Municipal Landfill Gas Recovery Feasibility at Oakridge County Landfill

Scenario

Project Type: Landfill gas (LFG) energy recovery feasibility study Location Context: A 35-year-old, unlined municipal solid waste landfill in temperate humid climate (Oakridge County, Indiana, USA), accepting ~120,000 Mg/year historically. Site has limited existing gas infrastructure and faces tightening state air quality regulations requiring LFG capture by 2026. Constraints: Budget cap of $1.8M for initial collection system; must demonstrate ≥75% capture efficiency to qualify for EPA LMOP incentives; no access to natural gas grid — only on-site electricity generation is viable.

Given Data

• Mass of Waste in the Landfill: 245,000 Mg
• Methane Generation Potential: 112 m³/Mg (based on 2023 waste characterization study showing higher food/yard waste fraction)
• Degradable Organic Carbon Fraction: 0.58 (measured via TOC analysis of core samples)
• Decay Rate Constant: 0.072 year⁻¹ (calibrated using 5 years of field gas probe data; elevated due to high moisture and moderate temperatures)
• Waste Age: 18 years (average age of active disposal cells)

Calculation

LandGEM uses the first-order kinetic model:

$$ LFG_rate = k \cdot L_0 \cdot M \cdot e^{-k \cdot t} $$

Where:

• $k$ = decay rate constant = 0.072 yr⁻¹
• $L_0$ = methane generation potential × degradable organic carbon fraction = $112 , \text{m}^3/\text{Mg} \times 0.58 = 64.96 , \text{m}^3/\text{Mg}$
• $M$ = mass of waste = 245,000 Mg
• $t$ = waste age = 18 years

Step-by-step:

1. Compute $k \cdot L_0 \cdot M = 0.072 \times 64.96 \times 245{,}000 = 1{,}144{,}512$ m³/year (initial rate coefficient)
2. Compute exponential decay term: $e^{-0.072 \times 18} = e^{-1.296} \approx 0.2736$
3. Multiply: $1{,}144{,}512 \times 0.2736 \approx 313{,}138$ m³/year

Rounded to two decimal places per tool spec: 313,138.00 m³/year

Result and Decision

The modeled landfill gas generation rate was 313,138.00 m³/year, equivalent to ~175,000 m³ CH₄/year (assuming 56% methane content). This supports an estimated 1.1 MW of electrical generation capacity — sufficient to power 850+ homes and meet >90% of on-site operational loads. Based on this result, the county approved Phase I: installation of a 42-well horizontal collector system with blower packages and a 1.2 MW internal combustion engine generator. The project qualified for $420k in EPA LMOP technical assistance and secured a 15-year PPA with the local co-op.

Lesson

Field-calibrated decay rates — not default literature values — are essential for accurate LFG forecasting; using the generic default (0.05 yr⁻¹) here would have underpredicted generation by 28%, risking undersized infrastructure and missed incentive eligibility.