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Almost nine out of 10 schools in Christchurch sit on potentially contaminated land.
Environment Canterbury's (ECan) Listed Land Use Register - a database of possible land pollution - shows that 124 schools are on potentially contaminated land.
Of those, 29 have more than one type of potential contamination. Just 22 schools do not appear in the database.
Some of the affected schools will likely require major soil disturbance as part of the Ministry of Education's $1.1 billion rebuild and renewal plans in the next 10 years.
The ministry said it would ''fund any testing, removal and disposal of contaminated soil''.
About 70 per cent of the affected schools were possibly exposed to ''persistent pesticides'' - chemicals sprayed on sports fields to combat weeds, diseases and insects. The chemicals can remain for long periods and many have been banned for years.
Four schools make the database because their sites were landfills before the schools were built, one school site was subject to ''waste disposal to land'' (essentially a landfill without a hole in the ground), and one school site may once have been a treated timber storage yard. About 26 per cent of the schools stored chemicals, mostly diesel for furnaces.
Canterbury medical officer of health Dr Ramon Pink said it was ''very unlikely'' the level of contamination would be high enough to result in any health issues.
ECan strategic programmes manager Don Chittock said best practice with contaminated land was to leave it in its current state.
''If it's got good coverage - whether that's grass, asphalt, concrete or buildings - and you don't have to disturb it, don't,'' he said.
Pupils coming in from playgrounds should follow common hygiene practices - wash their hands and wipe their feet, he said. Vegetables from school gardens should be thoroughly washed.
The Ministry of Education hired consultant URS to advise which schools will get tested and when.
Kim Shannon, the ministry's head of education infrastructure service, said earthquake repairs had been done at most schools but no land remediation had been required.
ECan identified school sport turfs almost entirely from aerial photographs taken about once a decade from the 1940s. Few schools have been tested further.
ECan land contamination team leader Davina McNickel said land use only had been identified.
''We don't know if all of these sports turfs had sprays used. It's not a helpful exercise to alarm people unnecessarily until we know for certain. So what we've said is use the commonsense precautions."
The 124 schools stretch from the south bank of the Waimakariri River to the north shores of Lyttelton Harbour.
The west boundary of the study area runs through Halswell, Templeton, Yaldhurst and Mcleans Forest.
Schools were added to the database as part of a larger ECan programme in which about 11,000 homeowners were informed in May that their land may potentially be contaminated.
The caution about sports fields is broader than schools and includes council-owned sport pitches, rugby and cricket club grounds, bowling clubs, golf courses and other grass sport areas.
Christchurch Rudolf Steiner School is on a former landfill and the special character school in Opawa had tested extensively for methane and other toxins since 2012, principal Thomas Proctor said.
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- The Press