Radioactivity in Groundwater in Lahontan Valley, Nevada

Radioactivity ingroundwater in LahontanU.S. Department of the InteriorU.S. Geological SurveyValley, NevadaRalph SeilerU.S. Geological SurveyCarson City, NevadaMarch 25, 2010

Expert-panel panel recommendations• The expert panel convened by the State ofNevada in 2001 was skeptical that exposureto a chemical in the water could explain theexcess leukemia cases.• The panel recommended that exposure toradioisotopes in drinking water be evaluated.March 25, 2010

Uranium decay series238UT½ = 4.5x10 9 y226RaαT½ = 1601 y222RnT½ = 3.8 dIn Lahontan Valley,uranium, radon, andpolonium are the onlysignificant radionuclides210PbT½ = 22.3 yβ210PoT½ = 138.4 dα206PbMarch 25, 2010

Drinking-water standards• The Maximum Contaminant Level (MCL) foruranium is 30 μg/L.• The MCL for radon is 300 pCi/L.• The only applicable standard for 210 Po in theUnited States is the MCL for adjusted grossalpha radioactivity, 15 pCi/L.• The Canadian Maximum Acceptable Concen-tration (MAC) specific for 210 Po is 5.4 pCi/L.March 25, 2010

Uranium levels200010002001-2009 dataUranium concentration, in μg/g1001010.1MedianMedianMCLUranium levels in domesticwells sometimes greatlyexceed the MCL, and oftenexceed it in the shallowaquifer.0.01IntermediateAquiferShallowAquiferFallonPublic SupplyMarch 25, 2010

The distribution of uraniumMarch 25, 2010

Radon levels100002001 dataRadon concentration, in pCi/L1000MedianMedianAlternativeMCLRadon levels in domesticwells all exceed the MCL,but are relatively lowcompared to many otherareas in the US.MCL100IntermediateAquiferShallowAquiferFallonPublic SupplyMarch 25, 2010

Polonium-210 levels2001002007-2009 dataPolonium-210 activity, in pCi/L1010.1MedianGross alphaMCLCanadian MACThese are some of thehighest 210 Po levelsreported for the US.0.01IntermediateAquiferShallowAquiferFallonPublic SupplyMarch 25, 2010

Temporal stability of Uranium and RadonUranium, μg/L, 2001100101UraniumWells sampled in 1989 hadalmost the same uraniumand radon levels whensampled again in 2001.0.10.1 1 10 100Uranium, μg/L, 1989Radon, pCi/L, in 20012500200015001000500Radon00 500 1000 1500 2000 2500Radon, pCi/L, in 1989March 25, 2010

Temporal stability of Polonium-210160140Well CDP-30Estimate from adjusted grossalpha radioactivityPolonium-210, in pCi/L12010080604020Measured 210 Po activityTheoretical decay lineassuming a contaminationevent in the pastTheoretical line assumingsteady-state production of50 pCi/LThe data suggestthe 210 Po has anatural sourceand its levels haveremained stable.01/97 1/98 1/99 1/00 1/01 1/02 1/03 1/04 1/05 1/06 1/07 1/08 1/09Time of SampleMarch 25, 2010

On-going research• 210 Po usually strongly binds to sediment, sowhy is it in the water in Lahontan Valley?• Bacteria that cause rotten-egg egg odors release itfrom the sediment, where it then binds todissolved organic matter in the water.• Fewer than 100 wells in the US are knownto have 210 Po levels >15 pCi/L, but is itreally that rare?March 25, 2010

210 Po rarity• 210 Po is rare, therefore nobody tests for it,therefore it continues to be rare.• The monitoring test for the presence of 210 Po,Gross Alpha Radioactivity, involves heating thesample planchet with a flame.• Some bacteria metabolize 210 Po and create volatileforms of it. In a Florida well about 50% of the 210 Powas volatile.• If 210 Po is volatile, the monitoring test may notaccurately reflect the amount of 210 Po in the watersample.March 25, 2010

Conclusion• Could we find 210 Po elsewhere if we look for it in theright geochemical settings? Many places have radiumor radon problems, which are related to uranium inthe environment.• Lahontan Valleyprobably isn’t t uniqueand other places mayalso have 210 Po.210 Po.USEPA Map of Radon Zones in the United StatesMarch 25, 2010