National Historic Village of Old Economy Uses Trenchless Technology to Expand its Sewer System and Satisfy State Environmental Consent Decree

First settled in the early 19th century, Ambridge is located in southwestern Pennsylvania on the east side of the Ohio River, 16 miles northwest of Pittsburgh. Ambridge was established as a Borough in 1905 after the American Bridge Company purchased the land from the Harmonist Society, which had settled the area in 1824 as "Oekonomie" (Old Economy). Today Ambridge is home to the National Historic Landmark of Old Economy Village, the last home of the Harmonist Society. Old Economy has many preserved buildings as well as a museum dedicated to the Harmonists and their way of life. The area around Old Economy Village has been designated a Historic District and is listed on the National Register of Historic Places.

Built in sandy soils, the Borough's existing gravity sewer is located under State Route (SR) 65 at a depth of over thirty feet. A consent decree had previously been issued to Ambridge by the Pennsylvania Department of Environmental Protection (DEP) to eliminate sewer overflows caused by the lack of capacity in the Borough's existing system.

Upgrading the existing sewer main would have been extremely complicated and expensive. In order to expand the system's capacity and minimize the impact on SR 65, NIRA Consulting determined the most cost effective and least disruptive approach was to build a pump station and install a new 20-inch force main parallel to SR 65. The parallel alignment placed a significant portion of the new force main in the middle of Old Economy Village. Many of the village structures sit on minimal, shallow sandstone foundations. Vibration and potential damage from construction of a new force main in close proximity to these structures were a major concern for property owners and the Historic District.

With the force main alignment located in a tightly developed area with vulnerable structures and sandy soil conditions, it became clear that horizontal directional drilling (HDD) with fused pipe was the most viable construction approach. Minimizing the HDD bore hole size was a design priority, leading to the selection of 20-inch DR21 Fusible PVC® pipe, which provided a smaller outside diameter pipe than 20-inch segmented pipe with bells or 24-inch HDPE pipe. Twenty-inch Fusible PVC® pipe offered a 200 psi pressure rating while providing the necessary pull force to maximize the length of the drill segments.

Pipeline Details and Project Summary
Project: Fourth Street Pump Station Force Main
Location: Ambridge, PA
Length: 5,000 LF
Pipe Size: 20-inch DR-21
Pressure Test: 125 psi
Owner: Ambridge Municipal Authority
Engineer: NIRA Consulting
Contractor: Alex E. Paris Contracting
HDD Subcontractors: Str8 to the Point, Rock Drill Solutions

To help monitor and protect Village properties from potential damage during drilling, each structure listed on the National Historic Registry was inspected and documented prior to the start of the force main installation. To provide further safeguards, Alex E. Paris Contracting and NIRA Consulting recommended the use of surface vibration monitoring equipment from Vibra-Tech.

Based on recordings from other historic construction sites around the globe, a vibration limit of 0.2 inches per second was established as a threshold to protect surrounding structures. At no time during construction did the HDD vibrations approach this threshold limit, proving that the design and construction efforts worked as planned.

General Contractor, Alex E. Paris of Atlasburg, PA hired Str8 to the Point and Rock Drill Solutions to perform directional drilling services on the project. Their meticulous approach and coordination resulted in a very successful installation during the spring and summer months. Care was taken to perform work in the tightly constricted areas and also to accommodate the interests of the Historic District. Weddings, school field trips, public tours, and even the annual fall festival were held while the trenchless installation took place.

Alex Paris III, President and CEO of Alex E. Paris Contracting Co. said, "We enjoyed working with Underground Solutions on the Ambridge Project. They have a great product and support staff. We definitely look forward to working with them on future projects."

Emile Ketterer, Project Engineer with NIRA Consultants of Coraopolis, PA stated, "This was the first occasion I had to design an HDD installation using large diameter Fusible PVC® pipe. The results were spectacular and the client was pleased with the how the work was conducted and with the end result".

Fusion Welding of 20-inch Fusible PVC® Pipe with a McElroy T900 Fusion Machine in the Heart of Old Economy Village

Fused Pipe String Entering Bore Hole at Northern End of Historic District