Medical Diver

Underwater Construction Team Two: Colorado Thompson Reservoir Dam Job

The US Bureau of Water Reclamation at Green Mountain Reservoir State Park accepted our bid to change out a Y-gate for the turbines at the base of the spillway and that set the ball rolling. CM1 Chris Taylor was the lead on this job, and he did a professional job indeed. Green Mountain is located at 7,000 feet above sea level. The Underwater Construction Battalion (UCT TWO) bid and won a job to change a Y-Gate out that diverts water from one turbine generator to the other. I Y-gate is a valve that pivots like a curtain coming up or going down. It is about 5 to 6 inches thick and made of steel. These have a 50-year maintenance span and were due for maintenance. We needed to place a large plug in the dam like a bathtub so they could do the maintenance on the Y-gate.

The water depth was about 200 feet and our average max working depth was 167 feet on top of the trash chute, aside from one inspection dive to check out the tapered seat the plug would rest on. That put us on a 170-dive table; when calculating the altitude, the deepest dive was an equivalent of diving to about 200 feet on air. The deeper inspection dive to 200 feet was completed by MDV Davy Daniels. We used 100 percent oxygen to start decompression in the water after the working phase. Once the pair of divers squared themselves away on the bottom, they would be hauled up to 50 foot of water depth and the gas would be shifted from air to 100 percent oxygen. After this decompression stop, they were hauled up to 40 feet. Then after the obligated time at the 40 foot stop, they would come up and over the top side, the dive tenders would undress them removing the dive helmet, umbilical, harness, boots, hot water suits and the divers would climb into a chamber with towels to dry off, sweat pants and tops to wear.

Once the divers left the 40 foot stop, we had to bring them to the surface in a controlled ascent, they would the climb the ladder out of the water and escorted to the dressing bench, undressed down to their dive shorts then escorted to one of the chambers and crawl inside with drying towels and sweat suits and recompressed down to an equivalent of 40 feet of sea water. All this had to be completed under five minutes or they miss their obligated decompression. More often than not we had them undressed in under three minutes using five or six tenders stripping the gear off by everybody taking boot, helmet, zippers, Velcro, and all in a hasty and much orchestrated team manner.

We would then compress the two divers in the chamber back down to an equivalent deep of 40 FSW breathing 100 percent O2 on bib masks. This way they were decompressing in a controlled warm environment. To increase the humidity of the dry compressed air of the recompression chamber, we used a wet towel in the chamber. This method is called Surface Decompression on Oxygen at Altitude (SUR D O2 at altitude). A very impressive technical diving experience to observe.