The Virginia Department of Transportation (VDOT)implements a number of different best management practices to meet pollutant load reductions associated with the Chesapeake Bay Total Maximum Daily Load(TMDL) Program. Although commonly implemented best management practices include structural practices such as bioretention filters and extended detention ponds, pollutant load reductions can also be met by reporting information on certain maintenance activities such as storm drain and pipe clean-outs. Storm drain and pipe clean-outs achieve pollutant load reductions by removing pollutant-containing material that has accumulated in the storm sewer system before it can be transported into the Chesapeake Bay or other regulated waters.
In order to claim pollutant load reductions associated with this work, certain information needs to be provided to support these claims. This information includes the mass of material removed from storm drains located in regulated areas, termed “municipal separate storm sewer system (MS4) service areas”; any default values used to calculate pollutant load reductions and how these values were developed; and a standard operating procedure documenting the processes used to collect and report this information.
The purpose of this study was to evaluate VDOT’s current practices for conducting these clean-outs, including a review of the contracts established with contracted clean-out crews and the landfills where this material is disposed. The scope of this study was limited to VDOT’s Richmond District; however, the findings and recommendations can be readily applied statewide.
The observations made during this study identified a number of key factors in VDOT’s current practices that require modification in order to report accurate pollutant load reductions provided by these clean-outs. This included noting when material is removed from specific storm drains during clean-outs and adding the MS4 service area to the geographic database used to schedule and report these activities. A recommendation was made that the VDOT consider increasing the comprehensiveness of its inventory of storm drains across the state since the current inventory is limited to storm drains located on interstate highways.
By use of the current inventory of storm drains and pipes in the Richmond District’s MS4 service area and default nutrient enrichment factors developed by the Chesapeake Stormwater Network and other default values from the literature, the pollutant load reductions provided by VDOT clean-outs were estimated assuming annual clean-out of each asset. The load reduction estimates were416 lb/yr, 2,626 lb/yr, and 168,241 lb/yr for total phosphorus, total nitrogen, and total suspended solids, respectively. Because of the purchase price of an equivalent amount of nutrient credits in the James River Watershed, these load reductions could represent a significant cost savings, from $4 million to $5 million per year for total phosphorus alone. Since these clean-outs are already being conducted as part of routine VDOT maintenance, the cost savings would be realized without additional work by VDOT operators or contractors in the field