Construction has been underway for a new residential subdivision along South Caln Road in Caln Township, Thorndale. For the past year, I have had the opportunity to visit the site two to three times a month to inspect the construction of infiltration beds being installed beneath several of the lots.

Since working at Howell Engineering for about a year, being able to see these systems constructed in the field has been one of the more interesting parts of my experience. We spend so much time looking at plans, profiles and details on a computer screen, but seeing those designs come to life in the field gives you a completely different appreciation for the work. It is fascinating to think that once construction is complete, most homeowners will have no idea that an entire stormwater management system is sitting beneath their lawn.

The construction of an infiltration bed involves several steps, each of which must be completed in accordance with the approved plans. The process begins by excavating the soil to the required depth and dimensions. Once the excavation is complete, a geotextile fabric is placed along the bottom and sides of the bed to help prevent surrounding soil from entering the stone bed.

Next, a large vertical yard drain structure is installed at the location and elevation shown on the plans. Clean stone is then placed within the excavation and carefully brought up to the required elevations. The distribution pipe is installed within the stone and connects to the yard drain. The distribution pipe contains openings along its length, allowing stormwater to spread throughout the stone bed rather than concentrating in one location. Additionally, a roof drainpipe connects to the yard drain, carrying runoff from the roof into the infiltration bed.

As additional stones are placed, the bed is gradually built up to its designed depth. On this project, the infiltration beds are typically 3 feet deep and 40 feet by 10 feet in size. The elevations of stone, piping and other components are important because they determine how the system will collect, distribute, store and infiltrate stormwater.

Once the stone and piping are installed and inspected, the geotextile fabric is folded over the top of the stone before the excavation is backfilled. The soil is then placed and graded according to the approved plans, eventually leaving behind what appears to be nothing more than an ordinary lawn and a yard drain.

Here are some pictures of the process…