Water Well Journal
Issue link: http://read.dmtmag.com/i/629532
got to make sure your loop well is grouted really well and it's a true representation of what this field is going to be. If you didn't get it grouted the way you wanted it or if there is some- thing else wrong with it, it will skew the data for the whole field." If the data is wrong, the field may be oversized or under- sized. That's why it's important to pay attention to the con- struction of the test bore. If you want extra accuracy, Williams suggests taking soil samples about every 10 feet. "What you do is you take good samples of the material you're drilling through and that will go to confirm your test as well," he notes. "You can really never have too much information." If you're working on a large loop field—about 50 loop wells or more—it's a good idea to do more than one test bore- hole. Williams prefers to set up his tests at the far ends of the field so he can get a good average across the entire field. "Anybody who drills can tell you you can move 10 feet away from one borehole and drill and find a completely dif- ferent set of geology," Henrich points out. "So, the thermal conductivity of that bore is going to change slightly as well." On most jobs with tests on multiple bores, Henrich sees results within a few hundredths of a point or a tenth or two of a point different. "So they're not the same by any means," he contends. "So getting an average when you're doing a bigger field is a very good idea. You're dealing with more energy, so you have more opportunity to have bigger mistakes." When you're ready to test, read all of the instructions be- fore starting. Although it's a simple test, following the steps in the instructions is one of the best ways to ensure an accurate test. "There's a pretty simple set of steps you need to do in order to get a good TC (thermal conductivity)—but you need to do those steps," Henrich emphasizes. "There's not a lot of room for creativity in testing, so read the steps and follow the steps." In general, the steps are: 1. Set up your equipment in the field 2. Get the native ground temperature 3. Purge the air from the loop 4. Start your equipment—including the heating element and data logger 5. Run your test 6. Collect and analyze your data and submit your report. Common errors in testing Even if all the steps are followed, there are common pit- falls that could skew your data results. For an accurate test, you need three things: stable power, consistent flow rate, and proper insulation. "Your goal is consistency," Henrich says. "It's about mak- ing the test as steady state as possible. Anything that gets in the way of that goal is something that needs to be mitigated or needs fixed." Inconsistent power generation is the biggest problem in the field. Generators without good voltage regulators or genera- tors that can't run for 48 hours straight are often to blame. CONDUCTIVITY from page 21 DACUM Codes To help meet your professional needs, this article covers skills and competencies found in DACUM charts for drillers and pump installers. DO refers to the drilling chart and GO to the geo- thermal chart. The letter and number immediately following is the skill on the chart covered by the article. This article covers: DOB-1, GOE-6, GOE-8 More information on DACUM and the charts are available at www.NGWA.org. 22 February 2016 WWJ waterwelljournal.com Graph shows the sum of the collected raw data of a conductivity test. The logarithmic graph where that data is plotted and analyzed for the calculated soil thermal conductivity value.