Hydrology cycle

The role of geologist in this field is rather small, considering the most of the drillers have their own understanding and ways of knowing their rocks and soils. Their understanding and knowledge is gained mostly from their hands-on experiences in past drillings. Geologist's terms like hard, soft, medium-grained, fine-grained or names of some common rocks might differ slightly or greatly from a driller's point of view. So it would be ideal if both geologist and driller can just sit and discuss and share notes on their understanding of certain 'terms' used, for the benefit of both parties that is! One cannot deny that it is the geologist who knows the 'ground' better and wouldn't it be wise to discuss with a qualified (undergone proper and formal education) geologist about the preparation or design of the borehole before the actual drilling take place? Problems like caving in the borehole or loss of circulation can be minimised or avoided if a driller is sufficiently informed of the expected geology in the place of interest. The team of drillers can also be better prepared if they can anticipate of what is actually ahead of them and thus will enable them to bring suffient or more suitable drilling tools and equipments to overcome any adversity that might occur during drilling. For example, the chert or quartzite which can be found in sedimentary rocks can be as abrasive as igneous rocks. And the driller would be thinking that he would be drilling in 'soft formation' rocks, only to find out later that his drilling bits has worn off very quickly. The total cost for the drilling would be definitely increased caused by the delay (time spent for troubleshooting) and replacement of new bits (quotations....purchase...and finally the delivery).

Other areas in which the geologist can lend a hand is the interpretation and identification of cuttings produced and sampled throughout drilling. Perhaps if a geologist could not be present at the time of drilling, it is possible that the identifications or naming the sample being done elsewhere, say in the office or laboratory. However it is important for the geologist to visit the site at least once in order to 'capture' and understand the geological setting at the drilling site. So if the logging is done solely on the driller's information, then the geological input after that is nothing more than just 'decorating' the final report and 'give' a professional outlook of the whole thing. How sad if this happens! And about geological (atlas scale) maps, the interpretation of rocks are done mostly by air-borne surveys, such as the air-photo or satellite captions. The interpretation from these photos or captions would be later 'matched' with documented or reported geological surveys in order to furnish the map with relevant informations. However, it must be noted that the map does not represent 100% accuracy of the actual condition at the site and the map has to be revised from time to time in order to include the latest development that has taken place (new highways, express routes, new townships etc.). That is why geological fieldtrip is important as it can be used to ascertain and 'adjust' the findings in the maps.

A geologist could also 'predict' or anticipate on the yield of groundwater that can be obtained/extracted from certain ground conditions. No doubt the water well driller can also do this, based on their experience and reference to published Hydrogeological map (1st Ed., 1975). However, lithological reference alone is insufficient as it would also depends on the 'history' of the geological setting (age, deposition environment, tectonic events etc.) and geomorphology of the place of interest (drainage, elevation etc.). For example, a drilling point in the limestone formation might give a prediction of 4000-6000 gallons/hr/well in the Hydrogeological map. But a check on the geo-history found that the formation is relatively young and located in close proximity with igneous intrusion. Thefore it is possible that this limestone body is not the karstic type (a lot of underground rivers & channels; caverns) and has been metamorphosed into marble (normally dense), resulting in low yield or no yield at all. Therefore, sufficient preliminary studies (desk or field studies) can be useful in anticipating the yield of groundwater in new places where drilling activity is unknown.

At times before a drilling task is undertaken, a groundwater propecting is generally carried out by conducting a resistivity survey (vertical profiling) in which the amount of survey points depends of the size of the area designated for the groundwater development. The survey could be carried out by a team of 5 with at least one experienced technician, but the interpretation of the resistivity results must be done by someone who is experienced (theorectically & practically sound) and at the same time have a clear understanding of the complexity of the geological setting in the survey area. The interpretation of the Vertical Electrical Sounding (VES) is mainly done based on the contrast of resisitivty values, where the values are compared against known resistivity values of different mediums such as saline water, fresh or brackish water in sandstone or shale formation etc. This technique, however, does not guarantee the amount of water that is to be abstracted from the ground. It can only determine the general quality of groundwater, whether it is fresh, saline or brackish (moderately saline).This survey, however, would be more reliable if resistivity result is correlated to a in-situ geological borehole log.

The task of drilling points selection has to be logical in terms of working space and must also be the most likely/suitable (normally near spring, water seepage from the ground/slope, near river or the lowest point at any given site) to strike groundwater. The selection should be also depends on the findings of any preliminary survey, such as VES and understanding of local topography / geology, in order to obtain the highest chance possible of striking groundwater at any given point!

The yield from the bore can be estimated roughly through an airlift method, whereby this test is to be conducted at a fixed interval, say 5m into the rock, concurrently with the drilling (as the bore is proceeding). An airlift test can also 'guide' as to which depth the inflow of groundwater is, based on a measurement in the field (V-notch). The yield from the bore may be compared relatively and this would definitely enhance the influx of water into the tubewell casing. This test also gives an indication of depths/zones where the slotted screen (installed together with the permanent casing) can be placed in order to tap the groundwater in the bore.

Another important area of water well drilling is the area of pumping test. Pumping tests are to be conducted at the end of the installation of the permanent casing (usually PVC class 'D' pipe) to ascertain the probable yield of the tubewell. To achieve this, 2 types of pumping method is recommended and normally used. Step drawdown test or also known as multi-rate test is conducted to ascertain the 'safe yield' of the well. The data is then plotted on a drawdown vs time semi-log graph to analyse the general pattern of the curve and to extract the data from the extrapolation of the individual curve. Theis method is utilised for the graph analysis and thus would produce some aquifer parameters from the pumping test data i.e. well efficiency.

The following test is the constant pumping test whereby the flow rate, Q is 'adjusted' to remain constant throughout the testing period (normally 8 to 24-hrs for confined aquifers and 72-hrs for unconfined aquifers). The drawdown curve could be utilised later in the management of the tubewell, in terms of selection of suitable submersible pump, duration of operation, suitable pumping rate etc.

All in all, it would be wise for the drillers to realise that geological input can help them to save unnecessary time, energy and money in attending or troubleshooting problems that can be identified or foresight earlier. The geologist on the other hand, must accept the challenge that not many lay people can understand their concerns or 'appreciate' their contributions in the field which is practically new to them. The geologist need, however, to be more accurate and precise in their contributions, by highlighting and producing good and clear presentation in their daily work.


Projects undertaken in relation to water well drilling: -

Tubewell Construction for Water Supply at UPM Puchong, Selangor (2000)
Tubewell Construction for Water Supply at Kalumpang, Selangor (2000)
Construction of 3 Tubewells for Water Supply at Beh Mineral's Factory in Lahat, Perak (2000)
Tubewell Construction for Mineral Water Prospecting at Gunung Pulai, Johor (2001)
Tubewell Construction for Water Supply at Kg. Menson, Cameron Highlands, Pahang (2001)
Tubewell Construction for Water Supply at USM Kubang Kerian, Kelantan (2001)
Tubewell Rehabilitation Works for Damai Laut Golf Resort, Lumut, Perak (2001)
Tubewell Rehabilitation Works for OUG Club, Selangor (2001)
Construction of 2 Tubewells for Water Supply at Maritime Village in Padang Matsirat, Langkawi, Kedah (2001)
Construction of 13 Tubewells for Temporary Water Supply at Bukit Antarabangsa, Selangor (2000 - 2001)


Projects undertaken in relation to groundwater sourcing: -

Resistivity Survey for Groundwater Prospecting (Saltwater) at Umbai, Melaka (2000)
Resistivity Survey for Groundwater Prospecting (Freshwater) at Maritime Village in Padang Matsirat, Langkawi, Kedah (2001)