Surface Water Sampling
Exploration Technique: Surface Water Sampling
|Exploration Technique Information|
|Exploration Group:||Field Techniques|
|Exploration Sub Group:||Field Sampling|
|Parent Exploration Technique:||Water Sampling|
|Information Provided by Technique|
|Hydrological:||Water composition and source of fluids|
Geothermal waters typically range in total dissolved solids (TDS) from a few hundred to > 350,000 parts per million (ppm).  Liquid dominated reservoirs usually have a composition dominated by Na, K and Cl, but in very saline systems reservoir waters can be Na, K, Ca, and Cl rich. Silica and trace element (As, B, Br, and Li) concentrations tend to be high compared to the average meteoric waters, and pH is generally between 6 and 9, although acidic saline liquids can also be associated with geothermal systems (as described above).
Waters sampled for chemical analysis are stored in brimful polyethylene bottles with Polyseal caps following filtration from a large syringe attached to a filter holder containing 0.8 um filter paper. Each individual sample consists of 10-500 mL of filtered water, depending on the requirements of lab analytical techniques to be applied later. Duplicates are taken at each sample point and then treated in the field in preparation for chemical analyses. A set of duplicates sampled from a single surface discharge might included a bottle of unacidified (untreated) water for anion analysis, a bottle of water acidified dropwise with dilute HCl to pH <2 for cation analysis, a bottle containing sampled water diluted with deionized water (between 1:5 and 1:10 ratio) for measurement of silica content.
Samples to be used for isotopic analysis are collected in glass bottles filled to the brim with raw (unfiltered) water and sealed with a Polyseal cap. As with standard compound and major/trace elemental analyses, analysis for isotopes of different elements requires specialized treatment of the sample in the field. For example, tritium analysis requires a significant volume of water (up to 500 mL), whereas analysis for stable isotopes that are present in greater abundance in natural samples requires less water to be sampled by a full order of magnitude (approximately 30 mL). In order to analyze the 13C content of dissolved HCO3, the water sample must be treated with NH4OH and then saturated with SrCl2. For analysis of the 18O content of dissolved SO4, the water sample is treated with formaldehyde.
For a detailed description of modern water sampling techniques, methods, and instrumentation, consult Chapter A4 of the National Field Manual for the Collection of Water-Quality Data, published online by the U.S. Geological Survey. A synopsis of geochemical sampling and analysis techniques used in geothermal exploration is also provided by Arnorsson et al. (2006).
- Encyclopedia of Volcanoes
- Chapter 4: Geochemistry
- Geothermal Waters: A Source of Energy and Metals
- Fraser E. Goff,Tamsin McCormick,Pat E. Trujillo Jr,Dale A. Counce,Charles O. Grigsby. 1982. Geochemical Data for 95 Thermal and Nonthermal Waters of the Valles Caldera - Southern Jemez Mountains Region, New Mexico. Los Alamos, NM: Los Alamos National Laboratory, NM. Report No.: LA-9367-OBES.
- John A. Musgrave,Fraser E. Goff,Lisa Shevenell,Patricio E. Trujillo Jr,Dale Counce,Gary Luedemann,Sammy Garcia,Bert Dennis,Jeffrey B. Hulen,Cathy Janik,Francisco A. Tomei. 1989. Selected Data from Continental Scientific Drilling Core Holes VC-1 and VC-2A, Valles Caldera, New Mexico. Los Alamos, NM: Los Alamos National Laboratory, NM. Report No.: Report No. unavailable.
- Chapter A4: Collection of Water Samples (ver. 2.0)
- Sampling and Analysis of Geothermal Fluids
|Page||Area||Activity Start Date||Activity End Date||Reference Material|
|Surface Water Sampling At Chena Geothermal Area (Holdmann, Et Al., 2006)||Chena Geothermal Area||1980||1980||
|Surface Water Sampling At Chena Geothermal Area (Waring, Et Al., 1917)||Chena Geothermal Area||1917||1917||
|Surface Water Sampling At Raft River Geothermal Area (1973)||Raft River Geothermal Area||1973||1973|