Stormwater system upgrades that take place during rail yard and transportation facility improvement projects have many complex components, from permitting to environmental issues. Sewer or water line replacements are frequently associated with new rail and transportation facilities.
Open cuts and dewatering activities can lead to unexpected compliance challenges. Proactively managing erosion and sedimentation issues is critical to prevent water quality problems and keep project compliance on track. Best management practices (BMPs), deployed and maintained on project sites throughout construction, can help meet project challenges and ensure that projects proceed on schedule and on budget.
Erosion and Sediment Issues
There are many project-specific considerations when upgrading an outdated storm sewer system, from the sewer’s current condition to its proximity to protected natural resources and sensitive species. Older brick sewers may be extensively damaged—with entire sections broken, collapsed, or clogged with sand and roots. Further challenges can result when sewer lines are located at or below a near surface groundwater table, which can result in a constant inflow of groundwater and sand through leaks and broken areas.
One potential solution, which TRC successfully used for a recent project in Indiana, is to clean out the existing brick sewer and installing a new line by slip-lining with a horizontal directional drill, in lieu of traditional trench installation methods. In many places for this project, attempts to slip-line were unsuccessful due to the brick sewer’s extremely poor conditions. Adding complication, the sewer ran through a nature preserve, which needed to be protected from all impact. To avoid causing extensive collapse of the brick sewer or damage to equipment, the decision was made to install more than 1,500 feet of the sewer through the preserve using open-cut methods. Because of the unexpected need to trench through the preserve, strict attention was given to preventing erosion and sedimentation issues. This proved invaluable, since extremely rainy weather complicated the work.
Erosion and sedimentation control BMPs can prevent runoff violations, especially if they are well-managed and meet site-specific conditions. Unstabilized soils are frequently displaced during heavy rains, and will travel along eroded pathways. Silt fence and other routinely used measures can be compromised. If a silt fence is located in an area with unexpected concentrated flow, the fabric will be undermined. If this is noticed, it’s important to repair the fence, divert the flow, and to install erosion control measures (such as seeding and matting) to stop the soil loss in the first place. It should be noted that any silt fence installed in an area where concentrated flow is a recurring problem means that the silt fence is the wrong BMP.
For our Indiana project, additional silt fence was installed, and dewatering stations were utilized in multiple locations. The dewatering systems focused on the use of geotextile fabric bags that filtered sediment, placed within lined settlement basins. The basins were situated in IDNR approved upland areas. The integrity of the dewatering bags and basins were checked frequently. As an added precaution to protect water quality at the preserve, a TRC senior ecologist routinely visited the trenching area to check the condition of dewatering stations, especially during or after rain events.
Challenges arise at most construction sites, especially if a series of strong rainstorms sweep through over several days, and if an unexpected need for dewatering occurs. During the spring and early summer, this almost always happens. Preparation in advance is important, as is having materials and supplies on hand. Keep in mind that state-specific materials may be needed. The use of straw bales is prohibited in some states for ditch check applications, but would be satisfactory for use in a settling basin (lined with geotextile fabric) for dewatering use. Additionally, the construction team must be aware of all likely pathways that excess water will follow. They should always be aware if sensitive resources are present in the vicinity, including high quality wetlands, waterways, and threatened or endangered species.
BMPs, deployed and maintained throughout various stages of construction can help meet project challenges, and will prevent non-compliance issues. The proactive TRC team provided construction and ecological oversight, preventing runoff issues during this challenging construction project through the preserve.