IDENTIFYING SOURCE AREAS FOR COLD-WATER RECHARGE TO THE HOT SPRINGS AT HOT SPRINGS NATIONAL PARK, ARKANSAS

The discharge from the hot springs at Hot Springs National Park consists of a deep thermal water source, and a shallow, cold-water component. The size of the cold-water recharge area was estimated from the general concept of the hydrologic budget, whereby the average annual shallow ground-water recharge (input) is equal to the average annual cold-water discharge (output) at the hot springs. The cold-water discharge at the hot springs was estimated from the average silica concentration of water samples collected from nine hot springs during low-flow conditions in September, 2000. Based on an estimated cold-water discharge of 17.8 million gallons per year, and an estimated ground-water recharge rate of 5 to 10 inches per year, the estimated size of the shallow, cold-water recharge area is 0.10 to 0.20 square mile. The shallow, cold-water recharge area appears to be bounded on three sides by low-permeability barriers, and extends upgradient approximately to the topographic and inferred ground-water divide. The size of the shallow, cold-water recharge area, based on these boundaries, is about 0.14 square mile.

Dyes were released along surface drainage at three locations upgradient from the hot springs on Hot Springs Mountain. Two of the dyes (fluorescein and eosine) flowed along surface drainage to Hot Springs Creek and were not detected above background levels at hot-water recovery sites. The third dye (rhodamine) was released about 1,000 feet upgradient of the hot springs and was detected above background levels at several hot-water recovery sites over a period of several weeks. Time of travel from the release point to the hot-water recovery sites ranged from 1 to 3 weeks. The flow path of the rhodamine dye to the hot-water sites is presumed to be along the recharge area western boundary where the Hot Springs Sandstone contacts the Stanley Shale, and along northeast-trending fractured lineaments. Presence of the dye verifies that this area is part of the recharge area to the hot springs, and that surface runoff enters the ground-water system at some point along the pathway of the rhodamine dye.