Design and Implementation of a Geochemical and Hydrologic Database for Nevada Mine Sites

Connor Newman

ABSTRACT
Regulatory agencies in the State of Nevada collect large quantities of geochemical and hydrologic data related to the permitting, operation, and closure of mine sites. Although these data currently aid agencies in the determination of applicable permitting decisions, they are not organized into a queryable electronic database format. A relational database, designed to ensure data integrity and usability for both state agencies and secondary users, is currently being populated that will contain all project-related geochemical and hydrologic data for permitted Nevada mine sites. Although not yet populated state-wide, the current database allows for advanced analytical functions related to the determination of groundwater flow paths, analysis of geochemical characteristics of groundwater and surface waters, and determination of regulatory compliance. Eventually the database will become publically available and possibly linked to other applicable datasets, improving public access to relevant observational data and advancing the understanding of hydrologic and geochemical processes affecting water within and near mine sites.

Keywords: Database design, mining, water quality, regional hydrogeochemistry
Citation: Newman, C., 2017, Design and Implementation of a Geochemical and Hydrologic Database for Nevada Mine Sites. Journal of the Nevada Water Resources Association, Summer 2017, p. 5-16.
DOI: 10.22542/jnwra/2017/1/1. Copyright 2017 Nevada Water Resources Association

Downhole Distributed Temperature Sensing in Fractured Rock

Matt Vitale, Frank Selker, John Selker, Peggy Young

ABSTRACT
Newmont’s Leeville Mine is located on the western side of the Tuscarora Range in northeastern Nevada. A 587 meter geotechnical pilot borehole in silty carbonate was drilled during 2012 prior to excavating a 10 m diameter vent shaft using ground freezing technology. Fiber optic cable was installed in the borehole and backfilled with cement-bentonite grout. In 2013 a distributed temperature interrogator was installed, which measured temperature along the fiber optic cable at 0.25 m and 0.02 °C resolution. After initial data were taken, a lower-resolution interrogator was installed for longer-term data collection, which measures temperature along the fiber optic cable at 1 m and 0.2 °C resolution. The intent was to utilize temperature for aquifer characterization. Daily measurements were programmed and run from December 21, 2013 through June 20, 2015 for a total of 546 daily temperature traces comprising 321,048 data points. Descriptive data analysis is presented, indicating a saturated zone 122 m below ground surface where a rapid temperature decrease of near 2 °C was seen. Similar downhole temperature changes are observed at 367 and 528 m coinciding with fracture flow zones where lateral water flow is suspected. Distinct slope profiles of the local geothermal gradient are evident between the fracture flow zones, indicating separate hydrostratigraphic units. The close-by ground freezing provided a thermal tracer of water movement. Temperature generally decreased over time because of the freeze process. Greater than 7 °C difference was observed in zones interpreted as lower permeability where conductive heat transfer was likely dominant. Advective flow at the 366 and 526 m depths showed substantially less temperature variability. It is at these depths where water flows through fractures at a greater velocity than the bulk rock and where the water temperature is indicative of the greater aquifer system. The smallest temperature change was less than 2 °C at 579 meters depth, which is interpreted to be the upper zone of the semi-saturated Roberts Mountain Thrust Fault.

Keywords: Distributed Temperature Sensing, Fiber Optic, Groundwater, Temperature
Citation: Vitale, M., Selker, F., Selker, J., Young, P., 2017, Downhole Distributed Temperature Sensing in Fractured Rock. Journal of the Nevada Water Resources Association, Summer 2017, p. 17-31.
DOI:10.22542/jnwra/2017/1/2. Copyright 2017 Nevada Water Resources Association.