Posted: Mon, 29 Aug 2011 08:16 AM - 14,220 Readers

By: Craig Bell

The debate on whether to halt construction of the city's Water Treatment Plant 4 has focused primarily on financial considerations, but has paid scant attention to the purposes of this investment: greater reliability, capacity, safety and protection of public health.

I was manager of systems planning for the Austin Water Utility for 15 years prior to 2004. The risks I see associated with not completing this facility are more than the inconveniences of failing to meet peak customer demands. Sudden and unpredictable crises would be made possible by, and aggravated by, the absence of resilience and dependability that the plant will contribute to Austin's water system.

From a treatment capacity standpoint, Austin's water system can coast along for a few more years if nothing major goes wrong. But many things can go awry, including pipe breaks, loss of power, pump failures, equipment out of service, operational mistakes and control system failures. Weather-related damage, and in this post-9/11 era, even sabotage, can affect the system.

The raw water intakes for our two remaining (and aging) water treatment plants, Davis and Ullrich, are close to the same location on Lake Austin. A single contamination event (imagine a large chemical spill on the Loop 360 bridge as an example) could shut down both plants for an extended period.

Even in water systems with ample redundancy and extra capacity, simple but unexpected problems can cause failures in the water distribution network. Supply to certain areas can be interrupted for long periods and pressure can drop rapidly and dramatically.

The consequences can be serious:

Low pressures and constraints in water supply and distribution can limit the ability of our firefighters to suppress large fires. The firefighters may not get the volumes of water they need to bring fires under control, save adjacent structures, and make rescues.

Very low-pressure episodes could develop in some areas — most likely in the higher elevations of each pressure zone — that could contaminate system pipes, requiring "boil water" notices because of the risk of sickness.

Large, industrial water users — typically, also large employers — may be forced to shut down production because of system problems in their pressure zones, negatively impacting the city's reputation.

The high northwest zones currently are the most vulnerable to water supply crises. Regardless of the treatment capacity at the existing plants, the system has limited ability to push treated water up to these zones through a series of relays.

For more than 20 years, we have configured the city's water system so that WTP 4 would fit into it seamlessly. In addition to drawing raw water from Lake Travis rather than Lake Austin, it would put treated water directly into the high northwest pressure zones where it is needed the most — and where the system has the most difficulty delivering it.

In previous years, I have argued that we could take the risk of delaying the construction of WTP 4. We all knew that the imposition of mandatory conservation for outside watering was so effective in reducing peak summer demands that it resembled adding a new treatment basin to the system.

I could not make that argument today — a mandatory outside watering ordinance is among the conservation measures that have taken effect since my retirement. Its dramatic impacts are now incorporated into the historic side of the water demand curves. That card has been played.

WTP 4 will add reliability, operational flexibility and a margin of safety to our water system. Further delay of its construction is now outside of my comfort zone.

Bell retired as Manager of Systems Planning for the Austin Water Utility in 2004 after 32 year career.