A catch basin retrofit fits Smart Sponge® media inside existing structures to add measurable pollutant reduction for metals, bacteria, TSS, and more — no pumps, power, or excavation required.
A catch basin retrofit stormwater treatment approach fits Smart Sponge® media directly inside an existing catch basin, converting it from a collection point into a treatment point. For MS4 and NPDES permit holders, this means adding measurable pollutant reduction without excavation, pumps, or power — using the sump volume that is already there.
What Does a Catch Basin Retrofit Actually Involve?
A standard catch basin is a below-grade box with a sump that settles coarse sediment and traps floating debris before water exits to the downstream conveyance system. That sump geometry captures gross solids, but dissolved and emulsified pollutants — oil sheen, dissolved metals, phosphorus, bacteria, and PFAS — pass through with the water column and reach outfalls unimpeded. A catch basin retrofit closes that gap by placing treatment media directly inside the sump volume that already exists, so the structure itself becomes the treatment point rather than just a collection point. Abtech's stormwater pit and catch basin filtration guidance covers this distinction in more detail: collection without media inside simply moves pollutants downstream instead of removing them.
The Ultra-Urban® Filter is the drop-in insert Abtech Industries supplies for this purpose. It is sized to the specific basin geometry, loaded with Smart Sponge® media, and installed without structural modification. Because the insert sits inside the sump that already exists, a retrofit generally does not require the excavation or civil construction that a new vault or structural BMP would demand.
Why Retrofit the Catch Basin Instead of Adding a Vault?
Municipalities, departments of transportation, and airports operating under MS4 and NPDES permits are required to demonstrate measurable pollutant reduction from paved catchments — inspectors expect documented evidence, not general maintenance logs. The catch basin's sump is central to that compliance story because it is where passive filtration media can be deployed at scale, treating hydrocarbons, dissolved metals, nutrients, TSS, and PFAS before discharge reaches receiving waters. Abtech's drop inlet vs catch basin stormwater treatment guide explains why a shallow drop inlet offers limited treatment opportunity in-structure, while a catch basin's deeper sump accommodates a filter insert without obstructing flow.
Retrofitting an existing catch basin before adding a new vault or structural device also keeps the project inside the existing infrastructure footprint.
How Does Smart Sponge® HM Handle Metals and Nutrient Loading?
Metal recycling yards, metal fabrication shops, and junk yard facilities concentrate zinc, copper, aluminum, iron, and lead in runoff from outdoor process areas — the same profile NPDES benchmark monitoring tracks in digested total-metals samples under sector-specific industrial permits. Smart Sponge® HM media is engineered to target heavy metals including lead, mercury, arsenic, chromium, zinc, and copper. Municipal stormwater and wastewater programs managing phosphorus-driven nutrient loading face a related but separate problem, and nutrient-focused media formulations can be selected alongside Smart Sponge® HM within the same treatment train rather than requiring a separate device for each pollutant.
Where Does Bacteria Fit Into a Catch Basin Retrofit?
Bacteria are among the hardest stormwater pollutants to control because a microbe cannot be screened out of the water the way trash or sediment can. Fecal coliform and E. coli are the standard indicator organisms for fresh water, and enterococci are used for marine and coastal water; when those indicators run high, discharge is treated as a health risk. Smart Sponge® Plus media targets E. coli and coliform bacteria and can be added to a catch basin retrofit where discharge reaches sensitive waters, such as beaches or recreational waterways covered under an MS4 permit.
How Does a Retrofit Address Trash, Debris, and TSS Together With Dissolved Pollutants?
A retrofit that only addresses gross solids leaves the dissolved fraction — metals, hydrocarbons, PFAS — moving straight through the sump and out to the outfall. Because the Ultra-Urban® Filter captures debris and floatables at the point of entry while Smart Sponge® media treats the water column passing through, a single insert can close both gaps in the same structure. High-porosity Smart Sponge® media captures suspended solids and particulates while maintaining flow, addressing sediment and TSS alongside contaminant-specific formulations for metals, hydrocarbons, nutrients, and bacteria — all within one retrofit rather than a device per pollutant.
Frequently Asked Questions
- Does a catch basin retrofit require excavation? — No. The Ultra-Urban® Filter is a drop-in insert sized to fit inside an existing catch basin without excavation or structural modification.
- Can one retrofit handle multiple contaminants? — Yes. Because different catchments present different pollutant mixes, Smart Sponge® media formulations — including HM for metals and Plus for bacteria — can be selected and combined within a single insert to address multiple treatment objectives at once.
- Does a catch basin retrofit guarantee MS4 or NPDES compliance? — A retrofit supports measurable pollutant reduction toward permit targets; it does not by itself guarantee that a site will pass every benchmark or permit condition, which depends on the full site and monitoring program.
- How do I know which Smart Sponge® media formulation fits my site? — Abtech's team starts with the site: evaluating conditions, reviewing the contaminant list, and determining whether testing or a pilot program is needed before recommending media.
- Will the retrofit slow down flow during a storm event?
Retrofit planning starts with site conditions and a contaminant list rather than a hardware choice. Readers evaluating a catch basin retrofit for an MS4, NPDES, or marina permit can schedule a site assessment to have Abtech's team review conditions and determine whether testing or a pilot program is warranted.