Removing Arsenic to Non-Detect

Pressure filtration system installation at Ione, Washington

Tightening Regulations

The Chippewa Water and Sewer District provides water distribution and sewer collection for the City of Ione, Washington. Raw water for the drinking water distribution system is supplied through two production wells and is treated with chlorination.

This water complied with all primary drinking water standards but continually fell short of the EPA’s secondary drinking water standards for iron and manganese. Seasonal peaks of iron and manganese clogged pipes and frequently produced aesthetic and odor issues, resulting in customer complaints.

In addition to iron and manganese, moderate levels of arsenic were also in the water. In 2003, Ione began planning for a new treatment plant to be in compliance with the anticipated requirement to increase arsenic removal. In 2006, EPA regulations for arsenic levels were reduced from 50 μg/L to 10 μg/L, compounding compliance issues.

Water Quality
	MCL	Well 1 Raw Water	Well 2 Raw Water
Iron	0.3 mg/L	0.63 mg/L	0.06 mg/L
Manganese	0.05 mg/L	0.32 mg/L	0.46 mg/L
Arsenic	10 μg/L	15–25 μg/L	15–25 μg/L

Equipment Selection

A comprehensive pilot study was completed to determine the best treatment method to remove arsenic, iron, and manganese. After comparing pressure filters to cartridge filters, bag filters, and other filtration methods, the engineer, in conjunction with the town council, selected a granular media pressure filtration system as the best available technology.

In 2008, WesTech was selected to provide three 50-percent-capacity vertical pressure filters, a complete chemical feed system, and a programmable logic control (PLC) system.

Vertical Pressure Filters
Quantity	3 filters
Size	10 ft diameter
Area per filter	78.5 ft²
Total filtration rate	3 gpm/ft²
Backwash flow rate	9 gpm/ft²

WesTech’s granular media vertical pressure filters effectively remove iron, manganese, and arsenic to meet primary and secondary standards. Individual, parallel operating vessels satisfy redundancy requirements and offer a design that is easily expanded to meet future needs.

To remove these contaminants most efficiently, WesTech customized the depth and type of granular media. The customized design allows Ione to improve water quality while keeping costs low. Due to the levels of naturally occurring iron, both the iron and arsenic coprecipitate without the addition of an iron-based coagulant such as ferric chloride or ferric sulfate.

Pressure Filter Media
Media	Depth	Effective Size
Anthracite coal	18 in	0.6–0.8 mm
Greensand Plus	18 in	0.3–0.35 mm
Support gravel	16 in	n/a

The plant was designed so that water can be pumped directly from the well and through the pressure filters with enough residual pressure to lift the treated water to the elevated storage tank.

Treated Water Quality
Iron	0.15 mg/L
Manganese	0.01 mg/L
Arsenic	Non-detect

Customer Satisfaction

Plant operators are impressed with the ease of operation provided by the WesTech PLC controls. Automatic backwashes can be controlled and plant adjustments made from the central control computer. Chris Chaney, the chief operator, said, “It’s a complex plant, but the way WesTech’s PLC is programed, it requires very little operator intervention.”

Low maintenance and operator friendly features were important aspects of the treatment system selection, since Chaney has many other responsibilities in addition to maintaining the treatment plant. Operators and residents alike were impressed with the inexpensive operation costs and the “perfect water” that was produced.

Before the new system was installed, the majority of homes used cartridge filters to reduce the negative aesthetic effects of the iron and manganese. Residents of Ione are pleased with the quality of water produced from the new treatment plant. They no longer need to worry about clogged pipes or brown laundry.

Since the installation of WesTech’s pressure filters, maintenance and residents’ individual treatment costs have been greatly reduced.