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
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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?
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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.
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Unrepresentative Soils
• Air fall abrasive blasting• Landfill Capping Materials• Mining Sites• Gas Works Sites• Rifle Ranges• Lead paint chips in soil
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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.
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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.
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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%.
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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%.
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US EPA 200.2“Total Recoverable” Metals
“Usual”1g soil + 4mL 50% HNO3 + 10mL 20% HCl
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US EPA 200.2“Total Recoverable” Metals
“Semi-macro”10g soil + 40mL 50% HNO3 + 100mL 20% HCl
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US EPA 200.2“Total Recoverable” Metals
“Macro”30g soil + 120mL 50% HNO3 + 300mL 20% HCl
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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
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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.
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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.
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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%
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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.
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Acknowledgements
• Environment Waikato (Ghassan Basheer & Nick Kim)
• Hill Labs staff (Ron Lindsay and non-routine section)
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