Drain Guards: How to Protect Storm Drains and Catch Basins

Quick Answer

A drain guard is a filter insert that hangs inside a catch basin under the grate. Stormwater keeps flowing into the drain while sediment, debris and oil get caught before they reach the storm sewer. For a standard parking lot grate, an Oil & Sediment drain guard is the usual pick. For big inlets, go to the 60" x 60" high capacity model. On a muddy construction site with little oil, a reusable model holds more sediment. If you lift the grate often, an adjustable frame model stays put. Inspect it after every significant rain and empty or replace it before it fills up.

How a drain guard works

The guard drops into the catch basin and the grate pinches it in place. Water passes through the filter fabric, and the fabric holds back silt, trash and leaves. Oil & Sediment models use a needle punched geotextile that also soaks up oil.

UltraTech rates a new Oil & Sediment drain guard at 90 gpm per square foot through the fabric. Built in overflow ports raise that to 770 gpm in a hard rain so the street or lot doesn't pond. Water that goes through the overflow is untreated, which is why a clean guard matters.

Storm drains usually run straight to a creek or river with no treatment. EPA calls inlet protection "often the last opportunity" to treat stormwater before it leaves a site, so drain guards show up in a lot of stormwater pollution prevention plans.

Drain guard types

Oil & Sediment drain guards

The workhorse. Use the 48" x 36" single, Part #9217, the Oil & Sediment Model, Part #9219, or the 10 Pack, Part #9218 when you're covering a whole site. Leftover skirt above the grate can stay on as a pre filter, or trim it with heavy duty scissors or a utility knife.

High Capacity 60" x 60"

The High Capacity Oil & Sediment Model, Part #9393 covers inlets up to 54" x 54". Its lifting straps hold up to 300 lbs; heavier loads may need a backhoe or forklift to pull.

Reusable drain guards

When the problem is mud, not oil, the Reusable Model, 24" x 48", Part #9342 holds up to 500 lbs and gets emptied and put back. The Curb Style, 24" x 36", Part #9330 fits curb inlets. Rebar can go in the removal flap pockets and stay there to keep it secure. The tradeoff: the polypropylene fabric doesn't absorb oil.

Adjustable frame and round models

Standard guards rely on the grate to pinch the fabric, so they can shift when the grate comes off. The Adjustable Frame Model, Part #8930 comes with its own frame and stays in place with the grate lifted. The fabric attaches with hook and loop, so you swap in replacement fabric, Part #8932 instead of buying a new unit. For round inlets, see the round adjustable frame in 22" to 25", Part #8920 and 25" to 29", Part #8921.

Installing a drain guard

1. Lift the grate. It's the hardest part of the job, and a second set of hands helps.
2. Drop the guard into the basin and lay the skirt over the rim.
3. Set the grate back down so it pinches the skirt.
4. Fish the four lifting straps up through the grate. To pull the guard later, run rebar, a steel rod or a shovel handle through the straps and lift the guard out with the grate.

Want the guard to stay at street level when the grate is off? Add retainers: 22" to 36" basins, Part #9237 or 36" to 62", Part #9238. They won't work on basins outside those ranges, on ledges on only two sides, or under grates with a big support rib underneath.

Maintenance: inspect, empty, replace

• Inspect after each significant rain. How long a guard lasts depends on rainfall and how dirty the runoff is. UltraTech's test units in Seattle and Florida were still working after more than a year.
• Empty out sand, silt and sediment and reuse the guard. EPA's inlet protection guidance says to remove sediment once capacity is down by about half.
• Replace a guard that's saturated with oil, gas or other hydrocarbons instead of reusing it.
• Replace torn fabric right away.
• Keep spares on hand so a full guard gets swapped the same day.

Curb inlets and gutters

Drain guards go under a grate. For an open curb face, use a Curb Guard Plus or Gutter Guard Plus instead. Our storm drain filter guide covers every inlet type and which media catches which pollutant.

Get a drain guard quote

Send us your grate size (inside dimensions of the catch basin opening), how many drains, and whether you're catching sediment only or oil too. We'll match the right model and quote shipping. Stormwater items are usually in stock and arrive in about 7 to 10 business days. Email orders@industrialandsafetysupply.com or use the button below.

Request a Drain Guard Quote

Frequently Asked Questions

What size drain guard do I need?

Measure the catch basin opening under the grate. The standard 48" x 36" Oil & Sediment guard fits drains up to 30" x 40". The 60" x 60" High Capacity model fits drains up to 54" x 54". Round inlets use the round adjustable frame sizes.

How often should a drain guard be replaced?

Inspect after each significant rain. Empty and reuse it when it's full of sediment. Replace it when it's saturated with oil or the fabric tears.

Will a drain guard cause flooding?

Oil & Sediment guards have overflow ports that pass up to 770 gpm in heavy rain. A badly clogged guard can still back water up, so keep it clean.

Can drain guards be reused?

Yes, in most cases. Empty out the sediment and put it back. Units saturated with oil, gas or other hydrocarbons should be replaced.

What's the difference between Oil & Sediment and reusable drain guards?

Oil & Sediment guards use a geotextile that catches sediment and absorbs oil. Reusable guards use polypropylene that holds more sediment (up to 500 lbs) but doesn't absorb oil.

Related guides

• Storm Drain Filters: How to Choose the Right One for Your Inlet
• Spill Containment Berms: Foam Wall vs Collapsible vs Drive Through vs Hard Wall