Field Investigation of Landfill Leachate Collection System Clogging

Leachate collection systems (LCSs) are designed to efficiently remove leachate from solid waste landfills. This prevents ponding of the leachate on the liner system, thus minimizing leachate migration to the environment. The depth of leachate on the liner is a regulatory design standard (<30 cm). The permeability of the LCS is a primary factor in determining the collection efficiency. The potential of LCS drainage materials (sand, gravel, and geotextiles) to clog as a result of biological growth and particulate clogging is an important issue that should be addressed in landfill design. The performance of individual components is known to decline in laboratory testing; however, little is known about permeability under true landfill conditions. Testing the drainage material in excavated LCSs for clogging is important in determining the extent to which individual components fail. Research was conducted to characterize the physical and chemical nature of drainage media collected from a 6-year-old leachate collection system. Hydraulic conductivity, grain size distribution, volatile solids, and metals analysis were performed on drainage sand samples to determine if any clogging had occurred. Likewise, permittivity tests were performed on geotextile samples. On average, the sand drainage layer permeability was reduced from 1.85 × 10⁻² to 1.23 × 10⁻² cm/s (33% reduction in flow). Likewise, the geotextile samples experienced an average decrease in permittivity from 6.4 to 3.3 s⁻¹ (48% reduction). Inspection of these results indicates that although the drainage media experienced a reduction in permeability and permittivity compared to original conditions, both the sand and the geotextile maintained their capacity for high flow rates, resulting in an acceptable increase of head on the liner.