To give an idea of the level of detail possible:

• We used annual run-time charts developed from the data to rank the 80-plus lift station basins and identify those with unusually high I&I. As a result, many of these wastewater basins have been scheduled for rehabilitation in the city's 2008–2012 capital improvement program.
• At one relatively new lift station, the data showed that the lead pump ran for two days after a very minor rain event, reflecting an impossible amount of flow. The public works department investigated and found a bad relay.
• The flow numbers and run-time patterns for a new high-end subdivision looked bizarre: huge water usage and almost no wastewater. We discovered that 80% of the homes there are occupied by childless working couples who shower at the gym on their way to or from work (little wastewater) and who water their landscaping extravagantly (lots of water use).
• The model highlighted some 210 potential sewage overflow points; the department agreed that some of those locations had been problems for years.

After validating the model for the existing system, we started “growing” the city with great confidence in the predictions generated. We found to our chagrin that the new model didn't always agree with our previous best-judgment estimates: Some of the projects we recommended two years earlier simply weren't good ideas, and some very beneficial projects that we hadn't envisioned materialized.

The result: a 47% reduction in projected capital needs, plus another $400,000 to $500,000 in annual projected savings for operations and maintenance.

The model and capital plan can be updated continually as new developments occur and as new data is collected. In addition, the model and the data enable the city to manage the system more effectively by focusing efforts where they're needed, which should help reduce operations and maintenance expense.

The model may even help lower the cost of new infrastructure construction in the future: Texas mandates that wastewater handling facilities be constructed with a “peaking factor” so that at any one instant, sewers can convey four times the average daily flow without surcharging. With its new model and data, the city can prove that its system is tight, and that it should be allowed to build new sewerage facilities to a lower peaking factor

This could potentially create huge cost savings without negatively impacting public health and safety—a positive outcome for taxpayers in more ways than one.

— Kirst is president of Kirst Kosmoski Inc. in Houston.

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