Human health and ecological effects were evaluated by examining the routes by which receptors may be exposed to captured gases released into the atmosphere, surface water, groundwater, or in surface soils.
The key exposure route that was evaluated in this risk assessment is the inhalation of gaseous COPCs released to the atmosphere. Potentially, receptors may also be exposed to COPCs released to: 1) surface water via swimming and subsequent releases from surface water; 2) groundwater via potable water use and subsequent releases from groundwater that is used to irrigate crops; and 3) soils via direct contact. As the inhalation of COPCs from the atmosphere was assumed to result in the highest levels of exposure, these secondary exposure pathways were not evaluated. Exposures via these secondary exposure
pathways are assumed to be relatively minor compared to exposures via the inhalation of airborne COPCs and, therefore, the omission of these exposure pathways is assumed to have resulted in only a relatively minor degree of underestimation in the risks.
Determining the potential for adverse effects from assumed exposures to gaseous COPCs released to the atmosphere, is a two step process, as follows:
1. Identify appropriate toxicity criteria for each COPC and each exposure duration (see Section 3); and
2. Estimate the potential for adverse effects to occur using the following equation:
criterion Toxicity
ion concentrat airborne
Predicted Risk Ratio =
Risk ratios less than 1 indicate that health effects are not likely to occur, while risk ratios greater than 1 indicate that health effects may occur. Higher risk ratios generally represent the potential for higher levels of health concern, although many of the toxicity criteria used here include safety factors to ensure the protection of sensitive individuals.
5.6.1 JEWETT, TX
For both the short-term and long-term release scenarios at the Jewett (TX) site, assumed exposures to CO2
did not exceed either the acute or chronic toxicity criteria, respectively (Table 5-11 and Table 5-12). This indicates that assumed exposures to potentially released CO2 is unlikely to pose a risk to residential receptors post-sequestration. Assumed exposures to H2S did not exceed toxicity criteria for the short-term release scenarios. Further, H2S was not assumed to be released through the caprock, and did not exceed toxicity criteria for term releases through both existing and induced faults. However, assumed long-term releases of H2S from all three types of wells resulted in assumed exposures to concentrations that exceeded the toxicity criteria within (745 feet) 227 meters of the release (Table 5-12). The locations of existing deep wells near the Jewett injection sites are shown in Figure 2-8. The 50-year sequestration plume footprint of the injection sites are located in an area of agricultural, range, and forested lands with a low population density, indicating that relatively few people would be exposed to any potential releases
5.5.2 DISPERSION MODELING
Following the determination of release rates, SCREEN3 was used to perform dispersion modeling to estimate concentrations in air for releases from the ground surface (i.e., for migration upwards through the caprock formation, releases from wells, and releases from fractures) at various distances from the source.
The modeling is described in detail in Section 4.4. The predicted concentrations in air are provided in the tables in Section 5.6 and are used to estimate the potential for adverse effects due to assumed exposures to the released COPCs.
5.6 Consequence Analysis
Human health and ecological effects were evaluated by examining the routes by which receptors may be exposed to captured gases released into the atmosphere, surface water, groundwater, or in surface soils.
The key exposure route that was evaluated in this risk assessment is the inhalation of gaseous COPCs released to the atmosphere. Potentially, receptors may also be exposed to COPCs released to: 1) surface water via swimming and subsequent releases from surface water; 2) groundwater via potable water use and subsequent releases from groundwater that is used to irrigate crops; and 3) soils via direct contact. As the inhalation of COPCs from the atmosphere was assumed to result in the highest levels of exposure, these secondary exposure pathways were not evaluated. Exposures via these secondary exposure
pathways are assumed to be relatively minor compared to exposures via the inhalation of airborne COPCs and, therefore, the omission of these exposure pathways is assumed to have resulted in only a relatively minor degree of underestimation in the risks.
Determining the potential for adverse effects from assumed exposures to gaseous COPCs released to the atmosphere, is a two step process, as follows:
1. Identify appropriate toxicity criteria for each COPC and each exposure duration (see Section 3); and
2. Estimate the potential for adverse effects to occur using the following equation:
criterion Toxicity
ion concentrat airborne
Predicted Risk Ratio =
Risk ratios less than 1 indicate that health effects are not likely to occur, while risk ratios greater than 1 indicate that health effects may occur. Higher risk ratios generally represent the potential for higher levels of health concern, although many of the toxicity criteria used here include safety factors to ensure the protection of sensitive individuals.
5.6.1 JEWETT, TX
For both the short-term and long-term release scenarios at the Jewett (TX) site, assumed exposures to CO2
did not exceed either the acute or chronic toxicity criteria, respectively (Table 5-11 and Table 5-12). This indicates that assumed exposures to potentially released CO2 is unlikely to pose a risk to residential receptors post-sequestration. Assumed exposures to H2S did not exceed toxicity criteria for the short-term release scenarios. Further, H2S was not assumed to be released through the caprock, and did not exceed toxicity criteria for term releases through both existing and induced faults. However, assumed long-term releases of H2S from all three types of wells resulted in assumed exposures to concentrations that exceeded the toxicity criteria within (745 feet) 227 meters of the release (Table 5-12). The locations of existing deep wells near the Jewett injection sites are shown in Figure 2-8. The 50-year sequestration plume footprint of the injection sites are located in an area of agricultural, range, and forested lands with a low population density, indicating that relatively few people would be exposed to any potential releases
from wells there. However, the no effect boundary for potential H2S releases via wells comes to within 1 mile of the town of Sand Hill and 0.1 miles (0.16 kilometers) of a prison yard. No other sensitive
receptors were located within the sequestration plume footprints. The results for a well release are illustrated in Figure 5-3.
Table 5-13 shows that the only likely ecological effects from assumed releases of CO2 and H2S are olfactory effects in moths and butterflies. These effects are not expected to significantly affect ecological communities. However, it should be noted that there are no ecological toxicity criteria available for H2S.
Figure 5-3. Area Within Which H2S Released from CO2 Injection Wells Exceeds Chronic Toxicity Criteria (i.e., 0.0014 ppmv H2S) at the Jewett (TX) Site
5.6.2 ODESSA, TX
For both the short-term and long-term release scenarios at the Odessa (TX) site, assumed exposures to CO2 did not exceed either the acute or chronic toxicity criteria, respectively (Table 5-14 and Table 5-15).
This indicates that assumed exposures to potentially released CO2 is unlikely to pose a risk to residential receptors post-sequestration. Assumed exposures to H2S did not exceed toxicity criteria for the short-term release scenarios. Further, H2S was not assumed to be released through the caprock and did not exceed toxicity criteria for term releases through both existing and induced faults. However, assumed long-term releases of H2S from all three types of wells resulted in assumed exposures to concentrations that exceeded the toxicity criteria within 909 feet (227 meters) of the release (Table 5-14). The locations of existing deep wells near the Odessa injection site are shown in Figure 2-8. The 50 year sequestration plume footprint is located in an area that is largely open and has a relatively low population density, indicating that relatively few people would be exposed to any potential releases from wells there. Further, there are no sensitive receptors within the sequestration plume footprint and the nearest town is 8 miles (13 kilometers) from the injection site. The results for a well release are illustrated in Figure 5-4.
Table 5-16 shows that the only likely ecological effects from assumed releases of CO2 and H2S are olfactory effects in several insects. These effects are not expected to significantly affect ecological communities. However, it should be noted that no ecological toxicity criteria were available for H2S.
Figure 5-4. Area Within Which H2S Released from CO2 Injection Wells Exceeds Chronic Toxicity Criteria (i.e., 0.0014 ppmv H2S) at the Odessa (TX) Site.
(Area shown is based on a release from a single well within the injection area. See Figure 2-11 for all wells at the injection site.)
5.6.3 MATTOON, IL
For the Mattoon (IL) site, there are no oil and gas wells within the 50-year sequestration footprint.
Therefore, emissions from oil and gas wells was assumed to be an incomplete release scenario at this site and exposures were not estimated. For the release scenarios that were quantified, both the short-term and long-term CO2 release scenarios did not exceed either the acute or chronic toxicity criteria, respectively (Table 5-17 and Table 5-18). This indicates that assumed exposures to potentially released CO2 is unlikely to pose a risk to residential receptors post-sequestration. Assumed exposures to H2S did not exceed toxicity criteria for the short-term release scenarios. Further, H2S was not assumed to be released through the caprock and did not exceed toxicity criteria for long-term releases through both existing and induced faults. However, assumed long-term releases of H2S from both well types resulted in assumed exposures to concentrations that exceeded the toxicity criteria within 745 feet (227 meters) of the release (Table 5-17). The 50-year sequestration plume footprint is located in an area that is largely farmland and has a relatively low population density, indicating that relatively few people would be exposed to any potential releases from wells there. However, the no effect boundary for potential H2S releases via wells comes to within 0.25 miles (0.4 kilometers) of the town of Mattoon and 1.4 miles of the nearest school.
The results for a well release are illustrated in Figure 5-5.
Table 5-19 shows that the only likely ecological effects from assumed releases of CO2 and H2S are olfactory effects in several insects. These effects are not expected to significantly affect ecological communities. However, it should be noted that there are no ecological toxicity criteria were available for H2S.
Figure 5-5. Area Within Which H2S Released from CO2 Injection Wells Exceeds Chronic Toxicity Criteria (i.e., 0.0014 ppmv H2S) at the Mattoon (IL) Site
5.6.4 TUSCOLA, IL
For the Tuscola (IL) site, there are no oil and gas wells within the 50-year sequestration footprint.
Therefore, emissions from oil and gas wells were assumed to be an incomplete release scenario at this site and exposures were not estimated. For the release scenarios that were quantified, both the short-term and long-term CO2 release scenarios did not exceed either the acute or chronic toxicity criteria, respectively (Table 5-20 and Table 5-21). This indicates that assumed exposures to potentially released CO2 is unlikely to pose a risk to residential receptors post-sequestration. Assumed exposures to H2S did not exceed toxicity criteria for the short-term release scenarios. Further, H2S was not assumed to be released through the caprock and did not exceed toxicity criteria for long-term releases through both existing and induced faults. However, assumed long-term releases of H2S from both well types resulted in assumed exposures to concentrations that exceeded the toxicity criteria within 745 feet (227 meters) of the release (Table 5-20). The 50 year sequestration plume footprint is located near a town in an area that is largely agricultural. The results for a well release are illustrated in Figure 5-6.
Table 5-22 shows that the only likely ecological effects from assumed releases of CO2 and H2S are olfactory effects in several insects. These effects are not expected to significantly affect ecological communities. However, it should be noted that there are no ecological toxicity criteria were available for H2S.
Figure 5-6. Area Within Which H2S Released from CO2 Injection Wells Exceeds Chronic Toxicity Criteria (i.e., 0.0014 ppmv H2S) at the Tuscola (IL) Site
Table 5-11. Acute Human Health Effects (Jewett, TX) Within 328 feet (100 meters) of Wells
Effects Exposures
Release Scenario Gas
Level
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 1,490 0.02
0.20 MRL - inh. Acute No effects 0.15 0.8
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 1,490 0.02
0.20 MRL - inh. Acute No effects 0.15 0.8 deep oil and gas wells
(days)
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 1,490 0.02
0.20 MRL - inh. Acute No effects 0.15 0.8 constructed wells (days)
H2S
Table 5-12. Chronic Human Health Effects (Jewett, TX)
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 0.076 0.000008
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 0.076 0.000002
50,000 Injury, Tremors
USEPA
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 4 0.0004
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 4 0.0001
50,000 Injury, Tremors
USEPA
Table 5-12 (continued). Chronic Human Health Effects (Jewett, TX)
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 2.2 0.0002
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 2.2 0.00006
50,000 Injury, Tremors
USEPA
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
Table 5-12 (continued). Chronic Human Health Effects (Jewett, TX)
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
Table 5-13. Chronic Effects on Biota (Jewett, TX)
380 increased growth, biomass
10,000 fungi, abnormal growth
0.000002 0.000008 0.00008 CO2
Table 5-13 (continued). Chronic Effects on Biota (Jewett, TX)
380 increased growth, biomass
10,000 fungi, abnormal growth
Table 5-13 (continued). Chronic Effects on Biota (Jewett, TX)
380 increased growth, biomass
10,000 fungi, abnormal growth
Table 5-13 (continued). Chronic Effects on Biota (Jewett, TX)
380 increased growth, biomass
10,000 fungi, abnormal growth
Table 5-13 (continued). Chronic Effects on Biota (Jewett, TX)
380 increased growth, biomass
10,000 fungi, abnormal growth
Table 5-13 (continued). Chronic Effects on Biota (Jewett, TX)
380 increased growth, biomass
10,000 fungi, abnormal growth
Table 5-14. Acute Human Health Effects (Odessa, TX) within 328 feet (100 meters) of wells
Effects Exposures
Release Scenario Gas
Level
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 149 0.002
0.20 MRL - inh. Acute No effects 0.015 0.08
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 149 0.002
0.20 MRL - inh. Acute No effects 0.015 0.08
deep oil and gas wells (days)
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 149 0.002
0.20 MRL - inh. Acute No effects 0.015 0.08
Table 5-15. Chronic Human Health Effects (Odessa, TX)
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 1.6 0.0002
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 1.6 0.00004
50,000 Injury, Tremors
USEPA
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 4.1 0.0004
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 4.1 0.0001
50,000 Injury, Tremors
USEPA
Table 5-15 (continued). Chronic Human Health Effects (Odessa, TX)
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 2.2 0.0002
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 2.2 0.00006
50,000 Injury, Tremors
USEPA
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
Table 5-15 (continued). Chronic Human Health Effects (Odessa, TX)
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
Table 5-16. Chronic Effects on Biota (Odessa, TX)
stimulation 1.6 380 increased growth,
biomass 1.6 0.5
1.6 700 increases/decreases
in plant respiration 1.6 10
poisoning 1.6 10,000 fungi, abnormal
growth 1.6 1,000
Table 5-16 (continued). Chronic Effects on Biota (Odessa, TX)
stimulation 4.1 380 increased growth,
biomass 4.1 0.5
4.1 700 increases/decreases
in plant respiration 4.1 10
poisoning 4.1 10,000 fungi, abnormal
growth 4.1 1,000
Table 5-16 (continued). Chronic Effects on Biota (Odessa, TX)
stimulation 2.2 380 increased growth,
biomass 2.2 0.5
2.2 700 increases/decreases
in plant respiration 2.2 10
poisoning 2.2 10,000 fungi, abnormal
growth 2.2 1,000
Table 5-16 (continued). Chronic Effects on Biota (Odessa, TX)
stimulation 60 380 increased growth,
biomass 60 0.5
60 700 increases/decreases
in plant respiration 60 10
poisoning 60 10,000 fungi, abnormal
growth 60 1,000
Table 5-16 (continued). Chronic Effects on Biota (Odessa, TX)
stimulation 60 380 increased growth,
biomass 60 0.5
60 700 increases/decreases
in plant respiration 60 10
poisoning 60 10,000 fungi, abnormal
growth 60 1,000
Table 5-16 (continued). Chronic Effects on Biota (Odessa, TX)
stimulation 60 380 increased growth,
biomass 60 0.5
60 700 increases/decreases
in plant respiration 60 10
poisoning 60 10,000 fungi, abnormal
growth 60 1,000
Table 5-17. Acute Human Health Effects (Mattoon, IL) Within 328 feet (100 meters) of Wells
Effects Exposures
Release Scenario Gas
Level
(ppmv) Type
Concentration
(ppmv) Risk Ratio 20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 298 0.004
0.20 MRL - inh. Acute No effects 0.029 0.1
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 NA NA
0.20 MRL - inh. Acute No effects NA NA
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 298 0.004
0.20 MRL - inh. Acute No effects 0.029 0.1
Table 5-18. Chronic Human Health Effects (Mattoon, IL)
Effects Exposures
Release Scenario Gas
Level
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 0.077 0.000008
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 0.077 0.000002
50,000 Injury, Tremors
USEPA
IRIS Not released Not released
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 3.7 0.0004
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 3.7 0.00009
50,000 Injury, Tremors
USEPA existing faults due to
effects of increased pressure
H2S
0.02 MRL-Int ATSDR < 3.3 (1) 0.0004 0.02
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 1.9 0.0002
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 1.9 0.00005
50,000 Injury, Tremors
USEPA induced faults due to
effects of increased pressure (local
over-pressure)
H2S 0.0014 RfC USEPA
IRIS < 3.3 (1) 0.00019 0.1
Table 5-18 (continued). Chronic Human Health Effects (Mattoon, IL)
Effects Exposures
Release Scenario Gas
Level
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
NA NA NA
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
NA NA NA
50,000 Injury, Tremors
USEPA through deep oil and
gas wells [No wells at this site]
H2S 0.0014 RfC USEPA
IRIS NA NA NA
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
Table 5-19. Chronic Effects on Biota (Mattoon, IL)
stimulation 0.077 380 increased growth,
biomass 0.077 0.5
0.077 700 increases/decreases
in plant respiration 0.077 10
mosquitoes,
poisoning 0.077 10,000 fungi, abnormal
growth 0.077 1,000
0.077 0.000002 0.000008 0.00008 CO2
Table 5-19 (continued). Chronic Effects on Biota (Mattoon, IL)
stimulation 3.7 380 increased growth,
biomass 3.7 0.5
3.7 700 increases/decreases
in plant respiration 3.7 10
poisoning 3.7 10,000 fungi, abnormal
growth 3.7 1,000
Table 5-19 (continued). Chronic Effects on Biota (Mattoon, IL)
stimulation 1.9 380 increased growth,
biomass 1.9 0.5
1.9 700 increases/decreases
in plant respiration 1.9 10
poisoning 1.9 10,000 fungi, abnormal
growth 1.9 1,000
Table 5-19 (continued). Chronic Effects on Biota (Mattoon, IL)
stimulation 60 380 increased growth,
biomass 60 0.5
60 700 increases/decreases
in plant respiration 60 10
poisoning 60 10,000 fungi, abnormal
growth 60 1,000
Table 5-19 (continued). Chronic Effects on Biota (Mattoon, IL)
stimulation NA 380 increased growth,
biomass NA 0.5
NA 700 increases/decreases
in plant respiration NA 10
poisoning NA 10,000 fungi, abnormal
growth NA 1,000
Table 5-19 (continued). Chronic Effects on Biota (Mattoon, IL)
stimulation 60 380 increased growth,
biomass 60 0.5
60 700 increases/decreases
in plant respiration 60 10
poisoning 60 10,000 fungi, abnormal
growth 60 1,000
Table 5-20. Acute Human Health Effects (Tuscola, IL) Within 328 Feet (100 Meters) of Wells
Effects Exposures
Release Scenario Gas
Level
(ppmv) Type
Concentration
(ppmv) Risk Ratio 20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 298 0.004
0.20 MRL - inh. Acute No effects 0.03 0.2
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 NA NA
0.20 MRL - inh. Acute No effects NA NA
20,000 Headache, etc.
Possible
70,000 Unconsciousness USEPA 2000 298 0.004
0.20 MRL - inh. Acute No effects 0.03 0.2
Table 5-21. Chronic Human Health Effects (Tuscola, IL)
Effects Exposures
Release Scenario Gas
Level
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 0.076 0.000008
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 0.076 0.000002
50,000 Injury, Tremors
USEPA
IRIS Not released Not released
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 3.7 0.0004
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 3.7 0.00009
50,000 Injury, Tremors
USEPA existing faults due to
effects of increased pressure
H2S
0.02 MRL-Int ATSDR < 3.3 (1) 0.0004 0.02
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 1.9 0.0002
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
< 3.3 (1) 1.9 0.00005
50,000 Injury, Tremors
USEPA induced faults due to
effects of increased pressure (local
over-pressure)
H2S 0.0014 RfC USEPA
IRIS < 3.3 (1) 0.00019 0.1
Table 5-21 (continued). Chronic Human Health Effects (Tuscola, IL)
Effects Exposures
Release Scenario Gas
Level
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA
10,000 human discomfort
USEPA (2000);
Saripalli (2003)
NA NA NA
40,000 Headache, etc.
USEPA (2000);
Saripalli (2003)
NA NA NA
50,000 Injury, Tremors
USEPA through deep oil and
gas wells [No Wells]
H2S 0.0014 RfC USEPA
IRIS NA NA NA
10,000 human discomfort
USEPA
40,000 Headache, etc.
USEPA
50,000 Injury, Tremors
USEPA