x Gross Solids

Snout Inlet Device (click to enlarge)

Gross solids are  trash, litter, debris, and coarse sediments that are conveyed by stormwater runoff or otherwise captured by stormwater systems.  Stormwater Maintenance, LLC (SWM) is involved in numerous monitoring and maintenance activities that involve gross solids.  These activities range from informal data collection based on routine inspections to maintaining best management practices (BMPs) that are intended to remove this specific type of pollutant.

Depending on the land use, most property owners have always been concerned about gross solids due to the negative visual aspects of having litter and trash on their sites.  However, once the solids enter the stormwater system they are usually out of sight and ignored.  Public areas, such as streets and highways often have very high pollutant loadings of gross solids due to littering.  Increased attention is being paid to these pollutants due to the implementation of Total Maximum Daily Load (TMDL) limits in some major municipalities.  Both the Baltimore Harbor and the Anacostia River Watershed (involving several jurisdictions) have TMDLs established or pending for trash.

Baltimore Harbor – Jones Falls Skimmer (click to enlarge)

With raised awareness on gross solids, the need for methods to remove these pollutants from the stormwater flow has increased.  These methods range from small inlet-based practices that capture the solids very close to the source to large netting systems and mechanically operated devices intended to treat flows from larger watersheds.

The topic has also raised the awareness of those in the academic and research communities.  The Center for Watershed Protection has ongoing research work on the topic.  The American Society of Civil Engineers has also issued guidance on monitoring gross solids that includes members of academia.

Methods for maintaining trash removal practices range from cleaning out normal catch basins by hand to removal of netting systems and the cleanout of structures with specialized equipment such as vac trucks.  One of the challenges of some of the TMDL requirements is the mandate to quantify the pollutant captured and removed by individual pollutant type.  This requires the separation of bottles, cans, paper, organic debris, etc. and is extraordinarily expensive, sometimes doubling the cost of maintenance.  Hopefully, feedback from those paying for maintenance to the regulatory bodies will eventually resolve this issue.

Fresh Creeks Trash Net System (click to enlarge)

SWM will continue to increase our involvement with gross solids as more structures are installed that require maintenance.  Click here to check out one of our gross solids maintenance projects on a tributary to the Anacostia River in the District of Columbia.