OVERBURDEN INJECTION CAN USUALLY BE COMPLETED USING READILY AVAILABLE DIRECT-PUSH TECHNOLOGY (DPT). However, subsurface conditions exist that may prevent the use of standard DPT to reach the targeted depth interval for assessment and treatment. These obstructions can be naturally occurring (hardpan/caliche, chert layers, dense fine-grained sediments, gravel, partially weathered rock, etc.) or anthropogenic (cut and fill, buried rubble like concrete, etc.).
AST has collaborated on the development of a drilling and backfilling methodology that gains access to these challenging geologies.
The injection locations are first pre-drilled to the desired depth using sonic, air rotary, or hollow-stem augers and the evacuated borehole is then backfilled with hydrated bentonite chips or pellets to seal the bore wall. DPT is then used to push through the bentonite to reach the desired injection depth intervals without compromising the bore seal. This technique has been used successfully on 30+ project sites across the country accessing depths as great as 180 feet below ground surface.