UCLA

Contamination of groundwater resources with naturally occurring arsenic (As) is a major health concern globally that affects millions of people. Experimental studies and geochemical modeling can be useful tools for understanding the mechanisms controlling speciation and partitioning of As, predicting the mobility and transfer of As, assessing the risks, and developing effective in-situ remediation schemes for affected areas.

The wide variety of experimental details used in the published adsorption studies, and limited number of studies conducted for adsorption of As on natural samples underscores the need for further research in this area. Application of currently available empirical models, and mechanistic surface complexation modeling (SCM) approaches for describing the adsorption of As on natural sediments is also challenging due to the complexity of the heterogeneous solid phases of porous media.

In Chapter 2, we compare different kinetic and equilibrium adsorption models for describing the adsorption data from batch experiments conducted on natural sediment samples collected from a contaminated site in New England, USA. We evaluate the capability and sensitivity of commonly used empirical models for modeling the concentrations of dissolved As as well as the relations between the derived model parameters and chemical/physical characteristics of sediments.

In Chapter 3, four different SCMs are developed to model the data from batch experiments conducted on natural sediment and groundwater samples. The SCMs used in this study vary in terms of 1) method for estimating the total number of sorption sites, 2) method for describing the surface site heterogeneity, and 3) method for applying electrostatic and pH-dependent correction factors to surface reaction constants. we utilize the easily-accessible modeling tools PHREEQC and FITEQL to predict and simulate the experimental results.

Chapter 4 focuses on batch and column experiments conducted to study the effectiveness of applying chemical amendments with the purpose of facilitating and enhancing natural attenuation of As in contaminated subsurface environments. The results will provide a qualitative basis for evaluating the suitability and efficiency of applying these methods in actual contaminated sites.