Monitoring Reclaimed Mine Land For Stray CO2

Hazards

Mathiba MoagaboKwame Awuah-Offei

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Outline

• Background• Study sites• Sampling

procedures• Data analysis• Results &

discussions• Conclusions

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BACKGROUND

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.

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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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STUDY SITES

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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

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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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SAMPLING PROCEDURES

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Flux Sampling

• LI-8100 automated flux system

• Collars installed for >24 hrs

• Each sampling point surveyed

• Chamber deployed for 2 minutes

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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

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DATA ANALYSIS

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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

21 1..

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2 1

1

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n n

ij i ji j

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nI w Z Z Z Z

n S w

Z ZS

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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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RESULTS & DISCUSSIONS

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Preliminary Statistics

Parameter

SAMPLE DAYMarch 30, 2010

March 31, 2010 April 1, 2010

Anderson-Darling Normality Test

A2 7.15 0.29 7.27 0.49 6.44 0.70p-value

< 0.005 0.600

< 0.005 0.216

< 0.005 0.064

Mean 2.345 0.269 2.512 0.330 2.960 0.401Standard Deviation 1.820 0.294 1.676 0.238 1.806 0.236Variance 3.313 0.086 2.809 0.056 3.262 0.056Skewness 2.167 0.187 2.355 0.493 2.095 -0.078Kurtosis 5.695 -0.175 7.077 0.147 5.539 1.540Number of Samples, N 131 131 131 131 130 130

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Preliminary Statistics

ParameterSAMPLE DAYJuly 13 2010 July 14 2010 July 16 2010

Anderson-Darling Normality Test

A2 1.57 0.88 0.68 1.89 0.63 0.26p-value <

0.0005 0.023 0.071 < 0.005 0.099 0.700Mean 5.029 0.664 8.859 2.132 7.878 2.00Standard Deviation 2.264 0.186 3.049 0.400 2.716 0.3539Variance 5.123 0.0345 9.295 0.160 7.374 0.1252Skewness

2.472 -0.4098 0.0934 -2.330 0.584-0.2614

Kurtosis12.627 1.6950 1.428 11.439 -0.008

-0.1342

Number of Samples, N 71 71 73 72 71 71

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Correlation Analysis

Day Correlated Variable

Soil temp. Soil moisture

March 30 Log of Flux 0.521 -0.402p-value < 0.0001 <0.0001

March 31 Log of Flux 0.280 -0.106p-value 0.001 0.230

April 1 Log flux 0.263 -0.325p-value 0.002 < 0.0001

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Spatial Dependence

Data Set No of Samples

Global Moran’s I

Expected Value

p-value

Pike Co. Day 1

136 0.4284 -0.0074 0.0000

Pike Co. Day 2

136 0.3190 -0.0074 0.0000

Pike Co. Day 3

132 0.2666 -0.0076 0.0000

Godin Day 1 71 -0.0404 -0.0143 0.6219Godin Day 2 71 0.1074 -0.0143 0.0755Godin Day 3 71 0.1535 -0.0143 0.0242

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Isotope Tests

-35-30-25-20-15-10-50

Depth (m)

δ13C

-CO

2 (

‰)

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Estimation

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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