Skip directly to search Skip directly to A to Z list Skip directly to site content

PUBLIC HEALTH ASSESSMENT

NORTH RAILROAD AVENUE PLUME
ESPAÑOLA, RIO ARRIBA COUNTY, NEW MEXICO


APPENDIX D: GROUNDWATER MODELING ANALYSES
by Morris L. Maslia(9)

Introduction

Exposures to toxic environmental contaminants are significant risk factors in human health and disease. To understand and manage these risk factors, environmental and public health managers must have knowledge of the source of the exposure, the fate of contaminants and transport pathways, the exposed population, exposure levels, and routes of the exposure as contaminants enter the human body. Thus, a description of the relationship between source concentration, exposure, dose, and risk of disease must be understood and quantified. Exposure can be determined by direct methods, such as measurement devices, and by indirect methods, such as models (Johnson 1992). Because direct methods cannot be used to estimate past exposures, models play an important role in providing insight and information when data are missing, insufficient, or unavailable. For example, environmental fate, transformation, and transport models are used to assist in understanding, relating, and quantifying sources of contamination to exposed populations within the human exposure assessment and modeling continuum as shown in Figure 1.

Models are developed and applied for different purposes and, as such, the type of model developed and how it is applied often depends on the questions one needs to address and the audience affected by model results. For example, types of model applications can be classified as screening, research, or assessment/decision-making. Each of these types of models can in turn be used in a deterministic, sensitivity, or probabilistic analysis (Cullen and Frey 1999). Models used for screening-level applications are typically based on assumptions that simplify governing mathematical equations. As such, these models are sometimes referred to as analytical models because the simplified governing equations can be solved by analytical or semi-analytical methods. The use of screening-level models is advantageous when trying to identify key focus areas or parameters of importance. These models are typically applied in human exposure assessment studies when the focus is to identify exposure of a population relative to some threshold value. Because the governing mathematical equations are simplified, these models typically require substantially fewer data than the more complex research-type models.

When trying to improve the understanding of the functioning of an actual groundwater flow system, for example, a more refined analysis may be required. In this situation, research-type models can be used to assist with understanding the functioning of the groundwater system. Typically, these models are referred to as numerical models because numerical methods are required to approximate the solutions to non-simplified or generalized mathematical equations. These more complex and data intensive models are typically applied to hazardous waste sites when trying to determine the extent to which a specific remedial action plan will effectively remediate contamination at the site. However, using more complex and data intensive models for an exposure scenario, rather than analytical models, may not result in a higher degree of reliability or confidence in the final human exposure assessment.

Models that are classified as assessment models are typically used as tools intended to aid in decision making. These types of models, for example, are used for rule-making or to address issues of regulatory compliance when determining if environmental standards or human health criteria are being met.

Description of Models Applied to the North Railroad Avenue Plume Site (NRAPS)

At the North Railroad Avenue Plume Site (NRAPS), both numerical and analytical models were applied. Duke Engineering & Services (DE&S) applied three-dimensional groundwater flow and contaminant transport (advection-dispersion) models for simulating future contaminant migration and concentrations in groundwater for their risk assessment and feasibility study (DE&S 2001a, b). This modeling activity consisted of applying: (1) the three-dimensional numerical modeling code MODFLOW (McDonald and Harbaugh 1988) to conduct groundwater flow modeling, and (2) the three-dimensional numerical modeling code MT3DMS (Zheng and Wang 1999) to conduct fate and transport modeling. Details pertaining to the numerical modeling analyses are provided in DE&S (2001b). The important factor to understand, however, is that the DE&S (2001b) modeling analyses did not address the issues of: (1) early (or historical) arrival of contaminated groundwater (breakthrough) at the Jemez water-supply well and (2) past exposure of the population of Española to contaminated groundwater.

As previously discussed, simplified mathematical models of groundwater flow and contaminant transport can be solved analytically. The focus of such models is to identify and characterize a small number of key parameters. To support the evaluation of the public health significance of contaminated groundwater that underlies the City of Española, ATSDR needed to address the issues of historical contamination of the Jemez water-supply well and the potential for past exposure to contaminated groundwater. Therefore, the analytical contaminant transport analysis system (ACTS, version 4.5; Aral 1998) was used to simulate breakthrough of contaminated groundwater at the well. ACTS was applied to the Shallow Aquifer using an infinite two-dimensional, Gaussian source, saturated flow aquifer model with constant dispersion coefficients. Input parameter values required for the models were obtained from data provide in DE&S (2001a) and the published literature (Table 1). The ACTS computational grid was located with reference to: (1) the City of Española, (2) the March 1999 potentiometric surface, and (3) direction of groundwater flow as shown in Figure 2.

ACTS model simulations were conducted to address the issue of contaminant breakthrough at the Jemez water-supply well and to estimate the possible exposure concentration at the well. For these issues, a deterministic ("single-point") approach for assessing the fate and transport of tetrachloroethylene (PCE) in groundwater was used.

To assess the ACTS model results, two issues needed further investigation. The first issue was the uncertainty associated with the concentration of PCE at the source (Norge Town Laundry). Initially, a PCE source concentration of 30,000 g/L was used for the ATSDR simulations using ACTS. The value of 30,000 g/L was used because this was the value estimated during the course of the remedial investigation by Duke Engineering & Services and used for numerical model simulations (DE&S 2001a, b). However, PCE is classified as a dense, non-aqueous phase liquid (DNAPL) with a density of 1.63 g/cm3, and groundwater contaminated with PCE could be subjected to density effects. These density effects would then violate the assumption (simplification) applied to both the numerical and analytical flow and transport models (DE&S 2001b, Aral 1998) that contaminants are completely miscible in groundwater. Typically, for modeling purposes, density effects are assumed to be negligible and can be ignored if the concentration of the contaminant in groundwater is approximately 5% or less of the contaminant's solubility limit in water. For the NRAPS, this equates to a PCE concentration in groundwater of 7,500 g/L or less because PCE has a solubility of 150 mg/L (ATSDR 1997). Thus, ATSDR thought it would be prudent to assess the validity of a source concentration of 30,000 g/L.

The second issue in need of additional investigation was the mechanism of PCE contamination of the Jemez water-supply well. That is, was contamination of the Jemez well solely the result of contaminant migration within the Shallow Aquifer (i.e., fate and transport within the Shallow Aquifer) or caused by an alternative mechanism such as the pumping action of the Jemez and Bond water-supply wells? It is important to emphasize that analytical models like ACTS do not account for the effects of pumping wells on contaminant transport and concentration within the solution domain. To apply analytical models, therefore, the assumption is made that groundwater velocity is constant and uniform in a longitudinal direction (i.e., there is no velocity variation in the lateral (y) and vertical (z) directions in the solution domain). Thus, the pumping action of the Jemez and Bond water-supply wells on the distribution of contaminants during the 20-year historical period cannot be directly simulated using analytical models.

To address the two issues discussed above (source concentration and mechanisms for PCE contamination at the Jemez well) Eastern Research Group, on behalf of ATSDR, conducted additional analytical modeling (Faye 2002) using the model code CXTFIT, version 2.0 (Torride et al. 1995). The CXTFIT model uses a non-linear, least-squares analysis to estimate and optimize fate and transport parameters applied to the simulation of one-dimensional, analytical subsurface solute transport. The areal extent and concentration distribution of PCE during May-June 1998 and the flow and transport line along which the CXTFIT simulations were conducted are shown in Figure 3. The flow and transport line is located approximately along the center of mass of the PCE plume (Figure 3) which also generally coincides with a y-coordinate value of about 550 feet on the ACTS computational grid (compare Figures 2 and 3).

Results of Analytical Modeling Analyses

Analysis of the Shallow Aquifer using CXTFIT provided an optimized estimate of the PCE source concentration of 3,129 g/L with lower and upper 95% confidence limits of 1,639 g/L and 4,620 g/L, respectively (Faye 2002). Comparing this to the solubility of PCE in groundwater (150,000 g/L), the optimized value is 2% of the solubility limit with lower and upper 95% confidence limits ranging from 1% to 3% of the solubility limit. This result is consistent with, and reinforces the concept discussed previously, that density effects can be neglected, for modeling purposes, when the concentration of PCE in groundwater is approximately 5% or less of the solubility limit in water. For the NRAPS, analytical model parameter values and the range of parameter values considered for model application were selected based on available site data (e.g., DE&S 2001a) and based on values published in the literature when site data were inconclusive, uncertain, or unavailable. Ranges of parameter values considered for model application are listed in Table 1.

Using the optimized estimates of source concentration, single-point values (from the ranges listed in Table 1) were selected for the simulation of transport and migration of PCE in the Shallow Aquifer. Hydrogeologic and transport parameters used for conducting deterministic ("single-point" value) simulations in ACTS are listed in Table 2. Three simulations were conducted using source concentration values of 3,129 g/L; 1,639 g/L; and 4,620 g/Lthe values obtained from the CXTFIT analysis (Faye 2002) representing the optimized lower and upper 95% confidence limit values. The source concentration value (along with the other parameter values listed in Table 2) that provided the best fit with observed field data collected in May-June 1998 (DE&S 2001a) was 1,639 g/L. (This represents 1% of the solubility limit for PCE of 150 mg/Lsee previous discussion.) A comparison of observed (measured) PCE groundwater concentrations at selected locations along a flow and transport line (Figure 3) with simulated PCE concentrations for three source concentration values is provided in Table 3. Also listed in Table 3 is the root-mean-square (RMS) value computed for each simulation. The RMS was computed using the difference between the observed PCE concentration and the simulated PCE concentration at different locations along the flow/transport line (and ACTS computational grid coordinate locations). As shown in Table 3, using a source concentration of 1,639 g/L resulted in the minimum RMS value for the analytical model simulations.

Analytical model simulation indicates that breakthrough of PCE at the Jemez well occurred at about 2,200 days (6 years) from the onset of PCE migration within the Shallow Aquifer . Thus, human exposure to PCE-contaminated groundwater from the Jemez water-supply well probably occurred for at least 14 years (1976-89). The simulated PCE concentration of groundwater at the Jemez water-supply well after 20 years (1970-89) is 0.65 g/L (using a source concentration of 1,639 g/L). The simulated concentration of 0.65 g/L, when compared to a concentration of 102 g/L measured in 1989, probably indicates that other mechanisms besides plume migration within the Shallow Aquifer are responsible for contamination of the Jemez water-supply well.

Discussion of Mechanisms for PCE Contamination at the Jemez Well

The simulation of PCE plume migration in the Shallow Aquifer at Española, New Mexico, using parameters suggested by ACTS simulation (Table 2) and best-fit estimates of source concentration suggested by CXTFIT analyses (Faye 2002), provide some justification that plume migration is at least partially responsible for contamination of the Jemez water-supply well. While arrival time of the concentration front at the Jemez water-supply well can be simulated acceptably with the analytical models (ACTS and CXTFIT), the simulated PCE concentration corresponding to 1989 (0.65 g/L) is significantly less than 102 g/Lthe concentration obtained from water samples collected from the Jemez well in 1989 (DE&S 2001a). Furthermore, the simulated concentration at the Jemez water-supply well after 28 years (corresponding to 1998) is only 1.7 g/L. These simulated concentrations are substantially less than the maximum PCE concentration of 102 g/L determined in samples obtained from the Jemez well during 1989-1991 (DE&S 2001a). If the ACTS simulated concentrations are only accurate to within an order of magnitude, then these results indicate that breakthrough at the Jemez water-supply well was not substantially caused by migration of PCE to the well within the Shallow Aquifer. Rather the ACTS simulations in conjunction with field data, particularly the PCE concentration of 570 g/L determined in samples collected at observation well R-15(D1) during January 1999 (DE&S 2001a, Table 2.23), strongly suggest that a mechanism other than advection and/or dispersion within the Shallow Aquifer was responsible for intrusion of contaminants at the Jemez water-supply well. Observation well R-15(D1) is finished in the upper part of the Deep Aquifer at a depth of 185 to 205 feet below land surface and is located about 600 feet west of the Jemez well. That relatively high concentrations of PCE occur at depth and substantially west of the center of solute mass in the Shallow Aquifer indicate that pumping from the Deep Aquifer at the Jemez water-supply well and probably at other supply wells in the Española area is primarily responsible for the vertical migration of PCE to the Deep Aquifer and for the intrusion of PCE and its degradation products, TCE and DCE, into the water-supply wells at relatively high concentrations.

Summary and Conclusions

The migration of aqueous phase PCE in the Shallow Aquifer at Española, New Mexico, was simulated by analytical models. Transport and solute transformation parameters applied to the simulation of PCE migration were estimated using the model code CXTFIT (Torride et al. 1995; Faye 2002) and by manually adjusting parameters to achieve a best-fit solution using the ACTS modeling software (Aral 1998). While previous analyses have assumed a source concentration of 30,000 g/L for the Shallow Aquifer (DE&S 2001b), analyses using CXTFIT suggest a significantly lower source concentration of 3,129 g/L with lower and upper 95% confidence limits of 1,639 and 4,620 g/L, respectively (Faye 2002). These lower values are also consistent with an accepted hypothesis that in order to neglect density effects associated with DNAPL compoundssuch as PCEfor model simulation, aqueous phase concentrations should be less than 5% of the compounds solubility limit7,500 g/L for PCE.

Simulation results using a best-fit analysis indicate that migration of PCE to the vicinity of the Jemez water-supply well occurred at about 2,200 days (6 years) from the onset of migration. Simulated PCE concentrations, however, were low and two orders of magnitude less than the maximum concentration of 102 g/L determined in samples collected at the Jemez water-supply well during 1989. This disparity and sample PCE data collected at observations wells finished in the Deep Aquifer indicate that PCE migration within the Shallow Aquifer probably was not the primary mechanism for the intrusion of PCE and its related degradation products, TCE and DCE, into the Jemez and other water-supply wells in the Española area. Rather, pumping at the Jemez and other water-supply wells, following contamination of the Shallow Aquifer at the source area near the Norge Town facility and the onset of PCE migration, probably facilitated vertical migration of PCE and its degradation products into the Intermediate and Deep Aquifers and into the radius of influence of the pumping wells. Thus, using results of simulation and field data would tend to indicate that concentrations at the Jemez water-supply well when it was operating were probably in the 100-500 g/L range during an exposure period of at least 14 years.

References

Anderson, M. P. (1979). "Using models to simulate the movement of contaminants through groundwaterflow systems." CRC critical reviews in environmental control, 9(2):97-156.

Aral, M. M. (1998). "Analytical contaminant transport analysis system (ACTS)." MultimediaEnvironmental Simulations Laboratory Report MESL-02-98, School of Civil and EnvironmentalEngineering, Georgia Institute of Technology, Atlanta, Georgia.

ATSDR. (1997). "Toxicological profile for tetrachloroethylene (PERC)." Agency for Toxic Substances andDisease Registry. Atlanta, Georgia. Available On-Line:http://www.atsdr.cdc.gov/toxprofiles/tp18.html

Buscheck, T. E., and Alcantar, C. M. (1995). "Regression techniques and analytical solutions to demonstrateintrinsic bioremediation." In: Intrinsic Bioremediation, Hinchee, R.E., Wilson, T.E., and Downey,D.C., editors. Batelle Press, Columbus, Ohio.

Cullen, A. C., and Frey, H. C. (1999). Probabilistic techniques in exposure assessment. Plenum Press, NewYork.

DE&S. (1999). "Technical memorandum, north railroad avenue plume superfund site, NPL#NMD986670156, Española, New Mexico." Duke Engineering and Services. August 1999.

DE&S. (2001a). "Remedial investigation report, north railroad avenue plume superfund site, NPL#NMD986670156, Española, New Mexico." Duke Engineering and Services. January 2001.

DE&S. (2001b). "Feasibility study report, north railroad avenue plume superfund site, NPL#NMD986670156, Española, New Mexico." Duke Engineering and Services. February 2001.

Faye, R. E. (2002). "Simulation of tetrachloroethylene (PCE) migration in the Shallow Aquifer at Espanola,New Mexico and related analyses of water supply contamination at the Jemez well." EasterResearch Group report, prepared for the Division of Health Assessment and Consultation, Agencyfor Toxic Substances and Disease Registry, U.S. Department of Health and Human Services.November 2002.

Fetter, C. W. (1993). Contaminant hydrogeology. Macmillan Publishing Company, New York

Gelhar, L. W., Welty, C., and Rehfeldt, K. R. (1992). "A critical review of data on field-scale dispersion inaquifers." Water Resources Research, 28(7):1955-74.

Hearn, G. A. (1985). "Mathematical model of the Tesuque aquifer system near Pojoague, New Mexico."U.S. Geological Survey Water-Supply Paper 2205, Reston, Virginia.

Johnson, B. L. (1992). "A précis on exposure assessment." Journal of environmental health, 55(1):6-9.

McDonald, M. G., and Harbaugh, A. W. (1988). "A modular three-dimensional finite-differencegroundwater flow model." Techniques of Water-Resources Investigations of the United StatesGeological Survey, Book 6, Chapter A1, Reston, Virginia.

Pankow, J. F., and Cherry J. A. (1996). Dense chlorinated solvents and other DNAPLs ingroundwater: history, behavior, and remediation. Waterloo Press, Portland, Oregon.

Toride, N., Leij, F. J., and van Genuchten, M. Th. 1995. "The CXTFIT code for estimating transport parametersfrom laboratory or field tracer experiments." Report No. 137, U.S. Salinity Laboratory, AgriculturalResearch Service, U.S. Department of Agriculture, Riverside, California.

Zheng, C., and Wang, P. P. 1999. "MT3DMS, a modular three-dimensional multispecies transport model forsimulation of advection, dispersion, and chemical reactions of contaminants in groundwater systems."Department of Geological Sciences and Department of Mathematics, University of Alabama, Tuscaloosa,Alabama.

Table 1.

Hydrogeologic and contaminant transport parameter values, North Railroad Avenue Plume Site, Española, New Mexico.
Property Value Reference
Hydraulic conductivity (K) 0.1-64 ft/d DE&S (2001b) 1
Hydraulic gradient, (i) 0.002 ft/ft DE&S (1999)
Porosity of soil (q) 0.15
0.10-0.20
DE&S (2001b)
Hearn (1985)
Infiltration (I) 0.4 in./yr DE&S (2001b)
Bulk density of soil (r) 1.93 g/mL DE&S (2001b)
Distribution coefficient of soil (KD) 0.06 mL/g DE&S (2001b)
Longitudinal dispersivity (L) 260 ft
175-350 ft
DE&S (2001b)
5%-10% of aquifer length of 3,500 ft; Fetter (1993), Gelhar et al. (1992)
Ratio of dispersivity (L/T) 100
10-300
DE&S (2001b)
Anderson (1979); Gelhar et al. (1992)
Retardation coefficient for PCE (R ) 1.78
1.01-5.9
DE&S (2001b)
Pankow and Cherry (1996)
Half-Life of PCE (T1/2) 6,728 d
0.75-9.9x108 yr
Buscheck and Alcantar (1995) 2
ATSDR (1997)
Solubility of PCE at 25ºC 150 mg/L ATSDR (1997)
Source concentration 30,000 µg/L
1,639-4,620 µg/L
DE&S (2001b)
Faye (2002) 3

1Data found in Appendix A of report.

2Half-life value of 6,728 days computed using site data and method of Buscheck and Alcantar (1995).

3Values based on simulation of source concentration using optimization code CXTFIT (Toride et al. 1995), with optimizedvalue being 3,129 g/L and lower and upper 95% confidence limits of 1,639 g/L and 4,620 g/L, respectively.


Table 2.

Parameter values used to simulate the fate and transport of PCE in groundwater for a deterministic ("single-point") analysis, North Railroad Avenue Plume Site, Española, New Mexico.1
Parameter Value Data Source and Calculation Method
Groundwater velocity (V) 0.08 ft/d

mathematical equation ; K =6.0 ft/d; i = 0.002 ft/ft; q = 0.15

Longitudinal dispersivity (L) 260 ft DE&S (2001b)
Longitudinal dispersion coefficient (Dx) 21 ft2/d Dx = LV
Lateral dispersion coefficient (Dy) 0.21 ft2/d

mathematical equation ; DE&S (2001b)

Infiltration (I) 0.4 in/yr DE&S (2001b)
Retardation coefficient for PCE (R) 1.78

mathematical equation ; DE&S (2001b)

Half-life of PCE (T1/2) 6,728 d Buscheck and Alcantar (1995); DE&S (2001b)
Source Concentration (Co) 1,639-4,620 µg/L2 Faye (2002)
X-coordinate length 3,200 ft ACTS computational grid geometry - refer to text
Discretization along x-direction 50 ft ACTS computational grid geometry- refer to text
Y-coordinate length 1,100 ft ACTS computational grid geometry- refer to text
Discretization along x-direction 25 ft ACTS computational grid geometry - refer to text
Location of contaminant source (x, y) 0.0 ft, 550 ft ACTS computational grid location - refer to text
Location of Jemez well (x, y) 800 ft, 375 ft ACTS computational grid location - refer to text
Standard deviation of Gaussian contaminant source (W) 40 ft Norge Town dry cleaning facility-estimate
Duration of simulation 10,220 d (28 yr) DE&S (2001a); estimated transport time from initial contamination (1970) to time of PCE data collection (May-June 1998)
Temporal discretization 365 d (1 yr) ACTS computational grid geometry- see text

1Simulations conducted using ACTS software (Aral 1998); two-dimensional, infinite, saturated flow, Gaussian source aquifer model with constant dispersion coefficients.

2Simulations conducted using source concentrations of 1,639 µg/L, 3,129 µg/L, and 4,620 µg/L; best fit with observed field data (May-June 1998, [DE&S 2001a]) achieved using source concentration f 1,639 µg/L–see text for explanation.


Table 3.

Comparison of measured and simulated PCE groundwater concentrations, North Railroad Avenue Plume Site, Española, New Mexico.1
Location2 Measured PCE Concentration (g/L)3 Simulations using ACTS4
X-coordinate (feet) Y-coordinate (feet) Normalized Concentration (C/Co) Source Concentration, Co (µg/L)5
3,129 1,639 4,620
75 550 1,100 0.837 2,619 1,372 3,874
260 550 590 0.541 1,693 887 2,504
375 550 340 0.409 1,280 670 1,893
600 550 170 0.229 717 375 1,060
900 550 150 0.092 288 151 426
1,310 550 85 0.018 56 30 83
1,590 550 27 0.0045 14 7 21
Root-mean square (RMS) of concentration difference (g/L)6 822 213 1,446

1Simulations conducted using ACTS software (Aral 1998); two-dimensional, infinite, saturated flow, Gaussian source aquifer model with constant dispersion coefficients.

2Coordinate locations referenced to ACTS computational grid shown in Figure 3.

3Data for May-June 1998 (DE&S 2001a).

4Simulation time is 10,220 days (28 years) which is the time from the approximate start of contamination (1970) to the time ofmeasurement (May-June 1998).

5Source concentration derived from CXTFIT parameter optimization (Faye 2002); 3,129 µg/L is optimized PCE source concentration; 1,639 and 4,620 µg/L represent lower and upper 95% confidence limits, respectively; simulated concentration values (columns 4, 5, and 6) are derived from multiplying normalized concentration (C/Co, column 4) by source concentration value (3,129 µg/L, 1,639 µg/L, or 4,620 µg/L).

6RMS computed by using difference between measured PCE concentration (column 3) and simulated PCE concentration(columns 5, 6, or 7).

Diagram showing human exposure assessment and modeling continuum
Figure 1. Diagram showing human exposure assessment and modeling continuum

Potentiometric surface, direction of groundwater flow, and location of ACTS computational grid, Shallow Aquifer
Figure 2. Potentiometric surface, direction of groundwater flow, and location of ACTS computational grid, Shallow Aquifer (modified from DE&S [1999]).

Area distribution of PCE concentration, May-June 1998, and flow and transport line used for CXTFIT simulations
Figure 3. Area distribution of PCE concentration, May-June 1998, and flow and transport line used for CXTFIT simulations. From Faye (2002) and modified from DE&S (2001a).


APPENDIX E: LEVELS OF PUBLIC HEALTH HAZARD

ATSDR categorizes exposure pathways at hazardous waste sites according to their level of public healthhazard to indicate whether people could be harmed by exposure pathways and site conditions. Thecategories are:

Urgent Public Health Hazard: This category applies to exposure pathways and sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects and require quick intervention to stop people from being exposed.
Public Health Hazard: The category applies to exposure pathways and sites that have certain physical features or evidence of chronic (long-term), site-related chemical exposure that could result in adverse health effects.
Indeterminate Public Health Hazard: The category applies to exposure pathways and sites where important information is lacking about chemical exposures, and a health determination cannot be made.
No Apparent Public Health Hazard: The category applies to pathways and sites where exposure to site-related chemicals may have occurred in the past or is still occurring, however, the exposure is not at levels expected to cause adverse health effects.
No Public Health Hazard: The category applies to pathways and sites where there is evidence of an absence of exposure to site-related chemicals.


APPENDIX F: RESPONSES TO COMMENTS RECEIVED ON THE NORTH RAILROAD AVENUE PLUME SITE
PUBLIC HEALTH ASSESSMENT PUBLIC COMMENT VERSION

Comment: The Public Health Assessment (PHA) does not address the issue of kidney cancer andthe possibility of abnormally high rate of a specific type of highly aggressive kidney cancer in men. Anecdotal reports from clinicians and community residents indicate that this may be a concern forthose drinking from this water system, even if the kidney cancer rates for Rio Arriba County as awhole are not elevated.

Response: The health literature indicates that human organs most susceptible to the effects oftetrachloroethylene (PCE) and, to a lesser extent trichloroethylene (TCE) are the nervous systemand the female reproductive system. Animal studies indicate adverse effects to the liver and kidney.

ATSDR evaluates specific population-level data for plausible health effects related to chemicalexposures. Because ATSDR is not a source/repository of state level health data, ATSDR requestsdata from state cancer surveillance/registry programs to make site-specific health evaluations.Because of the lack of historical records (period of exposures) and at the local geographic levelneeded (city level and smaller), the state was unable to generate this data. As a suggestion, the statecancer registry program, state epidemiologist of local health director could be contacted fordiscussions regarding identifying funding for specific cancer/health studies (i.e., kidney cancer inmen). It should be noted that the findings of the PHA did not include an increased risk for kidneyeffects, based on the exposures associated with the NRAP Site.

Comment: We would like to see more thorough investigation of cancer in Española with specialattention to rare and aggressive types of cancer. We would also like to see an investigation of agespecific cancer rates.

Response: As previously discussed, state data was not available at the level of detail needed toconduct an appropriate analysis. People who are interested in the availability of age specific cancerrates or information may contact the New Mexico Office of Epidemiology, P.O. Box 26110, SantaFe. NM 87502-6110 or call 505-827-0006 or 1-800-432-4404. Information about cancer rates andrisk factors may be found at the National Cancer Institute (NCI) and American Cancer Society(ACS) website. For many types of cancer, risk factors have been identified. Chemical contaminantsmay be one of many risk factors for cancer of the kidney; other risk factors include cigarettesmoking, abuse of analgesics, phenacetin-containing analgesics/drugs, relative high weight orobesity, and possibly industrial chemicals/fibers. Should citizens have concern for certain types orforms of rare aggressive cancers, citizens should contact their state epidemiologist as a startingpoint. By definition, rare cancer is difficult to study due to their rare occurrence, and thus posescientific challenges for statistical stability and personal recall of exposures. In addition, theindividuals potentially exposed to the highest concentrations of contaminants were the residentsliving closest to the Bond and Jemez wells due to the likelihood of less dilution with the water fromthe distribution system at these households. These individuals represent an even smaller subset ofthe population which poses difficulties in gaining statistically significant information.

Comment: We would like to see ATSDR conduct interviews with clinicians regarding cancerpatients who reside in Española, and if possible, interviews with community residents as well.

Response: Interviews with clinicians, patients and/or community have far reaching implicationsfor compliance with federal human subjects' protection laws, and for privacy protection.Consultations were conducted in the recent past as a part of the ATSDR PHA process. An ATSDRactivity of systematic interviewing for health effects would have to be approved and cleared undera health study protocol, and would be inappropriate given the PHA report conclusions. Clinicians,patients or community may call the ATSDR site lead, CDR Robert Knowles, toll free at 1-888-422-8737 should new information or data become available. ATSDR cannot tell a patient what causedhis/her cancer. ATSDR does not provide individual medical consultations for healthcare decisionmaking, this decision making should be made between the patient and his/her personal physician.

Comment: In the section on manganese (p.31), there is no mention of Parkinson's disease, and nomention of hazards of being exposed through inhalation of manganese.

Response: In order to address the comment, the following information has been included in the text:

Inhalation exposure to very high concentrations of manganese has been associated with severalneurological effects. Long-term exposure to high concentrations of manganese, typically in theworkplace, has been associated with a condition referred to as "manganism." The symptomsassociated with manganism are similar to those experienced by individuals with Parkinson'sdisease. These symptoms include mental and emotional disturbances, muscle weakness, speechimpairments, tremor, and other neurological effects.

Due to its chemical properties, manganese present in water is not expected to volatilize into air orto result in significant exposures through inhalation. Therefore, inhalation exposure to manganesein groundwater during showering and irrigational use is not expected to occur.

Comment: It states that there were samples taken from 7 private wells (p.20). Can you pleaseexplain in the report how many total private wells there are and why these were chosen? Is itpossible that other wells are contaminated, especially in the deeper zones/aquifers, but have not beentested?

Response: NMED has identified 18 water wells within the 1,000-foot radii of the Bond and Jemezwells. Eleven of these wells are no longer in use, six are used for irrigation, and one is being usedfor domestic water supply (the Cook residence Well). Samples were collected from 10 of these wells. Private wells were chosen for sampling with an emphasis on wells being used and wells instrategically important locations (i.e., wells close to contaminated wells or near suspected sources). A total of 12 private wells were identified south of the site in the Guachupangue area. All of thesewells have been sampled. NMED is unaware of any other private wells being used in the area thatmay be impacted by groundwater contamination.

Comment: Page 44 states "remedial operations began in 1995 and were terminated after about ayear without completing remediation". Can you explain in the document why this was notcompleted?

Response: Remediation of the petroleum hydrocarbon sites was terminated when the air spargingsystems ceased to be efficient. Samples collected from the emissions of these units indicated thatafter a period of one year, petroleum products were no longer being remediated from these sites.

Typos: p. 24, Second paragraph, second sentence, should read "various cancers types of cancer,"and third paragraph, first sentence should read "are not expected to results from".

Response: The text has been corrected.

Comment: Page 5, 3rd paragraph, 1st sentence. Text indicates that TCE and PCE "were firstdiscovered in 1989 during sampling initiated for two municipal supply wells (Bond and Jemezwells)." Were these wells ever tested for manganese? If so, what were the concentrations of thisconstituent? If not, why not?

Response: The Bond and Jemez wells were sampled for manganese in 1977, 1989, and 1990. The1977 and 1989 samples were below the detection limit of 0.05 mg/l. In 1990, the levels detectedwere 0.03 mg/l (Jemez well) and >0.01 mg/l (Bond well). The maximum level of manganese detectedin the Jemez well in 1990 is greater than 10 times below ATSDR's comparison value for drinkingwater. Therefore, it is unlikely that exposure to manganese would cause adverse health effects. However, manganese was identified as a community concern and ATSDR provided a response tothis concern in the PHA.

Comment: Page 6, 3rd bullet. Text indicates that "repairs have been made to the Norge Townfacility to efficiently prohibit future contaminant releases to groundwater. In addition, proposedremediation efforts at the site are considered adequately protective of public health." What repairswere made to the facility? What procedures are in place to ensure that the repairs remain intact? What are the proposed remediation efforts? Please justify how these proposed remediation effortswould be adequately protective of public health.

Response: The lint trap has been removed from service and filled with sand. The piping thatpreviously transported effluent from the Norge Town facility to the city sewer system has beenremoved completely and can not be used in the future.

The proposed remediation efforts include four phases. The first phase involves the cleanup of the dense, non-aqueous phase liquid (alsoreferred to as DNAPL), which is undissolved contamination associated with the site. This processwill be accomplished through the use of surfactant and/or co-solvent treatment. The second phaseconsists of remediating the "hot spots" and the down-gradient, dissolved-phase plume in the shallowzone through enhanced in-situ bioremediation. The third phase also consists of treatment in thedeep zone through enhanced in-situ bioremediation. The fourth phase consists of remediating thesoils with the use of soil vapor extraction to remediate the soils in areas affected adjacent to thesource area once the DNAPL is treated. The fourth phase also consists of sampling throughout thesite area to ensure effectiveness of the remedy and protectiveness of human health. Greater detailon the remediation process can be obtained from the Record of Decision (ROD) for the NRAP Site.

The public water supply, which provides drinking water to individuals within the City of Española,does not utilize water from the impacted wells (Bond and Jemez wells). The City of Española publicwater supply wells that are currently in use are not located in the impacted groundwater area andundergo periodic sampling to ensure that drinking water meets the requirements of EPA's SafeDrinking Water Act. Proposed cleanup efforts for the site are expected to remove the groundwatercontamination from the area. Periodic sampling of the impacted groundwater area will beconducted to monitor the effectiveness of the proposed cleanup actions.

Comment: Page 6, 2nd bullet after ATSDR recommendations. Recommendation that twelve privatedrinking water wells should be periodically monitored by NMED "until cleanup measures arecompleted to determine whether these wells remain unimpacted from local groundwatercontamination. What are the parameters for successful cleanup? Depending on the groundwaterflow rate, it would seem prudent to monitor for an appropriate period of time after the cleanup iscompleted to ensure that contaminants are not still migrating and cleanup was successful. The sameis true for active private wells that are used for non-drinking water purposes.

Response: The parameters for successful cleanup are discussed in detail in the ROD prepared forthe site. According to the ROD, groundwater will undergo remediation until contaminantconcentrations are below the Maximum Contaminant Levels for PCE and TCE of 5 g/L.

Based on the available groundwater data and the proposed cleanup activities, the 12 privatedrinking water wells located directly adjacent to Santa Clara Pueblo Trust Lands have not beenimpacted and are not expected to be impacted in the future. Additional sampling of the twelveprivate wells located directly adjacent to Santa Clara Pueblo Trust Lands to ensure that they remainunimpacted during remediation activities was recommended by ATSDR because these wells arecurrently being used for drinking water purposes. As discussed in this PHA, limited exposure isexpected to result from exposure to water from non-drinking water wells. As part of the cleanupactivities, monitoring wells located in the contaminant plume area and along the perimeter of theplume will be monitored periodically during the remediation efforts and for years following thecompletion of cleanup activities. Based on the available information on groundwater conditions andthe evaluations in this PHA, the proposed monitoring and ATSDR's recommendations areconsidered protective of public health.

Comment: Page 7, last sentence of the page. Text indicates that the "dissolved-phase groundwaterplume is hydraulically connected to the Rio Grande and extends to within 10 feet of the Rio Grande." PCE has been described in some literature as being a dense non-aqueous-phase liquid (DNAPL). Are there any DNAPLs associated with this site? If so, what measures have been taken to ensure thatthis plume does not migrate to other drinking water supply wells and thus, cause additional potentialpublic exposure?

Response: The site consists of both an undissolved area of contamination, referred to as DNAPL,and a dissolved-phase groundwater plume. The DNAPL area is located in close proximity to theNorge Town facility in comparison to the dissolved-phase groundwater plume that extends from theNorge Town facility to within 10 feet of the Rio Grande. As documented in the ROD for the NRAPSite, the DNAPL plume will be treated with surfactants and/or co-solvent treatment. Cleanup effortsfor the DNAPL is expected to remove between 90-98% of the residual DNAPL.

Comment: Page 10, Land Use Section. Is the plume static or moving? If the plume is not static,is the information provided in this section complete? Could additional entities be potentiallyaffected by the plume? Are there any other public water supply wells in the vicinity of the plume? If so, where are they located?

Response: The groundwater contamination is moving slowly south, southeast toward the RioGrande. Based on data provided to date, no other private or public water supply wells in the vicinityof the plume have been affected. The municipal supply wells currently being used by the City ofEspañola are up-gradient of the plume and should not be affected. In addition, these wells areperiodically monitored in accordance with the Safe Drinking Water Act to ensure that drinkingwater supplied to Española residents is safe to drink.

Comment: Page 11, 2nd to the last paragraph on the page. Text indicates the Las Cumbres LearningServices, Inc. is located near the eastern boundary of the shallow PCE plume. What is the drinkingwater supply for this day care center? What is the drinking water supply for the junior high school?

Response: Las Cumbres Learning Services, Inc. and the junior high school receive their drinkingwater from the City of Española public water supply, which is routinely sampled for compliance withEPA's Safe Drinking Water Act requirements.

Comment: Page 12, Evaluation Process. 1st paragraph, last sentence. Text indicates that "it shouldalso be noted that other contaminants may be evaluated further if concerns are received from thecommunity regarding the presence of the particular contaminant(s)." I am concerned about thecumulative chronic effects from the public being exposed to both a BTEX plume and the PCEplume. In addition, it is not clear what other constituents may be present in the contaminated area(for example: manganese).

Response: Based on information evaluated by ATSDR contaminants from the BTEX plume have notbeen detected in the Bond or Jemez wells. As stated in a previous comment, there is limitedinformation available that indicates that the NRAP and BTEX plumes are co-mingled. Even thoughgroundwater contamination exists from the BTEX plume, these contaminants have not been foundin the Bond, Jemez, or other City of Española municipal drinking water wells. Therefore, it isunlikely that residents have been exposed to BTEX contamination via ingestion. As noted in aprevious response, ATSDR reviewed manganese data from the Bond and Jemez wells from 1977through 1990 and found that levels were well below comparison values and therefore would beunlikely to cause adverse health effects.

Comment: Page 12, last paragraph on the page that continues on page 13. Text indicates that "Inthe event that the calculated, site-specific exposure dose for a chemical is greater than the establishedhealth guideline, it is then compared to the exposure doses from individual studies documented inthe scientific literature that have reported health effects. Estimated demographics for this siteindicated the presence of 467 children ages 6 and younger and 573 adults ages 65 and older. As youknow these populations are more susceptible to potential health effects from exposure than standardadult populations. However, it is unclear whether and how they have been figured into the exposurepathways. It is also unclear whether chronic effects were taken under consideration for the exposurepathways. The modeling on page 16 indicates that "for adults, an exposure duration of 14 years(based on the available data and groundwater modeling efforts) to 20 years (worst-case scenario)" When scientific literature is referenced it usually involves acute exposure to chemicals in anindustrial type scenario, which may not be relevant to this situation. Another example would be thaton-site soils are not considered an exposure pathway but I am unsure of whether the exposureconsidered children with pica that may be ingesting soil at the day care center or in a residence yard. Soil samples were only taken from 1 to 5 feet deep. Was there a decreasing trend that shows thereis not potential contamination that exceeds the 5-foot depth?

Response: To ensure that the health of the nation's children is protected, ATSDR has implementedan initiative to protect children from exposure to hazardous substances. Therefore, site-specificexposure doses were calculated for both adults and children as part of this PHA. Additionalinformation on the evaluation of childhood exposures is presented in the "ATSDR Child HealthInitiatives" Section of the PHA and Appendix C.

The potential for health effects resulting from chronic exposure to contaminants associated with theNRAP Site has been evaluated as part of this PHA. The health guidelines that were considered inthis PHA account for long-term exposure to contaminants.

Comparison Values (CVs) developed for children with pica behavior were used to evaluate theavailable soil data for the Las Cumbres day care center. No contaminants were found to exceed theestablished soil pica values at the day care center. Soil data is not available for residential yards.

Soil samples collected from the 1 to 5 feet deep range were considered in the evaluation of directcontact with contaminants. Typically, individuals' activities involve contact with soil from 0 to 2feet deep. Direct contact exposure to soil greater than 5 feet deep is not expected.

Comment: To evaluate the potential past human exposure of tetrachloroethylene (PCE) and trichloroethylene (TCE) in the City of Espanola drinking water, ATSDR used the maximum concentrations of these contaminants (PCE = 570 micrograms per liter (ug/L), TCE = 24 ug/L) detected in groundwater from monitoring wells R-15 (D1) and R-09(I2). NMED considers this methodology for estimating the past contaminant concentrations in the Jemez municipal well, by correlating it to current concentrations of contaminants in groundwater from R-15(D1) and R-09(I2) may be overestimating past drinking water contaminant concentrations based on the following:

  • The screened interval for R-15(D1) is only 20 feet (185 to 205 feet below groundsurface), and for R-09(I2) the screened interval is 15 feet (85 to 100 feet belowground surface). Although it is not known what interval the Jemez well wasscreened, we know that it completed to a depth of 260 feet below ground surface. Itis likely that the Jemez well was screened over a much larger interval in order tomaximize water production. Thus, water produced from the Jemez well wouldreflect much different groundwater contaminant concentrations than monitoring wellsthat are screened at discrete intervals where groundwater contamination is high. Contaminant dilution would most likely occur in the Jemez well, as it would pumpwater from several zones where groundwater contamination was much lower or non-existent.
  • Monitoring well R-15(D1) was installed in December 1998, which is almost 10 yearsafter the Jemez and Bond wells were removed from service. ATSDR usedcontaminant concentrations from R-15(D1) from a sampling event in 1999 thatindicated PCE in groundwater was 570 ug/L. NMED collected another groundwatersample from R-15(D1) in May 2002 in which PCE was detected at 970 ug/L. Thedata suggest that the contaminant concentration in groundwater at R-15(D1) isincreasing. It may not be appropriate to use concentrations in groundwater samplescollected in 1999 and suggest that they represent concentrations that may haveexisted in groundwater from 1970 through 1989.
  • The highest concentrations of PCE and TCE detected in the Jemez well were 102ug/L and 8.3 ug/L, respectively. These samples were collected in September 1991,almost two years after the well was removed from service. The initial samplescollected in December 1989, when the well was still in operation, had levels of PCEand TCE at 22.2 ug/L and 0.9 ug/L, respectively.

NMED recognizes the challenge in conducting a conservative exposure evaluationand simultaneously attempting to manage the uncertainty inherent in suchevaluations. NMED believes that if the highest levels of PCE (102 ug/L) and TCE(8.3 ug/L) detected in groundwater from the Jemez well were used to estimate thepotential past human exposure, the resulting evaluation would provide a morerealistic, yet still conservative, estimate of the exposure. For the reasons statedabove, using the highest concentrations from monitoring wells at the site may yieldan unrealistically high exposure assessment that contains a considerable degree ofuncertainty.

Response: The PHA process is intended to conservatively evaluate the potential forhealth effects resulting from exposure to hazardous waste. Several uncertaintiesexist and have been briefly discussed in the text (i.e., no groundwater data prior to1989, no mixing/dilution with unimpacted water assumed in the evaluation, use ofmonitoring well data due to lack of data from Bond and Jemez wells). In the absenceof data from the Bond and Jemez wells for the times of interest, ATSDR utilized themost conservative information available for the groundwater for public healthprotectiveness.

Comment: Please change all references in the report to monitor well R-09 to R-09(I2). Also, change references to R-15 to R-15(D1).

Response: The text has been amended, as requested.

Comment: Page 15, second bulleted paragraph: It is stated in this paragraph that "human exposureto PCE contaminated groundwater from the Jemez well probably occurred for approximately 14years." It is also stated "concentrations at the Jemez well during its operation were probably in therange of 100 ug/L to 500 ug/L." Considering that there are no analytical data for the Jemez wellprior to 1989, and given the points stated above in comment No. 1, it may be inappropriate to usethe term "probably" when making these assumptions. It is perhaps more appropriate to suggest thatcontamination potentially occurred for 14 years at concentrations of 100 ug/L to 500 ug/L.

Response: The suggested change to the text has been made.

Comment: Pages 16 through 18, Exposures from PCE and TCE: In determining the level of publichealth hazard due to the past exposure of PCE and TCE in drinking water, ATSDR compared thecalculated exposure doses to adults and children to the oral reference dose (RfD) for PCE and theprovisional RfD for TCE. However, calculated exposure doses were determined from the estimateddoses via ingestion, inhalation (showering), and direct contact (dermal exposure); the sums of thesedoses were then compared to oral RfDs.

It would perhaps be more appropriate to calculate exposure doses for each pathway in accordancewith accepted procedures (e.g., EPA's "Risk Assessment Guidance for Superfund") and comparethe calculated doses to pathway-specific toxicity values. If, however, such an approach was notpossible due to lack of toxicity values for the inhalation and dermal contact pathways, the text shouldmake mention of this circumstance. The rationale for assuming that the additional risk due toinhalation of PCE and TCE vapors during showering can be approximated as additional ingestionof drinking water should be stated in the text. The rationale for comparison of the dermal contactexposure dose (which is calculated as an absorbed dose) to oral RfDs for PCE and TCE (whichrepresent administered doses) should also be discussed.

Response: For clarity, ATSDR included additional information in the text to address the commentsraised. As part of this PHA, ATSDR assumed exposure via showering to be half the dose estimatedfrom ingestion of drinking water (equal to exposure to 1 liter of water per day). EPA Region 4Supplemental Guidance to the Risk Assessment Guidance for Superfund, November 1995, states thatit should be assumed that showering exposure is equivalent to exposure from ingestion of two litersof contaminated water per day. This value accounts for both inhalation and dermal exposure duringshowering. The guidance is based on the recommendations of The Risk Assessment Forum(Exposure to VOCs During Showering, Memorandum from Dorothy E. Patton, Chair, RiskAssessment Forum to F. Henry Habicht, II, July 10, 1991).

Because ATSDR's evaluation estimated dermal exposure during showering separately, exposuresassociated with inhalation during showering were assumed to be equal to 1 liter per day (or half theingestion rate of 2 liters per day). Estimated dermal doses were compared with oral RfDs, whichwere adjusted using chemical-specific gastrointestinal absorption factors to represent an "absorbeddose" rather than an "administered dose".

Per the comment, ATSDR has provided additional information regarding the rationale in AppendixC. In addition, estimated doses for ingestion, inhalation, and dermal exposure will be discussedseparately for clarity.

Comment: Page 17, 3rd and 4th paragraphs and Page 18, 2nd and 3rd paragraphs: It is stated that"Exposures associated with inhalation of PCE (and TCE) from contaminated water during showeringare considered to be very minimal and are not expected to result in adverse health effects" and"health effects from direct contact are not expected to result from exposure associated withcontaminated (PCE and TCE) drinking water." These statements seem to contradict ATSDR'sconclusion that PCE and TCE in drinking water posed a public health hazard from exposures thatwere calculated to include inhalation exposure due to showering and dermal exposure. If thecontributions of the inhalation and dermal contact pathways are small relative to the ingestionpathway, the text should discuss this circumstance. It would be also helpful for the Public HealthAssessment to provide details on the exposure dose calculations for each exposure pathwayevaluated.

Response: Compared with ingestion, less potential exposure to contaminants is expected to occuramong individuals exposed via inhalation and dermal contact. For ease in understanding, the PHAdoes not provide exposure pathway equations. However, a discussion of each of the exposurepathways and the assumptions used in this evaluation are presented in Appendix C of the PHA.

Comment: Page 29 and 30, Health Outcome Data Evaluation: ATSDR performed a healthoutcome data evaluation to determine whether the incidence rates of certain adverse health effectsare higher than expected in the area potentially affected by the site. ATSDR concluded that an"accurate meaningful comparative analysis of low birth weight is not possible" because Españolacity-level data is not available until the late 1980's. ATSDR also states that "cancer rates forchildren and adults were considered, however; varying population estimates for Española from1970-2000 created a concern for producing accurate rates"

Given that ATSDR concluded "past exposure to contaminants in drinking water posed a publichealth threat", it seems appropriate for ATSDR to make greater effort to investigate the potentialadverse health effects associated with the site. NMED suggests that ATSDR work closely with theEl Rio Arriba Environmental Health Association (EL RAEHA) to gather more community-specifichealth data. Data could be collected from interviews with local residents and local practitioners. Also local and regional (i.e., Albuquerque) hospitals may have records that can correlate incidencesof low birth weight and cancers with patients that have home addresses in Española. If datagathering efforts such as the ones suggested are precluded by patient confidentiality laws, the textshould discuss the obstacles to such studies.

Response: The gathering of community- and healthcare provider-specific health concerns and datais conducted by ATSDR throughout the PHA process. Health concerns and sources of data wereaddressed in the ATSDR hazard evaluation process including through personal and groupinterviews and discussions. Community health concerns are addressed beginning on page 30 of thePHA report. ATSDR will seek to coordinate with EL RAEHA for the recommendations listed in thePHA report, when appropriate.

ATSDR conducts health research at sites when exposures and other key factors are met. There aremany sites designated a public health threat where ATSDR does not conduct follow up research,most important is the rapid reduction or elimination of exposures from a public health perspective.ATSDR is conducting health effects research for these contaminants of concern at sites wheremeasured concentrations in drinking water were higher than those found and modeled for the NRAPSite (Camp LeJeune, N.C.; ATSDR TCE Sub registry). Current and future findings of these studieswill help to identify health risks relevant to persons exposed at the NRAP Site. ATSDR willdisseminate this information through final reports, published papers and the ATSDR website.

The commenter suggests the collection and analysis of more specific information including personaland healthcare data (hospitals, etc.); the comment is vague as to what type of specific information. According to ATSDR policy and guidelines, systematic data collection requires the use of astandardized questionnaire and an adequate number of participants in order to create generalizablefindings. The commenter should understand that this data collection process meets the definition andintent of a federal health study. Moreover, ATSDR does not recommend a health study based on theconsideration of all available information that was used for the PHA report. Lastly, new federalprivacy laws (HIPAA) may influence some local healthcare organizations from sharing data withATSDR. For HIPAA, compliance with federal law is the responsibility of the organization that servesas the repository of the data (i.e., hospital and doctor's office). Because the PHA report provideda rationale for not conducting a health study (no exposure data prior to 1989, magnitude ofexposures, when exposure stopped, limited population size), ATSDR concludes it would beinappropriate to elaborate on the federal privacy laws in the PHA report. This would create possibleconfusion for the reader.

Comment: Conclusions, 1st bullet: It is stated in the conclusion of the report that "past exposureto contaminants in drinking water posed a public health hazard." It is also stated in the conclusionsthat "because groundwater data are not available prior to 1989, the frequency, duration, andconcentrations of contaminants that individuals may have been exposed to in drinking water areunknown." Given that there is great uncertainty regarding the exposure concentrations that may havebeen subject to from contaminants in drinking water, it seems more appropriate to conclude,"Contaminants in drinking water may have posed a public health hazard."

Response: The ATSDR hazard categories include the following: 1) urgent public health hazard,2) public health hazard, 3) indeterminate public health hazard, 4) no apparent public health hazard,and 5) no public health hazard. ATSDR does not have a hazard category that refers to contaminantsthat may have posed a public health hazard. Based on the available information and ATSDR'shazard categories, it was necessary for the NRAP Site to be categorized as a public health hazard. It should be noted that the text of the PHA discusses the data limitations and other uncertaintiesassociated with the evaluation.

Comment: Appendix C, Page 54, Inhalation of Contaminants Present in Drinking Water: Toevaluate the potential exposure due to inhalation of contaminants in drinking water during showeringor bathing, ATSDR assumed that this exposure dose would be equal to ingesting 1 liter per day. TheATSDR Public Health Assessment Guidance Manual suggests that the appropriate method is toestimate the dose from contaminant concentrations in the air and inhalation rates. NMED suggeststhat the rationale for assuming the additional risk due to inhalation of PCE and TCE vapors duringshowering can be approximated as additional ingestion of drinking water be stated in Appendix C.

Response: ATSDR assumed exposure via showering to be half the dose estimated from ingestionof drinking water (equal to exposure to 1 liter of water per day). EPA Region 4 SupplementalGuidance to the Risk Assessment Guidance for Superfund, November 1995, states that it should beassumed that showering exposure is equivalent to exposure from ingestion of two liters ofcontaminated water per day. This value accounts for both inhalation and dermal exposure duringshowering. The guidance is based on the recommendations of The Risk Assessment Forum(Exposure to VOCs During Showering, Memorandum from Dorothy E. Patton, Chair, RiskAssessment Forum to F. Henry Habicht, II, July 10, 1991). Because ATSDR's evaluation estimateddermal exposure during showering separately, exposures associated with inhalation duringshowering were assumed to equal to 1 liter per day (or half the ingestion rate). A reference for this information has been included in the text of Appendix C.


APPENDIX G: ATSDR GLOSSARY OF ENVIRONMENTAL HEALTH TERMS

The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public health agencywith headquarters in Atlanta, Georgia, and 10 regional offices in the United States. ATSDR'smission is to serve the public by using the best science, taking responsive public health actions, andproviding trusted health information to prevent harmful exposures and diseases related to toxicsubstances. ATSDR is not a regulatory agency, unlike the U.S. Environmental Protection Agency(EPA), which is the federal agency that develops and enforces environmental laws to protect theenvironment and human health.

This glossary defines words used by ATSDR in communications with the public. It is not a completedictionary of environmental health terms. If you have questions or comments, call ATSDR's toll-free telephone number, 1-888-42-ATSDR (1-888-422-8737).

Absorption:
The process of taking in. For a person or animal, absorption is the process of a substance getting intothe body through the eyes, skin, stomach, intestines, or lungs.


Acute:
Occurring over a short time [compare with chronic].


Acute exposure:
Contact with a substance that occurs once or for only a short time (up to 14 days) [compare with intermediate duration exposure and chronic exposure].


Additive effect:
A biologic response to exposure to multiple substances that equals the sum of responses of all theindividual substances added together [compare with antagonistic effect and synergistic effect].


Adverse health effect:
A change in body function or cell structure that might lead to disease or health problems.


Aerobic:
Requiring oxygen [compare with anaerobic].


Ambient:
Surrounding (for example, ambient air).


Anaerobic:
Requiring the absence of oxygen [compare with aerobic].


Analyte:
A substance measured in the laboratory. A chemical for which a sample (such as water, air, orblood) is tested in a laboratory. For example, if the analyte is mercury, the laboratory test willdetermine the amount of mercury in the sample.


Analytic epidemiologic study:
A study that evaluates the association between exposure to hazardous substances and disease bytesting scientific hypotheses.


Antagonistic effect:
A biologic response to exposure to multiple substances that is less than would be expected if the known effects of the individual substances were added together [compare with additive effectand synergistic effect].


Background level:
An average or expected amount of a substance or radioactive material in a specific environment, ortypical amounts of substances that occur naturally in an environment.


Biodegradation:
Decomposition or breakdown of a substance through the action of microorganisms (such as bacteriaor fungi) or other natural physical processes (such as sunlight).


Biologic indicators of exposure study:
A study that uses (a) biomedical testing or (b) the measurement of a substance [an analyte], itsmetabolite, or another marker of exposure in human body fluids or tissues to confirm humanexposure to a hazardous substance [also see exposure investigation].


Biologic monitoring :
Measuring hazardous substances in biologic materials (such as blood, hair, urine, or breath) todetermine whether exposure has occurred. A blood test for lead is an example of biologicmonitoring.


Biologic uptake:
The transfer of substances from the environment to plants, animals, and humans.


Biomedical testing:
Testing of persons to find out whether a change in a body function might have occurred because ofexposure to a hazardous substance.


Biota:
Plants and animals in an environment. Some of these plants and animals might be sources of food,clothing, or medicines for people.


Body burden:
The total amount of a substance in the body. Some substances build up in the body because they arestored in fat or bone or because they leave the body very slowly.


CAP:
See Community Assistance Panel.


Cancer:
Any one of a group of diseases that occurs when cells in the body become abnormal and grow ormultiply out of control.


Cancer risk:
A theoretical risk of for getting cancer if exposed to a substance every day for 70 years (a lifetimeexposure). The true risk might be lower.


Carcinogen:
A substance that causes cancer.


Case study:
A medical or epidemiologic evaluation of one person or a small group of people to gatherinformation about specific health conditions and past exposures.


Case-control study:
A study that compares exposures of people who have a disease or condition (cases) with people whodo not have the disease or condition (controls). Exposures that are more common among the casesmay be considered as possible risk factors for the disease.


CAS registry number:
A unique number assigned to a substance or mixture by the American Chemical Society AbstractsService.


Central nervous system:
The part of the nervous system that consists of the brain and the spinal cord.


CERCLA:
[see Comprehensive Environmental Response, Compensation, and Liability Act of1980]


Chronic:
Occurring over a long time (more than 1 year) [compare with acute].


Chronic exposure:
Contact with a substance that occurs over a long time (more than 1 year) [compare with acuteexposure and intermediate duration exposure].


Cluster investigation:
A review of an unusual number, real or perceived, of health events (for example, reports of cancer)grouped together in time and location. Cluster investigations are designed to confirm case reports;determine whether they represent an unusual disease occurrence; and, if possible, explore possiblecauses and contributing environmental factors.


Community Assistance Panel (CAP):
A group of people, from a community and from health and environmental agencies, who work withATSDR to resolve issues and problems related to hazardous substances in the community. CAPmembers work with ATSDR to gather and review community health concerns, provide informationon how people might have been or might now be exposed to hazardous substances, and informATSDR on ways to involve the community in its activities.


Comparison value (CV):
Calculated concentration of a substance in air, water, food, or soil that is unlikely to cause harmful(adverse) health effects in exposed people. The CV is used as a screening level during the publichealth assessment process. Substances found in amounts greater than their CVs might be selectedfor further evaluation in the public health assessment process.


Completed exposure pathway:
[see exposure pathway].


Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA):
CERCLA, also known as Superfund, is the federal law that concerns the removal or cleanup ofhazardous substances in the environment and at hazardous waste sites. ATSDR, which was createdby CERCLA, is responsible for assessing health issues and supporting public health activities relatedto hazardous waste sites or other environmental releases of hazardous substances.


Concentration:
The amount of a substance present in a certain amount of soil, water, air, food, blood, hair, urine,breath, or any other media.


Contaminant:
A substance that is either present in an environment where it does not belong or is present at levelsthat might cause harmful (adverse) health effects.


Delayed health effect:
A disease or injury that happens as a result of exposures that might have occurred in the past.


Dermal:
Referring to the skin. For example, dermal absorption means passing through the skin.


Dermal contact:
Contact with (touching) the skin [see route of exposure].


Descriptive epidemiology:
The study of the amount and distribution of a disease in a specified population by person, place, andtime.


Detection limit:
The lowest concentration of a chemical that can reliably be distinguished from a zero concentration.


Disease prevention:
Measures used to prevent a disease or reduce its severity.


Disease registry:
A system of ongoing registration of all cases of a particular disease or health condition in a definedpopulation.


DOD:
United States Department of Defense.


DOE:
United States Department of Energy.


Dose (for chemicals that are not radioactive):
The amount of a substance to which a person is exposed over some time period. Dose is ameasurement of exposure. Dose is often expressed as milligram (amount) per kilogram (a measureof body weight) per day (a measure of time) when people eat or drink contaminated water, food, orsoil. In general, the greater the dose, the greater the likelihood of an effect. An "exposure dose" ishow much of a substance is encountered in the environment. An "absorbed dose" is the amount ofa substance that actually got into the body through the eyes, skin, stomach, intestines, or lungs.


Dose (for radioactive chemicals):
The radiation dose is the amount of energy from radiation that is actually absorbed by the body. Thisis not the same as measurements of the amount of radiation in the environment.


Dose-response relationship:
The relationship between the amount of exposure [dose] to a substance and the resulting changesin body function or health (response).


Environmental media:
Soil, water, air, biota (plants and animals), or any other parts of the environment that can containcontaminants.


Environmental media and transport mechanism:
Environmental media include water, air, soil, and biota (plants and animals). Transport mechanismsmove contaminants from the source to points where human exposure can occur. The environmentalmedia and transport mechanism is the second part of an exposure pathway.


EPA:
United States Environmental Protection Agency.


Epidemiologic surveillance:
The ongoing, systematic collection, analysis, and interpretation of health data. This activity alsoinvolves timely dissemination of the data and use for public health programs.


Epidemiology:
The study of the distribution and determinants of disease or health status in a population; the studyof the occurrence and causes of health effects in humans.


Exposure:
Contact with a substance by swallowing, breathing, or touching the skin or eyes. Exposure may beshort-term [acute exposure], of intermediate duration, or long-term [chronic exposure].


Exposure assessment :
The process of finding out how people come into contact with a hazardous substance, how often andfor how long they are in contact with the substance, and how much of the substance they are incontact with.


Exposure-dose reconstruction:
A method of estimating the amount of people's past exposure to hazardous substances. Computerand approximation methods are used when past information is limited, not available, or missing.


Exposure investigation:
The collection and analysis of site-specific information and biologic tests (when appropriate) todetermine whether people have been exposed to hazardous substances.


Exposure pathway:
The route a substance takes from its source (where it began) to its end point (where it ends), and how people can come into contact with (or get exposed to) it. An exposure pathway has five parts: a source of contamination (such as an abandoned business); an environmental media and transport mechanism (such as movement through groundwater); a point of exposure (such as a private well); a route of exposure (eating, drinking, breathing, or touching), and a receptor population (people potentially or actually exposed). When all five parts are present, the exposure pathway is termed a completed exposure pathway.


Exposure registry:
A system of ongoing followup of people who have had documented environmental exposures.


Feasibility study:
A study by EPA to determine the best way to clean up environmental contamination. A number offactors are considered, including health risk, costs, and what methods will work well.


Geographic information system (GIS) :
A mapping system that uses computers to collect, store, manipulate, analyze, and display data. Forexample, GIS can show the concentration of a contaminant within a community in relation to pointsof reference such as streets and homes.


Grand rounds:
Training sessions for physicians and other health care providers about health topics.


Groundwater:
Water beneath the earth's surface in the spaces between soil particles and between rock surfaces[compare with surface water].


Half-life (t):
The time it takes for half the original amount of a substance to disappear. In the environment, thehalf-life is the time it takes for half the original amount of a substance to disappear when it ischanged to another chemical by bacteria, fungi, sunlight, or other chemical processes. In the humanbody, the half-life is the time it takes for half the original amount of the substance to disappear, eitherby being changed to another substance or by leaving the body. In the case of radioactive material,the half life is the amount of time necessary for one half the initial number of radioactive atoms tochange or transform into another atom (that is normally not radioactive). After two half lives, 25%of the original number of radioactive atoms remain.


Hazard:
A source of potential harm from past, current, or future exposures.


Hazardous Substance Release and Health Effects Database (HazDat):
The scientific and administrative database system developed by ATSDR to manage data collection,retrieval, and analysis of site-specific information on hazardous substances, community healthconcerns, and public health activities.


Hazardous waste:
Potentially harmful substances that have been released or discarded into the environment.


Health consultation:
A review of available information or collection of new data to respond to a specific health questionor request for information about a potential environmental hazard. Health consultations are focusedon a specific exposure issue. Health consultations are therefore more limited than a public healthassessment, which reviews the exposure potential of each pathway and chemical [compare withpublic health assessment].


Health education:
Programs designed with a community to help it know about health risks and how to reduce theserisks.


Health investigation:
The collection and evaluation of information about the health of community residents. Thisinformation is used to describe or count the occurrence of a disease, symptom, or clinical measureand to estimate the possible association between the occurrence and exposure to hazardoussubstances.


Health promotion:
The process of enabling people to increase control over, and to improve, their health.


Health statistics review:
The analysis of existing health information (i.e., from death certificates, birth defects registries, andcancer registries) to determine if there is excess disease in a specific population, geographic area,and time period. A health statistics review is a descriptive epidemiologic study.


Indeterminate public health hazard:
The category used in ATSDR's public health assessment documents when a professional judgmentabout the level of health hazard cannot be made because information critical to such a decision islacking.


Incidence:
The number of new cases of disease in a defined population over a specific time period [contrastwith prevalence].


Ingestion:
The act of swallowing something through eating, drinking, or mouthing objects. A hazardoussubstance can enter the body this way [see route of exposure].


Inhalation:
The act of breathing. A hazardous substance can enter the body this way [see route of exposure].


Intermediate duration exposure:
Contact with a substance that occurs for more than 14 days and less than a year [compare with acuteexposure and chronic exposure].


In vitro:
In an artificial environment outside a living organism or body. For example, some toxicity testingis done on cell cultures or slices of tissue grown in the laboratory, rather than on a living animal[compare with in vivo].


In vivo:
Within a living organism or body. For example, some toxicity testing is done on whole animals,such as rats or mice [compare with in vitro].


Lowest-observed-adverse-effect level (LOAEL):
The lowest tested dose of a substance that has been reported to cause harmful (adverse) health effectsin people or animals.


Medical monitoring:
A set of medical tests and physical exams specifically designed to evaluate whether an individual'sexposure could negatively affect that person's health.


Metabolism:
The conversion or breakdown of a substance from one form to another by a living organism.


Metabolite:
Any product of metabolism.


mg/kg:
Milligram per kilogram.


mg/cm2:
Milligram per square centimeter (of a surface).


mg/m3:
Milligram per cubic meter; a measure of the concentration of a chemical in a known volume (a cubicmeter) of air, soil, or water.


Migration:
Moving from one location to another.


Minimal risk level (MRL):
An ATSDR estimate of daily human exposure to a hazardous substance at or below which thatsubstance is unlikely to pose a measurable risk of harmful (adverse), noncancerous effects. MRLsare calculated for a route of exposure (inhalation or oral) over a specified time period (acute,intermediate, or chronic). MRLs should not be used as predictors of harmful (adverse) health effects[see reference dose].


Morbidity:
State of being ill or diseased. Morbidity is the occurrence of a disease or condition that alters healthand quality of life.


Mortality:
Death. Usually the cause (a specific disease, condition, or injury) is stated.


Mutagen:
A substance that causes mutations (genetic damage).


Mutation:
A change (damage) to the DNA, genes, or chromosomes of living organisms.


National Priorities List for Uncontrolled Hazardous Waste Sites (National Priorities List orNPL):
EPA's list of the most serious uncontrolled or abandoned hazardous waste sites in the United States. The NPL is updated on a regular basis.


No apparent public health hazard:
A category used in ATSDR's public health assessments for sites where human exposure tocontaminated media might be occurring, might have occurred in the past, or might occur in thefuture, but where the exposure is not expected to cause any harmful health effects.


No-observed-adverse-effect level (NOAEL):
The highest tested dose of a substance that has been reported to have no harmful (adverse) healtheffects on people or animals.


No public health hazard:
A category used in ATSDR's public health assessment documents for sites where people have neverand will never come into contact with harmful amounts of site-related substances.


NPL:
[see National Priorities List for Uncontrolled Hazardous Waste Sites]


Physiologically based pharmacokinetic model (PBPK model):
A computer model that describes what happens to a chemical in the body. This model describes howthe chemical gets into the body, where it goes in the body, how it is changed by the body, and howit leaves the body.


Pica:
A craving to eat nonfood items, such as dirt, paint chips, and clay. Some children exhibit pica-related behavior.


Plume:
A volume of a substance that moves from its source to places farther away from the source. Plumescan be described by the volume of air or water they occupy and the direction they move. Forexample, a plume can be a column of smoke from a chimney or a substance moving withgroundwater.


Point of exposure:
The place where someone can come into contact with a substance present in the environment [seeexposure pathway].


Population:
A group or number of people living within a specified area or sharing similar characteristics (suchas occupation or age).


Potentially responsible party (PRP):
A company, government, or person legally responsible for cleaning up the pollution at a hazardouswaste site under Superfund. There may be more than one PRP for a particular site.


ppb:
Parts per billion.


ppm:
Parts per million.


Prevalence :
The number of existing disease cases in a defined population during a specific time period [contrastwith incidence].


Prevalence survey:
The measure of the current level of disease(s) or symptoms and exposures through a questionnairethat collects self-reported information from a defined population.


Prevention:
Actions that reduce exposure or other risks, keep people from getting sick, or keep disease fromgetting worse.


Public comment period:
An opportunity for the public to comment on agency findings or proposed activities contained indraft reports or documents. The public comment period is a limited time period during whichcomments will be accepted.


Public availability session:
An informal, drop-by meeting at which community members can meet one-on-one with ATSDRstaff members to discuss health and site-related concerns.


Public health action:
A list of steps to protect public health.


Public health advisory:
A statement made by ATSDR to EPA or a state regulatory agency that a release of hazardoussubstances poses an immediate threat to human health. The advisory includes recommendedmeasures to reduce exposure and reduce the threat to human health.


Public health assessment (PHA):
An ATSDR document that examines hazardous substances, health outcomes, and communityconcerns at a hazardous waste site to determine whether people could be harmed from coming intocontact with those substances. The PHA also lists actions that need to be taken to protect publichealth [compare with health consultation].


Public health hazard:
A category used in ATSDR's public health assessments for sites that pose a public health hazardbecause of long-term exposures (greater than 1 year) to sufficiently high levels of hazardoussubstances or radionuclides that could result in harmful health effects.


Public health hazard categories:
Public health hazard categories are statements about whether people could be harmed by conditionspresent at the site in the past, present, or future. One or more hazard categories might be appropriatefor each site. The five public health hazard categories are no public health hazard, no apparentpublic health hazard, indeterminate public health hazard, public health hazard, and urgentpublic health hazard.


Public health statement:
The first chapter of an ATSDR toxicological profile. The public health statement is a summarywritten in words that are easy to understand. The public health statement explains how people mightbe exposed to a specific substance and describes the known health effects of that substance.


Public meeting:
A public forum with community members for communication about a site.


Radioisotope:
An unstable or radioactive isotope (form) of an element that can change into another element bygiving off radiation.


Radionuclide:
Any radioactive isotope (form) of any element.


RCRA:
[See Resource Conservation and Recovery Act (1976, 1984)]


Receptor population:
People who could come into contact with hazardous substances [see exposure pathway].


Reference dose (RfD):
An EPA estimate, with uncertainty or safety factors built in, of the daily lifetime dose of a substancethat is unlikely to cause harm in humans.


Registry :
A systematic collection of information on persons exposed to a specific substance or having specificdiseases [see exposure registry and disease registry].


Remedial Investigation:
The CERCLA process of determining the type and extent of hazardous material contamination ata site.


Resource Conservation and Recovery Act (1976, 1984) (RCRA):
This Act regulates management and disposal of hazardous wastes currently generated, treated, stored,disposed of, or distributed.


RFA:
RCRA Facility Assessment. An assessment required by RCRA to identify potential and actualreleases of hazardous chemicals.


RfD:
See reference dose.


Risk:
The probability that something will cause injury or harm.


Risk reduction:
Actions that can decrease the likelihood that individuals, groups, or communities will experiencedisease or other health conditions.


Risk communication:
The exchange of information to increase understanding of health risks.


Route of exposure:
The way people come into contact with a hazardous substance. Three routes of exposure arebreathing [inhalation], eating or drinking [ingestion], or contact with the skin [dermal contact].


Safety factor:
[see uncertainty factor]


SARA:
[see Superfund Amendments and Reauthorization Act]


Sample:
A portion or piece of a whole. A selected subset of a population or subset of whatever is beingstudied. For example, in a study of people the sample is a number of people chosen from a largerpopulation [see population]. An environmental sample (for example, a small amount of soil orwater) might be collected to measure contamination in the environment at a specific location.


Sample size:
The number of units chosen from a population or environment.


Solvent:
A liquid capable of dissolving or dispersing another substance (for example, acetone or mineralspirits).


Source of contamination:
The place where a hazardous substance comes from, such as a landfill, waste pond, incinerator,storage tank, or drum. A source of contamination is the first part of an exposure pathway.


Special populations:
People who might be more sensitive or susceptible to exposure to hazardous substances because offactors such as age, occupation, sex, or behaviors (for example, cigarette smoking). Children,pregnant women, and older people are often considered special populations.


Stakeholder:
A person, group, or community who has an interest in activities at a hazardous waste site.


Statistics :
A branch of mathematics that deals with collecting, reviewing, summarizing, and interpreting dataor information. Statistics are used to determine whether differences between study groups aremeaningful.


Substance:
A chemical.


Substance-specific applied research:
A program of research designed to fill important data needs for specific hazardous substancesidentified in ATSDR's toxicological profiles. Filling these data needs would allow more accurateassessment of human risks from specific substances contaminating the environment. This researchmight include human studies or laboratory experiments to determine health effects resulting fromexposure to a given hazardous substance.


Superfund Amendments and Reauthorization Act (SARA):
In 1986, SARA amended CERCLA and expanded the health-related responsibilities of ATSDR. CERCLA and SARA direct ATSDR to look into the health effects from substance exposures athazardous waste sites and to perform activities including health education, health studies,surveillance, health consultations, and toxicological profiles.


Surface water:
Water on the surface of the earth, such as in lakes, rivers, streams, ponds, and springs [compare withgroundwater].


Surveillance:
[see epidemiologic surveillance]


Survey:
A systematic collection of information or data. A survey can be conducted to collect informationfrom a group of people or from the environment. Surveys of a group of people can be conducted bytelephone, by mail, or in person. Some surveys are done by interviewing a group of people [seeprevalence survey].


Synergistic effect:
A biologic response to multiple substances where one substance worsens the effect of anothersubstance. The combined effect of the substances acting together is greater than the sum of theeffects of the substances acting by themselves [see additive effect and antagonistic effect].


Teratogen :
A substance that causes defects in development between conception and birth. A teratogen is asubstance that causes a structural or functional birth defect.


Toxic agent:
Chemical or physical (for example, radiation, heat, cold, microwaves) agents which, under certaincircumstances of exposure, can cause harmful effects to living organisms.


Toxicological profile:
An ATSDR document that examines, summarizes, and interprets information about a hazardoussubstance to determine harmful levels of exposure and associated health effects. A toxicologicalprofile also identifies significant gaps in knowledge on the substance and describes areas wherefurther research is needed.


Toxicology:
The study of the harmful effects of substances on humans or animals.


Tumor:
An abnormal mass of tissue that results from excessive cell division that is uncontrolled andprogressive. Tumors perform no useful body function. Tumors can be either benign (not cancer)or malignant (cancer).


Uncertainty factor:
Mathematical adjustments for reasons of safety when knowledge is incomplete. For example, factorsused in the calculation of doses that are not harmful (adverse) to people. These factors are appliedto the lowest-observed-adverse-effect-level (LOAEL) or the no-observed-adverse-effect-level(NOAEL) to derive a minimal risk level (MRL). Uncertainty factors are used to account forvariations in people's sensitivity, for differences between animals and humans, and for differencesbetween a LOAEL and a NOAEL. Scientists use uncertainty factors when they have some, but notall, the information from animal or human studies to decide whether an exposure will cause harmto people [also sometimes called a safety factor].


Urgent public health hazard:
A category used in ATSDR's public health assessments for sites where short-term exposures (lessthan 1 year) to hazardous substances or conditions could result in harmful health effects that requirerapid intervention.


Volatile organic compounds (VOCs):
Organic compounds that evaporate readily into the air. VOCs include substances such as benzene,toluene, methylene chloride, and methyl chloroform.

9 Research Environmental Engineer, Division of Health Assessment and Consultation, Agency for Toxic Substances and Disease Registry, 1600 Clifton Road, Mail Stop E-32, Atlanta, Georgia 30333. Email: mmaslia@cdc.gov.



Table of Contents

  
 
USA.gov: 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

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #