Coal combustion residuals (CCRs), or coal ash, are a byproduct of burning coal. The ash has a variety of constituents including silicon, iron, and aluminum oxides along with trace amounts of heavy metals such as arsenic, selenium, mercury, boron, and chromium. Power plants are the main generator of CCRs and normally the ash is beneficially used or stored onsite in landfills or impoundments.

According to the Environmental Protection Agency, there are over 1,000 active coal ash sites in the United States. Many coal ash basins will require dewatering before remediation and/or closure activities can occur. This presentation details the design, construction, and results of a 650-foot long dewatering well installed in a 9-acre closed ash basin using horizontal directional drilling methods. The CCR materials at the site were characterized as fly ash (10 – 100 μm) and bottom ash (5 – 38 mm). Design challenges included well screen and casing selection and drilling/installation methodology. Well installation challenges included geometry of the landfill and unexpected site conditions encountered during well completion.

Once installed, the horizontal well performed better than anticipated. The level of water in the basin was drawn down by ~18 feet in less than four months and CCR-related constituents in the surrounding groundwater declined considerably.