You fill your pickup with tree clippings, run down to the dump, pay your fee, unload, leave. While at the dump you see a bunch of sea gulls flying around and heavy equipment moving dirt around, presumably to make room for the garbage.

And that's probably all the thought you give to it.But landfills are a lot more complicated than that. Take, for example, the Salt Lake landfill at 6030 W. 1300 South. It comprises 11 modules, encompassing 455 acres, and each module is carefully designed and constructed to keep foul garbage odors, litter and pollution from going to places other than the landfill.

According to a recent report of the Salt Lake Valley Solid Waste Management Facility (as it is formally known), each module is prepared to receive garbage by putting down a 2-foot-thick layer of compressed clay. Then a layer of high-density polyurethane is put down. These two layers keep rainfall and snowmelt from taking garbage particles and spreading them underground.

A "leachate collection system" - basically gravel - is placed over the bottom layers to collect liquids and garbage particles, and over that a fabric and soil layer. Only then is the module ready to receive garbage.

Once enough garbage is put down to fill the module, an impermeable cap is placed over it, and over the cap a final cover of soil, which is planted with grass to prevent erosion. The garbage then sits in its sealed compartment, unless it springs a leak, basically forever. After the big one hits, after the apocalypse comes, after humanity's remnants have crawled out of their holes and restarted their wretched lives, that garbage will still be there.

Last year the Salt Lake landfill completed module No. 5 out of 11.

The landfill is rapidly filling up, but its life will be extended five to seven years by a new garbage transfer station in South Salt Lake, which will take about 30 percent of the garbage that would have gone to the landfill and ship it to Carbon County.

"We're excited," said South Salt Lake Mayor Randy Fitts. "This is a win-win situation."

What's more, the total amount of garbage and other material put in the landfill for keeps is slowing down. The amount increased by only 3 percent in 1997 due to recycling, composting of yard waste and diversion of "clean" fill. The amount of material used in those activities increased 29 percent, and compost and wood chip sales increased 50 percent. To encourage residents to recycle, Salt Lake Mayor Deedee Corradini and landfill officials have recently reduced or eliminated certain recycling fees.