Environmental Health - Toxic Substances
U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12, 1999--Volume 3 of 3--Subsurface Contamination From Point Sources, Water-Resources Investigations Report 99-4018C
Borehole Packers for In Situ Geophysical and Microbial Investigations in Fractured Rock
By Allen M. Shapiro, John W. Lane, Jr., and Joseph R. Olimpio
Bedrock boreholes act as unnatural, high-permeability pathways that can disturb ambient hydraulic and geochemical conditions in the bedrock. To avoid the disturbances caused by open boreholes, many investigations require the use of packers to isolate discrete intervals of bedrock boreholes; packers are either pneumatic or mechanical devices that seal against the borehole wall and hydraulically isolate a section of the borehole. Usually, packers are constructed with a metal core pipe and metal pressure-tight fittings; in some in situ investigations, however, a metal-free environment is required. Pneumatic borehole packers were designed and constructed using a polyvinly-chloride (PVC) core pipe and teflon pressure-tight fittings. These PVC packers were used to conduct borehole radar surveys during hydraulic and tracer testing, as metal in the borehole attenuates the radar signal. The PVC packers also were used to collect water samples for analysis of dissolved hydrogen to characterize redox conditions at a hydrocarbon-contaminated fractured rock site, as metal-water interactions are known to produce dissolved hydrogen.