Abstract: In-situ Bioremediation of Groundwater Using a Horizontal Injection Well in Clay Soil, Madisonville, TN

Mark B. Miller, Dennis A. Clark, Maureen Handler, Zhing-Ming Huang

Tennessee's first horizontal groundwater remediation well was installed at Madisonville located in the eastern Valley and Ridge Province. The open-ended well, drilled through clay soil, is constructed of 280 feet HDPE pipe, 2 inches in diameter, with a screen length of 100 feet at 18 feet below ground surface. The purpose of the well is to remediate gasoline contaminated groundwater that resulted from a leaking underground storage tank (UST) system. The groundwater benzene and TPH plumes covered an area of one-half acre and extended beneath a rural grocery store.

Remediation is achieved by injecting aerated water, nutrients and microbes to reduce contaminant levels to drinking water standards. MODFLOW was utilized to computer-model the development of the groundwater mound that would result from injection. It was calculated that one horizontal injection well would equal the efficiency of 80 vertical injection wells. Benzene and TPH masses have been reduced by 92% and 95% respectively. BIOTRANS calculated the bio-decay rate to determine remediation time.

This system will reduce project life and eliminate additional costs associated with: operations and maintenance (versus vertical pump and treat), water disposal, emissions controls, well installations, and site disturbance. A "Minimum Economic Plume Size", the minimum plume volume required to support a horizontal system has been developed. Although costs per foot are greater for horizontal drilling than vertical drilling, project costs savings are realized later in the project.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas