The Designer’s POV: El Paso Eastside Interceptor
As El Paso’s eastside area continues to develop at a rapid pace, wastewater infrastructure needed to be expanded to keep up with growth. PSC designed the last two segments of the Eastside Interceptor that is a major piece of El Paso Water’s wastewater collection system.
The Eastside Interceptor was a complicated and difficult project. It wasn’t the longest pipeline we have designed at PSC, but it was notable because of the complex aspects of permitting with so many entities, very narrow rights of way, a 20 mgd by-pass and high groundwater. The interceptor was 60- and 66-inch HOBAS and HDPE lined RCP pipeline and included several 90-inch casing crossings. One of the unique aspects of this project was removing the 48-inch sewer interceptor line that was currently in service. Due to the location of the existing line, other utilities and the depth of the new line, the new line couldn’t be installed without removing the existing line. The entire alignment had to be dewatered.
The project had two TxDOT highway crossings, a touchy railway crossing, and multiple irrigation canal crossings. The design required the 90-inch steel casing for the crossing and the casings were installed using either a tunnel boring machine or auger bore machine. We assisted El Paso Water in obtaining permits and developed the tunneling specifications for this project. The downstream portion of this project was in a narrow right of way with limited access for residence. We designed this area to be installed by TBM using HOBAS jacking pipe.
The 20 mgd by-pass pumping operation could have a been a project in of itself. It required installing two polymer concrete manholes on top of an existing 48-inch line. Polymer concrete was used because a concrete base could be cast around the existing 48-inch line with a key that matched the polymer concrete manholes. Due to the high H2S levels, we wanted a manhole that could stand up to the corrosion and did not need to be cured and coated to save time. After the manholes were installed, 1,500 feet of parallel, 20-inch HDPE discharge line were installed to route the wastewater around the work area. The discharge line installation was part of an elaborate sequence of construction that required temporarily installing the discharge line under Texas 20 through one of the 90-inch casings. The by-pass required four pumps and generators and was left in place until deflection testing of the pipe was completed.
When we started our pre-design activities, we noticed the previous segments of line only specified fiberglass reinforced pipe. Due to the diameter ranges, the pipe material is somewhat limited. However, to help foster competitive prices, we worked with El Paso Water to specify HDPE-lined RCP as an acceptable pipe material for this project.
The move to include a second pipe material worked and was evident in the bid tabs with the last two segments coming almost $3 million less than the average of projected costs.
Mike Ramirez, PE, CNU-A, is a Principal and Team Leader in PSC’s Infrastructure Sector. He has years of engineering experience with an emphasis on large diameter pipelines, pumping facilities, GIS applications, collection and distribution modeling, and planning, design, and construction of water and wastewater projects. Mike has managed the planning, design or construction of over 100 miles of pipeline projects in the past 10 years, ranging from 6 inches to 90 inches. He also oversees Construction Management Services that PSC provides out of its El Paso Office.