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On April 18, 2002, the United States Environmental Protection Agency (US EPA), Region V,requested that the Agency for Toxic Substances and Disease Registry (ATSDR) assist in evaluatingwhether groundwater contamination impacting residential water wells in the Town of Pines, Indianaposes an immediate health threat to residents.

In April 2000, a Town of Pines resident contacted the Indiana Department of EnvironmentalManagement (IDEM) and reported concern for the quality of her well water. Sampling of thisresidential well in May of 2000 revealed elevated levels of volatile organic compounds (VOCs),including benzene. Subsequent testing (June 2000) of this and several other surrounding residentialwells indicated that VOCs as well as some metals were also elevated in residential wells. Elevationswere noted for a different set of metals than previously identified in samples collected in September2000. Further sampling of residential wells in November 2000, July 2001, and September 2001continued to reveal elevated levels of metals. Since April 2000, approximately 55 residential wellsin the Town of Pines, and 13 landfill monitoring wells have been sampled. In all cases, residentialwells exceeding US EPA Maximum Contaminant Levels (MCLs) for particular contaminants wereprovided with a treatment system appropriate for the contaminant of concern to reduce or eliminate exposure to contaminants in groundwater [1,2].

There are several potential sources for metals and VOC contamination in area groundwater. Thecommunity is located in the vicinity of three landfills. More than 100 homes lie north of theselandfills, all of which utilize private wells for drinking water. Chemical analytical data suggest thatthe residential area that has been sampled is down gradient from the Yard 520 landfill. Yard 520 isan active restricted waste facility and is adjacent to and south-southwest of the impacted residentialarea. The Pines Landfill and Lawrence Dump occupy property to the south and southeast of theimpacted residential area. The Pines Landfill and Lawrence Dump are abandoned. Additionally,there is some evidence that suggests fly ash from power plant processes was deposited as fill inmultiple areas in the community, including roads, driveways, and yards. However, the extent of the contamination in the groundwater has not been fully determined [1,2].


Appendix B contains summary tables of data collected by IDEM during the sampling eventsmentioned briefly above. These data were collected in an attempt to characterize and determine theextent of contamination in the groundwater plume beneath the Town of Pines. Overall, thegroundwater characterization thus far indicates elevated concentrations of a number of metals, and more intermittently, concentrations of VOCs [3].

USEPA has provided treatment for those homes that contained elevated VOCs, which appears tohave been effective in reducing the VOC levels in the drinking water. However, the treatmentsystems have not been effective in removing the high concentrations of metals in the water.Therefore, ATSDR has focused this assessment on the metals detected in the wells. ATSDRscreened concentrations of compounds against ATSDR and US EPA health-based guidelines.Contaminants that consistently exceeded these guidelines and also appear to be elevated in thegreatest number of wells include manganese, boron, and arsenic. These were selected for furtherevaluation as contaminants of concern (COCs). Lead was also chosen for further evaluation becauseits effects on the neurological development in children are well established in scientific literature,and contaminant concentrations in a small number of well samples exceeded applicable guidelinesthat are considered protective of public health. However, elevated levels of lead were inconsistentlydetected and could be related to variability in sampling methodology.


In evaluating this site, the ATSDR Strike Team focused on the US EPA request to address theurgency of providing an alternate water supply to area residents. The team based their response onthe data and site conditions provided by IDEM and US EPA. During the past two years, 55 wells ofthe 100 homes located in the area of concern have been sampled. Many of these wells haveunacceptably elevated levels of multiple contaminants that might present a threat to residents andchildren in the area [3].

The area has not been fully characterized and the plume has not been defined. Contaminantconcentrations have fluctuated throughout the two years of sampling--likely due to groundwaterflow dynamics. For example, the concentrations of manganese collected a year apart may bedifferent by as much as 8,000 parts per billion (ppb) at the same address [3]. This variabilityprecludes accurately predicting areas that are likely to be the most impacted. Because current dataare not complete in characterizing the extent of the contaminant plume in groundwater, selectivelychoosing homes for an alternate water supply will not be protective of public health. Providing analternate water supply for the entire impacted area is more appropriate.


As mentioned previously, ATSDR screened contaminant concentrations detected in wells againsthealth-based guidelines derived by ATSDR and US EPA. In the absence of a guideline for oneagency, the guideline for the other was used. When both agencies derived a guideline for thecontaminant, the most conservative was chosen for screening the data. The contaminants of concern(COCs) that were identified during this process include: arsenic, boron, lead, and manganese.

To determine estimated exposures of residents to COCs, ATSDR calculated exposure doses andcompared them to the applicable dose guidelines. In this case, ATSDR used Minimum Risk Levels(MRLs derived by ATSDR) and Reference Doses (RfDs derived by US EPA). Both MRLs andRfDs are estimates of daily human exposure to a hazardous substance that is likely to be withoutappreciable risk over a specified duration of exposure. To be protective of public health, ATSDRcalculated doses using conservative assumptions in its calculations. To protect residents, given theuncertainty of groundwater flow and the seemingly dynamic nature of contaminant concentrationthroughout the plume, it was assumed residents are exposed to the highest measured concentrationdetected in the wells. Exposure estimates were made for both adults and children. Adults wereassumed to weigh 70 kilograms (approximately 155 pounds) and children 10 kg (25 pounds). It wasalso assumed that adults drink 2 liters of water a day, and children drink 1 liter of water a day. Since many of the individuals in this community are longtime residents, it was assumed thatexposures could be chronic.

Doses were calculated for each contaminant of concern using the following equation:

IDw equals C times IR times EF divided by BW

IDw = ingestion exposure dose (milligrams per kilograms of body weight per day- mg/kg/day)
C = contaminant concentration (milligrams per liter- mg/L)
IR = ingestion rate (liters per day- L/day)
EF = exposure factor (unitless)
BW = body weight (in kilograms- kg)

This calculation was performed for each contaminant of concern, and a brief description of potential health implications follows.


Arsenic levels in residential wells ranged from below detection limits to 1,180 ppb. Since this level was the maximum detected concentration, it was selected for the exposure dose calculation:

Adults: IDw = 1.18mg/L times 2L/day times 1 divided by 70 = 0.0337 mg/kg/day.  Children: IDw = 1.18 mg/L times 1L/day times 1 divided by 10 = 0.118 mg/kg/day

Both the oral chronic MRL and RfD for non-cancer effects from arsenic exposure are 0.0003mg/kg/day. The residential well where 1,180 ppb of arsenic was detected has an exposure dose 112times the MRL and RfD for adults, and nearly 400 times the MRL and RfD for children.

Both the MRL and RfD for chronic exposure are based on effects on the skin resulting from ingestion of arsenic. The supporting studies used to derive these comparison values are from Tseng et al. (1968) and Tseng (1977). These studies document significant dermal effects including blackfoot, hyperpigmentation, and keratosis, experienced by a large number of Taiwanese farmers exposed to levels of 170 µg/L of arsenic in water (170 is the Lowest Observed Adverse Effect Level, or LOAEL). Levels between 1-17 µg/L were not observed to cause these effects (called the No Observed Adverse Effect Level, or NOAEL) [4,5,6,7].

Although most Town of Pines residential wells had concentrations near the NOAEL, severalexceeded the LOAEL for these effects. ATSDR was notified that the homes with wells containingthe highest concentrations of arsenic were given carbon filters to lower arsenic levels in water, andwere effective in doing so. However, it is possible that other residents could be exposed to theselevels of arsenic with a change of groundwater flow or contaminant concentrations.

It is important to note that arsenic has also been associated with other health outcomes other thandermal disease and lesions. Dermal endpoints are the most sensitive effects for humans, however,and thus were chosen for the derivation of MRLs and RfDs. Arsenic has been associated with cancerand gastrointestinal, respiratory, cardiovascular, and neurological effects, in addition to dermaleffects. Also, it should be noted that to derive the oral arsenic MRL, an uncertainty factor of 3 wasapplied to the NOAEL of 0.0008 mg/kg/day for human variability.

ATSDR concludes that potential elevations such as those observed in the residential wellsconstitute a threat to human health.


Boron was detected above health-based guidelines in almost every well sample in the data ATSDRreviewed, with levels as high as 14,400 ppb. It should be noted that concentrations in monitoringwells at Yard 520 (one of the three landfills) were approximately twice this level. Using 14,400 ppb to calculate doses:

Adults: IDw = 14.40 mg/L times 2L/day times 1 divided by 70 = 0.4114 mg/kg/day.  Children: IDw = 14.40 mg/L times 1L/day times 1 divided by 10 = 1.44 mg/kg/day

The ATSDR MRL for intermediate (14 to 365 days) exposure is 0.01 mg/kg/day. The US EPAoral RfD (0.09 mg/kg/day) is a chronic lifetime exposure, but is less conservative than the MRL. Tobe more protective of human health, the MRL was used for comparison. The daily dose estimatedfrom the highest concentration of boron is 41 times the MRL for adults and 144 times the MRL forchildren.

The oral MRL is based solely on findings in animal studies. The investigations reported prenataldevelopmental effects such as reduced fetal body weight or minor skeletal changes. The lowestobserved effect level (LOAEL) in these studies is 13.6 mg/kg/day for fetal rats exposed duringgestation days 0-17 and 0-20 [8]. The intermediate MRL was derived using an uncertainty factor of1,000 (10 for use of a LOAEL, 10 for extrapolation from animals to humans and 10 for humanvariability) [9].

The doses calculated from the maximum detection of boron in the residential wells sampled exceedthe MRL. ATSDR concludes that boron could pose a threat to human health.


Manganese concentrations in residential wells were detected in higher concentrations than any other contaminant. The highest concentration detected in residential wells was 15,100 ppb. This level was used in dose calculations for residents:

Adults: IDw = 15.10 mg/L times 2L/day times 1 divided by 70 = 0.4314 mg/kg/day.  Children: IDw = 15.10 mg/L times 1L/day times 1 divided by 10 = 1.51 mg/kg/day

Because ATSDR does not have an oral MRL for manganese, the US EPA oral RfD of 0.047mg/kg/day was used for comparison. The doses observed from the highest concentrations ofmanganese were 9 times the oral RfD for adults and 32 times the oral RfD for children.

The oral RfD is based on human data. The RfD for manganese is equal to the average daily intakeof manganese in the diet (10 mg/day) that is considered adequate and safe. However, the RfD wasderived using intake assumptions for adults in the calculations, not for children. This level wasbased on a composite of data from the World Health Organization, the National Research Council'sNational Academy of Sciences, and research on nutrition [10-12].

Several human studies have associated manganese exposure in drinking water with neurologicaleffects. Kondakis et al. (1989) reported decreased scores on neurological testing in a communityexposed to 1.6-2.3 mg/L of manganese compared to 0.08-0.25 mg/L in another community. Thestudy had limitations that included not being able to differentiate effects from dietary intake ofmanganese and the amount of water consumed [13].

Another human study by Kawamura et al. (1941) reported the effects of humans ingesting largeamounts of manganese in drinking water. The source of the manganese was 400 dry-cell batteriesburied near a drinking water well, resulting in high levels of zinc and manganese in groundwater.Twenty-five cases of manganese poisoning were reported, with symptoms including lethargy,increased muscle tonus, tremors, and mental disturbances. The most severe symptoms were observedin the elderly. The water was not analyzed immediately during the outbreak, but approximately 1month later, when it was estimated that the levels had decreased by about 50%. The measured levelsaveraged 14 mg/L, but it is believed the initial levels were as high as 28 mg/L. Please see theATSDR toxicological profile for arsenic for further discussion of these and other relevant studies[14-16].

Because wells tested in the Town of Pines had levels equivalent to those in these studies, ATSDRconcludes that manganese could pose a threat to human health.


The highest concentration of lead in the wells sampled was 199 ppb, at a single residence in July2001, with a 44.9 ppb reading in the duplicate sample. Resampling of that well in September, 2001showed a much lower result (6.6 ppb).

No MRL or RfD exists for lead. However, ATSDR has chosen to review pertinent data given thesensitivity of children to lead as they develop neurologically. As a worst case estimate of exposure to lead for this residence, the doses of lead for adults and children for the highest detected concentration are calculated as follows:

Adults: IDw = 0.199 mg/L times 2L/day times 1 divided by 70 = 0.0057 mg/kg/day.  Children: IDw = 0.199 mg/L times 1L/day times 1 divided by 10 = 0.0199 mg/kg/day

Due to the severe neurological effects of lead, exposure to lead from all sources is a general concern for children. Exposure to lead can be estimated by lead levels found in the bloodstream. The Centers for Disease Control and Prevention (CDC) has established a blood lead action level of 10 µg/dL for children [17]. Exposure to lead can occur through many sources, particularly soil, dust, lead-based paint, and drinking water. Many studies document the potential health threat of exposure to lead in drinking water. US EPA has established a drinking water action level for lead of 0.015 mg/L. For comparison to the dose estimates calculated above, exposure at the EPA action level would be a dose of 0.00043 mg/kg/day for adults, and 0.0015 mg/kg/day for children. The doses calculated for site-specific exposure for individuals who could be exposed to the highest concentration detected in the Town of Pines would exceed these doses. Additionally, the scientific literature reports LOAELs for some endpoints at or near the site specific dose calculated above.

Intermediate exposure to lead in water can elevate blood lead levels. In studies of exposure to monkeys, doses of between 0.05 and 0.1 mg/kg/day of lead in drinking water have been shown to increase the blood lead levels to between 30 and 53 µg/dL, and the levels of lead in humans as high as 40 µg/dL [18-21]. Under conditions of exposure to background levels of lead from other sources, even relatively short term exposure to the maximum detected concentration in water would be expected to elevate the blood lead levels in a child above 10 ug/dL. Considering the current recommendations for limiting blood lead levels in children to less than 10 µg/dL, ATSDR concludes that exposure to the highest lead concentrations in residential wells present a potential threat to human health in this community [22,23].

Combined Effects

The contaminants of concern in this consultation (arsenic, boron, manganese, and lead) canantagonize the absorption of other essential minerals in the gastrointestinal tract. It is known that aspeople age, it becomes more difficult to metabolize manganese. Calcium and iron compete forabsorption with manganese. Therefore individuals deficient in either calcium or iron, or both, maybe deficient because they cannot adequately metabolize and remove manganese. As a result, theimpact of exposure to these and other metals, as well as many VOCs, might be underestimated dueto the uncertainty associated with assessing the combined impact of this complex mixture.Generally, ATSDR assumes there is an additive risk to a target organ with a group or mixture ofcontributing contaminants. For example, many of the compounds detected in residential wells in theTown of Pines can affect the neurological system, such as aluminum, boron, lead, manganese,napthalene, toluene, and xylene. Thus, even chemicals present at lower levels that were NOTselected as a COC in this investigation may be of concern in this community because they may addto the toxicity of the identified COCs. Efforts to reduce exposure to these chemicals should target allcontaminants in the groundwater. This is particularly applicable to the selection of an appropriatewater treatment (e.g. water filtration).


ATSDR recognizes that in communities faced with contamination of air, water, soil, or food, theunique vulnerabilities of infants and children demand special emphasis. As part of its Child HealthInitiative, ATSDR is committed to evaluating the health impact of environmental contamination onchildren. The groundwater in the Town of Pines poses a significant threat to children's healthbecause they could be, or are currently being exposed to potentially high levels of metals inresidential drinking water.

Physical Hazards: ATSDR has not evaluated any physical hazards at this site.

EPA Information Request: Do current levels of contaminants in residential wells pose a threatto human health?

Yes, current levels of contaminants, in some instances, may pose a threat to adults and childrenliving in the area. ATSDR suggests an alternate water supply for impacted residential wells, andthe investigation of a long-term solution to water quality problems.


  1. Contaminated groundwater has significantly impacted the drinking water supply for manyresidents. Because the groundwater plume has not been fully characterized, it is uncertainhow many additional residential wells could be impacted by the plume in the future.

  2. Significant fluctuations in contaminant concentrations have occurred in individual homesduring the two years that sampling was conducted. Therefore, filters at the taps of selectedindividual homes are not adequate to provide long-term protection of drinking water for allresidents of the Town of Pines.

  3. Residential wells in the Town of Pines contain detected elevated levels of metals and VOCs. The extent of contamination is unknown.

  4. Levels of arsenic, boron, manganese, and lead have been detected in residential wells at levels similar or equal to those associated with adverse health effects noted in scientific literature.


  1. Provide bottled water to Town of Pines residents where sampling indicates elevated levels ofmetals and VOCs. (IDEM or US EPA)

  2. Investigate an alternate water supply as a long-term solution. (PRPs, IDEM, or USEPA)

  3. Conduct further sampling of the area to characterize the location of the plume, as well as the source of the plume. Provide bottled water to residents as needed during the plume investigation.

  4. Provide an alternate long-term water source: 1) to eliminate exposure to contaminants thatare known to cause health effects at the levels detected and 2) to eliminate the uncertainty ofrisk from additive effects of exposure to these contaminants.


Michelle A. Colledge
Environmental Health Scientist
Office of Regional Operations, Region 5
Agency for Toxic Substances and Disease Registry

Reviewed By:

Greg Zarus
Atmospheric Scientist/Strike Team Coordinator
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry
Selene Chou
Environmental Health Scientist
Division of Toxicology
Agency for Toxic Substances and Disease Registry
Mark D. Johnson
Office of Regional Operations, Region 5
Agency for Toxic Substances and Disease Registry
Sharon Wilbur
Environmental Health Scientist
Division of Toxicology
Agency for Toxic Substances and Disease Registry
Jan Pels
Environmental Scientist
Superfund Division
Region 5
United States Environmental Protection Agency
Moiz Mumtaz
Division of Toxicology
Agency for Toxic Substances and Disease Registry
Kenneth Theisen
On Scene Coordinator
Superfund Division
Region 5
United States Environmental Protection Agency
Tina Forrester
Deputy Director
Office of Regional Operations
Agency for Toxic Substances and Disease Registry
Mildred Johnson-Williams
Division of Toxicology
Agency for Toxic Substances and Disease Registry
Alan Susten
Assistant Director for Science
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry


  1. IDEM. Summary of Site Activities. Provided to ATSDR 4/18/2002. Site Investigation Section,Indiana Department of Environmental Management.

  2. IDEM. Integrated Assessment. Sections 2-4. Site Investigation Section, Indiana Department ofEnvironmental Management. September 2001.

  3. IDEM. Data Package of Significant Findings. Provided to ATSDR 4/18/02. Site InvestigationSection, Indiana Department of Environmental Management.

  4. Tseng, WP. 1977. Effects and dose-response relationships of skin cancer and blackfoot disease witharsenic. Environ. Health Perspect. 19: 109-119.

  5. Tseng, WP, HM Chu, SW How, JM Fong, CS Lin and S Yeh. 1968. Prevalence of skin cancer in anendemic area of chronic arsenicism in Taiwan. J. Natl. Cancer Inst. 40: 453-463.

  6. EPA. 2002. Integrated Risk Information System (IRIS). Arsenic.

  7. Agency for Toxic Substances and Disease Registry. 2000. Arsenic, Toxicological Profile.Department of Health and Human Services.

  8. Heindel JJ, CJ Price, CA Field, et al. 1991. Developmental toxicity of boric acid in mice and rats.Fund Appl Toxicol. 1992 Feb;18(2):266-77.

  9. Agency for Toxic Substances and Disease Registry. 2000. Boron, Toxicological Profile. Departmentof Health and Human Services.

  10. Freeland-Graves, JH, CW Bales and F Behmardi. 1987. Manganese requirements of humans. In:Nutritional Bioavailability of Manganese, C Kies, ed. American Chemical Society, Washington, DC.p. 90-104.

  11. NRC (National Research Council). 1989. Recommended Dietary Allowances, 10th ed. Food andNutrition Board, National Research Council, National Academy Press, Washington, DC. p. 230-235.

  12. WHO (World Health Organization). 1973. Trace Elements in Human Nutrition: Manganese. Reportof a WHO Expert Committee. Technical Report Service, 532, WHO, Geneva, Switzerland. p. 34-36.

  13. Kondakis, XG, N Makris, M Leotsinidis, M Prinou and T Papapetropoulos. 1989. Possible healtheffects of high manganese concentration in drinking water. Arch. Environ. Health. 44(3): 175-178.

  14. Kawamura, R, H Ikuta, S Fukuzumi, et al. 1941. Intoxication by manganese in well water. KitasatoArch. Exp. Med. 18: 145-169.

  15. EPA. 2002. Integrated Risk Information System (IRIS). Manganese.

  16. Agency for Toxic Substances and Disease Registry. 2000. Manganese, Toxicological Profile.Department of Health and Human Services.

  17. Centers for Disease Control and Prevention. 1991. Preventing lead poisoning in young children.Atlanta, GA: US Department of Health and Human Services, Public Health Service, Centers forDisease Control.

  18. Gilbert SG, DC Rice. 1987. Low-level lifetime lead exposure produces behavioral toxicity (spatialdiscrimination reversal) in adult monkeys. Toxicol Appl Pharmacol 91:484-490.

  19. Hilderbrand DC, VWT Der R. Griffin, et al. 1973. Effect of lead acetate on reproduction. Am JObstet Gynecol 115:1058-1065.

  20. Rice DC. 1985b. Chronic low-lead exposure from birth produces deficits in discrimination reversal inmonkeys. Toxicol Appl Pharmacol 77:201-210.

  21. Stuik EJ. 1974. Biological response of male and female volunteers to inorganic lead. Int Arch Arbeitsmed 33:83-97.

  22. EPA. 2002. Integrated Risk Information System (IRIS). Lead.

  23. Agency for Toxic Substances and Disease Registry. 2000. Lead, Toxicological Profile. Departmentof Health and Human Services.


Sampling Locations and Detected Concentrations of Benzene, MTBE, and Arsenic
Map 1. Sampling Locations and Detected Concentrations of Benzene, MTBE, and Arsenic

Sampling Locations and Detected Concentrations of Lead (Pb)
Map 2. Sampling Locations and Detected Concentrations of Lead (Pb)

Sample Location Map A
Map 3. Sample Location Map A

Sample Location Map B
Map 4. Sample Location Map B

Groundwater Sample: Location Map C
Map 5. Groundwater Sample: Location Map C


Table 1.

September 2000 Data
September 2000 Sampling Results- Metals and Organic Compounds in Groundwater (µg/L)
Type of Compound Compound Range of detected concentrations Average concentration Number of samples with detected concentrations
Metal Aluminum 106.0-1700.0 341.5 8
  Arsenic 17.2-1180.0 161.4 16
  Barium 34.0-355.0 116.3 26
  Copper 3.0-436.0 58.8 16
  Iron 150.0-17,000.0 3594.0 14
  Magnesium 1680.0-109,000.0 32,506.4 28
  Manganese 42.9-3970.0 733.5 26
  Nickel 12.3 12.3 1
  Sodium 1,020,000.0 1,020,000.0 1
  Vanadium 44.0 44.0 1
  Zinc 432.0-1320.0 876.0 2
Organics Benzene 7.6-180.0 75.0 15
  Ethyl benzene 71.0-78.0 74.5 2
  Hexachlorobutadiene 0.74-9.6 5.2 2
  Isopropyl benzene 2.9-9.6 5.1 3
  Isopropyl toluene 0.53 0.53 1
  Methylene chloride 0.75 0.75 1
  MTBE 1.4-8.7 5.3 3
  Napthalene 2.6-3.1 2.9 2
  n-Propylbenzene 13.0-15.0 14.0 2
  sec-Butyl benzene 0.98-1.1 1.04 2
  Toluene 1.2-1.6 1.4 2
  1,2,4-Trimethylbenzene 0.56-88.0 55.5 3
  1,3,5-Trimethylbenzene 1.1-6.6 3.0 3
  o-Xylene 31.0-37.0 34.0 2
  m,p-Xylene 100.0-110.0 105.0 2

Table 2.

November 2000 Data
November 2000 Sampling Results- Metals and Organic Compounds In Groundwater (µg/L)
Compound Range of detection Average concentration Number of samples with detected concentrations
Antimony 0.3 0.3 1
Arsenic 860 860.0 1
Copper 3.4-170 67.5 15
Iron 7.0-12,000 4569.0 3
Lead 0.22-10 5.54 20
Manganese 34-8200 1.62 29
Nickel 0.07-44 10.9 6
Sodium 140-890 309.0 19
Zinc 41-750 11.9 6

Table 3.

July 2001 Data
July 2001 Sampling Results- Metals in Groundwater (µg/L)
Compound Range of detection Average Concentration Number of samples with detected concentrations
Isopropyl benzene1.5-1.51.53

Table 4.

September 2001 Groundwater Sampling; Residential and Landfill Samples
September 2001 Sampling of Residential and Landfill Water Wells (µg/L)
Metal Range of residential concentrations Range of landfill concentrations Residential average concentration Landfill average concentrations Number of residential samples with detected concentrations Number of landfill samples with detected concentrations

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