You are here:
GROUND WATER SAMPLING ISSUES
Citation:
Paul*, C J. AND R W. Puls*. GROUND WATER SAMPLING ISSUES. Presented at Minnesota Water Pollution Control Board, St. Paul, Minnesota, 11/07/00.
Description:
Obtaining representative ground water samples is important for site assessment and
remedial performance monitoring objectives. Issues which must be considered prior to initiating a ground-water monitoring program include defining monitoring goals and objectives, sampling point/well installation and location, sampling device/method, welt purging and sampling, monitoring water levels, water quality indicator parameters, and filtration and sample handling. Monitoring well or sampling point installation can greatly influence samples collected, therefore it is important to minimize these impacts, from drilling through installation and development. Proper site characterization, including well delineated contaminant distribution, is necessary to determine proper placement of monitoring points. The sampling device or method used can significantly impact data quality and reliability. Low-flow purging and sampling techniques can minimize purge volumes and decrease monitoring costs as well as provide representative and reproducible ground water samples from conventional monitoring wells. Pump placement into monitoring wells should be conducted with as little disturbance to the water column as possible. Dedicated sampling devices reduce disturbance and minimize purge time. Water level should be monitored periodically throughout purging and sampling to measure draw-down for flow rate adjustment. Use of low-flow purging and sampling techniques or passive sample collection devices are alternative methods for obtaining representative samples from low permeability formations and fractured rock. Water quality indicator parameters are used to determine when adjacent formation water has entered the well screen. However, some parameters are more sensitive than others (e.g., redox, DO) and should be evaluated with time over several sampling events before establishing sampling protocol. Field filtration of samples depends on the sampling objective (e.g., dissolved) and consideration must be given to filter size, type, media, etc. Finally, to maintain sample integrity prior to analysis, consideration must be given to sample handling, containers used, and preservation methods.