MODELING ONE OF THE LARGEST SANITATION DISTRICTS IN THE U.S.

The Virginia metropolitan area known as “Hampton Roads” proudly boasts the world's largest natural harbor. But in 1925, the waters of Hampton Roads, which include Chesapeake Bay and surrounding rivers, were suffering from pollution caused by oyster fishing and rapid growth. The waters were about to be condemned! The Virginia General Assembly took steps that led to the formation, in 1940, of the Hampton Roads Sanitation District (HRSD).Today, HRSD is one of the largest metropolitan sanitation districts in the nation, with 2,614 square miles of service area. It may not be the biggest sanitation district in the country, but it's probably one of the top five, according to HRSD Chief of Planning Ross Schlobohm, PE. “We're not the largest, population or flow-wise,” he says, “but we do extend to a very large land area.”The pumping and pipe network configuration of the interceptor system for HRSD is most unusual. Instead of providing a dedicated direct path to each plant, the HRSD interceptors are inter-connected, so that the operators can control the flow-split to each plant. These interceptors provide service for more than 2,000 local pump stations, so the hydraulic gradients in the system must be maintained within the limitations of the “policy.” To accomplish these goals, various control stations, telemetry, and specialized “Pressure Reducing Pumping Stations” were developed.Obviously, this is an extremely flexible and wonderfully complex system. To predict the adequacy of existing systems, using various combinations of booster pumping and pressure control, and to provide a tool for analyzing the response of the entire system for future growth, the Engineers at HRSD needed a new computer MODEL of the entire system.To be usable, the model needed to be able to analyze the various combinations of gravity networks and multiple independent, interconnected pressure systems, and provide realistic simulation of the telemetry and pressure controls, all within the same scenario. It was also desirable to integrate the model into a GIS map base, which would provide the advantages of GIS for operational control and future planning. Also, the model needed to be customized to allow real data from the 350,000 customers to be automatically mapped into the model.Various software packages were evaluated, but most were not able to meet these specific needs. The software program FORCEMAIN© was chosen as the only available platform that could handle complex modeling requirements, and could be customized to meet the GIS database and customer demand mapping requirements.FORCEMAIN was developed by McKim & Creed Engineer Dan Cote, PE, and has been used by Clearwater, Hillsborough County, and LeHigh, Florida; Portsmouth, VA; and New Hanover County, NC. HRSD is the largest, most comprehensive user to date.