Tuesday, August 26, 2014

Backfilling the mikveh site

With our main objective of locating and confirming the existence of an early 20th century mikveh at 90 Jefferson Street accomplished, it was time to backfill.  We had gotten a lot of questions from visitors about whether the site would remain open so that the mikveh would be visible to future museum guests.  Ultimately, though, the best way to protect and conserve an archaeological resource is usually to backfill, or rebury the site.  In some cases, backfilling is even a required condition of permitting excavation.

Backfilling reestablishes a stable environment for archaeological resources, including exposed features (like our mikveh) and unexcavated artifacts.  It also helps to maintain the integrity of the stratigraphy (or layers of dirt) in areas that we didn't excavate.

Here at the Pecunies House site, the soil used to fill the foundation after the house was torn down in the 1960s was full of gravel, larger stones, and bricks.  The particle size or grain size of that 1960s fill was therefore rather large and this resulted in some fairly unstable sidewalls.  There were many voids throughout the fill, and rainwater from summer storms was seeping below the tarps we used to cover the site at night, meaning that the walls were deteriorating further.  Wall fall could compromise stratigraphy in the unexcavated units surrounding our excavation block.  We left portions of the site unexcavated (for example, we only excavated the late 18th century midden within one 1x1 meter unit) that we wanted to protect for possible future research.  We also wanted to protect the mikveh itself from the elements.  So, it was time to rebury our site.  However, we wanted to do so carefully.

Filter fabric covering the mikveh.
With the help of Atlantic Stone & Landscape, we began by wrapping the mikveh with filter fabric, a geosynthetic fabric which allows for normal water flow while containing soil particles.  The excavation block was then filled with new sand (clean of rocks and debris).  We tamped it down, added another layer of filter fabric, and topped the site with the topsoil we had saved from the beginning of our excavation.  It was pretty remarkable to see how quickly heavy machinery could do the job of filling in the block that had taken weeks to empty with our trowels and buckets!
New sand is distributed over the excavation block - thanks Jesse!
The site today!
Although the site has been backfilled, the project is far from over.  We have thousands of artifacts that we have begun to catalog here in the lab.  We also now have many photos, drawings, maps, and other materials -- even mikveh bricks! -- that will ensure the mikveh and its place within the early Jewish immigrant community is remembered.  Keep checking the blog for more updates as our research progresses!  

Friday, August 8, 2014

Memory versus Technology

By now, you've seen many photos of our excavation and are well aware of the huge volume of dirt that the archaeology team had to move this summer. And this was a relatively small-scale dig! So it goes without saying that archaeologists don’t generally undertake an excavation without spending a considerable amount of time deciding where to dig.

Historical archaeologists sometimes have a bit of a leg up when it comes to making those decisions. Often times, we have knowledge that a site is there before we ever break ground thanks to documents like maps, probate records, and even photos or oral histories if a site is recent enough.

Lucky for us, we had a few resources at our disposal. In addition to having the footprint of the house foundation still outlined in stones, we had the help of photographs of the house as well as oral histories about Jewish life in Puddle Dock collected as part of the museum’s research for the opening of the Shapiro house. These oral histories were useful in that they confirmed the existence of the mikveh at the Pecunies house, but they couldn't tell us exactly where in the house it was. Ronnie Pecunies, a member of the last family to occupy the house before it was demolished, still lives in Portsmouth and visited the site several times to relate his memories of the house and the neighborhood. He remembered the mikveh being in the eastern half of the basement.

Frontal view of the Pecunies house from Jefferson Street.

The memories and stories attached to a place are invaluable to archaeologists, but thanks to the leaps and bounds made every day when it comes to technology, there are more objective methods available to augment our knowledge. Peter Sablock, a professor of geological sciences at Salem State University, brought his equipment to Strawbery Banke and performed a survey on the site using a method of shallow geophysics called electro-magnetometry (EM). Most minerals possess a certain level of magnetism and an object's thermal history can affect those levels as well. In the case of our mikveh bricks, the minerals in the clay used to make them had magnetic signatures different from the soil around them and when the bricks were fired this increased their conductivity. So when we look at the readout from the EM survey, the location of the mikveh is incredibly clear.

EM reading showing magnetic conductivity.
Anomalies show up clearly in blue and red.
When we align the EM results with current aerial photos of the site and a 1910 Sanborn map detailing the house’s location, it becomes apparent that the mikveh was actually located in the western half of the basement and not the eastern half. In response to the geophysical survey, the archaeology crew opened another unit in the western part of the basement and, sure enough, that’s where we located the mikveh.

It was interesting to see how memory can be so accurate on some counts (Ronnie Pecunies remembered the white tiles inside the mikveh) and so unreliable in other ways. 

Aerial photo of the block with 1910 Sanborn map and the EM results overlaid.

Since the mikveh was not documented in any records, its rediscovery was solely the result of the memories of former Puddle Dock inhabitants. Using technology to augment what we knew from the oral histories, we were able to pinpoint the mikveh’s location. This partnership of human memory and technology is an important one for archaeologists and the example of the Pecunies house mikveh illustrates the potential for the combined usage of both when it comes to scientific research.