3.6 The GROUNDWATER_SOURCE entity
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A groundwater_source is
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The groundwater_source is the particular discrete interval(s) of the aquifer intersected by the groundwater_feature that supplies the groundwater that is the focus of observations and measurements. There are different types of groundwater_sources. The source may be transient, as with water bearing intervals (ie. water cuts) intersected during drilling that have been tested as an inadequate supply and subsequently cased off. Other sources, such as the intake of a production bore, are more permanent in nature. A groundwater_feature such as a bore can have many groundwater_sources through time, including many individual water cuts during drilling and many intakes that have been constructed. Bore rehabilitation may involve the construction of a new groundwater_source within a groundwater_feature, such as when the hole is deepened and a new well screen is installed at a different depth. Hence, where the groundwater_feature taps the aquifer can change through time, even to the extent of changing to a different aquifer system.
A groundwater_source can consist of more than one constructed inlet, hence there can be a one-to-many relationship with the construction_element entity. For example, a bore may consist of a casing string with several screened intervals separated down the hole by lengths of blank casing. Since, all of these screened intervals (inlet-type construction_elements) contribute to the groundwater that is extracted from the bore, they are all assigned to the same groundwater_source, for the purposes of the data collected about that extracted groundwater.
The purpose of the groundwater_source entity is to link groundwater data that is collected from a feature to the part(s) of the underlying aquifer system that the groundwater is derived from. This is particularly crucial for groundwater_features that intersect multiple aquifers, as the groundwater_source is used to differentiate data collected from one aquifer to data collected from another aquifer. It is important to note that a groundwater sample belongs to only one groundwater_source.
Table 3.7 Attributes of the groundwater_source entity
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Name |
Data Type |
Description |
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feature_ identifier |
character |
unique identifier for the groundwater_feature that the groundwater_source belongs to |
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source_number |
integer |
sequential number in combination with feature_identifier is used to uniquely define the groundwater_source within the groundwater_feature |
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datum_number |
integer |
sequential number in combination with feature_identifier is used to uniquely define the reference plane defining the origin for locating the groundwater_source (refer datum_plane entity) |
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construct_number(s) |
integer |
sequential number(s) in combination with feature_identifer is used to define the inlet-type construction_elements that make up the groundwater_source (refer construction_element entity) |
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interval_from |
number |
distance from datum_plane to start of groundwater_source, metres |
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interval_to |
number |
distance from datum_plane to end of groundwater_source, metres |
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code |
type of groundwater_source eg. production zone, water cut during construction |
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aquifer(s) |
character |
name of aquifer(s) or geological unit(s) that the groundwater_source intersects |
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comments |
character |
comments about groundwater_source |
Each source within a feature is assigned a source_ number, so that the combination of feature_identifier and source_number provides a unique identifier for the source. Hence this combination of feature_identifier and source_number is used to link data such as water levels and chemistry to the relevant source of groundwater (eg. aquifer).
Since a source may consist of one or many constructed inlets, the construct_number(s) are used to define the appropriate inlets within the feature that contribute the groundwater. The interval_from and interval_to are the minimum and maximum depths for a source down a bore. In the case of the single cased multiscreen bore this would be the starting depth of the shallowest screen and the finishing depth of the deepest screen, respectively, with the origin for these depths defined by the datum_number.
3.6.1 Examples of groundwater_sources
A groundwater_source can be:
- a water bearing interval intersected during construction but subsequently cased off;
- the intake of a production bore (eg. slotted casing interval, well screen, open hole);
- an individual inlet port in a multiport sampler;
- the down hole interval isolated by a packer system;
- an unlined leaky section of a tunnel;
- a discrete permeable fracture zone intersected by an incline;
- the complete set of perforated intervals on all the laterals of a radial collector; or
- the combination of well screens found in multiple holes that are connected to a single header.
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