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 µg/L was used for the ATSDR simulations using ACTS. The value of 30,000 µg/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 µg/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 µg/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 µg/L with lower and upper 95% confidence limits of 1,639 µg/L and 4,620 µg/L, respectively (Faye 2002). Comparing this to the solubility of PCE in groundwater (150,000 µg/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 µg/L; 1,639 µg/L; and 4,620 µg/L–the 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 µg/L. (This represents 1% of the solubility limit for PCE of 150 mg/L–see 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 µg/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 µg/L (using a source concentration of 1,639 µg/L). The simulated concentration of 0.65 µg/L, when compared to a concentration of 102 µg/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 µg/L) is significantly less than 102 µg/L–the 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 µg/L. These simulated concentrations are substantially less than the maximum PCE concentration of 102 µg/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 µg/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 µg/L for the Shallow Aquifer (DE&S 2001b), analyses using CXTFIT suggest a significantly lower source concentration of 3,129 µg/L with lower and upper 95% confidence limits of 1,639 and 4,620 µg/L, respectively (Faye 2002). These lower values are also consistent with an accepted hypothesis that in order to neglect density effects associated with DNAPL compounds–such as PCE–for model simulation, aqueous phase concentrations should be less than 5% of the compounds solubility limit–7,500 µg/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 µg/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 µg/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 groundwater flow systems." CRC critical reviews in environmental control, 9(2):97-156.
Aral, M. M. (1998). "Analytical contaminant transport analysis system (ACTS)." Multimedia Environmental Simulations Laboratory Report MESL-02-98, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia.
ATSDR. (1997). "Toxicological profile for tetrachloroethylene (PERC)." Agency for Toxic Substances and Disease 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 demonstrate intrinsic 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, New York.
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." Easter Research Group report, prepared for the Division of Health Assessment and Consultation, Agency for 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 in aquifers." 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-difference groundwater flow model." Techniques of Water-Resources Investigations of the United States Geological Survey, Book 6, Chapter A1, Reston, Virginia.
Pankow, J. F., and Cherry J. A. (1996). Dense chlorinated solvents and other DNAPLs in groundwater: 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 parameters from laboratory or field tracer experiments." Report No. 137, U.S. Salinity Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Riverside, California.
Zheng, C., and Wang, P. P. 1999. "MT3DMS, a modular three-dimensional multispecies transport model for simulation 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 (µL) | 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 (µL/µT) | 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 optimized value being 3,129 µg/L and lower and upper 95% confidence limits of 1,639 µg/L and 4,620 µg/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 |
|
| Longitudinal dispersivity (µL) | 260 ft | DE&S (2001b) |
| Longitudinal dispersion coefficient (Dx) | 21 ft2/d | Dx = µLV |
| Lateral dispersion coefficient (Dy) | 0.21 ft2/d |
|
| Infiltration (I) | 0.4 in/yr | DE&S (2001b) |
| Retardation coefficient for PCE (R) | 1.78 |
|
| 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 (µg/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 (µg/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 of measurement (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).
Figure 1. Diagram showing human exposure assessment and modeling continuum
APPENDIX E: LEVELS OF PUBLIC HEALTH HAZARD
ATSDR categorizes exposure pathways at hazardous waste sites according to their level of public health hazard to indicate whether people could be harmed by exposure pathways and site conditions. The categories 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 and the 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 for those drinking from this water system, even if the kidney cancer rates for Rio Arriba County as a whole are not elevated.
Response: The health literature indicates that human organs most susceptible to the effects of tetrachloroethylene (PCE) and, to a lesser extent trichloroethylene (TCE) are the nervous system and 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 chemical exposures. Because ATSDR is not a source/repository of state level health data, ATSDR requests data 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 level needed (city level and smaller), the state was unable to generate this data. As a suggestion, the state cancer registry program, state epidemiologist of local health director could be contacted for discussions regarding identifying funding for specific cancer/health studies (i.e., kidney cancer in men). It should be noted that the findings of the PHA did not include an increased risk for kidney effects, based on the exposures associated with the NRAP Site.
Comment: We would like to see more thorough investigation of cancer in Española with special attention to rare and aggressive types of cancer. We would also like to see an investigation of age specific cancer rates.
Response: As previously discussed, state data was not available at the level of detail needed to conduct an appropriate analysis. People who are interested in the availability of age specific cancer rates or information may contact the New Mexico Office of Epidemiology, P.O. Box 26110, Santa Fe. NM 87502-6110 or call 505-827-0006 or 1-800-432-4404. Information about cancer rates and risk 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 contaminants may be one of many risk factors for cancer of the kidney; other risk factors include cigarette smoking, abuse of analgesics, phenacetin-containing analgesics/drugs, relative high weight or obesity, and possibly industrial chemicals/fibers. Should citizens have concern for certain types or forms of rare aggressive cancers, citizens should contact their state epidemiologist as a starting point. By definition, rare cancer is difficult to study due to their rare occurrence, and thus pose scientific challenges for statistical stability and personal recall of exposures. In addition, the individuals potentially exposed to the highest concentrations of contaminants were the residents living closest to the Bond and Jemez wells due to the likelihood of less dilution with the water from the distribution system at these households. These individuals represent an even smaller subset of the population which poses difficulties in gaining statistically significant information.
Comment: We would like to see ATSDR conduct interviews with clinicians regarding cancer patients who reside in Española, and if possible, interviews with community residents as well.
Response: Interviews with clinicians, patients and/or community have far reaching implications for 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 ATSDR activity of systematic interviewing for health effects would have to be approved and cleared under a 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 caused his/her cancer. ATSDR does not provide individual medical consultations for healthcare decision making, 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 no mention 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 several neurological effects. Long-term exposure to high concentrations of manganese, typically in the workplace, has been associated with a condition referred to as "manganism." The symptoms associated with manganism are similar to those experienced by individuals with Parkinson's disease. These symptoms include mental and emotional disturbances, muscle weakness, speech impairments, tremor, and other neurological effects.
Due to its chemical properties, manganese present in water is not expected to volatilize into air or to result in significant exposures through inhalation. Therefore, inhalation exposure to manganese in 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 please explain in the report how many total private wells there are and why these were chosen? Is it possible that other wells are contaminated, especially in the deeper zones/aquifers, but have not been tested?
Response: NMED has identified 18 water wells within the 1,000-foot radii of the Bond and Jemez wells. Eleven of these wells are no longer in use, six are used for irrigation, and one is being used for 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 in strategically 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 these wells have been sampled. NMED is unaware of any other private wells being used in the area that may be impacted by groundwater contamination.
Comment: Page 44 states "remedial operations began in 1995 and were terminated after about a year without completing remediation". Can you explain in the document why this was not completed?
Response: Remediation of the petroleum hydrocarbon sites was terminated when the air sparging systems ceased to be efficient. Samples collected from the emissions of these units indicated that after 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 first discovered in 1989 during sampling initiated for two municipal supply wells (Bond and Jemez wells)." Were these wells ever tested for manganese? If so, what were the concentrations of this constituent? If not, why not?
Response: The Bond and Jemez wells were sampled for manganese in 1977, 1989, and 1990. The 1977 and 1989 samples were below the detection limit of 0.05 mg/l. In 1990, the levels detected were 0.03 mg/l (Jemez well) and >0.01 mg/l (Bond well). The maximum level of manganese detected in the Jemez well in 1990 is greater than 10 times below ATSDR's comparison value for drinking water. 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 to this concern in the PHA.
Comment: Page 6, 3rd bullet. Text indicates that "repairs have been made to the Norge Town facility to efficiently prohibit future contaminant releases to groundwater. In addition, proposed remediation efforts at the site are considered adequately protective of public health." What repairs were 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 efforts would be adequately protective of public health.
Response: The lint trap has been removed from service and filled with sand. The piping that previously transported effluent from the Norge Town facility to the city sewer system has been removed 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 (also referred to as DNAPL), which is undissolved contamination associated with the site. This process will be accomplished through the use of surfactant and/or co-solvent treatment. The second phase consists of remediating the "hot spots" and the down-gradient, dissolved-phase plume in the shallow zone through enhanced in-situ bioremediation. The third phase also consists of treatment in the deep zone through enhanced in-situ bioremediation. The fourth phase consists of remediating the soils with the use of soil vapor extraction to remediate the soils in areas affected adjacent to the source area once the DNAPL is treated. The fourth phase also consists of sampling throughout the site area to ensure effectiveness of the remedy and protectiveness of human health. Greater detail on 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 public water supply wells that are currently in use are not located in the impacted groundwater area and undergo periodic sampling to ensure that drinking water meets the requirements of EPA's Safe Drinking Water Act. Proposed cleanup efforts for the site are expected to remove the groundwater contamination from the area. Periodic sampling of the impacted groundwater area will be conducted to monitor the effectiveness of the proposed cleanup actions.
Comment: Page 6, 2nd bullet after ATSDR recommendations. Recommendation that twelve private drinking water wells should be periodically monitored by NMED "until cleanup measures are completed to determine whether these wells remain unimpacted from local groundwater contamination. What are the parameters for successful cleanup? Depending on the groundwater flow rate, it would seem prudent to monitor for an appropriate period of time after the cleanup is completed to ensure that contaminants are not still migrating and cleanup was successful. The same is 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 for the site. According to the ROD, groundwater will undergo remediation until contaminant concentrations are below the Maximum Contaminant Levels for PCE and TCE of 5 µg/L.
Based on the available groundwater data and the proposed cleanup activities, the 12 private drinking water wells located directly adjacent to Santa Clara Pueblo Trust Lands have not been impacted and are not expected to be impacted in the future. Additional sampling of the twelve private wells located directly adjacent to Santa Clara Pueblo Trust Lands to ensure that they remain unimpacted during remediation activities was recommended by ATSDR because these wells are currently being used for drinking water purposes. As discussed in this PHA, limited exposure is expected to result from exposure to water from non-drinking water wells. As part of the cleanup activities, monitoring wells located in the contaminant plume area and along the perimeter of the plume will be monitored periodically during the remediation efforts and for years following the completion of cleanup activities. Based on the available information on groundwater conditions and the evaluations in this PHA, the proposed monitoring and ATSDR's recommendations are considered protective of public health.
Comment: Page 7, last sentence of the page. Text indicates that the "dissolved-phase groundwater plume 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 that this plume does not migrate to other drinking water supply wells and thus, cause additional potential public 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 the Norge Town facility in comparison to the dissolved-phase groundwater plume that extends from the Norge Town facility to within 10 feet of the Rio Grande. As documented in the ROD for the NRAP Site, the DNAPL plume will be treated with surfactants and/or co-solvent treatment. Cleanup efforts for 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 potentially affected 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 Rio Grande. Based on data provided to date, no other private or public water supply wells in the vicinity of the plume have been affected. The municipal supply wells currently being used by the City of Española are up-gradient of the plume and should not be affected. In addition, these wells are periodically monitored in accordance with the Safe Drinking Water Act to ensure that drinking water supplied to Española residents is safe to drink.
Comment: Page 11, 2nd to the last paragraph on the page. Text indicates the Las Cumbres Learning Services, Inc. is located near the eastern boundary of the shallow PCE plume. What is the drinking water 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 drinking water from the City of Española public water supply, which is routinely sampled for compliance with EPA's Safe Drinking Water Act requirements.
Comment: Page 12, Evaluation Process. 1st paragraph, last sentence. Text indicates that "it should also be noted that other contaminants may be evaluated further if concerns are received from the community regarding the presence of the particular contaminant(s)." I am concerned about the cumulative chronic effects from the public being exposed to both a BTEX plume and the PCE plume. 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 not been detected in the Bond or Jemez wells. As stated in a previous comment, there is limited information available that indicates that the NRAP and BTEX plumes are co-mingled. Even though groundwater contamination exists from the BTEX plume, these contaminants have not been found in the Bond, Jemez, or other City of Española municipal drinking water wells. Therefore, it is unlikely that residents have been exposed to BTEX contamination via ingestion. As noted in a previous response, ATSDR reviewed manganese data from the Bond and Jemez wells from 1977 through 1990 and found that levels were well below comparison values and therefore would be unlikely to cause adverse health effects.
Comment: Page 12, last paragraph on the page that continues on page 13. Text indicates that "In the event that the calculated, site-specific exposure dose for a chemical is greater than the established health guideline, it is then compared to the exposure doses from individual studies documented in the scientific literature that have reported health effects. Estimated demographics for this site indicated the presence of 467 children ages 6 and younger and 573 adults ages 65 and older. As you know these populations are more susceptible to potential health effects from exposure than standard adult populations. However, it is unclear whether and how they have been figured into the exposure pathways. It is also unclear whether chronic effects were taken under consideration for the exposure pathways. 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 an industrial type scenario, which may not be relevant to this situation. Another example would be that on-site soils are not considered an exposure pathway but I am unsure of whether the exposure considered 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 there is not potential contamination that exceeds the 5-foot depth?
Response: To ensure that the health of the nation's children is protected, ATSDR has implemented an initiative to protect children from exposure to hazardous substances. Therefore, site-specific exposure doses were calculated for both adults and children as part of this PHA. Additional information on the evaluation of childhood exposures is presented in the "ATSDR Child Health Initiatives" Section of the PHA and Appendix C.
The potential for health effects resulting from chronic exposure to contaminants associated with the NRAP Site has been evaluated as part of this PHA. The health guidelines that were considered in this PHA account for long-term exposure to contaminants.
Comparison Values (CVs) developed for children with pica behavior were used to evaluate the available soil data for the Las Cumbres day care center. No contaminants were found to exceed the established 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 direct contact with contaminants. Typically, individuals' activities involve contact with soil from 0 to 2 feet 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:
NMED recognizes the challenge in conducting a conservative exposure evaluation and simultaneously attempting to manage the uncertainty inherent in such evaluations. 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 the potential past human exposure, the resulting evaluation would provide a more realistic, yet still conservative, estimate of the exposure. For the reasons stated above, using the highest concentrations from monitoring wells at the site may yield an unrealistically high exposure assessment that contains a considerable degree of uncertainty.
Response: The PHA process is intended to conservatively evaluate the potential for health effects resulting from exposure to hazardous waste. Several uncertainties exist and have been briefly discussed in the text (i.e., no groundwater data prior to 1989, no mixing/dilution with unimpacted water assumed in the evaluation, use of monitoring well data due to lack of data from Bond and Jemez wells). In the absence of data from the Bond and Jemez wells for the times of interest, ATSDR utilized the most conservative information available for the groundwater for public health protectiveness.
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 exposure to PCE contaminated groundwater from the Jemez well probably occurred for approximately 14 years." It is also stated "concentrations at the Jemez well during its operation were probably in the range of 100 ug/L to 500 ug/L." Considering that there are no analytical data for the Jemez well prior to 1989, and given the points stated above in comment No. 1, it may be inappropriate to use the term "probably" when making these assumptions. It is perhaps more appropriate to suggest that contamination 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 public health hazard due to the past exposure of PCE and TCE in drinking water, ATSDR compared the calculated exposure doses to adults and children to the oral reference dose (RfD) for PCE and the provisional RfD for TCE. However, calculated exposure doses were determined from the estimated doses via ingestion, inhalation (showering), and direct contact (dermal exposure); the sums of these doses were then compared to oral RfDs.
It would perhaps be more appropriate to calculate exposure doses for each pathway in accordance with accepted procedures (e.g., EPA's "Risk Assessment Guidance for Superfund") and compare the calculated doses to pathway-specific toxicity values. If, however, such an approach was not possible due to lack of toxicity values for the inhalation and dermal contact pathways, the text should make mention of this circumstance. The rationale for assuming that the additional risk due to inhalation of PCE and TCE vapors during showering can be approximated as additional ingestion of drinking water should be stated in the text. The rationale for comparison of the dermal contact exposure dose (which is calculated as an absorbed dose) to oral RfDs for PCE and TCE (which represent administered doses) should also be discussed.
Response: For clarity, ATSDR included additional information in the text to address the comments raised. As part of this PHA, ATSDR assumed exposure via showering to be half the dose estimated from ingestion of drinking water (equal to exposure to 1 liter of water per day). EPA Region 4 Supplemental Guidance to the Risk Assessment Guidance for Superfund, November 1995, states that it should be assumed that showering exposure is equivalent to exposure from ingestion of two liters of contaminated water per day. This value accounts for both inhalation and dermal exposure during showering. The guidance is based on the recommendations of The Risk Assessment Forum (Exposure to VOCs During Showering, Memorandum from Dorothy E. Patton, Chair, Risk Assessment Forum to F. Henry Habicht, II, July 10, 1991).
Because ATSDR's evaluation estimated dermal exposure during showering separately, exposures associated with inhalation during showering were assumed to be equal to 1 liter per day (or half the ingestion rate of 2 liters per day). Estimated dermal doses were compared with oral RfDs, which were adjusted using chemical-specific gastrointestinal absorption factors to represent an "absorbed dose" rather than an "administered dose".
Per the comment, ATSDR has provided additional information regarding the rationale in Appendix C. In addition, estimated doses for ingestion, inhalation, and dermal exposure will be discussed separately 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 showering are 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 with contaminated (PCE and TCE) drinking water." These statements seem to contradict ATSDR's conclusion that PCE and TCE in drinking water posed a public health hazard from exposures that were calculated to include inhalation exposure due to showering and dermal exposure. If the contributions of the inhalation and dermal contact pathways are small relative to the ingestion pathway, the text should discuss this circumstance. It would be also helpful for the Public Health Assessment to provide details on the exposure dose calculations for each exposure pathway evaluated.
Response: Compared with ingestion, less potential exposure to contaminants is expected to occur among individuals exposed via inhalation and dermal contact. For ease in understanding, the PHA does not provide exposure pathway equations. However, a discussion of each of the exposure pathways 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 health outcome data evaluation to determine whether the incidence rates of certain adverse health effects are 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 Española city-level data is not available until the late 1980's. ATSDR also states that "cancer rates for children and adults were considered, however; varying population estimates for Española from 1970-2000 created a concern for producing accurate rates"
Given that ATSDR concluded "past exposure to contaminants in drinking water posed a public health threat", it seems appropriate for ATSDR to make greater effort to investigate the potential adverse health effects associated with the site. NMED suggests that ATSDR work closely with the El Rio Arriba Environmental Health Association (EL RAEHA) to gather more community-specific health 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 incidences of low birth weight and cancers with patients that have home addresses in Española. If data gathering efforts such as the ones suggested are precluded by patient confidentiality laws, the text should discuss the obstacles to such studies.
Response: The gathering of community- and healthcare provider-specific health concerns and data is conducted by ATSDR throughout the PHA process. Health concerns and sources of data were addressed in the ATSDR hazard evaluation process including through personal and group interviews and discussions. Community health concerns are addressed beginning on page 30 of the PHA report. ATSDR will seek to coordinate with EL RAEHA for the recommendations listed in the PHA report, when appropriate.
ATSDR conducts health research at sites when exposures and other key factors are met. There are many 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 where measured concentrations in drinking water were higher than those found and modeled for the NRAP Site (Camp LeJeune, N.C.; ATSDR TCE Sub registry). Current and future findings of these studies will help to identify health risks relevant to persons exposed at the NRAP Site. ATSDR will disseminate this information through final reports, published papers and the ATSDR website.
The commenter suggests the collection and analysis of more specific information including personal and 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 a standardized questionnaire and an adequate number of participants in order to create generalizable findings. The commenter should understand that this data collection process meets the definition and intent of a federal health study. Moreover, ATSDR does not recommend a health study based on the consideration of all available information that was used for the PHA report. Lastly, new federal privacy laws (HIPAA) may influence some local healthcare organizations from sharing data with ATSDR. For HIPAA, compliance with federal law is the responsibility of the organization that serves as the repository of the data (i.e., hospital and doctor's office). Because the PHA report provided a rationale for not conducting a health study (no exposure data prior to 1989, magnitude of exposures, when exposure stopped, limited population size), ATSDR concludes it would be inappropriate to elaborate on the federal privacy laws in the PHA report. This would create possible confusion for the reader.
Comment: Conclusions, 1st bullet: It is stated in the conclusion of the report that "past exposure to contaminants in drinking water posed a public health hazard." It is also stated in the conclusions that "because groundwater data are not available prior to 1989, the frequency, duration, and concentrations of contaminants that individuals may have been exposed to in drinking water are unknown." Given that there is great uncertainty regarding the exposure concentrations that may have been 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 contaminants that may have posed a public health hazard. Based on the available information and ATSDR's hazard 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 uncertainties associated with the evaluation.
Comment: Appendix C, Page 54, Inhalation of Contaminants Present in Drinking Water: To evaluate the potential exposure due to inhalation of contaminants in drinking water during showering or bathing, ATSDR assumed that this exposure dose would be equal to ingesting 1 liter per day. The ATSDR Public Health Assessment Guidance Manual suggests that the appropriate method is to estimate the dose from contaminant concentrations in the air and inhalation rates. NMED suggests that the rationale for assuming the additional risk due to inhalation of PCE and TCE vapors during showering 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 ingestion of drinking water (equal to exposure to 1 liter of water per day). EPA Region 4 Supplemental Guidance to the Risk Assessment Guidance for Superfund, November 1995, states that it should be assumed that showering exposure is equivalent to exposure from ingestion of two liters of contaminated water per day. This value accounts for both inhalation and dermal exposure during showering. The guidance is based on the recommendations of The Risk Assessment Forum (Exposure to VOCs During Showering, Memorandum from Dorothy E. Patton, Chair, Risk Assessment Forum to F. Henry Habicht, II, July 10, 1991). Because ATSDR's evaluation estimated dermal exposure during showering separately, exposures associated with inhalation during showering 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 agency with headquarters in Atlanta, Georgia, and 10 regional offices in the United States. ATSDR's mission is to serve the public by using the best science, taking responsive public health actions, and providing trusted health information to prevent harmful exposures and diseases related to toxic substances. 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 the environment and human health.
This glossary defines words used by ATSDR in communications with the public. It is not a complete dictionary 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).
; K =6.0
ft/d; i = 0.002 ft/ft; q = 0.15
; DE&S (2001b)
; DE&S (2001b)
