USE OF CHLORIDE MASS-BALANCE FOR THE CALCULATION OF GROUNDWATER RECHARGE IN THE WETLANDS OF MOSQUITO CREEK LAKE IN NORTHEASTERN OHIO

This study employs natural concentrations of chloride dissolved in precipitation and groundwater to quantify the rate of groundwater recharge in the wetlands located on the western shore of Mosquito Creek Lake in northeastern Ohio. The study area is part of the wetlands that are protected and administered by the Division of Wildlife of the Ohio Department of Natural Resources.

Groundwater in the study area occurs under unconfined conditions at a shallow depth ranging from a few feet to less than one foot. Quantification of groundwater recharge is accomplished by using a mass-balance of the conservative chloride ion. The mass-balance utilizes three parameters: the concentration of chloride dissolved in precipitation, the volume of precipitation, and the concentration of chloride dissolved in groundwater. The three parameters are obtained from two precipitation gauges and three groundwater monitoring wells installed for this purpose. The three wells are located 100 feet from each other and the two gauges are 200 feet apart. The three parameters were measured weekly for a period of 4 months extending from the first week of April to the last week of July 2004. Significant groundwater recharge occurs in the study area during this period (late spring and early summer). Major sources of this recharge are snowmelt and direct precipitation. Recharge occurs through heterogeneous layers of sand, silt, clay, and some gravel.

The weekly chloride concentrations measured in groundwater varied from 4.0 to 11.5 mg/l, with a mean of 8.4 mg/l. The weekly precipitation volumes and chloride concentrations in precipitation ranged from 0.0 to 50.8 mm and 1.0 to 3.5 mg/l, respectively. Mean values of precipitation volumes and chloride concentrations in precipitation are 21.8 mm and 2.3 mg/l, respectively. Application of the mass-balance to the mean values yielded an average annual groundwater recharge rate of 311.2 mm (12.3 inches), which is about 27% of the total precipitation.