California Water Science Center

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008-3043

May 2008 Printed on recycled paper

Sacramento

San Francisco

Antelope Valley Ground-water Basin USGS RESEARCH HELPS THE COUNTY OF LOS 

ANGELES ADDRESS NEW ARSENIC STANDARDS

In January 2006, the U.S. Environmental Protection Agency (USEPA) 

enacted stringent standards on arsenic in drinking water. The new limits

raised concerns about wells in the Antelope Valley of northern Los 

Angeles County that had high levels of naturally occurring arsenic. To 

meet the new standard, Los Angeles County Waterworks District No. 

40, part of the Los Angeles County Department of Public Works, 

considered building arsenic-removal facilities at a cost of nearly $34 

million. Instead, the District initiated a well-modification project that 

was based on the findings of a U.S. Geological Survey (USGS) 

scientific investigation. 

Using a well flowmeter and down-hole sampler − invented by USGS 

scientists – the study team found that high-arsenic levels were concentrated in the deepest portions of the wells, 600 feet or more below the 

land surface. Using this finding, the District implemented a well 

modification pilot project where the deep portions of five wells were 

sealed off permanently, while preserving the ability to pump highquality water from the upper sections. Well screens in the upper 

sections were first cleaned using an innovative sonic technique to 

increase the yield of high-quality water. The deeper sections then were 

sealed using micro-fine cement technology. The District now pumps 

water that meets the new USEPA standard for arsenic from the affected 

wells. Arsenic concentrations are lower by an average of 84 percent, 

while well yield is lower by only 24 percent. The total cost of the 

modification project for the five wells was $608,580; a one-time net 

savings of 550 percent over construction of an arsenic-removal facility.

Well, before and

after modification

WATER TABLE

LACUSTRINE (CLAY)

DEPOSITS

1150 gallons

per minute

W

P

84 percent 

reduction in arsenic

24 percent 

reduction in yield

Water containing

 arsenic

Environmental Protection Agency 

(USEPA) acceptable water

WATER TABLE

LACUSTRINE (CLAY)

DEPOSITS

1450 gallons

per minute

Water containing

 arsenic

Environmental Protection Agency 

(USEPA) acceptable water

Not to scale

“For over a decade, the USGS 

has supported our management of the Antelope Valley’s

water resources by providing

excellent scientific research, 

modeling, and analyses. 

The well-modification 

project demonstrates the 

value of our cooperative 

efforts with the USGS.” 

Adam Ariki,

Assistant Deputy Director,

Los Angeles County

Department of Public Works

USGS scientists invented a well 

flowmeter and down-hole 

sampler that can measure how 

ground-water quality changes 

with depth, and used the information to trace sources of natural 

and man-made contaminants.

ell

lug

For more information about the 

USGS Cooperative Water Program, contact: 

Donna Schiffer, Acting Director, 

U.S. Geological Survey, 

California Water Science Center

916/278-3000 schiffer@usgs.gov

http://water.usgs.gov/coop