The work concerned the final closure of a landfill site of non-hazardous waste in the Municipality of Cagli (PU), specifically in “Località Ca’ Guglielo”, plus the consequent environmental restoration of the interested area.
Contractors where awarded on the sole basis of the award criterion for the most economically advantageous tender, based on the best value for money.
The drawing of the technical proposals, which importance was 50/100 allowed Krea the awarding of the contract by the elaboration of 24 technical proposals for improvement which mainly involved the protection of the environmental and hydro-geological side and the vegetative restoration of the entire area.
Description of the work stages:
STAGE 1 – Safety measures
The preliminary activity regarded the uncoupling, for each sector, of the transportation plumbs of the leachate and biogas.
Thereafter it was possible to proceed with the cut and removal of the upper temporary protecting plastic mats.
STAGE 2- Adjustment and leveling of the waste-mass – slope stabilization
The final closure operations of the landfill interested the movement of the internal waste in order to built the morphology panned in the executive project and approved by the accredited control agencies.
This activity was made by specialist personnel of the company, who operated by sectors to minimize potential problems for the external environment.
The significant inclination of some embankments could give rise to a unstable situation, for that reason it was necessary to realize mechanically stabilized earth with geocomposite nets.
In this way, the established solicitation which interacts in the structural increasing loads is liable to mobilize the traction resistance of the reinforcement by virtue of the own friction grip with the ground.
STAGE 3 – Realization of a deep drainage in the body of the landfill
To preserve the environment we realized a deep draining trench inside the waste-mass, in order to guarantee the hydraulic channeling of eventual leachate present inside the waste, to the underlying pitch.
The drainage was externally assembled for a maximum length of 10 mt, and then dropped inside the digging and then back covered; the digging and dropping operation was executed in a few hours to guarantee the stability of the entire embankments and of the waste-mass. The workers safety was guaranteed by absence of any operation inside the digging.
STAGE 4 – Final capping realization
In order to permit a secure anchorage of the capping and to reduce the traction strain on it by the land blanket on the body of the landfill, some trenches for geosynthetics anchorage where made; moreover the traction strain was also reduced by removing the covering ground in proximity of the border of the capping which was possible by the preliminary finding of the perimeter mats at the bottom of the pitch.
After that a stratigraphy of the geosynthetics package was made, from the bottom to the top:
- draining geocomposite with biogas capture function;
- impermeable geomembrane with raised gap on both sides with waterproofing function;
- draining geocomposite with rainfall water capture function;
- three-dimensional geogrid to hold and avoid a sliding of the ground:
To make the “hermetic filling of waste-mas” respect to the external environment a welding of the the planned geomembrane and the existing on the bottom of the waste containment pitch geomembrane was made after the laying of the geosynthetics until the external perimeter of the capping.
STAGE 5 – mountain underground water capture
A geological and hydro-geological study of the upstream the landfill was made because during the meteorological events the level of the ground water raises quickly up to a level near to the ground. This study found a particular geological formation in the area which captures the waterfall of the mountain and the upstream fields to the landfill.
After that, in order to monitor and contain the level of the ground water, a solution proposal was prepared.
The intervention requested the realization of 11 draining wells, with a maximum depth of 20 mt, each one equipped with a well pump.
STAGE 6 – Control of surface water and vegetative restoration
In order to guarantee the maintenance of the condition of stability of the final capping cover, an waste water system for the rainfall water of the covering ground of the capping was realized. To guarantee this function a net of surface water capturing ditches was made which channels the collected water in an external to the landfill body disposal net.
To fulfill the operation more than 25,000.00 cubic meters of vegative land where supplied and lied to cover the sarcophagus of the landfill.
One of the principal problems, surfaced since the planning stages, was the supplying of the necessary vegetative land to cover and restore completely the area.
Krea Costruzioni, in a close cooperation with the Contractor: Marche Multiservizi of the Municipality of Cagli (PU) in which area the landfill completely is situated, and the Municipality of Frontone (PU) neighboring with the site, has provided to supply and lie the necessary quantitative of the planned requirement, and anticipated the completion of the works, with rispect to the contractual terms which the same Krea reduced in order of time during the offer stage.
After the lying of the vegetative ground a study of the essence was made and a potentiated hydroseeding with planting of tree species was completed.