DEEP GROUNDWATER MODELING AND QUALITY IN THE DISTRICT TAMALANREA MAKASSAR
Muhammad Hamzah Syahruddin, Amiruddin
Geophysics, Unhas, Indonesia Email: [email protected]
ABSTRACT
Nowadays people tend to exploit the deep ground water because the water is relatively better than shallow groundwater. Exploitation of deep groundwater is growing fast due to groundwater drilling companies growing and affordable. Additionally, Makassar as the Big City is a center of population concentration, industrial district center, and the center of the economy in Sulawesi, causing the rate of exploitation of deep groundwater continues to increase to meet water needs. Therefore, the question that arises is how the distribution of the wellbore in Makassar. How reservoir wells drilled in Makassar. How is the quality of the wellbore in Makassar. Those questions will be answered by this study. This research is concentrated in district Tamalanrea. His method is to record the depth and quality of drilled wells owned by the community directly.
Data wells drilled in the District Tamalanrea with spacing of approximately 500 meters was found 57 wellbore. Details of the wellbore is drilled 17 deep wells, 21 wells drilled medium, and 19 shallow bore wells. So the number of wells drilled deep, medium and shallow in the district Tamalanrea balanced. The quality of shallow groundwater from artesian wells and bore wells medium, in the District Tamalanrea still good. The condition of the wellbore medium, in Tamalanrea there are 77.77% of fresh, clear 90.47%, and 70.17% did not smell. However, there wellbore medium saltiness. This shows the threat of saltwater intrusion into the groundwater reservoir in District Tamalanrea. While the deep bore wells in the District Tamalanrea situation is less good than the wellbore medium. Of the 17 deep bore wells inTamalanrea recorded in the district there are a number of six wells are salty and brackish taste. Deep bore wells in the taste salty and brackish was 35.29%. This shows that the threat of saltwater intrusion in District Tamalanrea high.
Keywords: groudwater, wellbore, modeling, quality, Tamalanrea
I. Introduction
The aquifer in Makassar City is a coastal aquifer. Groundwater aquifer systems in Makassar are coastal/swamp deposits aquifer, river deposit aquifer, and volcanic rocks aquifer. The landform is relatively flat, classified as alluvial plain with topography levels from 0-21 m above sea level (Alimuddin et.al, 2013). The aquifer in terms of the system consists of an unconfined aquifer, semi aquifer and a confined aquifer. The water flow in the aquifer is controlled by mechanical energy (Fetter, 1999).
The coastal plain aquifer contains a lot of water, making it easy to develop as a residential area. The development of settlements in the coastal area has caused more population density. So that the big cities in the world are in the coastal area. Makassar City is one of the big cities in Indonesia which is in the coastal area. About 60% -70% of the population of Makassar city uses ground water. And around 40% of the population of Makassar City uses water from the PDAM(Drinking water Company) in Putri and Hariyadi (2016). Almost all industrial companies in Makassar using groundwater include 395 Hotel and house for rent existing in the city of Makassar (Sudirman, 2016).
Population projections suggest that current Makassar’s population is1.29 million people and will increase by 38% by 2030. The estimated population of Makassar City has double by 2050. Increasing the population causes demand on water supplies increase and also increasing the volume of wastewater generated (Nihon Suido, Nippon Koei Co. Ltd and KRI international 2011a, Tjandraatmadja et al 2012).
Shallow ground water research in Makassar has been done by Syahruddin (2013).
The research was conducted by visiting people who have wellbores (wells pantek) spread in the city of Makassar. The results of this study indicate that the change of groundwater level is 60 cm to 370 cm from the 95 wellbores surveyed. The decrease of groundwater level in makassar city is on average one meter due to rainfall effect. Changes in the depth of the high groundwater level occur in the eastern region of Makassar. This indicates that the change of ground water level in the eastern part of Makassar City is more dynamic than the change of groundwater face in the western region of Makassar City. Therefore, the indication of groundwater decline is in the eastern part of Makassar City.
Further research conducted by Syahruddin (2014) to determine the quality of surface water in the city of Makassar. The results showed that the well water conductivity of wellbores in Makassar City was between 0.2 to 2.0 milliSiemen. The results of ground
water electric conductivity measurements in Makassar City indicate that almost half of the area in Makassar City have high conductivity groundwater. The result of water salinity measurement in the coastal city of Makassar is 2.51%. While the salinity of Tallo river that passes in Bukit Baruga housing is 2.22% and the salinity of river water in Jeneberang river estuaria is 2.45%. While the result of conversion of electrical conductivity into ground water salinity in Makassar City shows that salinity of wellbore water in Makassar City is 0,01% to 0,27%.
This research generally aims to conduct deep ground water mapping in Tamalanrea district, Makassar City. Conduct measurements and analyze the physical properties of boreholes in Tamalanrea with direct observation. Studying and analyzing reservoir capability of water wellbores in Makassar City. Specifically, it aims to monitor how the groundwater wellbore is used, how well the groundwater wellbore, and monitor how changes in groundwater wellbore quality occurred in the Tamalanrea area of Makassar City.
II. Research Sites
The area of Makassar city is in coordinates 5° 8' 0" S, 119° 25' 0" E. The topography height that varies between 1-25 meters from sea level. Makassar City is a flat coastal area with a slope of 0 - 5 degrees to the west. Makassar city center is located between two river estuaries, Tallo River and Jeneberang River. Tallo River estuary to the north and river jeneberang estuary in the south. The total area of Makassar city is approximately 175.77 km2 includes 11 islands in the Makassar Strait. The total area of the sea is approximately 100 Km ². Http://makassarkota.go.id/110-geografiskotamakassar.html.
Figure II.1 Map of research location of Tamalanrea district, Makassar City
The measurement points in the research in Makassar City were mapped using satellite data (www.wikimapia.com) and GPS. The position of the drilled wells surveyed using GPS map. The initial stages of this research are conducting activities that include library study, data inventory (geology, geohydrology, precipitation), simulation, and modeling. The next stage is the survey of the wellbore distribution in Makassar. How to depth, reservoir of bore well in Makassar City. Furthermore, qualitatively physical properties of the wellbore ground water in Tamalanrea Kota Makassar sub-district are conducted.
The initial stage of this research is to carry out activities that include literature study, data inventory (geology, geohydrology, rainfall), simulation, and modeling. The next stage is a survey of the distribution of bore wells in Makassar City. How deep and well is the bore well in Tamalanrea, Makassar City. Qualitatively, the physical properties and physical condition of the wellbore groundwater are carried out in the Tamalanrea District of Makassar City. In brief, a series of research activities and the results of this study can be described as shown in Figure II.2 below.
Research area
Figure II.2. Flowchart of research activities and research results
Groundwater quality in Makassar City is obtained qualitatively and quantitatively.
Qualitative data obtained by direct interview with the community. While quantitative data obtained through measurement of groundwater conductivity and salinity. Groundwater quality measurement using conductivity meter and salt meter. Several well water samples were taken to the laboratory to measure the salinity and conductivity.
III. RESEARCH RESULT
III.1 Distrubution of Bore Wells in Tamalanrea sub-District
The topography of Tamalanrea District is relatively flat and passes through the Tallo River and coastal areas. Tamalanrea District is an industrial center and education center in the city of Makassar. Therefore, Tamalanrea Sub-district has many borehole to water suplay industrial and population needs. Mapping of bore wells in Tamalanrea sub- district was carried out to determine the distribution well. Bore wells mapping is carried out from September to Oktober 2016.
Before mapping bore wells, a sketch is first done on a map of the position of the field survey points. In the sketch, the space between the position of the wellbore point and the other point of the wellbore is determined to be ± 500 meters. The results of the sketch on the map form the basis for finding the existence of a borehole in Tamalanrea District.
The bore well is searched around the position of the predetermined point on the map. The results of mapping the bore well in Tamalanrea District can be seen in Figure III.1.
Figure III.1 Distrubution of Bore Wells in Tamalanrea sub-District
From Figure III.1 it can be seen that the number of bore wells at ± 500 meters in the Tamalanrea District is 54 wells. The distribution of bore wells in Tamalanrea District is in the northwest-southeast direction. In the southeast, 33 bore wells were obtained including Unhas Campus, BTN Antara, BTN Bumi Bung Permai, Unhas Housing and BTP Housing. Whereas in the northwest, 21 bore wells were found covering Nusa Tamalanrea Indah, Kapasa and the warehousing and Parangloe industries.
In addition to measuring bore wells, topography was measured at each position of the wellbore point. Topographic measurements using GPS so that the topography measured is the topography of the earth ellipsoid. Topography was measured to find out how surface water flow in Tamalanrea District. Topography of Tamalanrea Subdistrict and its surface water flow during rain can be seen in Figure III.2.
Figure III.2 Topographic Contour and Surface Water Flow of Tamalanrea District In Figure III.2, topography of Tamalanrea District is at a height of zero to 18 meters from above sea level. The high part is north and south. The middle part forms a basin that gets lower to the west. Surface water flow is controlled by topographic surface.
Surface water flow can be seen that the majority of the surface water flow in Tamalanrea District flows westward and a small portion flows eastward. Surface water flow in Tamalanrea District which flows westward towards the estuary of the Tallo River. While the surface water flow to the east goes to the middle part of the Tallo River. So the flow of surface water in the District of Tamalanrea all flows to the Tallo River.
III.2 Depth Bore Wells Tamalanrea
The results of measurements of the depth of the bore well in Tamalanrea District are plotted in the image using a surfer. The depth of the bore well in Tamalanrea District is made in two types of images. The first image is the depth of the bore wells from the topography and the second image is the depth of the bore wells of the earth ellipsoid. The position and depth of the bore well in Tamalanrea District from the topography can be seen in Figure III.3. Whereas the position and depth of the bore wells in Tamalanrea District of the earth ellipsoid can be seen in Figure III.4.
From Figure III.3 the depth of the Tamalanrea bore well consists of 5 parts. The first part, is a depth of 105-200 meters. The second part, the depth of more than 60- 105 meters. The third part, the depth is greater than 48 - 60 meters. The fourth part, the depth is greater than 30-48 meters. The fifth part, the depth is greater than 5-30 meters.
Based on the measurement results in Figure III.3 the authors divide into three categories into the wellbore in Tamalanrea District. The three categories of bore wells are shallow bore wells, medium bore wells and deep bore wells. Shallow bore wells are at a depth smaller than 40 meters. Deep bore wells are in depths of more than 40 meters to 100 meters. Drilled wells that are categorized as deep wells are more than 100 meters deep.
The bore well in Tamalanrea District is based on Figure III.3 there are 10 deep bore wells.
Medium bore wells are 19 wells. While the borehole is shallow there are 32 wells.
To find out the position of the well from the earth ellipsoid, the well depth is reduced from the topography or altitude data from the ellipsoid. Earth's elipsoid is defined as the line of the Earth's circle approaching the mean sea level line (MSL). The depth of the bore well in Tamalanrea District of the earth ellipsoid can be seen in Figure III.4.
Figure III.4 Depth of the Tamalanrea bore well from Elipsoid Earth
In Figure III.4 it can be seen that the depth of the well in the District of Tamalanrea is almost entirely under the earth ellipsoid or below the average sea level. From the data of the Tamalanrea bore well there are only two wells that are right in the earth ellipsoid. This shows that if the exploitation of well water is very excessive, sea water intrusion will occur.
III.3 Quality Bore Wells Tamalanrea
Salinity of borehole water was measured using a salinity measuring instrument.
Some water samples taken from the wellbore then measured the salinity. The quality of bore wells in Tamalanrea District is known by direct interviews with the community of owners or users of boreholes. Data on the quality of bore wells taken is taste, color, and smell. The taste of ground water taken includes fresh, brackish and salty. Quality colors include clear or cloudy. While the quality of odor includes odor or odorless. The taste quality of the Tamalanrea District bore well can be seen in Figure III.5.
Figure III.5 Quality of Tamalnrea sub-district bore well water
In Figure III.5 shows that the bore wells in Tamalanrea are at shallow depths and that there are still many freshwater. while deep bore wells, many have salty and brackish taste. Most bore wells in the western part of Tamalanrea have brackish and salty taste.
Brackish and salty areas cover the western part of Tamajay, parangloe, and the southeastern part of BTP housing.
Medium well bore wells in the District of Tamalanrea with 21 wells. While the deep bore wells, in Tamalanrea, were recorded as many as 17 wells. The quality of medium depth Tamalanrea bore wells can be seen in Table III.1. While the quality of bore wells in Tamalanrea can be seen in Table III.2.
Tabel III.1 Water Quality Medium Depth of Bore Wells Tamalanrea
No Longitude Latitude Elev DT DE Kualitas
Br Cr Or
1 119,514902 5,132312 11 48 -37
2 119,510034 5,132826 14 60 -46 salty
3 119,510034 5,128334 15 50 -35
4 119,506143 5,136651 12 40 -28
5 119,497987 5,135975 10 40 -30
6 119,495921 5,142214 15 40 -25
7 119,477821 5,101176 0 48 -48
8 119,48285 5,100295 2 70 -68 salty
9 119,487578 5,102103 4 50 -46
10 119,473778 5,087138 5 50 -45 salty
11 119,477647 5,089045 5 60 -55
12 119,474818 5,082988 2 50 -48
13 119,470486 5,092689 6 40 -34
14 119,501237 5,123814 6 40 -34
15 119,50509 5,120009 11 70 -59
16 119,501058 5,119351 7 52 -45
17 119,48453 5,14321 4 50 -46 salty
18 119,49059 5,14475 14 60 -46
19 119,49227 5,14222 16 40 -24
20 119,49384 5,14018 11 50 -39
21 119,49856 5,14085 15 40 -25
-Depth of topography (DT)
-Depth of ellipsoid (DE), Bright(Br), Clear (Cr), Odorless (Or)
In Table III.1 it can be shown that most of the medium depth bore wells in
Tamalanrea is in percent then 77.77% fresh water, 90.47% clear, and 70.17% does not smell. However, the presence of a medium depth bore well that feels salty shows the threat of saltwater intrusion into the groundwater reservoir in Tamalanrea District.
Tabel III.2 Water Quality Deep Bore Wells in Tamalanrea
No Longitude Latitude Elev DT DE Kualitas
Br Cr Or
1 119,492441 5,095455 11 120 -109 brackish
2 119,487278 5,09608 8 175 -167
3 119,487974 5,091659 11 105 -94 brackish
4 119,491728 5,091879 16 100 -84 brackish
5 119,495014 5,098548 17 100 -83
6 119,481951 5,105637 1 100 -99 salty
7 119,49183 5,101111 8 100 -92
8 119,46514 5,092127 1 135 -134
9 119,467452 5,090841 3 125 -122 salty
10 119,469598 5,098988 5 125 -120 salty
11 119,482517 5,085649 13 100 -87
12 119,4883 5,12602 6 160 -154
13 119,48804 5,12628 7 175 -168
14 119,4921 5,12742 4 160 -156
15 119,49153 5,13111 17 160 -143
16 119,48927 5,14173 9 200 -191
17 119,49464 5,14485 17 100 -83
-Depth of Topography (DT)
-Depth of ellipsoid (DE), Bright (Br), clear (Cr), Odorless(Or)
In Table III.2 shows that the deep well, in Tamalanrea Subdistrict, is already worse than the medium depth bore wells. Of the 17 deep bore wells recorded in the District of Tamalanrea there are 6 smur which taste salty and brackish. If the bore wells in salt and brackish taste are in the percentage of 35.29%. This shows that the threat of saltwater intrusion in Tamalanrea District is getting higher.
Conclusion
Bore wells data in Tamalanrea District with a space of approximately 500 meters found 57 bore wells. The details of the bore wells are 17 deep bore wells, 21 medium depth bore wells, and. 19 shallow bore wells. So the number of deep, medium and shallow bore wells in the Tamalanrea sub-district is balanced. The quality of groundwater from shallow and medium depth bore wells in Tamalanrea District is still good. The condition of medium depth bore wells in Tamalanrea is 77.77% fresh water, 90.47% clear, and 70.17% does not smell. However, the presence of a medium depth bore well that feels salty shows the threat of saltwater intrusion into the groundwater reservoir in Tamalanrea District. Whereas deep bore wells in Tamalanrea Subdistrict are already worse than medium depth bore wells. Of the 17 deep bore wells recorded in the District of Tamalanrea there are 6 smur which taste salty and brackish. If the bore wells in salt and brackish taste are in the percentage of 35.29%. This shows that the threat of salt water intrusion in Tamalanrea District is high.
Acknowledgement
Thank you to the Unhas LP2M for funding this research in the BMIS scheme. Thank you also to the UNHAS rector and his staff as sponsors for presenting this paper at ASIA International Conference 2018 (AIC2018) Langkawi Malaysia.
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