Archaeology Update for the Week of October 1
As much as you might think we’d want to, we really can’t just jump out and get started digging right away. We’re taking this first week to do some initial preparation before the actual excavations start.
We have six excavation blocks planned to investigate this site (Blocks A-F). Each one of those blocks was pre-selected and roughly defined using computer-based mapping called Geographic Information Systems (GIS). But we also need to actually lay these blocks out on the ground. We use high-precision Global Positioning System (GPS) called Virtual Reference Stationing (VRS), which is a version of a two-GPS-receiver, dramatically-improved accuracy mapping system called Real-Time Kinematics (RTK). While the GPS that you have on your phone or in your car can tell you where you are in the world within an area roughly the size of small bedroom, VRS can tell you where you are within the eraser on the pencil that’s lying on the floor in that bedroom (well, less than a centimeter at least)! VRS does this by a surveying GPS receiver, called a Rover, getting its position from standard GPS then asking another GPS receiver nearby, one that’s been placed at a precisely-measured location, where does their GPS say they are relative to where it’s actually been placed. The fixed GPS receiver, called a “Base Station” is constantly using math to figure out how much the GPS information is off from its actual position – essentially broadcasting over and over “The GPS data says I’m at this position, but I know I’m 3.10224 meters to the northwest of that…The GPS data says I’m at this position, but I know I’m 3.10511 meters to the northwest of that…The GPS data says I’m at this position, but I know I’m 3.09288 meters to the northwest of that…”
The rover then receives that message and says, “Well, if the Base Station says that the GPS data is 3.09288 meters off, then I’m 3.09288 meters off as well!” And it, in turn, gives a much more precise location. Nifty stuff! Co-Principal Investigator and Project GIS Specialist, Joel Butler, looking serious as he poses for a photo before he lays out Block C with the VRS.In placing the blocks, it’s important, especially in a place like this, to make sure that those blocks avoid buried utilities (water lines, electric lines, etc.). First and foremost, we ABSOLUTELY don’t want to damage a water line and have someone’s faucet not work. Second, when a utility line is installed, it’s usually installed inside a trench that’s dug immediately beforehand. Digging that installation trench winds up mixing up and destroying any intact deposits that are located within it. That means that we won’t really learn anything from that soil if we excavate it – in other words: a lot of work for not much return. So we work with NBU’s utility locators to place the blocks to avoid those utilities.Remember when we said that all that digging in disturbed soil was not very useful? Well that also goes for the top layers of soil at the site, too. A lot of our previous work here has shown us that the upper soil layers are mixed from lots of modern construction and grading. It’s only after you go down a little bit that the un-mixed soils begin. Just like the utility trenches, we won’t really learn a lot by digging through the upper mixed soils, so we used a backhoe to remove those mixed upper soil layers more quickly (something that crews would take a couple days to get through, a backhoe can do in a couple hours) to get where the careful digging can begin quickly. Three of the blocks being dug first were cleared out while the other three will be cleared out a little farther along in the excavations. Finally, while the backhoe was here, we used it to dig out a small pit that will store water for the water screening. Whew! Lots of work but we’re getting set!