Thomas J. Halliwell, PE, LEED-AP is Principal at Grist.​  He has over 17 years of experience in civil engineering, site development, and green infrastructure design.

​Halliwell previously worked for over eight years as an embedded consultant within the Philadelphia Water Department (PWD) Green Stormwater Infrastructure (GSI) Implementation Unit, Office of Watersheds, and Planning & Research Unit.

​Before consulting in these roles for PWD, Halliwell designed sustainable site/civil projects for commercial, residential, and institutional developments. Innovative stormwater management featuring various applications of GSI and Low Impact Development (LID) techniques to manage stormwater discharge rate, volume, and quality were integral parts of these designs.

Halliwell has also completed detailed hydrologic studies of watersheds, and detailed hydraulic studies of storm sewer networks and open channels, and has completed flow and water quality monitoring studies of individual sites and designed urban stormwater retrofit systems. 

Grist’s design philosophy is rooted in environmental sustainability, and where necessary, environmental restoration. We believe in protecting, restoring, and enhancing the built environment by making the site's proposed hydrologic characteristics match the site's natural hydrologic cycle as closely as possible. We insist that projects improve both the surrounding natural and built environments.

Grist is a green infrastructure studio dedicated to providing environmentally sustainable and restorative engineering designs. We focus on projects where green design is important to the client and is a driving force for the project. Because of our small size, we can provide these services at a low cost to the client while maintaining exceptional focus and quality.

About Grist

​Vision Statement


CALL US:  (267) 332-8282