What’s that smell?

Wastewater treatment plant gives tour to locals, explains where it ends up

It’s a windy cool day just outside of Mammoth proper and spring is in the air. Pine, sage, blooming rabbitbrush and the clean, bright smell of lilac and aspen fill the morning.

Then, the north wind takes a quick turn and shifts to the south.

Spring vanishes. From the south, behind the Mammoth Community Water District front office building parking lot, traveling at wind speed, comes the unmistakable smell of human poop.

“Ooh, yuck,” 50 grown-ups said almost in unison, many with their faces screwed up in the unselfconscious way children have.


It shouldn’t be a surprise, really. The 50-some adults didn’t come here for a tour of lilacs or pines or aspen—they can get that at home.

They showed up for a tour of the district’s wastewater treatment plant, the first such tour for the public in the district’s long history. 

Everyone here knows that somewhere in that polite term, “wastewater,” lies a darker truth—that what goes down the toilet, the sink, the shower—doesn’t just disappear nicely and forever into the fine, clean spring air. It all has to end up somewhere.

And then something—or someone—has to deal with it.

 “I just wanted to see how it works,” said Paul Payne, a Mammoth businessman and longtime resident.

“It” consists of some 900,000 gallons of untreated sewage per day (at this time of year), 365 days a year—or about 100 gallons per person per day—with five times that amount on a busy weekend.

All of it—the raw sewage from the toilet; the coffee grinds, soap suds, detergent, and vegetable peelings that went through the garbage disposal; the grey water from the shower—has to be managed.

The days of dumping raw sewage into the rivers, creeks, and behind the house are over.

Betty Hylton, the district’s project specialist, explained the current process.

First, the solids—everything that comes out through the sewage pipes that tunnel under the streets of Mammoth (this does not include street runoff)—are separated from the liquid water through a series of steps, she said.

The water, with some suspended fine particles still in it, goes one way; the solids go another.

“The solids are settled by gravity, with the heaviest sinking to the bottom of settling ponds and the floating waste, like grease, is skimmed off the top,” Hylton said.

“These heavy solids go to a ‘digester’ where large colony microscopic ‘bugs’ (fungi, bacteria, protozoa and phytoplankton) are added and begin to grow.”

The ‘bugs’ begin to chow down on the ground up solids. The tanks are aerated to supply the bugs with oxygen. They eat and eat and eat and the more they eat, the stronger the smell.

“It’s the smell of decomposing organic material,” she said, pointing to a deep, concrete-lined vat.

The group is now far to the back of the district office, where the sound of huge machines and wind and the dark smell feel like a scene out of a bad film.

 “Once the bugs are done, we separate the rest of the liquid out of the sludge, and begin to push the sludge through the dewatering belt,” Hylton said, leading the group through the winding reaches of the district’s backyard to a giant room where the sound of the machinery drowns out even the rush of the wind.

Although the work of the “bugs” is mostly done by this time, the smell is still strong, here in this huge room where the giant dewatering belt press pushes a thick, dark brown mass through tight pipes and funnels, then up onto what looks like a huge, road roller compactor.

The brown stuff comes out in sheets an inch thick, which separates as it falls into tendrils of brown sludge, then drops with a “plop” into a big vat.

“No matter how much I told the sixth graders before [this group] that this was not poop, I couldn’t convince them,” Hylton said with a laugh.

She’s not faring much better with the adults here, either. It’s impossible not to think the same thing, watching the brown stuff come out in big funnels of goo.

But Hylton says at this point, the brown mass is mostly the carcasses of the billions and billions of bugs, sand, and whatever inorganic matter the bugs have not digested.

It still stinks, though.

This goo has a purpose. It is now harmless, bad as it looks and smells, and it will be pumped into trucks and driven to the Benton Crossing Landfill where is will be sun-dried, then mixed with soil and spread, every day, on top of the day’s waste as a sort of garbage dump frosting.

“It keeps the garbage from flying around, the gulls from chowing down on the garbage,” she said.

Who would have thought?

Figuring out what to do with the thousands of gallons of dirty water that was separated from the solids is a little more complex.

In many ways, it’s more difficult, Hylton said.

Dealing with the raw sewage and organic matter from kitchen sinks is relatively easy and straightforward—remove liquid, add bugs, wait, remove more liquid, add more bugs, wait, dewater, compress, send to dump.

But cleaning water of toxins, poisons, and bacteria of everyday modern life—that is much more challenging.

Water isn’t neatly contained in a condensed block of matter.

The water at every step of the process, including what’s pressed out by the dewatering belt press, is separated from the solid waste, treated with bugs, and aerated to allow the bugs to eat and grow.

Once the bugs become heavy enough to become large particles that can settle at the bottom of the tank, they go through the solid waste tanks.

The solids are once again removed and more bugs are added to the remaining water and the solids for a second round of treatment.

Finally, at the third level of treatment, the water is filtered and then chlorinated to remove any remaining bacteria or pathogens.

By the third time the leftover water exits from the wastewater treatment plant—this toilet, sink, and shower water—is clean enough to drink.

It heads south and east of town in pipes and into a series of man-made ponds called “Laurel Ponds,” which are nestled below the big bulk of Laurel Mountain.

Out there, it’s hard to tell the water full of ducks, seagulls, and grebes was ever anything but mountain water—until you see the giant pump/fountain at the end of one pond, spraying the water into the pond—and until you smell the sharp tang of chlorine that permeates the spring air.

The water is also used to water Mammoth’s golf courses; the “recycled” water noted on signs around the golf courses of town.

As noted above, the water is certified clean enough to drink, but Hylton acknowledges, when asked by one tour member, that the district’s technology is not up to cleaning what some scientists are beginning to consider to be one of the greatest modern threats to human and animal well-being—the presence of “endocrine disrupters.”

Endocrine disrupters are extremely dangerous by-products of the antibiotics, herbicides, pesticides, and medicines that get flushed down toilets (see box for more information).

“At such a small scale, it would be impossible for us to treat for such products, and the process for doing so is still under development,” she said.

Back at the water district, Hylton led the group back to the refuge of the front office where the smell of lilacs and spring once again take over.

She points to the solar panels that collect enough energy to power most of the wastewater treatment plant, but notes that no matter how you look at it, cleaning sewage is a huge, energy-intensive process.

“It’s something most of us take for granted, but it should not be,” she said.




  • Endocrine disrupters are the by-products of many synthetic chemicals, which negatively affect normal, hormonal functioning in animals, including people, according to recent articles in the magazine, Scientific American, the journal Science, and many others. They have been blamed on everything from increased rates of cancer worldwide to the decline of the world’s amphibians to the worldwide dramatic decrease in the fertility of human sperm.
  • While the endocrine disrupters in the water in Laurel Ponds will eventually sink down into the groundwater, where it will become part of the big aquifer that underlies this section of the Eastern Sierra, any effects on the groundwater will likely be dwarfed by the natural scale of the landscape against the relatively tiny human population. Where human populations outstrip the underwater aquifer’s natural ability to clean themselves, as in Southern California according to various recent studies, almost all sampled groundwater is now contaminated with endocrine disrupters, with consequences yet to be understood.