Effect of biogas generation on radon emissions from landfills receiving radium-bearing waste from shale gas development

Figures & data

Table 1. Uranium and thorium decay series leading to production of radon and thoron

^238U Series	Half-Life	^232Th Series	Half-Life
^238U	4.5 × 10^9 yr	^232Th	1.4 × 10^10 yr
^234Th	24 days	^228Ra	5.8 yr
^234Pa	1.2 min	^228Ac	6.1 hr
^234U	2.4 × 10^5 yr	^228Th	1.9 yr
^230Th	7.7 × 10^4 yr	^224Ra	3.7 days
^226Ra	1600 yr	^220Rn	56 sec
^222Rn	3.8 days	^216Po	0.15 sec
^218Po	3.1 min	^212Pb	11 hr
^214Pb	27 min	^212Bi	61 min
^214Bi	20 min	^212Po and ^208Tl	3 × 10^-7 sec, 3.1 min
^214Po	1.6 × 10^−4 sec	^208Pb	Stable
^210Pb	22 yr
^210Bi	5 days
^210Po	140 days
^206Pb	Stable
Notes: Half lives from Argonne National Laboratory, EVS, Human Health Fact Sheet, August 2005. http://www.ead.anl.gov/pub/doc/natural-decay-series.pdf.

Figure 1. Illustration of radon transport processes in a landfill and landfill construction used in numerical simulations (thicknesses not to scale).

Table 2. Hydraulic properties assigned to material types used in landfill model

Material	Saturated Hydraulic Conductivity (K h) (m/sec)	Porosity	Water Saturation	Vertical Anisotropy (K z/K h)
Vegetative layer	2 × 10^−5	0.3	0.2	0.1
Drainage layer	1 × 10^−3	0.3	0.01	1
Clay barrier	2 × 10^−7	0.4	0.3	0.1
Geomembrane	2 × 10^−14	0.01	NA	NA
TENORM waste	2 × 10^−5	0.4	0.3	0.1
Refuse	1 × 10^−4	0.4	0.3	0.1

Table 3. Transport properties assigned to material types used in landfill model

Material	Bulk Density (kg/m^3)	^226Ra (pCi/kg)	Rn Emanation Factor	Dispersivity (m)
Vegetative layer	1500	0	0.1	1
Drainage layer	1500	0	0.1	1
Clay barrier	1500	0	0.1	1
TENORM waste	1500	50,000	0.2	1
Refuse	1300	0	0.1	1

Figure 2. Configuration of LFG collection wells. (A) Passive vent wells. (B) Active collection system with central vent well.

Table 4. Summary of Radon emission rates from the landfill model simulations

	Emitted through Surface (pCi/sec)
Scenario	Advective	Diffusive	Emitted Through Wells (pCi/sec)	Total Atmospheric Emission (pCi/sec)	Decayed in Subsurface (pCi/sec)	Ratio Decayed to Emitted	Effective Surface Flux (pCi/m^−2-sec)
No gas control	0	3.9 × 10^5	0	3.9 × 10^5	5.1 × 10^6	13	9.8
Clay cover—No control	1.2 × 10^6	1.0 × 10^6	0	2.2 × 10^6	6.6 × 10^6	1.2	55
Clay cover—Passive	2.7 × 10^5	1.1 × 10^6	2.4 × 10^4	1.4 × 10^6	3.7 × 10^6	2.6	35
Clay cover—Active	6.6 × 10^4	7.6 × 10^5	6.6 × 10^4	8.9 × 10^5	4.3 × 10^6	4.8	22
Geomembrane—Passive	Negligible	Negligible	6.3 × 10^4	6.3 × 10^4	5.2 × 10^6	83	1.6
Geomembrane—Active	Negligible	Negligible	7.3 × 10^4	7.3 × 10^4	5.3 × 10^6	72	1.8

Figure 3. Summary of radon emission rates for the various landfill cover and LFG collection scenarios.

Figure 4. Radon mass decayed versus radon emissions from the LFG system.

Figure 5. Simulated atmospheric radon activity at 2-m elevation. (A) Landfill with no LFG production, emissions by diffusion only. (B) Landfill with clay cover and passive LFG vent system. (C) Landfill with geomembrane cover and passive LFG vent system. Note that atmospheric activities are computed analytically only at locations in the computational grid. The plumes would extend outside the computational grid (color figure available online).

Figure 6. Simulated atmospheric radon activities at 2-m elevation. (A) Landfill with clay cover, LFG generation, and no LFG control system. (B) Landfill with clay cover and active LFG control system. (C) Landfill with geomembrane cover and active LFG control system. Note that atmospheric activities are computed analytically only at locations in the computational. The plumes would extend outside the computational grid.

Figure 7. Equivalent ²²²Ra surface flux computed for the various landfill scenarios. Equivalent surface flux is the total emission rate from the landfill surface and LFG control wells divided by the landfill cell area.