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PUBLIC HEALTH ASSESSMENT

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


CONCLUSIONS, RECOMMENDATIONS, AND PUBLIC HEALTH ACTIONS

Conclusions

  1. Based on the data evaluated, ATSDR has assigned a public health hazard category for each of the pathways evaluated in this PHA. Appendix E presents a description of each of the public health hazard categories that were considered during the classification process.
    • Individuals within the City of Española may have previously drank, bathed, and showered with groundwater contaminated with PCE and TCE supplied by the Bond and Jemez wells in the municipal system. 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. The evaluation of potential health effects from exposure, conducted in this PHA, incorporated several conservative assumptions for health protectiveness which may have resulted in an overestimation of potential exposure to individuals. Based on the available groundwater data from public water supply well samples (Bond and Jemez wells) and monitoring wells [R-09(I2) and R-15(D1)], as well as information gained from groundwater modeling efforts, ATSDR concludes that past exposure to contaminants in drinking water posed a public health hazard, particularly to children and the developing fetus. The health effects of concern are developmental effects and childhood leukemia.

    • Individuals residing on the Santa Clara Pueblo did not receive their drinking water from the public water supply within the City of Española in the past. Therefore, these individuals were not exposed to contaminants from the Bond and Jemez wells. Individuals residing on the Santa Clara Pueblo received their water from private wells and Pueblo community supply wells. No contaminants have been detected in twelve private wells used for drinking water purposes, which are located directly adjacent to Santa Clara Pueblo Trust Land. Community supply wells have also not been impacted by contamination. Based on the available information, no health effects are expected among individuals from the Santa Clara Pueblo who use private wells and/or community supply wells for drinking water purposes. Therefore, no apparent public health hazard is posed from exposure.

    • Presently, some individuals within the City of Española use private well water for non-drinking water purposes. Groundwater from some of these wells has been impacted by PCE and TCE contamination associated with the NRAP site. Exposures to the contaminated water supplies are limited to dermal contact during swimming in pools that were filled with water from private wells and irrigation activities. Based upon the concentrations reported for the wells and toxicological evaluations, adverse health effects are not expected to occur. Therefore, ATSDR concludes that exposure to groundwater from private wells for non-drinking water uses poses no apparent public health hazard.

    • Due to elevated concentrations of PCE and TCE present in shallow groundwater, it is appropriate to consider whether there may be health effects related to the possible migration of contaminants from groundwater to the soil and into indoor air in residences and other buildings overlying the PCE plume within the City of Española. Based on the concentrations of contaminants measured in indoor air, no adverse health effects are expected to result. Therefore, ATSDR concludes that this pathway is classified as posing no apparent public health hazard.

    • Contaminants present in the shallow groundwater PCE plume may also volatilize into the outdoor air in areas above the groundwater contamination within the City of Española. These contaminants are quickly diluted by the large volume of outdoor air, which minimizes the likelihood of significant exposure. Therefore, ATSDR concludes that the outdoor air exposure pathway indicates no apparent public health hazard, based on the available outdoor air sampling data.

    • Exposure to contaminants present in on-site soil is likely to be intermittent. Additionally, exposure of individuals to the concentrations present in soil is not expected to result in adverse health effects. It is concluded that this pathway poses no apparent public health hazard.

    • No contaminants were detected above CVs in off-site soil. Therefore, no apparent public health hazard is posed from exposure.

    • No apparent public health hazard is posed from exposure to surface water and sediment, because no contaminants were detected above CVs.

  2. ATSDR has evaluated community health concerns and concludes that no adverse health effects are expected to occur based on the issues raised.

  3. The information reviewed by ATSDR indicates that repairs have been made to the Norge Town facility to effectively prohibit future contaminant releases to groundwater. In addition, proposed remediation efforts at the site are considered adequately protective of public health.

Recommendations

  1. It is recommended that no new private wells be installed in the vicinity of the site.

  2. Twelve private drinking water wells, located directly adjacent to Santa Clara Pueblo Trust Lands, should be periodically monitored by NMED to determine whether these wells remain unimpacted from local groundwater contamination.

  3. Active private wells within the City of Española that are used for non-drinking water purposes should be monitored periodically by NMED to determine whether the levels of contaminants (if present) are of public health significance.

  4. Based on the available data at this time, surface water and sediments have not been impacted by the contamination associated with the PCE groundwater plume. Over time, the shallow PCE plume is expected to migrate south/southeast and eventually discharge to the Rio Grande. As the plume migrates, the contaminants will be diluted and are also likely to breakdown. In addition, future remediation efforts proposed for contaminated soil and groundwater associated with the NRAP site are expected to significantly reduce the presence of PCE, TCE, and other related contaminants. However, because the Rio Grande is used for recreational purposes in the vicinity of the site, limited surface water and sediment sampling should be conducted periodically by NMED prior to the completion of remediation.

Public Health Actions

The Public Health Action Plan describes the actions designed to mitigate or prevent adverse human health effects that might result from exposure to hazardous substances associated with site contamination. Based on the findings of this PHA, no specific public health actions are warranted at the site. However, ATSDR will continue to collaborate with the appropriate federal, state, and local agencies to pursue the implementation of the recommendations outlined in this document. In addition, ATSDR will continue to review any new environmental and health outcome data associated with the NRAP site and include results in future updates of this document, if deemed necessary.

Past Actions

  • ATSDR advertised and conducted two 1-hour meetings on December 2nd and 3rd, 1998 at the Northern New Mexico Community College. The goal of the meeting was to have citizens meet with ATSDR staff and raise any health-related concerns about the site.

  • In April 1999 and July 2001, ATSDR attended EL RAEHA Steering Committee meetings. ATSDR staff from the Divisions of Health Assessment and Consultation and Health Education and Promotion presented background information about ATSDR, information on the PHA process, and possible options for community health education. Health-related concerns were also expressed by the community at the meeting.

  • ATSDR met with members of the Santa Clara Pueblo Governor's Office in May 2001 and August 2001. ATSDR provided an overview of the Agency and the PHA process. The tribe's concerns about the site and future involvement by ATSDR were also discussed during the meeting.

  • On March 7, 2003, ATSDR released the Public Comment Version of the PHA for a 60-day comment period, ending May 30, 2003. In late May 2003, EL RAEHA requested an extension of the comment period. The comment period was then extended for another 30 days, ending June 20, 2003.

  • In April 2003, ATSDR representatives held public availability sessions at the Northern New Mexico Community College and on the Santa Clara Pueblo to discuss the findings of the PHA and address the questions and comments of the community.

Future Actions

  • ATSDR will review any additional data that is collected and provide necessary updates to the PHA.

SITE TEAM

Robert Knowles
Environmental Health Scientist
Division of Health Assessment and Consultation

Annmarie DePasquale
Environmental Health Scientist
Division of Health Assessment and Consultation

Maria Teran-Maciver
Community Involvement Specialist
Division of Health Assessment and Consultation

Patrick Young
Regional Representative
Office of Regional Operations

Joe Maloney
Health Education Specialist
Division of Health Education and Promotion

Steve Inserra
Epidemiologist
Division of Health Studies

Dean Seneca
Tribal Coordinator
Division of Health Assessment and Consultation

Morris Maslia
Research Environmental Engineer
Division of Health Assessment and Consultation


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APPENDIX A: INFORMATION ON THE SEPARATE PETROLEUM-RELATED GROUNDWATER PLUME

Introduction

The initial release of the Public Health Assessment (PHA) for the North Railroad Avenue Plume Site(NRAP) site, issued in September 1999, included a brief evaluation of the limited data available fora separate petroleum plume, located within the City of Española (1). This appendix summarizes theinformation presented in the initial PHA and provides contact information for more information onthis site as the investigative process at the source(s) of the petroleum plume proceeds. This updatedPHA does not evaluate any additional data available for the site, because the investigation of thepetroleum plume is part of a separate, on-going environmental investigation conducted by the Stateof New Mexico Environment Department (NMED). Based on the data available at the time of theinitial release, individuals were not likely to be exposed to contaminants from the tetrachloroethylene(PCE) plume and the petroleum-related plume at the same time. Therefore, further evaluation of thepetroleum plume was not evaluated as part of this update, which focuses on the potential exposuresassociated with the PCE contamination from the NRAP site.

Background Information

In addition to impact from the Norge Town facility, shallow groundwater in the vicinity of the Cityof Española has become contaminated with petroleum hydrocarbons from two leaking undergroundstorage tanks. The tanks are associated with the Exxon El Centro and the Circle K Store, located inthe vicinity of the plaza area of Española and southwest of the Norge Town facility. The principalcontaminants reported are benzene, toluene, ethylbenzene, and xylenes, which are frequently referredto as BTEX contaminants. The BTEX groundwater plume is overlain largely by a public plaza andcommercial development. The shallow BTEX plume underlies a few businesses and service facilitiesand possibly some homes on Hill Street (2).

Two air sparging treatment systems were installed by NMED to remediate the petroleumcontamination levels in groundwater. Air and volatile organic compounds (VOCs) from thepetroleum products entrained from the contaminated groundwater were withdrawn from belowground and discharged into the surrounding air without treatment. Remedial operations began in1995 and were terminated after about a year without completing remediation. To evaluate thepotential for exposure to airborne contaminants by nearby residents, air emissions from the treatmentsystem were sampled during its operation. In addition, emission sample results were used to modelthe concentrations that could be expected at the nearest resident.

BTEX contaminants have been detected in numerous monitoring wells, which have been installedto collect environmental contamination data. It should be noted that individuals in the communityare not supplied groundwater from monitoring wells. In 1995, high levels of PCE were detected ingroundwater samples collected from monitoring wells installed as part of the investigation of theBTEX contaminant plume. It is thought that groundwater associated with the deeper PCE plumefrom the Norge Town facility migrated to the plaza area and was detected in the monitoring wellsinstalled to investigate the petroleum plume. Additionally, it is possible for BTEX contaminationto impact the groundwater at nearby private wells. However, all the available data from the privatenon-drinking and drinking water wells indicate that these wells have not been impacted by BTEXcontamination at this time. Surface water and sediment in the Rio Grande and the adjacent ditcheshave not been impacted by contaminants associated with the BTEX groundwater plume.

Site Investigations

Air samples from emission stacks, collected during the treatment system operation, were analyzedfor the presence of benzene, ethyl benzene, toluene, and xylenes. The emission sample analyses didnot include PCE or TCE, which may have also been present in the plume being treated. The resultsof the sampling indicate the presence of benzene, toluene, ethylbenzene, and xylenes at levelsranging from 31 to 110 milligrams per cubic meter (mg/m3). Sampling showed nonmethanehydrocarbon emissions totaled 9,300 mg/m3. The concentrations released at the elevated stacks arehigher than would occur in the normal breathing zone after mixing with ambient air. Therefore, airdata was modeled to estimate more likely exposure concentrations to nearby individuals. Airmodeling indicated lower concentrations at the nearest homes and the school and the junior highschool (3),(4). Appendix A, Table 1 provides summaries of the air sparging stack sample results andthe modeled data.

Appendix A, Table 1

Air Emissions Data: Source and Modeled (µg/m3)
Chemical Source1 Nearest Resident (Modeled)2 Jr. High School (Modeled)2 CV CV Source
Annual
Avg.
Maximum
1-hr.
Annual
Avg.
Maximum
1-hr.
Benzene 38,000 0.10 2.0 0.0070 2.0 0.10
4.0
50
CREG
Int. EMEG/MRL
Acute MEG/MRL
Toluene 62,000 0.15 6.0 0.10 5.0 80
400
1,000
Chronic EMEG
RfC
Acute EMEG/MRL
Ethylbenzene 31,000 0.10 2.0 0.070 2.0 1,000 Chronic RMEG/RfC
Xylenes 110,000 0.30 10 0.20 10 100
700
1,000
Chronic EMEG/MRL
Int. EMEG/MRL
Acute EMEG/MRL
TNH 9,300,000 22 900 200 1,000 NA NA

Notes:

1. Maximum detected concentration from samples collected at two emission stacks (contaminant source).
2. Concentrations have been modeled based on the maximum detected concentrations at the source.
Shaded concentrations indicate that comparison value(s) have been exceeded.
µg/m3 = micrograms per cubic meter
CV = Comparison Value
TNH = Total Nonmethane Hydrocarbons
NA = not available
CREG = Cancer Risk Evaluation
Int. = intermediate
EMEG = Environmental Media Evaluation Guide
RMEG = Reference Dose Media Evaluation Guide
MRL = Minimal Risk Level
RfC = Reference Concentration

Public Health Implications

Workers and others in the vicinity of the treatment unit used in 1995 were likely exposed viainhalation to petroleum-related chemicals in the past. While toluene, ethylbenzene, andxylenes were also detected in air samples (below their respective health-based value), themain constituent of concern in the BTEX plume regarding exposure is benzene. Theestimated 1-hour maximum concentrations and annual average of benzene in ambient air arebelow ATSDR's screening value for non-carcinogenic health effects (for example,Environmental Media Evaluation Guide). However, benzene concentrations exceed thehealth-based levels for cancerous effects (for example, Cancer Risk Evaluation Guide).

Benzene has been shown in human and animals studies to cause various types of cancers, inparticular leukemia. Key human studies indicate that cancer resulted among individualsexposed to benzene via inhalation for at least 10 years at concentrations that are manythousands of times greater than the concentrations associated with the air sparging units (5). Benzene emitted from the sparging units was quickly diluted by the large volume of ambientair. Because the remediation system was operational for only 1 year, exposure to benzenein ambient air was limited and health effects resulting from exposure are unlikely.

Conclusions of the Initial PHA

  • ATSDR concluded in the initial PHA that adverse non-cancerous and cancerous effectsare not expected to occur among individuals exposed to benzene and other petroleumcontaminants emitted from the air sparging units, which were in operation for one year.Therefore, ATSDR concludes that past exposure to air sparging emissions posed no apparent public health hazard.

Recommendations of the Initial PHA

  • It should be noted that exposures via inhalation may occur in the future if spargingoperations are reactivated without the treatment of air emissions from the system. Therefore, it was recommended in the initial PHA to perform periodic monitoring of airemissions in the event that the groundwater treatment system for the BTEX plume isreactivated. Sample analysis should include VOCs (PCE, BTEX, etc.). If high emissionlevels are recorded, ambient air modeling or monitoring should be considered to evaluatepotential exposure to the community.

  • Indoor air monitoring should be collected in areas overlying the BTEX plume. Monitoring should include at least those homes or other buildings that are closest to thelocations of high plume contaminant concentrations. In addition, the location of sensitive populations (for example, the elderly, infant children) should also be considered.

Contact for Additional Information

For additional information, including details on the status of the investigation of the petroleum-related groundwater plume in the plaza area of the City of Española, please contact the following person:

Chris Meehan
New Mexico Environment Department
Superfund/Grant
1190 St. Francis Dr., Rm N-2300
Santa Fe, NM 87505
505-476-3777
e-mail: chris_meehan@nmenv.state.nm.us


APPENDIX B: FIGURES

Vicinity Map, PCE Groundwater Plume
Figure 1. Vicinity Map, PCE Groundwater Plume

Site Map and Demographic Information
Figure 2. Site Map and Demographic Information


APPENDIX C: EXPLANATION OF EVALUATION PROCESS (6)

Step 1 - The Screening Process

In order to evaluate the available data, ATSDR used comparison values (CVs) to determine whichchemicals to examine more closely. CVs are the contaminant concentrations found in a specificmedia (for example: air, soil, or water) and are used to select contaminants for further evaluation. CVs incorporate assumptions of daily exposure to the chemical and a standard amount of air, water,and soil that someone may inhale or ingest each day. CVs are generated to be conservative and non-site specific. These values are used only to screen out chemicals that do not need further evaluation. CVs are not intended to be used as environmental clean-up levels or to indicate that health effectsoccur at concentrations that exceed these values.

CVs can be based on either carcinogenic (cancer-causing) or non-carcinogenic effects. Cancer-basedcomparison values are calculated from the U.S. Environmental Protection Agency's (EPA) oralcancer slope factor (CSF) or inhalation risk unit. CVs based on cancerous effects account for alifetime exposure (70 years) with an unacceptable theoretical excess lifetime cancer risk of 1 newcase per 1 million exposed people. Non-cancer values are calculated from ATSDR's Minimal RiskLevels (MRLs), EPA's Reference Doses (RfDs), or EPA's Reference Concentrations (RfCs). Whena cancer and non-cancer CV exists for the same chemical, the lower of these values is used in thecomparison for conservatism. The chemical and media-specific CVs utilized during the preparationof this PHA are listed below:

An Environmental Media Evaluation Guide (EMEG) is an estimated comparisonconcentration for which exposure is unlikely to cause adverse health effects, as determinedby ATSDR from its toxicological profiles for a specific chemical.

A Reference Dose Media Evaluation Guide (RMEG) is a comparison concentration thatis based on EPA's estimate of the daily exposure to a contaminant that is unlikely to causeadverse health effects.

A Cancer Risk Evaluation Guide (CREG) is a comparison concentration that is basedon an excess cancer rate of one in a million persons and is calculated using EPA's cancerslope factor (CSF).

A Maximum Contaminant Level (MCL) is a contaminant concentration that EPA deemsprotective of public health, and may consider the availability and economics of watertreatment technology.

A Life Time Health Advisory (LTHA) is developed by EPA and is considered a lifetimeexposure level for contaminants specifically in drinking water (assuming 20% of anindividual's exposure comes from drinking water) at which adverse, non-carcinogenichealth effects would not be expected to occur.

A Risk-Based Concentration (RBC) is developed by EPA Region III and used primarilyin the initial screening process of a baseline risk assessment. EPA toxicity factors havebeen combined with standard default assumptions in order to generate these values.

Preliminary Remediation Goal (PRG) is a screening tool, generated by EPA Region IX,which is used at the early stages of human exposure evaluation and clean-upconsiderations at contaminated sites. PRGs are risk-based concentrations derived fromstandardized equations, combining exposure assumptions and EPA toxicity data. Thesevalues are generic and do not take into account available site-specific information.

Step 2 - Evaluation of Public Health Implications

The next step in the evaluation process is to take those contaminants that are above theirrespective CVs and further identify which chemicals and exposure situations are likely to be ahealth hazard. Separate child and adult exposure doses (or the amount of a contaminant that getsinto a person's body) are calculated for site-specific exposure scenarios, using assumptionsregarding an individual's likelihood of accessing the site and contacting contamination. A briefexplanation of the calculation of estimated exposure doses for the site is presented below.Calculated doses are reported in units of milligrams per kilograms per day (mg/kg/day).

Exposure Dose Estimation

When chemical concentrations at the site exceed the established CVs, it is necessary for a morethorough evaluation of the chemical to be conducted. In order to evaluate the potential for humanexposure to contaminants present at the site and potential health effects from site-specific activities,ATSDR estimates human exposure to the site contaminant from different environmental media bycalculating exposure doses. A brief discussion of the calculations and assumptions is presented below.

Ingestion of Contaminants Present in Drinking Water

Exposure doses for ingestion of contaminants present in drinking water were calculatedusing the maximum detected concentration of PCE or TCE from the sample data, inmilligrams per liter (mg/L), multiplied by the drinking water ingestion rates of 2 litersper day (L/day) for adults and 1 L/day for children. The multiplication product wasdivided by the average body weights for adults and children are 70 kg (154 pounds) and16 kg (35 pounds), respectively.

Additionally, an exposure frequency of 365 days per year and exposure duration of 14years (based on the available data and groundwater modeling efforts) to 20 years(worst-case scenario) was incorporated into the dose calculations.

Inhalation of Contaminants Present in Drinking Water

For the evaluation of contaminants released (or volatilized) from water to the surrounding air duringshowering or bathing, it was assumed that the dose from inhalation was equal to the dose fromingestion of an additional 1 liter/day of drinking water(7). This is considered a protective approach,because actual exposures via inhalation are more likely to be overestimated, rather thanunderestimated, when this approach is utilized.

As with the ingestion dose calculation, an exposure frequency of 365 days per yearand exposure duration of 14 years (based on the available data and groundwatermodeling efforts) to 20 years (worst-case scenario) incorporated into the dosecalculations.

Direct Skin (or Dermal) Contact with Contaminants Present in Drinking Water

It was assumed that dermal exposure with drinking water occurred primarily duringshowering and bathing. Dermal absorption depends on numerous factors, including thearea of exposed skin, anatomical location of the exposed skin, length of contact,concentration of the chemical in contact with the skin, chemical-specific permeabilityfactors, and other factors. Because chemicals differ greatly in their potential to beabsorbed through the skin, each chemical needs to be evaluated separately. The assumedreceptor weights, exposure frequency, and exposure duration are the same as describedin the ingestion of drinking water calculation discussion.

Exposure doses for dermal contact with contaminants during showering and bathing,the maximum detected concentration measured in groundwater samples, in mg/L,was multiplied by the skin surface area exposure (18,150 and 7,195 cubic centimetersfor adults and children, respectively), the chemical-specific permeability constant, andan exposure time of 15 minutes per day.

Direct Skin (or Dermal) Contact with Contaminants Present in Non-Drinking Water

As discussed in the dermal evaluation of drinking water above, dermal absorptiondepends on a variety of factors, including the specific exposure situation and theproperties of each individual chemical. Dermal exposure to contaminants present innon-drinking water was assumed to occur in event this water source was used to fillswimming pools. The maximum detected concentration detected in private non-drinking water samples, measured in mg/L, was multiplied by the same surface areasused to calculate the dermal dose for drinking water exposure, the chemical-specificpermeability constant(8), and an exposure time of 2 hours per day to calculate the dermal dose.

Non-Cancer Health Effects

The doses calculated for exposure to each individual chemical are then compared to an establishedhealth guideline, such as a MRL or RfD, in order to assess whether adverse health impacts fromexposure are expected. These health guidelines, developed by ATSDR and EPA, are chemical-specific values that are based on the available scientific literature and are considered protective ofhuman health. Non-carcinogenic effects, unlike carcinogenic effects, are believed to have athreshold, that is, a dose below which adverse health effects will not occur. As a result, the currentpractice for deriving health guidelines is to identify, usually from animal toxicology experiments,a No Observed Adverse Effect Level (or NOAEL), which indicates that no effects are observed ata particular exposure level. This is the experimental exposure level in animals (and sometimeshumans) at which no adverse toxic effect is observed. The NOAEL is then modified with anuncertainty (or safety) factor, which reflects the degree of uncertainty that exists when experimentalanimal data are extrapolated to the general human population. The magnitude of the uncertaintyfactor considers various factors such as sensitive subpopulations (for example; children, pregnantwomen, and the elderly), extrapolation from animals to humans, and the completeness of availabledata. Thus, exposure doses at or below the established health guideline are not expected to resultin adverse health effects because these values are much lower (and more human health protective)than doses, which do not cause adverse health effects in laboratory animal studies. For non-cancerhealth effects, the following health guidelines are described below in more detail. It is important toconsider that the methodology used to develop these health guidelines does not provide anyinformation on the presence, absence, or level of cancer risk. Therefore, a separate cancer evaluationis necessary for potentially cancer-causing chemicals detected in samples at this site. A moredetailed discussion of the evaluation of cancer risks is presented in the following section.

Minimal Risk Levels (MRLs) - developed by ATSDR

ATSDR has developed MRLs for contaminants commonly found at hazardous waste sites. The MRL is an estimate of daily exposure to a contaminant below which non-cancer, adversehealth effects are unlikely to occur. MRLs are developed for different routes of exposure,such as inhalation and ingestion, and for lengths of exposure, such as acute (less than 14days), intermediate (15-364 days), and chronic (365 days or greater). At this time, ATSDRhas not developed MRLs for dermal exposure. A complete list of the available MRLs canbe found at http://www.atsdr.cdc.gov/mrls.html.

References Doses (RfDs) - developed by EPA

An estimate of the daily, lifetime exposure of human populations to a possible hazard thatis not likely to cause non-cancerous health effects. RfDs consider exposures to sensitive sub-populations, such as the elderly, children, and the developing fetus. EPA RfDs have beendeveloped using information from the available scientific literature and have been calculated for oral and inhalation exposures. A complete list of the available RfDs can be found at http://www.epa.gov/iris .

If the estimated exposure dose for a chemical is less than the health guideline value, the exposureis unlikely to result in non-cancer health effects. Non-cancer health effects from dermal exposurewas evaluated slightly differently that ingestion and inhalation exposure. Since health guidelinesare not available for dermal exposure, the calculated dermal dose was compared with the adjustedoral health guideline value (RfD or MRL). The oral health guideline value was adjusted using thegastrointestinal absorption factor to account for an "absorbed dose" (for dermal exposure) rather thanan "administered dose" (for ingestion exposure). To make this modification, the oral healthguideline value is multiplied by the gastrointestinal absorption factor.

If the calculated exposure dose is greater than the health guideline, the exposure dose is comparedto known toxicological values for the particular chemical and is discussed in more detail in the textof the PHA. The known toxicological values are doses derived from human and animal studies thatare summarized in the ATSDR Toxicological Profiles. A direct comparison of site-specific exposuredoses to study-derived exposures and doses found to cause adverse health effects is the basis fordeciding whether health effects are likely to occur.

Cancer Risks

Exposure to a cancer-causing compound, even at low concentrations, is assumed to be associatedwith some increased risk for evaluation purposes. The estimated excess risk of developing cancerfrom exposure to contaminants associated with the site was calculated by multiplying the site-specific adult exposure doses, with a slight modification, by EPA's chemical-specific Cancer SlopeFactors (CSFs or cancer potency estimates), which are available at http://www.epa.gov/iris . Calculated dermal doses were compared with the adjusted oral CSFs which were adjusted using thegastrointestinal absorption factor to account for an "absorbed dose" (for dermal exposure) rather thanan "administered dose" (for ingestion exposure). To make this modification, the oral CSF wasdivided by the gastrointestinal absorption factor.

An increased excess lifetime cancer risk is not a specific estimate of expected cancers. Rather, it isan estimate of the increase in the probability that a person may develop cancer sometime during hisor her lifetime following exposure to a particular contaminant. Therefore, the cancer risk calculationincorporates the equations and parameters (including the exposure duration and frequency) used tocalculate the dose estimates, but the estimated value is divided by 25,550 days (or the averagingtime), which is equal to a lifetime of exposure (70 years) for 365 days/year.

There are varying suggestions among the scientific community regarding an acceptable excesslifetime cancer risk, due to the uncertainties regarding the mechanism of cancer. Therecommendations of many scientists and EPA have been in the risk range of 1 in 1 million to 1 in10,000 (as referred to as 1 x 10-6 to 1 x 10-4) excess cancer cases. An increased lifetime cancer riskof one in one million or less is generally considered an insignificant increase in cancer risk. Animportant consideration when determining cancer risk estimates is that the risk calculationsincorporate several very conservative assumptions that are expected to overestimate actual exposurescenarios. For example, the method used to calculate EPA's CSFs assumes that high-dose animaldata can be used to estimate the risk for low dose exposures in humans. As previously stated, themethod also assumes that there is no safe level for exposure. Lastly, the method computes the 95%upper bound for the risk, rather than the average risk, suggesting that the cancer risk is actuallylower, perhaps by several orders of magnitude.

Because of the uncertainties involved with estimating carcinogenic risk, ATSDR employs a weight-of-evidence approach in evaluating all relevant data. Therefore, the carcinogenic risk is alsodescribed in words (qualitatively) rather than giving a numerical risk estimate only. The numericalrisk estimate must be considered in the context of the variables and assumptions involved in theirderivation and in the broader context of biomedical opinion, host factors, and actual exposureconditions. The actual parameters of environmental exposures have been given careful and thoroughconsideration in evaluating the assumptions and variables relating to both toxicity and exposure. Acomplete review of the toxicological data regarding the doses associated with the production ofcancer and the site-specific doses for the site is an important element in determining the likelihoodof exposed individuals being at a greater risk for cancer. A table with the numeric and qualitativecancer risk estimates for each of the completed exposure pathways is presented below.

Cancer Risk Estimates

Pathway Route(s) of Exposure Chemical Numeric Cancer Risk Estimate Qualitative Cancer Risk Estimate
Drinking Water - Public Water Supply1 Ingestion
Inhalation
Direct Contact
PCE-monitoring well 3.7x10-4 to 5.3x10-4 Moderate
TCE-monitoring well 5.3x10-6 to 7.5x10-4 Low
Non-Drinking Water -
Private Well Supply
Direct Contact PCE 2.6 x 10-5 Low-Moderate
TCE 4.2 x 10-6 Low
Chloroform 7.5 x 10-7 Insignificant
1,2-DCA 2.3 x 10-8 Insignificant

1. Drinking water supply estimates are based on data collected from monitoring wells in the vicinity of the contaminated public supply wells (Bond and Jemez wells). The ranges presented for the numeric cancer risk estimates for the public water supply reflect the results of calculations based on a 14-year exposure duration (based on groundwater modeling efforts) and a 20-year exposure duration (worst-case scenario; assumes exposure from the time operations began at the Norge Town facility).


Appendix C, Table 1.

Exposure Pathways for NRAP Site
PATHWAY NAME ENVIRONMENTAL MEDIA & TRANSPORT MECHANISMS POINT OF EXPOSURE ROUTE OF EXPOSURE EXPOSURE POPULATION TIME NOTES COMPLETE/
POTENTIAL EXPOSURE PATHWAY?
Groundwater; Public Water Supply Movement of contaminants discharged from the lint trap from soil to groundwater Municipal Drinking Water Ingestion, inhalation (showering), direct contact City water supply users Past -PCE and TCE detected
-Public water supply data available: 1989 to 1991
-Monitoring well data available: 1992 to 1999
YES
Groundwater, Private Wells
(Non-Drinking Water Purposes)
Movement of contaminants discharged from the lint trap from soil to groundwater Private Wells Direct Contact Residents with private wells Past, Present, Future -PCE, TCE, DCE, chloroform detected
-Data available for seven private wells within Española
YES
Indoor Air Volatilization of contaminants from soil and groundwater to indoor air Air within buildings overlying the groundwater plume Inhalation Workers, residents, etc. Past, Present, Future -1,1-Dichloroethene, 1,2,4-trimethylbenzene detected
-Data available Las Cumbres Learning Services, Inc. (office, classroom), Jr. High School library, and private residence on Chavez Street
YES
Outdoor Air Volatilization of contaminants from soil and groundwater to outdoor air Outdoor air in areas overlying the groundwater plume Inhalation Workers, residents, etc. Past, Present, Future -PCE, 1,2,4-trimethylbezene detected
-Data available from Las Cumbres play area and the lint trap (source)
YES
On-Site Soil Movement of contaminants discharged from the lint trap to soil Surface soil in the vicinity of the Norge Town facility (lint trap) Incidental ingestion, inhalation, direct contact Workers, trespasser, store patron (limited) Past, Present, Future -PCE, naturally-occurring metals
-Data available for area surrounding source (1996-1999)
-Exposure is considered very limited and not of public health concern
NO
Off-Site Soil Movement of contaminants discharged from the lint trap to soil Surface soil in areas in close proximity to the Norge Town facility Incidental ingestion, inhalation, direct contact Residents Past, Present, Future -No contaminants of concern detected in soil sampled collected from the Las Cumbres facility in 1999 NO
Groundwater, Private Wells (Drinking Water Purposes) Movement of contaminants discharged from the lint trap from soil to groundwater Private Wells Ingestion, inhalation (showering), direct contact Residents Past, Present, Future -No contaminants detected in the only potable private well located within the plume boundary (within the City of Española), which is not in use.
-No contaminants have been detected in private wells located on the Santa Pueblo
NO
Surface Water Movement of contaminants from groundwater to surface water Rio Grande and associated drainage ditches Direct contact Residents Past, Present, Future -No contaminants have been detected in surface water samples collected in 1996 and 1999 NO
Sediment Movement of contaminants from groundwater to surface water to sediment Rio Grande and associated drainage ditches Direct contact Residents Past, Present, Future -No contaminants have been detected in sediment samples collected in 1996 and 1999 NO
Fish Uptake Discharge of contaminants from groundwater to surface water (Rio Grande) Fish Consumption Ingestion Residents Past, Present, Future -No fish tissue samples have been collected.
-Surface water has not been impacted by the site, based on data collected in 1996 and 1999.
-PCE is not likely to bioaccumulate in fish.
NO
Animal Uptake Discharge of contaminants from groundwater to surface water that is given to livestock Livestock Consumption Ingestion Residents Past, Present, Future -Surface water has not been impacted by the site, based on data collected in 1996 and 1999
-PCE is not likely to bioaccumulate in livestock
NO



1 GLC Environmental Science and Engineering. Groundwater Remediation System Installation and Startup Report for the Exxon El Centro/Former Circle K Store No. 716, Española, New Mexico. Underground Storage Tank Bureau. December 26, 1995.
2 Duke Engineering and Services. Remedial Investigation Report. NRAP site Superfund Site. NPL #NMD986670156. Española, New Mexico. January 2001.
3 K. Winges and R. Wilson. Guideline on Air Quality Models, OAQPS, EPA, RTP, NC, EPA-450/2-78-027R.
4 Users Guide for the FMD, EPA-910/9-88-202R, EPA, Seattle, WA, 1990.
5 Integrated Risk Information System. U.S. Environmental Protection Agency. On-line at http://www.epa.gov/iris . Searched October 2001.
6 The evaluation process has been completed in accordance with the ATSDR PHA Guidance Manual, March 1992.
7 U.S. Environmental Protection Agency. EPA Region 4 Supplemental Guidance for Risk Assessment Guidance for Risk Assessment. November 1995.
8 U.S. Environmental Protection Agency. Dermal Exposure Assessment: Principles and Applications. January 1992.



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