Design of Remediation Extraction Wells, Considering a Historically Low Water Table, Northern New York State

In early 2010, design was underway for full scale remediation of an approximately 3.2-acre, half million gallon jet fuel plume in northern New York State, with a focus on LNAPL source removal for protection of groundwater.  Although the mid-Atlantic region had received record snowfall, northern New York was behind on precipitation, with a below average water table.  Based on site characterization and pilot study data, the smear zone and optimal depths for well placement had been determined.  As spring turned into early summer, northern New York received significantly less rainfall than normal and the water table began plunging toward historic lows.  Concern was raised about the ability to maintain extraction rates and operate the system within the smear zone with available drawdown.  A very tight schedule backed by consent decree forced a timely and prudent approach.

Grain size distribution analysis and well design (more typical of water supply wells) was performed to maximize well efficiency and production.  Well depth was designed, relative to the water table trend, to have a planned minimum two feet of available drawdown within the smear zone.  During the summer months, well installation proceeded as the water table continued to plunge.  Drillers familiar with installing wells with conventional designs had to overcome skepticism, and adapt to more careful and precise installation.

With design and installation of the extraction wells completed, the first phase (1 of 3) of the full scale remediation operated successfully at the designed rate from early September through completion in early November while the water table was near the historic low.  Through sound analysis of the grain size distribution, understanding the specific capacity, considering well losses, and adequately accounting for water level trends, the wells designed and installed were able to exceed all operational requirements.