Some ideas about screening level contaminated land assessments in South Africa

Proposal for refinement of Phase 1 Soil ScreeningCarl Steyn, Elize Herselman, Heidi Snyman

Key concepts

n Presentation focus: Soil screening for further assessmentn Constituent Specific Methodology considerationsn Observationally Adjusted Screening

n Focused Discrete Samplingn Profile Based Sampling

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Phase 1 vs Phase 2

n Phase 1 for further assessment vs Phase 2 risk assessment;n From the 2010 Framework Phase 1 - “State whether or not the area

should be investigated further or remediated immediately or whether any other measures should be taken to manage or neutralise the risk.” Preliminary site assessment using limited investigation and testing and if contamination is indicated, leads to Phase 2;

n Need to manage risk of inappropriate use of SSV values;

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Natural top soils

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Trace element Baseline concentration threshold(mg/kg)

SSV1(mg/kg)

Percentile of samples exceeding SSV1

(%)Arsenic 11.1 5.8 3.6Cadmium 2.7 7.5 0.4Chromium (III) 353 46,000 0Cobalt 68.5 300 0Copper 117 16 53.7Lead 65.8 20 24.5Manganese 2759 740 23.9Mercury 0.2 0.93 4.1Nickel 159 91 7.7Vanadium 361 150 16.3Zinc 115 240 0

The Dilemma

n These seemingly mismatched values highlights the difficulty in setting Phase 1 SSV by using a risk based approach;

n For a Phase 1 screening site specific information is seldom used to adjust risk based parameters and baseline conditions are not considered;

n Inappropriate screening at Phase 1 level will result in some elements and sites being screened for further detailed Phase 2 assessment and registered as contaminated when it could be naturally occurring soil concentrations;

n Alternatively, some elements and sites that hold a potential risk may not be screened for further investigation when warranted;

n Some uncertainty exists in screening soils for further assessment and registration as contaminated land;

n Some measure of refinement is required.

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Proposal for Refinement

n Constituent Specific Methodologies; andn Observationally Adjusted Screening.

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Constituent Specific Methodologies

n More Persistent vs Less Persistent Constituents;n More Persistent:

n Most metals;n SVOCs.

n Less Persistent:n Volatile organics;n Soluble / mobile constituents;n Some anions (e.g. Cl vs F);n Consideration of transformations (e.g. Most organics and Cr);

n Soil analysis is not always the most appropriate method of screening;n Constituent Specific Anthropogenic Baseline vs Background (e.g. Pb

and PAHs).

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Case study: Cr(III) & Cr(VI)

n Weathered saprolite with black clay topsoil

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n Dominated by vertic soil (high clay), weathered from norite and pyroxenite

Case study: Pb

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Yellow apedal soil, 10-20% clay

Pb – Anthropogenic baseline

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• Sandy soil• Total F baseline determined to

be 338 mg/kg;• Soluble baseline approximate

the SSV value of 30 mg/kg;• Appropriate distinction of

methodology is required for each of the anions.

Case study: F

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Observationally Adjusted Screening

n Focused Discrete Sampling:n Point sampling limits dilution effect;n Biased sampling; andn Targeting potential sources.

n Profile Based Sampling:n Distinction between waste, fill material and soil;n Utilisation of soil profile process to target contaminant accumulation;n Fixed depth sampling results in dilution of contaminant effects.

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Normal Anthropogenic

Soil profile

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Waste/fill layer

Case study: Mn

n Ferricreten Mn Concretions

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Case study: Mn

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Case study: Mn

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Case study: Ni associated with Mn

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Observed Clay Content

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Clay content SSV1

<10 % 10 - 20 % 20 - 35 % >35 %

Trace element Total threshold concentration (mg/kg)

Chromium 152 175 301 507 46000

Cobalt 28 31 54 126 300

Copper 47 58 80 215 16

Lead 33 49 49 81 20

Manganese 891 1035 3735 5864 740

Nickel 56 136 189 268 91

Vanadium 119 214 382 448 150

Zinc 65 91 91 116 240

Adjusting screening based on observation

Take home message

n Observationally Adjusted Screening:n Biased sampling based on source;n Discrete soil layer sampling;n Differentiate between source/waste and soil layers;n Soil properties (soil form, clay content)

n Constituent Specific Methodologies:n Specify analytical methodology;n Constituent specific considerations such as baseline conditions.

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Thank you

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