Drug enforcement agents discover a drug-smuggling tunnel in Arizona. Drug enforcement agents found another drug-smuggling tunnel in Arizona on Friday (July 13). The entrance to the tunnel was discovered behind the door of an apartment in the southern town of Nogales on the border with Mexico. The tunnel, about six feet deep and two by three feet in diameter ended in a drainage system on the Mexican side. An earlier marijuana bust in the neighbourhood provided agents with the lead on the tunnel's existence. DEA agents have filled the tunnel with cement since the discovery.