Use of Chemical and Isotopic Signatures to Distinguish Between Uranium Mill‐Related and Naturally Occurring Groundwater Constituents

Abstract

Chemical and isotopic signatures were determined in groundwater samples to aid in distinguishing the source of contamination in three desert arroyos and a buried channel (the swale) near Shiprock, New Mexico. The contamination in the swale and one of the arroyos, Many Devils Wash, was previously attributed to a former uranium mill site because of the similar suite of contaminants (nitrate, selenium, sulfate, and uranium) and the close (0.8 km) proximity. The other two arroyos are far removed from the mill site and could not have received contamination from it. Principal component and cluster analysis indicated similarities in groundwater chemistry among the swale and the three arroyos that contrasted with groundwater chemistry at the disposal cell. Disposal cell groundwater is characterized by high uranium and bicarbonate concentrations, whereas that in remaining study areas is characterized by high sodium and sulfate, but lower uranium concentrations. Mancos Shale forms the bedrock in the region and contains elevated concentrations of the same chemical constituents that appear in the swale and arroyo groundwater. Dissolved sulfate in arroyo groundwater was depleted in sulfur‐34, in contrast to mill‐derived sulfate with more enriched sulfur‐34. Uranium‐234 to uranium‐238 activity ratios (ARs) were near the secular equilibrium value of 1 in mill site groundwater, whereas ARs in all arroyo groundwater samples exceeded 2. Elevated tritium activities present in mill site groundwater (49 to 142 pCi/L) are attributed to the mill being operated during atomic bomb testing in the 1950s and 1960s. The combined chemical and isotopic results indicate that groundwater in Many Devils Wash and the swale was likely derived from the Mancos Shale and not from the milling operation.

Factors affecting the Faradaic efficiency of Fe(0) electrocoagulation

“…For arsenic contaminated groundwater (pH 7.5), we prepared a synthetic Bangladesh groundwater (SBGW) electrolyte solution following a recipe derived from a British Geological Survey analysis of thousands of groundwater wells in Bangladesh [39]. For groundwater co-contaminated by uranium and nitrate (pH 3.5-5.5), which can occur at sites of uranium enrichment [37], we prepared two nitrate contaminated groundwaters (NO 3 -GW 1 and NO 3 -GW 2) that were made to mimic the composition of contaminated groundwaters reported previously [40][41][42][43][44]. Because of their trace concentrations, arsenic and uranium were excluded from the synthetic groundwater recipes.…”

“…Source waters with low chloride levels, alkaline pH and high concentrations of nitrate, carbonate and other high affinity oxyanions can be a barrier to high Faradaic efficiency. Treatment influents with such solution chemistry can be encountered in nitrate contaminated groundwater systems, including those impacted by agricultural runoff [57], sewage [58], and radionuclide enrichment activities [37,42,44]. Furthermore, chloride concentrations in groundwaters contaminated by geogenic arsenic can be low and…”

Development of electrospun polymer nanofiber mats for removal of uranium from aqueous systems

“…Uranium concentrations in the area varied from 1.5 µg/L to 9280 µg/L, with 32 of the 33 samples being above that of the MCL. 6 At high uranium concentrations in water there is potential for increased toxicological risk for the public. Exposure studies found that people exposed to high uranium concentrations in water (620 µg/L average) had an average uranium concentration of 0.162 µg/L in their urine (highest detected at 9.55 µg/L) several months after exposure.…”

“…where the solubility constant (K sp ) is related to the soluble species activity raised to the power of their molar coefficient. 27 This is compared to that of groundwater near Shiprock, NM that had concentrations of HCO 3 between ~100-1500 mg/L (pH's between 6.4 and 7.7) 6 where CO 3 2would be at ~ 0.5% of these concentrations (0.5-7 mg/L). At such high concentrations in surface waters and ground waters, carbonates can compete with uranium hydrolysis products, creating highly soluble uranyl carbonate species and contributing to enhanced mobility of uranium in the environment.…”

“…Materials were tested over a range of uranium concentrations that varied from just below its MCL in drinking water (0.1 µM) to the more extreme levels of uranium contamination that may be present in some affected water resources (10 µM). 6 HDPA and HDEHP were both tested in acidic conditions (pH 2) because those are the conditions where they exhibited the best performance. Isotherm experiments with Aq and AOPAN were conducted at a pH of 6.8, as these conditions are more representative of surface and drinking water samples while also being a pH that both Aq and AOPAN performed well in.…”