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High Level Sewershed Evaluation

Location: Baltimore, Maryland Client: City of Baltimore

JMT's study of a major sewershed helped Baltimore prevent SSOs from impacting the Chesapeake Bay.

The City of Baltimore selected JMT, in joint venture, to complete a comprehensive evaluation of the 4,608-acre High Level Sewershed.  Nearly 100 years in age, and seriously impacted by silt and debris accumulations, the High Level Interceptor is the City's relief lifeline to Back River Wastewater Treatment Plant.  In the event of a serious failure of other sewers, the High Level Interceptor protects the City from sewer overflows, enabling diversion of wastewater and relieving other system segments. 

JMT performed field inspections of 6,000 manholes and over 900,000 LF of sewers using CCTV and SONAR, coupled with RTK GPS survey of manhole locations.  These inspections were coordinated with 500 meter-months of flow monitoring data furnished by our joint venture partner from more than 40 monitoring sites. Using this information, we created a complete physical model and dynamic, 2,000-node InfoWorks hydraulic model of 200 miles of sewers.  JMT's capacity evaluation identified bottlenecks that could cause between 4 and 20 million gallons of system SSOs during 2-year through 20-year storms.  JMT engineers worked through simulation of more than 50 alternatives of sewer rehabilitation, relief or replacement, and pipe, tank or deep-tunnel storage, to identify the least-cost implementation alternatives.  Our understanding of the sophisticated hydraulics within the High Level Interceptor enabled the JMT Team to evaluate capacity recovery scenarios that included removal of a deep debris/sediment bed within the Interceptor, and adjustment of the hydraulic grade line boundary constraint downstream at its junction with the City's Outfall Sewer.

The High Level Sewershed evaluation was performed within a state-of-the-art data management environment to ensure data accuracy.  JMT's GIS staff provided services such as database configuration, data management, custom application design, records research, and quality control procedures to support the project.  We managed data related to GIS, survey, manhole inspection, closed circuit television investigation, hydraulic modeling, and smoke and dye testing.

During the course of the study, JMT water/wastewater engineers performed planning and design including preparation of reports, cost estimates and contract documents for the rehabilitation and construction of certain improvements needed immediately to benefit the sanitary sewer system. 

The High Level Sewershed study had a demanding schedule and required monthly updates.  Schedule compliance and on-time project completion was crucial because of the Consent Decree between the City, U.S. Environmental Protection Agency, and Maryland Department of the Environment that enforced stipulated penalties for schedule noncompliance.

With JMT's support, Baltimore will alleviate SSOs and protect its Inner Harbor and the Chesapeake Bay from sewage pollution.   JMT implemented real-time actions to clean capacity-robbing debris and blockages, restore collapsed pipes, and supply the tools for ongoing capacity management.  


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