This document specifies characteristics and related requirements@ assessment methods@ the marking and assessment and verification of constancy of performance (AVCP) procedures for prefabricated tertiary treatment units used for populations up to 50 inhabitants. Prefabricated tertiary treatment units in accordance with this document are: ? used for the tertiary treatment of domestic wastewater coming from: a) products in accordance with EN 12566-3 or EN 12566-6 or; b) installation designed and constructed in accordance with CEN/TR 12566-5. Equivalent secondary treated effluent may come from existing systems. ? made of concrete@ steel@ Unplasticized Polyvinylchloride (PVC-U)@ Polyethylene (PE)@ Polypropylene (PP)@ Glass Reinforced Polyester (GRP-UP)@ Polydicyclopentadiene (PDCPD)@ PVC and/or EPDM. ? used buried in the ground; ? with or without extension shaft; ? made of prefabricated components that are factory or site-assembled by one manufacturer and which are tested as a whole. This document does not cover prefabricated tertiary treatment units: ? where vehicle loads apply to it; ? with direct infiltration into the ground (non-watertight); ? made of retrofit kits (see definition in 3.1.9); ? forming part of products covered by EN 12566-3 and EN 12566-6; ? for microorganism reduction. The assessment methods specified in this document establish the performance of the prefabricated tertiary treatment unit@ needed to verify its suitability for the condition in which it is normally installed