Leahy Well Ion Exchange System Design for Bellflower Somerset Mutual Water Company

Summary

Team E2 collaborated with AKM Consulting Engineers to redesign the Leahy Well to achieve a 3,000 GPM water capacity and to develop on-site treatment for perfluoroalkyl and polyfluoroalkyl substances (PFAS) via Ion Exchange (IX) for the Bellflower Somerset Mutual Water Company (BSMWC) in Bellflower, CA.

PFAS is a broad term used to describe the thousands of variants of the man-made, synthetic chemicals that are used in everyday products such as non-stick pans, hydrophobic clothing, and consumer goods. When presented in high concentrations and ingested through drinking water, PFAS can be associated with adverse health effects such as cancer, high blood pressure, and liver damage.

The project incorporates 3 on-site cartridge filters to remove Total Suspended Solids (TSS) from the water influent before it is treated through 4 Ion Exchange tanks to reduce PFAS concentrations via anionic exchange to undetectable levels that comply with current Environmental Protection Agency (EPA) and Consumer Confidence Report Drinking Levels (CCRDL) standards. The project will provide customers of Bellflower Somerset Mutual Water Company with safe and consumable drinking water.

With the addition of the cartridge filters and IX tanks, the well pump system was also reconfigured to reach the desired pumping needs due to additional treatment losses, with an average daily flow demand reduction from 3,500 to 3,000 GPM.

Technical Approach/Methodology

The project was first approached by determining the total head losses accrued through the treatment systems. With the addition of new piping to account for the treatment tanks and cartridge filter installation, Team E-2 reconfigured the pumping system speed to account for any additional head losses.

In order to achieve this, Team E-2 used engineering manufacturing data on pipe bends and valves to calculate the total minor losses associated with pipe bends or valve installations through friction losses. Team E-2 also utilized the Hazen-Williams equation to calculate all the major losses in the horizontal pipes while accounting for the material type, pipe length, water velocity, and hydraulic gradient. Changes in pressure drops between cartridge filters were also accounted for with a range of pressure drops between 1 and 10 PSI, which were solved based on an assumption of filter saturation and its cleanliness. Resin pressure drops were calculated by referring to charts provided by the manufacturer, Purolite, which detailed the pressure drops per IX tank based on the respective water flow capacity.

Team E-2 also determined the total volume of resin needed per IX tank to reach a minimum empty bed contact time (EBCT) of 2 minutes, allowing proper PFAS elimination from the water as it travels through the resin media. The volume of resin needed was calculated based on the minimum commercially available quantity of resin media provided by Purolite while maintaining an approximate EBCT of 2 minutes.

After all of the total dynamic head (TDH) calculations were quantified through the use of AutoCAD and Excel software, Team E-2 reconfigured the pumping speed of the well pump by using the affinity laws to scale both the total dynamic head and the flow rate to reach target TDH values based on system losses, pump drawdown, seasonal aquifer level variation, and a constant pumping pressure of 65PSI. All affinity law scaling was completed through the use of Excel.

Outcomes

At the end of the project, Team E-2 was able to successfully design all aspects of the project that were to be accounted for before entering bidding under AKM Consulting Engineers. The team was successful in the simulated installation of the cartridge filters and Ion Exchange tanks via AutoCAD while maximizing the amount of space provided on the site for the treatment mechanisms. The team was also successful in determining the new operational speeds of the pump system, which will be automatically controlled through an on-site Variable Frequency Drive (VFD) controller. Currently, the project has entered the bidding phase under AKM Consulting Engineers and will begin construction in Bellflower in the following months.

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