Highway extension to cross recharge zone
Sixty acres along the higher elevations of the 5-mile extension of the King Expressway will be protected from development, a conservation measure the state is taking to safeguard the city’s namesake thermal springs.
The northern half of the two-lane extension connecting the Highway 70 east interchange to the junction of highways 5 and 7 will traverse part of the more than 30-squaremile area that collects water for Hot Springs National Park’s thermal springs, according to a report re-evaluating a 2005 environmental
assessment.
The report approved in April by the Federal Highway Administration said the extension will not directly affect the recharge area’s ability to capture and convey water to the thermal springs. But development along the corridor, particularly at higher elevations, has the potential to alter the temperature and flow of the springs, a hydrologist recently explained to the Garland County Quorum Court.
Water has to enter ground fractures and faults in the recharge area at a minimum elevation of 660 feet to make the more than
4,000-year journey to the springs, said Phillip Hays of the U.S. Geological Survey’s Lower Mississippi-Gulf Water Science Center. That height gives water the pressure to reach depths of up to 7,000 feet, where it gets heated to 170 degrees before rising to the surface.
Putting drainage and impermeable surfaces at higher elevations would block or divert rainfall that would otherwise replenish the springs, he said, explaining that large scale development at the threshold elevation or higher could immediately affect flow and temperature.
“The highway itself is a pretty small footprint,” he told the quorum court. “But an auxiliary thing to worry about is development to follow. We could have significant land use change and land cover change. More impermeable surfaces often follow highways. We might want to think about what follows this construction.”
The report said the corridor will cross 189 acres of the estimated
23,838-acre recharge area, the boundaries of which USGS recently expanded. The area is about four times the size of the national park and lies mostly outside its borders.
The report said 59.6 acres of the affected 189 acres are above the threshold elevation.
“(The Arkansas Department of Transportation) will purchase
60 acres of mitigation land above 660 feet mean sea level in the recharge area to permanently protect it from development,” the report said.
The corridor ArDOT has begun acquiring right of way for tracks closely to the one identified in the 2005 environmental assessment conducted ahead of the initial plan to extend the expressway. It was shelved after thermal water was found in a private well in the Bratton Drive Area more than 5 miles east of the national park. A USGS study published in 2009 said the well was unrelated to the park’s thermal water system.
The Greer Well in the Thousand Dripping Springs recharge area is the closest hot water well to the corridor, according to the report. It lies west of Promise Land Drive and east of the park’s recharge area.
Hays said in addition to a thermal flow path, water from the park’s springs also flows from cold water sources. That water can reach the springs within hours to days of entering the ground, mixing with hot water that travels from much greater depths.
The report said cold water can constitute up to 30 percent of the springs’ flow during periods of heavy rain. Hays said that ratio is why some springs can have temperatures of less than 100 degrees. Overdevelopment in the higher elevations of the thermal recharge area could upset the hot-cold mix, reducing temperatures he said currently average from 150 to 160 degrees.
“The cold water component is going to stay there, because that’s from a short flow path,” he said. “What you’ll end up doing is changing the mix of that hot water. The springs could get cooler if you significantly affect things up there such as drainage.”
Hays said low-density housing in the Indian Mountain area is the most significant development that has occurred in the recharge area, as its formidable, unforgiving terrain has mostly discouraged residential and commercial construction.
“It’s only been a few years that we’ve done enough work to begin to understand what the recharge area is,” he said. “Now we know, partly by luck, we’ve had some protection of those higher, really rugged, areas, just because development hasn’t occurred yet.
“(ArDOT) has said, ‘We don’t want to be the highway department that ruins the national park, ruins a resource like this that the city is built upon.’ They’re very concerned about this and want to do the right thing.”
ArDOT said it plans to put the project out for bid by the end of the year. Garland County voters approved a temporary 0.625 percent sales tax in a June 2016 special election to finance $30 million of the estimated $60 million project. The state has said the county’s obligation will not exceed $30 million.
Eighteen residents and two businesses will be displaced by the extension, according to the report.