Presenter:  Marcus Wright & Dave Bull, Golder Associates (NZ) & Richard Malcolm, Hill Laboratories

Speciation of Hydrocarbons – when you need to know more!    The 1999 MfE Guidelines for Assessing and Managing Petroleum Hydrocarbon Contaminated Sites in New Zealand present pragmatic, risk adverse soil acceptance criteria that are protective of human health and water quality..  The Guidelines make generic assumptions in deriving the Tier 1 values; they divide the Total Petroleum Hydrocarbon (TPH) concentration into three bands with one physical, chemical and toxicological characteristic per band, applied to both its ‘aliphatic’ and ‘aromatic’ components.    Reality may differ.  Some petroleum products may be lighter or heavier than the band average, have more aromatic content or none at all. Within soil, the composition and properties of petroleum products change as they age, migrate, volatilize, dissolve or degrade. The proportion of naphthalene, usually the risk driver for the middle band, is often less than assumed.  The three-band system cannot recognize these changes occurring.  Perceived risk based on Tier 1 guidance may therefore be misleading and be overly conservative.    The consequence of applying the Guidelines too rigidly is over-cautious remediation, such as over-excavation.  If speciating the soil, soil vapour and water impact gives a better understanding of risk, unnecessary excavation or over-elaborate in-situ remediation can be avoided. The net result being a more sustainable remedial outcome within an effects-based regulatory regime.    To manage petroleum impact, a more detailed understanding is required of its components, particularly if Tier 2 health risk assessment is required by the NES.  The TPH CWG 1998 series used in developing the MfE Guidelines uses an aliphatic-aromatic split, each with six hydrocarbon bands. Speciating this way allows a risk assessor to use peer-reviewed international models such as RISC, RBCA or RTM to more accurately determine site specific/Tier 2 criteria.  There are a number of different methodologies worldwide that have been used to carry out this more detailed speciation.     In this paper Golder and Hill Laboratories jointly explore issues associated with the more detailed TPH speciation, implications of applying this to Tier 2 health risk assessment and the practicalities of extending the current New Zealand TPH analysis methodology and reporting.

Presentation title:  Speciation of hydrocarbons – when you need to know more!

Event: WasteMINZ Conference 2013

Date: Wednesday 23 October 2013