CRYPTIC ARTESIAN FLOW OF BULL SPRING: A KARST RARITY

Investigation of a sewage-contaminated karst spring in the southern Bluegrass of Kentucky, evolved into a series of rejected hypotheses of the origin of pollution. Bull Spring discharges 0.15 cfs at low flow and ~1.0 cfs during high flow conditions, and was heavily contaminated by sewage. The tainted flow displaced normal biota and discolored the receiving stream for hundreds of feet, producing a septic odor.

Bull Sp. discharges from the eastern bank of Balls Branch, a tributary of Clarks Run. The spring emerges at a bluff, from crevices and bedding-plane partings over a 30 ft-wide horizon. It drops ~1 foot to the bedrock channel of Balls Branch and was categorized as a free-draining, gravity or falling spring, and appears perched.

The following four hypotheses for the origin of the contamination were tested and rejected. (1) The initial hypothesis suggested that a local septic system, ~1200 ft to the ESE, had failed and was the source of sewage; a tracer test did not indicate a failed system. (2) Using the Unit Base Flow method, a second hypothesis projected a 1.5 mi2 drainage basin, to the east, upland of “perched” spring. Tracer tests documented radial flow to four small basins, rather than to Bull Sp. (3) A 19 million-gallon sewage lagoon, elevated ~27 ft above Clarks Run, was located 0.5 miles west of Bull Sp. This potential source, was rejected due to results of a lagoon leakage/evaporation test. (4) Two miles SW of Bull Sp., the intersection of a forced main and a mapped fault which terminates near the spring, generated the fourth hypothesis. This leakage into the fault system, 100 ft higher than Bull Sp., was tested by two different dyes into the forced main on either side of the intersection. Both dyes were recovered in Bull Sp. in less than a day. A leak had been discovered, though down-line of the hypothesized location.

A pump station located N of Clarks Run was eventually isolated as the leak-point; ~10 gpm of sewage was entering a complex artesian flow route, beneath both Clarks Run and Balls Br., ultimately discharging from an apparently perched spring. Similar artesian flow, from apparent falling springs, has been identified in a small number of karst drainage-basin distributaries. Although the watershed of a falling spring typically lies upland of the spring, complex karst flow in faulted areas and distributaries prove exceptions to the rule.