In 1990 the Minnesota Geological Survey (MGS) purchased a van and a downhole geophysical logging system with support from the Legislative Commission on Minnesota Resources. MGS had previous logging experience using borrowed equipment and realized the value of this kind of geologic data and the wide variety of applications to which it could be applied.Geophysical logging provides high-quality, objective measurements of sediment, rock, and aquifer properties in a very cost-effective manner. We can extract important information from existing boreholes, greatly increasing opportunities to gather data, and reducing the need for expensive drilling. The LCMR has also provided support in recent years for upgrading the equipment and adding additional tools and capabilities. The current system provides digitally recorded data from natural gamma, SP, resistivity, caliper, and EM flowmeter probes. Our database of borehole logs includes over 2,500 feet of logged hole from 5625 holes. Interpreting the logging data allows us to identify which formations are penetrated by the borehole, how the borehole is constructed, and where water enters or leaves the borehole. This information has been applied to many geologic investigations including:
1990 LCMR project on the sensitivity of the Prairie du Chien- Jordan aquifer.
2001 LCMR project on ground water flow within the Praire du Chien aquifer.
The County Geologic Atlas and Regional Hydrogeologic Assessment Program.
All MGS drilling programs.
Support for Minnesota Department of Health well construction, well abandonment, enforcement, and wellhead protection programs.
Metropolitan Council project on ground water availability in the northwest metro area.
2001 LCMR project on the impact of quarries on ground water systems.
Adding geologic context to ground water monitoring programs.
The logging system is used almost daily, logging about 200 boreholes every year. The data is used on virtually every MGS project and has also supported external programs of the DNR, the Health Department, Met Council, counties, cities, and the USGS.