SUE Helps Map Underground Conditions in a Historic Mining Town

While Tonopah, Nevada, isn’t one of the state’s most popular tourist destinations, the town has a rich history dating back to the discovery of the state’s second most prosperous silver mines. Located between Reno and Las Vegas, the town’s Main Street is a highly traveled thoroughfare. The Nevada Department of Transportation planned a series of safety and aesthetic improvements as part of a complete streets initiative for three miles of the roadway. KCI provided subsurface utility engineering (SUE) and oversaw investigations and mapping of underground conditions to assist in preparation of design plans.

Miners quickly flocked to the ore-rich town of Tonopah, which was originally named Butler.
Miners quickly flocked to the ore-rich town of Tonopah, which was originally named Butler.

Tonopah was founded by Jim Butler in 1900, who had discovered a major silver strike in the area. Mining was big business, and just twelve months later, the town’s population had grown to 250. Now the town is home to approximately 2,500 residents along with regular tourist traffic visiting the historic mining park during the day and/or star gazing at night.

Tonopah and its many surrounding mines were definitely no flash in the pan. From 1900 to 1921, claims produced nearly $121 million in gold, silver, lead and copper. The last mine closed at the beginning of World War II.
Tonopah and its many surrounding mines were definitely no flash in the pan. From 1900 to 1921, claims produced nearly $121 million in gold, silver, lead and copper. The last mine closed at the beginning of World War II.

Although the town is small, Main Street carries heavy traffic traveling between Nevada’s two largest cities. Planned improvements should relieve congestion, improve efficiency and enhance safety throughout the corridor. Recognizing the potential for voids associated with previous mining and construction activities, the Nevada Department of Transportation called in KCI to document the underground conditions and existing utilities along the roadway.

Crews utilized various SUE tools and all ASCE-defined quality levels along the corridor. Technicians used electromagnetic detection equipment to designate conductive utilities, ground penetrating radar for non-conductive infrastructure, and vacuum excavation to visually confirm and survey the location of underground electric, telecommunications, water, sewer and gas lines. Overall, our team completed 82,950 linear feet of Quality Level D, C and B designating and 89 Quality Level A test holes.

In addition to the utilities present, it was critical to identify voids associated with old basements and underground tunnels because heavy equipment used during construction could potentially cause a collapse.

Richard Torrens, Jr.Practice Leader

Richard Torrens, Jr.

With the utility mapping complete, the focus of the project turned to identifying known and unknown voids. Mapping of the mines ranged from very limited to non-existent. KCI worked with subcontractor Geoview Inc. to identify the appropriate geophysical techniques to use in mapping any potential hollow areas. Electrical resistivity, ground penetrating radar and microgravity methods were employed along the corridor to document subsurface conditions to a depth of 20 feet.

Multiple geophysical tests, including microgravity analyses, were combined to create a detailed map of underground voids along the roadway.
Multiple geophysical tests, including microgravity analyses, were combined to create a detailed map of underground voids along the roadway.

KCI technicians supported the field work by entering several buildings where basements were known to exist, verifying their footprint, and locating the roadside edges of the basements by using a sonde that allowed our crew at the surface to detect the corners of each underground room, some of which were reportedly haunted.

Our team documented underground basements that extended under the roadway. Some still had glass blocks embedded in the ceiling that would have originally been sitting within the sidewalk surface as a light source for the room below.
Our team documented underground basements that extended under the roadway. Some still had glass blocks embedded in the ceiling that would have originally been sitting within the sidewalk surface as a light source for the room below.

Over the course of a year, our team completed detailed field investigations throughout the three-mile corridor to document existing conditions. Plan preparation is underway, and construction of the complete streets project is tentatively scheduled to begin in late 2019.