Commercial Diving: Good Housekeeping Keeps Your Water Clean
Vacuum cleaning is usually associated with housework, and I think I am correct in saying it is usually carried out by the females in the house. That's not being sexist, its just that males like to tinker with the lawn mower or the car and are usually unaware that they have carried the dirt back inside on their shoes.
On Ground Storage
I do think it is unusual for a group of commercial divers to get enthusiastic about vacuuming, but that is exactly what happens at Descend, although it never includes the carpets in the showroom. What is does involve is a relatively new way of cleaning potable water reservoirs using divers. For the uninitiated "potable" water is drinking water and it is not necessarily drinkable straight out of the local river. It has to be treated before it becomes potable. That means a process of filtration and the adding of various chemicals including flocculants, which cause the dirt particles to stick together, which makes them heavy. They then drop out of the water column to the bottom of the reservoir where the dirt accumulates with the chemical residue, usually aluminum oxide, to form a fluffy white powder. Now the more this powder accumulates the more chemical has to be added, and the less effective the treatment becomes, so at regular intervals the residue has to be removed.
Elevated Storage
 | | Elevated Storage |  |
|
In days gone by the water authorities simply pulled the plug on the reservoir and let the water go down the drain. They then had a team of men go into the tank with shovels and power hoses to get rid of the residue and when it is all shoveled and hosed out they refill the reservoir.
The problems with manual cleaning are numerous. It is time consuming and therefore expensive. When the tanks are refilled the process always stirs up any sediment or dirt that has not been removed and the water becomes turbid. The housewives complain that their washing is dirty and they don't want to give the kids a drink of water because it looks dirty. While the reservoir is empty mains become empty and particularly the old earthware mains can collapse, as it is really the water inside that keeps them stable. If a main collapses under a road, that can be really expensive.
Added to that expense is the cost of the water wasted, remembering that it was already treated and of course on one is very happy if a reservoir is off line for too long. In some cases reservoirs cannot be cleaned manually as there is no back up reservoir to provide the community with continuous supply.
Large In Ground Storage
 | | Large In Ground Storage | |
|
Enter the diving team. In 1995 Descend designed a way to clean reservoirs using divers. We started by putting a suction plate over the outlet valve and vacuumed to waste. This works very successfully however, not all reservoirs had accessible scour valves, so we moved on to a suction pump system.
Our system consists of 3 "trash pump, floating suction hose and a custom designed aluminum vacuum head. The head has adjustable wheels to allow the height off the bottom to be altered to cater for the difference in concrete or steel tank bottoms and it also has an adjustable scoop on the front to adjust for various heights of sediment.
The process if very much like vacuuming a carpet. The diver very carefully moves the vacuum head over the reservoir floor, picking up the silt which goes up the suction pipe and out of the reservoir to waste.
 | | Rick and Diver | |
|
One of the big challenges is that the divers and all of their equipment must be environmentally clean. Authorities are very careful about who and what actually enters your drinking water. All of our divers wear dry suits and full helmets, usually with helmet lights and all of the equipment must be fully decontaminated with a Medis bath prior to entering the reservoir.
A major problem with this type of work, is the suction created by the outlet pipes. Where the reservoirs cannot be isolated, the divers need to work with a live outlet and the danger that the diver might inadvertently get sucked onto the outlet. We overcame this problem, by fitting mesh cages over all live outlets. Other problems include internal pylons that support the roof but tend to tangle umbilicals and joins in the floor or stiffing ribs on steel floors that prevent the easy rolling of the vacuum head, and weed growth in open reservoirs all add to the difficulty of cleaning.
We recently cleaned a 30 metre diameter tank that had been in service for almost 20 years. In addition to about one metre deep of chemical residue we found approximately five cubic metres of sand had accumulated at the inlet and had to be removed as well. That one tank took us just over 40 hours of vacuuming to get it spotless. Just as well it was a do and charge job.
The advantages of using divers for this type of work includes;
- Less turbidity as the divers take great care how they move about in the tanks.
- No main breakages as they don't get emptied.
- No water wastage. The tanks stay full.
- No down time because we vacuum the reservoirs live.
- More cost effective than manual cleaning
On Ground Storage
 | | On Ground Storage | |
|
Descend now has a number of water authorities in N.S.W. and central Victoria who use their services with excellent results. Styles vary from large in ground open concrete reservoirs of some 5000 square metres of floor area to fully enclosed in ground and on ground tanks to elevated high rise tanks. Every community has at least one water storage, bigger cities like Albury have some 50 storages and Sydney or Melbourne over 500 storages. All needing regular cleaning so we think the future for commercial diving is looking good.
For more information about commercial diving or to view a video clip of divers in action in a reservoir visit Descends web site at www.descend.com.au or contact Descend Underwater Training Centre, 1/826 David Street, Albury 2640 - 0260411405 or email descend @albury.net.au
|
