Oil, grease, and fuel are among the most common pollutants in urban stormwater. Every parking lot, roadway, fueling station, and equipment yard sheds a thin film of petroleum, and rain carries it straight into catch basins and then into creeks, harbors, and the waters communities depend on. For the agencies and operators who hold stormwater permits, hydrocarbons are also one of the hardest pollutants to keep out of a discharge sample.
This guide covers where stormwater hydrocarbons come from, why regulators track them, the main ways to treat them, and what to look for when you choose a filter.
Where hydrocarbons in stormwater come from
Hydrocarbons reach the storm drain from dozens of small, continuous sources rather than one big spill. The usual contributors are:
- Vehicle drips: motor oil, transmission and hydraulic fluid, and grease from parking lots, roads, and fleet yards
- Tire and asphalt wear that grinds petroleum compounds into road dust
- Atmospheric deposition from exhaust and combustion that settles onto paved surfaces between storms
- Fueling operations at gas stations, truck stops, transit depots, and marina docks
- Industrial and equipment yards, wash-down areas, and material handling zones
- Airports, where jet fuel, deicing operations, and ground equipment concentrate hydrocarbon loads
Once runoff hits the pavement, those hydrocarbons show up in two forms. Free-floating oil rises to the surface as a visible sheen. The harder fraction is emulsified and dissolved hydrocarbons, which bind to fine sediment and stay suspended in the water column. Any treatment that only skims the surface will miss that second fraction, and it is the fraction that most often shows up in a lab result.
Why hydrocarbons are a compliance problem
Hydrocarbons carry both a regulatory cost and an environmental one.
On the regulatory side, MS4 and NPDES permit holders are responsible for keeping discharges free of the pollutants that cause a sheen or push a receiving water past its quality standards. A visible sheen at an outfall can be enough to document a problem on its own. Industrial sites carry a heavier monitoring burden. Under the EPA Multi-Sector General Permit and the state industrial general permits that mirror it, many facilities sample their stormwater for oil and grease and total petroleum hydrocarbons (TPH). California's Industrial General Permit, for example, sets annual and instantaneous action levels for oil and grease, and an exceedance triggers a corrective-action process that costs staff time and money to work through. Where a receiving water is already impaired, a TMDL can layer on stricter limits still.
On the environmental side, the polycyclic aromatic hydrocarbons (PAHs) in petroleum are toxic to aquatic life at low concentrations, accumulate in sediment, and move up the food chain. A sheen also reduces oxygen exchange at the water surface. For a coastal or harbor operator, that same runoff threatens shellfish beds, swimming areas, and the permits that keep a marina open.
The takeaway for a stormwater program is that hydrocarbons need to be intercepted close to the source, before runoff leaves the site and a sample gets pulled.
Common ways to treat hydrocarbons in stormwater
There is no single right answer, and the best choice depends on flow, footprint, and how concentrated the hydrocarbon load is. The main options are:
- Oil and water separators (API and CPI units): Effective on concentrated, steady flows such as a maintenance building drain, but they carry a large footprint and need regular pumping and upkeep. They are less suited to the flashy, intermittent flows of open-site stormwater.
- Hydrodynamic separators: Vortex units that spin out sediment and capture floatables and some free oil. They do little for the emulsified fraction and need vacuum maintenance.
- Sorbent booms, socks, and pillows: Passive products that soak up free-floating oil and sheen. They are inexpensive and easy to deploy, though many reach capacity quickly and can release captured oil if they are overloaded.
- Media filtration at the catch basin: Drop-in inserts and booms that filter runoff through an engineered sorbent as it enters the drain. This treats hydrocarbons at the source, fits existing infrastructure, and handles both the free and emulsified fractions when the media is designed for it.
For most municipal, DOT, airport, and commercial sites, treating at the catch basin gives the best balance of performance, footprint, and cost, which is why sorbent media filtration has become the workhorse of hydrocarbon control.
How sorbent media filtration works at the catch basin
Catch basin media filtration puts the treatment where the pollution enters the system. Runoff passes through a sorbent media held in an insert or boom, the media binds the hydrocarbons, and the treated water continues into the drain. A high-flow design lets clean water pass during a heavy storm and bypasses excess flow so the basin never floods.
Abtech's Smart Sponge media is built for this job. It is an oil-attracting polymer that pulls free and emulsified hydrocarbons out of the water on contact and locks them into a stable, non-leaching solid, so captured oil stays captured even under high flow and does not wring back out. The same media is engineered to handle the mix of pollutants that travels with oil in real runoff, from sediment and metals to bacteria, which is the full range of contaminants Smart Sponge treats. The binding chemistry that Abtech relies on in demanding industrial water applications carries directly into the lower concentrations found in stormwater.
In the field, that media is deployed as Ultra-Urban Filter inserts and booms, sized to the basin, as a passive system that needs no pumps or power. For the compliance-driven version of this setup, see how Abtech frames stormwater treatment for MS4 and NPDES compliance.
What to look for in a stormwater hydrocarbon filter
Not every insert or sorbent performs the same way. When you evaluate options for a site, weigh:
- Both fractions: Confirm the media captures emulsified and dissolved hydrocarbons, not only surface sheen. The dissolved fraction is what shows up in a TPH or oil and grease result.
- Non-leaching capture: The filter should hold hydrocarbons permanently under storm flow rather than release them once it loads up.
- Peak flow and bypass: Match the unit's treated flow rate to your basin and drainage area, with a bypass so a large storm cannot back up the system.
- Capacity and maintenance: Understand how much the media holds, how often it needs changing, and how the spent media is disposed of.
- Field and third-party data: Prioritize documented field performance in installations like yours, backed by real-world results.
- Permit fit: Make sure the solution maps to your specific driver, whether that is an MS4 program, an industrial permit, or a TMDL.
Field results
Hydrocarbon filtration earns its keep in the hardest environments. Airports concentrate fuel, oil, and deicing runoff across large paved catchments, and Abtech's inserts have been put to work on exactly that problem, as covered in Ultra-Urban Filters for airport stormwater. The same approach carries over to fueling docks, marinas, and harbors, where the priority is keeping fuel sheen and dock runoff out of the water, which is the focus of Abtech's coastal solutions.
Frequently asked questions
What removes hydrocarbons from stormwater?
Sorbent media filtration at the catch basin is the most common method for open-site stormwater. Runoff passes through an oil-attracting media in an insert or boom that binds the hydrocarbons and lets treated water continue into the drain. Oil and water separators and hydrodynamic separators are also used, usually on more concentrated or centralized flows.
What are hydrocarbons in stormwater runoff?
They are the petroleum compounds that wash off paved surfaces, including motor oil, grease, fuel, and the PAHs from tire and asphalt wear and vehicle exhaust. They appear both as free-floating oil that forms a surface sheen and as an emulsified fraction bound to fine sediment.
Do catch basin inserts remove oil and grease?
Yes, when the insert uses a media designed for hydrocarbons. A sorbent media insert captures free and emulsified oil as runoff enters the basin. Screen-only or sediment-only inserts will catch trash and coarse solids but do little for dissolved hydrocarbons.
How often does a stormwater oil filter need maintenance?
It depends on the hydrocarbon load, the surrounding land use, and rainfall. High-load sites such as fueling areas and busy parking structures need more frequent media changes than low-traffic sites. Build an inspection schedule around your wet season and adjust as you learn the site.
Match a hydrocarbon filter to your site
Hydrocarbons are a predictable, controllable part of any stormwater program once you treat them at the source. If you are working toward an MS4, NPDES, or industrial permit target, Abtech can help you size the right insert or boom for your basins and drainage area. Explore Abtech's stormwater solutions or get in touch to talk through your site.