HDPE Pipes in Contaminated Ground Conditions

You could contact the pipe manufacture for chemical compatibility for the Polycylic aromatic hydrocarbon group. They would be your best bet.

Or you could check different HDPE chemical resistance charts online.

Since this could be a potable water line it would be best to check with the manufacture to make sure the PHA's won't leach through or compromise the pipe in the long term.

You have gotten good first response. While I believe I have heard there has been some use of common hdpe piping through even some contaminated soil areas, and maybe even for water lines (perhaps with the perception or buying the spiel sometimes put out there by at least some hdpe manufacturers and fusers, that it is a "jointless" and "leak-proof" piping system, that will thus protect the product?), contaminated soils are in general however at least a quite worrisome and possibly in some cases very bad application for at least the following three reasons: 1. This type pipe material wall will be subject to some degree of absorption, permeation and swell from many volatile contaminants, and basically regardless of hydrostatic pressure differentials in either direction across the wall of the pipe. As per e.g. the document at    http://deq.mt.gov/LUST/TechGuidDocs/Techguid16.pdf (and others), such behavior changes pipe properties and also involves "a myriad of risks" and potential "liabilities" as potable water carrier, and even some other applications like sewer and drainage etc. 2. While the referenced document does say that once the plastic pipe wall is permeated/contaminated, it "will need to be removed and replaced", it is also true e.g. per the caveat on page 4 of the document at http://www.ctsi-va.com/index_files/pp750fusionproceduresandqualificationguide.PDF that once the pipe wall absorbs hydrocarbon contaminants the ability to make preferred/proper fusion pipeline extensions, sidewall fusion taps, or even maintenance repairs by preferred fusion etc. is essentially lost (it can be argued of course such maintenance and future connection ability when necessary is a quite critical ability for pipelines). 3. While other sorts of common plastic pipelines e.g. pvc etc. are also involved in many permeation incidents, I think the most recorded permeation incidents of contaminants into e.g. working (potable) water pipelines involve the polyolefin plastic pipelines (of which hdpe is of course one type of population). The uneasy truth that is unstated in many such reports is that once permeation is noticed, it is very likely that Customers/Consumers have been drinking contaminated water at some concentrations. This is not an attractive situation nor desired outcome for water providers, at least in the USA (and probably now some other) environments.