3.11 The SAMPLE entity

A range of measurements and observations about aspects of a groundwater_feature may be taken during an event. The sample is the specific object that is the focus of measurement, observation or interpretation. Hence a sample may be of:

• the groundwater found within the groundwater_feature;
• the hydrogeological medium surrounding the groundwater_feature or derived from the construction of the groundwater_feature (eg. drill cuttings);
• the construction_elements that make up the groundwater_feature (eg. casing);
• a part of the surroundings (as is the case for barometric readings of atmospheric pressure); or
• a composite of these features. This is true for geophysical logs that measure the combined signal from both the rock matrix and the in-situ fluid (eg. resistivity).

Table 3.12 Attributes of the sample entity

The sample entity is generic in the sense that it covers two broad types, namely:

• in-situ objects that are studied in the field. Hence, the surrounding hydrogeology is the sample that is being investigated using wireline geophysical logging. The in-situ groundwater within the casing of a bore derived from a constructed inlet within the feature is the sample that is measured in terms of water level monitoring; and
• discrete samples that are physically removed for the purpose of further laboratory analysis. This is the case for typical groundwater samples extracted, processed and bottled for detailed chemical analysis, drill cuttings bagged for palynological determinations or samples of casing taken for corrosion testing.

Each sample is uniquely defined by the combination of feature_identifier, event_feature_identifier, event_number and sample_number. The sample_number is a sequential number used to differentiate samples from a particular groundwater feature for a particular event. The event_feature_ identifier attribute recognises that measurements may not necessarily be taken from the groundwater_feature that the event has been assigned to, as in the case in some aquifer tests. This caters for the situation where water levels are measured from an observation bore (defined by the feature_identifier) and not from the actual pumped bore that is the main focus of the event (defined by the event_feature_identifier). Samples can be accessed from a groundwater_feature identified by the feature_identifier during an event (defined by the event_feature_identifier and the event_number), by a person from an organisation. Note that an event can have many samples.

The medium attribute describes the material that is sampled, whether it is a variant of a solid, liquid or gas. Groundwater can be sampled for detailed chemical analysis or a depth to groundwater level can be made in the field. Rock or soil samples derived from the construction of the groundwater_feature can be dispatched for grain size, geotechnical or palynological analysis or the lithology can be logged in the field. Samples of construction_elements of the feature like casing can be taken for studies such as corrosion or encrustation. Atmospheric conditions can also be monitored. Hence different media can be sampled. The type attribute defines whether the sample is in-situ or discrete, and if the latter can be used to describe whether the sample is a replicate, blank, spike and so on.

The sample can relate to a particular interval in time, as defined by the sample_start_date and sample_duration. The sample may also be taken from a depth interval within the groundwater_feature, defined by interval_from and interval_to in reference to an origin (defined by the feature_identifier and datum_number). This is the down hole interval that drill cuttings are taken, the interval within the water column in the bore that the groundwater sample was extracted or examined in-situ, or the interval down hole that the geophysical survey was run. In combination with the feature_identifier, the source_number is used to define the groundwater_source relating to a groundwater sample. This is critical in linking the water level data or chemical analyses of a groundwater sample to the relevant aquifer from which the groundwater was sourced. In a similar way, the construct_number is used to define the construction_element relating to a sample of a construction_element within the groundwater_feature itself. The sample_method and the treatment(s) used in the course of collecting and preparing the sample for analysis can be described.

Discrete samples that are physically extracted and dispatched for further analysis also have a range of additional properties. The samples may be assigned identification both during collection (field identifier) as well as upon receipt in the laboratory (lab identifier). A volume of sample is stored in a container made of a particular container material. The sample is received by the laboratory on the receive date, whereupon the analysis is finalised on the complete date.

Each of these additional properties of a sample is stored as a sample_property. This entity allows flexibility into the data model by enabling the allowable properties of a sample to be readily expanded. A property of a sample can be recorded numerically as a value or as a text string description.

Table 3.13 Attributes of the sample_property entity

3.11.1 Examples of samples

A sample can be:

• the total sequence of drill cuttings derived from the interval between the ground surface and the bottom of hole, that were logged by a geologist;
• the hydrogeological medium found within a defined interval down the hole whose properties were measured by a wireline geophysical survey;
• the column of groundwater inside the feature derived from the well screen (a groundwater_source) and from which water level measurements were taken;
• the discrete sample of core taken from 201-201.4m depth that was collected for palynological examination; or
• the bottle of groundwater pumped from the bore and dispatched for chemical analysis.