WorldWide Drilling Resource

Notes from the Groundwater Guy by Thomas E. Ballard, P.G., C.H.G. Southeast Hydrogeology, PLLC Sometimes There Is Just Not Enough Water I recently got a phone call from a colleague whom I team up with on well projects from time to time. He had an interesting dilemma he was trying to work through that I thought might be instructive to oth- ers. My colleague was working with a small community water system which drilled a 700-foot open hole well into a moderately dipping sandstone unit that was both overlain and underlain by relatively impermeable shale. The sand- stone unit was 227 feet thick and dipped at 48 degrees, so the well penetrated the sandstone for approximately 375 feet. In spite of multiple short pumping tests which indicated the well should produce about 10 gallons per minute, the well actually produced 1-2 gallons per minute, which was far less than necessary for the water system. Needing more water, the water system decided to put in another well in the same sandstone unit, which is the only poten- tially viable aquifer within their service area. Their reasoning for the new well was if they could intercept a greater interval of the sandstone, it would increase their well yield. So they proposed drilling a 70-degree well to intercept the sand- stone at a depth of 300 feet along strike of the sandstone unit to try to maximize the interval of the aquifer the well inter- cepted. Putt ing aside the chal lenges of drilling, constructing, and operating an angle well for water supply, their real problem was not intercepting more of the aquifer in the well, but rather how much water the aquifer was capable of producing, period. It is unlikely they will see any signif- icant improvements in yield from the new well because the aquifer is just not capable of producing any more water. In this case, with the impermeable shale above and below the aquifer and some general knowledge of the hydrogeologic characteristics of the sandstone, we can easily calculate how much water the aquifer is capable of storing and yield- ing to the well within its radius of influ- ence. Couple this with rainfal l in the known area of the surface exposure of the aquifer, and we can calculate the amount of recharge avai lable to the aqui fer to replace the water being pumped out. Ultimately, we can deter- mine what the well is capable of produc- ing from this limited aquifer. Sometimes, you just need to ask the right questions! Tom Tom Ballard may be contacted via e-mail to michele@ worldwidedrillingresource.com WTR 29 WorldWide Drilling Resource ® DECEMBER 2018 The World of Minerals Minerals will return next month with Gold!