Nelson quarry backfilled with contaminated soil
Elevated levels of arsenic, nickel, lead, chromium and other chemicals have been found in the soil used to backfill a quarry near Nelson.
Work has stopped at the Downer-operated Staplegrove Farm site at Waimea West while an investigation is under way. Its application to renew its resource consent is also on hold.
Tasman District Council environmental information manager Rob Smith said the property was placed on the Hazardous Activities and Industries List (HAIL) register on September 15 following a report by a soil scientist on the gravel extraction site.
However, Smith said he did not see any reason for the public to be concerned.
The property was on the register as limited sampling had been undertaken and the risks to people and/or the environment was not known.
‘‘Further testing of the site is being undertaken to assess risk,’’ he said. ‘‘The HAIL register status will be reviewed on the basis of further information.’’
Smith said PAHs were elevated ‘‘compared to the recommended clean fill criteria’’ for the Tasman district.
‘‘The concentrations of PAHs are within the range for background soils in the urban area,’’ he said. ‘‘The chromium and nickel is naturally elevated in ultramafic soils, and arsenic and lead pesticide residues can be found on many of the ex-orchard soils in the Tasman region.’’
A soil scientist’s report on the quarry examined 10 random sites of ground restored after gravel extractions between 2008 and 2013.
‘‘In all of the pits, foreign debris was present ... including concrete, wood remnants (posts and other), plastic pieces, brick, metals, plastic and metal pipe, and asphalt-like substances,’’ the report says.
At the waste fill area, there was a variety of earth materials, much with no clear origin.
‘‘A typical excavation for a Nelson house site or subdivision would produce clean overburden, usually brown in colour, but there appears to be little of this type of earth matter present,’’ the report says.
Foreign substances were widespread and of a similar nature to those seen in the pit sites.
‘‘The presence of some fused, vesicular glassy material suggests an origin from a high-temperature process and some baked earth material and charred wood is indicative of burning processes. The presence of asphalt ... suggests an origin from road materials.’’
Foreign objects were ‘‘not being removed but buried’’ with the spreading process while water ponding pointed to poor drainage within the fill materials..
It would be difficult to quantify the amount of foreign substances ‘‘but a guess would be somewhere within the range of 1-5 per cent in some loads’’.
‘‘Since foreign materials are the likely source of the soil contaminants found in the chemical analyses, the inclusion of such material in the backfill should be avoided,’’ the report says.
Chemical analyses of the soil samples indicated the presence of contaminants including heavy metals ‘‘at some concentrations appreciably above background values’’.
The report says the ‘‘deposited fill materials’’ were ‘‘detrimental to the short and long-term productive capacity of the land’’.
‘‘What was a well-drained soil has now been replaced with earth material that has inferior physical and drainage properties and which impact on land management and potential crop use.’’
The scientist says removing the foreign material from the already restored land ‘‘is probably impractical’’.
‘‘It is suggested, however, that consideration be given to screening the backfill materials before being brought to the site, in order to avoid this problem.’’
Downer South Island general manager Scott Ford said in a written statement that external consultants were assessing the situation to ’’provide guidance on any remediation required’’.
‘‘We will continue to work with Tasman District Council on this issue and take appropriate action as required,’’ the statement says. ‘‘We have halted work at the site while the investigation is under way.’’
Smith said Downer was to produce an acceptable plan to restore the capacity of the land and then implement that plan.
When asked if any enforcement action was under way or being considered, Smith said the focus was on restoration of the soil structure and general suitability for horticultural use.