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HEALTH CONSULTATION

Churchill County Tap Water

FALLON LEUKEMIA PROJECT
FALLON, CHURCHILL COUNTY, NEVADA


BACKGROUND AND STATEMENT OF ISSUES

In July 2000, the Nevada Department of Human Resources, Nevada State Health Division(NSHD), identified an increase in the incidence rate of leukemia in children from ChurchillCounty, Nevada. Most of the leukemia cases were from the city of Fallon, the largest population center in the county. Approximately 7,540 residents live in Fallon and about 24,000 people livein the surrounding unincorporated parts of Churchill County, a 5,000 square-mile area [1].

In March 2001, the NSHD asked the Agency for Toxic Substances and Disease Registry(ATSDR) and the National Center for Environmental Health (NCEH) to evaluate environmentalrisk factors that might be linked to the childhood leukemia cluster in the Fallon area. NCEH wasasked to design and conduct a cross-sectional exposure assessment of selective contaminants using environmental (household) and biologic specimens for case families and for a referencepopulation [2]. ATSDR was asked to evaluate contaminant releases in Churchill County andprovide an assessment of completed exposure pathways for the case families.

ATSDR and NCEH developed a Public Health Action Plan that identified the pathways to beevaluated for available sampling data, data gaps, and potential human exposures [3]. Thesepathways include groundwater, air, soil, surface water, sediment, and biota [3].

This health consultation addresses the potential environmental pathways for human exposure tocontaminated drinking water in Churchill County. ATSDR evaluated the availableenvironmental sampling information to determine potential exposure to contaminants found indrinking water. The information reviewed includes data collected by the U.S. Geological Survey(USGS) and Water Research and Development, Inc. ATSDR released a public comment versionof this document in July 2003, but received no comments.

ATSDR's EVALUATION PROCESS

ATSDR's approach to evaluating a potential health concern has two components. The firstcomponent involves a screening process that might indicate the need for further analysis. Thesecond component involves a weight-of-evidence approach that integrates estimates of likelyexposure with information about the toxicology and epidemiology of the substances of interest.

Screening is a process of comparing appropriate environmental concentrations and doses toATSDR or U.S. Environmental Protection Agency (EPA) comparison values (CVs). These CVsinclude:

  • ATSDR Environmental Media Evaluation Guides (EMEGs),
  • Reference Media Evaluation Guides (RMEGs),
  • Minimal Risk Levels (MRLs),
  • Cancer Risk Evaluation Guidelines (CREGs),
  • EPA Reference Concentrations (RfCs),
  • EPA Reference Doses (RfDs), and
  • Risk-Based Concentrations (RBCs).

These health-based CVs are media-specific concentrations that are considered "safe" underdefault conditions of exposure. Default conditions are typically based on estimates of exposurein most (i.e., the 90th percentile or more) of the general population. CVs are not thresholds oftoxicity, but levels at which ATSDR believes that even long-term exposure to sensitivepopulations would not result in an increase in the likelihood of developing adverse health effects.A level above a CV does not mean health effects are expected, but represents a point at whichfurther evaluation is warranted.

CVs are based on a variety of toxicological and exposure assumptions that might not reflectactual exposure conditions and risk of adverse health outcomes. ATSDR evaluates informationrelated to the contaminant and on site-specific exposure conditions. Such information mightinclude biological plausibility, mechanisms of action, cumulative interactions, health outcomedata, strength of epidemiologic and animal studies, and toxicologic and pharmacologiccharacteristics.

Drinking Water Sources in the Fallon Area

In Churchill County, groundwater is the sole source of drinking water [R. Seiler, USGS, personalcommunication, 2003]. A basalt aquifer and two sedimentary aquifers are used as sources ofdrinking water. Groundwater from the basalt aquifer is distinctly different from that in thesedimentary aquifers [4]. The basalt aquifer is the source of water for municipal supply to thecity of Fallon, Naval Air Station Fallon, and the Fallon Paiute-Shoshone Tribe [4].

The shallow sedimentary aquifer extends from the water table to a depth of 50 feet below landsurface [4]. The intermediate sedimentary aquifer is considered to extend from a depth of 50feet below land surface to between 500 and 1000 feet [4]. A deep sedimentary aquifer,considered non-potable, extends from 500 to 1000 feet below land surface to depths of severalthousand feet [4]. The basalt aquifer has been described as an asymmetrical, mushroom-shapedbody of basalt exposed at Rattlesnake Hill [4].

Overall, dissolved arsenic concentrations in Churchill County groundwater exceed the maximumcontaminant level (MCL) of 10 parts per billion (ppb) promulgated by EPA. The combination ofhigh pH and high arsenic concentrations is characteristic of groundwater in the western UnitedStates that also has high arsenic concentrations [5].

Residential Drinking Water Sampling Results

In 2002, the USGS conducted residential tap water sampling as part of NCEH's cross-sectionalexposure assessment. USGS personnel collected a tap water sample from each of 77 locations. These locations included 76 case and control residences and one supermarket water dispenser. Tap water in Churchill County is drawn from several well sources. These sources include publicwater supply wells in the basalt aquifer and private wells drawing water from various depths. Inaddition, many residents reported using bottled water for drinking [6].

Of the 76 household taps sampled, 42 of them used private wells as a water source and 34 usedthe public water supply. Sixteen homes used reverse osmosis (RO) water treatment units toremove metals and other contaminants [6]. All tap water samples were analyzed for metals andvolatile organic compounds (VOCs) [7].


DISCUSSION

Exposure pathways are the different ways that contaminants move in the environment and thedifferent ways that people can come into contact with these contaminants (i.e., touching,breathing, or eating/drinking them). A completed exposure pathway exists when informationshows that people have come into contact with a contaminant in soil, air, or water. Completedexposure pathways can occur in the past or present. The exposure pathways associated withdrinking water are ingestion, dermal exposure, and inhalation.

DATA EVALUATION

Metals

ATSDR compared the levels found in residential tap water with health-based CVs to identifypotential contaminants of concern (COCs). Several metals were found at levels below theATSDR drinking water screening values, EPA MCLs, or EPA Region III Risk-BasedConcentrations. These metals were barium, beryllium, cadmium, chromium, cobalt, copper, lead,nickel, selenium, silver, thallium, and zinc and were eliminated from consideration.

Antimony, arsenic, tungsten, uranium, and vanadium were also found in residential drinkingwater (Table 1). Ingestion is the primary route of exposure for metals in drinking water.

Table 1.

Summary of Potential Metals of Concern in Tap Water
Substance Number of Detections Maximum Concentration (ppb) Average Detected Concentration (ppb) Comparison Value (ppb)
Antimony 14 13 3.0 4
Arsenic 77 874 81.7 101
Tungsten 77 337 19.9 NA2
Uranium 74 290 14.1 301
Vanadium 42 430 45 30

1 U.S. EPA Maximum Contaminant Level
2 NA means "not available".

Antimony

Antimony was detected in 14 tap water samples at concentrations ranging from 0.9-13 ppb. The highest measured concentration (13 ppb) was found in water collected from a supermarketdrinking water dispenser. The highest antimony level found in residential tap water (6.3 ppb)was from a domestic well less than 50 feet deep.

The maximum level exceeds the ATSDR chronic RMEG for children (4 ppb) by a factor of 3.25.However, the RMEG incorporates an uncertainty factor of 1,000 and most people use more thanone source of drinking water throughout the day. As a result, even the highest antimony levelfound is not expected to produce any adverse health effects [8].

Arsenic

Arsenic can be released to water from the natural weathering of soil and rocks and can also leach from soil and minerals into groundwater. In some western states with mineral deposits high in arsenic, groundwater levels of up to 3,400 µg/L arsenic have been found. Most arsenic in natural waters is a mixture of arsenate (trivalent arsenic or AsIII) and arsenite (pentavalent arsenic or AsV), with arsenate (AsIII) usually predominating [10]. Most of the arsenic in the basalt aquifer is present as arsenate (AsIII).

Health risks from exposure to arsenic in groundwater occur as a result of ingestion and notdermal or inhalation exposure. Ingestion of arsenic can increase the risk for skin cancer andinternal cancers: liver, lung, bladder, and kidney. The lowest-observable-adverse-effect level forlung cancer in humans is reported as 0.0011 mg/kg/day [15]. Assuming that drinking water isthe sole arsenic source for a 70-kg adult, this dose corresponds to 38.5 ppb in drinking water.

Arsenic levels in 66 of the 77 tap water samples collected were above the EPA MaximumContaminant Level (MCL) for arsenic in drinking water (10 ppb) [9]. The concentrations oftotal arsenic detected in the tap water samples ranged from 2 to 874 ppb. The highest tap waterarsenic level (874 ppb) was from a residential domestic well in the shallow (<50 feet deep)aquifer. The median level of arsenic was 35 ppb in this shallow aquifer. The highest arsenicconcentration found in tap water obtained from intermediate-depth wells was 683 ppb (medianlevel 21.5 ppb). The highest arsenic concentration found in tap water from the public drinkingwater supply was 102 ppb. The median level of arsenic in the public water supply was 90.5 ppb. Of the 72 tap water samples collected from shallow or intermediate-depth wells, five samplesshowed arsenic levels greater than 200 ppb. These highest results were 245, 257, 463, 683, and874 ppb.

The arsenic levels in all collected tap water samples exceed the ATSDR EMEG for a child'schronic (long-term) ingestion of arsenic in drinking water. ATSDR based this EMEG on aTaiwanese drinking water study and determined that 0.0008 milligrams per kilogram per day(mg/kg/day) was the highest intake not associated with an adverse noncancerous effect (or no-observed-adverse-effect level [NOAEL]) [10]. Assuming that drinking water is the sole arsenicsource for a 70-kg adult, this dose corresponds to 28 ppb in drinking water.

Collectively, however, similar studies in India, Mexico, Chile, and the Western United States indicate that the threshold for hyperkeratosis and hyperpigmentation is approximately 0.01 mg/kg/day or about 700 micrograms of arsenic a day for a 70-kg adult. The estimated intake from drinking the highest total arsenic level found (874 ppb) in Churchill County could exceed 1750 micrograms per day (µg/day) based on a consumption of more than 2 liters of water per day.

The effects observed in the Taiwanese drinking water study have never been seen in U.S. populations exposed to 100-200 ppb arsenic [10]. Because of the ordinarily efficient methylation, or detoxification, of ingested arsenic, blood levels of arsenic do not begin to rise until intake exceeds 200-250 µg/day and a person's methylation capacity is reduced [11]. In a Utah study in which a low incidence (<5%) of hyperkeratosis was observed, arsenical hyperkeratosis was dose-related and exhibited a threshold of 350-400 µg/day [12]. In people with adequate methylation capacity, that capacity becomes saturated between 500 and 1000 µg/day [13].

Because of the limitations of studies performed with Third World populations, it is not currentlypossible to identify a valid threshold of arsenical effects in U.S. populations. These limitations include inadequate control for confounding factors, underestimated total exposure, and higher susceptibility due to poor nutrition [14].

Arsenic levels in many of the tap water samples substantially exceed the recently revised EPAdrinking water standard for arsenic. On January 22, 2001, EPA adopted a new standard for arsenic in drinking water, lowering it from 50 ppb to 10 ppb. Public water systems must complywith the 10 ppb standard beginning January 23, 2006 [16].

Tungsten

Tungsten was found in all tap water samples at levels ranging from 0.25 to 337 ppb. The highestlevels were found in samples collected from residences whose drinking water source is a privatewell.

EPA has no MCL for tungsten and does not list the element in its IRIS databank. The healtheffects and levels of concern for tungsten in drinking water are not known. Most of the knownadverse health effects of tungsten, such as irritation of the respiratory tract, are associated withinhalation exposures in industrial settings. The National Institute for Occupational Safety andHealth (NIOSH) has established an exposure limit of 5 mg/m3 in air [17]. In experimentalanimals, large overdoses have produced central nervous system disturbances, diarrhea,respiratory failure, and death [18]. No evidence exists to suggest that tungsten, at the levelsdetected in Churchill County tap water, pose any hazard to human health. However, NCEHrequested that the National Institute of Environmental Health Sciences (NIEHS) conducttoxicological studies for tungsten.

Uranium

Uranium was found in 74 of 77 tap water samples at levels ranging from 0.004 to 290 ppb. Nineof these results exceeded the 30 ppb EPA MCL for uranium. In general, the highest uraniumlevels were found at residences with private wells less than 50 feet deep.

Uranium is a naturally occurring radioactive element that is present in nearly all rocks and soils. Parts of the western United States have higher than average uranium levels because of naturalgeological formations. Natural uranium consists of isotopic mixtures of 234U, 235U, and 238U andenters groundwater through erosion of rock and soil. Although radiation exposure has beengenerally assumed to be carcinogenic at all dose levels, no correlation has been established atdoses that occur from exposure to natural radiation [19]. As a result, the health effectsassociated with oral exposure to natural uranium appear to be solely chemical in nature and notradiologic. Toxicologic studies indicate that long-term exposures to uranium in drinking waterat the highest levels found in Churchill County might pose an increased risk for kidney damage[19].

Vanadium

Vanadium was detected in 42 tap water samples at levels ranging from 10 to 430 ppb. Six ofthese levels exceeded the ATSDR intermediate EMEG of 30 ppb for children. Those sixelevated levels were from samples collected at residences in which tap water comes from privatewells. All samples collected from the public drinking water supply contained vanadium levels of30 ppb or less.

The maximum concentration of vanadium (430 ppb) is not likely to pose a public health threat. The ATSDR MRL for vanadium (0.003 mg/kg/day) was derived from a NOAEL of 300 µg/kg/day for renal effects in rats and includes an uncertainty factor of 100 [20]. Another study suggests that the NOAEL in humans for renal effects could be more than four times higher than the rat NOAEL [21].

Volatile Organic Compounds (VOCs)

ATSDR compared levels of VOCs found in residential tap water with health-based CVs toidentify potential contaminants of concern (COCs). Several VOCs were found at levels belowthe ATSDR screening values for drinking water, EPA MCLs, or EPA Region III PlanningRemediation Guides. As a result, these substances were eliminated from the list of potentialCOCs. The other VOCs found in residential drinking water along with their measured levels andcomparison values are shown in Table 2.

Table 2.

Summary of Potential VOCs of Concern in Drinking Water
Substance Number of Detections Maximum Concentration (ppb) Average Detected Level (ppb) Comparison Value (ppb)
Bromoform1 27 16.5 5.01 4
Chlorodibromomethane1 26 1.9 0.988 0.4
1-Ethyl-2-Methylbenzene 1 0.84 0.84 NA2
Benzene, 1,2,3,5-Tetramethyl Benzene 1 0.2 0.2 NA
Ethyl Tert-Butyl Ether 1 0.02 0.02 NA
Methyl-4-(1-Methylethyl)Benzene 1 0.02 0.02 NA

1 One of four chemicals known as trihalomethanes (THMs)
2 NA means "Not Available".

Trihalomethanes

Bromoform and chlorodibromomethane are chemicals known as trihalomethanes (THMs). THMs are disinfection byproducts formed when chlorine or other disinfectants used to controlmicrobial contaminants in drinking water react with naturally occurring organic and inorganicmatter in water. The four THMs are chloroform, bromodichloromethane,dibromochloromethane, and bromoform. EPA set an MCL of 0.1 parts per million (0.1 ppm) forthe combination of bromoform and chlorodibromomethane and other THMs that occur inchlorinated water. EPA has developed a new standard for total trihalomethanes (TTHM) at amaximum allowable annual average level of 80 ppb. This standard will become effective for thefirst time in December 2003 for small surface water and all ground water systems [22]. Even themaximum TTHM levels found in the tap water samples are well below the EPA standard [23].

Other VOCs

No screening values exist for four of the VOCs measured in tap water samples. These VOCs are1-Ethyl-2-Methylbenzene; Benzene; 1,2,3,5-Tetramethyl Benzene; Ethyl Tert-Butyl Ether; andMethyl-4-(1-Methylethyl)Benzene. However, each of these compounds was detected in onlyone sample and at less than 1 ppb. As a result, these VOCs are not expected to be a public healthconcern.

Previous USGS Groundwater Sampling

During the summer of 2001, USGS sampled 100 public supply, domestic, and industrial wells inthe Fallon area [R. Seiler, USGS, personal communication, 2003]. One of the main purposes ofthe sampling was to characterize the current water quality of all drinking water sources in theFallon area. In addition, wells sampled by USGS in 1989 were re-sampled in order to determinewhether changes in water quality had occurred since that time. These samples were analyzed forseveral constituents, including:

  • metals;
  • VOCs;
  • pesticides;
  • uranium isotopes;
  • radon; and
  • alpha, beta, gamma radioactivity [24].

USGS concluded that few samples contained VOCs or pesticides. All reported VOCconcentrations in drinking water wells were less than ATSDR screening values. Substancesassociated with fuel (benzene, toluene, ethyl benzene, xylene, and polycyclic aromatichydrocarbons) were found in only one well at an industrial site. The quality of the water in thethree aquifers used for drinking water has not changed since 1989. Arsenic, uranium, and radonin groundwater commonly exceed drinking water standards [24].


CHILDREN'S HEALTH CONSIDERATIONS

ATSDR recognizes that the unique vulnerabilities of infants and children require specialemphasis in communities faced with environmental contamination. For this evaluation, ATSDRhas taken into account that children could be exposed to environmental contaminants intapwater.


CONCLUSIONS

ATSDR evaluated tap water data as part of its environmental pathway analysis for ChurchillCounty.

  • Because arsenic levels are of concern in municipal and private wells and becauseuranium levels are of concern in shallow private wells, ATSDR categorizes theChurchill County tap water as a public health hazard.

  • Tap water is safe for bathing, showering, and laundry uses.

RECOMMENDATIONS

Restrict consumption of tap water in Churchill County as a primary drinking water source untilthe new water treatment plant is operational.


REFERENCES

  1. US Census Bureau. Census 2000 Redistricting Data (Public Law 94-171) Summary File,Matrices PL1 and PL2. Washington (DC): US Census Bureau; 2000.

  2. Nevada State Health Division (NSHD). Letter to Dr. Jeffrey Koplan from Dr. MaryGuinan concerning a request for assistance in the investigation of excess cases of acutelymphocytic leukemia in children in Fallon, Nevada. Carson City, Nevada. March 7, 2001.

  3. Agency for Toxic Substances and Disease Registry (ATSDR). Draft Public HealthAction Plan for the Fallon Leukemia Cluster Investigation. Atlanta: US Department of Healthand Human Services: 2001.

  4. Maurer DK, Welch AH. Hydrogeology and Geochemistry of the Fallon Basalt andAdjacent Aquifers, and Potential Sources of Basalt Recharge, in Churchill County, Nevada. Carson City (NV): US Geological Survey; 2001. Water Resources Investigation Report 01-4130.

  5. Welch, A.H., Westjohn, D.B., Helsel, D.R., and Wanty, R.B., 2000, Arsenic in GroundWater of the United States: Occurrence and geochemistry: Ground Water, v. 38, no. 4, p.589-604.

  6. US Geological Survey. Groundwater Sampling Results; Presented at NCEH and ATSDRFindings for the Churchill County Leukemia Investigation; 2003 Feb 12, Fallon, Nevada.

  7. US Geological Survey. Fallon tap water sampling activities plan. Carson City, NV: USGeological Survey; 2002.

  8. Agency for Toxic Substances and Disease Registry (ATSDR. Toxicological profile forantimony. Atlanta: US Department of Health and Human Services; 1992.

  9. US Environmental Protection Agency (EPA). National primary drinking waterregulations; arsenic and clarifications to contaminants monitoring. Fed Reg 2001; 66(14):6875-7066. Available from URL: http://www.epa.gov/safewater/ars/arsenic_finalrule.html.

  10. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile forarsenic. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service;2000.

  11. Southwick JW, Western AE, Beck MM, et al. 1981. Community health associated witharsenic in drinking water in Millard County, Utah. Cincinnati, OH: US Environmental ProtectionAgency, Health Effects Research Laboratory, EPA-600/1-81-064. NTIS no. PB82-108374.

  12. Lewis DR, Southwick JW, Ouellet-Helstrom R, Rench J, Calderon RL. Drinking WaterArsenic in Utah: A Cohort Mortality Study. Environ Health Perspect 1999;107(5)359-365.

  13. Marcus WL, Rispin AS. 1988. Threshold carcinogenicity using arsenic as an example. In:Cothern CR, Mehlman MA, Marcus WL, eds. Advances in modern environmental toxicology:Vol XV: Risk assessment and risk management of industrial and environmental chemicals.Princeton, NJ: Princeton Scientific Publishing Co., 133-158

  14. Roychowdhury T, Uchino T, Tokunaga H, Ando M, Survey of arsenic in foodcomposites from an arsenic affected area in West Bengal, India. Food Chem Toxicol 2002;40:1611-21.

  15. Ferreccio C, Conzalea Psych C, Milosavjlevic Stat V, et al. 1998. Lung cancer andarsenic exposure in drinking water: a case-control study in northern Chile. Cad Saude Publica14(Suppl.3):193-198.

  16. US Environmental Protection Agency (EPA). Arsenic in Drinking Water. Available fromURL: http://www.epa.gov/safewater/arsenic.html

  17. National Institute for Occupational Safety and Health (NIOSH). Pocket guide to chemicalhazards. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service;1997.

  18. Sax, Dangerous Properties of Industrial Chemicals, 8th Ed.

  19. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile foruranium. Atlanta: US Department of Health and Human Services; 1999.

  20. Agency for Toxic Substances and Disease Registry (ATSDR). 1992. Toxicologicalprofile for vanadium. Atlanta: US Department of Health and Human Services; 1992.

  21. Dimond EG, Caravaca J, Benchimol A. 1963. Vanadium: Excretion, toxicity, lipid effectin man. Am J Clin Nutr 12:49-53.

  22. US Environmental Protection Agency (EPA). Disinfection byproducts: a referenceresource. Washington (DC): US Environmental Protection Agency; no date. Available fromURL: http://www.epa.gov/enviro/html/icr/gloss_dbp.html

  23. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile forbromoform and chlorodibromomethane. Atlanta, GA: U.S. Department of Health and HumanServices; 1990.

  24. Seiler R. USGS Ground-Water Investigation Related to the Leukemia Cluster in theFallon Area of Churchill County, Nevada. Carson City (NV): US Geological Survey; 2002.

PREPARERS OF REPORT

Authors

Gail Scogin
Environmental Health Scientist
Exposure Investigation Section
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation

Frank Schnell, PhD
Toxicologist
Petitions Response Section
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation


Technical Assistance

Steve Martin
Computer Information System Support Contractor
Information Resources Management Branch
Office of Program Operations & Management


Reviewers

John E. Abraham, PhD
Chief, Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation

Susan Metcalf, MD
Chief, Exposure Investigation Section
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation

Susan Moore
Chief, Consultation Section
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation

Wendy Kaye, PhD
Chief, Epidemiology and Surveillance Branch
Division of Health Studies


APPENDIX

Table A.

Potential Contaminants of Concern from 34 Tap Water Samples from Municipal Water Supply (2002)
Substance Number of Detections Minimum Concentration (ppb) Maximum Concentration (ppb) Mean Concentration (ppb) Comparison Value (ppb)
Arsenic 32 2 102 74.8 0.02
Bromoform 26 0.07 16.5 5.2 4
Chlorodibromomethane 2 0.1 1.9 1.02 0.4
Sulfate 34 1 91.4 66.2 NA1
Tungsten 34 0.25 27.2 19.1 NA
Vanadium 26 20 30 29.6 30

1 NA means "Not Available".


Table B. Potential Contaminants of Concern from 18 Tap Water Samples Collected from Private Wells More than 50 Feet Deep (2002)

Table B.

Potential Contaminants of Concern from 18 Tap Water Samples Collected from Private Wells More than 50 Feet Deep (2002)
Substance Number of Detections Minimum Concentration (ppb) Maximum Concentration (ppb) Mean Concentration (ppb) Comparison Value (ppb)
1,2,3-Trimethylbenzene 1 0.8 0.8 0.8 NA1
1,2,4-Trimethylbenzene 2 1.6 3.19 1.6 NA
1,2,3,5-Tetramethyl Benzene 1 0.2 0.2 0.2 NA
1-Ethyl-2-Methylbenzene 1 0.84 0.84 0.84 NA
Arsenic 18 3 683 102 0.02
Ethyl Tert-Butyl Ether 1 0.02 0.02 0.02 NA
Methyl-4-(1-Methylethyl)Benzene 1 0.02 0.02 0.02 NA
N-Propyl Benzene 1 0.09 0.09 0.09 NA
Sulfate 18 0.1 169 45.5 NA
Tungsten 18 0.25 337 37.5 NA
Vanadium 4 20 170 75 30

1 NA means "Not Available".


Table C.

Potential Contaminants of Concern from 18 Tap Water Samples Collected from Private Wells Less than 50 Feet Deep (2002)
Substance Number of Detections Minimum Concentration (ppb) Maximum Concentration (ppb) Mean Concentration (ppb) Comparison Value (ppb)
Antimony 6 0.9 6.3 2.5 4
Arsenic 17 5 874 96.9 0.02
Sulfate 18 0.9 529 118 NA1
Tungsten 18 0.9 148 10.5 NA
Uranium 18 0.009 290 48.4 30
Vanadium 9 10 430 82.2 30

1 NA means "Not Available".


Table D.

Potential Contaminants of Concern from 6 Tap Water Samples Collected from Private Wells at Unspecified Depths (2002)
Substance Number of Detections Minimum Concentration (ppb) Maximum Concentration (ppb) Mean Concentration (ppb) Comparison Value (ppb)
Arsenic 5 18 87 45.8 0.02
Sulfate 7 0.1 142 59.9 NA1
Tungsten 7 0.25 7.07 2.37 NA
Uranium 6 0.015 0.015 0.015 30
Vanadium 3 10 40 26.7 30

1 NA means "Not Available".



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