By Gary Papic, Saskatchewan Environment and Resource Management, Watrous
Many communities in Saskatchewan experience dirty water, erratic chlorine residuals and unpleasant tastes and odours in their drinking water. Quite often this is the result of poor water line maintenance. Fire hydrants are flushed at least twice per year in an effort to correct these problems, but generally this provides inadequate results. Foam swabbing has proven to be an effective, inexpensive and relatively simple method of cleaning water mains. Special foam (polyurethane) swabs, or "pigs" as they are affectionately known, are inserted into the water main, either through a hydrant or an entry point in the water treatment facility. The swabs then travel along the water main and scrub the scale encrustations and slime build-ups from the inner pipe wall. The loosened debris and swabs are eventually flushed out at an exit point.
Office preparation is initially required to organize such a project. A map showing all of the mains, hydrants and valves is used to plan the exact routes for the foam swabs to follow. The first route should only be about 1000 feet or less to familiarize workers with the process and to determine the condition of the distribution system.
All residents and businesses should be informed of the swabbing operation well in advance to allow for the rescheduling of their daily activities. It is good public relations to explain when, where and why the mains are being swabbed.
Field work to verify all valve and hydrant locations is then required to ensure their proper operation. When hydrants are dismantled for use as entry or exit points for the swabs, it is an opportune time to undertake some hydrant maintenance. It's now critical to make sure that the water supply reservoirs are full and that reserve for fire protection is maintained. The swab diameter required is determined by multiplying 1 1/4> times the pipe diameter for water mains that are under 12 inches, and 1 1/2 times for mains over 12 inches. The length of the swab will be 2 times the pipe's diameter.
Swabs can be launched through a disassembled hydrant using a pumper truck to provide water pressure (generally, 15 to 25 psi for 30 to 40 seconds) to propel the swab into the water main. They can also be introduced from the treatment plant either through a special launching device, a disassembled check valve or a water meter.
When the swab is in the distribution system, water pressure in the range of 12-15 psi is sufficient to set them in motion. The speed with which a swab travels is dependent on several factors such as water pressure, line diameter, distance and sludge build-up. About two and one half feet per second would be an average speed.
Always protect properties from contaminated flows by using large plastic mats or a fire hose to direct the flow of debris-laden water toward a gutter or sewer. Shortly before the swab emerges from the exit hydrant, the clear water will discolour noticeably. A reddish colour will indicate iron contamination; manganese or organic waste will yield a greyish to black colour.
Quite often a disinfectant (hypochlorite) is placed ahead of the swab as a safety measure, but also as an indicator that the swab is nearing the hydrant by the sharp chlorine odour it produces.
Small water systems (no less than 2 inches in diameter) can also be swabbed in the same fashion, providing "flush-outs" are installed at the ends of the water mains that are to be swabbed.
It is recommended that communal water systems be swabbed at least every 3 to 5 years, or annually if necessary.