Curt Madsen, P.E. TRC Environmental Corporation

November 28, 2012

Landfill Leachate Collection System Design

CEE 427

• Primary criteria…route leachate off liner to collection sump• Designed to limit head to 12 inches or less • Minimum base slope of 0.5%• Maximum flow distance to collection pipe of 130 feet• Minimum hydraulic conductivity of 1x10-2 cm/s of drainage

layer aggregate• Minimum 1-foot-thick select aggregate fill drainage layer

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General (Referencing Wisconsin s. NR 504.06(5))

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• Used to size pipes, pumps, tank storage volume, estimate treatment costs

• Based on NR 512.12(3)(a) and (b)– 6 inches/year for unclosed areas– 1 inch/year for closed areas (with composite cover)

• Values above are more conservative than Help Model

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Leachate Generation

• Consists of select aggregate layer, collection piping, sumps, FM transfer pipes and cleanout access piping

• Select aggregate drainage layer placed on geotextile cushion (min 12 oz/yd)

• Aggregate is used to allow for future leachate recirculation• Drainage layer consists of rounded to sub-angular (then use

16 oz/yd) stone with Unif. Coeff. < 4; max. particle diam. of 1.5 inches; a max. of 5% passes #4 sieve; no more than 5% passing #200 sieve

• Minimum pipe slope is 0.5% (typically greater)• Collection piping placed in V-trenches (per NR 504.06(5)(d))

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Leachate Collection System

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• Piping consists of 6-inch diameter perforated SDR 11 HDPE pipe

• Pipe strength calculations (attached)• Perforated 0.5-inch holes, 2 rows set at 45 degrees and placed

@ 6-inches• Minimum of 6-inches of bedding material placed under pipe• Minimum of 18-inches of bedding material placed over pipe• Performed piping and permeability calculations to confirm

required hydraulic conductivity without excessive migration of fines

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Leachate Collection System (continued)

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• Collection pipes extend to sump• Perimeter cleanouts installed at both ends of pipe• Lower portion of cleanout on side-slope may be perforated• Leachate headwell

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Leachate Collection System (continued)

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• Leachate drains to collection sumps (fill with similar select aggregate)

• Sump volume sized to satisfy NR 504.06(5)(j) and accommodate sediment

• Inclined riser (18-inch-diameter SDR-17 HDPE) terminates into a vault

• Sump area must accommodate remedial installations• Use back-flow preventer valves• Submersible pumps / controlled with transducers / run-time

meter

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Leachate Removal and Storage System

• Provide valves to isolate systems• Pumps (place on PE skid plate) • From vault leachate transferred to tank via forcemain (double

cased)• Minimum 4-day tank storage volume required (secondary

containment)

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Leachate Removal and Storage System (continued)

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• Maximum “clean-out” length may not exceed 2,000 feet (NR 504.06(6))

• Minimum 0.5% slope after accounting for primary and secondary settlement (100 yr)

• Similar bedding material requirements• Utilize sweep bends (minimum radius of 10 pipe diameters)

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Extended Length Leachate Collection Line Considerations

• Pipe strength calculations– Purpose, methodology, assumptions, results, references– Figures– Calculations

• Watkins’ Method• Modified Iowa Formula• Corrugated pipe (downslope flumes)

• Piping and permeability calculations– Purpose, methodology, assumptions, results, references– Calculations

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Attachments

Questions?Curt Madsen, P.E.P: 608-826-3640 | E: cmadsen@trcsolutions.comwww.trcsolutions.com