Just a few suggestions:
Get written permission from the property owner to dive, and to conduct your tests.
Dive dry and if possible, use a FFM, there might be contaminants in the water.
Take only what you need on the dive, a bulky BCD and 50 pounds of extra toys wont help a bit if all you need is the z-knife that is stuck behind the camera, that is attached to the strap that holds your bug bag, that has you signal mirror on it, that is folded inside of your line arrow bag, that is...
Do a drive by... get a small boat and a depth finder to check the depths and obstacles. Make a map of the quarry before jumping in and hoping for the best. a good DF can let you know what to expect on the bottom other than silt, etc.
Get water samples done if possible. Preferably a few at different depths just in case it is contaminated and the thermocline, or other 'cline keeps it separated.
Make sure everyone is experienced before you jump in the water, it may be cold, black water, full of fishing lines, snakes, etc. Make sure your team is prepared before you start and everyone knows what to do, who to call, how to direct EMS, and everything else in case of an emergency.
Dont take a chance on getting hurt to find out what is at the bottom.
Those are just a few of the things I go over before hitting a virgin quarry or dive site.
Sorry if I left anything out, which I am sure I did. Hope it helps