Occurrence and geochemistry of radium in water from principal drinking-water aquifer systems of the United States (original) (raw)
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Radium geochemistry of ground waters in Paleozoic carbonate aquifers, midcontinent, USA
Applied Geochemistry, 2001
The purpose of this study was to elucidate the processes controlling the distribution and behavior of the longerlived Ra isotopes in continuous Paleozoic carbonate aquifers of parts of Missouri, Kansas, and Oklahoma. Activities of ( 228 Ra) and ( 226 Ra) were analyzed in fresh and saline ground waters, brines, and rocks. The¯uids have a wide salinity range (200±250,000 mg l À1 total dissolved solids). The ( 226 Ra) activity ranges from 0.66±7660 dpm kg À1 and correlates with salinity and other alkaline earth element (Ca, Sr, and Ba) concentrations. The range of ( 228 Ra: 226 Ra) ratios in the¯uids (0.06±1.48) is similar to that in the aquifer rocks (0.21±1.53). The relatively low mean¯uid ( 228 Ra: 226 Ra) ratio (0.30) re¯ects the low Th:U ratio of the predominant carbonate aquifer rock. Radium occurs mostly (r77%) as Ra 2+ species in the¯uids. Salinity-dependent sorption±desorption processes (with log K values from 10 0 ±10 4 and negatively correlated with salinity), involving Th-enriched surface coatings on aquifer¯ow channels, can explain the rapid solid±¯uid transfer of Ra isotopes in the system and the correlation of Ra with salinity. 7
Editorial handling by M. Kersten a b s t r a c t Salinization in groundwater systems can induce water-rock interaction, including the release of naturallyoccurring trace elements of health significance such as radium (Ra), with possible implications for the usability of water resources in addition to the increase of dissolved solids (TDS) concentrations. In general, radium mobility is limited by chemical removal mechanisms including adsorption onto clays and/or Mn and Fe oxides, exchange processes, and coprecipitation with secondary barite. In order to examine the effect of aquifer salinity gradients on the distribution of naturally-occurring Ra in fresh to saline groundwater and the relationship to water-rock interaction and Ra removal mechanisms, two contrasting systems were investigated: the shallow unconfined coastal aquifer in Agadir (southwestern Morocco) and the confined Cretaceous (Cape Fear) and Pliocene (Yorktown) aquifers of the Atlantic Coastal Plain (North Carolina, USA). Geochemical and isotopic indicators of salinity sources (e.g. cation ratios, d 18 O, d 2 H, Br À /Cl À , d 34 S-SO 2À 4 ; d 18 O-SO 2À 4 ) were used to identify the relative contributions of seawater and other saline waters and subsequent geochemical modification by waterrock interaction. Radium activities ( 224 Ra, 226 Ra, 228 Ra), radon-222, alkaline earth metal (Mg, Ca, Sr, Ba) concentrations and ratios, and 87 Sr/ 86 Sr ratios were analyzed to identify water-rock interaction processes affecting alkaline earth metals including Ra. The Morocco coastal aquifer is generally oxic, exhibits a range of salinity and water types (Cl À 163-2120 mg/L, median 932 mg/L), and exhibits Ca/Na ratios above the seawater value, typical of monovalent-divalent cation exchange (base-exchange reactions) in coastal aquifers. In contrast, the Atlantic Coastal Plain aquifers are anoxic, sulfate-reducing, cover a wider salinity range (Cl À 5-9890 mg/L, median 800 mg/L) representing a transition between Na-HCO À 3 and Na-Cl À waters, and exhibit Ca/Na ratios below that of modern seawater typical of reverse base-exchange reactions. Possible salinity sources in the Morocco coastal aquifer include seawater intrusion, Mesozoic evaporites, other natural saline waters, and/or wastewater, whereas the Atlantic Coastal Plain is primarily affected by old seawater present in the aquifer system. Radium activities are generally low and vary significantly within each aquifer, for example 226 Ra ranges from 1.8-27.7 mBq/L in the Morocco coastal aquifer (median 8.1 mBq/L) and 1.9-214 mBq/L in the Atlantic Coastal Plain (median 18.9 mBq/L). The highest Ra activities were observed in the most saline wells sampled in the Atlantic Coastal Plain. At total dissolved solids (TDS) concentrations above an apparent threshold of 5000mg/L,radiumactivitiesincreaseinagenerallylinearfashionwithsalinityintheAtlanticCoastalPlain,broadlycomparabletopreviousstudiesindicatingathresholdrangeof5000 mg/L, radium activities increase in a generally linear fashion with salinity in the Atlantic Coastal Plain, broadly comparable to previous studies indicating a threshold range of 5000mg/L,radiumactivitiesincreaseinagenerallylinearfashionwithsalinityintheAtlanticCoastalPlain,broadlycomparabletopreviousstudiesindicatingathresholdrangeof3000-10,000 mg/L. At lower TDS concentrations, water-rock interaction processes that vary with local aquifer conditions appear to control Ra distribution rather than merely salinity. In the Morocco coastal aquifer, adsorption of Ra and coprecipitation with secondary barite are apparently favorable to control Ra levels in groundwater. Radium removal in the anoxic Atlantic Coastal Plain aquifers appears to be associated with adsorption and/or exchange processes, with the additional possibility of barite precipitation in the Cape Fear aquifer indicated by barite saturation. Overall, the locally-variable factors that can control Ra sources and mobility in fresh to brackish groundwater at near-neutral pH include variation in solid-phase radioactivity, redox state affecting adsorption sites, availability of competing divalent cations, and barite saturation.
Illinois State Water Survey, 2021
The St. Peter Sandstone is part of the Cambrian-Ordovician aquifer system in the Midwestern U.S. and is a major aquifer covering a large area, including central Illinois. Recharge to the St. Peter Sandstone during the Pleistocene and Holocene has come from multiple locations and displaced in situ brines, which have altered the geochemistry. Radium (Ra) levels are above the drinking water standard of 5 picocuries per liter (pCi/L) in many community water supply wells open to the St. Peter Sandstone. The purpose of this research was to examine sources and sinks of Ra and other radioisotopes in the Middle Illinois water supply planning region. Both 226 Ra and 228 Ra are found in the groundwater, indicating that both uranium and thorium (238 U and 232 Th) decay chains are important in the aquifer. Many of the wells sampled were open to formations overlying and underlying the St. Peter Sandstone, and shale facies in those units may be sources of U to the St. Peter. Radon (222 Rn) data indicate that most of the 226 Ra is associated with the solid phase. In a region where the St. Peter Sandstone is at or near the land surface and active recharge is occurring, adsorption to Fe-and/or Mn-oxyhydroxides appears to be the major control on Ra concentrations in solution. High sulfate (SO 4 2-) concentrations in the confined regions of the aquifer indicate that barite solubility is a control on Ra concentrations in these regions. Sorption/desorption reactions also likely play a role in Ra solubility. Pleistocene meltwater recharge has exerted a strong influence on the Ra and U geochemistry in the St. Peter Sandstone. Multiple episodes of fresh Pleistocene water that penetrated far into the St. Peter appear to have brought in oxygen that caused U to be solubilized, transported, and then reprecipitated out of solution once more reducing conditions were re-established. Fractionation of U isotopes occurred as a result of the fluctuating redox conditions and is especially pervasive in the Central region of our study area. These impacts of Pleistocene recharge may be prevalent locally due to the proximity of the aquifer's northward recharge zone where the St. Peter Sandstone outcrops and subcrops.
Radium-226 and radium-228 in shallow ground water, southern New Jersey
Fact Sheet
Concentrations of total radium (the sum of radium-226 and radium-228) and gross alpha-particle activities in drinking water that exceed the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) are known to cause cancer. Results of investigations by the U.S. Geological Survey (USGS) in cooperation with the New Jersey Department of Environmental Protection (NJDEP) indicate that concentrations of total radium in water samples from 33 percent of 170 wells in the Kirkwood-Cohansey aquifer system in southern New Jersey exceeded the MCL of 5 pCi/L (picocuries per liter) (fig. 1). Wells containing water in which concentrations of total radium were greater than the MCL typically are found where the Bridgeton Formation crops out, in or near an agricultural area, where ground water is acidic (pH less than 5), and where nitrate concentrations generally exceed 5 mg/L (milligrams per liter). Leaching of nitrogen, calcium, and magnesium from agricultural chemicals (fertilizer, lime) applied to cropland may increase the mobility of radium in ground water. Gross alphaparticle activities exceeded the USEPA MCL of 15 pCi/L in water from 14 percent of 127 wells. A statistically significant 2:1 ratio between gross alpha-particle activity and concentration of total radium indicates that gross alpha-particle activity can be used as a screening tool to predict the presence of water that may have a high total-radium concentration.
1982
reports on the activities of 226 Ra in ground water in varied geographic and geologic provinces (Scott and Barker 1962, Cherdyntsev 1971, Kaufmann and Bliss 1977, Michel and Moore 1980a). Radium-228 studies in ground water are few compared to 226 Ra due to the difficulties in present analytical procedures for 228 Ra. Krause (1959) reported 228 Ra activities in deep sandstone aquifers in Iowa, Illinois, Wisconsin and Missouri ranging