Master Plan & Contingency Plan, Charleston, SC

A Sewer Tunnel System Replacement & Contingency Plan

As a result of the STAG monies obtained through the Corps of Engineers, Hussey Gay Bell and Black & Veatch teamed to produce a Master Plan for the replacement of Charleston Water System’s failing sewer tunnel system. Hussey Gay Bell’s task also included the preparation of a Contingency Pumping Plan for the Ashley and Cooper River legs of the tunnel system in the event of a failure in the existing tunnels. This plan included pump and force main sizing and force main routing for multiple scenarios of potential tunnel failures.

Prior to the development of the master plan, the Charleston Water System (CWS) experienced several catastrophic events in their deep level sanitary sewer tunnel conveyance system. As a result of severe corrosion to the concrete carrier pipe, several partial tunnel collapses nearly resulted in the complete blockage of almost 10 mgd of flow in the Ashley River Tunnel leg of the system. Potentially hundreds of thousands of gallons of raw sewage were within several feet of overflowing into the City’s streets. This occurrence along with similar events ultimately spurred CWS to replace the Ashley and Cooper River tunnel system over the following six-year period. However, prior to this replacement project CWS retained Hussey Gay Bell to develop a citywide “Tunnel System Contingency Wastewater Pumping Plan” to mitigate a catastrophic event.

Due to the potential for a tunnel collapse, Hussey Gay Bell was tasked with developing a plan of action to by-pass wastewater flows between access points in the system at drop pipes and shaft locations. For both the Ashley and Cooper River branches of the tunnel fifteen emergency by-pass pumping scenarios were identified. To prepare for potential failure event(s), a detailed “Implementation Plan” was developed for each scenario to include: a work procedure, key personnel to contact, flow data estimates, required pumping capacity and head conditions, force main sizing and lengths quantified, necessary road and railroad crossings and a detail routing plan for placement of an above ground temporary force main.

The worst-case peak flow scenario included preparing for the by-pass pumping of almost 10 mgd through 3,000 LF of dual 12-inch diameter force mains through the streets of the Charleston peninsula. As a proactive move, CWS stockpiled sufficient piping, road crossings and miscellaneous supplies and contracted with Godwin Pumps to set up and operate the by-pass system.

Master Plan & Contingency Plan
Charleston, SC

Completed in 2009, the CWS Wastewater Tunnel System Master Plan and Contingency Wastewater Pumping Plan provided solutions for a failing sewer tunnel system and potential tunnel failures.

Hussey Gay Bell's Status Re: COVID-19

Dear Clients, Industry Partners and Friends of the Firm:

Throughout Hussey Gay Bell’s 62-year history, we have seen times of prosperity and times of struggle. The common denominator during these six decades has been our commitment to our clients, employees and the communities in which we serve. As we now face the COVID-19 crisis, this resolve is no less diminished. 

Currently our offices in Savannah, Charleston, Columbia, Atlanta, Nashville and Statesboro are open and operating, per jurisdictional guidelines. Our leadership team continues to monitor the fluid COVID-19 situation and has adopted new procedures within our offices to ensure the health and well-being of Hussey Gay Bell's greatest asset - our employees and associates. We are adhering to recommendations from the CDC and limiting face-to-face interactions, restricting non-essential travel, and utilizing video conferencing and other smart technologies for communications. We have also developed contingency plans so that we remain in a position of strength to continue our projects remotely, if and when needed, for the weeks and months to come. 

While the typical way we interact with you may be temporarily disrupted, we remain resolute in our dedication to providing the same level of exceptional service you deserve. Thank you for the continued trust you have placed in Hussey Gay Bell for all of these years. We are committed to a high level of service to you, despite these difficult times. We will all emerge from this crisis stronger and more resilient.

Stay safe!

Sincerely,

G. Holmes Bell, IV, PE

Hussey Gay Bell CEO & Chairman