Tale of the Crypto

Page 3 of 6

"Here's a sample taken upstream of Val Vista," he says, referring to a water treatment plant in the East Valley co-owned by the cities of Phoenix and Mesa. As he shakes the jar, tiny particles of dust and dirt swirl in the otherwise clear liquid.

He lifts the other jar.
"This is a sample taken immediately downstream," he says. It's as brown and murky as a stool sample from the dysentery ward.

When water flows out of the Salt River Project canals and into any Valley water treatment plant, it is first doused with pure carbon to absorb the musky taste and odor of river water. Then it is mixed with alum, which binds to solids suspended in the water and carries them to the bottom. The sediment that settles to the bottom of the treatment plant is the sludge. And since cryptosporidium generally is carried in suspended solids, much of it should be removed from the water at that point.

After the coagulation process, the plant adds chlorine to the water, which kills giardia, fecal coliform and other parasites and bacteria. However, chlorine does not kill cryptosporidium because it is encased in an egglike cyst, or oocyst, that keeps the chlorine out.

Then the water is filtered through charcoal and sand and stones, which remove most of the remaining impurities.

And although crypto has never been detected in treated Phoenix or Tempe water (it was detected once in Mesa), that is no guarantee that it isn't there. The only completely safe waters are those that have been treated with ozone, or filtered through a process known as reverse osmosis, or boiled.

Water treatment experts agree that most of the cryptosporidium oocysts are removed by the coagulation and filtration processes in water treatment plants and end up in the sludge or the water that is used to backwash the filters.

The water treatment plants in Tempe and Chandler run those wastes through "dewatering" facilities that dry the sludge enough that it can be trucked directly to a landfill.

But the cities of Phoenix, Mesa and Glendale dump the sludge and backwash back into the SRP canals. The Phoenix-Mesa coowned Val Vista plant has sludge-drying equipment, but it doesn't run because the Phoenix City Council will not budget money for its operation. (Phoenix, incidentally, is not allowed to dump sludge at its water treatment plant on the federally funded Central Arizona Project canal.)

"The purpose of their water treatment plant is to filter that out," says Cherrington, still swirling his water samples. "And what they filter out is the sludge. So the very purpose of the plant is to concentrate what cryptosporidium is in there. And then they take it and dump it back in and say that the cryptosporidium content is less."

Between September and November of 1995, the City of Phoenix ran two studies of SRP canal water. One study measured the levels of crypto oocysts upstream and downstream of the various treatment plants; theother looked at how the sludge and backwash discharges affected the turbidity, or cloudiness, of the water. Since crypto attaches itself to solids in the water, increased turbidity could mean a higher likelihood of finding crypto.

Tempe officials didn't need a study to tell them that Phoenix discharges were reaching their plants. They could see it.

In an August letter to the City of Phoenix, W. Thomas Gallier, deputy public works director for Tempe, wrote, "The issue for us isn't whether sludge reaches our plant; it is whether there is an increased risk to Tempe's drinking water supply due to Phoenix's discharge of concentrated cryptosporidium oocysts in their alum sludge.... It is agreed that there is cryptosporidium in the Val Vista alum sludge. Every day that sludge is discharged into the SRP Canal system and subsequently to the South Tempe Water Treatment Plant, we are exposing ourself to potential cryptosporidium problems."

In fact, the Phoenix study showed that turbidity increased at the downstream plants by 100 percent to 350 percent after slug discharges upstream. So Phoenix experimented with different release scenarios and found that, if the sludge was discharged continuously, it did not significantly raise the turbidity, though it still increased the amount of aluminum--and, one supposes, everything attached to it--floating down the canals.

The Phoenix study also found crypto.
Going into the Phoenix Squaw Peak water treatment plant on the Arizona Canal near 24th Street, the researchers measured as many as 29 oocysts per 100 liters of water; downstream at the Phoenix Deer Valley plant, just west of I17, they found readings as high as 110 oocysts per 100 liters.

And although six of seven "events" showed increased crypto levels downstream, they didn't show any consistent increases. In one event, the crypto count dropped precipitously. When the numbers were crunched through standard statistical analysis, they came out as colorless as tap water.

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Michael Kiefer