Located at an altitude of over 2000m on the upper part of the Fully commune, the Sorniot site includes a hamlet of several mayens, a mountain pasture with its cheese dairy, a hut and a colony. All these entities produce wastewater which cannot be discharged as it is but must be treated beforehand. At present, this treatment is carried out by a mini-STEP on the spot, but the latter is somewhat undersized, no longer meets the standards and will eventually have to be decommissioned.

Therefore, the municipality is looking for an alternative and innovative solution to treat the water of the Sorniot site, for a peak load equivalent to about 120 PE, while taking into account several criteria specific to the site, namely:

• The difference in use over the year, from a few p.e. in winter to peaks of over 100 p.e. in summer
• The proximity of a drinking water catchment area
• The karst nature of the area
• Water protection zones
• The distance to the plain

The difficulty of accessing the site, particularly in winter (only feasible by helicopter).

Various solutions have been proposed, but each of them poses its own problems:

1. One solution would be to repatriate all the wastewater to the plain and treat it with the rest of the commune’s wastewater. This solution would make it possible to preserve the safety of the catchment areas, but would involve disproportionate costs, as it would require the installation of a pipe running down the entire slope.
2. An alternative solution studied was to upgrade and expand the existing mini-WTP to enable it to treat all wastewater on site and to discharge the treated water outside the protection zone (i.e. below the catchment areas). This option was not chosen as the costs are similar to option 1. Furthermore, due to the specificities of the site, it is difficult to guarantee that such a WWTP could be efficient enough to treat all discharges throughout the year. In particular, due to the very different seasonal use, the minimum discharge load necessary for the WWTP to function properly may not be achieved in winter. The winter temperatures at such an altitude complicate matters further. In addition, due to the configuration of the site, the possibility of discharging treated water to an open active field is quite limited.
   A similar solution with discharge into the natural environment in the Poteu fault in the water protection zone was not accepted by the environmental department for the same reasons.
3. A third option could be to treat the wastewater of the different entities (hamlet, alpine pasture, hut and settlement) independently. This solution implies different concepts of water sanitation depending on the types of producers, while guaranteeing the safety of the area (separation of discharges, management of grey water, etc.).

The proposed solution should therefore make it possible to
– Efficiently treat peak loads equivalent to 120 p.e., but remain functional with loads of only a few p.e. in winter
– Guarantee optimal and safe treatment to ensure that the surrounding water catchment areas are not impacted
– To carry out the proposed project at a moderate cost
– Ensure that the various environmental protection standards and requirements are met

In the absence of an alternative solution, the municipality will have to quickly implement the most costly and least innovative solution, namely the connection of Sorniot directly to the municipal wastewater network.