T134 Geophysical Solutions to Geological Problems: Current Research Results and the Annual George P. Woollard Award Presentation (Posters)

Monday, 20 October 2014
9:00 AM - 6:30 PM
Exhibition Hall C

USE OF GEOPHYSICAL METHODS FOR EXPLORATION OF ECONOMIC ROCK SOURCES IN TIMBER SALE SITES IN WESTERN WASHINGTON, PACIFIC NORTHWEST OF THE UNITED STATES

Paper number: T134-4
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Three million acres of federally-endowed trust lands in Washington State are managed by the Washington State Department of Natural Resources (WADNR) State Lands Division to provide revenue for the construction of public schools, colleges and other state buildings as well as support for certain state services. Road rock sources are needed for timber harvest and can be challenging to find. If quality rock is not found close to a timber sale area, a project can fail and represent a revenue loss to the trust beneficiaries. For this reason rock exploration methods are sought that are reliable, relatively inexpensive, unobtrusive, ecologically sound, and portable for use in remote locations.

The primary objectives of our work are to provide a cost effective and practical geophysical method or combination of methods to 1) locate new bedrock sources, and 2) expand existing quarries that is needed by WADNR engineers and foresters to develop rock aggregate required for forest road construction. In addition, we want to a) identify the extent and thickness of overburden soils (that will be stripped and later used in reclamation), b) characterize the rock quality beneath the overburden (typically hard, dense rock is preferred or required as coarse base rock and finer crushed rock for road surfacing without excessive fines content), and c) identify if groundwater is present and a significant concern.

Our approach includes geologic reconnaissance in combination with using one or more of the following geophysical methods: active/passive shallow seismic, single-station passive seismic, electric resistivity (OHM-Mapper), Ground Penetration Radar (GPR), and Electromagnetic Induction (EMI) data. Our main goal is to evaluate use of various geophysical methods to identify feasible rock sources. To meet this goal, we had used geophysical instruments available in the WADNR-Division of Geology and Earth Resources (DGER), as well as the instruments loaned from Geometrics Inc. and Northwest Geophysics LLC, to acquire data at the Perry Creek rock quarry site, 18 miles NW of Olympia, Washington.

We will present results of our experimental study using the different geophysical methods and show the feasibility of using each method to explore for high quality rock at timber sale areas.