LOW PRESSURE SEWERS AND THEIR HDPE PIPE – AN ENVIRONMENTAL NIGHTMARE?
The Low Pressure section of the Cudjoe Regional Wastewater System (CRWS) will have over 100 miles of High Density Polyethylene (HDPE) Pipe, ranging in size from 2” to 8” that will be buried 2’ to 4’ under the surface. It will be under pressures of 15psi to 60psi. The Low Pressure System is asserted to be a low cost, reliable, wastewater collection system that will save money on initial sewer system installation. But what are its long term costs? Could it be an environmental disaster in the future due to pipe failures? Or perhaps a financial disaster if the piping needs replacement in a few years?
The Florida Keys are a series of coral (limestone) islands. In most areas of the lower Keys, there is salt water flowing only a few feet below the surface. Limestone, with a high water table, is naturally unstable. Sink holes, dips, settling of buildings and shifting roadbeds occur over time. Idiots dig and drill without checking. Each home with a grinder pump (projected to be 2,800) will pump into a series of headers and ultimately into an 8” plastic line that runs over 20 miles from Big Pine to Lower Sugarloaf. In addition, 275 lift stations that consist of large concrete tanks with up to 5 grinder pumps will take the gravity feeds and pump them into the same lines.
The problem, in general, is that HDPE pipe has a tendency to become brittle and crack over time. It is inevitable that failures will occur at some time in the future. Our specific problem is that when cracks occur and effluent leaks, it is very likely that it will go right into our porous limestone aquifer. Eventually the effluent will reach our pristine waters, but this could be some distance away. Complicating things is that there is no way to monitor for leaks in a pressure system. With gravity, when there is a leak, salt water will leak into the pipe and be detected at the waste treatment plant and looked for in the manholes it flows through. A vacuum system line failure is noticed immediately and can be found through simple diagnostic troubleshooting. A leak in a pressurized sewer system might go undetected for months or longer. We may discover that the incremental improvement in sewage treatment we seek is lost through a collection system that is ill designed for our environment.
There is an excellent web site at http://hdpefailures.com/ that provides numerous examples of failures and should have been read by our County Engineer before this system was signed approved. For other ways the LPS/grinder system costs more, go to www.newtoncoalition.com or contact us at [email protected].
Walt Drabinski
Sir Isaac Newton Coalition
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See also Rebuttal by Camille George Rubeiz, the Director of Engineering (M&I) for the Plastics Pipe Institute.