Marcus Bosch, the corporation's property services general manager, told the Chronicle yesterday that Housing NZ was made aware of the issue on April 7 after learning of the prospective purchaser's test results.
"We then requested pre-emptive testing which confirmed the presence of methamphetamine in two locations in the house," Mr Bosch said.
He said there were two phases of testing for methamphetamine. The first is a pre-emptive test that determines whether it is present or not; the second is a comprehensive test (including air and surface testing) that determines the level of contamination and results in recommendations for repairing the property.
Mr Bosch said readings of less than 0.5 micrograms per 100sq cm were deemed safe.
"Readings of 0.5 micrograms per 100sq cm or greater indicate steps must be taken to make the property safe for habitation, if that's possible."
Remedial measures can range from specialised cleaning through to re-fitting a property or even demolition.
On April 8 the corporation requested comprehensive testing of the property and preliminary results indicated the presence of meth at a negligible level of less than 0.02 micrograms per 100sq cm. The air test results are pending.
Mr Bosch said on the same day the prospective purchaser was offered the opportunity to exit the sale and purchase contract they had signed.
"As this is the third instance of methamphetamine being identified in a Wanganui house we have on the market, we have been trialling a pilot programme in Wanganui that will test homes for methamphetamine to determine whether they are fit for sale on the open market," he said.
"The 19 Wanganui properties already listed with real estate agents will have been tested by April 17. No sale and purchase agreements will be entered into until the properties have received a clear (negative) test reading.
"To date we've tested seven vacant properties in Wanganui with three positive readings for the presence of methamphetamine. We're still awaiting results for one property."
Mr Bosch said Housing NZ placed great importance on the safety of its properties and tenants and would not knowingly place a methamphetamine-affected property on the market.