Environmentally Sensitive Areas, Sewer Design to Construction - Lessons Learned

Authors:

  • Chris Caro - Washington Suburban Sanitary Commission
  • Lawrence Latour - Hazen and Sawyer

The Washington Suburban Sanitary Commission (WSSC) contracted Hazen and Sawyer (Hazen) to identify, develop, and design access roads for the rehabilitation of right-of-way manholes and pipe segments assigned Priority 1 rankings, as reported in the Sewer Repair, Replacement, and Rehabilitation Plan (SR3 Plan). Under this Sewer Basic Ordering Agreement (BOA) contract, Hazen developed a design for the Piscataway Creek Environmentally Sensitive Area (ESA). The design objective was to provide the most feasible access routes for asset rehabilitation for designated Priority 1 manholes and pipe segments located in ESAs. The design also included access consideration for manholes located immediately upstream and downstream of the Priority 1 manholes. The goal of the project is to mitigate environmental disturbance with a cost-effective design. The project consists of 90 project areas accessing approximately 337 Priority 1 manholes and 163 Priority 1 pipe segments. A total of 506 manholes and 380 pipes were recommended for rehabilitation.

The design included full access paths suitable for the use of tractor trailers and other large vehicles passing through private property, park property, wetlands, and streams. As commonly found in a gravity sewer system, the assets are located in low laying areas with significant topography, typically adjacent to streams and wetlands. To properly determine the most beneficial route alignment, several access path alternatives were analyzed in the field with environmental and civil engineers. A project of this size and complexity required coordination with a multitude of federal, state and local permitting agencies. In addition, hundreds of right-of-entry agreements from private homeowners and homeowner associations were acquired to allow access. To adequately design access to assets, Hazen communicated with local general contractors to determine their means and methods for rehabilitation. This was essential to streamline the project and provide the appropriate access for construction. In instances where assets were located adjacent to water bodies, significant site condition changes were observed between the design and construction phases. These changes in field condition highlighted the need and benefit of having the design engineer tasked with construction management to assist with field adjustments.

This presentation will discuss the lessons learned taking a project from design to construction. It will explore possible future standardization of design criteria within WSSC infrastructure projects with the intent of limiting the number of change orders needed by the contractor. This will better provide accurate methodology and assumptions for determining contract line items. The presentation will also present the benefits of the SR3 project to reduce SSOs, protect exposed assets and improve water quality. Working in ESAs creates a unique project where the rehabilitation of the assets is the easy part with the most challenging aspects being the permitting and providing adequate access for construction.

For more information, please contact the author at llatour@hazenandsawyer.com.

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