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Abstract

Fouling of water supply wells is a common problem dating from the time humans started using groundwater resources for water supply. In the groundwater remediation field, fouling of recovery and treatment systems has been a similarly common operating problem. Thus, it is not surprising, with the increased use of in-situ remedial methods, that fouling of in-situ treatment units is becoming a major design concern. In-situ treatment units include recovery wells, injection wells, recirculating wells, flow-through treatment cells, and in some cases, geologic formations themselves. The very effectiveness of these units depends greatly upon retention of permeability or hydraulic capacity. Capacity can be dramatically reduced due to fouling by naturally occurring inorganic precipitates or by microbial deposits.

One of the least surprising instances of fouling of an in-situ treatment unit involves various bioenhancement techniques, where nutrients are injected with the intention of enhancing certain types of bioactivity and subsequent biodegradation of contamination. The data presented in this paper are derived from experience at remedial sites where bioenhancement activities have been self-defeating by causing a loss of permeability in injection wells, surrounding geological formations, or down-gradient recovery or recirculation wells. In these cases, non-oxidizing biocides, bio-dispersants, saponification agents or other additives have been applied to retain permeability in the hydraulic “bottlenecks” of these systems, such as injection wells and surrounding formations. Data collected from such applications shows that proper characterization of fouling mechanisms and subsequent application of well-designed deposit control programs can eliminate operational problems associated with fouling arising from bioenhancement.

This paper introduces the key concepts in deposit control practices as they apply to fouling of in-situ treatment units. It provides an overview of the various agents and techniques used in such deposit control programs. Regulatory and design issues are discussed, and subsequently illustrated by a series of brief case studies.

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