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Abstract: Shallow Saline Groundwaters of the Queenston-Medina Subcrop, Western New York State

Sear-Brown Group, Rochester, NY
Clemson University, Clemson, SC
Weizmann Institute of Science, Rehovot, Israel

Saline groundwaters of basinal origin are present in association with methane at shallow depths along the Queenston/Medina outcrop belt of western New York. These waters are extensively characterized at landfill sites because they contain some chemical constituents (sodium, calcium, magnesium, potassium, and chloride) that are common in leachate. Analysis of the groundwater, and consideration of the local and regional geology, is useful in differentiating basinal origin from landfill origin.

At the outcrop belt, the Queenston/Medina pore fluids commonly attain total dissolved solids concentrations (TDS) of 30,000 mg/l at depths of 100 ft below ground surface. The saline waters are overlain by calcium-bicarbonate waters with TDS concentrations less than 500 mg/l. The basinal brines, in which TDS concentrations reach in excess of 250,000 mg/l, are a sodiumcalcium chloride type with a Cl/Br ratio of 100-150 and a light stable isotopic signature. A brinespray recharge origin, which is probably pre-Quaternary because of paleogeographic constraints, is interpreted for the basinal fluids based on the Cl/Br ratio and isotope composition.

In the subsurface, Queenston/Medina facies exhibit low porosity, low permeability and high brine retention. At the outcrop, porosity is slightly higher due to fracturing and dissolution of carbonate cement. Permeability generally remains low, however, and the presence of the saline fluids suggests that specific retention remains high. Flushing of residual saline waters from low permeability, joint-bound blocks of strata by fresh meteoric waters apparently has not keep pace with post-glacial isostatic rebound of these strata.

AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio