Intakes

Cutting Time and Costs

By Doug Mund

Rural and regional water systems rely on a number of types of sources for their raw water supply. Some purchase their water from cities, wholesale water supply districts or other entities. Others rely on wells. Still others draw from surface water like lakes and rivers. Drawing water from a lake or river requires design and construction of sometimes expensive intakes-the points at which the water is drawn from the source.

Intakes can be costly, running well into the millions of dollars. Traditional inclined tube type intake construction involves cranes and barges. The barges are large enough to require disassembly in order to transport them to the construction site with reassembly required before they can be used. Typical inclined tube construction also involves major displacement of material within the waterway which may be subject to a lengthy and sometimes difficult permit approval process: and time may be critical. Drought conditions in many parts of the country have created emergencies for a number of systems relying on surface water. Low water levels have resulted in reversion of once deep lakes to river conditions. In some cases water levels have dropped to within inches of intake screens, and in some cases the screens are completely above water.

In one case low water levels led to a four day disruption in water service to the system's customers followed by boil order period of testing mandated due to the system being depressurized. Lack of potable water resulted in closing of schools, hospitals, government buildings and many local businesses. Besides disrupting commerce and daily activity and creating financial hardship, the situation posed serious health risks as well.

With little time to waste, it was decided that horizontal drilling technology would be employed to drastically reduce the time and cost required to ensure a reliable intake. As its name implies, directional drilling allows boring or tunneling from a location on the shore under the earth and lake or river bed to the desired depth and location within the waterway. After boring daylights at the desired location in the waterway, pipe is floated out on the surface of the water, weighted and sunk to the bottom, then pulled back through the tunnel. Once in place, an intake screen support structure is installed and connected within the waterway at the end of the pipe, the intake screen installed, and the system is back in business. Directional drilling can eliminate the need for barges and cranes altogether. The result not only reduces construction costs significantly, it is less disruptive to the environment as well. For this particular project a grant was secured in late June and the project designed, permitted, and bid by mid August, construction began in September and the project operational by early December. This was less than half the time a conventional inclined tube intake project is anticipated to have taken.

Of course, systems don't need an emergency to take advantage of this technology. Systems are reducing intake construction costs and time to service substantially by using horizontal drilling. The technology can also be utilized to add additional tubes to existing intake facilities to either replace undersized or faulty facilities or to increase capacity and/or reliability.

And who doesn't want to save time and money and provide peace of mind for their customers?