All planning applications for dwellings in a rural setting must be accompanied by an Percolation Test Report which is carried out in accordance with the guidelines set out in the EPA Code Of Practice ” Wastewater Treatment & Disposal Systems Serving Single Houses (p.e.<10)"
The process involved excavation of one large trial pit, 2.1m deep together with three secondary trenches all of which were 800mm bgl. Each trench had a hole (P) excavated by hand 300 x 300 x 450mm deep located centrally in the trench. There was also a series of 3 no. holes, identical to the latter holes (T) which were excavated in the topsoil. These holes, when tested gave an indication of the percolation rate of the subsoil.
Fig. 1.1 – The Trial Hole
The three primary levels of risk which can be encountered are groundwater, rock or an impermeable subsoil layer. Should the above test fail, then the level of risk closest to the surface in this location would be the impermeable subsoil layer. Basically, any effluent discharged in this location could pond and cause significant risk.
Allied to this test / investigation is the profiling of the various soil types, an over view of which follows.
Small amounts of the excavated subsoil material are wetted and rolled into small balls as shown above.
In conjunction with the previous test, “Ribbons” are formed by pressing the sample between the thumb and forefinger. The length of the ribbon formed before it breaks apart will also assist in giving the soil its classification.
A desktop study is also undertaken to establish what soil types are predominate in the area prior to any excavation. During the site visit, all potential risks are recorded such as proximity to wells, streams, outcrops and the direction of the groundwater flow is recorded. A profile of the soil types can also be obtained from the cross section in the trial hole and indicators to be picked would be mottling of the side walls which would indicate a seasonally high water table or preferential flow paths which could assist percolation.
All of this information is considered when compiling the percolation test report which outlines the findings will accompany the planning application. It’s important to note that as with any test the outcome can be a pass or a fail.