WasteMinz 2011 In Search of A Representative Soil Sample

s o lutio ns fo r y o ur e nviro nm e nt PATTLE DELAMORE PARTNERS LTD

©PDP 01/07/16

PATTLE DELAMORE PARTNERS LTD s o lutio ns fo r y o ur e nviro nm e ntPATTLE DELAMORE PARTNERS LTD s o lutio ns fo r y o ur e nviro nm e nt

Andrew Rumsby Peter RobinsonPattle Delamore Partners Ltd R J Hill Laboratories LtdAuckland Hamilton

WasteMINZ Annual conferenceRotorua 5-7 October 2011

PATTLE DELAMORE PARTNERS LTD s o lutio ns fo r y o ur e nviro nm e nt

In Search of a Representative Soil Sample


Introduction

• Consent required representative soil sample to be collected from each site.

• What is a representative soil samples.• How can a 1 gram soil sample represent ???? kg of

soil?• What are the causes of sampling error which makes

a sample unrepresentative?


Representative Soil Sample• US EPA defines a

representative soil sample as being a sample which can be expected to exhibit the average properties of the universe or whole.

• Precision of any soil sample is controlled by the step with the largest error.


Unrepresentative Soils

• Air fall abrasive blasting• Landfill Capping Materials• Mining Sites• Gas Works Sites• Rifle Ranges• Lead paint chips in soil


Sources of Sampling Errors1. Constitution Heterogeneity (Fundamental

error), 2. Distributional Heterogeneity (group and

segregation error), 3. Short and long-range heterogeneity

(Heterogeneity Fluctuation error), 4. Periodic error, 5. Increment delimitation error, 6. Increment extraction error, and 7. Analytical error.


Sources of Sampling Errors• 92% of the total variation comes from the

sampling location (Constitution Heterogeneity, Distribution Heterogeneity, Heterogeneity Fluctuation error),

• 8% after the sample was collected (increment delimitation and increment extraction error); and

• less than 1% from the laboratory analysis.


Multi-increment Sampling• Multi-increment sampling guidelines from Department

of Environmental Conservation, Hawaii State Department of Health, ASTM and the US EPA.

• Use particle sampling theory to determine optimum sample size.

• Compositing to minimise sampling error.• Determining if removal of the greater than 2 mm

fraction could bias the sample (grinding may be required in some situations).

• Triplicate analysis should be less than 30%.


Particle Sampling Theory

m

dFE

)(20 3

=

FE = Fundamental error20 = sampling constantD= maximum particle size (cm)M= sample mass analysed (g)

•For >2 mm sample 8 to 10 g sample is needed to reduce fundamental error to less than 15%.


US EPA 200.2“Total Recoverable” Metals

“Usual”1g soil + 4mL 50% HNO3 + 10mL 20% HCl



“Semi-macro”10g soil + 40mL 50% HNO3 + 100mL 20% HCl



“Macro”30g soil + 120mL 50% HNO3 + 300mL 20% HCl


Larger subsamples = higher cost

• More acid needed• Fewer digests/batch• More space• Cleaning glassware• Less disposables

Standard digest = $15Semi-macro = $40

Macro = $100Plus extra prep charges for

the larger digests


Compositing Samples•Composite samples typically display smaller variability than a discrete samples.•5 to 10 samples•May need up to 30 samples if very heteorgenis.


Sampling Methodology•Use 50 mm hand auger to collect a sample over 0-100 mm interval.•Collected up to 7 samples which were composited together and analysed as discrete samples.•Use 1 g, 10 g and 30 g extraction of composites and analysed in triplicate.•Compared calculated %RSD for each sample.


ResultsElement Discrete 1g Composite 1g Composite,10g Composite, 30g

mean %RSD mean %RSD mean %RSD mean %RSD

Arsenic 7.3 23.4% 6 0.0% 7.0 0.0% 7.0 0.0%

Cadmium 0.7 52.2% 0.64 5.6% 0.69 3.0% 0.72 7.3%

Chromium 5.7 13.2% 4 0.0% 4.0 0.0% 4.3 13.3%

Copper 16.7 59.6% 15.7 3.7% 19.0 0.0% 20 2.8%

Lead 76.3 87.3% 69.7 4.6% 88.7 3.4% 98 1.2%

Mercury 0.4 17.7% 0.31 3.2% 0.31 2.6% 0.34 7.5%

Nickel <2 NC <2 NC <2 NC <2 NC

Zinc 71.3 35.9% 62.3 3.3% 75.3 2.0% 78.0 1.3%


Conclusion

Use of Multi-increment sampling techniques can be used to obtain a representative soil sample from traditionally difficult site which have a high degree of heterogeneity within the contaminant distribution.

s o lutio ns fo r y o ur e nviro nm e nt PATTLE DELAMORE PARTNERS LTD

©PDP 01/07/16

Acknowledgements

• Environment Waikato (Ghassan Basheer & Nick Kim)

• Hill Labs staff (Ron Lindsay and non-routine section)


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