san diego on the border with tijuana, mexico. this is a tunnel that stretched about 7650 feet from tijuana into a warehouse or would have stretched into a warehouse on the other side of the border and we're about 70 feet underground right now. >> that's one of the deeper tunnels we've found. >> reporter: lance is part of a specialized team of border patrol agents known as the tunnel rats. they work underground, 1/2 gaiting newly discovered tunnels and sewer systems. >> reporter: do you think these tunnels started appearing as a response -- as more fencing went up in this area? >> oh, i'm sure it probably did. but we're also still talking there's a lot of stuff they have to move. >> reporter: homeland security officials say in the last ten years nearly 30 tunnels have been discovered just in the san diego area alone. >> they will continue to go on between the u.s. and mexican border, yes, it will continue. there's a way that these drug trafficking organizations can stay undetected and...