(Washington) -- Pennsylvania's junior U.S. Senator is calling on UGI Corporation to fully explain what caused a gas pipeline explosion last month in Millersville, Lancaster County. On October 31st, a two-story building was destroyed and nearly 100 homes and businesses were evacuated in the borough as a result of the incident. Democratic Senator Bob Casey says too many questions remain as to what caused the explosion and what's being done to prevent similar incidents in the future. In a letter to UGI's President, John Walsh, Casey calls on the utility to conduct an open and transparent investigation into the cause. He days the answers given by the company after nearly three weeks are inadequate. The explosion occured after Verizon contractors struck a gas line, while digging to bury fiber optic cables and the gas ignited. UGI initially said it marked the gas line properly, but two days later, said that was not the case.