I was writing a post partially referring to the all-important maintenance person, and I went to link to an old post and found I had never written it. How could this be? So here's the post that was so critical, I was convinced I had written it before:
Environmental investigations rely heavily on the history of a site. What was produced here, and where might have the raw materials/off-spec product/finished stuff have gone? If the site is relatively young, you can look at past environmental filings with the local and state agencies, but your site's history (and contamination) may pre-date most environmental regulations. Another great resource is Sanborn fire insurance maps, which lay out all the processes and plant details and can go back to the early 1900s.
But if you really want to know the skinny on what happened at a now-defunct site, you need to track down someone who worked there, who knew what really went on there. Your most valuable resource is the old maintenance guy, who was there forever and is still alive to tell you about it. Old Maintenance Guy is usually happy to tell all sorts of war stories. Best case scenario, you can take Old Maintenance Guy for a walk around the ruins of the site, and seeing what's left will jog his memory, and he'll be able to provide all sorts of details that you perhaps hadn't considered before: When did this process begin? Was it messy? Did they dump chemicals down the drain, or give away off-spec solids as "clean fill"? When did the plant actually close down, and was it an orderly process, or did the owners shutter it and leave in the night? What were the neighboring plants like?
An active facility will often have an Old Maintenance Guy, and he can be a great resource for other reasons as well. In the planning stages of an investigation? Old Maintenance Guy may
remember where the old oil tanks and other potential sources may have
been. Need to know where the utilities are? Old Maintenance Guy remembers when they were put in, or knows who may have access to the as-built drawings. Trying to get somewhere that's been locked for so long, nobody knows how to get in? Old Maintenance Guy has the key and knows how to convince the lock to open.
The best thing about an Old Maintenance Guy is that it warms his cockles to be an expert. He gets an audience of scientists and drillers who need his hidden knowledge, which likely nobody else has cared about for years. Often, the best thing we can do in return is for me to explain the one thing he doesn't know about the facility (the geology underneath it) and for the drillers to explain how their complicated, overly persnickety machine works. Win win.