If the language in the closure letter is just CYA language then I'd call it an HREC. (Unless, of course, the tank was not leaking in which case it would not be any kind of REC.)
On the other hand, if there is actually some residual contamination then you're right: it doesn't matter if there is an actual AUL. If the residual contamination is, or likely is, above residential standards then it's a CREC. If the levels are low enough to be considered de minimis then it's an HREC.
These can be touchy situations. I also ran into a situation where a UST was closed and the regulator noted "residual contamination." It turned out what he was referring to as residual was a soil sample under the dispensers with over 1,000 ppm TPH. I called this out as a REC, progressed to a Phase II and a boring at this location identified contaminated soil (exceeding state cleanup guidance) down to about 17' bgs. I'm not sure how this could have been a CREC. If residual contamination is, in reality, likely to be something more than residual (it's kind of a catch all term), then it probably is uncontrolled.
It's worth noting, I think, that UST closures can be very subjective. What one regulator will write off as residual, another will require investigation or further removal. This is particularly the case where investigation and/or removal would be very costly (eg, adjacent to / under foundations) and significant contamination seems unlikely.
In your case, does the documentation often include lab data?
And we all know that ain't easy.....
Aromatic hydrocarbons, particularly nitrated compounds, were major constituents of some of them-- e.g TNT is trinitrotoluene.
TNP was picric acid, 2,4,6 trinitrophenol. Picric acid was the new thing then, produced in a powdered form (known in the UK as Lyddite and in Japan as Shimose). The US also made a derivative, ammonium picrate, under the name Explosive D, aka Dunnite. The drawback to these was that TNP isn't stable and degrades into highly unstable daughter products that are conspicuously shock sensitive.
Nitroglycerine was very widely produced-- large mining or construction projects often had the stuff produced on site on an as-needed basis because it easy to make but was extremely dangerous to transport. It was also the 'daddy product' for a lot of other explosives. Take glycerol, add nitric acid to make nitric acid esters. Mix that with diatomaceous earth and you have Dynamite. Mix it about 60/40 with nitrocellulose and add some petroleum jelly to make a sort of resin, and you get cordite. Add nitrocellulose, saltpeter, and wood pulp and you have gelignite, which was sort of a poor man's dynamite.
Nitrocellulose (aka cellulose nitrate, made by dissolving cellulose in nitric acid) was used in a lot of high explosive formulations, e.g. torpedo warheads. Nitrocellulose was also used in to celluloid as used in commercial plastics, shirt collars, and movie film reels. MA still has a law on the books under the Fire Marshal's Code strictly forbidding the transport of celluloid film on streetcars.
Mercury fulminate was used primarily for blasting caps and detonators.
Black powder was still widely produced into the 1920s, for construction blasting, fireworks, stump removal, and the millions of older civilian firearms that remained in use.
Nitroamine explosives like RDX and HMX were mostly developed on an industrial scale in the late 1930s. The main advantage of these over the older nitroaromatics is that they're much more stable-- C4 is a nitroamine with a plasticized and binder and you can even burn it without it exploding, and HMX is handled by melting it and pouring it into e.g. artillery shell casings. Quite a lot of warships were lost in the Great War when one or two hits set off their magazines.
Naphthalene a major chemical precursor to lighter aromatics and substituted benzenes like toluene, so you may have lots of that depending on what parts of the overall process your site included. A lot of the aromatic hydrocarbons they used for this work were byproducts of the manufactured gas industry-- during both World Wars the Federal Government basically sequestered a lot of the light oil gasworks byproducts for munitions production, and most of the benzene production was diverted from solvent production to making synthetic phenol for TNP. If you had a very large site they may have even done some distillation of coal tar or light oils.
Mercury (fulminate), nitroglycerine, TNT and maybe RDX are I believe the most likely suspects. RDX was developed late 19th century but not widely used until World War II so far as I know.
I got an AEP certification when I first started, for the very same reasons you cite. It does make you look better when providing your credentials to clients.
NREP is a legit and honest organization. The test is fair, not too easy, and they do follow up to make sure you meet their CE requirements.
However...NREP is not as widely recognized or accepted as they probably should be. In fact, no credentialing organization is. This is a hot topic in the consulting industry these days. I've seen many such discussions on Commonground, LinkedIn, and the like. I've even seen some newly-formed organizations that are reportedly rushing to fill the credentialing void. But I'll believe it when I see it. Once upon a time, California had their own credential for EPs...then they did away with it for budgetary reasons.
IMO, for now, you're either an EP or not. Other than that, I think PE and PG certifications are the most relevant and recognized in our field.
So until you've accumulated the requisite experience to call yourself an EP, an AEP certification certainly won't hurt! Go for it. And good luck to you!
Did we ever get a location for this?
I would like to take a closer look at an old topo and what is there more recently
Not a golf course - there are no greens.
Are you comfortable giving an approx current address or lat/long?
Seeing as it's in Los Angeles and those circles appear to be related to fluid storage of some site, my first thought is oil wells. But, the grass around it looks well maintained and there appears to be some sort of order to them so I also considered a golf course, perhaps during some kind of construction or maintenance project, although the number of them doesn't work out.
Sure, this Forum has been a very valuable tool for me generally being the only person in my office who does Phase I ESAs. Can't really ask some of these questions of office staff.
Thanks for the follow up.
It's an SBA loan also, and after finding the ACOE Report, they are still concerned about fill materials brought in, even though they were sampled as part of the soils investigation associated with removal of sewage disposal structures.
Property owner has decided to conduct Phase II before selling property.