Microsoft Word Marcellus Radon doc

Table 1. Uranium Content and Depth of Marcellus Shale in Four Cores

Location of the Core	Depth of Sample (feet)	Uranium Content (ppm)
Allegheny Cty, PA	7342 – 7465	8.9 – 67.7
Tomkins Cty, NY	1380 – 1420	25 – 53
Livingston Cty, NY	543 – 576	16.6 – 83.7
Knox Cty, OH	1027 – 1127	32.5 – 41.1

The four cores were taken from different geographical locations, but the characteristics of the identified Marcellus shale layer, specifically the high uranium and carbon content, are consistent. As mentioned earlier, DEC reports uranium content up to 100 ppm. The thickness of the Marcellus shale formation varies between 0 and 250 feet, according to isopach maps.

To compare the uranium content in parts per million (weight) to radioactive concentration in picocuries per gram, we use the correspondence¹⁴

2.97 ppm = 1 pCi/g U-238

Using this relationship, the U-238 ranges up to 28 pCi/g, or 33 times background for radium-226, assuming U-238 and Ra-226 are in secular equilibrium, as it is in Marcellus Shale formation. That is, the USGS measurements and the GAPI logs are consistent. The range of 6.6 to 30 pCi/g is our starting point for the concentrations of Ra-226 in the natural Marcellus Shale formation, to determine radon concentrations at the wellhead.

Numerical simulation shows the high concentrations of radon that will be found at the wellhead for Marcellus Shale gas, based on a variety of realistic assumptions. These assumptions include the rate at which radon is generated by radium-226 which, in turn, depends on the radium concentration in the shale. Otherwise there are no major uncertainties about the rate at which radon is produced. The radon’s ability to escape from the rock matrix and be entrained by the natural gas flowing inward toward the well bore is less certain, but it can be estimated reasonably well. Our assumptions in the model we employed are listed in Table 2.