Hydrocarbons are organic chemical compounds composed exclusively of hydrogen and carbon atoms. In the context of stormwater management, hydrocarbons are a major class of organic pollutants commonly found in runoff, originating primarily from petroleum-based substances such as fuels, oils, greases, and asphalt-derived materials.
Hydrocarbons can exist in many forms, ranging from light, volatile compounds such as gasoline constituents to heavier, more persistent compounds such as motor oil and asphalt binders. They are often categorized into groups such as aliphatic hydrocarbons, which include straight or branched chains, and aromatic hydrocarbons, which include ring-shaped structures such as polycyclic aromatic hydrocarbons (PAHs). Many aromatic hydrocarbons, especially PAHs, are of particular concern due to their toxicity, persistence, and potential carcinogenic properties.
In stormwater systems, hydrocarbons are typically introduced through urban and transportation-related activities. Common sources include vehicle leaks and exhaust residues, tire and brake wear, fueling operations, industrial activities, and atmospheric deposition. During rainfall events, these substances accumulate on impervious surfaces like roads and parking lots and are then washed off into drainage systems, where they may be transported to receiving waters.
Hydrocarbons in stormwater may be present in dissolved form, but more often they are associated with suspended solids, adhering to sediment particles. This association influences their transport, deposition, and treatment, as they can settle in catch basins, detention ponds, or sediment traps. However, finer particles carrying hydrocarbons may remain suspended and be conveyed downstream.
From an environmental perspective, hydrocarbons can have significant impacts on aquatic systems. They can create surface films that reduce oxygen exchange, impair aquatic life, and contaminate sediments. Certain hydrocarbons are toxic to fish and invertebrates and may bioaccumulate within the food web. In addition, they can degrade water quality and affect the suitability of water bodies for recreational or ecological use.
Stormwater best management practices (BMPs) aimed at controlling hydrocarbons typically focus on source control, sedimentation, filtration, and adsorption. Practices such as oil-water separators, vegetated swales, bioretention systems, and constructed wetlands can help remove or break down hydrocarbons through physical, chemical, and biological processes.
Hydrocarbons are carbon and hydrogen-based compounds commonly introduced into stormwater from human activities, and they represent a significant class of pollutants that influence water quality, sediment contamination, and ecological health in drainage systems.