And, as the Hilltown Water and Sewer Authority can testify, the township also is the home to naturally occurring arsenic in its groundwater. When measured in early 2003, arsenic levels in surrounding groundwater measured 15 to more than 20 parts per billion (ppb). When the United States Environmental Protection Agency (EPA) reduced the federal arsenic standard to a maximum contamination level of 10 ppb in drinking water beginning January 2006, the Authority had to act.
“We volunteered for the Environmental Technology Verification Program and tested an iron-based adsorption treatment technology from ADI International,” said Butch Erwin, operations manager, Hilltown Water and Sewer Authority. “The pilot test provided valuable information for our future system requirements, which included not only the reduction of arsenic levels, but of manganese and iron levels, too.”
The pilot test was conducted at the Township’s well station number one in Sellersville, Pa., from October 8, 2003, through May 28, 2004. The feed water for the verification test was drawn from an on-site chlorine detention tank,
containing groundwater that had been disinfected with sodium hypochlorite.
The feed water, with an average total arsenic concentration of 21 ppb and a pH of 7.6, was treated with sulfuric acid to lower the pH to 6.4 prior to treatment. When operated under the manufacturer’s specified conditions for the site and at the design flow rate of 1.7 gallons per minute (gpm), the ADI system reduced the total arsenic concentration from an average of 21 ppb in the feed water to an average of 7 ppb in the treated water.
While the arsenic removal system was judged to be effective, iron and manganese levels remained high. Manganese levels were measured at up to 0.10 parts per million (ppm), exceeding the EPA’s tier two limit of 0.05 ppm. Levels of iron were measured at 0.145 ppm compared to the EPA limit of 0.3 ppm. While the iron and manganese levels were not health risks, they did prompt customer complaints of discolored water and mineral deposits in bathtubs, showers, sinks and toilets. According to Erwin, the need to add sulfuric acid to the water was another reason to look for an alternative arsenic treatment technology. “Adding sulfuric acid to the treatment unit represented not only an additional step, but an additional expense as well. And from a safety standpoint, we’d prefer not to have to keep undiluted sulfuric acid on site.”
Nevertheless, Erwin and his colleagues were convinced of the efficacy of iron-based media, so they investigated similar technologies. The SORB 33® arsenic removal system utilizing Bayoxide® E33 media from Severn Trent Services had been selected for use at several other EPA demonstration sites, so Erwin decided to find out more about the technology. When he learned that Severn Trent also was introducing the Omni-SORB™ iron and manganese pre-treatment system, it appeared the combined technologies might provide the ideal solution for Hilltown Township’s water filtration needs.