Clogging by incrustations of nine groundwater heat pump (GWHP) systems in Melhus, Norway have been investigated by field and laboratory methods for water quality and incrustation composition. Iron oxides incrust systems extracting relatively shallow, low-saline groundwater, while iron sulfides are associated with deeper, more saline groundwater. Hydrochemical conditions in iron oxide clogged GWHP systems are favorable for the growth of iron-oxidizing bacteria. Also, sediment deposits clog the well systems. The variety of incrustation problems detected in Melhus emphasizes that clogging must be expected and dealt with, instead of solely attempted avoided through system design or re-location
