Furlong Wastewater Treatment Plant, Bucks County, Pennsylvania

Hydrogeologic and sinkhole maps, eyewitness accounts, and historical records were researched for an initial assessment of the site. Core borings and percussion probes were then performed along a 100-ft grid, with coverage being tighter in locations of known sinkhole collapse or suspicious fracture traces indicated by aerial photos. In order to stabilize the conditions for long-term performance and manage geologic risk, we developed an effective 3-tiered remediation/safeguard approach that was implemented during design, pre-construction, and construction.

In design of the HDPE liner, we accounted for the risk of undetected voids and a 10-ft wide collapse by strengthening the section with a biaxial geogrid and non-woven geotextile. Pre-construction involved compaction grouting to repair three known sinkhole areas by injecting 2,000 cubic yards into the soil and rock. For construction, we specified a special 20-ton roller. Construction testing and inspection QA/QC services provided by GeoStructures on this project included:

• Subgrade preparation
• Rapid response sinkhole remediation
• Embankment fill and soil cover compaction
• Field and laboratory testing of geosynthetics & seaming
• As-built liner panel layout