Cap Design Calculator

Design multi-layer engineered caps for contaminated sites per EPA/RCRA guidance.

Cap length (m)

Cap width (m)

Gas vent layer (1=yes, 0=no)

Barrier type (0=clay, 1=geomembrane+clay)

Local frost depth (m)

Cap surface slope (%)

Annual precipitation (mm)

Tab to move between fields

Cap area (m²)

5,000

Total cap thickness (m)

2.25

Total material volume (m³)

11,250

Gas vent layer (m³)1,500

Compacted clay (m³)3,000

Geomembrane area (m²)0

Drainage layer (m³)1,500

Protection layer (m³)4,500

Topsoil (m³)750

Drainage adequacy (%)100

How to Use This Calculator

Enter cap length and width in meters to define the capping footprint.
Select barrier type (compacted clay or geomembrane + clay) and specify local frost depth.
Enable the gas vent layer option if landfill gas migration is a concern.
Set cap surface slope (%) and annual precipitation to verify drainage adequacy.
Review total cap thickness, layer volumes (clay, drainage, topsoil), and drainage adequacy rating.

How the result changes with Cap length (m)

Cap length (m)	Cap area (m²)	Total cap thickness (m)	Total material volume (m³)
1,001	50,050	2.25	112,612.5
3,501	175,050	2.25	393,862.5
6,500	325,000	2.25	731,250
9,000	450,000	2.25	1,012,500

Cap length (m): Length of the cap footprint in meters.
Cap width (m): Width of the cap footprint in meters.
Gas vent layer (1=yes, 0=no): Include a gas vent/collection layer for sites with volatile organics or landfill gas.
Barrier type (0=clay, 1=geomembrane+clay): 0 = compacted clay only (600mm); 1 = HDPE geomembrane + reduced clay (300mm).
Local frost depth (m): Maximum frost penetration depth for your region. Protection layer must exceed this.
Cap surface slope (%): Minimum 2% for drainage. Steeper = better drainage but erosion risk.
Annual precipitation (mm): Mean annual precipitation for drainage adequacy check.

Cap area (m²): Total surface area of the engineered cap.
Total cap thickness (m): Combined thickness of all cap layers.
Gas vent layer (m³): Volume of granular material for gas collection layer.
Compacted clay (m³): Volume of compacted clay barrier material.
Geomembrane area (m²): HDPE geomembrane area including 10% for overlaps. Zero if clay-only barrier.
Drainage layer (m³): Volume of sand/gravel for drainage layer.
Protection layer (m³): Volume of fill for frost/root protection layer.
Topsoil (m³): Volume of topsoil for vegetation support.
Total material volume (m³): Combined volume of all cap layers.
Drainage adequacy (%): Ratio of drainage capacity to peak infiltration. Should be >100%.

Identify Input Parameters
4 parameters
Cap length (m) = 100, Cap width (m) = 50, Gas vent layer (1=yes, 0=no) = 1, Barrier type (0=clay, 1=geomembrane+clay) = 0 = 7 input(s) provided
Calculate Cap area
Cap area = capLength * capWidth
5000 = 5000
Calculate Total cap thickness
Total cap thickness = gasVentThickness + clayBarrierThickness +
2.25 = 2.25
Calculate Total material volume
Total material volume = gasVentVolume + clayVolume + drainageVolume + protectionVolume + topsoilVolume
11250 = 11250
Calculate Gas vent layer
Gas vent layer = capArea * gasVentThickness
1500 = 1500
Calculate Compacted clay
Compacted clay = capArea * clayBarrierThickness
3000 = 3000