Jianghai Xia, Kansas Geological Survey, The University of Kansas, Lawrence, Kansas
Stephen L. Williams, The City of Hutchinson, Kansas

The City of Hutchinson designed seven sites with a total area of 512,000 ft2 to search for abandoned brine wells after the City researched literature of the salt mining history in Hutchinson area. A high-resolution magnetic survey was conducted on these seven sites in May 2002. Twenty-three anomalies were verified by excavation with a backhoe, of which are five were identified as brine wells, four as suspected brine wells, one probable water well, and one probable gas pipe. A monopole anomaly with more than 12,000 nanoteslas in amplitude is a basic criterion to identify a well with an 8-inch metal case. A monopole anomaly with several thousand nanoteslas in amplitude is a basic criterion to identify a 2.5-inch or 4-inch well. The high-resolution magnetic method with theodolite-defined grids was successful in locating the abandoned brine wells in the City of Hutchinson, Kansas.
On January 17, 2001, a natural gas explosion and fire destroyed two downtown Hutchinson businesses. The next day another explosion occurred at a mobile home park three miles away. Two residents died of injuries from the explosion, which forced the evacuation of hundreds of people as gas geysers began erupting in the area. The geysers spewed a mixture of natural gas and saltwater. The pathways to the land surface at both the explosion sites and the geysers were abandoned brine wells used for solution mining of salt (www.kgs.ukans.edu/Hydro/Hutch/Background/index.html, Allison, 2001). To find these abandoned brine wells is a part of the Hutchinson Response Project. Some known wells in the mobile home park had steel cased pipes. The length of vertical steel pipe normally is 400 – 700 ft. An electromagnetic (EM) method was used to successfully locate one abandoned brine well at a depth of 5 ft (Xia, 2002a). Uniquely identifying well-generated EM anomaly in historical salt mining sites remains as a challenge. In addition, the investigation depth of the EM method is still an attractive research topic. However, Relatively much higher anomalies could be observed in high-resolution magnetic measurements based on forward calculations. The maximum magnetic signal caused by this pipe can be higher than 15,000 nanoteslas (nT) on the top of the normal geomagnetic field in Hutchinson, Kansas. This huge anomaly shows great promise in locating brine wells in the City noise environment.

Figure 1a. A theodolite was used to define grids for high-resolution magnetic survey. David Laflen (left)and Gang Tian (right) are defining grids.





Figure 1b. A portable cesium magnetometer G-858 was used to measure the total component of thegeomagnetic field. Xia is performing the magnetic survey. A traffic cone is acting as a line guide.



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