USGS-OWQ: NFM 4.2 Ground-Water Sampling: Collection of ground-water samples at supply and monitoring wells
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Official Method Name
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Collection of ground-water samples at supply and monitoring wells |
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Current Revision
| 2006 |
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Media
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WATER |
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Instrumentation
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Not Applicable |
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Method Subcategory
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Sampling/Preparation |
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Method Source
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Citation
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Brief Method Summary
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Prepare to collect samples for chemical or microbial analysis by making accurate depth-to-water measurements and ensuring that standing water is evacuated (purged) from the well. Well-installation and well-yield data should be known and kept in a field folder. Communication of the well with the aquifer should be checked every 3 to 4 years. Standard purge procedure involves purging three or more well volumes of standing water from the well while monitoring change in field properties (e.g., water level, pH, temperature, specific electrical conductance, dissolved-oxygen concentrations, and turbidity), generally using a submersible pump. The actual number of well-volumes of water removed depends on recent pumping history, water-level recovery, stabilization of targeted field-property values (figure 4-12), knowledge of borehole and aquifer hydraulics for the well, and professional judgment. Consult section 4.2.3B for exceptions to the standard well-purging procedures, including guidance on the ?low-flow? purging method. Sample collection begins when field measurements indicate that fresh formation water is being withdrawn, and is a contiguous process with purging. The rate of pumping for sampling should be the same as that for purging, and produce a smooth, non-turbulent flow of water. The rate of flow for filling sample bottles should not exceed 500 mL/min for bottles 250 mL or greater in volume or 150 mL/min for 40-mL VOC vials. Flow should be constant and uninterrupted while purging and sampling ground-water wells. Collect and process samples using non-contaminating equipment : samples for organic-compound analysis, avoid contact with plastics except for fluorocarbon polymer; samples for inorganic-constituent analysis, avoid contact with metal. Supply-well sampling: standard purging procedures may be modified, especially for wells that are pumped daily; determine if sample contamination is a threat from permanently installed pump or other equipment or |
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Scope and Application
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The standard USGS procedure for collecting ground-water samples consists of six basic steps: 1) implement safety precautions and site and clean-sampling preparations, 2) measure water level, 3) purge the well and monitor field-property measurements, 4) withdraw the sample, 5) process the sample, and 6) clean the equipment. The procedures used for supply wells differ somewhat from those used for monitor wells. The main differences involve the purging procedures used, logistical difficulties with differing well construction materials and equipment found in supply wells, and the type of system used to withdraw the sample: for example, centrifugal pumps permanently installed in supply wells versus portable or dedicated submersible pumps used in monitor wells. |
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Applicable Concentration Range
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Depends on project requirements and objectives, site and sampling conditions, and type of sampling equipment. |
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Interferences
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Ensure that there are no water-storage tanks, holding or pressurization tanks, or chemical disinfection or water-softening systems connected inline between the pump and tap/faucet to which sample tubing will be connected. Obtain written permission to install a tap if it is necessary for bypassing a holding tank or treatment system. |
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Quality Control Requirements
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Refer to section 4.0 on clean-sampling methods and to section 4.3 on collection of quality-control samples. Follow the appropriate quality-control procedures for the sample analyte (organic, inorganic, or microbiological). Adhere to project data-quality objectives and requirements. |
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Sample Handling
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Refer to section 4.0 on clean-sampling methods; and to the instructions in section 4.1 for handling surface-water samples and in section 4.2 for handling ground-water samples. |
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Maximum Holding Time
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Samples should be appropriately processed, treated, and submitted for analysis as soon after collection as possible. |
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Relative Cost
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Unknown |
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Sample Preparation Methods
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See http://pubs.water.usgs.gov/twri9A/ |
