Contribution of cadmium detected in groundwater monitoring wells from lignite of the Yegua Formation, Angelina County, Texas

The Angelina County Waste Management Center (ACWMC) has three on-site groundwater monitoring wells that consistently have levels of cadmium (Cd) above the maximum contaminant level (MCL) for drinking water. The ACWMC is excavated into the Eocene Yegua Formation which contains lignite seams. Oxidation of the lignite seams contributes to Cd concentrations detected in monitoring wells. Lignites from the study area were analyzed and found to have between 0.54 and 3.98 ppm of Cd per 0.5g sample. Near well MW-12A, there is an estimated volume of 625ft3 (18m3) of lignite, which contains a calculated value of 27g to 201g of Cd. Oxidation of organic matter and sulfides in the lignite cause the groundwater to become acidic and leach metals such as Cd from the lignite. This oxidation is a result of the excavation of the landfill, which allowed oxygenated waters to interact with subsurface lignite.