Here is a paper discussing remediation and clean up strategies that may clear things up with respect to the aquifer.
Quote:
Crude oil released to land or marine environment is immediately subject to a verity of physical, chemical and biological changes [6, 7]. At sea, crude oil, which is usually lighter than water, will spread over the water surface area. After a short time the thickness of the oil film on the water surface will amount to less than 1 mm. The velocity of propagation of the oil on water surface depends on the type of oil, water temperature, and weathering processes such
as; atmospheric temperature, wind and tide. The evaporation of the light components will take place immediately and up to around 40 % of a crude oil may evaporate during a short period of time [8]. This Treatment Techniques of Oil-Contaminated Soil and Water Aquifers process will lead to an increase in the viscosity of the spilled oil. Another part of the oil will be loaded into the water, since some volatile hydrocarbon components, such as
benzene, toluene, and the xylenes have some water solubility in the range of 150-1800
mg/l and are toxic [7].
Thus, the removal of the hydrocarbon from soil and from water surface is an essential practice to prevent groundwater contamination. Any remained portion of crude oil in the ground acts as a permanent source of contamination. The removal efficiency of crude oil from contaminated sites requires information about the composition of the crude oil and the type of soil. For instance, the heavy crude oil does not readily penetrate porous media and its density may be near that of water. The toxicity of this class of oil is low. However, the cleanup of such type of oil is very difficult. The weathering or evaporation of volatiles may produce solid or tarry oil. The average or medium crude oil is more toxic than the heavy crude oil and has the tendency to penetrate into porous media. The light crude oil (volatile oil) spreads rapidly on solid or water surface and penetrates porous surface. This type of oil is usually highly toxic. "
On initial reading, the author asserts that heavy crude is less toxic than light crude, and it appears I was in error in that regard, although dilbit and heavy crude are similar in properties they are not identical.
These are the points to ponder, though.
1)The diluent used to make the bitumen flow is very toxic, and would be very slow to disperse in an underground aquifer as it can’t evaporate as described in the paper.
2) Less toxic doesn’t mean non-toxic and the heavy portions are going to be a bear to remove by known conventional means.