WorldWide Drilling Resource

43 WorldWide Drilling Resource ® MARCH 2015 Geothermal Borehole Trench Inspection by Peter Tavino Litchfield Geothermal This is part three of the WWDR series for inspectors of ground loop installations. We covered drilling and loop insertion in January, and grouting in February. I enjoy seeing the excavation, heat fusion, concrete coring, and pressure testing work done by experienced drilling contractors or pipe fitters. When it is time to dig the 4½-foot-deep trench from each borehole to the building, the site is usually a mess from the cuttings now on the surface behind silt fencing or in a pit. Topsoil has been saved as feasi- ble, and the mini excavator digs around the 6-inch-diameter steel casing to allow it to be sawzall cut or torch burned at 48-54 inches deep. Going deeper below frost is unnecessary and could violate OSHA [Occupational Safety & Health Administration] trench shoring safety reg- ulations. Ladders and ramps are used by workers, but the inspector should stay on the upper ground. Be sure grout plops out when the 5-foot section of casing is removed. If not, enter the trench to see and meas- ure the level below. A few feet of sand or cuttings may be added to bring the grout level to the bottom of the trench. Or consider bentonite hole plug and the additional grouting operation to top it off properly. Observe proper heat fusion times for the 90-degree elbows, but do not micromanage the approved fusion tech- nician. In Connecticut, we provide a plastic cushion between the sharp cas- ing steel just cut or burned, and the plas- tic loop elbows that could rub against it as water flows. At the building, if the excavator bucket scrapes the tar or rubber wall waterproofing, have those spots patched. Cores of 3-4 inches through a 10-inch concrete wall from the outside with hose water runoff is routine. Crumbling block or historic rock foundations (cyclopean masonry which could only be lifted by a giant) present other challenges. Be sure core is proper for link sealing water tight- ness. If the loop goes over a rock wall foundation (as I have never seen), be sure it is insulated and protected. Backfilling with wet clumps of cut- tings at the 90-degree elbows may be worse than dropping small boulders on it. Sand is expensive, so inspect that in situ backfill is appropriate. Many drilling contractors ask what the pressure test should be. The best seems to be 90 psi on a 100-psi gauge. (Not over 100 where slow leakage can- not be read.) Leave the gauge in place until the heating and cooling contractor removes it days later. Thirty-minute ther- mal fluctuations are normal. As always, progress photos of cov- ered work and as-built deviation from the design should be documented. Tracer tape is suggested but not imperative. Restored lawn in retrofits should be seeded and hayed as confirmed. With proper installation and inspec- tion verification, the owner should be assured of receiving a 50- or 100-year useful loop life. The statements and comments in this article are based on information and references believed to be true and factual. If you have any questions or comments, please forward them to me in care of WWDR . Pete Peter Tavino may be contacted via e-mail at michele@ worldwidedrillingresource.com On March 1, 1921, Erle Halliburton patented “Method and Means for Cementing Oil Wells”, which improved well integrity.