Water Flows of MSW Landfills and Implications for Long-Term Emissions

Abstract

A test landfill served for experiments to describe the water and material household of municipal solid waste (MSW) landfills. Special emphasis was given to the determination of the influence of the water flow on the substance balance. Therefore, a water balance was measured and the discharge was modeled by means of a mathematical model. A model, which separates the landfill into an area of preferential flow and an area of matrix flow fits best water flow data measured from 1987 to 1989 in the Breitenau landfill of 95,000 t MSW. This test landfill consists of three compartments C1, C2 and C3 with different covering systems. Leachate amount was highest in C1 with a permeable cover of silt and gravel. The lowest amount of leachate was found in C3 with a less permeable cover of gravel, humus, and plants. The values for C2 lie in between. An input–output balance for the substances C, N, S, P, Cl, Na, Ca, Fe, Zn, Pb, Cd and Cu was prepared. Contrary to the expectations the output of some substances was higher for C2 than for C1 with more leachate. Possibly a higher flow rate leads to preferential water flows that contact only small parts of the landfill body while most part of the landfill stays more or less dry. The substance balance reveals that most of the substances still remain in the landfill after 15 years of leaching. Hence, focusing on leachate concentrations only results in underestimating the after-care period of MSW landfills. Leachate concentrations reflect just a small part of a landfill. Understanding water flows and measuring substance balances improve considerably the assessment of the long-term emission potentials of landfills.