Crude oil contamination hazard
Soil contamination or soil pollution is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity, agricultural chemicals, or improper disposal of waste. The most common chemicals involved are petroleum hydrocarbons, polynuclear aromatic hydrocarbons (such as naphthalene and benzo(a)pyrene), solvents, pesticides, lead, and other heavy metals. Contamination is correlated with the degree of industrialization and intensity of chemical usage.


http://en.wikipedia.org/wiki/Soil_contamination


  The acute health effects of hydrocarbon mixtures are generally associated with exposure concentrations at thousands of ppm. However, the exposure concentration and exposure duration leading to the onset of acute health effects varies between individual hydrocarbons, and this may influence the effects of exposure to mixtures.Health effects associated with a single exposure to hydrocarbons are asphyxiation, narcosis (ie depression of the central nervous system; anaesthesia), cardiac arrest and aspiration. Of these, the first two are probably the most significant in the offshore context.


http://www.hse.gov.uk/offshore/notices/sn_04_04.htm


  In relation to the assessment of vapour risk,petroleum hydrocarbons and chlorinated hydrocarbons differ in their potential forvapour intrusion (VI) risks, primarily because petroleum hydrocarbons (PHCs) readily
  biodegrade in the subsurface when sufficient oxygen is available(USEPA 2011,2012a). Hence while a number of aspects of this guidance are general and can beapplied to a range of volatile compounds, the guidance is intended to specificallyaddress PVI and should not be applied to sites contaminated with other compounds
  including chlorinated hydrocarbons and landfill gas. 


http://clu-in.org/download/issues/vi/CRCCARETechreport23-PetroleumhydrocarbonvapourintrusionassessmentAustralianguidance2.pdf


  Organic compounds can be a major pollution problem in groundwater. Their presence in water can create a hazard to public health and the environment. This page will focus on the BTEX's which makes up one of the main groups of soluble organic compounds that find their way into our soil and groundwater. One of the most common sources for BTEX-contamination of soil and groundwater are spills involving the release of petroleum products such as gasoline, diesel fuel and lubricating and heating oil from leaking oil tanks. Because of their polarity and very soluble characteristics, the organic chemicals (BTEX's) of petroleum products will be able to enter the soil and groundwater systems and cause serious pollution problems.


http://www.webapps.cee.vt.edu/ewr/environmental/teach/gwprimer/btex/btex.html




  Petroleum vapours at percentage concentrations are flammable, potentially explosive
  and acutely toxic; lower explosive limits (LEL) for many volatile hydrocarbons are in the
  low percentage range. Petroleum vapours are denser than air. Some components of
  petroleum vapour are also chronically toxic at trace concentrations and as such are also
  considered under the heading VOCs [volatile organic compounds ].


http://www.epa.nsw.gov.au/resources/clm/120932GroundGas.pdf

This document contains site investigation details which describes how to find traces of compounds in soil and water.
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