In order to confirm the similar behavior of Eu and Am in heterogeneous geological materials, we carried out the batch experiments for determining the sorption property of radionuclides,¹⁵²Eu and²⁴¹Am. We used four different types of core rocks including biotite banded gneiss, biotite gneiss, metabasite and andestic tuff, and selected two samples per each lithology, one of which is fracture-bearing and another is fracture-free. Except for metabasites, rock samples of each type are similar in their compositions. We calculated sorption ratios of two radionuclides from the experimental results. Biotite gneiss and tuff had similar sorption trends for¹⁵²Eu and²⁴¹Am regardless of the existence of fractures, whereas two metabasite samples showed very different sorption properties. Such difference in the sorption trends revealed a close relationship with chemical compositions of the host rocks. Nevertheless,¹⁵²Eu and²⁴¹Am showed similar adsorption trends for all the samples with variable contact times regardless of petrography and pH variations, and particularly, the sorption trends of¹⁵²Eu and²⁴¹Am in the metabasites were similar. This observation suggests that Eu and Am have similar sorption properties on geological materials. Therefore, Eu can be used as a useful analogue of Am in all kinds of geological environments regardless of variations in lithology and pH of groundwater. In addition, sorption ratios of¹⁵²Eu and²⁴¹ Am are correlated with the contents of P₂O₅ and TiO₂, suggesting that the chemical components such as P₂O₅ and TiO₂ might be important for deciphering the interaction between the radionuclide and groundwater.

Groundwater response to tidal effect in a finite leaky confined coastal aquifer is analyzed considering the impact of hydraulic head at the source bed (upper unconfined aquifer). For the groundwater response analysis, the impact of head at the source bed and the effect of boundary condition on the inland side are discussed. The shape of hydraulic head at the source bed is considered in two cases; (1) constant head, using mean groundwater level of concerning domain that may or may not be equal to mean sea level, and (2) linearly increasing head with distance from the coastline. The dimensional and nondimensional boundary value problems are solved for hydraulic head in the aquifer using Laplace transform technique, and the results are obtained by the numerical inversion of the transformed solution. Evaluation of the solution indicates that, near the coastline, the hydraulic head in a leaky confined aquifer is mostly influenced by the tidal effect, while the distance from the coastline increases, the effect of head in the source bed rises. A sensitivity analysis is conducted to show the importance of the hydraulic head and its shape at the source bed as well as leakance, which affects the head in a confined leaky coastal aquifer. The solution derived in this study is useful for there may be a natural or an artificial barrier on the inland side that acts as a no flux boundary. The study considering this boundary condition implies that care must be taken when aquifer parameters are estimated using previous analytical solutions, since boundary conditions on the inland side affect the head of leaky confined aquifer, and thus may mislead to erroneous aquifer parameter estimation.

Interactions between groundwater and aquifer rock can result in anomalously high levels of radium (Ra) and radon (Rn) in groundwaters. An understanding of aquifer mineralogy and determining the sources of natural radionuclides are, therefore, essential to design possible means for improving groundwater quality. The Cambrian Hickory Sandstones and Cap Mountain Limestones constitute important aquifers in the area surrounding the Llano Uplift in central Texas. Groundwaters produced from these aquifers, however, have anomalous concentrations of Ra and Rn, much greater than the maximum contaminant levels (MCL) suggested by the USEPA. To determine the sources of Ra and Rn, the abundance, distribution, and nature of occurrence of U and Th, parent radionuclides of Ra and Rn, were examined in cored aquifer rock samples.

The Hickory, 136 m thick, consists of a coarse-grained sandstone lower submember, a calcareous sandstone middle, and a fossiliferous and hematitic sandstone upper, with thin shale laminae throughout. The Cap Mountain, 44 m thick, is a sandy limestone. Detrital materials are composed of 77% quartz, 19% feldspars, and 4% lithic fragments, and are classified as subarkose. Accessory minerals are less than 1% in average. Authigenic minerals, primarily clay, Fe-oxide minerals and carbonate, make up 18% of the bulk rock. Porosity is of secondary origin.

Analysis of U in a total of 128 sandstone and shale samples shows an average of 3.8 ppm, ranging from 1 to 8.5 ppm. Th concentrations in 21 bulk rock samples range from 8.4 to 18.6 ppm, averaging 13.7 ppm. The U and Th contents are similar to those of the underlying Precambrian granites, from which much of the sediments were derived. The primary modes of U occurrence are in: (1) biogenic materials such as phosphatic brachiopod fragments and intraclasts; (2) thin shaly laminae enriched in phyllosilicates; (3) authigenic minerals, particularly hydroxyl-oxides of iron and clay minerals; and (4) detrital accessory minerals.

Mobilization of U and its decay products by groundwaters can account for the Ra and Rn anomaly in the produced water, particularly interacting with intervals of high concentrations of shaly laminae, phosphatic materials, or iron-oxide cements.