Obtaining representative ground water samples in a fractured and karstic formation

Journal Article · Sun Mar 01 04:00:00 EST 1998 · Ground Water

DOI:https://doi.org/10.1111/j.1745-6584.1998.tb01090.x· OSTI ID:577328

McCarthy, J ^[1]; Shevenell, L ^[2]

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1. Oak Ridge National Lab., TN (United States). Environmental Sciences Div.
2. Univ. of Nevada, Reno, NV (United States). Nevada Bureau of Mines and Geology

Environmental concerns about the migration of toxic contaminants in subsurface systems can be addressed only if ground water can be accessed in a manner that yields a sample that is representative of the mobile load of contaminants. Ground water was sampled from a number of wells along recharge pathways between fractured shale and karstic carbonate formations to determine the effect of sampling methods on the colloid abundance and the chemical and hydrologic mechanisms controlling the abundance of ground water colloids. Low-flow minimal drawdown purging and sampling produced samples with much lower and more consistent turbidity than had been obtained during compliance monitoring of the same wells using much higher flow rates and purging of three well volumes. Although some low-yielding wells required very low pumping rates to prevent drawdown, water quality parameters stabilized fairly quickly. The total volume of water removed during purging was small (usually only a few liters), and did not appear to be related to either the casing volume or the screen volume of the well. This lack of correlation may indicate that a limited volume of the formation is samples at the low flow rates. Since only a portion of long screened intervals appear to be sampled, care must be given to placement of the sample tubing to access zones where contaminant migration is expected.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC05-84OR21400; AC05-96OR22464
• OSTI ID: 577328
• Journal Information: Ground Water, Journal Name: Ground Water Journal Issue: 2 Vol. 36; ISSN GRWAAP; ISSN 0017-467X
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ENVIRONMENTAL TRANSPORT
GEOLOGIC FRACTURES
GROUND WATER
SAMPLING
TOXIC MATERIALS
WATER POLLUTION