HTGCD Old Hundred Dedicated Monitoring Well: Summary of Drilling Operations and Well Evaluation


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December 2018


The Hays Trinity Groundwater Conservation District (HTGCD) Old Hundred Dedicated Monitor Well is the fourth and final well in a two-year drilling and evaluation program designed for western Hays County. Drilling began on August 18, 2018 and the well bottomed in the Hammett formation at 560 feet after drilling a full Middle Trinity section. The Old Hundred Ranch is owned by the Curtis and Willett families who graciously donated access to a portion of their property for the monitor well. The well was drilled on a heavily wooded hillside just south of Cypress Creek, on the northern outskirts of Wimberley, Texas. This report contains the results of the well drilling and evaluation program. The Old Hundred well was drilled for the HTGCD by Geoprojects International. The data collection goals of the program, including geophysical logging, downhole camera survey, pump testing, and geochemical sampling and analysis were successfully completed. The Upper Glen Rose carbonate section is exposed at ground level. Minor water was encountered at the base of the Upper Trinity and there were important groundwater flows observed in the Lower Glen Rose and Cow Creek formations. The borehole was cased and completed isolating the Cow Creek sub-aquifer unit. Two piezometers were installed in the borehole annulus; one with screened interval opposite the Lower Glen Rose, “upper reef” and the other at the base of the Upper Glen Rose. A pump was set in the main casing and the well was developed and subsequently tested at 80 gallons-per-minute (gpm) for 48hours with 30 feet of drawdown. A water sample was collected for geochemical analysis. In addition to the testing and sampling operations an extensive formation evaluation program was completed including: cutting samples collection and description, a downhole video camera and a geophysical logging program. The planned coring program was limited to a single core because of borehole conditions (excessive water from overlying aquifer units). The following highlights are noted: 1. A well-deve


Old Hundred, Dedicated, Monitor Well

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HTGCD Technical Report, Vol. 2018, no. 1218 (2018-12-01).