In all cases where a planning application involves a proposal to use a septic tank or other on-site treatment system, a site assessment is required. This is to ensure ground waters are protected.
The system of site assessment required under the EPA document involves several elements:
- A desk study which looks at available documented information on a site. This includes information on the soils, geology, location of wells and streams etc.
- A visual assessment which involves looking at the site and its surroundings to gain an indication of how well or poorly drained the site is likely to be and what targets are likely to be at risk in the area (e.g. rivers and streams bounding a site, public or private wells in close proximity to the site).
- On-site investigations including an assessment of the soil profile up to a depth of 2m, or greater in some cases, and percolation tests to confirm the drainage conditions. This test is done by excavating a series of holes on site to test the hydrology of the ground conditions. The holes are made up of one large trial hole 2.1m deep x 1m wide x approx. 3m long with a sloped entrance for access, this hole is to assess the water table and bedrock. Six other holes are then dug, three of which are “P’ test holes dug with a spade at the top of the surface to assess the upper limits of the subsoil, they are 300mm long x 300mm wide x 400mm deep and finally we dig three further holes called the “T” test holes which are 1m wide x 1m long x 500mm deep and inside that hole we then dig a spade hole 300mm x 300mm x 400mm. The “T” test is to give us an indication what conditions are like further down or at the location of the inlet of the proposed pipe. The trial holes can be located adjacent to where the proposed percolation area is to be constructed.
- Recommendations as to the form of wastewater treatment, if any, are best suited to the site conditions.