EPA sitting on its hands: Marshall

South Australian opposition leader Stephen Marshall says the state's environmental watchdog should have acted faster on groundwater contamination in Adelaide's suburbs.

The Environment Protection Authority has confirmed it will extend a contamination testing zone to Mitchell Park after receiving advice that chemical vapours were likely to have spread to houses.

Residents in 25 homes in nearby Clovelly Park this month learnt they will be relocated after elevated levels of TCE, used as a metal cleaner in industrial settings, were found in their soil and air.

TCE can be carcinogenic when people are exposed to high levels over an extended period.

Despite EPA tests revealing in 2009 that Mitchell Park was at risk from drifting chemical vapours, according to Mr Marshall, no further tests were conducted in the suburb.

The opposition leader took aim at EPA chairwoman Mia Handshin, who has defended the agency's handling of the contamination issue.

"She thinks the EPA is doing a splendid job," Mr Marshall told reporters on Monday.

"Well, let me tell you, the EPA has been sitting on its hands for an extended period of time."

Ms Handshin told the Sunday Mail that protecting the public and environment were "core priorities" of the authority.