SOFIA (Bulgaria), February 1 (SeeNews) - Bulgarian state-owned gas transmission system operator Bulgartransgaz said on Friday that it has signed a 21.9 million levs ($12.8 million/11.2 million euro) contract with a tie-up led by Russia's Zapadgazenergoinvest for construction of a main gas pipeline between valve station Batultsi and VS Kalugerovo, in the country's northwest.