Wow, my first discussion that I've read since registering for commonground (registered today so I could read this discussion) and I have so many things I am not going to say.

My perspective is that of a commercial property owner; a P.E. (chemical engineering); a former manufacturer's environmental compliance manager; an environmental consultant who not only has conducted phase I's, and phase II's but has designed and installed groundwater and soil remediation systems for years all over the country; a Phase I writer, site inspector and report reviewer; and someone who has had the "pleasure" of being winched into and out of buried oil-water separator systems (with appropriate PPE) to clean and inspect them.

Without being given the discharge point for the O/W system and the historical records of the materials discharged to it, I would call it a REC and provide in my discussion of findings the reason for classifying it as a REC.  Regulations, corporate SOP's, etc. are general and don't account for every individual case.  An O/W separator is classified as a process (not storage) tank by EPA and OSHA (to the best of my recollection), but does have the potential to "store" separated chemicals by design - hence the conflicting concerns over regulated actions versus liability concerns.  Even if the O/W tank were pumped out, if the contractor or facility manager did not refill the tank to the appropriate operating level with clean water, a large volume of whatever chemicals were flushed to it could potentially be discharged to ???? until the liquid height in the tank rose above the bottom of the oil dam.

We have typically recommended a visual inspection of the cleaned O/W tank if the management seems responsible.  We have also advised that probing around the tank would be recommended if any structural cracks or flaws were observed during the physical inspection.  A probing assessment around an O/W separator tank should be significantly less expensive than remediating even a moderate amount of released regulated waste below and alongside the tank.  Many environmental drillers have small units that can easily operate within a maintenance bay, and the cost for analysis of the sample(s) is similar to the cost of analyzing the sludge prior to pumping out the O/W tank.

For O/W sludge to be accepted by most certified landfills, a full characterization of the sludge is typically required to demonstrate that the waste is not classified as "hazardous waste".  The reasoning for requiring the screening didn't go away when most shops stopped using chlorinated solvents.

Compared to some recommendations I have read about in Phase I's, the LSA for this one is not overly conservative if properly explained in the discussion of findings.

I hope I pass the test of not being personal in my comments, sometimes that is a challenge for me :)