Arsenic and Augers

My first summer blog comes after three weeks of laboratory analyses and hot days spent at Jamestown fort, gathering groundwater samples, bantering with tourists and befriending sunbeaten archaeologists. Roughly 65 groundwater samples have been collected from the settlement and analysed for arsenic, iron and DOC (dissolved organic carbon). Measuring iron is relatively simple but requires a few hours of preparation and then ‘doping’ samples by hand with various reagents to produce a delightful magenta-violet color. Simply put, the more purple the sample becomes, the more iron content.  When it comes to measuring arsenic, a large and admittedly intimidating machine called a VARIAN Atomic Absorption Spectrometer, is used, and must be treated gingerly, as discovered when this beast demanded a full day of troubleshooting before it would run smoothly. Once attached to a 50psi Argon tank and the inner quartz cell is heated to 950 degrees Celsius, my groundwater samples are heated and turned into a gas which contains any arsenic in the sample.  A beam of light is then sent through the gas;  the less light thats passes through, the more arsenic in the sample.

EPA standards for drinking water quality state that concentrations of arsenic and iron must not exceed 0.01 ppm (part per million) and 0.3 ppm, respectively. And, in general, groundwater contains 1-2 ppm dissolved organic carbon. So.. would you want to drink Jamestown water? Probably not. Arsenic concentrations in one sample exceeded EPA limits, and almost all of the 65 samples analysed had elevated iron levels, with the most extreme containing almost 200x more iron than allowable. Organic carbon was elevated aswell, almost 25x higher in one analysed sample than is characteristic of most groundwater systems.

On June 19th, my partner Kyle Stark and I went to Jamestown fort to install two nested wells with the former state geologist of Virginia, Rick Berquist, and our own geomorphologist Greg Hancock. I thought the process of installing a well was more complicated and laborious, but alas, the whole operation was rather straightforward and quick. The bore holes were created by pushing augers into the ground; these metal corkscrews will lift dirt out of the ground without disrupting the adjacent sediments. Each auger is five feet long, so in order to drill our wells to a depth of ~30 feet, multiple augers were used. Once we achieved the depth we wanted, the augers were lifted out of the ground, and the sediments were removed and laid out on the ground to create a sediment depth profile. Roughly twenty feet below the surface within Jamestown settlement, there is a geologic unit called the Shirley Formation (one of my favorite formations!) which is characterized by very cohesive, compact and play-doh-like grey clay, which still preserves trace amounts of Pleistocene tree material! Thus far, this day was my absolute favorite! I had an opportunity to meet one of the most well respected geologists in Virginia (THE Man), Rick Berquist, and also was able to use professional field equipment for my research. Drilling the bore holes was muddy and messy, but that made it all the more fun! Not to mention the Indian pipe bowl and colonial lead bullet we got a glimpse of only moments after having been freshly removed from an archaeologists’ dig site twenty feet away!