in datastax documentation it is mentioned read repair happens for consistency level one , even there is one quiz on this in DS-201 . I have attached image for that .
below link is from apache cassandra :
please refer screenshot attached below and notice highlighted part .
also in apache cassandra documentation it is mentioned . "If read repair is performed it is made only on the replicas that are not up-to-date and that are involved in the read request. The number of replicas involved in a read request would be based on the read consistency level ."
above line stats that only those many replicas are checked in numbers as the per the consistency level set . So if consistency level is set to ONE . Only one replica will be checked and data will be sent to client .