PRELIMINARY RESULTS OF GEOCHEMICAL SAMPLING AND IMPLICATIONS FOR ENVIRONMENTAL INVESTIGATIONS IN THE SOUTHERN SHENANDOAH VALLEY, VIRGINIA

As an integral part of its detailed mapping projects, Virginia's Division of Mineral Resources (VDMR) collects rock samples for geochemical analysis. The analytical results (Actlabs, Ontario) provide information on the concentrations of major, minor, trace and rare earth elements. These data are used primarily to correlate rock types and locate mineral resources, but can also support environmental investigations. The results of approximately 40 clastic rock analyses from the southern Shenandoah Valley, coupled with about 60 clastic rock samples from the West Virginia Geological and Economic Survey, provide useful information regarding sulfide oxidation potential and the background concentrations of metals.

Many areas of the Shenandoah Valley underlain by clastic rocks are prime land for commercial and residential growth. The exposure of sulfur-bearing rocks during site development may result in acid-rock drainage. Understanding the concentrations of sulfur in these rocks is essential for identifying areas of high risk for building hazards. A recent study by Orndorff (2001) suggests that rocks containing more than 0.2 percent sulfur have the potential for acid-rock drainage and warrant further analysis prior to development. Thirty-two percent of the samples analyzed in this study exceed the sulfur threshold suggested by Orndorff. Samples were collected from the Martinsburg, Millboro, Bloomsburg, and Massanutten Formations, as well as the formations of the Chilhowie Group in the Blue Ridge. Most of the high-sulfur samples in the Shenandoah Valley were from the lower Martinsburg Formation.

Whole rock geochemical analyses provide critical information on elemental background concentrations for use in geotechnical and environmental investigations. Elemental concentrations in the rocks may provide a range of possible elemental concentrations in soil. The mean concentration of elements in the clastic rocks was compared to existing health-based standards listed by the Environmental Protection Agency for soil. Results indicate that, on average, the elemental concentrations in clastic rock samples exceed health-based standards for Al, As, and V. These data can be used by industry and environmental organizations to determine the level of remediation necessary to return a developed site to its natural state.