by Frank Kneib
The Maryland Intercounty Connector (ICC) project has finally become a reality. Approved in May 2006, the project began in the fall of 2007 and is expected to be completed in 2010. Since the project's early beginnings nearly 50 years ago, environmental groups and local homeowners have been concerned about the environmental impact of the project. Approval was given only after Maryland agreed upon mitigations for the environmental, economic, and community requirements.
The six–lane, 18–mile toll highway will cut through park land and residential communities between the Interstate 270 and Interstate 95 corridors across Montgomery and Prince George's counties, claiming nearly 60 homes in its path. The estimated cost is $2.4 billion and could rise to $3 billion with financing costs, making it the most expensive new highway project in the region, and one of the most expensive in the nation.
The ICC will link existing and proposed development areas between the I–270/I–370 and I–95/US1 corridors with a multimodal east–west highway, limiting access and accommodating an efficient route for the movement of passengers and goods.
Within each of the major watersheds in the approximated 4,300 acres, state–of–the–art stormwater controls and stormwater management sites are in place to ensure Best Management Practices (BMPs) and prevent stormwater pollution. There are 21 special project sites, totaling 620 acres, designed to improve water quality, protect brown trout, and safeguard other environmentally sensitive elements in the Upper Paint Branch watershed.
Impaired Watershed Requirements
The Chesapeake Bay is a 303(d) listed impaired watershed for nutrients and sediment. The Maryland Department of the Environment (MDE) has set an NTU discharge limit of a 50 NTU monthly average, and a 150 NTU daily maximum for this project. Due to these requirements and the fact that red clay materials are located along much of the project's path, it was expected that standard BMPs for erosion control and sediment control (such as silt fences and sediment bags) would not be sufficient to meet these requirements.
After presenting to the Inter–Agency Working Group (IAWG), a team from Rain for Rent, along with the providers of StormKlear Water Treatment, laid out a solution to meet the specific needs of the stormwater treatment for this project.
Treatment System
Rain for Rent designed a 50 to 200 gpm system with a Tube Settler using a StormKlear chitosan injection as the first means of settling. Chitosan, an approved polymer made from crab shells, naturally neutralizes the negative surface charge of the dirt particles, causing them to settle. After the chitosan injection, the sediment flocculates and the water filters through a sand media and bag system.
Because the ICC project is directed through a wetlands area, pollution prevention was a major concern and the stormwater pollution prevention plan was highly scrutinized. Turbidity requirements averaging a 50 NTU discharge rating were imposed, while allowing for out–of–compliance events to occasionally spike to 150 NTU. Each step of the filtration process was critical and enabled the project to stay in compliance with the turbidity requirements of the MDE.
Treatment Process
ICC stormwater runoff was stored in ponds prior to treatment. Pumps moved the water from the ponds to the tube settler where the chitosan was injected. This process ensured that the water quality parameters were met and allowed for higher flow rates. Consequently, higher flow rates ensured that no off–specification water left the site, even during rain events.
The tube settler works in conjunction with pumps and other filtration equipment. The fluid stream is pumped from the pond using a 4–inch DV100 Power Prime™ pump. During the pumping operation, StormKlear chitosan is introduced into the fluid stream, which starts the process of treating the water. The treated water enters the tube settler where it flows through a tortuous path designed to slow the fluid down and to allow more time for flocculation to occur, sending particulates down into a sump area where they can be easily removed.
After the settling process, the cleaned water is pumped into a 36–3 Sand Media Filter, which removes remaining suspended solids from the fluid stream to an approximate level of 20 to 25 microns.
The final step is to polish the water so that it meets the accepted turbidity level for the specific project. This is done using bag and, if needed, particulate filters to remove the remaining suspended solids down to as low as 0.5 micron. Finer submicron filtration is also available if needed.
After the filtration process, the clean water is discharged into a channel that drains into the creek. This water is tested every 30 minutes to ensure the turbidity levels stay well below the required levels.
Going Forward
Rain for Rent has been asked by the contractor to build additional mobile treatment trailers based on the growth of the project. With multiple locations requiring treatment, system mobility is crucial. These mobile trailers allow the customer to meet their turbidity requirements while at the same time working safely within the designated highway project areas.
About the Author
Frank Kneib has been managing the StormKlear stormwater business for HaloSource Inc. since 2007 and is a Certified Erosion & Sediment Control Lead with Washington State.
