Monitoring Well Installation, Purging, and Sampling Techniques — Part 2: Case Histories

Abstract

Three case histories are presented to illustrate the problems encountered using some monitoring well installation, purging, and sampling techniques. Hollow‐stem auger‐ing was found to pose problems during the installation of monitoring wells in terms of potential for cross‐contamination of strata, the inability to emplace an adequate filter pack, the potential for smearing natural clays into sand and gravel strata, and the possible need for excessive purging of sediments that accumulate between sampling events. Cable tool drilling was found to allow construction of high quality wells, but was slow and expensive. Concern over the potential for increased emissions of noxious vapors from the borehole when drilling with the air rotary method prevented its use in situations where highly contaminated strata were likely to be encountered. A hybrid drilling technique, augering with temporary casing, was able to provide the advantages, and minimize the disadvantages, of the foregoing drilling methods. The installation of vertically separated clusters of monitoring wells lent important insights into the potential movement of a contaminant plume. Detailed aquifer tests provided needed information on the hydraulic behavior of the subsurface strata occupied by the plume so that potential pathways of contaminant transport could be more accurately identified. Obtaining reliable data from such tests depended greatly on the ability of each monitoring well to act as a high quality hydraulic observation well. The selection of drilling and installation techniques that ensured minimal disturbance of the near‐borehole environment provided the best guarantee of such performance.

Ground water purging and sampling methods: History vs. hysteria

“…At the same time, further neglect of the unique hydraulic characteristics of monitoring wells led to the use of high-rate pumping devices. The need for more effective and documented sampling methods was driven by the more stringent sampling and analytical data quality objectives, which are placed on micropollutant compliance monitoring programs (Clark and Baxter 1989;Keely and Boateng 1987;Barcelona 1988). In addition, high-flow rate purging resulted in the production of large volumes of potentially contaminated water that required costly handling and treatment.…”

“…It was further recognized that purging was necessary due to in-well water quality changes (Barcelona and Helfrich 1986). The need for more effective and documented sampling methods was driven by the more stringent sampling and analytical data quality objectives, which are placed on micropollutant compliance monitoring programs (Clark and Baxter 1989;Keely and Boateng 1987;Barcelona 1988).…”

Physical Measurements in Subsurface Hydrology

“… Keely and Boateng (1987a,b) examined the commonly employed methodology for the installation, purging and sampling of monitoring wells. Many problems associated with augering wells were identified, and there is a discussion of the advantages and disadvantages of cable tool drilling.…”

Kinetics of chromate reduction during naphthalene degradation in a mixed culture

“…However, organic compounds are frequently detected along with toxic metals at polluted sites or in water streams. Aromatic compounds and chromate were extensively detected as cocontaminants (Canter, 1986;Carlo et al, 1993;Keely and Boateng, 1987;Patterson, 1985; U.S. EPA, 1990a). The inhibitory influences of cocontaminant metals such as chromate on the rate of bioremediation were noted by other investigators (Topp and Hanson, 1990;U.S.…”