GROUNDWATER HYDROGEOCHEMISTRY
Groundwater contains a variety of chemical constituents at different concentrations. The greater part of the soluble constituents in groundwater comes from soluble minerals in soils and sedimentary rocks (Waterwatch, 2005). A much smaller part has its origin in the atmosphere and surface water bodies. For most groundwaters, 95% of the ions are represented by only a few major ionic species: the positively charged cations sodium (Na+), potassium (K+), calcium (Ca2+) and magnesium (Mg2+), and the negatively charged anions chloride (Cl-), sulfate (SO42-), bicarbonate (HCO3-) and nitrate (NO3-). These ionic species when added together account for most of the salinity that is commonly referred to as total mineralisation or total dissolved solids (TDS).
Chemical signatures of groundwater, in terms of concentrations and isotopic ratios, can be used to understand groundwater processes. Isotopic methods have received a great share of attention as tracers in hydrogeology, but it is important to validate any interpretation with other chemical, hydraulic, geophysical or geological approaches. Since most hydrogeological situations are complex, a multi-parameter approach is often advantageous. In many instances, the hydrogeochemistry may be used effectively to derive parameters such as recharge, discharge and mixing rates. For example, changes in the groundwater chemistry can be used to track the movement of water, yielding information such as water residence time in the saturated zone, identifying recharge processes and the source of recharge water.
The unsaturated zone is a special case where major ion composition, particularly chloride concentrations, can play a major role in recharge studies, providing quantitative estimates that are difficult or costly to measure using other methods.
The potential applications of inorganic chemical tracers are shown conceptually in Figure 1. Fluxes of solutes from rainfall and runoff are shown (natural and anthropogenic) as well as reactions within the soil and in the saturated zone. Note the distinction between open system and closed system with respect to the gas phases (principally carbon dioxide, CO2, and oxygen, O2) in the unsaturated and saturated zones respectively.
MICROBIOLOGICAL QUALITY OF GROUNDWATER
Groundwater also contains a broad spectrum of microbial types similar to those found in surface soils and waters. These microbes encompass bacteria, fungi and protozoa, and are representative of most physiological types. On occasion pathogenic viruses, bacteria and protozoans of gastrointestinal origin from domestic, agricultural and other anthropogenic activities, may infiltrate through soils, sediments and rocks to the underlying groundwater (Plazinska, 2000). Measurement of microbiological quality of groundwater is difficult and costly. However, to allow quick and relatively inexpensive detection of faecal contamination in drinking water, faecal indicator bacteria (FIB) are used as surrogates in a number of studies (Plazinska, 2000). The National Health and Medical Research Council (NHMRC, 2003) recommend the
use of E.Coli as a primary indicator of faecal contamination of drinking water.
Figure : Conceptual diagram of the hydrogeochemical cycle incorporating the processes affecting the transport and reactions involving major ions (adapted from Back et al. 1993)
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Groundwater contains a variety of chemical constituents at different concentrations. The greater part of the soluble constituents in groundwater comes from soluble minerals in soils and sedimentary rocks (Waterwatch, 2005). A much smaller part has its origin in the atmosphere and surface water bodies. For most groundwaters, 95% of the ions are represented by only a few major ionic species: the positively charged cations sodium (Na+), potassium (K+), calcium (Ca2+) and magnesium (Mg2+), and the negatively charged anions chloride (Cl-), sulfate (SO42-), bicarbonate (HCO3-) and nitrate (NO3-). These ionic species when added together account for most of the salinity that is commonly referred to as total mineralisation or total dissolved solids (TDS).
Chemical signatures of groundwater, in terms of concentrations and isotopic ratios, can be used to understand groundwater processes. Isotopic methods have received a great share of attention as tracers in hydrogeology, but it is important to validate any interpretation with other chemical, hydraulic, geophysical or geological approaches. Since most hydrogeological situations are complex, a multi-parameter approach is often advantageous. In many instances, the hydrogeochemistry may be used effectively to derive parameters such as recharge, discharge and mixing rates. For example, changes in the groundwater chemistry can be used to track the movement of water, yielding information such as water residence time in the saturated zone, identifying recharge processes and the source of recharge water.
The unsaturated zone is a special case where major ion composition, particularly chloride concentrations, can play a major role in recharge studies, providing quantitative estimates that are difficult or costly to measure using other methods.
The potential applications of inorganic chemical tracers are shown conceptually in Figure 1. Fluxes of solutes from rainfall and runoff are shown (natural and anthropogenic) as well as reactions within the soil and in the saturated zone. Note the distinction between open system and closed system with respect to the gas phases (principally carbon dioxide, CO2, and oxygen, O2) in the unsaturated and saturated zones respectively.
MICROBIOLOGICAL QUALITY OF GROUNDWATER
Groundwater also contains a broad spectrum of microbial types similar to those found in surface soils and waters. These microbes encompass bacteria, fungi and protozoa, and are representative of most physiological types. On occasion pathogenic viruses, bacteria and protozoans of gastrointestinal origin from domestic, agricultural and other anthropogenic activities, may infiltrate through soils, sediments and rocks to the underlying groundwater (Plazinska, 2000). Measurement of microbiological quality of groundwater is difficult and costly. However, to allow quick and relatively inexpensive detection of faecal contamination in drinking water, faecal indicator bacteria (FIB) are used as surrogates in a number of studies (Plazinska, 2000). The National Health and Medical Research Council (NHMRC, 2003) recommend the
use of E.Coli as a primary indicator of faecal contamination of drinking water.
Figure : Conceptual diagram of the hydrogeochemical cycle incorporating the processes affecting the transport and reactions involving major ions (adapted from Back et al. 1993)
Senior Consultant S J Builders Australia, Visit www.sjbuilders.com.au
Craigieburn New Homes
Cranbourne New Homes
New Homes In Berwick
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