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HEALTH CONSULTATION

Active Soil Gas Data Review

CHILLUM PERC SITE
(a/k/a CHILLUM PERCHLOROETHYLENE)
CHILLUM, PRINCE GEORGES COUNTY, MARYLAND


TABLES (Cont.)

Table 7.

Summary of MTBE active soil vapor data, Chillum perc site, Chillum, Maryland
Sample ID Laboratory MTBE Value (g/m3) Lab Qualifier Date
001 QES 275.5 J 5/9/2002
002 QES 3787.6 J 5/9/2002
003 QES 2.4 NJ 4/12/2002
004 QES     4/12/2002
005 QES 173.7 J 5/9/2002
006 QES 84.8 J 5/9/2002
007 QES 219.9 NJ 5/8/2002
008 QES 98.1 NJ 5/8/2002
010 QES 2.1 NJ 4/12/2002
012 QES 101.7 NJ 5/8/2002
013 QES 234.9 NJ 5/8/2002
014 QES 224.3 NJ 5/8/2002
015 QES 275 NJ 5/8/2002
016 QES     4/12/2002
017 QES     4/12/2002
018 QES 297 NJ 5/8/2002
019 QES     5/3/2002
020 QES 44.5 NJ 4/11/2002
021 QES     4/11/2002
022 QES 3.3 NJ 4/11/2002
023 QES 184.9 NJ 4/11/2002
024 QES     4/11/2002
025 QES 144.4 NJ 4/11/2002
026 QES 93 NJ 4/11/2002
027 QES     4/11/2002
030 QES 3.8   1/31/2002
031 QES 2.2 NJ 4/12/2002
032 QES     4/12/2002
033 QES     4/12/2002
034 QES 60.1 NJ 4/10/2002
035 QES 127.2 NJ 4/10/2002
036 QES     5/3/2002
037 QES     5/3/2002
038 QES     4/10/2002
039 QES 66.9 NJ 4/10/2002
040 QES 44.2 NJ 4/10/2002
041 QES     4/10/2002
043 QES 310.3 NJ 4/10/2002
044 QES 12.4   1/31/2002
046 QES 7.8   2/8/2002
047 QES 9   2/8/2002
048 QES     5/3/2002
049 QES     5/3/2002
050 QES 10.2   2/7/2002
052 QES 13.7   2/6/2002
054 QES 7.6   2/7/2002
057 QES 8.6   1/30/2002
059 QES 23.2   1/28/2002
061 QES 29.8   1/31/2002
063 QES 421.7 NJ 5/8/2002
064 QES 198.3 NJ 5/8/2002
067 QES 10.6   1/29/2002
072 QES 37.3   1/28/2002
073 QES 3.1   1/29/2002
078 QES 35.8   1/28/2002
074 QES 23   1/28/2002
081 QES 6.66 NJ 2/11/2002
083 QES 5.18 NJ 2/11/2002
084 QES 3.33 NJ 2/11/2002
085 QES 45.2   2/6/2002
086 QES 11.9   2/6/2002
001 GF-CHEVRON   U 5/9/2002
002 GF-CHEVRON 110   5/9/2002
003 GF-CHEVRON   U 4/12/2002
004 GF-CHEVRON   U 4/12/2002
005 GF-CHEVRON   U 5/9/2002
006 GF-CHEVRON   U 5/9/2002
007 GF-CHEVRON   U 5/8/2002
008 GF-CHEVRON   U 5/8/2002
010 GF-CHEVRON   U 4/12/2002
012 GF-CHEVRON   U 5/8/2002
013 GF-CHEVRON 38   5/8/2002
014 GF-CHEVRON 52   5/8/2002
015 GF-CHEVRON 52   5/8/2002
016 GF-CHEVRON   U 4/12/2002
017 GF-CHEVRON   U 4/12/2002
018 GF-CHEVRON   U 5/8/2002
019 GF-CHEVRON   U 5/3/2002
020 GF-CHEVRON   U 4/11/2002
021 GF-CHEVRON   U 4/11/2002
022 GF-CHEVRON   U 4/11/2002
023 GF-CHEVRON   U 4/11/2002
024 GF-CHEVRON   U 4/11/2002
025 GF-CHEVRON   U 4/11/2002
026 GF-CHEVRON   U 4/11/2002
027 GF-CHEVRON 29   4/11/2002
028 GF-CHEVRON   U 1/31/2002
031 GF-CHEVRON   U 4/12/2002
033 GF-CHEVRON   U 4/12/2002
034 GF-CHEVRON   U 4/10/2002
035 GF-CHEVRON   U 4/10/2002
036 GF-CHEVRON   U 5/3/2002
037 GF-CHEVRON 37   5/3/2002
038 GF-CHEVRON   U 4/10/2002
039 GF-CHEVRON   U 4/10/2002
040 GF-CHEVRON   U 4/10/2002
042 GF-CHEVRON   U 4/10/2002
043 GF-CHEVRON   U 4/10/2002
044 GF-CHEVRON   U 1/31/2002
046 GF-CHEVRON   U 2/8/2002
047 GF-CHEVRON   U 2/8/2002
048 GF-CHEVRON 11   5/3/2002
049 GF-CHEVRON   U 5/3/2002
050 GF-CHEVRON   U 2/7/2002
052 GF-CHEVRON   U 2/6/2002
054 GF-CHEVRON   U 2/7/2002
057 GF-CHEVRON 39   1/30/2002
056 GF-CHEVRON 26   1/30/2002
059 GF-CHEVRON   U 1/28/2002
061 GF-CHEVRON   U 1/31/2002
063 GF-CHEVRON 53   5/8/2002
064 GF-CHEVRON   U 5/8/2002
067 GF-CHEVRON 42   1/29/2002
068 GF-CHEVRON   U 1/28/2002
071 GF-CHEVRON 67   1/29/2002
078 GF-CHEVRON 37   1/28/2002
074 GF-CHEVRON 33   1/28/2002
081 GF-CHEVRON   U 2/11/2002
082 GF-CHEVRON   U 2/11/2002
084 GF-CHEVRON   U 2/11/2002
085 GF-CHEVRON   U 2/6/2002
086 GF-CHEVRON   U 2/6/2002
101 USACE 32    
106 USACE 29    
112 USACE 18    
115 USACE 14    
118 USACE 33    
126 USACE 558    
133 USACE 2.4    
140 USACE 27    
141 USACE 17    
144 USACE 1210    
151 USACE 149    
011 QES 3.7 NJ 4/12/2002
029 QES 8.1   1/31/2002
045 QES 47.1   1/31/2002
051 QES 21.9   2/7/2002
053 QES 7.2   2/6/2002
058 QES 241.7   1/30/2002
055 QES 21   1/30/2002
060 QES 18.4   1/28/2002
062 QES 16.3   1/31/2002
065 QES 78.8   1/29/2002
066 QES 10   1/29/2002
069 QES 41.4   1/28/2002
070 QES 69.7   1/29/2002
079 QES 58.7   1/28/2002
075 QES 31.5   1/28/2002
087 QES 6.8   2/6/2002
153 EPA REMOVAL      
154 EPA REMOVAL      
011 GF-CHEVRON   U 4/12/2002
029 GF-CHEVRON   U 1/31/2002
045 GF-CHEVRON   U 1/31/2002
051 GF-CHEVRON   U 2/7/2002
053 GF-CHEVRON   U 2/6/2002
058 GF-CHEVRON 46   1/30/2002
060 GF-CHEVRON   U 1/28/2002
062 GF-CHEVRON 11 NJ 1/31/2002
065 GF-CHEVRON 67   1/29/2002
066 GF-CHEVRON 35   1/29/2002
069 GF-CHEVRON 57   1/28/2002
070 GF-CHEVRON 70   1/29/2002
079 GF-CHEVRON 36   1/28/2002
075 GF-CHEVRON 31   1/28/2002
088 GF-CHEVRON   U 2/6/2002
091 USACE 19    
096 USACE 13    
100 USACE 30    
111 USACE 15    
119 USACE 16    
127 USACE 39.6    
131 USACE 1.5    
130 USACE 1.5    
145 USACE 26    
152 USACE 71.6    

Notes:

QES: Quality Environmental Solutions
USACE: U.S. Army Corp of Engineers
GF-Chevron: Gannett Fleming, Inc. (contractor of Chevron)
J: Compound was detected; quantification is approximate because of limitations identified during the quality control review.
NJ: Compound was analyzed for, but not detected; quantification is approximate because of limitations identified during the quality control review.
U: Compound was analyzed for, but not detected.
Blank cell: not detected


Table 8.

Summary of indoor air data, Chillum perc site, Chillum, Maryland (g/m3)
Chemical Concentration Comparison Value
acetone 2 31,000 (CEMEG)
benzene 1 32 (DHAC Guideline)
hexane 3 200 (RMEG)
2-propanol 2, 130 491,534 (TLV-TWA for n-propanol)
propene 1 344,213 (TLV-TWA)
toluene 1 3,830 (CEMEG)

Notes:

CEMEG: Chronic Environmental Media Evaluation Guide
DHAC: Division of Health Assessment and Consultation
RMEG: Reference Dose Media Evaluation Guide
TLV-TWA: Threshold Limit Value for a Time-Weighted Average


APPENDIX A: ATSDR'S COMPARISON VALUES AND DEFINITIONS

ATSDR comparison values (CVs) are media-specific concentrations considered safe under default exposure scenario. ATSDR uses them as screening values to identify contaminants (site-specific substances) that require further evaluation to determine the potential for adverse health effects.

Generally, a chemical at a site requires further evaluation when its maximum concentration in air, water, or soil exceeds one of ATSDR's comparison values. Comparison values are not, however, thresholds of toxicity. While concentrations at or below the relevant comparison value may reasonably be considered safe, it does not automatically follow that any environmental concentration that exceeds a comparison value would be expected to produce adverse health effects. Indeed, the purpose behind highly conservative, health-based standards and guidelines is to enable health professionals to recognize and resolve potential public health problems before they become actual health hazards. The probability that adverse health outcomes will actually occur as a result of exposure to environmental contaminants depends on individual lifestyle and genetic factors and site-specific conditions that affect the route, magnitude, and duration of actual exposure-not on environmental concentrations alone.

ATSDR derives screening values based on non-cancer effects by dividing NOAELs (no-observed-adverse-effect levels) or LOAELs (lowest-observed-adverse-effect levels). These levels stem from animal or human studies and include cumulative safety margins (variously called safety factors, uncertainty factors, and modifying factors) that typically range from 10 to 1,000 or more.

By contrast, cancer-based screening values come from linear extrapolation from animal data obtained at high doses because human cancer incidence data for very low levels of exposure simply do not exist, and probably never will.

Listed below are the comparison values that ATSDR uses to select chemicals for further evaluation, along with the abbreviations for the most common units of measure.

EMEG = Environmental Media Evaluation Guides
RMEG = Reference Dose Media Evaluation Guide
MRLs = Minimal Risk Levels
ppm = Parts Per Million, e.g., mg/L or mg/kg
ppb = Parts Per Billion, e.g., µg/L or µg/kg
kg = Kilogram (1,000 grams)
mg = Milligram (0.001 grams)
µg = Microgram (0.000001 grams) µg/m3
L = Liter
m3 = Cubic Meter (used in reference to a volume of air equal to 1,000 liters)

Acute Exposure is defined as exposure to a chemical for a duration of 14 days or less.

American Conference of Governmental Industrial Hygienists (ACGIH): A professional organization that establishes and publishes standards for occupational settings for five, 8-hour days per week.

ACGIH Threshold Limit Value for a Time Weighted Average (TLV-TWA): Airborne concentrations of substances and represents conditions, under which nearly all workers may be repeatedly exposed for a normal 8-hour workday and a 40-hour work week, week after week, without adverse effect.

Cancer Risk Evaluation Guides (CREG): Estimated contaminant concentrations in water, soil, or air that would be expected to cause no more than one excess cancer in a million persons exposed over a lifetime. CREGs are calculated from EPA's cancer slope factors.

Chronic Exposure: Exposure to a chemical for 365 days or more.

Environmental Media Evaluation Guides (EMEGs): Concentrations of a contaminant in water, soil, or air unlikely to produce any appreciable risk of adverse, non-cancer effects over a specified duration of exposure. EMEGs are derived from ATSDR minimal risk levels by factoring in default body weights and ingestion rates. ATSDR computes separate EMEGs for acute (<14 days), intermediate (15–364 days), and chronic (>365 days) exposures.

Intermediate Exposure: Exposure to a chemical for a duration of 15-364 days.

Lowest Observed Adverse Effect Level (LOAELs): The lowest exposure level of a chemical in a study, or group of studies, that produces statistically or biologically significant increase(s) in frequency or severity of adverse health effects between the exposed and control populations.

Maximum Contaminant Level (MCL): Contaminant concentrations in drinking water that EPA deems protective of public health (considering the availability and economics of water treatment technology) over a lifetime (70 years) at an exposure rate of two liters of water per day.

Minimal Risk Levels (MRL): Estimate of daily human exposure to a hazardous substance that is likely to be without an appreciable risk of adverse noncancer health effects over a specified route and duration of exposure.

No Observed Adverse Effect Level (NOAEL): The dose of a chemical at which there were no statistically or biologically significant increases in frequency or severity of adverse health effects seen between the exposed population and its appropriate control. Effects may be produced at this dose, but they are not considered to be adverse.

Uncertainty Factor (UF): A factor used in deriving the MRL or reference dose or reference concentration from exposure data.

The following comparison values were used for this health consultation:

  • Environmental Media Evaluation Guide (EMEGs)
  • Reference Dose Media Evaluation Guide (RMEGs)
  • Cancer Risk Evaluation Guides (CREGs)
  • Minimal Risk Levels (MRLs)
  • American Conference of Government Industrial Hygienists (ACGIH) Threshold Limit Value (TLVs).

APPENDIX B: GLOSSARY OF TERMS FOR VAPOR INTRUSION

Soil vapor: Air within the pore spaces of soil.

Active Soil Vapor Sampling: The withdrawal of the soil vapor from the subsurface and subsequent analysis of the vapor over a short time period (a few minutes) by pumping air from a void created at designed depth.

Advection: The process by which soil gas moves according to differences in pressure, temperature, or other factors.

Diffusion: The process whereby soil gas moves from an area of higher concentration to an area of lower concentration.

Fick's Law: This law states that diffusive transport of VOCs is governed by a concentration gradient and an effective coefficient of diffusity.

Passive Soil Vapor Sampling: The process of the burial of an adsorbent in the ground with subsequent retrieval and measurement of the adsorbent.

Preferential Pathways: Naturally occurring and/or anthropogenic subsurface pathways expected to have a high intrinsic gas permeability (vadose zone) or high conductivity (saturated zone) and thus influence the flow or migration of contaminated vapor or groundwater. (EPA VI guide)

Barometric Influences: Fluctuations in barometric pressure that can affect the steady state soil vapor profile (particularly in the shallow vadose zone); such fluctuations can influence measurements taken to characterize indoor air risk.

Dual-phase Extraction (DPE): The system used to extract both soil gas and ground water from the same extraction well to remediate soil and ground water contaminated with VOCs.

Shallow Soil Vapor Samples: Samples with sampling depth <5 feet below the bottom of the basement slab.

Deep Soil Vapor Samples: Samples from depths >5 feet below the bottom of the basement slab.

Dual-Phase Vacuum Extraction (DVE) System: A high vacuum system to extract both soil gas and ground water from the same extraction well to remediate soil and ground water contaminated with VOCs.

Attenuation Factor: The ratio of the indoor air concentration of some chemical divided by the equilibrium soil gas concentration of that chemical immediately above the source.

Volatile Organic Compounds (VOCs): Organic compounds that evaporate readily into the air.

Volatility: The capacity of a liquid to form vapors. Volatility can be measured through a liquid's vapor pressure.


APPENDIX C: ATSDR'S LEVELS OF PUBLIC HEALTH HAZARD

CATEGORY A: URGENT PUBLIC HEALTH HAZARD

This category is used for sites where short-term exposures (<1 year) to hazardous substances or conditions could result in adverse health effects that require rapid intervention.

This determination represents a professional judgment based on critical data that ATSDR has judged sufficient to support a decision. Such a designation does not necessarily mean that the available data are complete; in some cases, additional data may be required to confirm or further support the decision made.

Criteria:

Evaluation of available relevant information* indicates that site-specific conditions or likely exposures have had, are having, or are likely to have an adverse impact on human health that requires immediate action or intervention. Such site-specific conditions or exposures may include the presence of serious physical or safety hazards, such as open mine shafts, poorly stored or maintained flammable/explosive substances, or medical devices, which, if ruptured, could release radioactive materials.

CATEGORY B: PUBLIC HEALTH HAZARD

This category is used for sites that pose a public health hazard because of the existence of long-term exposures (>1 yr) to hazardous substances or conditions that could result in adverse health effects.

This determination represents a professional judgment based on critical data that ATSDR has judged sufficient to support a decision. Such a designation does not necessarily mean that the available data are complete; in some cases, additional data may be required to confirm or further support the decision made.

Criteria:

Evaluation of available relevant information* suggests that, under site-specific conditions of exposure, long-term exposures to site-specific contaminants (including radionuclides) have had, are having, or are likely to have an adverse impact on human health that requires one or more public health interventions. Such site-specific exposures may include the presence of serious physical hazards, such as open mine shafts, poorly stored or maintained flammable/explosive substances, or medical devices which, if ruptured, could release radioactive materials.

CATEGORY C: INDETERMINATE PUBLIC HEALTH HAZARD

This category indicates that a professional judgment on the level of health hazard cannot be made because information critical to such a decision is lacking.

Criteria:

This category is used for sites for which available critical data are insufficient with regard to the extent of exposure and/or toxicological properties at estimated exposure levels. The health assessor must determine, using professional judgment, the "criticality" of such data and the likelihood that the data can and will be obtained in a timely manner. Where some data–even limited data–are available, health assessors should to the extent possible select other hazard categories and support their decision with a clear narrative that explains the limits of the data and the rationale for the decision.

CATEGORY D: NO APPARENT PUBLIC HEALTH HAZARD

This category is used for sites where human exposure to contaminated media may be occurring, may have occurred in the past, and/or may occur in the future, but the exposure is not expected to cause any adverse health effects.

This determination represents a professional judgment based on critical data that ATSDR has judged sufficient to support a decision. Such a designation does not necessarily mean that the available data are complete; in some cases, additional data may be required to confirm or further support the decision made.

Criteria:

Available relevant information* indicates that, under site-specific conditions of exposure, exposures to site-specific contaminants in the past, present, or future are not likely to result in adverse impact on human health.

CATEGORY E: NO PUBLIC HEALTH HAZARD

This category is used for sites that, because of the absence of exposure, do NOT pose a public health hazard.

Criteria:

Sufficient evidence indicates that no human exposures to contaminated media have occurred, none are occurring, and none are likely to occur in the future.

* Examples include environmental, demographic, health outcome, exposure, toxicological, medical, or epidemiologic data, as well as community health concerns information.



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