If archaeological remains are identified by non-invasive techniques, evaluation by test excavation may be required to further assess their nature, extent and quality.
This systematic survey can be undertaken at various levels of detail from trial trenching to test excavation. The scope and form differs between countries but also between different projects. Controlled test excavation of one or more areas across a site delivers a much firmer basis for assessing the nature, extent and significance of archaeological features.
Trial trenching (or test pitting) is an efficient and common archaeological survey method. It aims to identify the extent of archaeological deposits in the studied area to determine the extent of the site. This comprises limited subsurface excavation of an appropriate percentage of the area to be developed. The trenches or pits are excavated until natural subsoil or bedrock is reached. Sometimes, the material may be sieved to retrieve small artefacts or ecofacts. The purpose of invasive evaluation is not to fully excavate remains, however a limited programme of post-excavation analysis is necessary in order to study the results of the evaluation and to process, analyse and conserve samples, artefacts and ecofacts where necessary.