Presented at Society for Mining, Metallurgy & Exploration (SME) 2012 Annual Meeting. This talk covered research done by a coorporative agreement with the US Office of Surface Mining, Reclamation & Enforcement.

1. Monitoring Reclaimed Mine
Land For Stray CO2 Hazards
Mathiba Moagabo
Kwame Awuah-Offei
1

2. Outline
• Background
• Study sites
• Sampling procedures
• Data analysis
• Results & discussions
• Conclusions
2

3. BACKGROUND
3

4. Background
• Elevated CO2 concentrations in homes is now being
recognized as a safety & health hazard
• Incidents of potentially lethal concentrations reported:
– CO2 > 25% (MSHA action level = 0.5%)
– O2 < 10% (MSHA a. l. = 19.5%)
• Attributed to AMD-carbonate neutralization
• Several cases reported in several parts of the Appalachia
(OH, PA, WV, IN), UK, Canada.

5. Project Objective
To develop a soil CO2 flux survey
protocol for assessing reclaimed mine
land, to determine the hazard potential
and to delineate, potentially, hazardous
areas
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6. STUDY SITES
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7. Site 1: Hudson Site
• Located in Pike Co., IN
• Latitude: 38°19’ 2”
• Longitude: 87°08’ 27”
• Coal mined from 1986 to
1992
• Spoil material extends to
~11.6 m below
• ~36 ha Reclaimed with lime amendment and about
0.91 m of top soil capping
• Episodes of elevated concentrations of stray CO2
since 2006 7

8. Site 2: Godin Site
• Located in Sommerset Co.,
PA
• Latitude: 40°08′ 02″
• Longitude: 79°02′ 52″
• Home built on 70 ft thick,
reclaimed mine spoil
• Permit required spoiling pit cleanings in pods
>10 ft above pit floor with 20 tons/acre of lime
amendment
• CO2 intrusions into home reported in 2003
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9. SAMPLING PROCEDURES
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10. Flux Sampling
• LI-8100 automated flux
system
• Collars installed for >24
hrs
• Each sampling point
surveyed
• Chamber deployed for 2
minutes
10

11. 11

12. Isotope Sampling
• Method 1
– Grab samples from 2 ft
deep slam bars and bore
holes
• Method 2
– Multiple (3) gas samples
drawn during chamber
deployment
– Method accounts for
isotope fractionation and
gas mixing 12

13. DATA ANALYSIS
13

14. Tests of Correlation
• Pearson correlation coefficients used to
assess correlation
• Moran’s I statistic used to assess spatial
correlation
• Significance of correlations assessed at
95% confidence
n n
n
I wij Z si Z Z sj Z
n 1 S 2 w.. i 1 j 1
n 2
Z si Z
S2 i 1
n 1 14

15. Geostatistical Analysis
• Included variogram
modeling, estimation, and probability
maps using sequential Gaussian
simulation (sGs)
• We used GS+ version 9
• Spherical variogram model selected
• 1,000 simulations (sGs)
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16. RESULTS & DISCUSSIONS
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17. Preliminary Statistics
SAMPLE DAY
Parameter March 30, 2010 March 31, 2010 April 1, 2010
Anderson- A2 7.15 0.29 7.27 0.49 6.44 0.70
Darling p-value
Normality Test < 0.005 0.600 < 0.005 0.216 < 0.005 0.064
Mean 2.345 0.269 2.512 0.330 2.960 0.401
Standard Deviation 1.820 0.294 1.676 0.238 1.806 0.236
Variance 3.313 0.086 2.809 0.056 3.262 0.056
Skewness 2.167 0.187 2.355 0.493 2.095 -0.078
Kurtosis 5.695 -0.175 7.077 0.147 5.539 1.540
Number of Samples, N 131 131 131 131 130 130
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18. Preliminary Statistics
SAMPLE DAY
Parameter July 13 2010 July 14 2010 July 16 2010
Anderson- A2 1.57 0.88 0.68 1.89 0.63 0.26
Darling p-
Normality value <
Test 0.0005 0.023 0.071 < 0.005 0.099 0.700
Mean 5.029 0.664 8.859 2.132 7.878 2.00
Standard Deviation 2.264 0.186 3.049 0.400 2.716 0.3539
Variance 5.123 0.0345 9.295 0.160 7.374 0.1252
Skewness 2.472 -0.4098 0.0934 -2.330 0.584 -0.2614
Kurtosis 12.627 1.6950 1.428 11.439 -0.008 -0.1342
Number of
Samples, N 71 71 73 72 71 71
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19. Correlation Analysis
Day Correlated Variable Soil temp. Soil moisture
March 30 Log of Flux 0.521 -0.402
p-value < 0.0001 <0.0001
March 31 Log of Flux 0.280 -0.106
p-value 0.001 0.230
April 1 Log flux 0.263 -0.325
p-value 0.002 < 0.0001
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20. Spatial Dependence
Data Set No of Global Moran’s Expected Value p-value
Samples I
Pike Co. Day 136 0.4284 -0.0074 0.0000
1
Pike Co. Day 136 0.3190 -0.0074 0.0000
2
Pike Co. Day 132 0.2666 -0.0076 0.0000
3
Godin Day 1 71 -0.0404 -0.0143 0.6219
Godin Day 2 71 0.1074 -0.0143 0.0755
Godin Day 3 71 0.1535 -0.0143 0.0242
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21. Isotope Tests
Depth (m)
0 0.61 5.79 11.58
0
-10
δ13C-CO2 ( ‰)
-20
-30
-40
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22. Estimation
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23. Conclusions
• Soil temperature and moisture content are
important factors that influence soil gas emission
• Spatial dependence should not be assumed, but
must be evaluated for each site
• The spatial variability in soil CO2 emissions
appears to be controlled by gas permeability and
macro-porosity
• This project has developed a soil CO2 flux survey
protocol
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