Dewatering CCR- The Current State of Practice

摘要

The past several years have seen numerous applications of dewatering techniques in CCR. Those techniques include rim ditching and sumping, wellpoints and deep wells, as well as horizontally installed drainage methods. Access to the surface of any ash pond still remains the initial challenge. Deeper ponds lend themselves to the use of widely spaced wells for dewatering. Unfortunately, wells are typically installed with sizable drill rigs. Access had been facilitated with floating roads or a shallow crust provided with wellpoint dewatering. Wellpoints are now commonly installed by hand from very wet and unstable pond surfaces using temporarily stabilized working platforms. Based on preliminary CPT data, the target depth of penetration of the dewatering system is anticipated. CPT data will provide some indication of the ponds hydrogeological behavior. Early field testing is typically performed to verify the hydrogeological behavior and depth of penetration of the dewatering devices. Pilot tests have been performed with shallow wellpoints and wells up to 150 ft (46 m) in depth. Advancements in dewatering techniques in CCR include high capacity well / wellpoint screen that is compatible with the difficult behavior of ash, the use of variable frequency driven pumps that are effective in very low yielding conditions, and where the ash water chemistry is prone to well fouling. This paper will highlight recent applications of the common dewatering techniques, as well as benefits and complexities more recently understood associated with dewatering and ash stabilization.