RESONANT SONIC DRILLING AT THREE FORMER MGP SITES: BENEFITS AND LIMITATIONS

摘要

Resonant sonic drilling was utilized at three MGP sites in New York State to install deep monitoring wells beneath tar. The experience gained at the three sites demonstrated that resonant sonic drilling is a cost- and time-effective technology for evaluating deep subsurface conditions at former MGP sites. The method was able to obtain continuous, representative soil cores in formations where conventional drilling methods failed. The quality of soil samples obtained and the small amount of soil cuttings generated by the sonic method were also advantageous. A resonant sonic well installation method using temporary casing was developed and approved by the New York State Department of Environmental Conservation. This temporary casing method was used at five well locations and subsequent groundwater monitoring data demonstrate that the method was successful in preventing the downward migration of tar. Permanently grouted casings are not recommended for use with the resonant sonic method. Based on our cost analysis for two sites, the cost per linear foot to install resonant sonic wells ranged from $132 to $158, while the cost per linear foot to conventionally install wells ranged from $140 to $189. A cost comparison could not be made for the third site. At one site, the resonant sonic method generated only six drums of investigation-derived waste for two approximately 115-foot deep wells, while conventional drilling methods generated 44 drums of waste for comparable depth wells. However, one substantial drawback to the method was the generation of fluids when used in very low conductivity soils. Disposal costs of fluids generated in low conductivity formations may substantially impact the savings from reduced soil cuttings. The method is likely not cost-effective for installing wells shallower than about 30 to 40 feet deep due to longer set-up/breakdown time and high mobilization fees.