3.12 The PARAMETER entity

Parameters are the properties that were measured, observed or interpreted during an event relating to a groundwater_feature. Common groundwater properties measured in the field include depth to standing water level, pressure, rate of discharge, electrical conductivity and temperature. A discrete sample of groundwater can then be dispatched to the laboratory for major ion, nutrient, isotope or pesticide analysis. Each chemical compound that is analysed is a parameter. Rock type, colour, grain size and degree of weathering are properties that can be attributed to rock samples in the field. Subsequent laboratory investigations may be made to determine parameters that relate to petrology, mineralogy or palynology. Parameters may also be interpretive. This is the case for coefficients such as transmissivity and storativity that are estimated by the data analysis of an aquifer test. Hence, there are different types of parameters, whether they be field, laboratory or analytically based.

Table 3.14 Attributes of the parameter entity

The parameter is related to the particular event as defined by the event_feature_identifier and the event_number. A parameter is defined in terms of the property that is measured and conditions under which it is measured, such as the equipment or methodology used. Hence, if during an event, water levels were initially taken using an electric contact device and then by an audible plopper, these are essentially two different parameters even though they are measuring the same property. The equipment used to measure the property, the analytical method used, the associated error, detection limits and any correction factor applied, can be defined.

The data standards have a comprehensive property domain, that spans hydrogeological, meteorological, chemical, physical, geophysical and biological characteristics. Standard identifiers such as CAS registered numbers for chemical analytes are used wherever possible. Also, standard units of measurement have been assigned to many of the properties, and multiplication factors have been compiled to assist in unit conversion.

Each parameter is uniquely defined by the combination of event_feature_identifier, event_number and parameter_number. Note that the parameter is uniquely referenced to an event, rather than the sample. This is because a single parameter (ie. combination of property measured, equipment used, analytical method applied, etc) can be applied to many samples. This is the case when a series of discrete groundwater samples are collected during an event, with the field pH measured for each sample using the same probe. A sample can be analysed for a number of different parameters. This is the case when a groundwater sample is analysed for a suite of major and minor ions or when the down hole hydrogeology is measured using a suite of geophysical wireline logs. Hence many parameters can be measured, observed or interpreted for a sample.