Greenhouse Gas Potential from leaking Natural Gas in Massachusetts

Here is my calculation for the Greenhouse Gas Potential from the 8 billion cubic feet of natural gas (methane, or CH4) lost each year in the state of Massachusetts:

Convert to cubic meters: 8 x 10^9 ft^3 x 0.028 m^3/ft^3 = 2.26 x 10^8 m^3 CH4

or, 2.26 x 10^11 liters of CH4

assume (accepting a bit of temperature and pressure error) 22.4 liters per mole for an ideal gas at standard temperature and pressure.

2.26 x 10^11 liters x 1 mol/22.4 liters = 10^10 moles CH4

use 1 mole CH4 = 16 grams

10^10 moles CH4 x 16 grams/mol = 1.6 x 10^11 grams CH4

use CH4 25X the Greenhouse Gas Potential of CO2
(ref: http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf)

= 4.0 x 10^12 g eCO2 = 4 Million Metric Tonnes equivalent CO2 per year in Massachusetts in lost natural gas.

This is about 4-5% of the total state greenhouse gas emissions inventory
(ref: http://www.mass.gov/dep/air/climate/ghg08inv.pdf)