Garver introduces city to advanced arsenic-treatment technology
High arsenic levels within drinking water have forced cities to shut down their supply wells, resulting in the surrender of expensive infrastructure and accumulation of idle assets. Norman, Okla. is one such municipality that lost half of its well field. Rather than accept this forfeiture, city leaders opted to pursue an innovative arsenic removal system to reclaim their abandoned wells—a decision that has provided a cost-effective answer for other cities seeking wellhead treatment solutions.
In 2006, the Environmental Protection Agency lowered the maximum contaminant level (MCL) for arsenic in drinking water from 50 micrograms per liter (µg/L) to 10 µg/L. Several municipalities in central Oklahoma depend on groundwater from the Garber-Wellington aquifer, which contains naturally occurring arsenic concentrations that are above the new MCL. Consequently, all non-compliant wells were removed from service, with cities shutting down otherwise high-quality wells that had been in production for decades. The City of Norman lost 15 wells and realized an approximate 50-percent reduction in its well field capacity. In addition, the University of Oklahoma was forced to remove 10 campus wells from drinking water service. As a result, the university became an immediate customer of Norman's drinking water system.
The new arsenic rule translated into added expenses for the City of Norman. To meet drinking water demand, the city's surface water treatment plant increased water production, and the city was required to purchase supplemental treated water from the City of Oklahoma City. Additionally, the cost to drill replacement wells at locations within the Garber-Wellington aquifer where arsenic concentrations were below the MCL carried a price tag of nearly $8.5 million.
Taking a proactive approach, Norman officials piloted a wellhead arsenic removal system on Well No. 31—one of a handful of wells that tested above 40 µg/L of arsenic. Providing program management, engineering, regulatory assistance, system start-up and project reporting, Garver worked with the city, University of Oklahoma, Urban Contractors, Severn Trent Services and the Oklahoma Department of Environmental Quality to ensure the debut of the SORB 33® Arsenic Removal System in Oklahoma was a success and would help recover lost city assets.
The SORB 33® system employs an adsorptive process that flows pressurized water through a fixed bed pressure vessel containing a ferric oxide (Bayoxide® E33) media. As water passes through the media, arsenic attaches to the surface. Exhausted media can then be removed and sent to a non-hazardous landfill for disposal.
"This pilot demonstration project is unique," said Garver Project Engineer Mary Elizabeth Mach. "First, granular ferric oxide had never been tested on the Garber-Wellington aquifer or even in Oklahoma. Second, because the pilot's objective was to produce safe drinking water, product water was pumped into Norman's distribution system to generate a revenue stream and help offset the piloting cost. Given the ground-breaking nature of this project, the City of Norman had to meet heightened regulatory agency requirements for safe drinking water."
Throughout the yearlong demonstration, the adsorption system successfully removed arsenic from Well No. 31 and provided product water with arsenic levels safely below 10 µg/L. As an added bonus, nearly 75 million gallons of drinking water were produced during the demonstration, generating more than $150,000 in revenue for the city.
"Garver introduced us to an advanced treatment technology that provided Norman an immediate solution to reclaiming existing water supply infrastructure we had lost due to the new arsenic standard," said City of Norman Mayor Cindy Rosenthal. "We are proud of being the first community in Oklahoma to demonstrate a cost-comparative choice for other central Oklahoma communities that rely on the Garber-Wellington aquifer for water supply."
Garver estimates that the operation and maintenance unit cost for Norman's optimized wellhead arsenic removal system is approximately $1.10 per 1,000 gallons. In comparison, the City of Norman pays $4.47 per 1,000 gallons when required to purchase water from Oklahoma City.
"The city found that the cost of this arsenic system is a competitive way to produce finished water," Mach said. "This is true especially when comparing it to the cost of expanding conventional surface water treatment plants, drilling new wells or buying finished water from neighboring municipalities."
Garver's Oklahoma Water Team Leader Michael Graves said the wellhead arsenic removal system also proved to be operational and maintenance friendly. "The media is easy to manage and requires infrequent handling. The spent media is classified as nonhazardous, so it could be disposed of in state-approved, nonhazardous solid waste landfills. In addition, for Norman, the media demonstrated longer-than-anticipated run time, and the arsenic breakthrough curves were very predictable, enabling the operations staff ample time to schedule media changeouts. Finally, the zero-waste-discharge aspect of the process was very advantageous given our wellhead treatment site did not have sanitary sewer utilities."
The city is currently making provisions to convert the arsenic removal system to permanent infrastructure at Well No. 31. They are also pursuing opportunities for collective treatment of high-arsenic wells at other locations within the distribution system. The City of Norman takes pride in forging new ground for Oklahoma as they reclaim lost infrastructure and put back into operation the high-arsenic wells, which at one time were doomed to be abandoned.
Will This Technology Work For You?
Both large municipalities and small cities can benefit from arsenic adsorption technology. It is especially useful in rural areas without nearby wastewater facilities.
"This technology is a completely self-contained system," said Garver Project Engineer Mary Elizabeth Mach. "While some arsenic removal technologies—like ion exchange—need access to a nearby sewer for wastestream disposal, this system only requires treatment infrastructure and electricity. No hazardous waste is generated, and the only excess material leaving the site is the exhausted media."
It is important for cities to know the composition of its ground water when considering this adsorption method, such as the valence state of arsenic. Does the water contain arsenic III, which is difficult to remove and must first be oxidized to arsenic V before adsorption? Are competing elements like uranium, chromium, sulfate and vanadium present?
"These ions have been shown to compete with arsenic on adsorption media," Mach said. "The media can capture some of those ions and effectively reduce its lifespan."
Mach also said the adsorption process needs to operate between 7 to 7.5 pH for optimum performance. If the ground water's natural pH baseline falls outside the optimum range, pH adjustment may prove necessary.
"If the pH is outside the optimum range, we've demonstrated that adjusting the pH still allows the system to be cost effective," Mach said.