WorldWide Drilling Resource

A Consultant’s Perspective by Edward E. Everett, CPG Strata Environmental Services, Inc. Water Level Data Recorders - A Blessing or a Curse? My hydrogeologic education and early experience in the field involved manually collecting aquifer test data, then taking the data, plotting it by hand on logarithmic graph paper, then doing manual curve matching to determine aquifer characteristics. Some equations just required entering various data into the formula and calculating the results (with the use of those new-fangled calculators). If a calculation resulted in a transmis- sivity value of 43,576.2 gallons per day per foot (GPD/ft), we rounded up the number to 44,000 GPD/ft, or if we wanted to be precise, we rounded the number to 43,600 GPD/ft. I understand the concept of GPD/ft, but now we use feet squared per day, which I cannot wrap my brain around. Importantly, we understood we were characterizing an aquifer of many acres, or even square miles from data collected from a couple of wells representing a miniscule percentage of the aquifer area. Consequently, it was our opinion that rounding of our calculated numbers was probably as accurate as we needed to be, given the amount of information we had on the aquifer. Now we collect aquifer test data with data loggers which can be programmed to collect water levels at just about any designated time interval. In a recent test, I set the loggers to record on a logarithmic scale, with a maximum time interval of 15 minutes. During the initial start of the test, the data loggers recorded 63 readings in the first minute, with the number of readings decreasing until the 15-minute increment was reached after 2.5 hours. Where I work, our regulatory agencies want the early time data because it is “so important”. So what do roughly 100 readings in the first three minutes of the test tell us? (We used to have to hustle to get three readings in this same time period.) Pump discharge is based on total dynamic head, so when water levels in a well are high (at the start of a test), the pump will produce a higher volume of water. Most of the time, the drop pipe and discharge pipe are empty when the test starts, fur- ther reducing total dynamic head. This is especially true when testing a well hooked to an irrigation system, which may have hundreds of feet of piping before the water reaches the irrigation heads. Eventually, the system reaches an equilibrium pres- sure, the water level in the well reaches relatively stability, and the pumping rate remains constant. At that time, we meet the requirements of a constant-rate aquifer test. So what does all the early time data tell us? In my opinion, it tells us more about the system configuration and pump design than it actually tells us about the aquifer response to pumping. This information occurs after system pressure stabi- www.starironworks.com 257 Caroline Street Punxsutawney, PA 15767 800-927-0560 • 814-427-2555 Fax: 814-427-5164 SERVINGTHECONSTRUCTION INDUSTRY Serving the Drilling Industry 25 WorldWide Drilling Resource ® AUGUST 2019 WTR Everett cont’d on page 44.