Phase 2 – site specific investigation

Summary of results

Tonkin & Taylor Ltd2 July 2012

Summary of investigation• 206 residential properties and 1 ECC• 6 residential properties not included

in the investigation• 544 investigation locations – hand

augers• Approx 30 sample locations per ha • 1668 soil samples• All samples analysed with the XRF• 409 samples (25%) analysed at the

lab

Subsurface materials• East of Tararu Road

– Fill placed in late 1800s– Discontinuous layers of silty sand - mullock– Minimal evidence of processed mine tailings or industrial

waste• East of Moanataiari Street

– Fill placed between 1870s – 1940s– Discontinuous layers of silt, sand and clay - mullock– Minimal evidence of processed mine tailings or industrial

waste• West of Moanataiari Street

– Fill placed in 1960s– Discontinuous layers of silt, sand and clay - local

quarried rock– Minimal evidence of industrial waste

Subsurface materials• Groundwater

– Present at 0.8 - 1.2 below ground level– Slightly above sea level

• Fill depth– Natural ground encountered at some locations

in the east (<1m fill depth)– 0.95 and 1.6m deep in groundwater wells

• Cap in eastern area– No visible difference in surface material

ResultsEastern area Western area Selected

soil assessment

criteriaAverage Maximum % exceeding

assessment criteria

Average Maximum % exceeding assessment

criteria

mg/kg mg/kg % mg/kg mg/kg % mg/kg

Arsenic 259 4700 96.5 77 1000 75.4 20

Cadmium 0.86 22 2.5 0.62 21 1.0 3

Chromium 14 70 - 19 125 - -

Copper 71 790 - 50 500 - -

Mercury 8.4 113 0.0 1.2 49 0.0 310

Nickel 7.4 41 0.0 10.4 350 0.0 600

Lead 287 7200 22.8 78 1590 8.7 210

Zinc 236 3800 0.0 155 5900 0.0 7000

Antimony 11.0 157 7.4 3.9 42 0.5 31

Thallium 1.8 26 44.6 0.6 3.5 9.2 1Summary of laboratory results

Key contaminants• Arsenic

– Most concentrations exceed 20 mg/kg– Consistently high in east– Consistently lower in west– Good fit with site history

Key contaminants• Lead

– Present in isolated clusters only– Mostly affecting eastern area– Clusters can be linked to

site history

Key contaminants• Thallium

– Mostly affecting eastern area– Associated with elevated

arsenic

Certainty• Heterogeneity of soils• Testing (XRF and laboratory)• Receptor behaviour (now and in the

future)• Toxicology (eg bioavailability)

Certainty• Conservative• Ministry for the Environment Guidance• Number of samples• Careful logging of soils• Field and laboratory quality assurance

and control• Staged approach

XRF = 400mg/kg

Laboratory = 1000 mg/kg

Certainty

XRF = 400 mg/kg

Laboratory = 1000 mg/kg

Human Health Guideline = 100 mg/kg

Certainty

XRF = 500 mg/kg

Laboratory = 550 mg/kg

Certainty

XRF = 500 mg/kg

Laboratory = 550 mg/kg

Human Health Guideline = 525 mg/kg

Certainty

Ground model