Drilling Replacement Monitoring Wells near the San Juan Coal Mine, NW New Mexico

Science Center Objects

The San Juan Coal Mine, an underground mine located about 12 miles west-northwest of Farmington, NM, supplies coal to the adjacent San Juan Generating Station. 


In 1977 the USGS drilled 24 coal exploration test holes in the area of the present mine; groundwater monitoring wells were installed in three of the test holes and have been monitored by the USGS from 1978 to 2014. Utilizing the monitoring data to construct groundwater flow models. In 2014 the active underground mining face was projected to intersect and undermine the locations of two of the USGS monitoring wells. The company operating the mine, BHP Billiton, informed the USGS of the planned undermining schedule and of the need to plug two of the existing wells. In exchange BHP Billiton offered to drill two replacement monitoring wells. The old USGS wells were plugged in 2014 and the new wells were drilled in 2016.

Old USGS well (with bullet -perforated casing) plugged, NM WSC

Old USGS well (with bullet -perforated casing) plugged, NM WSC

(Credit: Fred Gebhardt, USGS New Mexico Water Science Center. Public domain.)


  • Plug existing monitoring wells
  • Drill replacement monitoring wells
  • Complete new wells in different formations so they will provide groundwater level data in support of regional groundwater assessments
  • Continue collecting groundwater level measurements


In late February-early March 2016 BHP Billiton drilled two replacement wells. The deep well’s screen was set at the bottom of the Pictured Cliffs Formation; the shallow well’s screen was set in the #8 coal seam, in the Fruitland Formation. The new wells were completed flush with land surface.

In the near future the third original monitoring well will also be plugged, and relocated to another location.