Document Detail

Implications of observed and simulated ambient flow in monitoring wells.
MedLine Citation:
PMID:  11708451     Owner:  NLM     Status:  MEDLINE    
A recent paper by Hutchins and Acree (2000) has called attention to ground water sampling bias due to ambient (natural gradient-induced) flows in monitoring wells. Data collected with borehole flowmeters have shown that such ambient flows are ubiquitous in both confined and unconfined aquifers. Developed herein is a detailed three-dimensional model of flow and transport in the vicinity of a fully penetrating monitoring well. The model was used to simulate a measured ambient flow distribution around a test well in a heterogeneous aquifer at the Savannah River Site (SRS) near Aiken, South Carolina. Simulated ambient flows agreed well with measurements. Natural flow was upward, so water entered the well mainly through high K layers in the lower portion of the aquifer and exited through similar layers in the upper portion. The maximum upward discharge in the well was about 0.28 L/min, which implied an induced exchange of 12 m3/month from the bottom half of the aquifer to the upper half. Tracer transport simulations then illustrated how a contaminant located initially in a lower portion of the aquifer was continuously transported into the upper portion and diluted throughout the entire well by in-flowing water. Even after full purging or micropurging, samples from such a well will yield misleading and ambiguous data concerning solute concentrations, location of a contaminant source, and plume geometry. For all of these reasons, use of long-screened monitoring wells should be phased out, unless an appropriate multilevel sampling device prevents vertical flow.
B A Elci; F J Molz; W R Waldrop
Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Ground water     Volume:  39     ISSN:  0017-467X     ISO Abbreviation:  Ground Water     Publication Date:    2001 Nov-Dec
Date Detail:
Created Date:  2001-11-15     Completed Date:  2002-02-20     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9882886     Medline TA:  Ground Water     Country:  United States    
Other Details:
Languages:  eng     Pagination:  853-62     Citation Subset:  IM    
Environmental Engineering and Science, Clemson University, Anderson, SC 29625, USA.
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MeSH Terms
Environmental Monitoring*
Models, Theoretical*
Water Movements*
Water Supply
Reg. No./Substance:
Comment In:
Ground Water. 2004 Jan-Feb;42(1):137-8; discussion 138-9   [PMID:  14763627 ]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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