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Tuesday, September 07, 2010
Water Saved Isn't Always Water Earned
By John Fleck
Journal Staff Writer
The largest tributary on the middle Rio Grande doesn't look like much.
All of 250 feet long, the little river in Bernalillo County's South Valley comes out clear, albeit with a slightly musty smell, as it spills into the muddy Rio Grande.
It is unusually popular with bike riders, bird watchers and people who fish. Unusual, that is, given its source — the metro area's largest sewage treatment plant.
"The birds are fantastic," said Joe Lavandowski, a retired 70-something bicyclist who stops by the sewage treatment plant outfall on his weekly Thursday bike ride with his friend Paul Pizzoli.
"Last time we were down here, there were three guys fishing," Lavandowski said as he stopped beside the quiet stream last Thursday.
To the north, you have to go all the way to the Rio Chama, north of Española, to find a Rio Grande tributary larger than the outfall from the metro area's Southside Water Reclamation Plant.
Two big pipes carry water out of the 100-acre treatment plant, under a bike trail and over an irrigation drain before dumping it into a rock-lined channel. Every sewer-connected Albuquerque and Bernalillo County toilet flush, once the bad stuff has been cleaned out, ends up here, on the east bank of the Rio Grande.
By most accounts, the cleaning out is being done reasonably well. Conflict in the 1990s over contamination in the effluent led to the investment of some $60 million in improved treatment technology to meet more stringent Environmental Protection Agency guidelines.
These days, the questions have more to do with water quantity. This being a desert, all those flushes add up to a significant source of water. Calling this an important Rio Grande tributary is more than rhetorical flourish.
The details of how and why it matters is what journalists sometimes call a "MEGO" issue — My Eyes Glaze Over. But it's important, so if you'll bear with me, I'll offer a brief primer in New Mexico water supply and water rights accounting, as applied to the reclamation plant's little river.
For much of its history, Albuquerque's water came from pumped groundwater. In the long run, that has the effect of depleting the Rio Grande, gallon for gallon, as water leaks out of the river bottom to fill the holes being created by our pumps' great sucking. Water law requires the Albuquerque Bernalillo County Water Utility Authority to make up for some of that impact, and "return flows" are one way to do it.
The return flow issue makes for some complicated water policy discussions because of a common misunderstanding of what our net water supply really is. For every 100 gallons we withdraw from the system (from groundwater or the river), we're putting 50 gallons back into the system via this stream so others can use it. Our net consumptive use is just 50 gallons.
There are two types of water efficiencies we can implement. One type would involve, for example, reducing outdoor watering. A gallon of outdoor watering is entirely consumptive, so saving that gallon by tearing up a piece of lawn saves a gallon of net consumptive use. That gallon never had a chance to get back to the river.
Saving a gallon by installing a low-water toilet is different. If it uses a gallon less per flush, that means one less gallon withdrawn from the system in the first place, as well as one less gallon returned to the river. The effect on our net consumptive use is effectively zero. There are good reasons to do the low-flow toilet anyway — energy consumption in pumping and treating the water, line losses, cost. Best just to leave that gallon where it is, rather than take it out and put it back again. But things like low-flow toilets and other indoor water efficiencies don't save as much water, in terms of our overall water budget, as people often think.
A groundbreaking last week at the sewage treatment plant illustrates the issue. Dignitaries did the traditional shovel-in-dirt ritual to ceremonially launch construction of a treatment plant that will add an extra level of cleaning to about 5 percent of the wastewater now going into the Rio Grande. Instead of sending it to the river, it will be pumped into a newly built network of pipes to irrigate parks on Albuquerque's south side.
In other words, instead of returning it to the system, it will be consumptively used. We'll be able to reduce our groundwater pumping or river diversions by a like amount, but it's not like we're getting free water here. In terms of the overall amount of water in the system, the net effect is essentially zero.
The project may make sense in terms of the arcane water rights accounting rules that apply to the Albuquerque Bernalillo County Water Utility Authority.
But Bruce Thomson, the head of the University of New Mexico's Water Resources Program, points out that using cleaned-up sewage to water parks isn't actually saving water, it's merely shifting the source of supply from one part of the system to another.
"It doesn't reduce your consumptive use," Thomson said.
UpFront is a daily front-page opinion column. John Fleck can be reached at 823-3916 or firstname.lastname@example.org.