Municipal Sewage Authority of the Township of Sewickley

This was a $21 million project that services approximately 1300 customers located in the Herminie, Rillton, Cowansburg, Sunshine and Keystone areas of Sewickley Township, Westmoreland County. The project included approximately 40 miles of various diameter sewers ranging from 6″ through 18″, 890 manholes, two pump stations and a 0.44 mgd Sequencing Batch Reactor (SBR) to provide a cost-effective wastewater collection and treatment solution for the Authority. Gibson-Thomas was involved in all aspects of the project from feasibility studies, Act 537 approval, funding, design, permitting, construction inspection and management. This project dramatically increased the water quality of streams and tributaries of Sewickley Creek by eliminating raw and inadequately treated sewage that previously discharged from homes and businesses into the waterways.

Gibson-Thomas delineated wetlands, prepared erosion and sediment control plans, and completed stream and wetland crossing permits, NPDES Part I and Part II permits, and highway occupancy permits. As part of the environmental permitting process, a search was performed for threatened and endangered plants and animals. There was a potential impact for snow trillium, a PA rare plant, and a population of the species found during the botanical survey was avoided by rerouting a portion of the sanitary sewer around the plants.

Due to the possibility of mine subsidence at the location of the treatment plant, grouting of mine voids was required. Gibson-Thomas coordinated investigation of the mine voids and developed specifications for contractors to follow to successfully fill the voids and prevent subsidence.


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Gibson-Thomas is a multi-discipline consulting engineering firm established in 1916 in Latrobe, Pennsylvania. Our past experience, key staff and commitment to total client satisfaction are the major factors that our clients consider when contracting with Gibson-Thomas.

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