Several case studies indicate that the design, construction, and long-term operation of filter and drainage systems playing an integral part in CCR disposal facilities can be problematic.
These systems may include, but are not limited to, blanket and toe drains, drainage trenches and columns, and other leachate collection features. Several factors contribute to problems experienced with these systems in varying degrees and based on conditions that are unique to each specific site. However, there are some common elements found to have more pronounced effects on the functionality of CCR filter and drainage systems that span multiple sites. Characteristics of CCRs (e.g., wet vs. dry processing, fly ash vs. gypsum, etc.), particle size compatibility with selected filter media, granular filter thickness, and construction practices have been observed to significantly impact the effectiveness of filter and drainage systems resulting in partial or complete clogging that can, and on occasion has, resulted in both instability and potential permit violation concerns.This paper presents a few case studies where the drainage system was significantly compromised, in one instance after less than six months of operation, because selected filter media was found to be insufficient for proper retention and filtration of CCRs. The paper will also discuss unique challenges of designing filter and drainage systems for CCRs, pros and cons of using various synthetic and natural products, considerations for design and construction practices including constructability and cost, and ongoing industry initiatives to develop, test, and optimize filter and drainage materials for CCR related applications.