Baxter Water Treatment Plant Raw Water Basin Dredging

REMOVING 202,000 CUBIC YARDS OF SEDIMENT FROM A RAW WATER BASIN RESTORES WATER STORAGE CAPACITY AND SUPPORTS WATER TREATMENT FOR PHILADELPHIA RESIDENTS

Our Client’s Challenge

The Philadelphia Water Department (PWD) is the public water utility for the City of Philadelphia, providing integrated drinking water, wastewater, and stormwater services for over 2 million residents in the city and surrounding communities. The PWD sources its drinking water from the Delaware and Schuylkill Rivers. The Samuel S. Baxter Water Treatment Plant (WTP), the largest of PWD’s three WTPs, pulls and treats water from the Delaware River to supply approximately 60% of the area’s drinking water.

The PWD diverts water from the Delaware River into a 24-acre manufactured raw water basin for temporary storage before treatment. Over time, river sediment accumulates in the basin, diminishing the basin’s water storage capacity. The PWD conducts maintenance dredging to remove the sediment, restore the basin to its designed capacity, and deliver over 200 million gallons of quality water daily to its customers.

Our Solution

When the PWD last dredged the basin in 2008, 350,000 cubic yards of material were removed. Based on a 2018 bathymetric survey, Gannett Fleming determined the sediment’s location, depth, and volume that had accumulated since the previous dredging. The sediment layer totaled 202,000 cubic yards and ranged from 3 to 17 feet thick.

Gannett Fleming coordinated with the Pennsylvania Department of Environmental Protection and the New Jersey Department of Environmental Protection (NJDEP) to prepare a sediment sampling and analysis plan (SSAP). The SSAP received approval from the NJDEP Office of Dredging and Sediment Technology and satisfied the regulatory requirements for disposing of dredge material.

A barge supported the drilling equipment to locate and obtain sample cores. Samples were photographed, logged, and prepared for laboratory analysis according to the approved SSAP. Gannett Fleming prepared a sediment sampling and analysis report summarizing the analytical results to support dredge material disposal and project permitting.

Concurrent with the sediment sampling, Gannett Fleming environmental scientists conducted a wetland delineation around the work area. The discovery of wetlands would have necessitated additional avoidance measures or possibly changed permit authorizations. The fieldwork confirmed the absence of wetlands, allowing federal and state coordination and permitting to proceed on schedule.

Gannett Fleming coordinated with the Pennsylvania Natural Heritage Program to comply with the Pennsylvania Conservation Explorer and Pennsylvania Natural Diversity Inventory (PNDI) environmental review process. The project’s PNDI identified potential conflicts with species of concern, including bald eagles, marsh wrens, turtles, and protected plant species. Gannett Fleming coordinated with the Pennsylvania Game Commission to minimize impact in each case.

When the project area was identified as being within proximity of a known bald eagle nest, Gannett Fleming completed a bald eagle screening with supporting mapping and concluded that the dredging project would not affect the eagle’s nesting activities based on the project’s distance from the nest and landscape buffers. While not protected under the Endangered Species Act, bald eagles are federally protected under the Bald and Golden Eagle Protection Act.

Key Features

202,000 cubic yards of sediment dredged from the basin’s bottom.
Dredged material was transferred by pipe to barges for transporting downstream to a confined disposal facility in New Jersey.
Threatened and endangered species coordination and impact mitigation.

Outcomes

The raw water basin was restored to its designed capacity, supporting a reliable water supply for Philadelphia area residents.
Careful consideration for endangered and threatened species supports their continued survival.