Limitations on the collection of representative samples from small diameter monitoring wells
One decision to be made when scoping a ground-water contamination investigation is what size and type of monitoring well to install. Four-inch diameter wells are often used in temperate climates when the depth to water or the volume of water to be purged is great, and two-inch diameter wells are specified where purging can be conducted efficiently using a bailer or a small-diameter bladder pump. The recent availability of high-volume submersible pumps capable of use in two-inch diameter monitoring wells makes it possible to specify two-inch diameter wells where four-inch diameter wells were previously required. Design of these wells is critical to the attainment of representative ground-water samples. Based on the length of the screened interval, the size of the screen openings, and whether the screen is slotted or wound, there is a maximum discharge rate from any well that, if exceeded, will results in turbulent flow into the well. The transition from laminar to turbulent flow results in pressure changes which could result in loss of carbon dioxide and other volatile gases, subsequently changing pH and dissolved solids content. The pumping rate should be regulated so that the entrance velocity of water into a well remains below the threshold velocity, maintaining laminar flow during purging and sampling. The maximum discharge rate during purging should be based on the hydraulic conductivity of the aquifer, the length of saturated well screen, the width of the screen openings, and the total open area within the screen.
- Research Organization:
- Westinghouse Environmental Management Co. of Ohio, Cincinnati, OH (United States). Fernald Environmental Management Project
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC05-86OR21600
- OSTI ID:
- 10127072
- Report Number(s):
- FEMP-2258; CONF-9205103-1; ON: DE92008535
- Resource Relation:
- Conference: 6. national outdoor action conference on aquifer restoration, ground water monitoring and geophysical methods,Las Vegas, NV (United States),11-13 May 1992; Other Information: PBD: 7 Jan 1992
- Country of Publication:
- United States
- Language:
- English
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