How to Choose Storm Drain Inlet Protection: 4 Questions That Decide It (With EPA Rules and Real Prices)

The right storm drain inlet protection comes from three facts about the inlet, not from the catalog: whether the opening is a flat grate, a grate with a curb throat, or a curb opening alone; whether the runoff carries sediment, oil, or both; and how much water has to keep moving through the drain once the filter loads up. A flat grate on a construction site takes a reusable drain guard under the grate, UltraTech 9840 at $46.00 for a 24 inch by 24 inch basin, or a grate guard on top of it, UltraTech 9858 at $48.00 for a 36 inch by 36 inch grate. A grate at a loading dock or fuel island, where the pollutant is oil as much as dirt, takes an oil and sediment drain guard under the grate, UltraTech 9219 at $48.00, or a magnetic inlet guard on top, UltraTech 9163 at $99.00 for a curb-style basin. A curb opening with no grate takes a foam-wedged curb guard, UltraTech 9251 at $143.00 per 4 foot section. The four questions below take you from the inlet to the part number, with the federal rule quoted from 40 CFR 450.21 and 122.26, the inspection rules from EPA's fact sheet and two state standards, and every flow rate and capacity from UltraTech's spec sheets.

Does the EPA require storm drain inlet protection?

Not by that name, and not with a drawing. 40 CFR 450.21(a) tells a construction operator to "design, install and maintain effective erosion controls and sediment controls to minimize the discharge of pollutants," and paragraph (a)(5) narrows it to "minimize sediment discharges from the site." Inlet protection is the control that does that at the one point every paved site drains to. EPA's December 2021 fact sheet on storm drain inlet protection calls it the "last opportunity to provide treatment to stormwater prior to discharge," tells you to install it before any soil is disturbed in the drainage area, and caps the drainage area feeding one inlet at about 1 acre. The word "must" comes from the state permit: Minnesota's, as the MPCA stormwater manual summarizes it, requires every storm drain inlet to be protected throughout construction until every source draining to it is stabilized.

Who the rule reaches is set by 40 CFR 122.26. Paragraph (b)(15)(i) defines small construction activity as clearing, grading and excavating that results in land disturbance "of equal to or greater than one acre and less than five acres," and paragraph (b)(14)(x) covers five acres and up, plus any smaller lot inside a larger common plan of development. The same section reaches a working facility: paragraph (b)(14)(xi) lists SIC codes 4221 to 4225, public warehousing and storage, among the facilities whose stormwater discharge is "associated with industrial activity," and the exit is paragraph (g), which lets a facility certify "no exposure," defined as "all industrial materials and activities are protected by a storm resistant shelter." A yard with drums outside, a fuel island, or a dock where trucks and forklifts drip onto pavement that drains to a catch basin does not meet that definition, and that is the site a stormwater plan protects with a catch basin insert. For construction, 40 CFR 450.21(e)(3) also prohibits discharges of "fuels, oils, or other pollutants used in vehicle and equipment operation and maintenance" outright, which is why the oil-absorbing models in Question 2 exist.

Question 1: What kind of inlet are you protecting?

Walk to the drain and look at the opening, because the opening picks the product family before anything else does. A flat grate in a lot, yard or dock apron is a drop inlet. A grate with a vertical slot in the curb behind it is a combination inlet, and water enters through both. A slot in the curb with no grate is a curb inlet. A grate sitting in dirt before paving is a field inlet, and that one gets fabric and a frame around it rather than anything in it.

Wisconsin DNR Technical Standard 1060, the January 2022 standard WisDOT projects build to, sorts the choice the same way: fabric and frame before paving, then a bag inside the inlet (its Type D) once the lot is paved and the structure is deep enough, with a flat under-grate fabric (Type B) or a curb-style unit (Type C) as the fallback for shallow inlets. Its depth rules for a bag are specific: keep 3 inches of clearance between the bag and the inlet sides, cinch the bag in inlets less than 30 inches deep, and do not let it extend below the lowest outlet in an inlet with a sump. UltraTech's reusable drain guard bag is 36 inches deep per the manufacturer's product page, so measure the basin before you order one. The standard also rules rock bags, straw bales and stone weepers out for WisDOT work and for any inlet next to traffic, which is the answer to "can I just use sandbags."

A combination inlet needs the curb-style version of whichever family you pick, because a filter that covers the grate and leaves the throat open filters half the water. UltraTech builds curb-style versions of the reusable drain guard (9847, 9330, 9332), the grate guard (9859 to 9863) and the Inlet Guard Plus (9163 to 9165), with curb deflectors from 32 inches on the 24 inch by 24 inch units to 56 inches on the 24 inch by 48 inch units per the Warehouse Gear Hub listings. A curb inlet with no grate takes the Ultra-Curb Guard Plus, a 3 foot or 4 foot section of woven polypropylene with Filter-Tex absorbent and foam wedges that UltraTech's flyer says "wedge securely into the inlet"; sections connect to cover a longer throat. Measure the grate's outside length and width, and the throat length if there is one, before you look at prices. The Inlet Guard Plus cannot be trimmed, so it has to match the grate; the under-grate drain guards have a skirt you trim after the grate is set back down.

Inlet you have	Where the filter sits	UltraTech family we stock	Sizes on Warehouse Gear Hub	Price as listed
Flat grate (drop inlet), paved	Under the grate	Drain Guard: Oil and Sediment, Oil and Sediment Plus, Trash and Debris, Reusable	24 x 24 in to 60 x 60 in; 48 x 36 in is the standard Oil and Sediment size	$27.00 to $63.00 per unit for these four lines
Flat grate (drop inlet), paved	Over the grate	Grate Guard (sediment) or Inlet Guard Plus (oil and sediment, magnetic)	Grate Guard 36 x 36 in; Inlet Guard Plus 24 x 24, 24 x 36, 24 x 48 in	$48.00 to $81.00
Combination inlet (grate plus curb throat)	Under or over the grate, with a curb deflector	Curb-style Reusable Drain Guard, Grate Guard, or Inlet Guard Plus	18 x 30 in to 28 x 42 in, deflector 32 to 56 in	$69.00 to $144.00
Curb inlet (throat only, no grate)	Inside the throat, foam wedged	Ultra-Curb Guard Plus, modular	3 ft (9248) and 4 ft (9251) sections	$124.00 and $143.00

Question 2: Is the problem sediment, oil, or both?

The fabric decides this, and the two fabrics do different jobs. UltraTech's reusable drain guard and its grate guard are woven polypropylene built for dirt by the hundred pounds: the reusable bag "is capable of containing up to five hundred (500) pounds of silt, soil, and dirt," and the same page says it "won't capture hydrocarbons." That is the construction site product. The Oil and Sediment drain guards, the Inlet Guard Plus and the Curb Guard Plus use a nonwoven geotextile that UltraTech says "helps remove oil and other hydrocarbons," and the Plus models add Ultra-Filter-Tex absorbent strips. That is the dock, fuel island and maintenance yard product.

The oil numbers come from UltraTech's Ultra-Drain Guard page. The standard 48 inch by 36 inch Oil and Sediment unit, part 9217, absorbs "up to .87 gal (3.5 L)" of oil and holds up to 40 lb of sediment. The Plus version, part 9219, raises absorption to 1.38 gallons because the Filter-Tex strips add 0.51 gallons; the 60 inch by 60 inch units run 1.55 gallons (9356) and 2.06 gallons (9358), and the Curb Guard Plus absorbs 1 gallon per 3 foot section and 1.4 gallons per 4 foot section per its flyer. One caution from UltraTech: Filter-Tex is designed for hydrocarbons and does not absorb synthetic oils, though the needle-punched geotextile itself does. If your forklifts run synthetic hydraulic fluid, the standard Oil and Sediment unit does as much as the Plus for that fluid, and you save $21.00 per drain.

Sediment is a particle-size question. Wisconsin's Table 2 assigns its woven FF fabric to coarse soils, sand at an average particle diameter of 0.0625 mm and up, and switches to nonwoven fabrics for silt loam and clay. UltraTech's Drain Guard spec sheet rates its nonwoven at a No. 80 sieve apparent opening size under ASTM D4751, 525 lb puncture strength under ASTM D6241, and 70 percent strength retained after 500 hours of UV under ASTM D4355. EPA's fact sheet sets the expectation for every insert on the market: internal controls are "generally only useful for larger sediment," and the one study it cites, Clary et al. (2011), found median total suspended solids across 11 internal controls fell from 52 mg/L to 33 mg/L. The silt fence, the stabilized entrance and the sweeper upstream do most of the work; the insert catches what gets past them. For floatables, the Trash and Debris drain guard (9227, $32.00) is a 1 cubic foot insert for the leaves, cups and plastic pellets that clog a grate before any sediment does.

Model we stock	Fabric	Captures	Oil capacity (UltraTech)	Sediment capacity (UltraTech)	Overflow	Price as listed
9217 Drain Guard, Oil and Sediment, 48 x 36 in	Nonwoven geotextile	Sediment, oil, hydrocarbons	0.87 gal	40 lb	Bypass ports, 770 gpm	$27.00
9219 Drain Guard Plus, Oil and Sediment, 48 x 36 in	Nonwoven geotextile plus Filter-Tex strips	Sediment, oil, hydrocarbons	1.38 gal	40 lb	Bypass ports, 770 gpm	$48.00
9227 Drain Guard, Trash and Debris, 48 x 36 in	Trash and Debris model	Floatables, leaves, trash	None	1 cu ft	Not specified	$32.00
9840 Drain Guard, Reusable, 24 x 24 in, regular flow	Woven polypropylene	Sediment, dirt, debris only	None	500 lb	8 overflow ports	$46.00
9341 Drain Guard, Reusable, 24 x 24 in, high flow	High flow woven	Sediment, dirt, debris only	None	500 lb	4 overflow ports	$51.00
9858 Grate Guard, 36 x 36 in, over the grate	High flow woven	Sediment, silt, debris only	None	Not rated; swept off at street level	No overflow ports	$48.00
9163 Inlet Guard Plus, curb-style, 24 x 24 in, over the grate	Nonwoven geotextile, magnetic	Sediment, oil, hydrocarbons	Not rated	Not rated; swept off at street level	Built-in overflow port	$99.00
9251 Curb Guard Plus, 4 ft section, curb throat	Woven polypropylene plus Filter-Tex	Sediment, oil	1.4 gal	Not rated	Passes flow without ponding, per UltraTech	$143.00

Question 3: Above the grate or below it?

An under-grate drain guard disappears once the grate is back in place, and that is its main advantage and its main cost. UltraTech's installation steps are to raise the grate, place the insert over the opening, lower the grate and pinch the fabric between the grating and the ledge; the FAQ on the same page calls lifting the grate the hardest part of the job and recommends a second person. Four lifting straps sewn into the top come back out through the grating so the loaded unit lifts with the grate instead of dropping into the basin. Nothing sits on the surface, so sweepers and theft are not a problem, and EPA's fact sheet points internal controls at areas with heavy construction traffic and at inlets where roadway flooding is a concern. The cost is that every inspection and cleanout means pulling the grate again, which is why the Connecticut Stormwater Quality Manual says catch basin inserts "should only be used where a full-time maintenance person is on-site," and warns that a clogged insert aggravates flooding.

An above-grate guard trades that for a filter you can see and sweep. The Ultra-Grate Guard slides over the grate, closes with hook and loop, and keeps everything "at street level," so sediment comes off "with a broom, flat shovel or similar tool" without lifting the grate; each unit is 4 inches thick and weighs 2 lb per the product flyer. The Ultra-Inlet Guard Plus is simpler still: per UltraTech's product page, you "simply line it up with the grating and lay it on top," and rare earth magnets sewn into the corners hold it. It is low profile enough to drive over, weighs 5 lb, and uses the same oil-removing nonwoven geotextile as the Oil and Sediment drain guards. UltraTech is candid about the trade: the Inlet Guard Plus is more exposed to street sweeper damage, theft and vandalism than an under-grate product, and it cannot be trimmed, so a grate 2 inches off a stock size needs a custom order. The Grate Guard's black fabric is "very clearly visible," and UltraTech's own advice is to use an under-grate product at a shopping center or office frontage where that matters.

The practical split: on a paved construction lot with a sweeper, the Grate Guard is cleaned in minutes by whoever is sweeping anyway. At a warehouse or fuel island with one or two drains inspected after storms, the under-grate Oil and Sediment drain guard holds the oil out of sight, and UltraTech reports field units in Seattle and Florida still working more than a year after installation. On a combination inlet in a truck court where forklifts cross the grate, the Inlet Guard Plus gives you the oil fabric without a grate lift, as long as the grate is a stock size.

Question 4: How much water has to bypass, and how often will you clean it?

A filter that cannot let water past it when it is full is a dam, and a dam at a storm drain floods the lot. EPA's fact sheet puts the design rule in one line: the water ponded over the device must not rise above any surrounding low point, or stormwater escapes the inlet and erodes somewhere else, and some controls need an emergency overflow. Wisconsin's rigid-frame bag type requires bypass overflows that pass at least the inlet's design flow, and Minnesota's winter guidance asks for overflow assurance on every inlet device so flow bypasses a frozen filter. The UltraTech numbers are on the spec sheet: the nonwoven fabric passes 90 gal/min/ft² when new under ASTM D4491, and the bypass ports pass 770 gpm, which is 1.7 cubic feet per second. UltraTech's product page adds the part people miss: water that leaves through the overflow leaves untreated. The reusable bags come two ways, regular flow fabric with 8 overflow ports and high flow fabric with 4, and each Warehouse Gear Hub listing states the fabric and port count in its title. The Inlet Guard Plus carries a built-in overflow port. The 36 inch by 36 inch Grate Guard has no overflow ports and relies on its high flow fabric, so it belongs on a grate that is not the low point of the lot.

How full is too full is written down, and the three sources agree closely. EPA: check every control after each storm, remove sediment when a settling area has lost half its capacity, and clear the device if it has not drained within 48 hours. Wisconsin: inspect at least weekly and within 24 hours after 0.5 inches or more of rain in a 24 hour period, and remove sediment from a bag when it is within 6 inches of the bottom of the overflow holes or when water is still standing within 6 inches of them 24 hours after a storm. Minnesota's permit uses the same 7 day and 0.5 inch trigger and adds a deadline: a nonfunctioning device gets replaced or repaired by the end of the next business day. UltraTech's own guidance is to inspect after each significant rain, empty and reuse a unit filled with sand or silt, and replace a unit saturated with oil, gas or other hydrocarbons, because a major rain can flush those pollutants back out.

Cleanout is where the under-grate and over-grate choice turns into labor hours. A loaded reusable bag holds up to 500 lb, and UltraTech says to remove it with at least two people or a backhoe or forklift, after sliding rebar into the removal flap pockets. A Grate Guard is swept. EPA estimates maintenance at about 60 percent of construction cost for inlet protection and prices a filter fabric inlet control at $210 in New York's 2020 dollars; the UltraTech units here run $27.00 to $143.00, so over a season the cleaning, not the fabric, is the bill. Two winter rules close the loop: Wisconsin says to stabilize the area and remove the protection before winter to prevent flooding, then replace it before spring disturbance, and Minnesota says to break ice by hand or with steam, never with salt.

Which storm drain inlet protection should you buy?

Match your inlet and your pollutant to the line that describes them. Prices are as listed on Warehouse Gear Hub as of this writing.

• Paved construction site, flat grate, dirt by the wheelbarrow: Reusable Drain Guard under the grate, 9840 ($46.00) for a 24 x 24 inch basin, 9841 ($48.00) for 27 x 27, 9842 ($51.00) for 30 x 30, 9845 ($63.00) for 36 x 36. Pick the high flow version (9341 at $51.00 for 24 x 24) where the grate is the low point of the lot.
• Same site, but the crew sweeps the lot and nobody wants to lift grates: Grate Guard over the grate, 9858 ($48.00) for a 36 x 36 inch grate; curb-style units for combination inlets run 9860 ($79.00) for 24 x 36 to 9862 ($82.00) for 24 x 48.
• Warehouse dock, fuel island or maintenance yard with a few drains: Oil and Sediment Drain Guard under the grate, 9217 ($27.00) for a standard 48 x 36 inch basin, or the Plus 9219 ($48.00) for 1.38 gallons of oil capacity. Ten-packs are 9218 ($251.00) and 9220 ($430.00).
• Combination inlet in a truck court, forklifts crossing it, stock-size grate: Inlet Guard Plus on top, curb-style 9163 ($99.00) for 24 x 24, 9164 ($122.00) for 24 x 36, 9165 ($144.00) for 24 x 48. Flat-grate versions 9160 to 9162 are $52.00 to $81.00.
• Curb inlet with no grate: Curb Guard Plus, 9248 ($124.00) per 3 foot section or 9251 ($143.00) per 4 foot section, joined to run the 4 to 6 inches past each end of the opening that Stormwater Solutions' field guidance calls for on curb devices.
• Drain that clogs with leaves and litter before it sees mud: Trash and Debris Drain Guard, 9227 ($32.00), or the ten-pack 9229 ($313.00).
• Every site: a spare per drain family, because Wisconsin and Minnesota both put the repair deadline at the next business day, and the swap happens when the unit is full, not when the order arrives.

Every unit above is in the drain guard collection, the grate guard collection and the curb inlet guard collection. Warehouse Gear Hub is an authorized UltraTech dealer, we match prices, and we quote volume orders for contractors and facilities that buy inserts by the case. Call 1-800-794-1049, 8 AM to 4 PM Central, with the grate's outside dimensions, the basin depth, and whether the problem is dirt or oil, and we will size it in one call. For the drain seals and plugs that close a drain completely during a spill, a different job from filtering it, read our storm drain spill guide; for the pump discharge on the same site, our dewatering bag guide.

Frequently Asked Questions

What is storm drain inlet protection?

A temporary device installed in, on or around a storm drain inlet to keep sediment and debris out of the storm sewer while the area draining to it is disturbed or carrying construction traffic. EPA's fact sheet splits the devices into internal controls, filter inserts placed inside the drain, and external controls, fabric or stone barriers that pond water around the inlet so sediment settles. The UltraTech products in this guide are internal controls (drain guards under the grate) and surface controls on the grate or in the curb throat (grate guards, inlet guards and curb guards).

Is storm drain inlet protection required?

On a permitted construction site, yes. 40 CFR 450.21(a) requires sediment controls that "minimize sediment discharges from the site," 40 CFR 122.26(b)(15) brings any site disturbing one acre or more under the permit, and state permits such as Minnesota's require every storm drain inlet to be protected until the area draining to it is stabilized. At an industrial facility, 40 CFR 122.26(b)(14)(xi) lists public warehousing (SIC 4221 to 4225) among industrial activities, and a facility that cannot certify no exposure under paragraph (g) carries a stormwater plan that names the inlet controls it uses.

How often should inlet protection be inspected?

At least once every 7 days and within 24 hours after 0.5 inches or more of rain in 24 hours, per both the Wisconsin DNR standard and the Minnesota construction permit; EPA's fact sheet says after each storm. Remove sediment when the device is half full (EPA) or within 6 inches of the overflow holes on a bag insert (Wisconsin), and repair or replace a failed device by the end of the next business day (Minnesota).

When should inlet protection be removed?

When the area draining to the inlet is stabilized with vegetation or pavement, per both the Wisconsin standard and the Minnesota permit. Wisconsin adds a seasonal rule: stabilize and remove the protection before winter to prevent flooding, then reinstall it before spring disturbance. Minnesota allows removal from a specific inlet over a documented safety concern, but says it does not want a blanket policy of pulling every inlet device before winter.

Do catch basin inserts cause flooding?

A full one with no bypass does. The Connecticut Stormwater Quality Manual warns that clogging aggravates flooding and calls for a high-flow bypass on every insert. UltraTech's Oil and Sediment drain guards have bypass ports rated at 770 gpm (1.7 cfs), the reusable bags have 4 or 8 overflow ports, and the Inlet Guard Plus has a built-in overflow port. Water through the bypass is untreated, so the bypass is flood insurance, not a reason to skip the cleanout.

Can you drive over storm drain inlet protection?

Over an under-grate drain guard, yes; nothing sits above the grate once it is reinstalled. UltraTech describes the Inlet Guard Plus as low profile enough to be driven over. The Grate Guard sits 4 inches above the grate, and UltraTech notes that any above-grate unit is more exposed to street sweeper damage than an under-grate one.

How much does storm drain inlet protection cost?

On Warehouse Gear Hub as of this writing: Oil and Sediment Drain Guard 48 x 36 inch $27.00, the Plus $48.00, Trash and Debris $32.00, flat-grate Reusable Drain Guards $46.00 to $63.00 by size, Grate Guard 36 x 36 inch $48.00 and curb-style $79.00 to $82.00, Inlet Guard Plus $52.00 to $144.00, and Curb Guard Plus $124.00 per 3 foot section or $143.00 per 4 foot section. EPA's fact sheet puts maintenance at about 60 percent of installed cost over a project, so budget the cleanout labor alongside the unit.