I had to excavate our parkway rain garden to a ponding depth of six inches. It was a very simple task, except for the treasure hunting aspect of our urban soils.
I didn’t want to start with the excavation until I had a barrier around the rain garden. Although the drop into the bottom of the rain garden wouldn’t be more than nine inches, I still was worried someone could fall into it. Now that I had a fence surrounding the parkway rain garden, with the exception of the fence panels, I was ready to start digging.
My goal was to plant my rain garden plants into a medium that resembles top soil. That was not an unrealistic goal, considering that the top layer in the parkway was a fairly good quality topsoil. But what was lurking underneath made things a lot more interesting. In a way, it was a little bit like archeological discovery that told a story corroborated by the surrounding landscape.
The parkway rain garden will stretch across two city lots. To the east is a vacant lot. It once had a building on it, but that was torn down. I am not quite sure when but it must have been sometime after the 60s. To the west is the lot on which sits our house, which was built in 1902. It think it is fair to assume to most buildings on our block were built around that time, including the house that once stood proudly on the vacant lot.
In my preparations for excavating I noticed that the parkway at the vacant lot had topsoil layer of about four inches, followed by a good six to eight inches of soil mixed with rubble. Below that was a decent layer of dark colored subsoil.
The parkway section in front of our house did not have the rubble layer. The topsoil slowly transitioned into an equally dark colored subsoil. It comes close to an uncontaminated or clean soil profile.
That may speak to the construction methods around 1900. I could assume that the crews cleaned up the site once they were done with the building, but I seriously doubt that. I think it is more likely that back in the day, builders didn’t use the equipment we have available today, and thus didn’t recklessly ruin the soils the way we do today.
The rubble layer at the vacant lot, on the other hand, most likely dates back to the tear down of the building.
Overall and given our urban environment we are blessed with decent soils, which we could maintain as long as I could find a way to address the rubble layer.
My method was as follows: I started by excavating and saving the topsoil, which is now in a stock pile in the vacant lot. Next I excavated the rubble layer and hauled it off site. Once I started excavating to the west, I relocated part of that topsoil to the east, until I had met my ponding depth of six inches.
A Tom Sawyer moment
When I started excavating, it was still summer break and the kids on the block were stifled by boredom, including four brothers who live two houses down. First they found some distraction by watching me dig. That lasted about ten minutes. Then they riddled me with questions. That lasted a little longer. Then they argued among each other who would do the best job digging. And finally they were begging me to help.
I got my spare shovel and let them have a try. To my surprise, the youngest and smallest of the four was not only the most skillful, but also the most relentless. He almost kept up with me. And once the last of his brothers had his turn, he wanted right back into the game – and I was grateful for the help!