Abstract: Remediation of a Volatile Organic Compound Plume in an Anisotropic, Fractured Bedrock Groundwater System

Lawrence F. Roach, Craig G. Robertson, Charles A. Rine

This New York site has a history of halogenated solvent usage and is underlain by mica schist bedrock which is covered by glacial deposits. Dilute wastewater releases resulted in a 2,000-foot long plume of dissolved volatile organic compounds, the shape of which reflects the control of bedrock fractures on groundwater flow. The site has a large number of bedrock monitoring points with 34 wells, including nine well clusters.

Constant rate aquifer tests were conducted at five bedrock wells within the plume. These tests were conducted at rates of between 8 and 26 gallons per minute and involved as many as 31 bedrock observation wells. The aquifer tests indicate strong anisotropy in response to pumping in both a horizontal and vertical sense as expressed by drawdown in observation wells.

Remediation consists of five years of bedrock groundwater withdrawal at near-source and two downgradient locations for hydraulic control and areal reduction of the plume. The combined drawdown produced by these pumping centers conforms to the drawdown predicted by the additive drawdowns observed in individual aquifer tests. The asymmetrically shaped area of influence also conforms to predictions based on aquifer tests and has resulted in a capture zone which includes all of the plume. Concentrations within the plume are decreasing rapidly with some wells experiencing a reduction in concentrations of greater than 90%. The plume area has been reduced by approximately 50%.

AAPG Search and Discovery Article #90954©1995 AAPG Eastern Section, Schenectady, New York