14.1 Storm Drain Inlet Protection: At-Grade, Curb, Block & Gravel, Excavated, Fabric Drop, Gravel Bag, Stone Collar, and Pre-Manufactured

Free CESSWI Certified Erosion, Sediment and Stormwater Inspector Study Guide 2026 Exam

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1 Chapter 1: CESSWI Program Overview, Scope of Practice & Professional Ethics

1.1 CESSWI Scope of Practice, Eligibility, and Exam Structure 1.2 Certification Renewal, PDH Requirements, and Audit Policies 1.3 EnviroCert Code of Ethics and Professional Conduct

2 Chapter 2: Federal, State, and Local Stormwater Regulations

2.1 Federal Water-Pollution History and Stormwater Phases 2.2 CWA Sections, Water Quality, and Related Federal Programs 2.3 EPA Construction Permit Coverage and Operational Clocks 2.4 Industrial MSGP and Municipal MS4 Programs 2.5 Regulatory Compliance, Enforcement Mechanisms, and Penalties

3 Chapter 3: Soil Mechanics, Erosion Processes, and Climatic Factors

3.1 Soil Formation, Horizons, and Geomorphology 3.2 Soil Texture, Mechanics, and Revegetation 3.3 Splash, Sheet, Rill, Gully, Channel Erosion, and Slope Movement 3.4 Wind Erosion, Sediment Transport, Climatic Erosivity, and Resource Impacts

4 Chapter 4: Hydrology, Runoff Characteristics, and Drainage Principles

4.1 The Hydrologic Cycle, Watershed Drainage Planning, and Precipitation 4.2 Hydrologic Soil Groups, Disturbed Profiles, and Time Parameters 4.3 Hydrograph Characteristics, Curve Numbers, and Runoff Estimation Equations

5 Chapter 5: Inspection Fundamentals, Duties, and Field Procedures

5.1 Inspector Roles, Scope of Authority, and Core Professional Skills 5.2 Pre-Inspection Document Review and Inspector Support Equipment 5.3 Systematic Field Inspection Sequence, Post-Inspection Meetings, and Follow-Through

6 Chapter 6: Inspection Elements for Active Construction Sites

6.1 Pre-Construction Meetings, Entrance Posting, and On-Site Document Inspections 6.2 Inspecting Active Construction Controls and Diagnosing BMP Failure Modes 6.3 Final Stabilization Verification, Final Inspections, and Notice of Termination

7 Chapter 7: Stormwater Monitoring, Field Sampling, and Chain of Custody

7.1 Permit Monitoring Triggers and Water-Quality Indicators 7.2 Sampling Preparation and Analytical Parameters 7.3 Sampling Locations, Collection Methods, and Field Meter Calibration 7.4 Sample Preservation, Data Recording, Shipping, and Chain of Custody

8 Chapter 8: Inspection Documentation, Reporting, and Map Management

8.1 Inspection Notes and Evidence Procedures 8.2 Objective Findings and Photographic Evidence 8.3 Proper Reporting Techniques and Corrective Action Log Management 8.4 Site Drawing (Map) Management, Compliance Resolution, and Enforcement Records

9 Chapter 9: Professional Communication and Site Safety for Inspectors

9.1 Communication Protocols in Pre-Construction, Post-Inspection, and O&M Meetings 9.2 Dealing with Difficult People, Problematic Sites, and Unpleasant Findings 9.3 Site Hazard Recognition: Physical, Biological, Trenching, and Confined Spaces 9.4 Hazardous Substances, Safety Data Sheets (SDS), Spill Response, and PPE

10 Chapter 10: Stormwater Plan Reading, Map Interpretation, and Site Calculations

10.1 Stormwater Plan Types, Credentials, and Authority 10.2 SWPPP Components and Permit Notifications 10.3 Civil Plan Sets, Legends, Phased Sequencing, and Living Site Maps 10.4 Topography, Contour Lines, Slope Calculations, and Plan Amendments

11 Chapter 11: BMP Framework, Site Planning, and Erosion Control Practices

11.1 Six Functional BMP Categories, Preservation of Vegetation, Phasing, and Tree Protection 11.2 Seeding and Sod Establishment 11.3 Hydroseeding and Hydromulching Inspection 11.4 Mulch and Rolled Erosion-Control Products 11.5 Tackifiers, Soil Binders, Roughening, and Temporary Cover

12 Chapter 12: Perimeter, Linear, and In-Water Sediment Control Practices

12.1 Perimeter & Sheet-Flow Sediment Barriers: Silt Fence, Fiber Rolls, Straw Bales, and Filter Dikes 12.2 Access & Roadside Sediment/Runoff Controls: Stabilized Entrances, Cut-Back Curbs, and Ditch Checks 12.3 In-Water & Dewatering Controls: Temporary Stream Crossings, Turbidity Curtains, and Sediment Bags

13 Chapter 13: Sediment Basins, Traps, and Runoff Conveyance Controls

13.1 Sediment Basins and Traps 13.2 Porous Baffles and Surface Skimmers 13.3 Runoff Conveyances: Diversions, Swales, Pipe Slope Drains, and Rock Check Dams 13.4 Riprap and Gabion Inspection 13.5 Retaining Walls, Outlet Protection, and Wet Ponds

14 Chapter 14: Storm Drain Inlet Protection and Good Housekeeping BMPs

14.1 Storm Drain Inlet Protection: At-Grade, Curb, Block & Gravel, Excavated, Fabric Drop, Gravel Bag, Stone Collar, and Pre-Manufactured 14.2 Good Housekeeping Part 1: Concrete Washout, Equipment Maintenance, Materials Management, and Secondary Containment 14.3 Good Housekeeping Part 2: Stockpiles, Dust Control, Wind Fence, Street Cleaning, Sanitary Waste, and Trash

15 Chapter 15: Post-Construction Stormwater Management BMPs

15.1 Vegetative & Structural Dispersion BMPs: Final Ground Cover, Headwalls, Level Spreaders, Filter Strips, and Riparian Buffers 15.2 Permeable Surfaces and Construction Protection 15.3 Infiltration, Bioretention, and Media Filters 15.4 Detention, Retention & Proprietary BMPs: Dry/Wet Basins, Wetlands, Inline Storage, Catch Basin Inserts, Vaults, and Manufactured Devices

14.1 Storm Drain Inlet Protection: At-Grade, Curb, Block & Gravel, Excavated, Fabric Drop, Gravel Bag, Stone Collar, and Pre-Manufactured

Key Takeaways Explain This Topic AI

Storm drain inlet protection devices are strictly secondary backups ('last line of defense') limited to small drainage areas of 1.0 acre or less with shallow sheet or gutter flow, and never replace upslope erosion control or primary perimeter sediment barriers.

Every inlet protection device installed in paved streets, parking lots, or near buildings must incorporate a built-in high-flow overflow bypass (such as a 2- to 4-inch curb throat gap, depressed center weir, or under-grate bag overflow slots) to prevent roadway flooding, hydroplaning hazards, and structural property damage.

Block and gravel inlet protection uses 8 in. x 8 in. x 16 in. concrete masonry units laid 1 to 2 courses high with one or two blocks per side turned on their sides as dewatering weep holes, wrapped on the exterior with 1/2-inch wire mesh and banked with 1- to 2-inch washed stone at a 2H:1V slope.

Gravel bag inlet barriers must always be filled with coarse washed pea gravel or 3/4-inch crushed stone—never fine sand—and saturated under-grate filter bags (150 to 400 lb when half-full) must be lifted out vertically with equipment straps rather than pried with a shovel.

Last updated: October 2026

Note

Using dimensions in this section: Construction dimensions, material sizes, slopes, cleanout fractions, and drawdown ranges below describe example practice details. Verify the approved design, manufacturer instructions, and applicable permit before using a number as an inspection acceptance criterion. Regulatory thresholds identified explicitly as EPA/OSHA requirements remain distinct.

Role, Limitations, and the Mandatory High-Flow Overflow Rule ( 12.4.9 )

Once storm drain pipes, street catch basins, and field drop inlets are constructed on a project site, they create a direct hydraulic conduit from the active grading footprint to underground storm sewers, Municipal Separate Storm Sewer Systems (MS4s), and receiving surface waters. Unlike overland sheet flow that crosses vegetated buffers or passes through large sediment basins, turbid runoff that enters an unprotected drop inlet receives zero downstream filtration before discharging at the storm sewer outfall.

Secondary Backup Only ("Last Line of Defense")

In the CESSWI inspection hierarchy ( Review Manual Section 12.4.9 ), storm drain inlet protection is strictly a secondary backup measure —often called the "last line of defense" —and is never a substitute for upslope soil stabilization (erosion control) and primary perimeter sediment barriers . Because storm drain inlets are positioned at localized low points or along narrow street gutters, inlet protection devices possess minuscule hydraulic storage volumes and very short detention residence times. Consequently:

Maximum Drainage Area Limit: Individual storm drain inlet protection devices are restricted to small, gentle contributory drainage areas of ≤ 1.0 acre \le 1.0\text{ acre} ≤ 1.0 acre per inlet receiving shallow sheet flow or low-velocity gutter flow.

Rapid Blinding Risk: If upslope cut-and-fill slopes or graded pads are left bare without mulch, blankets, or phased seeding, heavy sediment loads will blind geotextile pores or choke aggregate voids within the first few minutes of a storm, rendering the inlet device ineffective for the remainder of the event.

Clay and Fine Silt Limitation: Because detention times around an inlet grate are measured in seconds or a few minutes, inlet barriers primarily trap coarse sand, gravel, and heavy silt aggregates via miniature ponding check-dam action rather than settling out colloidal clays.

Mandatory High-Flow Overflow / Bypass Rule (Crucial Exam Concept): Every storm drain inlet protection device installed in paved roadways, active traffic lanes, parking lots, or near building pads MUST incorporate a built-in high-flow overflow bypass —such as a depressed center weir crest, a 2 - to 4 -inch 2\text{- to }4\text{-inch} 2 - to 4 -inch vertical clearance gap at the top of a curb-opening throat, a low-stage block weir, or open high-flow bypass ports near the top collar of an under-grate filter bag. If an inlet device completely seals the inlet without an overflow bypass, blinding during an intense thunderstorm will prevent stormwater from entering the catch basin, causing impounded runoff to flood active traffic lanes (creating severe vehicle hydroplaning hazards), overtop street curbs, erode adjacent lots, or flood nearby building foundations and basements . Wrapping an active storm drain grate in impermeable plastic sheeting or solid plywood is strictly prohibited (impermeable covers are permitted only for brief minutes during active asphalt tack-coating, sealcoating, or saw-cutting operations when rain is not occurring).

The 8 Official Subtypes of Storm Drain Inlet Protection ( 12.4.9.1 – 12.4.9.8 )

A CESSWI inspector must verify that the specific inlet protection subtype selected in the SWPPP matches the physical inlet geometry (at-grade drop grate vs. vertical curb throat), surface condition (unpaved earthen sump vs. paved roadway), and traffic exposure.

1. At-Grade Inlet Protection ( 12.4.9.1 )

At-grade inlet protection is installed around flat or grated drop inlets located in open unpaved or grassy drainage swales, landscaped yard sumps, highway median depressions, or parking lot low points where surface runoff approaches the inlet structure radially from all four sides ( 360 ∘ 360^\circ 36 0 ∘ ) . Because flow converges from every direction, the barrier must form a continuous 360 ∘ 360^\circ 36 0 ∘ perimeter enclosure around the grate. The top crest of an at-grade perimeter barrier must be constructed at a uniform, level elevation below the surrounding rim of the sump so that when ponded water exceeds the design filtration depth, excess runoff spills uniformly over the top of the barrier directly into the center grate rather than concentrating around one side and scouring a bypass gully.

2. Curb Inlet Protection ( 12.4.9.2 )

Curb inlet protection safeguards vertical curb-opening throats along paved streets and parking lot perimeters (installed either as a standalone vertical curb throat or a combination curb-and-gutter grate inlet). Common configurations include wire-backed woven geotextile stretched over a wooden 2 × 4 2\times 4 2 × 4 weir frame, elongated cylindrical gravel filter tubes, compost filter socks, or reusable foam-core mesh curb logs anchored across the throat opening and extended several feet upstream along the curb gutter to act as miniature gutter check dams.

Mandatory 2 - to 4 -Inch 2\text{- to }4\text{-Inch} 2 - to 4 -Inch Overflow Clearance: Every curb inlet barrier must maintain a continuous 2 - to 4 -inch 2\text{- to }4\text{-inch} 2 - to 4 -inch open clearance gap between the top of the barrier device and the top lintel of the curb throat (or incorporate a recessed center overflow notch/weir). During low-intensity storms, gutter flow ponds behind the barrier, drops its coarse sand load in the gutter apron, and filters slowly through the stone or fabric; during heavy downpours, once ponded gutter water reaches the top of the barrier, excess flow spills cleanly through the 2 - to 4 -inch 2\text{- to }4\text{-inch} 2 - to 4 -inch top gap directly into the curb throat instead of backing up into active traffic lanes.

3. Block and Gravel Inlet Protection ( 12.4.9.3 )

Block and gravel inlet protection is a heavy-duty structural sediment barrier built around a four-sided drop inlet using standard 8 in. × 8 in. × 16 in. 8\text{ in.} \times 8\text{ in.} \times 16\text{ in.} 8 in. × 8 in. × 16 in. concrete masonry units (CMU cinder blocks) paired with wire mesh and washed stone:

CMU Block Wall ( 1 to 2 Courses 1\text{ to }2\text{ Courses} 1 to 2 Courses ): Lay a continuous ring of CMU blocks 1 to 2 courses 1\text{ to }2\text{ courses} 1 to 2 courses ( 8 to 16 inches 8\text{ to }16\text{ inches} 8 to 16 inches ) high without mortar around the outside perimeter of the concrete inlet apron (setting the bottom course in a shallow 2 - to 4 -inch 2\text{- to }4\text{-inch} 2 - to 4 -inch leveling trench if placed on bare soil).

Horizontal Dewatering Weep Blocks: On each of the four sides of the inlet, lay one or two CMU blocks ON THEIR SIDES (horizontally) in the bottom course so their open hollow cores face outward toward approaching runoff, functioning as slow dewatering weep holes between storm events.

1 / 2 -Inch 1/2\text{-Inch} 1/2 -Inch Hardware Wire Mesh: Place 1 / 2 -inch 1/2\text{-inch} 1/2 -inch hardware wire mesh (hardware cloth) over the outside face of the CMU block wall—especially covering all outward-facing open block cores—so the exterior stone aggregate cannot wash through the block openings and fall down the storm drain inlet.

Washed Stone Filter Bank ( 2 H : 1 V 2\text{H}:1\text{V} 2 H : 1 V ): Bank clean, coarse 1 - to 2 -inch 1\text{- to }2\text{-inch} 1 - to 2 -inch washed crushed stone against the outside of the wire mesh up to the top elevation of the CMU block wall at a 2 H : 1 V 2\text{H}:1\text{V} 2 H : 1 V or flatter outer slope.

Operational Advantages: Block and gravel barriers are exceptionally sturdy, will not bow or collapse inward over the grate under hydrostatic water pressure, cannot float during submergence, and act as a reliable broad-crested masonry weir that allows high flows to spill safely over the top course of blocks into the grate.

4. Excavated Impoundment Inlet Protection ( 12.4.9.4 )

Excavated impoundment inlet protection (also called an excavated drop inlet sediment trap) is constructed by excavating a temporary circular or rectangular settling basin completely surrounding an unpaved field drop inlet :

Excavation Dimensions & Storage: Excavate a perimeter moat 1 to 2 feet 1\text{ to }2\text{ feet} 1 to 2 feet deep below the elevation of the inlet grate crest, with side slopes no steeper than ≤ 2 H : 1 V \le 2\text{H}:1\text{V} ≤ 2 H : 1 V and a total sediment storage volume of 35 to 67 yd 3 per acre 35\text{ to }67\text{ yd}^3\text{ per acre} 35 to 67 yd 3 per acre of drainage area.

Hydraulic Mechanism: As sediment-laden sheet or swale flow enters the excavated depression around the concrete riser box, the sudden expansion in flow depth and cross-sectional area sharply reduces flow velocity. Coarse sand and heavy silt settle out onto the floor of the excavated pool before clarified water rises to the concrete rim elevation and spills over into the grate (often paired with small gravel-protected weep holes at the base of the riser so standing water drains completely within 24 to 48 hours 24\text{ to }48\text{ hours} 24 to 48 hours ).

5. Fabric Drop Inlet Protection ( 12.4.9.5 )

Fabric drop inlet protection utilizes woven monofilament geotextile fabric in two distinct field configurations, each with critical structural and safety rules:

Framed Geotextile Box Barrier (Unpaved Field Sumps Only): Staked tightly around the four sides of an unpaved field drop inlet located in an earthen sump draining ≤ 1.0 acre \le 1.0\text{ acre} ≤ 1.0 acre . Heavy wooden stakes ( 2 × 4 in. 2\times 4\text{ in.} 2 × 4 in. ) are driven around the grate perimeter at a maximum spacing of 3 feet 3\text{ feet} 3 feet apart , and horizontal wooden top framing strips ( 1 × 4 1\times 4 1 × 4 or 2 × 4 2\times 4 2 × 4 lumber) are nailed securely across the tops of all stakes to form a rigid structural frame. Without top framing braces, the hydrostatic pressure of ponded water pushes the stakes and fabric inward, collapsing the barrier directly over the grate and blocking all flow. The bottom edge of the geotextile must be trenched 6 to 12 inches 6\text{ to }12\text{ inches} 6 to 12 inches deep and backfilled with compacted soil to prevent undercutting, and total fabric height above ground is limited to 1.5 to 2.0 feet 1.5\text{ to }2.0\text{ feet} 1.5 to 2.0 feet so major storm flows can overtop the frame into the grate.

Under-Grate Filter Bag ("Witches Hat" / Dandy Sack): A conical or rectangular woven geotextile filter bag lowered inside the catch basin rim beneath the cast-iron grate, held in place by pinching its top collar flange under the heavy grate. Every under-grate filter bag must feature built-in high-flow overflow/bypass slots or ports near the top collar (so stormwater can bypass into the catch basin if the bottom cone blinds with fine silt) and heavy-duty sewn nylon lifting straps .

Under-Grate Filter Bag Cleanout Hazard (High-Probability Exam Scenario): When an under-grate filter bag reaches 1 / 2 full 1/2\text{ full} 1/2 full ( 50 % 50\% 50% capacity) of wet sand and silt, the saturated bag weighs 150 to 400 lb 150\text{ to }400\text{ lb} 150 to 400 lb . Maintenance crews must pull the cast-iron grate and lift the bag vertically out of the catch basin using mechanical lifting equipment (a backhoe bucket hook, skid-steer fork, or boom strap hooked through the bag's nylon lifting straps). NEVER allow workers to pry or dig a heavy filter bag out of an inlet frame with a steel shovel or pry bar —doing so tears the tensioned fabric and dumps 100 % 100\% 100% of the trapped sediment straight down the underground storm sewer pipe!

6. Gravel Bag Berm Inlet Protection ( 12.4.9.6 )

Gravel bag berm inlet protection consists of durable woven polypropylene or heavy burlap bags filled with clean, washed pea gravel or 3 / 4 -inch 3/4\text{-inch} 3/4 -inch crushed stone , stacked in a tightly butted horseshoe or ring check-dam around an at-grade inlet or arranged as angled gutter check dams upstream of a curb inlet. When stacking two courses high, overlap bag joints in a running-bond brick pattern so no vertical gaps exist between bags.

Crucial Exam Trap — Never Use Sandbags for Inlet Protection: Inlet protection bags must always be filled with coarse washed gravel , NEVER fine sand ! Coarse washed gravel allows low-flow permeability through bag interstices and is heavy enough that if a bag tears or is run over by a construction vehicle tire in a paved street gutter, the coarse aggregate remains on the pavement where it can be swept up. Conversely, when a sandbag splits open under UV degradation or truck traffic right in front of a catch basin, the fine sand washes immediately into the storm drain inlet, adding direct sediment pollution to the storm sewer instead of removing it .

7. Stone Collar Inlet Protection ( 12.4.9.7 )

Stone collar inlet protection forms a 360 ∘ 360^\circ 36 0 ∘ porous aggregate ring around the perimeter of an at-grade drop inlet grate using clean, washed 1.5 - to 3 -inch 1.5\text{- to }3\text{-inch} 1.5 - to 3 -inch coarse stone held within a circular welded wire-mesh cage, hardware-cloth ring, or heavy-duty cylindrical mesh filter sock. The stone collar creates a shallow ponding zone around the grate that causes coarse sand to settle on the upstream approach apron while filtering sheet flow through the aggregate void spaces and allowing high-stage runoff to spill unobstructed over the stone ring into the center grate.

8. Pre-Manufactured Inlet Protection ( 12.4.9.8 )

Pre-manufactured inlet protection encompasses commercial, reusable, proprietary inlet guards—including magnetic or tension-mounted perforated metal/polymer curb screens, high-visibility pop-up overflow filter domes ("bonnets"), encased coconut-coir or synthetic-foam curb logs, and rigid polymer catch-basin frame inserts with replaceable filter cartridges. Because hydraulic flow-through rates, internal overflow weir heights, and mounting clips vary significantly by product model, pre-manufactured inlet devices must be selected, installed, anchored, and cleaned strictly according to the manufacturer's specifications .

Comparison of All 8 Storm Drain Inlet Protection Subtypes

Inlet Protection Subtype Review Manual Ref. Target Inlet & Location Key Construction & Material Specs Built-In High-Flow Overflow Mechanism

At-Grade Inlet Protection 12.4.9.1 Grated drop inlets in open swales, yard sumps, or parking lot low points ( 360 ∘ 360^\circ 36 0 ∘ radial approach flow) Continuous 360 ∘ 360^\circ 36 0 ∘ perimeter barrier around grate; uniform level top crest below sump rim Uniform 360 ∘ 360^\circ 36 0 ∘ overtopping over the level top crest directly into the center grate

Curb Inlet Protection 12.4.9.2 Vertical curb-opening throats along paved streets and gutters Wire-backed fabric on 2 × 4 2\times 4 2 × 4 frame, gravel tubes, or curb logs extended upstream in gutter Mandatory 2 - to 4 -inch 2\text{- to }4\text{-inch} 2 - to 4 -inch vertical clearance gap at top of curb throat (or depressed center weir)

Block and Gravel 12.4.9.3 Four-sided drop inlets needing sturdy, non-collapsing protection 8 × 8 × 16 in. 8\times 8\times 16\text{ in.} 8 × 8 × 16 in. CMU blocks ( 1 to 2 courses 1\text{ to }2\text{ courses} 1 to 2 courses ); 1 to 2 1\text{ to }2 1 to 2 blocks/side laid on side as weep holes; 1 / 2 -in. 1/2\text{-in.} 1/2 -in. wire mesh; 1 - to 2 -in. 1\text{- to }2\text{-in.} 1 - to 2 -in. washed stone at 2 H : 1 V 2\text{H}:1\text{V} 2 H : 1 V High flows spill over the 8 - to 16 -in. 8\text{- to }16\text{-in.} 8 - to 16 -in. CMU block wall crest directly into the grate

Excavated Impoundment 12.4.9.4 Unpaved field drop inlets in earthen swales or sumps Excavated moat 1 to 2 ft 1\text{ to }2\text{ ft} 1 to 2 ft deep around riser; ≤ 2 H : 1 V \le 2\text{H}:1\text{V} ≤ 2 H : 1 V side slopes; 35 to 67 yd 3 / acre 35\text{ to }67\text{ yd}^3/\text{acre} 35 to 67 yd 3 / acre storage volume Clarified water rises to the concrete inlet rim elevation and spills into the grate

Fabric Drop (Framed Box or Under-Grate Bag) 12.4.9.5 Framed box: unpaved sumps ≤ 1.0 acre \le 1.0\text{ acre} ≤ 1.0 acre only; Under-grate bag: paved street/parking grates Framed box: stakes ≤ 3 ft \le 3\text{ ft} ≤ 3 ft apart with nailed top framing strips and 6 - to 12 -in. 6\text{- to }12\text{-in.} 6 - to 12 -in. trench; Bag: nylon lifting straps, clean at 1 / 2 full 1/2\text{ full} 1/2 full Framed box: overtops 1.5 - to 2.0 -ft 1.5\text{- to }2.0\text{-ft} 1.5 - to 2.0 -ft frame crest; Under-grate bag: top-collar bypass slots/ports

Gravel Bag Berm 12.4.9.6 Paved street gutters, curb throats, and paved at-grade grates Woven polypropylene/burlap bags filled with washed pea gravel or 3 / 4 -in. 3/4\text{-in.} 3/4 -in. stone (NEVER fine sand!) Depressed center bag weir or 2 - to 4 -in. 2\text{- to }4\text{-in.} 2 - to 4 -in. gap below curb top

Stone Collar 12.4.9.7 At-grade grates in sumps or paved aprons 360 ∘ 360^\circ 36 0 ∘ collar of 1.5 - to 3 -in. 1.5\text{- to }3\text{-in.} 1.5 - to 3 -in. washed aggregate inside wire-mesh ring or heavy filter sock Overtops low stone collar ring ( 6 to 12 in. 6\text{ to }12\text{ in.} 6 to 12 in. high) into center grate

Pre-Manufactured 12.4.9.8 Paved curb throats, combination inlets, and parking lot grates Commercial curb screens, pop-up filter domes, coir/foam logs, or rigid inserts installed per manufacturer specs Engineered internal bypass weirs, pop-up domes, or upper overflow louvers