EDITOR'S NOTE -- This is the last article in a series designed to update readers on the status of the Edwards-Trinity (High Plains) Aquifer drilled in Wolfforth--CEM.
By Jason Coleman, P.E.
HPWD General Manager
In the first two articles of this series, we described the geophysical logging and construction of the test well at Wolfforth. The results of the pump test and water quality test are presented in this concluding article of the series.
After the temporary well was constructed in the Edwards-Trinity (High Plains) (ETHP) aquifer, the contractor used an airlift procedure to help remove the drilling mud and develop the well. It is necessary to remove the cake of mud in the borehole wall so that the formation water is transmitted to the well casing. The contractor then installed a submersible pump for test pumping the well. Over a twelve hour period of test pumping, the well did not produce much more than ten gallons per minute. As a result, the test pump was removed in favor of additional well development techniques. These processes involved more air lifting, as well as a chemical treatment to help remove any remaining drilling mud. Despite these efforts, little improvement in the well productivity was realized. Our conclusion is that the limestone rocks do not contain significant cracks or void spaces at this location.
The formation water produced during test pumping was also tested at this time. The results of this analysis show very high dissolved mineral content. The water was tested by hand sampler in the field, at a certified laboratory, and with a continuous monitoring probe. All three methods produced very similar results. You may recall that public drinking water systems must have total dissolved solids (TDS) of less than five hundred milligrams per liter. A TDS of 500 mg/L is roughly the same as conductivity of 810 microsiemens per centimeter (uS/cm).
The chart shown on the front page of this electronic newsletter indicates the test well conductivity ranges from 8,000-16,000 uS/cm, much higher than the allowable for public drinking water.
Scientific publications indicate that water quality in the ETHP Aquifer is generally a bit higher in TDS than Ogallala. However at this location, the ETHP results are more than ten times higher in TDS than the Ogallala. This leads us to question whether the sampled water is truly indicative of the ETHP, or if there is a Dockum Aquifer influence in the sampled water. HPWD studies show that water quality of this same TDS level is present in the Dockum Aquifer. We also know that “upconing” may occur in the Dockum, which could result in the high TDS results from these samples. More work should be performed in the ETHP water quality sampling before we may conclusively resolve this question.