GROUND-WATER TEMPERATURE IN A FRACTURED DOLOMITE AQUIFER DURING AQUIFER TESTING

Ground-water temperature and water-level data were analyzed for three 72-hour aquifer tests conducted in fractured dolomite of the Allentown formation in the Valley and Ridge physiographic province of northern New Jersey. One test was conducted in October 2003, and two in June 2005. The data were collected at 3-minute intervals in pumping well 1A and four observation wells located at a maximum distance of 750 feet from the pumping well. Small changes in ground-water temperature, only tenths of a degree Farenheit (F), measured in well boreholes provide clues to the hydrologic interconnection between shallow and deep water-bearing zones and the adjacent Wallkill River.

Ground-water temperature trends in response to pumping varied by well location, depth within the aquifer and whether or not inflatable well seals (packers) were used to separate the shallow (generally < 250 feet) and deep flow zones. Before pumping began in the June 2005 tests, temperature in the shallow zone ranged from 53.4 F to 53.9 F. Temperature in the deep zone was 52.0 F, or approximately 1.7 F colder than the shallow zone. In Observation Well 2, where borehole geophysical logs indicate numerous open fractures and cavernous zones throughout the vertical extent of the aquifer, ground-water temperature remained unchanged during the tests. This suggests that, despite drawdown in the observation well, water passing through the borehole was derived from the same source(s) as prior to the pumping and that the open fracture network allowed for thorough mixing of water in the shallow and deep zones. In Observation Well 3, where discrete shallow and deep flow zones were identified prior to the testing, borehole ground-water temperature decreased by 0.6 F in 72 hours as flow to the well was derived increasingly from colder water in the deep flow zone. In Pumping Well 1A, an increase of 0.4 F in shallow ground-water temperature corresponds to a recharge boundary interpreted from the water-level data and suggests diversion of warmer (76 F) water from the adjacent Wallkill River. The research indicates that temperature data can provide valuable information for interpreting complex fractured-rock flow systems.