizona waste sites is available.
Soil
Volatile organic compounds present in soil can be absorbed on the soil, move through soils, or be released to the air through volatilization.
Inorganic contaminants in sub-surface soils would not be expected to result in human exposure unless groundwater becomes contaminated.
Groundwater Exposure
Exposure to contaminated groundwater in private wells is considered the most important exposure route at Arizona waste sites, and this risk analysis will focus on exposures in this media.
Twenty-one of the sites in Arizona have groundwater contamination that have migrated off-site and have the potential for exposure. Individuals who may be exposed include those using private unregulated wells for domestic purposes.
At some point in the remedial process, a well survey should be completed. However, not all sites have had well surveys, and sites with surveys may not have sample results for all wells. Not all of the groundwater plumes have been clearly defined.
In addition, there is no statutory limitation of the installation of wells at these sites. Therefore, there may be some human exposure to contamination in groundwater from these waste sites in Arizona.
Estimation Methods
In order to accurately evaluate the potential magnitude of the health risks presented by these sites the following information must be determined:
o The number and uses of wells in the zones influenced by the contamination
o The concentration of contaminants in these wells
o The number of persons drinking the water.
For sites that have adequate data available, estimates of risk are based on application of the EPA Risk Assessment Guidance for the Superfund document. These risk estimates use standard default exposure factors, the average concentration of contaminants in all wells for each site, and EPA slope factors.
Unfortunately, adequate data are not available for all Arizona sites. Therefore, health risks estimates are made using estimates that extrapolate from some of the better characterized sites.
Table 7.4 presents 18 of the best characterized sites in Arizona. If a site-specific risk estimate had not yet been conducted for a site, then the risk estimate from the Miracle Mile risk assessment was applied (ADHS, 1993b).
Table 7.4 Exposure and Risk Estimates at 18 Arizona Waste Sites
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Site Name | Site Specific Data Used to | Estimated Number of | Estimated Number of | 9-Year ELCR Estimate | 30-Year ELCR Estimate | 70-Year | | | | | | | | Population | | | Derive ELCR Estimate | Private Wells | Persons Served | | | Risk | ===================================================================================================================================================================================== | Motorola 52nd St. Facility | Yes | 1 | 3 | 1E-4 | 4E-4 | 0.0003 - 0.001 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | North Indian Bend Wash | | 20 | 100 | 5E-5 | 2E-4 | 0.005 - 0.02 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Phoenix Goodyear Airport | | 1 | 5 | 5E-5 | 2E-4 | 0.0003 - 0.001 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | South Indian Bend Wash | | 20 | 100 | 5E-5 | 2E-4 | 0.005 - 0.02 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Tucson Area Airport | | 15 | 75 | 5E-5 | 2E-4 | 0.0038 - 0.01 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Broadway Landfill | | 10 | 50 | 5E-5 | 2E-4 | 0.0025 - 0.01 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | East Central Phoenix | | 20 | 100 | 5E-5 | 2E-4 | 0.005 - 0.02 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | East Washington | | 10 | 50 | 5E-5 | 2E-4 | 0.0025 - 0.01 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Estes Landfill | Yes | 5 | 25 | 8E-4 | 3E-3 | 0.02 - 0.07 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Miracle Mile Interchange | | 72 | 360 | 5E-5 | 2E-4 | 0.018 - 0.07 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Nogales Wash | | 8 | 40 | 5E-5 | 2E-4 | 0.002 - 0.008 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | City of Payson | | 21 | 105 | 1E-5 | 1E-4 | 0.001 - 0.01 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Silverbell Landfill | | 5 | 25 | 5E-5 | 2E-4 | 0.001 - 0.005 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Sky Harbor Airport | | 5 | 25 | 5E-5 | 2E-4 | 0.001 - 0.005 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | West Central Phoenix | | 20 | 100 | 5E-5 | 2E-4 | 0.005 - 0.02 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | West Van Buren | | 20 | 100 | 5E-5 | 2E-4 | 0.005 - 0.02 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | El Camino Del Cerro Landfill | Yes | 14 | 70 | 2E-4 | 9E-4 | 0.014 -0.06 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Motorola 56th St. Facility | Yes | 6 | 30 | 5E-4 | 2E-3 | 0.015 - 0.06 | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | Totals | | 303 | 1,363 | | | 0.1 - 0.4 | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Results
In order to account for health risks that may be presented by the remaining 46 sites, the total population risk ranges were multiplied by 3.5. To adjust for undiscovered sites, the revised risk range estimates were then doubled. Annual population risk estimates were calculated by dividing the 70 year population risk estimate by 70 years.
Table 7.5 presents the aggregate risk estimates from all Arizona waste sites.
Table 7.5 Aggregate Risk Estimates from all Arizona Waste Sites
-------------------------------------------------------------------------------------------- | Yearly Estimate of Excess Cancer | | 70 Year Estimate of Excess Cancer | | | Cases | | Cases | | -------------------------------------------------------------------------------------------- | Low | High | Low | High | ============================================================================================ | 0.01 | 0.04 | 0.7 | 2.8 | --------------------------------------------------------------------------------------------
The estimated number of excess cancer cases presented in Table 9.5 are low for the following two reasons:
o The estimated number of Arizonans exposed to groundwater contamination is small.
o The individual excess lifetime cancer risk estimates for these sites are between 8,000 in 10,000 and 5,000 in 100,000.
Uncertainties
Achieving accurate estimates of the health risks as a result of exposure to chemicals from these waste sites requires estimates of the number of Arizonans exposed, the concentrations of contaminants in the exposure media, the amount of exposure, and toxicological information about each of the chemicals of concern.
The risk assessment estimates in this section are based on a number of assumptions regarding contaminant concentrations and fate, exposures, doses, and toxicity information.
There is uncertainty associated with the process at all stages. Although point estimates of risk are made, it should be recognized that each one represents a range of possibilities and is really only an indicator.
Care is taken at each step to ensure that assumptions and estimates are upper bounds. These final estimates must be considered rough estimates of the potential health risks from exposure to contaminated groundwater at Arizona hazardous waste sites.
Conclusion
The calculated incremental increase in the number of cancer cases as a result of exposure to contaminants from waste sites in Arizona on an annual basis was between 0.01 and 0.04 cases per year.
Uncertainties in the analysis combine to create uncertainty of approximately two or three orders of magnitude.
Taking the extremes of the calculated range as point estimates, the actual number of excess cancer cases is likely to be less than one case per year.
Resource Conservation and Recovery Sites
The Resource Conservation and Recovery Act (RCRA) was passed in 1976 to safely handle and dispose of hazardous waste nationwide.
The goals of RCRA are to:
o Protect human health and the environment
o Reduce waste and conserve energy and natural resources
o Reduce or eliminate the generation of solid and hazardous waste as expeditiously as possible.
Subtitle C of the RCRA requires that hazardous material be tracked from the time it is generated until the time it is disposed of. Similarly, the RCRA requires permits for all facilities that store or treat or dispose of substantial quantities of hazardous waste.
The purpose of the following subsections is to evaluate the potential health risks from releases of hazardous waste at facilities regulated under the RCRA.
Arizona RCRA Subtitle C Handlers and Facilities
Hazardous waste treatment, storage and disposal (TSD) facilities are divided into a number of categories based upon the activities and method of disposal used at the facility.
Generators of hazardous waste are classified according the quantities generated (large, small, and exempt). The number of facilities and generators, by category in Arizona, is displayed in Table 7.6 (ADEQ, 1994).
Table 7.6 Types and Numbers of RCRA Facilities in Arizona
------------------------------------------------------- | Facility Type | Number in | | | Arizona | ======================================================= | Land Disposal Only | 3 | ------------------------------------------------------- | Land Disposal and Incineration | 0 | ------------------------------------------------------- | Land Disposal and Storage/Treatment | 4 | ------------------------------------------------------- | Incineration Only | 0 | ------------------------------------------------------- | Incineration and Storage/Treatment | 1 | ------------------------------------------------------- | Storage/Treatment Only | 34 | ------------------------------------------------------- | Total TSD Facilities | 42 | ------------------------------------------------------- | Regulated Generators (not TSD) | 987 | ------------------------------------------------------- | Small Quantity Generators | 2,141 | ------------------------------------------------------- | Conditionally Exempt Generators | 727 | ------------------------------------------------------- | Total Generators | 3,855 | -------------------------------------------------------
Methods
The health risk analysis for exposure to releases from TSD facilities and generator activities uses risk information developed by USEPA Region IX, and information about the number and types of waste facilities and generators in Arizona.
The number of facilities in each category was determined using the USEPA Region IX RCRIS database (ADEQ, 1994). The analysis uses risk calculations developed by EPA for each facility category (USEPA, 1990).
The risk calculations for each category of waste facility are available as part of the November 29, 1990 Region IX Comparative Risk Project.
The analysis extrapolates risks from individual sites to risks in each of seven categories for air and groundwater exposure. The analysis uses releases from ten chemicals based upon their perceived presence as contaminants at RCRA sites.
Exposures were developed using standard assumptions and population values in a one-mile radius surrounding facilities. Details about the assumptions made to develop the risk estimates are presented in the November 29, 1990 document (USEPA).
Uncertainties
The risk analysis presented here makes a number of assumptions which contribute to uncertainty in the results.
o Risk factor derivations have been extrapolated from a small number of facilities and applied to the much larger universe of all RCRA sites.
o Population exposure estimates are based on population densities within a one-mile radius of facilities.
o Assumptions are made that concentrations in environmental media represent actual exposure concentrations.
o Uncertainties exist in deriving toxicity data.
All of these combine to create uncertainty of perhaps two or three orders of magnitude. Therefore, the estimates must be considered rough estimates of the potential health risks from exposure to contaminants from RCRA facilities in Arizona.
Conclusion
The estimated incremental increase in the number of cancer cases as a result of exposure to contaminants from RCRA facilities in Arizona is approximately 0.04 cases per year.
Considering the 0.04 cases per year as a point estimate, and the uncertainty of approximately two or three orders of magnitude, the Committee estimates that the actual number of excess cancer cases would be less than one per year.
Leaking Underground Storage Tanks
Introduction
Leaking underground storage tanks (USTs) have lead to soil and groundwater contamination in Arizona.
According to ADEQ (1992), of the 23,938 USTs in Arizona, 3,649 have leaked. Of these leaking USTs, about 10-20% have affected groundwater. Approximately 98% of USTs in Arizona are used for storage of petroleum products.
Exposure Pathways
The most probable pathway for human exposure to leaking USTs is through ingestion of water from private domestic wells. According to 1990 U.S. Census data, approximately 77,000 private wells are used as a source of drinking water for about 215,000 of the state's residents. The vast majority of active private domestic wells used for potable purposes are located in rural areas not served by public or private water systems.
Depths to groundwater in Arizona range from just a few feet below ground surface to over 1,000 feet below ground surface. Shallow groundwater is most likely to be contaminated by USTs, and the areal extent of UST contamination is generally quite limited. For an exposure pathway to exist, each of the following conditions must be met:
o Groundwater must be contaminated by releases from a UST.
o Wells must produce groundwater from the portion of the aquifer that is contaminated, generally the uppermost part.
o A private domestic well must be very close to a leaking UST (because UST contaminant plumes are limited in areal extent).
o A private domestic well must be used for potable purposes.
o A private domestic well must be hydrologically downgradient from a leaking UST. However, this is not true in all cases.
Most USTs are located in urban areas where private domestic wells do not exist or are not used for potable purposes, so exposure pathways do not exist. According to ADHS, probably only a few wells in Arizona meet all conditions listed above, so risk is low.
However, there are some areas where UST contamination has impacted groundwater where private domestic wells are in use.
o In Willcox, leaking USTs have caused community-wide groundwater contamination.
o In Prescott, USTs have contaminated shallow groundwater that is withdrawn by private domestic wells.
o In Tonopah, where groundwater is about 250 feet below surface, leaking USTs have contaminated groundwater that may be a drinking water source for private domestic well users.
In many cases, domestic wells are no longer used for drinking when municipal water service is available, so many of these older private domestic wells are used for turf irrigation, stock watering, or other non-potable uses. Generally speaking, risk is considered low because of limited exposure through ingestion.
Another exposure pathway is inhalation due to diffusion from soils contaminated by leaking USTs. ADHS states that risk from this exposure is negligible.
Conclusion
Ingestion of water from private domestic wells contaminated by leaking USTs is probably the most likely exposure pathway for USTs. Because several limiting conditions must be met before exposure can occur, however, risk is considered low.
Exposure via inhalation from diffusion of UST contamination of soils is a very low risk.