HEAVY VEHICLE MAINTENANCE FACILITY
An Engineering Excellence Award-Winning Project

S&ME challenged the imagination by selecting a technology, normally used in far different situations, to successfully meet significant and unusual challenges for this project. As far as we know, this is an original application, an engineering solution never before used to meet such site circumstances.

S&ME was contracted by Charlotte-Mecklenburg (County) Storm Water Services to design a best management (BMP) facility to control rinse water and storm water run-off for water quality improvement. The site, called the Central Yard, is a municipal vehicle-maintenance and parking complex with a washpad designed for the removal of collected debris and rinsing of sanitation-collection and vacuum trucks, and street-sweepers. To successfully meet the challenges of the site, S&ME's efforts virtually spanned its major service areas.

In evaluating site conditions for the BMP system, S&ME found serious space limitations at the site. Traditional stormwater BMPs for the potential pollutants of concern are area dependant, and the local sewer utility would not accept the stormwater run-off. Further, the feasible location for a BMP system was within an existing parking area. Space was a major system-design consideration.

S&ME designed a primary and a secondary stormwater treatment system to meet the extraordinary conditions. The primary treatment system was a pre-manufactured storm water BMP structure to handle all run-off from the facility to remove total suspended solids and greases. S&ME developed and designed a site-specific subsurface wetland storm water BMP structure to serve as secondary, "first flush" stormwater treatment. 

Normally, for such a facility, the typical solution would be to design subsurface stormwater detention. However, here, storm sewers and water lines ran throughout the site. There was also heavy truck traffic and parking for large vehicles to contend with. The client did not want to operate a wastewater plant, and we lacked the space typically required for a wetland treatment system that might have served in more conventional site conditions.

S&ME looked at an existing steep and eroding slope within the facility and fashioned a design to utilize this otherwise useless feature for the owner's benefit. We used gabions to do this. Typically, gabions are used along stream banks to stabilize side slopes and for retaining walls. Our design incorporated a gabion-reinforced slope technique, stair stepping down the slope to provide a foundation for a geosynthetic liner system. The system provides stormwater detention and treatment filtering cells for the "first flush" of stormwater from the facility. The constructed BMP system provides treatment for a wide range of stormwater pollutants of concern including the most major one in this project, fecal coliform. 

This original design represents a breakthrough in engineering practice. The project provides a landmark case history that spurs the evolution of urban-retrofit stormwater best-management practices for surface-water quality improvement.

S&ME professionals were deeply involved in gaining necessary approvals for the project. For example, the senior project manager for the city's Engineering and Property Management department wrote:

"S&ME did an excellent job of overseeing the process of evaluating the wishes and requirements of each city department [involved] while balancing the cost with the need. S&ME was instrumental in obtaining a key signoff from the utility department and in helping them understand the need for the project."