Abstract: State Regulatory Oversight of a Pilot Horizontal Well for DNAPL Recovery: A Case Study

William H. Schramm, Ellen S. Broussard

Pre RCRA disposal of still bottoms, sludge and waste product occurred onsite in unlined pits at a chlorinated-solvent manufacturing facility. Pits were excavated in unconsolidated sediments of Holocene age, which are underlain by Pleistocene clays, channel sands, and massive sands of the Chicot Aquifer. Waste materials containing significant amounts of chlorinated solvents have undergone gravity separation and formed a Dense Nonaqueous Phase Liquid (DNAPL) layer within the uppermost sediments.

Well points connected to a vacuum recovery system installed in the early 1980s attempted to recover contaminated groundwater. The true extent of DNAPL was not realized until evaluation of this system proved that recovery was not providing significant reduction in contaminant levels. Upon further study, it was realized that the vacuum system could not recover the dense phase material, and only recovered the dissolved portion.

The Agency (LDEQ) requested further augmentation of the system or alternative methods to efficiently and effectively recover DNAPL. The Company has initiated the installation of a pilot horizontal recovery well. Advantages of horizontal over vertical wells include: fewer surface locations and appurtenances, greater capture zone, cost reduction for maintenance and accessories, lower worker exposure, and greater effectiveness in DNAPL recovery. Anticipated problems include preventing worker exposure to waste materials, maintaining vertical emplacement control, preventing loss of mud through surficial pathways, and minimizing waste production.

LDEQ involvement includes evaluation of system effectiveness, recommendations for improvement, appraisal and approval of alternative measures, onsite inspection and observation, and cooperative involvement in planning and implementation of new technologies.

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