Groundwater survey

Much of the Russian literature on He geochemistry has discussed the association of high He concentrations in groundwaters with deep faults. In general, samples have been taken from pumped bores at depths of 60-100 m. Where shallower waters have been sampled, results are less certain because of upward-degassing gradients and dilution near the surface (Eremeev et al., 1973 Bashorin, 1980). The conclusions of much of this work are that the He content of the groundwaters is less dependent on the radioactivity of the 

Leakage along faults in the basaltic basement, possibly coupled with some geothermal activity, was considered to be the cause of high He concentrations (up to 14.18 pL/L) in groundwaters in Gujarat and Rajasthan, India (Datta et al., 1980). The distribution of some high values seemed to be related to known faults and the concentration appeared to have an inverse relationship to the thickness of the cover rocks. 

Helium surveys could be considered, therefore, to be effective in locating faults and permeable zones, which might be the sites of certain types of mineral deposits. Examples are given of He anomalies associated with carbonatites, Au-quartz veins, Pb-Zn-Ba veins and Cu-pyrite veins (Eremeev et al., 1973), stockwork Mo-deposits (Ovchiimikov et al., 

volcanogenic sulphides emplaced in faults (Bulashevich and Kartashov, 1976) and kimberlites (Kravtsov et al. 1976, 1979). However, except in the case of U- and Th-bearing deposits, the He and other rare gases in faults originate deep in the crust, or perhaps the mantle, and are indifferent to ore deposition (Ovchinnikov et al., 1973). Thus they indicate only a potential site, not the mineralisation itself When the fractures contain radioactive mineralisation, the He flux can increase markedly (Tugarinov and Osipov, 

1974) and should be reflected in the He content of groundwaters. However, comparison of absolute values for the purposes of mineral exploration can be confounded by the unknown effects of factors such as the depth and permeability of the fracture and its proximity to the sampling site. 

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Groundwater contamination by agrochemicals from non-point sources has been well documented in a number of countries [26-28, 30-32], The pesticides that have been detected in regional council groundwater surveys include 2,4-D, Amitrole, Picloram, Simazine and Atrazine [20]. 

Klaseus, T.G. (1988). Pesticides and Groundwater Surveys of Selected Minnesota Wells. Minnesota Department of Health and Minnesota Department of Agriculture. Prepared for Legislative Commission on Minnesota Resources, 93 pp. 

A California groundwater survey in 1982 showed no pesticides (i.e., DBCP, EDB, carbofuran, or simazine) in the Santa Maria or Salinas Valley groundwater basins (76). DBCP was present in 6 of 23 wells in the Upper Santa Ana basin (0.1-8 ppb), and in 21 of 166 wells in the San Joaquin basin (0.1-10 ppb). The authors were unable to correlate well characteristics with DBCP concentration in water. Simazine was also found in 5 wells, carbofuran in 1 well, and EDB in 2 wells. 

Some states have conducted surveys of water quality. Currently the information available on the status of the quality of the national groundwater resource is inadequate to draw any conclusions. Generally, assessments of water quality are available only for localized areas. The EPA has proposed a national groundwater survey for 1986-88. The preliminary draft calls for sampling 1500-2000 wells for approximately 90 pesticide analytes (9 ). Even... 

Bell, F.G. and Maud, R.R. 2000. A groundwater survey of the greater Durban area and environs, Natal, South Africa. Environmental Geology, 39, 925-936. 

Laboratory measurements The determinations recommended in this, and the previous section on field measurements, are valuable in exploring both sandstone and vein deposits. Most should be used on any uranium survey. The more parameters that there are in the exploration model the less is the possibility of misinterpretation and the better the target definition. As a rule, a groundwater survey should not be attempted with less than determinations of pH, uranium, arsenic, sulphate and total dissolved solids. Helium, dissolved oxygen and bicarbonate are highly recommended. With a little experience hydrogen sulphide concentration can be estimated from the strength of its smell. 

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