Posted by Robert Wells
One of the most enjoyable aspects of arboriculture is the variety of unusual situations that we encounter each day. Every job presents its own unique set of challenges that often require some creativity to solve.
We were recently called in by a contractor for the New Jersey Dept. of Transportation to advise them on the best way to remove a long dead elm stump that had grown into the foundation of an historic grist mill on the Stoney Brook River in Princeton New Jersey. In fact, the 30 foot tall laid stone wall in the image below is the only remaining portion of the Quaker Settlement Mill that was one of the first structures built in Princeton in the 1670’s. The Quaker Meeting House was erected a few hundred yards away and by 1700 this was a thriving community. Seventy seven year later years later having crossed the Stoney Brook Bridge where the Mill was located, Washington’s troops fought the Battle of Princeton in Clarke’s orchard a half mile away.
The wall is bowed in spots and the cement chinking has largely eroded. Many of the red shale stone that make up this structure are loose or have fallen out. Additionally the wall is located less than three feet from a busy State Highway that accommodates over 30,000 vehicles a day, many of them heavy trucks that rattle this compromised structure and daily threaten to collapse it. For over 70 years an American elm grew at the base of the wall and established a robust root system that worked its way into many of the cracks and interstices between the stones, uplifting and pushing aside an entire two foot section. Then, perhaps 10-15 years ago this elm, like so many others, succumbed to Dutch Elm Disease and was cut down. The final cut was made at two feet and the stump was left in place to rot.
In early February of 2017, a heavy rainstorm took out a section of the bridge abutment and it became clear that emergency repairs would have to be made, including rebuilding and repointing of the last remaining wall of the Mill. Before that could happen all remnants of the elm stump would have to be removed. However, close inspection revealed that the area between the wall and the stump was very unstable and that hasty or careless removal of the stump might cause the wall to collapse. Our suggested course of action was to first erect a protective support structure and then to release the roots on the back side and lift the stump remnant with an excavator with a thumb attachment. The embedded roots would be exposed with an air spade and removed with a hammer and chisel. Quick drying hydraulic cement would be used to fill in the voids as the work progresses.
Hopefully a bit of creative thought and careful workmanship in the removal of these physical roots will help us to preserve some of our historic roots for a few more years.