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Oct 25, 2007

Shearon Harris: Does Energy Conservation = Water Conservation?


I just read in the N&O that Shearon Harris and the City of Durham use about the same amount of water each day: 33 million gallons per day for the power plant vs. 28 million gallons per day for the Durham water system.

So does this mean that conserving electricity is an immediate method of conserving water?  It's not clear to me.  Shearon Harris draws from Harris Lake, while Durham drinking water comes from Lake Michie Reservoir and the Little River Reservoir.  How tightly is Harris Lake's water supply tied to the other two?

Here's a primer on the hydrological cycle (how water moves around the planet).  Scroll ~3/4 down the page for a graphic showing how US household water consumption compares to other countries.  You won't be surprised.


Photo: nrc.gov

12:20 AM in Misc.Blog 2007, News, Triangulations | Permalink


I think the bulk of the water gets recirculated back into the lake.

While saving power is good, what would probably happen is that Progress Energy would just sell any surplus to other utilities, because it's actually cheaper to run a nuclear power plant than it is most other power plants. But that would have the good side effect of probably reducing emissions from some other coal- or gas-fired power plant.

I imagine at this point someone who actually knows what's going on will come by, take a couple of rapier passes at what I've said, and tear it to ribbons. :)

Posted by: Joseph H. Vilas | Oct 25, 2007 9:34:24 AM

"saving about 375 million gallons of water [over 24 days of planned shutdown] that would have evaporated if the power plant had been using water for cooling during normal operations."

Thanks, Joe. I just double checked the article, and from what I can math out, ~40% of the water evaporates, and ~60% (presumably) gets returned to the lake.

That said, you've reminded me of several related physical distinctions I wanted to mention/ask about. Among them: water spent on the lawn vs. water flushed down the toilet. A lot of lawn water evaporates. Water flushed down the toilet goes to a wastewater treatment plant which then discharges to, umm.... where exactly? My understanding is that the standard practice is to discharge treated wastewater to some kind of reservoir or lagoon that eventually feeds back to the area's groundwater. But I don't know how that works exactly in Durham.

Car washing water goes down a drain which goes to... where exactly? Now and then you see signs on drain grates saying "don't pollute! this goes back to our freshwater streams and lakes!" But which grates go to something intermediary, like a treatment plant?

Anyone who can point to good Durham links? Muchas gracias.

Posted by: Phil | Oct 25, 2007 11:16:52 AM

Stormwater goes right to streams: http://www.durhamnc.gov/departments/works/stormwater.cfm

This is a grossly fascinating diagram: http://www.durhamnc.gov/departments/wm/goflow/theflow.htm

I've always thought a great field trip for preschoolers was the wastewater treatment plant; that's all they talk about, right?

Posted by: Valerie | Oct 26, 2007 1:48:42 PM

Valerie, thanks for the Durham interactive link on wastewater (theflow.htm) - a good one to show my kids. I think school kids should visit a potable (drinking) water plant, but a wastewater plant would be just a little too, well, crappy. Your link shows the bar screen at the beginning of the treatment process, capturing sticks and boxes. In reality, there are lots of weirder things it captures (a rainbow assortment of used condoms, for example).

Related to Phil's post, in the interest of reducing water use, my corporate cafeteria has (temporarily?) switched from washable dishes & trays to disposable stuff. I can't help but wonder whether the long view supports this switch. Sure, less dishwashing seems sensible - but the water isn't disappearing, just requiring treatment. Plus, this switch means more landfill material generated, and how much water to manufacture the disposable stuff....

Posted by: --Lisa S. | Oct 26, 2007 2:40:53 PM

A rainbow assortment of condoms?! And more?! Sounds even cooler than the dump field trip. We are SO there. :D

Posted by: Valerie | Oct 26, 2007 8:15:38 PM

According to one of my former engineering colleagues who used to work in a WWTP, the veterans all have stories of finding aborted babies in the grate. Sorry to say.

Posted by: Phil | Oct 26, 2007 8:59:11 PM

The cooling water from Shearon Harris goes back into the lake, minus the evaporated part. I didn't realize the loss was that big. The cooling water can pick up some metals and salts while passing through all that piping. Treated wastewater from the southern Durham municipal plant goes into the river and into Jordan Lake, as does Chapel Hill's WW. The E. Club Blvd. treatment plant could go to Jordan or Falls, I'm not sure. The WW is highly treated and sanitized. It probably still has a non-trivial amount of pharmaceuticals in it, though. So flush hard--it's a long way to Cary.

Posted by: Glenn | Oct 26, 2007 10:32:05 PM