Small scale sewage disposal
On the southern edge of Wackernheim - a town between Mainz and Bingen above the Rhine valley - lies the 'Schneckenbangert' farmland site. A new residential estate is currently being developed for which a sewerage system using HDPE pipes and HDPE Friafit fittings from Friatec is being brought on line.
The sewerage network will consist of a gravity pipeline on a site of around 5 ha with a 1-15% slope. Above the foul effluent pipe, a drainage trench with coarse ballast will also be installed to collect stormwater and channel it to surrounding soak-aways.
In total 17 levels and 18 concrete inspection chambers are being installed. In the inspection chambers 36 HDPE Friafit ASF adapters are being incorporated so that after fitting the AEM sewage insert sleeve and pipe, the bottom of the gutter is guaranteed to be on the same level. The ASFs will take 36 HDPE Friafit AEM sewage insert sleeves. The AEMs are optimally fitted into the ASFs using an elastomer interface as an articulating joint.
AEM sewage insert sleeves join the concrete inspection chamber to the HDPE pipe via a push fit connection at one end and via the Friamat fusion system, using a total of 400 HDPE Friafit d 180 AM sewage sleeves. This gives leak and root proof joints, which are secure under end loading. For the 90 plot connections, one HDPE inspection chamber is used per plot.
Foul effluent in the Schneckenbangert residential area will go from the sewerage system into the combined sewer from Wackernheim and will then be fed into the Heidesheim STP. After treatment, effluent flows through a flood ditch into the Rhine.
The purpose of a drainage trench, filled with coarse ballast, is to collect stormwater and to allow it to seep away over time in the soak-aways.
To save space, the stormwater drainage trench will be positioned above the foul sewer. For this, several pre-conditions have to be met:
- Sewage must not get into the storm soak-away area, nor rainwater into the sewer.
- The foul sewer must be absolutely leak-proof and secure under end loadings; this is guaranteed by the Friafit sewage system.
- The drainage trench, which is approximately 750mm deep, is filled with coarse ballast and must be protected against clogging.
This is why foul sewer pipes are surrounded with sand and bedded in a geotextile. The ballast in the drainage trench is likewise provided with its own geotextile sheathing. Included as part of these protective measures are so-called HDPE ‘retaining skirts’ which are intended to prevent erosion of the sand while stormwater seeps away.