Originally created 04/28/01

Turning milk containers into pilings

Do you use those plastic, gallon-size milk or juice containers? Next time you toss one of them into the recycling bin, think for a moment about where it may go. There's a chance that your plastic jug could play a role in keeping the nation's ports and harbors clean.

Your jug, along with 14,000 other gallon-size plastic containers, could end up being recycled into a single plastic pier piling in the San Diego Bay. If that happens, there will be a number of environmental benefits. Aside from keeping the material from the landfill, it will help solve a problem that has bedeviled harbor masters ever since people began building docks and piers.

The wooden pilings in docks or piers are like magnets for marine borers. Like termites on dry land, marine borers use the wood for food, weakening and eventually destroying the structure. Because of marine borers, a typical untreated wood piling at the Port of San Diego will need to be replaced in less than two years.

This often is a time-consuming and expensive process. The piling can be 70 feet long. And to replace it, a barge crane will have to use a hydraulic hammer to pound the new piling into the seabed. And just the use of the crane costs $500 an hour.

There's also the problem of removing the old piling. Divers may have to go 40 or 50 feet down to help take out the underwater stumps of the pilings if they break off during removal.

A longer-lasting alternative is wood pilings treated with ammoniacal copper zinc arsenate (ACZA). This treatment repels the marine borers, and the pilings will last for five to seven years. The downside is that the same chemicals that repel marine borers are also toxic to other aquatic life. The San Diego Bay has seven miles of piers with almost 3,500 pilings. If each one of these pilings were leaching ACZA into the water, it would be a disaster for nearby marine life.

Until recently the Navy and others agencies involved with ports had an unpleasant choice. They could use untreated wooden pilings, knowing the pilings would have to be replaced in a couple of years. Or they could choose the longer-lasting but more toxic ACZA-treated pilings.

Fortunately, six years ago Mike Magee and other members of the Navy Environmental Leadership Program (NELP) heard about an attractive alternative. The program's mission is to find innovative ways for managing the Navy's environmental programs. And the innovation in this case was plastic pier pilings.

Because plastic doesn't degrade in sea water the way wood does, engineers predicted that pilings made from plastic should last 40 years.

McGee and his colleague Ed Bonnes reasoned that if the engineers were right, this would dramatically reduce the cost of maintaining the harbor. Taxpayers would benefit, but a greater advantage is that plastic pilings don 't leach toxins into the water.

The Environmental Protection Agency has tests for determining whether a particular plastic formulation interacts with seawater. The plastic pier pilings came out with top ratings.

The Navy Environmental Leadership Program is monitoring the 1,200 pilings that have been installed so far. If the plastic pilings live up to their potential, then their use will be extended throughout the Navy.

On the Net: Visit the NELP Web site at: http://nelp.navy.mil


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