They wait until dark. They find a desolate spot. Then, they dump truckloads of used tires and drive away.
   Illegal tire dumpers struck at least four locations in North Andover and Lawrence in the past month, mostly along the Route 114 corridor. In their wake, they left an eyesore and a financial mess.
   "It would wipe out our budget," said Bob Rauseo, president of the Shawsheen River Watershed Association, who would like to clean up the tire piles along the Shawsheen, but doesn't have the money to do it.
   While walking along the river banks with other volunteers, Rauseo recently discovered tire dumps behind an abandoned Pizza Hut on Route 114 in Lawrence and under the double-decker bridge that crosses the Merrimack River. About 200 tires are stacked at each site.
   He fears the tires will end up in the river, where they create sandbars and divert the water flow.
   It costs hundreds of dollars to remove the tires. Massachusetts and New Hampshire banned them from land-fills, so tires must be disposed of through a recycler who shreds or melts the rubber. A regular car tire costs $2 to $5 to dispose of legally. Larger tires can cost much more, around $10 for a sport utility vehicle tire and hundreds of dollars for a construction vehicle tire.
   North Andover police suspect they know who is dumpmg the tires, but they need more evidence. Several tire dealers and service station owners called police after they read about tires being dumped behind the North Andover Mall and near an old ski area, both on Route 114. The business owners told police that people approached them and offered to take away their used tires at prices that seemed too good to be true.
   Mary Sullivan, owner of Independent Tire in Lawrence, said she has been approached by haulers who she suspects weren't operating legally.
   "It's tempting, but it's not worth it," Sullivan said.
   Sullivan pays about $700 a month to have her used tires hauled away properly. A company in Maine shreds the tires and uses the recycled rubber for asphalt.
   North Andover investigators are trying to track the tires through registration numbers imprinted on the rubber, but it's long process. Police Lt. Paul Gallagher said the tires must be traced through the manufacturer, the wholesaler, the retailer and then the buyer. Gallagher is more hopeful that someone will see the illegal activity and report a license plate number.
   Most of the time, police never find the culprit. So who cleans up the mess? The property owner.
  "If you don't know who is doing it, it's your property and we can't blame anyone else," said Louise A. Ferris, director of the inspectional services in Lawrence.
   Health inspectors fine property owners $70 for unsightly mounds of trash including tires. If the owner doesn't pick it up promptly, inspectors can issue a $70 fine each day.
   "I send my guys down there right away," Ferris said. "As long as it is a reachable owner that we can find, it's an automatic fine."
   If police or inspectors find someone in the act of dumping trash illegally, the fine is $300, she said.
   The Riverwalk buildings, a series of mills along the Merrimack River, has become a popular dumping place to the chagrin of the property managers.
   "It creates a big problem for us," said Deborah A. Isensee, office manager at Riverwalk Development inc, "Between consuming parking spaces and the eyesore, it's not good for business."
   Isensee is trying to figure out what to do with a pile of 100 truck tires that was left in a corner of a parking lot. The nearest tire shredder is J.P. Routhier in Littleton, Mass.
   Another option is right in Lawrence. Unlike most communities, Lawrence allows its residents to drop off tires at its recycling center at the Department of Public Works, 1 Auburn St. Residents pay $2 a tire. The center opens two Saturdays a month, from 8 a.m. to noon. The next recycling day is March 9.
   City workers stuff the tires into a tractor-trailer and haul it to Littleton. The truck fills up every two weeks, but sometimes the city doesn't have enough money to deliver it.
   Lawrence recently won a $80,000 grant to educate school children about recycling and illegal dumping. City officials hope the program will help cleanup the city. Rauseo, of the river association, said communities must attack the problem in several ways. Police, landowners and citizens need to be more vigilant, he said. Government officials need to work better with property owners to pick up the piles, and landowners need to restrict access to their properties. Rauseo would also like to see a tire deposit program similar to soda can deposits.
   "But the best thing would be to catch someone," he said.

OUR VIEW
Make risk of dumping too costly
We need higher fines for those who dump tires illegally.

   Used automobile tires are an undesirable but inevitable consequence of our modern, mobile society.We love our cars, and each of them has four fires. The trucks that transport our food, clothing and other goods and the vehicles that help construct our homes, buildings and roads have bigger ones and more of them.
    In the bad old days, used tires would be stacked into great mounds, man-made mountains of rubber. Water pooled in the hollow interiors of the tires, forming breeding grounds for mosquitoes and other pests.
    From time to time, the tire mountains would catch fire, sending plumes of acrid black smoke into the air. Tire mounds can burn for years.Tires also used to be buried in landfills, where they would remain forever, never decaying.
   Thoughtful states like Massachusetts and New Hampshire eventually banned the burying of tires. Now, they must be disposed of through recyclers, which grind them up for other uses, such as mixing with asphalt for roads.
   But recyclers do not provide this service for free. So there is now a charge of about $5 to dispose of a passenger car tire. Light truck tires cost $10 to dispose of but larger construction vehicle tires can cost hundreds.
   Most people never notice this charge. They simply pay it as part of having their tires replaced. But for those who own fleets of vehicles, or who collect used tires as they sell new ones, it can be a huge expense.The result is that tires are being dumped.
    In the Merrimack Valley, huge illegal tire dumps have been found along the river.We need to be more aggressive in fighting this damage to our environment. Right now, property owners are fined for tires dumped on their property. But often, they are the victims of this crime.If caught in the act, a tire dumper faces a fine of just $300.
    This is far too small a price to pay given the cost of disposing of tires legally. Dumpers are making a simple economic calculation here. It's well worth the cost of being caught.Officials have to change the equation by sharply increasing the fine for dumping to the point where it is no longer worth the risk.
   That would do much to remove this blight from our environment.