During the planning of any of our projects a vital element is to consider the potential substrata within the excavation area, this allows us to determine any delays we may experience in our project. In certain areas in the country the chances of hitting solid rock are certainly higher than others, a number of factors can attribute to this including soil depth and geological makeup.

In Cumbria certain parts are more likely to require the use of a hydraulic breaker which was certainly the case on a recent job we undertook in Cumberland. The site was requiring a new sewage treatment plant to be installed to suit the non-compliant septic tank.

The system we advised to install to suit the dwelling was the Klargester BioDisc package sewage treatment plant, this unit was selected as the best to suit this application due to the low power consumption, high effluent quality and nearly soundless/ odourless operation.

We excavated to intercept the existing inlet drainage to divert from the old septic tank, which was currently discharging to the nearby watercourse, 6 metres of new inlet drainage was required to redirect the incoming flow to the new installation location.

Due to the proposed outfall location being the nearby watercourse which the septic tank had been discharging to previously under the 2020 General Binding Rules a new Sewage treatment plant must be installed to BS EN12566-3 Standards.

Trial excavations were initially carried out and it became quickly clear that solid rock was going to be a recurring theme throughout the scope of works. However, a 5-ton Excavator with a breaker made easy work of the boulders we were uncovering.

There are some factors that need to be taken into consideration when looking at unfavourable ground conditions such as:

• Length of time required to carry out the excavations.
• Additional materials need to install the system such as additional concrete to account for the voids left by the breakdown of boulders/ slabs of rock.
• Additional specific machinery requirements and subsequent additional costs.

The outfall from this treatment plant then connected on to the old discharge line with the installation of 9 metres of new outlet pipework being installed and a new suitable sample point as required under Building control requirements. Once the installation works had been completed and inspected by Building control as satisfactory our team then backfilled all excavations and left site to a tidy machine finish.