This document explains an approach for assessment of limit values for contaminants that may be found in biomethane. Limit values are generally required as an adjunct to a biomethane specification (such as parts 1 and 2 of EN 16723, or an equivalent National specification) or as part of a Network Entry Agreement for injection of biomethane into gas networks. The methodology employed will permit derivation of limit values based solely on consideration of potential for impact on human health and does not consider other impacts, such as integrity and operation of plant and pipelines used to convey biomethane or appliances involved in its combustion or other regulations like CLP regulation. Where consideration of such impacts would result in proposing lower limit values than those based on health impacts, then the lowest limit values should generally be proposed.