Groundwater

Contamination in the

Rialto-Colton Basin

RWQCB, Santa Ana Region

July 17, 2012

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Overview

– Early investigations

– Two source areas

• County/Stonehurst

• 160-acre site

– Agency roles

– County groundwater remedy

The Problem

• Perchlorate detected in 1997

• Some wells shut down in 2002

• First Regional Board orders issued

in 2002

• Investigation of sources and

extent of contamination

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Regional Board Role

• Lead agency for County

groundwater remedy

• Lead agency for Stonehurst site

• Investigation of 160-acre site until

2008; proposed CAO

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County Groundwater Remedy

• CAO adopted in 2003 and revised

in 2004

• Requires cleanup and

replacement water

• Treatment system for Rialto #3

and two additional extraction wells

• Began operation in 2006

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