The redevelopment of downtown Rockville, Maryland has been a long-term economic goal of the city, which is the second largest in Maryland after Baltimore. Montgomery County, the State of Maryland, a private development company, and the city, are jointly funding the reconstruction of the infrastructure of the Town Center, which includes roads, sidewalks, storm drains and utilities.

Covering 10 acres, the purpose of the redevelopment is to create a town atmosphere that will attract commercial and residential development to the new Town Center.

As part of the city's stormwater management program to control nonpoint source runoff, this redevelopment project required water quality controls that were both effective and economical. After an extensive review of options, the Stormceptor® System was selected by the civil engineering designer and the city.

The civil engineering design firm for the project is Macris, Hendricks and Glascock of Gaithersburg, Maryland; they chose the system due to its design and construction flexibility in a retrofit application. Robert H. Goodin, Director of Rockville's Public Works Department said: "The system will provide effective water quality control for stormwater runoff, the flexibility to minimize impacts to the existing roads and utilities and a low cost alternative for stormwater quality management."

The project required three - Stormceptor 1800 US Gallon units (Model STC 1800). The STC 1800 unit is a pre-engineered, precast concrete manhole separator manufactured by CSR - Hydro Conduit.

The general contractor for the project is Donohoe Construction of Bethesda, Maryland and the utility subcontractor is Busy Ditch of Gaithersburg, Maryland. Larry McIntyre, field supervisor of Busy Ditch said: Installation was smooth and fast. It took only 4 hours to install and connect up. There was minimal impact to traffic or the surrounding utilities."

Stormceptor is a patented pollution prevention technology that removes oil and sediment from stormwater runoff, and holds them for safe and easy removal. It will not release trapped pollutants between servicing, even during periods of peak water flow. Designed to replace more costly and less efficient conventional water quality inlets, and fully tested by Environment Canada's National Water Research Institute, Stormceptor is installed as part of the storm drain system, does not require the use of valuable real estate, and is both easy and inexpensive to maintain.

The equipment is utilized in place of conventional manhole structures in the stormsewer system, reducing the overall cost of stormwater management for new developments and facilitating stormwater quality control retrofits for existing developments. Manufactured from easily assembled concrete components that are pre-engineered for traffic loading, it can be installed in residential, commercial, industrial, and road projects.

Under normal design flow operating conditions, which represent approximately 85% of the annual runoff volume, stormwater flows into the upper pre-engineered diversion chamber, is diverted by a V-shaped weir down a drop pipe, and into the lower separation chamber. This downward flow is directed horizontally, by right angle fittings, around the circular walls of the chamber towards the outlet pipe.

Above and below this flow zone, oil, sediment, and other pollutants accumulate in relative quiescence. Up to 80% of the inflowing fines and course sediment load settle permanently to the floor of the chamber, while the petroleum products and volatile vapors rise into the air tight storage area above. Outflows contain less than 10 mg/litre of oil.

During high flow conditions such as intense storms, stormwater flows over the inlet weir and across the upper diversion chamber into the downstream sewer. Water which overflows the weir creates a backwater effect in the outlet pipe from the treatment chamber, ensuring that excessive flow will not enter the lower treatment chamber which would otherwise scour and resuspend the settled sediment and the stored petroleum. During high flows, bedload sediment continues to hit the weir and collect in the lower treatment chamber where it remains, with any residual petroleum products, for yearly removal.