Urban soils review
Background |
Soil tests at childcare facilities |
Investigation of other sites |
Victoria Park | Remediation |
Contaminants
Background
Auckland City has done a desktop study looking at the historical land use of all of the 1,409 properties it owns. This study
was undertaken to identify any properties, which could potentially be contaminated due to past land use activity on or near council
sites.
Land, which in the past, was used for industrial, horticultural or agricultural purposes can sometimes have contaminated soil.
This is because these kinds of activities often involve the storage or use of chemicals, fuel or waste.
All soil in metropolitan areas, like Auckland, is likely to have concentrations of substances that are by-products of past activity
on the land. This is because land use in cities often changes as they grow. Areas that were once farm land or industrial land, later
become used for residential purposes.
The council's desktop study identified approximately 185 sites, which could potentially be contaminated due to their past use.
Auckland City is now undertaking a soil-testing regime to determine whether any of these sites are actually contaminated.
The council is beginning by testing land that is used by childcare facilities. This is because children are one of the most sensitive
groups in our community to potential contaminants.
Soil tests at childcare facilities
Auckland City's desktop study identified nine childcare facility sites, which could potentially be contaminated due to their
historical land use.
These sites are:
- Learning at the Point, Huia Street, Pt Chevalier
- Mt Wellington Playcentre, Vic Cowen Park, Mt Wellington
- Ellerslie Playgroup, 7 Ramsgate Street, Ellerslie
- Auckland Central Playcentre, 124 Wellington Street, Freeman's Bay
- Barnados Early Learning Centre, 52 Hepburn Street, Freeman's Bay
- Mt Albert Playcentre, 25 Phyllis Street, Mt Albert
- Ferndale Kindergarten, 830 New North Road, Mt Albert
- Onehunga Playcentre, 47 Hill Street, Onehunga
- Freemans Bay Kindergarten, 16 Tahuna Street, Freemans Bay
Learning at the Point, Huia Street, Pt Chevalier
This property was flagged for investigation because there was once an automotive rewinder on site.
Soil testing was carried out and identified elevated levels of some heavy metals and polycyclic aromatic
hydrocarbons (PAHs), including benzo-a-pyrene.
The council moved to remediate the site in May 2005. This involved:
- removal of old bark and sand in the playground area
- installation of a high-strength barrier below ground before new bark and sand were laid down
- on-going maintenance of bark levels to a minimum of 30 centimetres above ground.
In January 2006, a grassed area around the entrance was removed and replaced with clean soil in conjunction with tree planting.
The council has developed an on-going site management plan for the property to ensure that the work done to date is effective in
maintaining a barrier between the soil and children on site.
Mt Wellington Playcentre, Vic Cowen Park
This site was investigated because there had been some evidence of unauthorised fill activity in another section of the park.
Soil tests were undertaken in December 2005 and showed slightly elevated levels of polycyclic aromatic hydrocarbons (PAHs),
including benzo-a-pyrene in localised areas of the site.
The site was remediated in January 2006. This involved the removal of surface soil, the installation of an anchored barrier mat
below the surface and re-filling the site with clean soil before it was landscaped.
Ellerslie Playgroup, 7 Ramsgate Street, Ellerslie
Soil tests were taken at this property because it was once sited on a vehicle depot.
Results showed elevated levels of polycyclic aromatic hydrocarbons (PAHs), including benzo-a-pyrene at one area of the site. This
area has since been paved over.
As a precautionary measure, the council has removed the top layer of soil
under the barked area at the front of the gate and replaced this with clean soil and new bark. Existing barrier matting under the barked area has also been replaced with high-strength bidim material.
Auckland Central Playcentre, 124 Wellington Street, Freeman's Bay
This site was investigated because there was once an ice cream cone factory and a furniture factory on site.
Further investigations and soil testing revealed that fill material from the Beaumont Gas Works was probably used on the land.
The soil testing showed elevated levels of polycyclic aromatic hydrocarbons PAHs, including benzo-a-pyrene.
As soon as the final test results came through, Auckland City put down a high strength barrier mat over all exposed areas of soil and
grass to limit the exposure of anyone on site.
The council has now remediated the site and landscaping work is
complete.
Blood tests for children and staff who attended the Auckland Central Playcentre show that all those tested had lead levels well
within the normal range. This indicates that their exposure to contaminants is likely to have been low and therefore any associated
health risk is likely to be low.
Barnardos Early Learning Centre at Freeman's Bay
Soil tests were taken at this site on 30 March 2006 because the property had once been adjacent to an automotive workshop.
Test results revealed concentrations of polycyclic aromatic hydrocarbons (PAHs), including benzo-a-pyrene in the soil.
Auckland City has put down a high-strength barrier mat over all exposed areas of soil and grass to limit the exposure of anyone on
site to the contaminated soil.
The council has now remediated the site and landscaping work is
complete.
Blood tests for children and staff who attended the Barnardos Early Learning Centre show that all but one of those tested had lead
levels well within the normal range. The Auckland Regional Public Health Service (ARPHS) has investigated the sole marginal exceedance
and has concluded that this reading relates to laboratory error, as a retest shows no blood lead exceedance. This
indicates that exposure to contaminants is likely to have been low and therefore any associated health risk is likely to be low.
Mt Albert Playcentre, 25 Phyllis Street, Mt Albert
This site was investigated because it is adjacent to a closed landfill, which is now used as a reserve.
Testing was done at the site on 5 April 2006. The soil test results revealed concentrations of the PAH benzo-a-pyrene in localised
areas of the site.
The council has remediated the site and
landscaping works are complete.
Ferndale Kindergarten, 830 New North Road, Mt Albert
This site was flagged on the desktop study because it was once near a former horticultural site.
Soil testing was done at the site on 7 and 8 April 2006. The test results revealed high levels of lead, arsenic and the PAH,
benzo-a-pyrene in one area of the site. Elevated levels of benzo-a-pyrene were also found across the site.
Auckland City has sealed all exposed areas of soil and grass with a high-strength barrier mat.
The council has remediated the site and
landscaping works are complete.
Blood tests for children and staff who attended the Ferndale Kindergarten show that all those tested had lead levels well within the
normal range. This indicates that their exposure to contaminants is likely to have been low and therefore any associated health risk
is likely to be low.
Onehunga Playcentre, 42 Hill Street, Onehunga
Soil testing was carried out on this site on 5 and 6 April because there was once a separate garage and laundry on site.
The results show elevated concentrations of lead and the PAH, benzo-a-pyrene on site.
Auckland City sealed all exposed areas of soil and grass with a high-strength barrier mat.
The council remediated the site on 20 and 21 April
and landscaping works are complete.
Blood tests for children and staff who attended the Onehunga Playcentre show that all those tested had blood lead levels within the
normal range. This indicates that their exposure to contaminants is likely to have been low and therefore any associated health risk
is likely to be low.
Freemans Bay Kindergarten, 16 Tahuna Street, Freemans Bay
The council decided to carry out soil tests at the Freeman's Bay Kindergarten in Tahuna Street. This facility is also on
council-owned land.
This testing regime was taken as a precautionary measure given that two other sites in close proximity showed evidence of
land contamination from imported fill.
The soil test results showed elevated levels of lead and the PAH
benzo-a-pyrene in areas of the site.
Remediation and landscaping work are now complete.
Investigation of other sites
Auckland City is now investigating other council-owned sites, which could
potentially be contaminated.
The desktop study identified a number of sites that warrant further
investigation due to their historical use for industrial, agricultural or
horticultural purposes.
The council's top priority was to carry out testing at council-owned
childcare facilities, which were identified as possibly contaminated.
It is now investigating whether there is any soil contamination at certain
parks.
The parks the council is investigating include:
- Victoria Park
- Vic Cowen Park
- Captain Springs Reserve
- Riversdale Reserve
- Ferndale Park
Action will be taken at any site where levels of contamination are found that
pose a threat to human health for those who use the parks.
Victoria Park
Victoria Park was identified as a potentially contaminated site because of
its proximity to the former Beaumont Street Gas Works, and from research about
what materials may have historically been used to fill areas of the park.
Soil testing was initially carried out in 2004-2005, with further testing done
in late 2006.
The 2004-05 testing identified moderate surface levels of the chemical,
benzo-a-pyrene, in isolated areas around the playground. Hotspots of
benzo-a-pyrene and lead were also found at depth. Levels of contamination in the
sports park were found to be low and a human health risk assessment carried out
has indicated the health risk to sports users and casual users is minimal.
As a precautionary measure, the council organised for the areas of benzo-a-pyrene found to be barriered with a combination of matting, topsoil and
bark. These measures serve to limit exposure for playground users reducing
potential health risks.
Further tests carried out in late 2006, identified benzo-a-pyrene in surface
soil under the trees next to the playground. These levels were much higher than
those discovered elsewhere in the park or the playground and the council moved
to fence off the treeline and playground area and remediate the site under
urgency. A wider testing regime was then carried out under trees throughout
Victoria Park. The results showed two isolated surface areas of benzo-a-pyrene
contamination in soil under trees near Halsey and Fanshawe Streets.
The decision to close and remediate affected areas of the site has been
supported by the Auckland Regional Public Health Service.
The medical advice provided to the council is that benzo-a-pyrene is prevalent
in all urban environments and presents a much greater risk to people when it is
airborne, for instance in smog, traffic emissions and cigarette smoke. However,
high levels of surface soil contaminants can also pose a risk to children,
especially those who may have tendencies to consume soil.
Auckland City Council fenced off the treeline and playground area of Victoria
Park on 8 December 2006 and the two areas of localised contamination under trees
elsewhere in the park on 10 January 2007. Cautionary signage was installed and
letters issued to nearby residents about the contamination levels found and the
remediation programme. Remediation began on 22 January 2007 and was completed at the
end of May.
The council developed a remediation strategy specific to Victoria Park which
provides long-term protection of human health, while ensuring that the ongoing
health of scheduled heritage trees is also protected. The strategy involved the
removal of contaminated soil throughout the park which poses a significant risk
to human health, and includes implementation of specialised barrier systems to
protect against residual deeper contamination, installation of drainage systems,
stainless steel mesh, permeable concrete and topsoil. Prototype air spades were
used under carefully controlled conditions by specialist arborists Greenscene to
remove contaminated soil around trees without damaging the root systems of
heritage trees.
The playground area is likely to be closed for several months while the new play
equipment is installed.
Remediation
The council believes it is best to take a precautionary approach in dealing
with soil contamination and remediates sites where necessary.
Auckland City employs specialist contractors to carry out remediation works.
There are two general approaches to remediation, both of which effectively
seal off contaminated soil. This is done by ensuring that there is at least
half-a-metre of clean material between users of the site and any remaining
contaminated soil. The two approaches are outlined below.
Capping:
- an impermeable barrier mat, known as a geotextile fabric, is placed over
the contaminated soil
- half-a-metre of clean protective material is placed on top of the
barrier mat
- the area is stabilised at surface
- the site is monitored into the future.
Removal of soil:
- the top half-metre of contaminated soil is removed
- an impermeable barrier mat, known as a geotextile fabric, is placed over
the remaining soil
- the site is filled with clean soil
- the area is stabilised at surface
- the site is monitored into the future.
Special health and safety precautions are taken during the remediation works
to ensure that the impact on neighbouring properties is limited. These
precautions include:
- fencing off the site
- signs outside the site limiting entry to the property
- installing a shade cloth around the site boundary as a barrier between
the property and its neighbours
- installing sprinklers to trap dust and prevent it from spreading
- a dust monitor downwind of the site to monitor dust levels
- covering drains on site to prevent soil and dust from getting into
stormwater
- using covered soil removal trucks with double-locking tailgates
- a traffic management plan to ensure pedestrians have easy movement
around the area
- signs to inform road users that heavy vehicles are in the vicinity.
Remediation works will be postponed in heavy rain or wind and will resume as
soon as weather conditions improve.
