NOGALES, AZ (Tucson News Now) - Every few feet along the international border in Nogales there is evidence of an underground war between drug smugglers and Border Patrol agents.
"One area specially here has seen a lot of traffic," Border Patrol Agent Mathew Eisenhauer said.
Just feet from the border, concrete patches line International Street. It is a lasting sign of the old tunnels once used to move drugs from Mexico into the U.S.
MOBILE USERS: A slide show look at ground zero for the battle between drug smugglers.
This year, only three tunnels have been found. Border Patrol agents credit the decrease to the Homeland Security Investigations' Tunnel Task Force.
Deputy Patrol Agent in Charge Kevin Hecht took Tucson News Now behind the scenes of the dirty job.
"This is one of the areas we proactively patrol. As you can see, there is a lot of sediment and debris but no footprints. There is no activity," Hecht said as he descended into one of the sewer lines.
Border Patrol agents said it's rare to see people in the sewer pipes or tunnels. On average, drug traffickers can get $800 for each pound of marijuana, compared with anywhere from $700 to $1,500 for each person smuggled into the U.S.
Agents say the majority of the tunnels are less than a mile long.
"They aren't hauling around big pieces of industrial equipment. They are doing this with primitive technology, essentially by hand," Eisenhauer said.
The sewer lines used to be a gold mine for traffickers.
"They would ... feed narcotics through the grate and they would take off with anywhere between 100 to 1,500 pounds," Hecht said.
But the task force just added a new member, a camera-equipped robot that can be sent into sewer lines and even through tunnels to investigate.
"We just put the robot in the hole and the robot does the job," Hecht said.
When the robot is sent down the sewer line and it finds nothing, it is a sign this tunnel task force is working.
"A guy that makes a tunnel - there are millions of those. They can replace those. When you start taking people with the money out of it and the financiers out of it, you are making much more of an impact," Hecht said.
Just a few years ago, Border Patrol agents said they would be called out to places along the border at least once a week about some kind of tunnel activity but since they stepped up their patrols, the calls have decreased.