Water Resources

Hydrogeological Investigations

Hydrogeological investigations in relation to water resources are often the initial and preliminary work that provides insight and greater understanding into a new area being reviewed for water resources.

Work can include planning and collation of existing data into developing a conceptual model of the hydrogeology of this particular area. Actual field investigations may include bore census of existing bores and exploration drilling on a regional scale at sparse distances over a particular area, often using RAB or RC drilling methods.

Groundwater Exploration

Groundwater exploration in relation to water resources is the field investigation using drilling methods to delineate aquifers over a particular area being studied.

Groundwater exploration drilling methods may include mud rotary, RC or RAB and may also include air-core. Drilling is often closely spaced with drill traverses 500 – 1000 metres apart. Groundwater exploration may also include methods from hydrogeological investigations. Namely: bore census, water level measurements, EC profiling as well as field measurements from drilling including airlift yields and field water chemistry, such as EC and pH.

Groundwater exploration may be based on several geophysical methods such as ground gravity, Hoist EM, electromagnetic surveys or transient electromagnetic surveys.

Scoping & Pre-Feasibility Studies

 Scoping and pre-feasibility studies in relation to water resources is a desktop study into an area already under review from a groundwater exploration point of view, where there may be some available data or inferred or probable water resources.

The pre-feasibility component is an examination or an assessment of water resources on an aerial extent, taking into account storage and aquifer thickness. There may be available groundwater or aquifer or hydrogeological information that pertains to probable or inferred yields and this may then be able to lead into an establishment of a possible borefield or development of a water resource.

The scoping part of the study may include the definition of how many bores, the size of the borefield, bore spacing or depth yields, number of bores, number of monitor bores, field testing components, etc. The scoping may also include test pumping components and what works are required to establish a borefield from groundwater exploration through to borefield development, testing, modeling and reporting.

Borefield Design & Development

The work in relation to borefield design for water resources often follows groundwater exploration once it is known what water resources are available and after sufficient exploration has been done to generally delineate a water resource.

Borefield design is frequently undertaken following some preliminary numerical groundwater modeling to determine bore spacing, preliminary yield estimates and nominal bore design.

Detailed bore or borefield design is undertaken whilst developing the borefield; usually in a phased approach following detailed delineation of drilling targets where nominal bore locations have been sighted. Borefield development is undertaken through the utilisation of specialist water bore drilling rigs. For fractured rock environments this may include a normal circulation air hammer drilling method and for palaeochannel-type borefields, mud rotary drilling methods are the preferred choice.

Groundwater exploration and borefield development are often undertaken concurrently and, in some cases, this may be done by separate drilling contractors using separate drilling methods. For example, this has been achieved successfully by the Principal during the Grey Mare Stage 2 Borefield Development with air-core drilling for groundwater exploration to delineate targets and subsequent mud rotary drilling for the production bores and monitor bores.

Borefield design and development may also take into account the required yield by client and correlating that with possible sustainable yields from the aquifer to get the best outcome for the client, as well as maintaining sustainable levels of abstraction from the water resource. Borefield design and development usually has some component of engineering and collaboration with engineers from a design point of view.

The outcome of a borefield development is a schedule of production bores with recommended pumping rates and pump inlet depth settings. Borefield development includes the drilling and installation of production bores at the most favorable and best yielding sites that meet the criteria for yield and salinity. In addition to a selected number of monitor bores that are drilled at proximal locations to production bores, regional monitoring bore sites that may also include salinity monitoring bores, regional water level bores and those bores at greater distance from installed production bores.

 Test Pumping & Hydraulic Analysis

 Test pumping and hydraulic analysis is generally part of borefield development.

Test pumping generally follows the installation of production bores and monitoring bores. In addition, test pumping can be undertaken on pre-existing bores from earlier completed bores. Test pumping is usually conducted by contractors or sub-contractors, who are experienced in installing submersible pumps and carrying out the test pumping scope of works under the direct supervision of groundwater professionals. Test pumping is undertaken in accordance with Australian Standards AS 2368.1990.

Following the installation of the pump, tests may include a preliminary test to establish the correct operating procedure of the pump, flow meter and flow rates. The next test is a step draw-down test involving, usually, four steps at 60 or 100 minutes each step, with an increasing rate of discharge for each step with no recovery.

The following test is usually a constant discharge test, which is generally undertaken following full recovery of the production to at least 95% of the original standing water level following the step draw-down test. The constant rate test is usually undertaken over a 48 hour period of a constant pumping rate. Immediately following this 48 hour period, a recovery test is undertaken, which is usually a 12 hour period, or in some cases to 95% recovery.

Water levels are measured in the production bore being pumped, as well as a number of selected monitor bores either close to the production bore as well as further away. Often monitor bores in different aquifers, shallow and deep may also be monitored.

Water depths measured are reduced from the standing water level, or initial water level, prior to the tests to determine the draw-down during the tests. The draw-downs are then plotted semi-logarithmically to enable hydraulic analysis by groundwater professionals.

Hydraulic analysis of test pumping data follows the data reduction and plotting of the testing data, such as aquifer properties and parameters which can be estimated from the plotted data. Aquifer parameters may include transmissivity or storativity from monitor bores and transmissivity from monitor bores and from the pump bore only. These parameters are generally obtained from the constant rate tests and recovery tests through various analytical methods. The transmissivity estimates, used in conjunction with aquifer thicknesses, can provide hydraulic conductivity estimates of the aquifer being tested.

The step draw-down test can provide a number of parameters that generally relate to well efficiency, well characteristics and specific capacity of the bore. The step test is generally used to determine the nominal pumping rate for the constant rate test. The constant rate test can also provide through the rearranging of the well equation and hydraulic analysis the determination of long term yields. The hydraulic analysis, which provides estimates of aquifer parameters through the testing at various production bores, will provide valuable information that is then input into the numerical model. Depending on the quality of the data available that is input into the model, the model may be able to provide predictions into long term yields of the water resource. The rearranging of well equation and the use of this method would be only applicable for multiple boundary type aquifers, strip aquifers or fractured rock aquifers, where multiple boundaries or partial boundaries are observed. This does not apply for production bores that have observed leakage.

Hydrological Investigations

Hydrological investigations in relation to water resources involves the study, collation and compilation of surface water data, catchment yields and, in some cases, surface water run-off.

The investigations are generally undertaken in a desktop study with literature research and review of existing data and existing reports. Work may also include the acquisition of hydrometeorological and rainfall data and investigation of potential surface water harvesting sites for water resources. In addition, stream flow measurements may be available as well as river levels and other field measurements.

Site investigations may include reconnaissance of a client’s area or area of potential concern or interest.

Artificial Recharge Studies

This work includes the investigation of suitable sites for disposal of waste groundwater or waste surface water whereby the holding of large volumes of water in paddock style evaporation ponds may be unsuitable.

Artificial recharge may also include re-injection wells, infiltration into shallow aquifers or deep injection into fractured rock aquifers. Studies may include infiltration tests, permeability tests, re-injection test pumping and observation of water levels.