The work at Tillsonburg Well 2 was part of various infrastructure improvements to the Tillsonburg Water Treatment plant, and included well testing, rehabilitation and upgrades.
With 20 years of experience in the well industry we can confidently classify the mechanisms causing well performance decline and develop a specialized rehabilitation effort, which specifically addresses the problems encountered during the preliminary testing and video inspections. Initial well performance testing at Tillsonburg Well 2 showed that the well’s specific capacity had declined to less than half of its original capacity. Diagnostic video inspections showed severe plugging of the well screen. It was decided that the rehabilitation at Tillsonburg Well 2 required brushing of the casing, followed by two chemical treatments. An acid polymer solution was injected into the well to dissolve mineral encrustation, as well as biological growth. Following a period to allow the acid to react, it was subsequently airlifted out of the well with all the additional waste and dissolved mineral. Post-rehabilitation results showed that the rehabilitation effort was successful in recovering most of the well’s lost performance.
In addition to chemical acidification, the County of Oxford expressed interest in potentially lining the well based on the results of the initial video inspection by another contractor which showed a significant amount of scale build-up and some pitting of the casing. However, before any decision was made to install a liner, a casing thickness log was recommended by Lotowater to determine if the build-up was aesthetic or whether its structural integrity had in fact been compromised. Our ABI-40 Acoustic Televiewer tool was used, which can accurately log the shape and diameter of the borehole by transmitting ultrasonic pulses and recording their amplitude and arrival time. The tool is capable of logging both the inner radius and outer radius of the casing, and generating an image which will show any deformations or failures. A casing thickness log completed at Tillsonburg Well 2 showed that the well casing was actually in acceptable condition with no obvious signs of thinning, saving the client tens of thousands of dollars in expensive and unnecessary repairs.
Tillsonburg Well 2 was excavated several meters below grade and the existing casing was cut down to facilitate the installation of a pitless adapter, and steel gravel fill tubes which could be used to replace the gravel pack as it settles. A cement cap, followed by a bentonite grout, was installed to seal the annular space. This was designed to maximize the security of the well by eliminating the potential for surface water infiltration. A new casing extension along with a vented well cap was then installed and the surrounding area was backfilled.