Slime from sewer lines may not be harmless

I read with interest the July 20 article about “pigs” being used to remove the material that adheres to the pipes of the North Liberty sewer lines (“It's a dirty job, but these ‘pigs' are built for it”).

This “foul smelling slime” may not be harmless. It could contain high levels of toxic material, such as polychlorinated biphenyls (PCBs) and disease causing pathogens, and should not be piped into the sewage treatment plant.

In 2007, after the Milwaukee Metropolitan Sewerage District cleaned its sewer lines, the oily ooze that was removed contained high levels of PCB that had been piped into the Jones Island treatment plant and concentrated in the resulting biosolids. Mulch and the contaminated sludge had already been spread on dozens of city parks and playgrounds and had to be removed, at great cost, to out-of-state hazardous waste landfills.

North Liberty would do well to test the oily ooze that is adhering to the “pigs.” If it contains toxic chemicals or antibiotic resistant pathogens, and is washed into the treatment plant, the plants' biosolids should not be land applied.

For more information on the risks of spreading biosolids on land, visit www.sludgefacts.org.

Caroline Snyder

North Sandwich, N.H.

Emeritus professor,

Rochester Institute of Technology