DERIVATION OF HYDROCARBON SOIL ACCEPTANCE CRITERIA FOR THE PROTECTION OF SURFACE WATER QUALITY Stephen Thomson URS New Zealand Limited
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DERIVATION OF HYDROCARBON SOIL ACCEPTANCE CRITERIA FOR THE PROTECTION OF SURFACE WATER QUALITY Stephen Thomson URS New Zealand Limited
Acknowledgements Oil Industry Environmental Working Group Shane Moore www.urscorp.co.nz
Presentation Outline Background. Derivation of SW Criteria. Application of SW Criteria. www.urscorp.co.nz
Background Guidelines for Assessing and Managing Petroleum Hydrocarbon Contaminated Sites in New Zealand (MfE 1999) sometimes known as the Oil Industry Guidelines. Designed to assist both industry and regulatory authorities in developing uniform and suitable methods of site investigation, contamination assessment, modelling and site management with respect to petroleum hydrocarbon contaminated sites. www.urscorp.co.nz
Background Protection of Groundwater Criteria Include acceptance criteria for the protection of groundwater quality along with other exposure pathways. The approach adopted for deriving soil acceptance criteria for the protection of groundwater quality in sensitive aquifers is considered to be sound, it is however also very conservative. The approach provides protection to the groundwater immediately below the contaminated source within the confines of a site; it does not consider any attenuation of contaminants during transport in groundwater away from the source and therefore is overly conservative for many situations. www.urscorp.co.nz
www.urscorp.co.nz Background Protection of Groundwater Criteria
Background Protection of Groundwater Criteria Sensitive Aquifer when groundwater is: Artesian. < 10 m bgl. Can yield water at a useful rate (i.e. has a reasonable permeability). Source of contamination is < 100 m from a surface water body. www.urscorp.co.nz
Background Protection of Groundwater Criteria > 100m Low Permeability Soils Low Permeability Soils (sandy silt, silty clay, clay, peat) (sandy silt, silty clay, clay, peat) Surface Water Environmental Receptor X www.urscorp.co.nz
Background Protection of Groundwater Criteria In the absence of established soil acceptance criteria for the protection of surface water, many regulatory agencies are routinely making direct reference to groundwater protection criteria to ensure that a nearby surface water body is adequately protected from potential contaminant impact. Often overly conservative. www.urscorp.co.nz
Background Protection of Groundwater Criteria For example. Clay soil type (i.e. not sensitive due to yield) Groundwater at 2 m bgl. Surface water within 100 m of source. Acceptance criteria applied is 0.0054 mg/kg. www.urscorp.co.nz
Background Object OIEWG engaged URS to develop soil acceptance criteria for the protection of surface water quality, in situations where an aquifer was not sensitive due to potential yield (i.e. low permeability soils, Sandy SILT, Silty CLAY, CLAY and PEAT). www.urscorp.co.nz
Derivation of SW Criteria MfE Leaching Model Contaminant Flow Model Low Permeability Soils (sandy silt, silty clay, clay, peat) Equal to ANZECC X Y www.urscorp.co.nz
Derivation of SW Criteria Adopted Soil Acceptance Criteria Revised Criteria C 0* leaching Factor Corrected C 0 C0* ANZECC C Seepage Velocity (V s m/yr) Predicted Concentration at Receptor ( g/m 3 ) Distribution Coefficient Kd foc Koc X Ki V s e Retardation factor Rf 1 Kd Contaminant velocity Kd(V c foc m/yr) Koc 0.2 Vc V s Rf Travel time (yr) d t V c Half Lives N t t 1 2 Y C C 0 N 2 www.urscorp.co.nz
Revised Criteria Adopted Soil Acceptance Criteria C 0* 3 7.0 g/m leaching Factor Corrected C 0 ANZECC C0* 2.51mg/l C Inputs parameters: Soil Type: Sandy Silt Fraction of organic carbon foc = 0.003 Benzene (Koc) = 83 cm 3 /g Bulk density (ρ) = 1.9 tonnes/m 3 Porosity (η) = 0.45 Hydraulic conductivity (K) = 1.16 x 10-5 m/yr Hydraulic gradient (i) = 0.005 Effective porosity (η e ) = 0.25 Distance (d) = 25 m Half life (t 1/2 ) = 5 years ANZECC 95% Benzene = 0.95 g/m 3 Rf = Retardation factor Seepage Velocity (V s m/yr) Predicted Concentration at Receptor ( g/m 3 ) Initial GW Conc. (C 0 ) 1 g/m 3 Distribution Coefficient Kd foc Koc 0.2 X Ki V s 7.3m / yr e Retardation factor Rf 1 Kd 2.1 Contaminant velocity (V c m/yr) V V s c 3.6m / yr Rf Travel time (yr) d t 7 yrs V c Half Lives t N t 1 2 C C 0 0.3784mg / l N 2 Y 1.4 www.urscorp.co.nz
Derivation of SW Criteria: Sources of Data and Assumptions Parameters Hydrogeology Source Dimensions Chemical Properties Property Geology Sandy Silt Silty Clay Clay Peat Source Water filled porosity 0.27 0.44 0.48 0.23 MfE, Table 4.7 Effective Porosity 0.25 0.15 0.1 0.25 1 Davis & De Wiest Total Porosity 0.45 0.5 0.5 0.46 MfE, Table 4.7 Hydraulic Gradient 0.005 0.01 0.05 0.005 Typical values Hydraulic Conductivity 1.60E-05 1.60E-07 1.60E-08 1.60E-05 MfE, Table 4E1c (m/s) Infiltration Rate 82 34 14 14 MfE, Table 4E1b (mm/yr) Fraction of Organic 0.003 0.003 0.003 0.12 MfE, Table 4.7 Carbon Bulk Density (tonnes/m 3 ) 1.9 1.8 1.8 1.6 MfE, Table 4.7 Width (m) 15 Representative value Length (m) 15 MfE, Appendix 4E Thickness (m) 2 MfE, Appendix 4E Henry s Law Koc COMPOUND SPECIFIC MfE, Appendix 4J (cm 3 /g) 1: The effective porosity sourced from Davis & De Wiest is slightly higher than the water filled porosity sourced from Table 4.7 of the MfE Guidelines. To maintain consistency with other soil types, the effective porosity from Davis & De Wiest has been adopted in this assessment. www.urscorp.co.nz
Derivation of SW Criteria: Sources of Data and Assumptions Compounds % Composition of Petrol Fuels (96 Octane) (MfE Guidelines, 1999) Benzene 3.3 Toluene 12.2 Ethylbenzene 2.1 Xylenes 12.2 Compounds % Composition of Diesel Fuels (MfE Guidelines, 1999) Naphthalene 3 Pyrene 0.4 Benzo(a)pyrene 0.0001 1 1: Tancell et al. www.urscorp.co.nz
Derivation of SW Criteria: Sources of Data and Assumptions Effective Solubility Effective solubility was set as the maximum concentration that could be reached in groundwater source area. If source concentration exceeds effective solubility then most likely exceed threshold for formation of LNAPL Effective solubilities calculated by weight ratios were adopted. Analyte Weight % Ratios (g/m 3 ) Mole Fraction Ratios (g/m 3 ) Benzene 59 49 Toluene 63 62 Ethylbenzene 3 4 Xylenes 21 24 www.urscorp.co.nz
Revised Criteria Adopted Soil Acceptance Criteria C 0* 3 7.0 g/m leaching Factor Effective Solubility Corrected C 0 ANZECC C0* 2.51mg/l C Inputs parameters: Soil Type: Sandy Silt Fraction of organic carbon foc = 0.003 Benzene (Koc) = 83 cm 3 /g Bulk density (ρ) = 1.9 tonnes/m 3 Porosity (η) = 0.45 Hydraulic conductivity (K) = 1.16 x 10-5 m/yr Hydraulic gradient (i) = 0.005 Effective porosity (η e ) = 0.25 Distance (d) = 25 m Half life (t 1/2 ) = 5 years ANZECC 95% Benzene = 0.95 g/m 3 Rf = Retardation factor Seepage Velocity (V s m/yr) Predicted Concentration at Receptor ( g/m 3 ) Initial GW Conc. (C 0 ) 1 g/m 3 Distribution Coefficient Kd foc Koc 0.2 X Ki V s 7.3m / yr e Retardation factor Rf 1 Kd 2.1 Contaminant velocity (V c m/yr) V V s c 3.6m / yr Rf Travel time (yr) d t 7 yrs V c Half Lives t N t 1 2 C C 0 0.3784mg / l N 2 Y 1.4 www.urscorp.co.nz
Surface Water Criteria Soil Acceptance Criteria for the Protection of Surface Water: 25m from Source, 90% ANZECC (mg/kg) - 96 Octane Sandy SILT MAHs Soil Type / Contaminant Groundwater Depth 2 m Depth of Contamination Surface (<1m) 1m 4m >4m Groundwater Depth 4 m Groundwater Depth 8m Groundwater Depth 4 m Groundwater Depth 8m Groundwater Depth 8m Benzene 10 (158) (1652) 29 (697) (71) Toluene 17 (284) ID 52 S (128) Ethylbenzene (77) ID ID S ID S Xylenes (30) S ID (90) S S PAHs Naphthalene (25.0) S ID (55.9) ID ID Pyrene S ID ID ID ID ID Benzo(a)pyrene S ID ID ID ID ID (Brackets) denote values exceed threshold likely to correspond to formation of residual separate phase hydrocarbons - PROTECTION OF SURFACE WATER UNLIKELY TO BE LIMITING PATHWAY denote values exceed threshold likely to correspond to formation of residual separate phase hydrocarbons - USE CRITERIA S FOR SURFACE SOILS AND GW2 FOR SCREENING ID Indicates insufficient data provided in MfE Guidelines to derive acceptance criteria (leaching factors) www.urscorp.co.nz
Application of Criteria In instances where the aquifer underlying the subject site is not considered to be sensitive the criteria for the protection of surface water presented in this study could be applied as the de-facto Tier 1 screening criteria. That is for clay, silty clay, sandy silt and peat soils. www.urscorp.co.nz
Application of Criteria Should not be applied for use at sites Where the geology is highly heterogeneous (for example fill), Where the topography and likely hydraulic gradient are steep, Where the potential exists for significant preferential pathways (such as subsurface services, high permeability lenses or fractures) exist, or LNAPL is present. www.urscorp.co.nz
Application of Criteria For soils classified as sandy silt, a qualitative assessment of the hydraulic conductivity, hydraulic gradient and the effective porosity should be made to ensure that the site conditions are within an acceptable range of those adopted for the model. www.urscorp.co.nz
References ANZECC, 2000: Australian and New Zealand Guidelines for Fresh and Marine Water Quality. Australian and New Zealand Environment and Conservation Council and the Agriculture and Resource Management Council of Australia and New Zealand, October 2000. Canadian Councils for Ministers for the Environment. 2002: Canadian Environmental Quality Guidelines. Davis SN and De Wiest RJM, 1966: Hydrogeology. John Wiley and Sons, New York. Domenico P.A. and Schwartz F.W 1990, Physical and Chemical Hydrogeology. John Wiley and Sons, New York. GML Ruiz-Aguilar, K O Reilly and PJJ Alverez: A Comparison of Benzene and Toluene Plume Lengths for Sites Contaminated with Regular vs. Ethanol-Amended Gasoline. Ground Water Monitoring & Remediation Winter 2003. Ministry for the Environment: Guidelines for the Assessment and Management of Petroleum Hydrocarbon Contaminated Sites in New Zealand. Ministry for the Environment, August 1999. Ministry for the Environment: Contaminated Land Management Guidelines No.2 Hierarchy and Application in New Zealand of Environmental Guideline Values. Ministry for the Environment, October 2003. Ministry of Economic Development: New Zealand Petroleum Products Specifications Regulations 2002, July 2002. Proposed Auckland Regional Plan: Air, Land and Water. Decisions Version December 2008. Tancell P.J, Rhead M.M, Trier C.J, Bell M.A, Fussey D.E: The sources of benzo[a]pyrene in diesel exhaust emissions. The Science of Total Environment. 162(1995) 179-186, 1995. URS New Zealand Limited 2000: Effects-Based Landfill Classification for Hydrocarbon Contaminated Waste Disposal. Report prepared for the Ministry for the Environment. Woodward-Clyde (NZ) Limited (now URS), November 2000. URS New Zealand Limited 2003: Waste Acceptance Criteria for Class A Landfills. Report prepared for the Ministry for the Environment. URS New Zealand Limited, August 2003. www.urscorp.co.nz
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