In October 2001 the US Environmental Protection Agency (EPA) announced it was revising the arsenic maximum contaminant level (MCL) from 50 micrograms per liter (µg/L, or parts per billion) to 10 µg/L. It also proposed a research program to conduct a series of full-scale, on-site demonstrations of arsenic removal technologies.
   
With EPA budget and Congressional add-on funds amounting to around $20 million, EPA has funded 50 demonstration projects in 27 different states during the past six years.
   
The main objectives of the program are to evaluate system performance, to characterize residuals produced and to determine the capital and operation and maintenance (O/M) costs of the technology being demonstrated. The technologies demonstrated have consisted of adsorptive media (10 different media products), iron removal, anion exchange, coagulation/filtration and point-of-use (POU) reverse osmosis (RO).

Selecting a demonstration
Selection of the technology for demonstration was a cooperative decision made by the water system, state agency and EPA from solicited proposals. The decision was based upon a number of factors, with the most significant ones being source water quality, residuals generated and on-site disposal options, and estimated capital and operation/maintenance costs.
   
Although the majority of the selected demonstration sites had only arsenic to contend with, several sites had a second co-occurring contaminant such as uranium, nitrate, radium, or antimony.
   
One site, the Sunset Ranch Development near Homedale, ID, had three contaminants: arsenic at 53-64 µg/L, uranium at 23-31 µg/l and nitrate (as N) at 6-12 milligrams per liter (mg/L). The source-water arsenic was speciated and found to be predominately in the oxidized form as As(V) (95 percent).

Vanadium, too
The source water also had vanadium at 29-39 µg/L and high total dissolved solids (TDS) at 648-730 mg/L.
   
Because of the multiple contaminant issue and because the site consisted of only 10 homes, POU reverse osmosis (RO) systems supplied by Kinetico, Inc. were selected for the demonstration.
   
The 10 homes in the development were served by one 20-gallons per minute (gpm) source. There was no central treatment system, although several homes had water softeners because of the water hardness of approximately 240 mg/L (as CaCO3).
   
For the demonstration study, water softeners were installed in remaining homes so that all homes in the study had the same technology: a home point-of-entry (POE) water softener and an under-the-sink POU RO system.

Analysis of samples
For one year ¡ª July 2005 through June 2006 ¡ª monthly water samples were collected from 20 locations, including the source water, softened water and RO-treated water at nine residences, and the RO reject water at the one residence.
 
The samples were analyzed for approximately 20 water parameters. The arsenic was also speciated for As(III) and As(V) at one location four times during the study.
   
Raw water hardness consisted of approximately 78 percent calcium hardness and 22 percent magnesium hardness. The home water softeners reduced the hardness to an average of 1.7 mg/L (as CaCO3) that was further reduced an average of 0.5 mg/L by the RO units.
   
The RO systems in all homes achieved a significant reduction of all three major contaminants: arsenic, uranium and nitrate. Arsenic was reduced by over 99 percent to less than 1 µg/L, well below the 10 µg/L MCL.
   
The nitrate was lowered to 1 mg/L (90 percent) and the uranium to less than 0.1 µg/L (99 percent). Vanadium was reduced by 99 percent and TDS by 96 percent. The results of the sampling program are shown in the accompanying table.

Residuals
Two residuals were produced by each treatment system: brine waste from the POE home water softener and reject water from the POU RO system. Both the water softener spent brine and the RO reject water were discharged directly to septic tanks at the individual homes.
   
The RO reject water was sampled from one home and, as expected, it contained elevated levels of TDS, arsenic, nitrate, and other inorganic salts when compared with those in raw water.
   
The RO reject water contained 55.9-92.3 µg/L of arsenic, 8.3-19.2 mg/L of nitrate (as N), 23.0-42.3 µg/L of uranium, and 740-1,080 mg/L of TDS.

One-half of detection limit used for non-detect samples for calculations.
Note: Uranium and vanadium measured at one residence only.
IN = Source Water    WS = After Water Softeners    RO = After RO Systems

Many innovative systems
The EPA Arsenic Demonstration Program is providing detailed performance and cost data on the many new and innovative treatment systems included in the program.
   
Because of the continuous and extensive monitoring by EPA through its contractor, Battelle, usually on a weekly basis, many state drinking water programs have allowed the newer technologies to be installed on a full-scale basis without pilot testing.
   
The POU RO demonstration project at the Sunset Ranch Development in Idaho is one example of the many successful full-scale EPA projects currently under way.