A Guide to Safe Field Operations
U.S. Geological Survey Open-File Report 95-777

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Ground-Water Activities

This section of the guide discusses safety issues that are common to most of our ground-water activities. It includes procedures and guidelines to avoid personal injuries when conducting well inventory, collecting water-level data, instrumenting and repairing observation wells, drilling observation wells, conducting aquifer tests, geophysical logging of wells, and conducting surface-geophysical measurements.

Well Inventory

Wells are the primary source of ground-water data. Well inventories, either for project investigations or for basic data collection networks, usually require an intensive search for a large number of wells in a localized area. Data collection in most project wells are discontinued in a few years upon completion of the project. Wells included in the basic data collection network are selected to represent regional coverage and various ground-water conditions and are usually operated for long periods of time.

Private landowners, their dogs, and some of their livestock (bulls, horses, certain breeds of cattle, buffalo, boar, hogs, etc.) must be recognized as potential risks while conducting well inventories. Consider the following recommendations:

Collecting Water-Level Data

Fluctuations of water-levels in aquifers are obtained primarily from direct measurements with a steel tape, battery powered electric tapes, air lines equipment with pressure gages, and graphical or punch tape stage recorders. In recent years, electronic pressure transducers and data recorders have been used to measure water levels.

Collecting water-level data with a steel or electric tape is a relatively safe activity, but a few simple procedures must be followed to minimize personal injury and property damage. If the well is pumping, special precautions must be taken.

Instrumentation and Repairing Observation Wells

Observation wells usually are equipped with digital, punched-tape recorders and are used to monitor changes in water levels and to provide long-term statistics for assessing the impacts of climatic and man-induced changes. Another method uses a data logger with pressure transducers capable of recording very frequent fluctuations of the water levels in wells. This method is used for short-term projects such as measuring drawdowns during aquifer tests.

Installing instruments and repairing observation wells are relatively safe activities, but a number of procedures listed below must be followed to avoid personal injury or infringing on someone's rights.

Drilling Observation Wells

To obtain information on the subsurface and hydrology of an area, it is often necessary to drill test wells, to collect drill cuttings of formations penetrated by, or to make borehole geophysical studies involving the use of specialized logging equipment. Field personnel assigned to such projects are exposed to dangers when working around heavy machinery, and must have a thorough understanding of the drilling equipment and its operation. The following guidelines must be followed to avoid accidents while working at well drilling sites.

Conducting Aquifer Tests

Aquifer tests are routinely conducted as part of subsurface hydrologic project activities. An aquifer test involves pumping a well at a constant rate to stress the aquifer. The rate of water-level depletion is measured in the pumped well and nearby monitoring wells and the data are used to determine the hydraulic properties of the aquifer. The fluctuations in water levels are measured either electronically, mechanically, or manually. The hydraulic characteristics of the aquifer are determined graphically or analytically.

The following points need to be considered when conducting aquifer tests:

Occasionally, project work calls for aquifer testing with a high-capacity pump. A pump contractor is usually hired to install the pump, maintain it in running condition throughout the test, and remove it when the test is completed. The responsibility of the employees assigned to the site is to:

Geophysical Logging of Wells

Geophysical logging sometimes provides the only means of obtaining subsurface information. Geophysical logging can be used for determining geologic formations, aquifer characteristics, and physical properties of wells. Most geophysical logging equipment used by the USGS is permanently mounted on heavyweight carryall trucks. The equipment includes a single or multi-conductor cable and a pen and ink recorder and solid-state recorders. Data are collected by lowering sensing devices in the borehole and recording the data on a graphic chart and magnetic tape. The logger also is useful for collecting water samples at different depths by lowering a sampler into the well. The logger is generally powered by a generator, and the cable is raised and lowered with a power winch.

To minimize the potential for accidents, consider the following guidelines.

Surface Geophysical Measurements

Surface geophysical methods are often used to study the subsurface without the expense of drilling wells. These methods include electrical resistivity measurements, electromagnetic, seismic, magnetic and ground-penetrating radar surveys, and gravity techniques. The electrical resistivity, electromagnetics, and seismic methods are the most widely used for ground-water exploration. Electrical resistivity measurements require an electrode array to detect zones of high or low subsurface resistivity. The seismic surveys use an energy source such as explosives or hammers and an array of receivers to detect velocity difference between different earth materials.

Personnel who conduct surface geophysical surveys must have a thorough understanding of the equipment and its operation. General guidelines to follow are:

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A Guide to Safe Field Operations
U.S. Geological Survey Open-File Report 95-777

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