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When the Environmental Protection Agency dropped the maximum contaminant level for arsenic in public drinking water from 50 micrograms per liter (µg/L) to below 10 µg/L in 2006, numerous cities in Oklahoma were faced with finding ways to bring their supply sourced in large by the Garber-Wellington Aquifer into compliance. Norman had to shut down a third of its wells, effectively reducing the municipality’s water supply during peak months and resulting in the loss of millions of dollars of precious revenue.
Garver is acting as project manager and design engineer for a turn-key wellhead arsenic removal system at Norman’s well No. 31, one of a handful of wells that tested between 40 µg/L and 70 µg/L. The Severn Trent Services SORB 33® Arsenic Removal System has successfully been used in the United States and is making its debut in Oklahoma.
The project seeks to offer Norman a way to produce treated water capable of meeting the unfunded EPA arsenic-level mandates and return the non-compliant wells back to service. In the process, officials will closely watch the system to see if its performance is sustainable, if the method’s life cycle is cost effective, and whether a bacteriological disinfection is required before system-wide implementation.
The full-scale system applies a pump-and-treat process which sends pressurized water through a stationary filter vessel containing a ferric oxide media. As water is forced through the fixed bed, arsenic is attracted to the media, and the water is reduced to a compliant level below 7 µg/L. The media—a dry, crystalline granular—is designed to adsorb a large amount of arsenic to achieve long operating cycles, reduce pressure drops, and improve the operational cost. It does not need to be replaced for six months to two years, and the expired media is sent to a non-hazardous landfill.
The arsenic, which is a naturally occurring element in the Garber-Wellington Aquifer, is separated from the drinking water through a combination of adsorption, occlusion, and solid-solution formation by reacting with ferric oxide ions.
To allow the media to treat up to 40 percent more water before it is replaced, the Norman system uses a lead-lag configuration. The two lead filters operate until they reach a set level, and one is valved to the lag filter for polishing and further arsenic removal. Once the second lead is changed out, the lag filter takes its place, and a new filter is installed as the lag.
Although this technology has been used throughout western portions of the United States, this project is the first of its kind in the state of Oklahoma. |
