Actual Intake Flow Measurements and Benefits for 316(b) Compliance

The U.S. Environmental Protection Agency (EPA) released its final Clean Water Act §316(b) Rule on October 14, 2014.  The study requirements for facilities drawing greater than 125 MGD are significant: submission of a Comprehensive Entrainment Characterization Study and evaluation of entrainment reduction technologies (including closed-cycle cooling, fine-mesh screens, and water reuse) and their impacts and benefits.  Therefore, accurately characterizing the flow rate at a given plant is critical.  Over time, the performance of circulating water pumps can degrade, resulting in a difference between the design intake flow (DIF) and the actual intake flow (AIF).  In some cases the AIF of a circulating water pump can be 10% to 20% below the DIF.  Measuring flow more precisely in the field could have the following potential benefits to plant operators if AIF is shown to be less than DIF:

• Could avoid the additional entrainment-related studies required,
• Through-screen velocity would also be less, making it more likely to meet the 0.5-ft/sec criterion, and
• Estimates of total entrainment for which the operator is responsible would be less

 This paper will focus on methods to determine the feasibility of measuring flow for this purpose and the technologies available to do so.