Sorry I have no advice on the topic, other than to AVOID disturbing that site at any cost, unless your work somehow involves cleaning it up. Otherwise I would view touching anything in a contaminated site as super high risk activity.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

Thanks for the reply. I am actually working in conjunction with the EPA and they will actually be doing the work. I am currently just working on the design of the utilities. The EPA wanted a rough design for everything and a construction detail if I could provide one. I was doing as much research as possible before giving them anything. Thanks anyway!

OH, OK. Now I don't mind giving some advice. In that case, the only way I'd do it is by doing a horizontal directional drill through it. Minimizes the disturbance to the smallest possible amount. Gaps around the pipe can be sealed with bentonite.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

Once again, thanks for the help. I'll definitely keep that in mind and pass it along.

You will need to work closely with the EPA on the site specific saftey requirements for this project. The contractor will need to develop a specific health and safety plan for the project. They will most likely have to use breathing apparatuses and monitor the quality of the air. The amount of personal protective gear required will depend on the levels of contamination.
Horizontal directional drilling for installing the utilities is a good option to minimize the disturbance. However, this is not an option if you are installing gravity sewer. You could possibly jack and bore a casing pipe if you have gravity sewer.
Depending on the amount pipe you need to get through the contaminated area, boring and directional drilling may not make economical sense . If you are looking to open cut the trenches, it would be wise to avoid full depth flowable fill as backfill. This is expensive and requires special disposal of all of your spoils. You could possible place flowable fill or concrete dams intermittently along the trench to minimize the contaminated groundwater from migrating along the trench. When you strip the soil cap, this should be seperated from the sub-soil and placed on plastic so that it can be re-used as a soil cap after backfilling the trench.