HDPE Compatibility 2

[baltmore]

I was planning on using HDPE pipe for GW collection.

The EPA's Chemical Compatibility Table says that HDPE is "Unsatisfactory" when Benzene is present.

Although I've been told that Benzene is the most common driver for gas station site remediation, and that HDPE is fairly common in that arena.

Anyone know if HDPE is problem with Benzene or any references that I could use.

Thanks for any suggestions

 

[bimr]

"The dose makes the poison" is taken to mean that the higher the dose, the greater the effect. And this implies that low exposures are less important. Indeed, based on "the dose makes the poison" it is commonly argued that "background" levels of contamination aren't worth worrying about.

If you are planning on using HDPE piping with a concentrated bezene solution, HDPE will probably not be suitable.

If you are planning on a short term project and are pumping an aqueous solution with a couple of ppm of bezene, HDPE will hold up fine.

 

[justbuildit]

I have bid on landfills with HDPE geomembrane liners (60mil) and HPDE pipe leachate recovery systems. You might want to try a google search on leachate compatibility with HDPE materials and what typical concentrations of benzene are in leachate. Just a thought.

 

[rconner]

Volatiles such as benzene (and other constituents of common gasoline such as toluene et al) and plastic pipes are an interesting combination. There are those who allege there is no problem, or that plastics are "common(ly)" used, at least as long as the concentration of these constituents is low. However, I believe there appears to now be some regulatory scrutiny of this combination in some areas e.g. contaminated soils, and also some interesting theories or explanations of behavior have even been expounded by some forensic pipe folks at least dealing with unexpected failures in some process industries etc. In this regard, I read in one such paper by Michelle Knight of Noveon presented at NACE "Corrosion2003" talking about softening (failures) of some plastic pipes, "Softening of the material may also be caused by absorption of solvents and plasticizers, either from the process fluid itself, or the external environment. When solvents are absorbed from the process fluid, it may be a simple case of having specified the wrong material for the known conditions. However, it may be a case of an unknown contaminant in the process fluid causing failure of the pipe where it would have been expected to be successful. Chemical contamination can arise from a variety of sources... The effect of minor constituents in the process fluid may also be underestimated. Waste streams containing "only 50ppm of toluene" may sound innocuous enough, however, when contaminants are not water-soluble, they are floating along in the process stream as tiny bubbles of pure solvent. When these bubbles come in contact with the pipe wall, they will be immediately absorbed by it, eventually leading to softening and failure of the piping system."
With regard specifically to hdpe pipe, one wonders also if contamination due to absorption of hydrocarbons over time might eventually even cause some perhaps non-obvious future problems, such as difficulties in fusion welding pipeline repairs/cut-ins or taps?
There is a thread at

http://www.eng-tips.com/viewthread.cfm?qid=119794

with some arguably related references and of course a growing matrix of problems associated with generally more concentrated exposures in service station areas etc. e.g. as explained at

http://www.dep.state.fl.us/waste/qu...lexpipeandsemi-rigidmatrixflorida28feb06.xls.

 

[Ussuri]

Wavin manufacture a product called Trigon. It is a special barrier pipe for transporting potable water through contaminated land. I have never used it but might be worth a look if the HDPE is concerning you.

http://co-uk.wavin.com/master/maste...643&middleTemplateName=oc_middle_content_link

 

[rconner]

Very interesting; however, at least in quickly glancing at this system I'm not sure exactly how/if? the aluminum (foil?) layer would prevent the plastic on the inside or the outside from being "softened"? I guess, however, if the aluminum layer were structurally strong enough (sort of like a metal pipe??) it perhaps wouldn't matter. I agree it's probably at least some better than a plain plastic pipe.

 

[bimr]

Here is a paper that discusses HDPE use in landfills. I would assume that a landfill environment would more closely represent the type of chemical exposure that you would be experiencing with a remediation project.

http://www.waste-ind.com/camden/articles/HDPE Durability Article.pdf

Note that there are additional references listed in the paper.

 

[rconner]

bimr, good article on durability of "geomembranes" (or films) though it appears with some disclaimers on what of the total systems are considered in the discussion -- is it possible, however that such films are arguably some different than pipes, both in the aspects of inexorable structural demands in some applications, as well as continual flow (by the plastic surface) containing a volatile contaminant as explained by Ms. Knight as I've quoted above?

 

[bimr]

rconner,

Engineering is ultimately a matter of expert judgment based on sound (but necessarily complete) evidence.

If you absolutely, positively want to verify the compatibility of HDPE (or any other piping material) with the contained fluid, you would have to demonstrate it with an actual sample of the fluid according to the procedures in the following link.

http://yosemite.epa.gov/osw/rcra.ns...D8254EEE4301F8525670F006C1E36/$file/12708.pdf

Most people do not have the time nor the resources to go out and test every application on every project so that you can be assured that you are scientifically correct 100% of the time.

baltmore is talking about a gas station project. That would generally be a small site maybe 150 ft x 150 ft. The piping would probably be mostly 1-2 inches in diameter. The pumped fluid is probably at low operating pressures. The concentration of benzene in gasoline product is only 1-2%, so the concentration in remedial ground water will be much less. 4-5 mg/l of benzene in the ground water would probably be considered to be a high level of contamination. He is probably talking about a short-term project, not something that will go for 20 years. In short, remediation at a gas station would not be considered to be a demanding application.

In light of the above comments, even if the piping material that you selected turned out to be inappropriate, the consequences of the piping decision are not that great. Nobody is going to be injured. The worst case, you probably have to replace some small bore piping that costs about $5 for 10 feet.

On the other hand, if you were selecting a landfill liner that must last indefinitely, you would not want to be so flippant with the liner selection since the consequences of a failure may be extremely costly.