This
is an example of a high end paper, A+.
This paper was reviewed by
several students and the instructor.
The instructor's comments are first.
One of the student reviewers had some editing suggestions, so the paper
with those suggestions is first, followed by the original paper. You can get to the original
paper via this hyperlink.
Grading
Mark each category 5 to 10:
10 = Yes, very well
9 = Yes
8 = Adequate
7 = Not quite adequate
6 = No
5 = Definitely no.
For comment:
Did the paper raise questions you would like answered? Name some.
Why is the RA based on drinking water, if the ground water is not used for drinking?
Other comments:
You described the risk assessment well, but I did not find much analysis or criticism of the RA. The references are tied to the original work and not the analysis.
Student Review
For comment:
Did the paper raise questions you would like answered? Name some.
Other comments:
none
Student Review
For comment:
Did the paper raise questions you would like answered? Name some.
A very well written paper.
Other comments:
none
Student Review
For comment:
Did the paper raise questions you would like answered? Name some.
What other chemicals are present in the plum other than BTEX and TCE.
Other comments:
Individual comments throughout paper using track changes.
The paper has a flow problem. Try providing better grouping and specific sections.
Nice paper overall. I enjoyed reading it. Thanks
Here I have inserted the paper
with comments by the reviewer. The
reviewer did a first class technical edit.
When I get these back for my own work, I like to study them and see if I
can learn something.
This is Paper # ___8________
You are Student # __1_____
Instructions.
Read the following paper and fill out this sheet as described below. You may want to type some comments into the paper itself, if you do, be sure to use a different color font AND put a note on this sheet that you have commented within the paper. Unless you have a lot of comments, it is better is to copy the section you want to refer to and paste in at the bottom of this page. That may lengthen this cover page to several sheets. That's OK.
All authors will get the anonymous student reviews comments and mine, which will not be anonymous. The final paper grade will be the instructor's judgment, but the instructor will carefully consider the student reviews comments.
Mark each category 5 to 10:
10 = Yes, very well
9 = Yes
8 = Adequate
7 = Not quite adequate
6 = No
5 = Definitely no.
For comment:
Did the paper raise questions you would like answered? Name some.
What other chemicals are present in the plum other than BTEX and TCE.
Other comments:
Individual comments throughout paper using track changes.
The paper has a flow problem. Try providing better grouping and specific sections.
Nice paper overall. I enjoyed reading it. Thanks
Human Health Risks due to Trichloroethene
in Groundwater
at a Site on Shemya Island
prepared
in partial fulfillment of the requirements for EQE 693
30
April 2001
This paper reviews a risk assessment (RA) performed for various
impacted sites at Eareckson Air Station on Shemya Island. In particular, this paper focuses on Site SS23, a former drum storage area, and
discusses the use of the RA and its conclusions in determining regulatory
action for the site. Of particular
interest at this site is trichloroethene (also known as trichloroethylene or
TCE) in groundwater at the site. Other volatile organic compounds (including
benzene, toluene, ethylbenzene, and xylenes) as well as metals (lead and
arsenic) have been found in at site monitoring
wells
at the site. However, TCE
in groundwater appears at higher concentrations, more frequently over time, and
over a greater spatial area than other contaminants; therefore, it is the
contaminant that will be discussed in this paper.
Regulatory Background
Eareckson Air Station is not a CERCLA site; however, the Air Force is following the framework provided in the National Contingency Plan (NCP) for assessing contaminants at Eareckson Air Station. In lieu of the United State Environmental Protection Agency (EPA) oversight required under the NCP, the State of Alaska Department of Environmental Conservation (ADEC) is supervising site remediation decisions. An RA was performed in 1996 based on data collected from1988 through 1994. At the time the RA was performed, ADEC had established cleanup levels for petroleum contaminated soils only and relied on RAs to establish cleanup levels for other potential contaminants. Subsequent to the conclusion of the RA, but before Records of Decision were established, the ADEC revised its contaminated sites requirements (18 AAC 75). Pertinent to this site, the 1999 regulations provided the following:
· All groundwater is assumed to be a potential drinking water source, unless specified physical conditions are demonstrated and specified institutional processes are pursued.
· Three methods for establishing groundwater cleanup levels were defined. These include:
1. Numeric values specified by ADEC (the Table C values)
2. Ten times the Table C values, if it is established that the groundwater is not a current or potential future drinking water source
3. Cleanup levels established by a site-specific RA conducted following ADEC guidance.
· If the first method for establishing groundwater cleanup levels is used, cumulative site risk must be calculated and must meet or be below a risk level of 1E-5 for carcinogenic constituents and 1 for noncarcinogenic constituents.
For this site, TCE levels in
groundwater for this site clearly exceeds
Table
C and ten times Table C values. Treatment of the entire
groundwater system to meet these cleanup levels does not appear feasible. Therefore, it is appropriate to consider
establishing cleanup levels by conducting a RA. It is desirable to use as much of the information and results
from the 1996 RA so that repetition and redundancy is avoided.
General Background (put this section before
regulatory background)
Shemya Island is located near the western end of the Aleutian
Archipelago. The island is fairly
small, (relative) approximately
4.5 miles long and 2 miles wide. The
United States established an air station on the island in the 1940s to support
the Aleutian campaign during World War II.
Since then, the military has used the island almost
continuously under several different installation names., although
the installation has been identified by several different names. The installation is still in operation for
strategic surveillance and defense. and cCurrently
there are approximately 30 to 60 on-site contractor personnel who operate and
maintain installation facilities.
Shemya Island enjoys has (flowery, keep it simple)a
marine climate, with moist conditions and temperature variances moderated by
the Pacific Ocean. The mean annual
temperature is 39 degrees Fahrenheit, the mean annual precipitation is 30
inches,
and the mean annual wind speed is 15 knots with no prevailing direction (USAF
1996).
Site Background. Site SS23, the former Drum Storage
Area, covers an area of approximately 30
acres. It consists of eight former
hardstands (asphalt-covered work areas) located adjacent to an abandoned runway
on the west end of Shemya Island. The
hardstands were used in the late 1980s and early 1990s for drum storage,
cleaning, and crushing operations. It is
assumedAssumption is that releases from these
drums are the sources of contamination in soils and groundwater at the
site. In particular, TCE, which is an
industrial solvent used to clean and degrease metals, is likely to have been associated
with drums stored and crushed at the site.
Groundwater levels are variable at SS23 due to topography fluctuations. Groundwater is generally present at 5 to 10 feet below ground surface (bgs) near the northern end of SS23 and between 20 and 30 feet bgs near the southern end. Groundwater at the site is not presently a source of drinking water and the site is not in a zone of recharge for the established drinking water source for the installation.
Historic Sampling. Surface soil (less than 3 feet bgs) samples were collected at SS23 during 1988 and 1994 investigations. Subsurface soil data was collected during 1988, 1993, and 1994 investigations. Fifty-six soil boreholes were sampled in 1994 alone. The majority of the samples collected were analyzed using field screening techniques to bias locations of samples sent to a fixed (commercial) analytical laboratory so that the samples came from areas of highest contamination. A total of 3 surface soil and 20 subsurface soil samples were submitted to a fixed laboratory for analysis. Low levels of TCE were found in surface soils in 1988 and 1994. TCE was found in higher concentrations in subsurface soils, to depths of 20 feet. The 1996 RA states, based on both fixed laboratory analyses and field screening results, that TCE concentrations increased with depth and appeared to be migrating to the west-southwest via groundwater (USAF 1996).
Groundwater samples have been collectedcollection
occurred from various monitoring wells associated with SS23 since
1993. In addition, groundwater samples
were collected from many of the boreholes advanced in 1994. Groundwater samples were sent to a fixed
laboratory for analysis. Constituents
detected in groundwater above laboratory method reporting limits were primarily
BTEX and TCE. The analytical method for TCE
has remained constant over time. Results
of analyses for TCE are presented in Table 1.
Table 1 Maximum Values of Analytical Results for TCE in Groundwater at Site SS23
|
Monitoring Well |
Units |
Sample Collection Date |
Groundwater Cleanup Levels1 (18 AAC 75) |
|||||
|
10/25 – 11/08/93 |
10/31-11/07/94 |
09/95 |
08/31-09/11/98 |
06/05-06/07/99 |
08/03 – 08/09/00 |
|||
|
SS23-MW03 |
mg/L |
NS |
1,090 |
NS |
1,425.7 |
1,200 |
835 |
5 |
|
SS23-MW06 |
mg/L |
NS |
656 |
NS |
963.6 |
1,400 |
1,190 |
5 |
|
MW-31 |
mg/L |
NS |
NS |
9.1 |
1.2/1.1 |
3.4 |
ND(<1) |
5 |
|
MW-32 |
mg/L |
89J/ND3,4 |
80J |
NS |
ND (<1) |
ND(<1) |
72 |
5 |
Key:
|
< – less than |
MRL – method reporting
limit |
|
1 – From Table C, 18 AAC 75.345 |
NA – Standard or value not
available |
|
3 – Field duplicate. |
ND – TCE not detected above
MRL (shown in parentheses) |
|
4 – An MRL is not
available. |
NS – No sample was
collected at this location on these dates |
|
AAC – Alaska Administrative
Code |
TCE – trichloroethene |
|
J – estimated value |
Bold values
exceed applicable groundwater cleanup level |
|
mg/L – micrograms per liter |
|
|
Source: USAF 1996; USAF 1999; USAF 2000; and USAF
2001. |
|
As can be seen in Table 1, the highest concentrations of TCE have been found in Monitoring Well 6 (SS23-MW06) and Monitoring Well 3 (SS23-MW03). SS23-MW06 was completed in the borehole that had the highest concentration of TCE in soils. According to maps presented in the 1996 RA, SW23-MW03 is downgradient of MW06; MW-31 is down and slightly crossgradient from MW06. MW-32 is slightly upgradient of MW06. (should provide site map)
Discussion of the Risk
Assessment
Three aspects of 1996 RA are considered in the following section: data evaluation and characteristics of the source of TCE; exposure characteristics; and toxicity aspects.
Data Evaluation and
Characteristics of the Source of TCE
Representative data. Groundwater samples have been collected from up to 13 monitoring wells installed in the vicinity of SS23. Of these, samples of groundwater from four wells have at least once shown levels of TCE greater than Table C values (Table 1). The various wells are spatially somewhat random, in that they included locations that were upgradient, downgradient, crossgradient and at the point of the assumed source. This is consistent with methods described for developing a concentration term (USEPA 1992) and the use of results from these wells in the 1996 RA appears defensible. However, in order to extend the RA through 2000, the use of pooled data from different years (1988 through 2000) appears to violate the assumptions for determining a concentration. On the other hand, it seems inappropriate to limit the analysis to a subset of the data. The use of additional data, spread temporally over 12 years, would need to be evaluated for an updated RA.
Volatilization. TCE has a relatively high vapor pressure and is likely to volatilize easily (Ney 1995). In fact, exposure to air (air stripping) is a common method for treating water with high levels of TCE. However, oxygen is not readily available in groundwater, and this process for attenuation over time is not considered significant, and was not discussed in the 1996 RA.
Biodegradation. Biodegradation of petroleum hydrocarbons in aquifers is known to occur in sediments and soils. It is generally thought that this process is slower in cold aquifers than in temperate aquifers. However, indigenous microorganisms capable of this type of biodegradation in cold groundwater have been shown to have similar rates of degradation to those found in more temperate locations (Bradley 1995). Although biodegradation does not appear to have been considered in the 1996 RA at this site, it may be helpful in determining the rate of degradation of TCE at the site,.
Transport. TCE’s high (1,300 mg/L) water solubility (Watts 1997) indicates that it is likely to leach or run off easily and not likely to be sorbed onto soil particles (Ney 1995). There was evidence of leaching via groundwater in the concentrations of TCE found in various boreholes and locations at the site (USAF 1996) and it is expected that TCE has been mobilized from the source soils by water.
Exposure Assessment
The 1999 ADEC regulations imply that the ingestion of groundwater pathway must be considered. However, the 1996 RA conceptual site model (USAF 1996) concluded that human contact with groundwater, including ingestion, dermal contact, and inhalation, were not complete pathways at Site SS23. Therefore, the results of the 1996 RA for this particular site cannot be used to comply with the 1999 regulations. By chance, another site at the installation, Site OT48, was evaluated for human health effects due to exposure to TCE via groundwater. Site OT48 is the current water gallery for the installation.
The exposure criteria at OT48 included consideration of the exposure setting (a remote island with temporary residents) and three potentially exposed populations with two exposure levels each (average and reasonable maximum exposure) for each of three exposure pathways. Parameter values for the risk characterization based on these scenarios is well documented in the RA. One parameter that differs from general default values is the exposure duration. For all sites on Shemya Island, the exposure duration for the reasonable maximum exposures was assumed to be 5 years, rather than the standard default of 30 years. In addition, for groundwater as a drinking water source, the land use is assumed to be residential rather than industrial. The assumptions for these parameters carry over from Site OT48 to SS23.
The RA discusses in general terms that the exposure point concentration was determined as the minimum of the 95 percent upper confidence limit (UCL) of the arithmetic mean concentration for TCE based on the sampling results used or the site maximum value. This is approach is documented in EPA guidance (USEPA 1992). The actual value used for Site OT48 is not well documented in the RA; however, it appears that the exposure point concentration was taken as the maximum site concentration, out of 5 results from primary samples collected from 1988 through 1994, of 16 mg/L. There was much more data collected at SS23. Therefore, extrapolation of this methodology to Site SS23 requires an evaluation of the site 95 percent UCL mean concentration before the exposure can be calculated. It may also require an evaluation of the use of temporally varied samples, as discussed above.
Toxicity Assessment
The International Agency for Research on Cancer (IARC) has determined that TCE is not classifiable as to human carcinogenicity (ATSDR 1997). The EPA has classified TCE as a possible or probably human carcinogen (Faust 1993). ADEC guidance on conducting RAs (ADEC 2000) suggest the following hierarchy for toxicity criteria:
· USEPA Integrated Risk Information System (IRIS)
· Health Effects Assessment Summary Table (HEAST)
· Other EPA criteria documents
· Agency for Toxic Substances and Disease Registry (ATSDR) Minimal Risk Levels for Hazardous Substances
Reference doses and slope factors for TCE are not included in the IRIS database. This database indicates that the reference dose for chronic oral exposure and the reference concentration for chronic inhalation exposure are not available and that the carcinogen assessment summary has been withdrawn pending further review by EPA’s Carcinogen Risk Assessment Verification Endeavor (CRAVE) work group. The HEAST database is limited to toxicity assessment of radionuclides; TCE is not a radionuclide. Provisional toxicity values for TCE have been developed in an EPA criteria documents (EPA 1995). The values presented in that document are identical to those proposed in a study conducted for the Department of Energy (Faust1993). The ATSDR database presents minimal risk levels for inhalation and oral routes (ATSDR, 2000); these are based on noncancer health effects only. Toxicity values from these sources are presented in Table 2.
Table 2 Toxicity Values and Minimum Risk Levels for TCE
|
Type of Value |
Toxicity Value or Minimum
Risk Level |
Source |
|
|
|
Oral |
Inhalation |
|
|
Slope Factor |
1.1E-2 (mg/kg-day)-1 |
6.00E-3 (mg/kg-day)-1 |
Faust 1993; USEPA 1995 |
|
Reference
Dose or Concentration |
Acute: 0.2 mg/kg/day |
Acute: 2 ppm Intermediate: 0.1 ppm |
ATSDR, 2000 |
Key: mg/kg
– milligrams per kilogram ppm – parts per million
A toxicity profile for TCE was presented as part of the 1996 RA, essentially citing EPA documents for the carcinogenic toxicity values of TCE. The slope factors used in the 1996 RA are the same as those presented in Table 2. Therefore, these are acceptable values for updating the RA, unless further work is finalized by CRAVE. However, the RA did not include an evaluation of non-cancerous effects of TCE and these would need to be included.
Cleanup Levels and other
Regulatory Criteria
Using assumptions made in the RA for groundwater at OT48 and the ADEC promulgated acceptable carcinogenic risk of 1E-5, back calculation yields a risk-based concentration for TCE in groundwater of 77 mg/L. As a point of reference, a study conducted in Finland (Vartiainen 1993) indicated that concentrations of up to 212 mg/L of TCE in drinking water did not increase incident rates for total cancer, liver cancer, non-Hodgkin’s lymphomas, Hodgkin’s disease, multiple myeloma, or leukemia.
If the RA approach were not used for establishing cleanup levels, then the Table C values would be used. The Table C value for TCE, 5 mg/L, is the same as the primary maximum contaminant levels (MCLs) for drinking water (18 AAC 80). Even if an updated RA determines that a concentration higher than the Table C value is protective of human health, any public drinking water system developed using this site’s groundwater would be subject to the MCLs and would most likely be required to provide additional treatment.
Extension of Risk
Characterization Results from OT48 to Site SS23
The risk due to contact with groundwater calculated at OT48 could presumably be scaled to reflect the risk at SS23, based on scaling the exposure point concentration. Determining the exposure point concentration would include an evaluation of the temporally varied data to determine the site’s 95 percent UCL mean . The non-cancerous risks must also be calculated, based on ATSDR criteria.
In addition, fate and transport modeling may be required in order to determine the change in TCE concentration over time, especially if the maximum value of TEC in groundwater, based on remaining concentrations of TCE in soils, has not been captured in the groundwater data to date. Contrary to soils data at SS023, no TCE in soils was found associated with OT48. Therefore, constituent release and migration, including migration to groundwater, was not considered at Site OT48, since the source of TCE was not known. However, these mechanisms are an issue at SS23, since soil contamination was apparent, as was evidence of migration of the contaminant through subsurface soil. A representative exposure point concentration would need to be developed. This would entail either using soil data from 1994 and determining an exposure point concentration based on biased sampling. Alternatively, new samples could be collected that represent current site conditions. Following determination of the soil concentration value, constituent release, degradation, and migration, all significant for TCE, will need to be evaluated. Fate and transport modeling were not required at OT48, because the samples came directly from the exposure point. Since the exposure point for groundwater from SS23 is not known (it is only considered a potential drinking water source), fate and transport modeling may be required to determine the concentrations in groundwater in the future at this site. Therefore, the migration to groundwater route, based on concentrations of TCE in soils, will require further evaluation.
Finally, other constituents were found in soils and groundwater at SS23, which must also be included in the extension of the risk assessment.
This review showed that assumptions made in the 1996 RA are not consistent with the revised ADEC regulations. An updated RA at SS23 will require additional fate and transport modeling to fully characterize site risks based on the potential for use of groundwater at the site.
References:
Agency for Toxic Substances and Disease Registry (ATSDR). 1997. ToxFAQs for Trichloroethylene (TCE). http:\\www.atsdr.cdc.gov/tfacts19.html. September
ATSDR. 2000. Minimal Risk Levels (MRLs) for Hazardous Substances. http:\\www.atsdr.cdc.gov/mrls.html. February
Alaska Department of Environmental Conservation (ADEC). 1999. Oil and Hazardous Substances Pollution Control Regulations (as amended through January 22, 1999) (18 AAC 75).
ADEC. 2000. Risk Assessment Procedures Manual. ADEC, Division of Spill Prevention and Response, Contaminated Sites Remediation Program. 8 June.
Bradley, P.M. and F.H Chapelle. 1995. Rapid Toluene Mineralization by Aquifer Microorganisms at Adak, Alaska: Implications for Intrinsic Bioremediation in Cold Environments. Environmental Science and Technology (ES&T). 29(11), (p. 2778-2781)
Faust, R.A. 1993. Toxicity Summary for Trichloroethene. Prepared for Oak Ridge Reservation Environmental Restoration Program. Prepared by Rosmarie A. Faust, Ph.D. Chemical Hazard Evaluation Group. Biomedical Environmental Information Analysis Section. Health and Safety Research Division. Oak Ridge National Laboratory. Oak Ridge, Tennessee. March.
Ney, R.E. Jr. Ph.D. 1995. Fate and Transport of Organic Chemicals in the Environment. A Practical Guide. Government Institutes, Inc. Rockville, Maryland.
United States Air Force (USAF). 1996. Remedial Investigation/Feasibility Study Report. Volume III. Prepared for the U.S. Air Force, 611th Air Support Group, 611th Civil Engineer Squadron, Elmendorf AFB, Alaska, Eareckson Air Station, Alaska. January.
USAF. 1999. Remedial Investigation Basewide Groundwater Monitoring Report, August – September 1998. Prepared for the U.S. Air Force, 611th Air Support Group, 611th Civil Engineer Squadron, Elmendorf AFB, Alaska, Eareckson Air Station, Alaska. June.
USAF. 2000. Comprehensive Basewide Monitoring Report. June 1999 Basewide Monitoring Activities and Findings. Final. United States Air Force, 611th Air Support Group. 611th Civil Engineer Squadron. Elmendorf AFB, Alaska. Eareckson Air Station, Alaska. January.
USAF. 2001. Year 2000 Basewide Monitoring Report. Draft Final. United States Air Force, 611th Air Support Group. 611th Civil Engineer Squadron. Elmendorf AFB, Alaska. Eareckson Air Station, Alaska. April.
United States Environmental Protection Agency. (USEPA) 1992. Supplemental Guidance to RAGS: Calculating the Concentration Term. Office of Emergency and Remedial Response. Hazardous Site Evaluation Division, OS-230. Publication 9285.7-081. May.
USEPA. 1995. Risk Assessment Issue Paper for: Carcinogenicity Information for Trichloroethylene (TCE) (CASRN 79-10-6). Superfund Technical Support Center, National Center for Environmental Assessment . Cincinnati, OH.
USEPA. 2001. Integrated Risk Information System.
Vartiainen, T, E. Pukkala, T. Rienoja, T. Strandman, K. Kaksonen. 1993. Population exposure to tri- and tetrachloroethene and cancer risk: Two cases of drinking water population. Chemosphere. 27(7) p. 1171-1181.
Watts, R.J. 1997. Hazardous Wastes: Sources, Pathways, and Receptors. John Wiley and Sons, New York.
Human Health Risks due to
Trichloroethene in Groundwater
at
a Site on Shemya Island
prepared
in partial fulfillment of the requirements for EQE 693
30
April 2001
This paper reviews a risk assessment (RA) performed for various impacted sites at Eareckson Air Station on Shemya Island. In particular, this paper focuses on Site SS23, a former drum storage area, and discusses the use of the RA and its conclusions in determining regulatory action for the site. Of particular interest at this site is trichloroethene (also known as trichloroethylene or TCE) in groundwater at the site. Other volatile organic compounds (including benzene, toluene, ethylbenzene, and xylenes) as well as metals (lead and arsenic) have been found in monitoring wells at the site. However, TCE in groundwater appears at higher concentrations, more frequently over time, and over a greater spatial area than other contaminants; therefore, it is the contaminant that will be discussed in this paper.
Regulatory Background
Eareckson Air Station is not a CERCLA site; however, the Air Force is following the framework provided in the National Contingency Plan (NCP) for assessing contaminants at Eareckson Air Station. In lieu of the United State Environmental Protection Agency (EPA) oversight required under the NCP, the State of Alaska Department of Environmental Conservation (ADEC) is supervising site remediation decisions. A RA was performed in 1996 based on data collected from1988 through 1994. At the time the RA was performed, ADEC had established cleanup levels for petroleum contaminated soils only and relied on RAs to establish cleanup levels for other potential contaminants. Subsequent to the conclusion of the RA, but before Records of Decision were established, the ADEC revised its contaminated sites requirements (18 AAC 75). Pertinent to this site, the 1999 regulations provided the following:
· All groundwater is assumed to be a potential drinking water source, unless specified physical conditions are demonstrated and specified institutional processes are pursued.
· Three methods for establishing groundwater cleanup levels were defined. These include:
4. Numeric values specified by ADEC (the Table C values)
5. Ten times the Table C values, if it is established that the groundwater is not a current or potential future drinking water source
6. Cleanup levels established by a site-specific RA conducted following ADEC guidance.
· If the first method for establishing groundwater cleanup levels is used, cumulative site risk must be calculated and must meet or be below a risk level of 1E-5 for carcinogenic constituents and 1 for noncarcinogenic constituents.
For this site, TCE levels in groundwater clearly exceed Table C and ten times Table C values. Treatment of the entire groundwater system to meet these cleanup levels does not appear feasible. Therefore, it is appropriate to consider establishing cleanup levels by conducting a RA. It is desirable to use as much of the information and results from the 1996 RA so that repetition and redundancy is avoided.
General Background
Shemya Island is located near the western end of the Aleutian Archipelago. The island is fairly small, approximately 4.5 miles long and 2 miles wide. The United States established an air station on the island in the 1940s to support the Aleutian campaign during World War II. Since then, the military has used the island almost continuously, although the installation has been identified by several different names. The installation is still in operation for strategic surveillance and defense and currently there are approximately 30 to 60 on-site contractor personnel who operate and maintain installation facilities.
Shemya Island enjoys a marine climate, with moist conditions and temperature variances moderated by the Pacific Ocean. The mean annual temperature is 39 degrees Fahrenheit, the mean annual precipitation is 30 inches and the mean annual wind speed is 15 knots with no prevailing direction (USAF 1996).
Site Background. Site SS23, the former Drum Storage Area, covers an area of approximately 30 acres. It consists of eight former hardstands (asphalt-covered work areas) located adjacent to an abandoned runway on the west end of Shemya Island. The hardstands were used in the late 1980s and early 1990s for drum storage, cleaning, and crushing operations. It is assumed that releases from these drums are the sources of contamination in soils and groundwater at the site. In particular, TCE, which is an industrial solvent used to clean and degrease metals, is likely to have been associated with drums stored and crushed at the site.
Groundwater levels are variable at SS23 due to topography fluctuations. Groundwater is generally present at 5 to 10 feet below ground surface (bgs) near the northern end of SS23 and between 20 and 30 feet bgs near the southern end. Groundwater at the site is not presently a source of drinking water and the site is not in a zone of recharge for the established drinking water source for the installation.
Historic Sampling. Surface soil (less than 3 feet bgs) samples were collected at SS23 during 1988 and 1994 investigations. Subsurface soil data was collected during 1988, 1993, and 1994 investigations. Fifty-six soil boreholes were sampled in 1994 alone. The majority of the samples collected were analyzed using field screening techniques to bias locations of samples sent to a fixed (commercial) analytical laboratory so that the samples came from areas of highest contamination. A total of 3 surface soil and 20 subsurface soil samples were submitted to a fixed laboratory for analysis. Low levels of TCE were found in surface soils in 1988 and 1994. TCE was found in higher concentrations in subsurface soils, to depths of 20 feet. The 1996 RA states, based on both fixed laboratory analyses and field screening results, that TCE concentrations increased with depth and appeared to be migrating to the west-southwest via groundwater (USAF 1996).
Groundwater samples have been collected from various monitoring wells associated with SS23 since 1993. In addition, groundwater samples were collected from many of the boreholes advanced in 1994. Groundwater samples were sent to a fixed laboratory for analysis. Constituents detected in groundwater above laboratory method reporting limits were primarily BTEX and TCE. The analytical method for TCE has remained constant over time. Results of analyses for TCE are presented in Table 1.
Table 1 Maximum Values of Analytical Results for TCE in Groundwater at Site SS23
|
Monitoring Well |
Units |
Sample Collection Date |
Groundwater Cleanup Levels1 (18 AAC 75) |
|||||
|
10/25 – 11/08/93 |
10/31-11/07/94 |
09/95 |
08/31-09/11/98 |
06/05-06/07/99 |
08/03 – 08/09/00 |
|||
|
SS23-MW03 |
mg/L |
NS |
1,090 |
NS |
1,425.7 |
1,200 |
835 |
5 |
|
SS23-MW06 |
mg/L |
NS |
656 |
NS |
963.6 |
1,400 |
1,190 |
5 |
|
MW-31 |
mg/L |
NS |
NS |
9.1 |
1.2/1.1 |
3.4 |
ND(<1) |
5 |
|
MW-32 |
mg/L |
89J/ND3,4 |
80J |
NS |
ND (<1) |
ND(<1) |
72 |
5 |
Key:
|
< – less than |
MRL – method reporting
limit |
|
1 – From Table C, 18 AAC 75.345 |
NA – Standard or value not
available |
|
3 – Field duplicate. |
ND – TCE not detected above
MRL (shown in parentheses) |
|
4 – An MRL is not
available. |
NS – No sample was
collected at this location on these dates |
|
AAC – Alaska Administrative
Code |
TCE – trichloroethene |
|
J – estimated value |
Bold values
exceed applicable groundwater cleanup level |
|
mg/L – micrograms per liter |
|
|
Source: USAF 1996; USAF 1999; USAF 2000; and USAF
2001. |
|
As can be seen in Table 1, the highest concentrations of TCE have been found in Monitoring Well 6 (SS23-MW06) and Monitoring Well 3 (SS23-MW03). SS23-MW06 was completed in the borehole that had the highest concentration of TCE in soils. According to maps presented in the 1996 RA, SW23-MW03 is downgradient of MW06; MW-31 is down and slightly crossgradient from MW06. MW-32 is slightly upgradient of MW06.
Discussion of the Risk
Assessment
Three aspects of 1996 RA are considered in the following section: data evaluation and characteristics of the source of TCE; exposure characteristics; and toxicity aspects.
Data Evaluation and
Characteristics of the Source of TCE
Representative data. Groundwater samples have been collected from up to 13 monitoring wells installed in the vicinity of SS23. Of these, samples of groundwater from four wells have at least once shown levels of TCE greater than Table C values (Table 1). The various wells are spatially somewhat random, in that they included locations that were upgradient, downgradient, crossgradient and at the point of the assumed source. This is consistent with methods described for developing a concentration term (USEPA 1992) and the use of results from these wells in the 1996 RA appears defensible. However, in order to extend the RA through 2000, the use of pooled data from different years (1988 through 2000) appears to violate the assumptions for determining a concentration. On the other hand, it seems inappropriate to limit the analysis to a subset of the data. The use of additional data, spread temporally over 12 years, would need to be evaluated for an updated RA.
Volatilization. TCE has a relatively high vapor pressure and is likely to volatilize easily (Ney 1995). In fact, exposure to air (air stripping) is a common method for treating water with high levels of TCE. However, oxygen is not readily available in groundwater, and this process for attenuation over time is not considered significant, and was not discussed in the 1996 RA.
Biodegradation. Biodegradation of petroleum hydrocarbons TCE is not in aquifers is known to occur in sediments and soils. It is generally thought that this process is slower in cold aquifers than in temperate aquifers. However, indigenous microorganisms capable of this type of biodegradation in cold groundwater have been shown to have similar rates of degradation to those found in more temperate locations (Bradley 1995). Although biodegradation does not appear to have been considered in the 1996 RA at this site, it may be helpful in determining the rate of degradation of TCE at the site,.
Transport. TCE’s high (1,300 mg/L) water solubility (Watts 1997) indicates that it is likely to leach or run off easily and not likely to be sorbed onto soil particles (Ney 1995). There was evidence of leaching via groundwater in the concentrations of TCE found in various boreholes and locations at the site (USAF 1996) and it is expected that TCE has been mobilized from the source soils by water.
Exposure Assessment
The 1999 ADEC regulations imply that the ingestion of groundwater pathway must be considered. However, the 1996 RA conceptual site model (USAF 1996) concluded that human contact with groundwater, including ingestion, dermal contact, and inhalation, were not complete pathways at Site SS23. Therefore, the results of the 1996 RA for this particular site cannot be used to comply with the 1999 regulations. By chance, another site at the installation, Site OT48, was evaluated for human health effects due to exposure to TCE via groundwater. Site OT48 is the current water gallery for the installation.
The exposure criteria at OT48 included consideration of the exposure setting (a remote island with temporary residents) and three potentially exposed populations with two exposure levels each (average and reasonable maximum exposure) for each of three exposure pathways. Parameter values for the risk characterization based on these scenarios is well documented in the RA. One parameter that differs from general default values is the exposure duration. For all sites on Shemya Island, the exposure duration for the reasonable maximum exposures was assumed to be 5 years, rather than the standard default of 30 years. In addition, for groundwater as a drinking water source, the land use is assumed to be residential rather than industrial. The assumptions for these parameters carry over from Site OT48 to SS23.
The RA discusses in general terms that the exposure point concentration was determined as the minimum of the 95 percent upper confidence limit (UCL) of the arithmetic mean concentration for TCE based on the sampling results used or the site maximum value. This is approach is documented in EPA guidance (USEPA 1992). The actual value used for Site OT48 is not well documented in the RA; however, it appears that the exposure point concentration was taken as the maximum site concentration, out of 5 results from primary samples collected from 1988 through 1994, of 16 mg/L. There was much more data collected at SS23. Therefore, extrapolation of this methodology to Site SS23 requires an evaluation of the site 95 percent UCL mean concentration before the exposure can be calculated. It may also require an evaluation of the use of temporally varied samples, as discussed above.
Toxicity Assessment
The International Agency for Research on Cancer (IARC) has determined that TCE is not classifiable as to human carcinogenicity (ATSDR 1997). The EPA has classified TCE as a possible or probably human carcinogen (Faust 1993). ADEC guidance on conducting RAs (ADEC 2000) suggest the following hierarchy for toxicity criteria:
· USEPA Integrated Risk Information System (IRIS)
· Health Effects Assessment Summary Table (HEAST)
· Other EPA criteria documents
· Agency for Toxic Substances and Disease Registry (ATSDR) Minimal Risk Levels for Hazardous Substances
Reference doses and slope factors for TCE are not included in the IRIS database. This database indicates that the reference dose for chronic oral exposure and the reference concentration for chronic inhalation exposure are not available and that the carcinogen assessment summary has been withdrawn pending further review by EPA’s Carcinogen Risk Assessment Verification Endeavor (CRAVE) work group. The HEAST database is limited to toxicity assessment of radionuclides; TCE is not a radionuclide. Provisional toxicity values for TCE have been developed in an EPA criteria documents (EPA 1995). The values presented in that document are identical to those proposed in a study conducted for the Department of Energy (Faust1993). The ATSDR database presents minimal risk levels for inhalation and oral routes (ATSDR, 2000); these are based on noncancer health effects only. Toxicity values from these sources are presented in Table 2.
Table 2 Toxicity Values and Minimum Risk Levels for TCE
|
Type of Value |
Toxicity Value or Minimum
Risk Level |
Source |
|
|
|
Oral |
Inhalation |
|
|
Slope Factor |
1.1E-2 (mg/kg-day)-1 |
6.00E-3 (mg/kg-day)-1 |
Faust 1993; USEPA 1995 |
|
Reference
Dose or Concentration |
Acute: 0.2 mg/kg/day |
Acute: 2 ppm Intermediate: 0.1 ppm |
ATSDR, 2000 |
Key: mg/kg
– milligrams per kilogram ppm – parts per million
A toxicity profile for TCE was presented as part of the 1996 RA, essentially citing EPA documents for the carcinogenic toxicity values of TCE. The slope factors used in the 1996 RA are the same as those presented in Table 2. Therefore, these are acceptable values for updating the RA, unless further work is finalized by CRAVE. However, the RA did not include an evaluation of non-cancerous effects of TCE and these would need to be included.
Cleanup Levels and other
Regulatory Criteria
Using assumptions made in the RA for groundwater at OT48 and the ADEC promulgated acceptable carcinogenic risk of 1E-5, back calculation yields a risk-based concentration for TCE in groundwater of 77 mg/L. As a point of reference, a study conducted in Finland (Vartiainen 1993) indicated that concentrations of up to 212 mg/L of TCE in drinking water did not increase incident rates for total cancer, liver cancer, non-Hodgkin’s lymphomas, Hodgkin’s disease, multiple myeloma, or leukemia.
If the RA approach were not used for establishing cleanup levels, then the Table C values would be used. The Table C value for TCE, 5 mg/L, is the same as the primary maximum contaminant levels (MCLs) for drinking water (18 AAC 80). Even if an updated RA determines that a concentration higher than the Table C value is protective of human health, any public drinking water system developed using this site’s groundwater would be subject to the MCLs and would most likely be required to provide additional treatment.
Extension of Risk
Characterization Results from OT48 to Site SS23
The risk due to contact with groundwater calculated at OT48 could presumably be scaled to reflect the risk at SS23, based on scaling the exposure point concentration. Determining the exposure point concentration would include an evaluation of the temporally varied data to determine the site’s 95 percent UCL mean . The non-cancerous non-cancer or non-carcinogenic is better risks must also be calculated, based on ATSDR criteria.
In addition, fate and transport modeling may be required in order to determine the change in TCE concentration over time, especially if the maximum value of TEC in groundwater, based on remaining concentrations of TCE in soils, has not been captured in the groundwater data to date. Contrary to soils data at SS023, no TCE in soils was found associated with OT48. Therefore, constituent release and migration, including migration to groundwater, was not considered at Site OT48, since the source of TCE was not known. However, these mechanisms are an issue at SS23, since soil contamination was apparent, as was evidence of migration of the contaminant through subsurface soil. A representative exposure point concentration would need to be developed. This would entail either using soil data from 1994 and determining an exposure point concentration based on biased sampling. Alternatively, new samples could be collected that represent current site conditions. Following determination of the soil concentration value, constituent release, degradation, and migration, all significant for TCE, will need to be evaluated. Fate and transport modeling were not required at OT48, because the samples came directly from the exposure point. Since the exposure point for groundwater from SS23 is not known (it is only considered a potential drinking water source), fate and transport modeling may be required to determine the concentrations in groundwater in the future at this site. Therefore, the migration to groundwater route, based on concentrations of TCE in soils, will require further evaluation.
Finally, other constituents were found in soils and groundwater at SS23, which must also be included in the extension of the risk assessment.
This review showed that assumptions made in the 1996 RA are not consistent with the revised ADEC regulations. An updated RA at SS23 will require additional fate and transport modeling to fully characterize site risks based on the potential for use of groundwater at the site.
References:
Agency for Toxic Substances and Disease Registry (ATSDR). 1997. ToxFAQs for Trichloroethylene (TCE). http:\\www.atsdr.cdc.gov/tfacts19.html. September
ATSDR. 2000. Minimal Risk Levels (MRLs) for Hazardous Substances. http:\\www.atsdr.cdc.gov/mrls.html. February
Alaska Department of Environmental Conservation (ADEC). 1999. Oil and Hazardous Substances Pollution Control Regulations (as amended through January 22, 1999) (18 AAC 75).
ADEC. 2000. Risk Assessment Procedures Manual. ADEC, Division of Spill Prevention and Response, Contaminated Sites Remediation Program. 8 June.
Bradley, P.M. and F.H Chapelle. 1995. Rapid Toluene Mineralization by Aquifer Microorganisms at Adak, Alaska: Implications for Intrinsic Bioremediation in Cold Environments. Environmental Science and Technology (ES&T). 29(11), (p. 2778-2781)
Faust, R.A. 1993. Toxicity Summary for Trichloroethene. Prepared for Oak Ridge Reservation Environmental Restoration Program. Prepared by Rosmarie A. Faust, Ph.D. Chemical Hazard Evaluation Group. Biomedical Environmental Information Analysis Section. Health and Safety Research Division. Oak Ridge National Laboratory. Oak Ridge, Tennessee. March.
Ney, R.E. Jr. Ph.D. 1995. Fate and Transport of Organic Chemicals in the Environment. A Practical Guide. Government Institutes, Inc. Rockville, Maryland.
United States Air Force (USAF). 1996. Remedial Investigation/Feasibility Study Report. Volume III. Prepared for the U.S. Air Force, 611th Air Support Group, 611th Civil Engineer Squadron, Elmendorf AFB, Alaska, Eareckson Air Station, Alaska. January.
USAF. 1999. Remedial Investigation Basewide Groundwater Monitoring Report, August – September 1998. Prepared for the U.S. Air Force, 611th Air Support Group, 611th Civil Engineer Squadron, Elmendorf AFB, Alaska, Eareckson Air Station, Alaska. June.
USAF. 2000. Comprehensive Basewide Monitoring Report. June 1999 Basewide Monitoring Activities and Findings. Final. United States Air Force, 611th Air Support Group. 611th Civil Engineer Squadron. Elmendorf AFB, Alaska. Eareckson Air Station, Alaska. January.
USAF. 2001. Year 2000 Basewide Monitoring Report. Draft Final. United States Air Force, 611th Air Support Group. 611th Civil Engineer Squadron. Elmendorf AFB, Alaska. Eareckson Air Station, Alaska. April.
United States Environmental Protection Agency. (USEPA) 1992. Supplemental Guidance to RAGS: Calculating the Concentration Term. Office of Emergency and Remedial Response. Hazardous Site Evaluation Division, OS-230. Publication 9285.7-081. May.
USEPA. 1995. Risk Assessment Issue Paper for: Carcinogenicity Information for Trichloroethylene (TCE) (CASRN 79-10-6). Superfund Technical Support Center, National Center for Environmental Assessment . Cincinnati, OH.
USEPA. 2001. Integrated Risk Information System.
Vartiainen, T, E. Pukkala, T. Rienoja, T. Strandman, K. Kaksonen. 1993. Population exposure to tri- and tetrachloroethene and cancer risk: Two cases of drinking water population. Chemosphere. 27(7) p. 1171-1181.
Watts, R.J. 1997. Hazardous Wastes: Sources, Pathways, and Receptors. John Wiley and Sons, New York.