Title: Relation Between pH and Occurrence of Trace Elements and Radionuclides in Water from Private Wells,
Central Oklahoma, 2011
Carol Becker, Hydrologist, U.S. Geological Survey, Oklahoma Water Science Center
202 NW 66th, Bldg. 7, Oklahoma City, OK 72116
405 810-4436 cjbecker@usgs.gov
Uranium and gross-alpha particle activities exceeded Maximum Contaminant Levels in water samples
collected from some private wells in the Kickapoo Tribe of Oklahoma Jurisdictional Area in Lincoln and
Pottawatomie Counties, Oklahoma in 1999. Residents in this rural area use private wells to obtain
groundwater from Quaternary-aged terrace deposits and the Permian-aged Garber-Wellington aquifer
for domestic purposes. Previous studies have shown that elevated groundwater pH from cationexchange processes in the aquifer causes selected metals such as arsenic, chromium, selenium, and
uranium to desorb from mineral surfaces (if present) and become mobile in water. Based on this
information, the U.S. Geological Survey, in cooperation with the Kickapoo Tribe of Oklahoma, conducted
a study in 2011 to describe the occurrence of selected trace elements and radionuclides in groundwater
and to determine if pH could be used as a surrogate to quickly and inexpensively identify wells that
might contain large concentrations.
Groundwater pH and specific conductance were measured in the field from 59 private wells. Twenty of
the 59 wells also were sampled for dissolved concentrations of major ions, trace elements, gross-alpha
and gross-beta particle activities, uranium, radium-226, radium-228, and radon-222 gas. Uranium
concentrations ranged from 0.02 to 383 micrograms per liter with 5 of 20 samples exceeding the
Maximum Contaminant Level of 30 micrograms per liter. The five wells with uranium concentrations
exceeding 30 micrograms per liter had pH values ranging from 8.0 to 8.5. Concentrations of uranium,
radon-222, and gross-alpha particle activity had positive correlations to pH, with the highest
concentrations of those constituents being measured in samples with pH values of 8.0 or above. The
groundwater samples contained dissolved oxygen and high concentrations of bicarbonate; these
characteristics are also factors in increasing uranium solubility.
Water-quality data collected for this study show that pH values above 8.0 are associated with potentially
large concentrations of uranium, radon-222, and gross alpha-particle activity in the study area. High pH
values also are associated with potentially large concentrations of arsenic, chromium, and selenium in
groundwater when these elements occur in the aquifer matrix along groundwater-flow paths.