Optimization of the natural attenuation applied to the rehabilitation of the old landfills

1. Optimization of the natural attenuation applied to the rehabilitation of the old landfills Statistical analysis, bibliographical research and proposition of solutions Presentation : Thierry CHASSAGNAC CSD AZUR

2. Report • The old landfills produce biogas and leachates • The environment strongly decreases the impacts in particular conditions • Several dozens thousand sites are concerned in France Interest to study and to develop the natural attenuation • Objectives of the study(ADEME) • Estimate the number of sites concerned by the natural attenuation • Identify the mechanisms of the natural attenuation • Propose solutions adapted to old landfills

3. 34 evaluation criteria representative of 8 families - geologic substratum - sensibility of the landscapes and the environments - landfill dimensions - sensibility of groundwater - sensibility of habitat and population - deposit composition - sensibility of surface waters - landfill age Allocation of a raw note for every criterion (+1 note of doubt by criterion) 34 raw notes (+ 34 doubt notes) 4 environments Catégory of risk of environment : A, B, C or D Catégory of risk of environment : A, B, C or D Catégory of risk of environment : A, B, C or D Catégory of risk of environment : A, B, C or D Global risk category of the site= Risk category of the most affected environment CSD AZUR Method

4. Principle of the statistical analysis • 6 regional diagnoses of landfills : 1410 referenced sites • 34 criteria aggregated in the form of risk notes by environments : • surface waters, groundwater, natural environment, human environment 4 category of risks : A - emergency situation B - strong to average potential risk C - average to weak potential risks D - weak to no potential risks • Enumeration • 18 % of sites are in direct and permanent connection with groundwater : • 7 % spring zone • 11 % backfilling of old water depressions (quarry) Study interest A : emergency C : middle D : weak B : strong

5. 1 - no resource 2 - improbable resource 3 - likely resource of moderate importance, exploited or not 4 - important to average resource, recognized, not exploited 5 - important resource, exploited and recognized < 1000 1000 to 5000 5000 to 10000 > 10000 1 - no resource 2 - improbable resource 3 - likely resource of moderate importance, exploited or not 4 - important to average resource, recognized, not exploited 5 - important resource, exploited and recognized > 20 m 10 à 20 m 2 à 10 m < 2 m • Typology of sites in connection with groundwater (comparison to the other sites) : • more risks • ground waters : • permeable substratum • potential resources • subsurface groundwater • surface waters : • near streams • high flow • potential resources • nearness and density of population • more vast and less thick

6. Mechanisms of natural attenuation for the leachates 1. Underground wet mechanism : the infiltration - percolation • Unitarian processes : • filtration • adsorption • precipitation • dispersal • nitrification • dénitrification • degradation of the organic matter • Parameters : • water • oxygen • geometry of the filter • soil condition • pollution burden to be treated • temperature • pH • redox potential The infiltration percolation allows : to hold the polluting particulate elements to hold inorganic pollutants (sorption) the degradation of organic pollutants by microorganism the treatment of the nitrogenous compounds by particular microorganisms

7. Mechanisms of natural attenuation for the leachates 2. Superficial wet mechanism : lagooning • Unitarian processes : • consumption of nitrogen and phosphor • degradation of organic matter • decantation • volatilization • photolysis • waters disinfection • Parameters : • residence time • oxygen • pollution burden • temperature • pH • redox potential The lagooning allows : the decantation of suspended solids and their trapping in the bottom of ponds the photolysis notably of halogen compounds the degradation of the organic compounds by microorganisms the consumption of nitrogen and phosphor by micro and macrophytes

8. Mechanisms of natural attenuation for the leachates 3. The phytoremediation • Unitarian processes : • phytostabilization in the rhizosphere • adsorption on roots • detention in the roots • rhizodegradation • phytovolatilization • accumulation • degradation • action on the heat flows • Parameters : • water • oxygen • chelates • pollution burden to be treated • plants cycles “ The phytoremediation is the use of plants, their associated microbiote, amendments and agricultural technics to eliminate, contain, or make less toxic environmental pollutants ” (Cunningham). The phytoremediation allows : the consumption of nutriments (nitrogen, phosphor, potassium, micronutrient) the consumption of trace metals the degradation of the organic compounds by rhizospheric microorganisms

9. Mechanisms of natural attenuation for the gas releases • The properties of the cover : • interception of meteoric waters • limitation of the flight of wastes • support of the vegetalization • the oxidation of the methan : methanotrophic microorganisms • Parameters : • thickness of the cover • food continuance • organic matter ( use of compost) • vegetal densityof the cover • inhibitors

10. Typical solution for sites in spring zone

11. Typical solution for sites in backfilling of old water depressions

12. Comparison of the costs of rehabilitation to those of the classic treatments Typical landfill of 2 hectars on 10 meters in thickness (200 000 m3) and having received 10 000 tons of waste during 20 years 1. Case of sites in spring zone  7 - 14 times less high investment costs 2. Case of a backfilling of an old water depression  1,5 - 5 times less high costs

13. Treatment of the gas releases (case of the weak production of biogas) : methan oxidation in the cover • Composition of the cover (from bottom to top) • screen limiting water input • drainage layer of infiltrated waters • treatment layer of biogas : • mineral layer • organic layer • vegetation  Identical costs to those of a classic cover (600 k€ / 2 ha), supplement from 1 to 3 € / m2 for organic amendment

14. SECTION Surface filtration bed : channel type PLANE Surface filtration bed : baffle type DETAIL SECTION Soil baffle Plans of the superficial filtration bed with macrophytes

15. SECTION Gravel 0-30 Sand 0-10 Low permeability soil Control piezometric tubes PROFILE Clogged zone Distorsion of the clogged zone Piezometric level Plans of the underground filtration bed with macrophytes

16. Plans of the peripheral lagoon with microphytes

17. Macrophytes zone Macrophytes zone Microphytes zone Water level fluctuation zone Optional overpit Plan of the lagoon with macrophytes

18. 1 3 4 2 Biological treatment 1 IN : Raw leachates OUT Phragmites Typha Willows 2 3 4