Environ. Sci. Technol. 1994, 28, 2423-2427
RESEARCH COMMUNICATIONS New Sampling Devices for Environmental Characterization of Groundwater and Dissolved Gas Chemistry (CH4, N2, He) Barbara Sherwood Lollar,'vt Sham K. Frape,? and S. M. Weises Department of Earth Sciences, University of Waterloo, Waterloo, ON, Canada N2L 3G1, and Institut fur Hydrologle (G.S.F.), D-8042 Neuherberg, Germany TIMERS
Introduction The objective of this paper is to highlight an underutilized resource in groundwater chemistry investigations and to introduce an innovative set of sampling devices designed to take advantage of this resource. While boreholes drilled for oil and gas exploration have long been used to derive hydrogeologic information (1, 21, boreholes drilled for mineral exploration have rarely been taken advantage of. Throughout crystalline rock terrains on the Canadian and Fennoscandian Shields in particular, large numbers of uncased exploration boreholes extend from the surface and from underground mine workings. These boreholes intersect hydrogeologic regimes ranging from near-surface meteoric groundwaters to deep saline formation waters and brines (3, 4 ) . This paper will demonstrate how sampling devices developed at the University of Waterloo can be used to take advantage of such borehole networks and to provide a wealth of geochemical and isotopic data on both dissolved gas and groundwater chemistries (5,6). While the use of uncased boreholes does not permit the detailed stratigraphic interval sampling control of conventional cased and packered sampling instrumentation, it nonetheless presents certain distinct advantages. By taking advantage of existing boreholes, this sampling approach eliminates the high cost of mounting an independent drilling program and provides an economical reconnaissance tool. The technique is ideally suited to provide rapid, low-cost evaluation of groundwater properties in unconventional hydrogeologic settings such as underground excavations and to provide preliminary data on which to base the selection of boreholes for more extensive casing installation and instrumentation. A variety of downhole sampling devices have been developed in recent years (4, 7-10). Each however has limitations with respect to flexibility of sample type and sample size, maximum operating pressures and depth, portability, and adaptability to nonideal field conditions. In order to overcome these deficiencies, the Waterloo samplers were designed to be narrow-diameter (3.18 cm), self-contained units (with internal power units and triggering devices), capable of withstanding external pressures of up to 10 000 KPa and of operating in both freshwater
poRi I
BATTERY RECHARGING TRIGGER SWITCH
CASING
I
AlTACHMENT LINKS
I
I
SAMPLE CHAMBER
PRESSURE RELEASE VALVE 1 SAMPLE COLLECTlON PORT
Figure 1. Schematic of University of Waterloo water sampling device. Figure is not to scale. Total length, 1.5 m; diameter, 3.18 cm; sample vessel length, 0.75 m; volume, 350 mL.
and in highly saline formation waters and brines. Their design emphasized maximum flexibility with respect to environmental sampling. Originally designed to collect water and gas samples for compositional and stable isotope analysis, these devices have been successfully used for sampling for rare gas isotopes and volatile organics (DMS, dimethyl sulfide). Envisaged as tools for reconnaissance sampling and regional surveying of groundwater characteristics, their design emphasizes moderate cost, portability, and adaptability to a wide variety of hydrogeological field conditions. Experimental Section
* Address correspondence to this author at her present address: Department of Geology, University of Toronto, Toronto, ON, Canada M5S 3B1.E-mail address:
[email protected]. + University of Waterloo. Institut fur Hydrologie.
Water Sampler Design. The water sampler consists of a 1.5 m long, 3.18 cm diameter stainless steel probe weighing
