DID A ‘MID-CENTURY PULSE OF GROUNDWATER' CONTROL CAYUGA AND SENECA LAKES WATER QUALITY?

Since the late 1800s, salt mining waste and water retention time have controlled the majority of the chloride concentration in Seneca and Cayuga Lakes. From around 1900 to the early 1960s, lake chloride concentrations increased at a fairly steady rate. In 1967, water treatment plants’ lake-water chloride concentrations rose and fell 30 to 40 mg/l above a rising background of around 146 mg/l between May and November. Some scientists attribute the cause of the Seneca Lake peak to ‘a mid-century pulse of groundwater’.

Was there a ‘mid-century pulse of groundwater’? Maybe not. First, although Seneca Lake flows into Cayuga Lake, the occurrence of the 1967 peaks on both lakes make a groundwater source less likely. The 1980s chloride decline (documented by other researchers) suggests Seneca Lake’s influence on Cayuga Lake chloride values is minimal. Second, a lake bottom groundwater source needs to fill the lakes’ large volume (Seneca Lake, 15,539.5 million m³; Cayuga Lake, 9379.4 million m³). Although several researchers note higher chloride values near the lake bottoms, the long retention times (39.2 ± 24.2 years for Seneca Lake and 7.74 ± 3.02 years for Cayuga Lake) would preclude rapid flushing of large amounts of salt associated with the 1967 peaks from the lakes.

Timing of the 1967 chloride anomaly appears related an annual cycle. Minor chloride peaks for some years suggest a slight annual epilimnal increase in chlorides. I hypothesize the chloride anomaly is related to the thermocline cycle. An atypically high thermocline develops and the salt mine waste flows along a thermocline to the water treatment plants’ usually epilimnal intakes. Chloride values rise with summer thermocline development (June to July), plateau (July to September), and decline with the fall thermocline deepening (October to November).