Site Suitability Assessment (SSA)

The purpose of an EPA Site Suitability Assessment is to determine the suitability of the site for a wastewater treatment system. The assessment will also help to predict the wastewater flow through the subsoil and into the sub-surface materials. The site characterisation process outlined here is applicable to the development of a single house and more extensive site characterisation is required for cluster and large-scale developments.

The key to installing a reliable on-site system that minimises the potential for pollution is to select and design a suitable treatment system following a thorough site assessment. For a subsoil to be effective as a medium for treating wastewater, it should retain the wastewater for a sufficient length of time, and it should be largely unsaturated and hence aerated. Only after a site assessment has been completed can an on-site system be chosen.

The information collected in the evaluation will be used to select the on-site system.

In designing a wastewater treatment system to treat and dispose of the wastewater, three factors should be considered:

• Are there any site restrictions on the site?

• Is the site suitable to treat the wastewater? (Attenuation)

• Is the site able to dispose of the wastewater? (Hydraulic load)

To assess the factors a site characterisation is undertaken.

This includes:

1. A Desk Study; and, if there are no site restrictions,

2. An On-site Evaluation, consisting of:

• A Visual Assessment;

• A Trial Hole; and

• Percolation Tests;

3. Conclusion and Recommendation (selection and design of a wastewater treatment system).

To assist in the selection of the on-site system and to standardise the assessment process, a site characterisation form should be completed. The completed form including photographs, site plans, cross sections and design details should accompany all planning applications for on-site wastewater treatment systems for single houses.