Arsenic Removal to Meet EPA Standards

Pressure filter installation at Victorville, California

Meeting EPA Regulations

Victor Valley Water District began planning for arsenic removal in early 2001 to be in compliance with the anticipated requirement to increase arsenic removal. In the 2006 EPA regulation change, acceptable arsenic levels were reduced from 50 μg/L to 10 μg/L.

Victor Valley receives its water from 22 active production wells. These wells produce 5.5 billion gallons annually and service 65,000 customers in the San Bernadino Valley. Low to moderate (2 to 21 μg/L) levels of naturally occurring arsenic were found during the testing of the wells. Between 2002 and 2004, nearly half of the wells tested above the 10 μg/L limit.

Victor Valley Water District, with Carollo Engineers, conducted a series of pilot plant studies to compare arsenic removal technologies. A packaged ion exchange system was evaluated against a coagulation/filtration (C/F) process under several different scenarios. After reviewing the pilot plant results and comparing costs, Victor Valley selected the C/F system.

Arsenic Removal Technologies
Cost (Low to High)	Advantages	Disadvantages
Coagulation/filtration	Simple proven technology Widely accepted Moderate operator training	pH sensitive Potential disposal issues of backwash waste As⁺³ and As⁺⁵ must be fully oxidized
Lime softening	High level arsenic treatment Simple operational change for existing LS facilities	pH sensitive (requires post treatment adjustment) Requires filtration Significant sludge generation
Adsorptive media	High As⁺⁵ selectivity Effectively treats water with high TDS	Highly pH sensitive Hazardous chemical use in media regeneration High concentration of SeO₄^-2, F-, Cl-, and SO₄^-2 may limit arsenic removal
Ion exchange	Low contact times Removal of multiple anions, including arsenic, chromium, and uranium	Requires removal of iron, manganese, sulfides, etc. to prevent fouling Brine waste disposal
Membrane filtration	High arsenic removal efficiency Removal of multiple contaminants	Reject water disposal Poor production efficiency Requires pretreatment
Adapted from Carollo Engineers

Equipment Selection

WesTech was selected to provide a total of 11 vertical pressure filters and supporting instrumentation for the project. 4 pressure filters were placed at the Balsam plant and 7 at the El Evado plant. All 11 filters together produce 15 MGD.

Vertical Pressure Filters
Dimensions	12 ft diameter
Area per filter	113 ft²
Filtration rate	Nominal: 6.4 gpm/ft² (724 gpm) Maximum: 7.5 gpm/ft² (848 gpm)
Backwash flow rate	20 gpm/ft²

While natural arsenic levels were just above the EPA’s limit, the amount of water to treat was sizable. Due to the high flow rate associated with the well sites, significant quantities of large filtration area vessels were required for adequate arsenic removal.

Pressure Filter Media
Media	Depth	Effective Size
Anthracite coal	30 in	1.1 mm
Sand	18 in	0.55 mm

WesTech has extensive experience in designing and constructing pressure filters. The large quantity of vessels were customized to match the water quality and remove the desired amount of arsenic.

Customized filters provided Victor Valley with the level of performance needed to comply with the EPA requirements. The unique header and lateral underdrain design developed by WesTech, in collaboration with Carollo, ensured uniform distribution of flow in the vessels.

Arsenic Removal
	Before Treatment	After Treatment
El Evado	10.9 μg/L	8 μg/L
Balsam	12 μg/L	8 μg/L

Optimizing the media type and depth, WesTech improved filter run times and provided the most efficient pressure filter for arsenic removal.

Header and lateral underdrain with media retention nozzles

Customer Satisfaction

The WesTech Vertical Pressure Filters effectively removed arsenic to meet the EPA standard. Individual, parallel operating vessels satisfy redundancy requirements and offer a design that is easily expanded to meet future needs.

By employing WesTech’s vertical pressure filters, Victor Valley is now in compliance with EPA regulations and consistently produces high quality water to the San Bernadino Valley.