April 2008 – Carollo Engineers announced that Central Contra Costa Sanitary District (CCCSD) has begun construction on a new interceptor pipeline to connect the gravity flow collection system of Concord, California with an existing 102-inch interceptor operated by CCCSD. The overall success of this project is predicated on Carollo’s planning and design using sophisticated trenchless technology to counter geographic challenges.

Along with construction of an open-cut sewer line that crosses under live stream flow in Walnut Creek, the project includes tunneling two sizeable sewer pipes (96- and 72-inch diameters) to depths of more than 30 feet. Because the project’s path runs directly through a highly developed, high-traffic urban area, Carollo implemented an action plan that integrates extensive trenchless design elements to resolve numerous concerns of the city, business owners and the general public.

Carollo engineered customized solutions for each of the site-specific challenges, especially where trenchless elements were deployed, including:

• Implementing a settlement monitoring plan to address settlement in areas of shallow earth cover.

• Deploying an Earth-Pressure Balanced Machine (EPBM) to address ground subsidence and tunneling under groundwater pressure.

• Obtaining regulatory approval for the complicated sequencing of an open-cut sewer pipe crossing beneath Walnut Creek.

• Devising underground structures, including a flow metering structure and junction structures along the length of the pipe, to advance the overall tunneling approach.

“This project was complicated not only by various terrain issues and soil conditions, but also by the large number of stakeholders impacted by construction,” said Alex Rozul, Project Manager for CCCSD. Heavily traveled city streets in the construction area service a number of local businesses, including big-box home stores and government offices. Existing interceptor sewers, storm drains, and fiber optic cables also present challenges.

According to Rozul, “The Carollo team was conscientious in the analysis, design and planning stages to address private, public, and regulatory concerns. We were impressed by their ability to resolve the engineering and design challenges while at the same time reassure, handle negotiations, and gain the approval of all the affected parties and regulatory agencies.”

Carollo’s Project Manager, Tim Tekippe, agrees that Carollo’s strengths were particularly suited to the scope and complexity of the project. “In developing the best overall solution for Concord, Carollo had the resources to analyze and assess each alternative strategy, on both technical merit and how the strategy might impact traffic patterns, property rights, and regulatory approvals.” Early on, when it became apparent that the depth and magnitude of shoring required for open-cut construction in the urban areas would be too disruptive, Carollo chose trenchless strategies, such as tunneling and microtunneling, as the lowest-cost, most effective option.

For 75 years, Carollo has provided a full range of innovative planning, design and construction management services to meet the water and wastewater needs of municipalities, public agencies, private developers and industrial firms.