NGWA Event and Education Recordings Archive

The Capitan Reef limestone encompasses the Permian-age Delaware Basin, and sedimentary rocks associated with the Capitan reef is one of the most continuous and well-studied ancient carbonate shelf margins in the world.  The hydrogeologic framework of the Capitan Reef Complex (CRCX) aquifer was originally defined by Hiss (1975) and then adopted by the Texas Water Development Board (TWDB) as a designated minor aquifer.  As a result of data from supply wells completed in the down-dip portion of the eastern arm, the CRCX aquifer has been considered as a brackish groundwater resource.  The extent of the CRCX aquifer was modified by Standen and others (2009), but a significant portion between Fort Stockton and the Glass Mountains remained largely as a data gap area.  Most of this data gap area includes the La Escalera Ranch, a privately owned contiguous 225,000 acre area centered over the CRCX aquifer recharge area directly north of the Glass Mountains.  During 2014, well log, down-hole video survey, water quality, and pumping test data were collected from the La Escalera Ranch and analyzed.  It was found that previous work by Hiss (1975) and Standen and others (2009) did not include the Tessey Limestone when defining the extent of the aquifer, even though it is recognized as part of the CRCX aquifer system.  The Tessey Limestone was combined with the Capitan Limestone to re-define the extent of the CRCX aquifer. Water level and water quality data were used to re-evaluate recharge estimates.  The CRCX aquifer is a karst system containing a large volume of fresh groundwater in storage with a significant rate of recharge.  The fresh groundwater zone averages 1,500 ft in thickness, and covers an area of about 15 by 20 miles.  Recharge estimates range from 20,000 to 36,000 ac-ft/yr, and Total Dissolved Solid content ranges from 300 to 1,200 mg/L.