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The effectiveness of water-treatment systems for arsenic used in 11 homes in Southwestern and Central Ohio, 2013

Scientific Investigations Report 2015-5156

Prepared in cooperation with Miami Conservancy District
By:
and
DOI:10.3133/sir20155156

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Abstract

In 2013, the U.S. Geological Survey and the Miami Conservancy District investigated the effectiveness of methods used to remove arsenic from drinking water at 11 homes in southwestern and central Ohio. The untreated (raw) ground-water had arsenic concentrations of 7.7–382 micrograms per liter (µg/L), and the median concentration was 30 µg/L. The pH was neutral to slightly alkaline, and redox conditions were strongly reducing, as indicated by high concentrations of iron. The predominant arsenic species was arsenite (As3+), which is difficult to treat because it exists in water as an uncharged compound (H3AsO3).

The water-treatment systems included (1) seven single-tap reverse-osmosis systems, (2) two whole-house oxidation/filtration systems, and (3) two systems that included wholehouse anion exchange and single-tap reverse osmosis. All but one system included pretreatment by a water softener, and two systems included preoxidation to convert arsenite (As3+) to arsenate (As5+) before treatment by anion exchange.

None of the treatment systems removed all of the arsenic from the drinking water. About one-half of the systems decreased the arsenic concentration to less than the maximum contamination level of 10 µg/L. The effectiveness of the systems varied widely; the percentage of arsenic removed ranged from 2 to 90 percent, and the median was 65 percent.

At some sites, the low effectiveness of arsenic removal may have been related to system maintenance and(or) operation issues. At two sites, homeowners acknowledged that the treatment systems had not been maintained for several years. At two other sites, the treatment systems were being maintained, but the water-quality data indicated that one of the components was not working, unbeknownst to the homeowner. EPA research at a small number of sites in Ohio indicated that operation and maintenance of some arsenic-treatment systems was not always simple.

Another factor that affected system effectiveness was the quality of the raw water. In general, the treatment systems were less effective at treating higher concentrations of arsenic. For five sites with raw-water arsenic concentrations of 10–30 µg/L, the systems removed 65–81 percent of the arsenic, and the final concentrations were less than the maximum contamination level. For three sites with higher raw-water arsenic concentrations (50–75 µg/L), the systems removed 22–34 percent of the arsenic; and the final concentrations were 4–5 times more than the maximum contamination level. Other characteristics of the raw water may have affected the performance of treatment systems; in general, raw water with the higher arsenic concentrations also had higher pH, higher concentrations of organic carbon and ammonia, and more reducing (methanogenic) redox conditions.

For sites with raw-water arsenic concentrations of 10–30 µg/L, two types of systems (reverse osmosis and oxidation/filtration) removed similar amounts of arsenic, but the quality of the treated water differed in other respects. Reverse osmosis caused substantial decreases in pH, alkalinity, and concentrations of most ions. On the other hand, oxidation/filtration using manganese-based media caused a large increase of manganese concentrations, from less than 50 µg/L in raw water to more than 700 µg/L in outflow from the oxidation filtration units.

It is not known if the results of this study are widely applicable; the number of systems sampled was relatively small, and each system was sampled only once. Further study may be warranted to investigate whether available methods of arsenic removal are effective/practical for residential use in areas like Ohio, were groundwater with elevated arsenic concentrations is strongly reducing, and the predominant arsenic species is arsenite (As3+).

Suggested Citation

Thomas, M.A., and Ekberg, Mike, 2016, The effectiveness of water-treatment systems for arsenic used in 11 homes in Southwestern and Central Ohio, 2013: U.S. Geological Survey Scientific Investigations Report 2015–5156, 26 p., http://dx.doi.org/10.3133/sir20155156.

ISSN: 2328-0328 (online)

ISSN: 2328-031X (print)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Sidebar—Arsenic Treatment Terms Used in this Report
  • Methods
  • Quality of Raw Water
  • Types of Water-Treatment Systems Sampled
  • Effectiveness of The Water-Treatment Systems
  • Factors Related To Effectiveness of Arsenic Removal
  • Summary of Results
  • References Cited

Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
The effectiveness of water-treatment systems for arsenic used in 11 homes in Southwestern and Central Ohio, 2013
Series title:
Scientific Investigations Report
Series number:
2015-5156
ISBN:
978-1-4113-4006-0
DOI:
10.3133/sir20155156
Year Published:
2016
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Ohio Water Science Center
Description:
Report: vi, 26 p.; Table
Country:
United States
State:
Ohio
Online Only (Y/N):
N
Additional Online Files (Y/N):
Y