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An Analysis of Low‐Flow Ground Water Sampling Methodology
Author(s) -
Sevee John E.,
White Carol A.,
Maher David J.
Publication year - 2000
Publication title -
groundwater monitoring and remediation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 47
eISSN - 1745-6592
pISSN - 1069-3629
DOI - 10.1111/j.1745-6592.2000.tb00269.x
Subject(s) - drawdown (hydrology) , aquifer , hydraulic conductivity , slug test , sampling (signal processing) , groundwater , flow (mathematics) , water level , aquifer test , soil science , environmental science , geology , water well , water flow , hydraulic head , hydrology (agriculture) , geotechnical engineering , mechanics , soil water , groundwater recharge , engineering , physics , electrical engineering , filter (signal processing) , cartography , geography
Abstract Low‐flow ground water sampling methodology can minimize well disturbance and aggravated colloid transport into samples obtained from monitoring wells. However, in low hydraulic conductivity formations, low‐flow sampling methodology can cause excessive drawdown that can result in screen desaturation and high ground water velocities in the vicinity of the well, causing unwanted colloid and soil transport into ground water samples taken from the well. Ground water velocities may increase several fold above that of the natural setting. To examine the drawdown behavior of a monitoring well, mathematical relationships can be developed that allow prediction of the steady‐state drawdown for constant low‐flow pumping rates based on well geometry and aquifer properties. The equations also estimate the time necessary to reach drawdown equilibrium. These same equations can be used to estimate the relative contribution of water entering a sampling device from either the well standpipe or the aquifer. Such equations can be useful in planning a low‐flow sampling program and may suggest when to collect a water sample. In low hydraulic conductivity formations, the equations suggest that drawdown may not stabilize for well depths, violating the minimal drawdown requirement of the low‐flow technique. In such cases, it may be more appropriate to collect a slug or passive sample from the well screen, under the assumption that the water in the well screen is in equilibrium with the surrounding aquifer.