ABSTRACT: Methodology for the In-Field Design of Monitoring Wells in Heterogeneous Fine-Grained Formations
ZEMO, DAWN A., Geomatrix Consultants, Inc., San Francisco, CA, and STEPHEN D. REYNOLDS, California Department of Toxic Substances Control, Sacramento, CA
As part of the remedial investigation for a southern California Superfund site, clusters of depth-staggered monitoring wells were installed in heterogeneous unconsolidated alluvium. Filter packs and well screens had to be properly designed so that groundwater samples and hydraulic head data would be suitable for use in litigation. The highly variable geometry and texture of the sediments precluded the use of a generic well design and suggested the need for a method of in-field design of monitoring wells.
To provide timely well design parameters, representative core samples of intervals to be screened were analyzed on site. Simultaneously with the geophysical logging of the core boring, samples were sieved and the grain-size distribution data were used to design the filter packs as wells screens. This approach provided a means by which each well could be tailored to the specific zone of interest without delaying the pace of drilling and well construction or incurring costs above those normally associated with the more conventional approach employing a generic well design.