International Conference on Urban Hydrology for the 21 st Century 14-18 th October, Kuala Lumpur1 Geological Mapping and Groundwater Physical-Chemical Prop erties Characterization An Approach to Spring Recharge Area Conservation D. Erwin Irawan Department of Geology, Institut Teknologi dan Sains Bandung Jl. Ir. H. Juanda No. 215, 4 0135 Bandung, Indonesia e-mail: [email protected]Deny Juanda P. Department of Geology, Institut Teknologi Bandung Jl. Ganesha No. 10, 40132 Bandung, Indonesia e-mail: d [email protected]et.id Abstract The overall depletion of groundwater has escalated conservation issues by many govermental and non govermental agencies. A hydrogeological study has been carried out on spring belt of Ciremai Volcano, Kabupaten Kuningan, West Java Province, to determine the spring’s recharge –discharge system. This study used 3 methods: surface geological mapping and spring observations; interpretation of physical and chemical characteristic of water; and groundwater travel time prediction. The spring belt can be divided into 3 zones based on the aquifer: Zone 1 lahar pore space aquifer system, Zone 2 lava flows fracture aquifer system, and Zone 3 pyroclastic breccias pore space aquifer system. Field permeability test shows high permeability values. Lahar residual soil shows the largest permeability value of 1.26 - 2.53 cm/min, followed by pyroclastic breccias soil 1.5 cm/min, and lava soil 0.5–1.2 cm/min. The condition indicates the soil material is potential to infiltrate rain water into the aquifer. From chemical analysis, the rain water had low conductivity and bicarbonate type water, while most ofthe groundwater samples were classified in to 3 types: Mesothermic, low conductivity, bicarbonate type; Hypothermic, low conductivity, bicarbonate type (Cibulan spring), Hyperthermic water with high conductivity, NaK-bicarbonate type (Sangkanurip spring). The type 1 and type 2 water were likely similar to rain water characteristics. Both water types were included in meteoric water cycles. While, type 3 is possibly influenced by high mineralization of Na and K from volcanic gas enrichment. Potentiometric map on the spring belt area shows a radial flow regionally, showed by 2 major flow directions, SW-NE on Area 1 with 0.4 of hydr aulic gradient and NW-SE on Area 2 with gr adient of0.3. The groundwater flow on both areas were controlled by undulating morphology. Surface observations around Cibulan spring indicates heterogeneous geological conditions. Permeable lahar deposit serves as confined aquifer. While potentiometric analysis shows eastward groundwater flow with 0.3 of gradient value. The flow is parallel to ridges and valleys orientation, proving that morphology plays significant role to control groundwater movement. Moreover, rainfall and spring discharge fluctuation data shows 3 months of average difference between rainfall’s peak and spring discharge’s . The result i nferred that the groundwater travel time is around 3 months. All the indications prove a local recharge –discharge system and very dependent to rainfall. Therefore, the recharge area is very limited and controlled by aquifer distributions, morphology, and hydrogeologic boundary. The delineation can assist i n contructing conservation program. Key words: groundwater basin analysis, volcanic aquifer system
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Abstract The overall depletion of groundwater has escalated conservation issues by manygovermental and non govermental agencies. A hydrogeological study has been carried out on spring
belt of Ciremai Volcano, Kabupaten Kuningan, West Java Province, to determine the spring’s
recharge – discharge system. This study used 3 methods: surface geological mapping and spring
observations; interpretation of physical and chemical characteristic of water; and groundwater travel
time prediction.
The spring belt can be divided into 3 zones based on the aquifer: Zone 1 lahar pore space aquifer
system, Zone 2 lava flows fracture aquifer system, and Zone 3 pyroclastic breccias pore space aquifer
system. Field permeability test shows high permeability values. Lahar residual soil shows the largest
permeability value of 1.26 - 2.53 cm/min, followed by pyroclastic breccias soil 1.5 cm/min, and lava
soil 0.5 – 1.2 cm/min. The condition indicates the soil material is potential to infiltrate rain water into
the aquifer.
From chemical analysis, the rain water had low conductivity and bicarbonate type water, while most of
the groundwater samples were classified in to 3 types: Mesothermic, low conductivity, bicarbonate
type; Hypothermic, low conductivity, bicarbonate type (Cibulan spring), Hyperthermic water with
high conductivity, NaK-bicarbonate type (Sangkanurip spring). The type 1 and type 2 water were
likely similar to rain water characteristics. Both water types were included in meteoric water cycles.
While, type 3 is possibly influenced by high mineralization of Na and K from volcanic gas
enrichment.
Potentiometric map on the spring belt area shows a radial flow regionally, showed by 2 major flow
directions, SW-NE on Area 1 with 0.4 of hydraulic gradient and NW-SE on Area 2 with gradient of
0.3. The groundwater flow on both areas were controlled by undulating morphology.
Surface observations around Cibulan spring indicates heterogeneous geological conditions. Permeablelahar deposit serves as confined aquifer. While potentiometric analysis shows eastward groundwater
flow with 0.3 of gradient value. The flow is parallel to ridges and valleys orientation, proving that
morphology plays significant role to control groundwater movement. Moreover, rainfall and spring
discharge fluctuation data shows 3 months of average difference between rainfall’s peak and spring
discharge’s. The result inferred that the groundwater travel time is around 3 months.
All the indications prove a local recharge – discharge system and very dependent to rainfall.
Therefore, the recharge area is very limited and controlled by aquifer distributions, morphology, and
hydrogeologic boundary. The delineation can assist in contructing conservation program.
Key words: groundwater basin analysis, volcanic aquifer system
International Conference on Urban Hydrology for the 21 st Century
14-18th October, Kuala Lumpur
2
1. INTRODUCTION
As widely known, Indonesia is a part of ring of fire, consisting of almost 130 Quartenary volcanoes.
The unconsolidated quartenary volcanic deposit sets up a good volcanic aquifer shown by spring belt
in many cases. Mean while, due to the vast growth of population and industry, the groundwater
resources has been decreasing rapidly. The overall depletion has escalated conservation issues bymany govermental and non govermental agencies.
Concerning the conservation issues, identifying and delineating the groundwater basin should be the
first step in order to determine the suitable groundwater conservation plans. According to Mandel
(1981)1, the delineation of groundwater systems aims at the recognition of the hydrogeologic
boundaries enclosing the system, the mechanisms of recharge, and discharge, along with the flow
paths of groundwater from recharge areas to discharge areas.
Some previous research by the author in identifying the recharge-discharge system on volcanic aquifer
system has been carried out, as follows: Asseggaf and Puradimaja (1998)2; Irawan et.al (2000)
3;
Irawan (2001)4, and Irawan et.al. (2001)
5All the research were using physical-chemical properties
analysis, combined with surface and subsurface geological observations. The general result is that theradial groundwater flow in volcanic area is controlled by the spreading of volcanic aquifer, the
hydrogeologic boundary, and the morphological feature in the area.
Another case study has been carried out on east slope of Mt. Ciremai. It is a strato-type volcano with
elevation of 3072 masl, situated 20 km south of Cirebon, Kecamatan Cilimus – Jalaksana, Kabupaten
Kuningan, West Java Province (Figure 1). Its diameter from the peak to the foot slope is about 10 km.
The location was selected because of the large amount of groundwater which are forming spring belt
with no less than 300 springs; discharged over 1500 l/sec of water (IWACO-WASECO, 19896). The
scientific interest is to determine the hydrogeological conditions and the recharge – discharge system,
which controlled such large amount of spring discharge.
2. THE METHODS
The technique used in this study was a combination of the aquifer characteristic study and
groundwater behaviour study (see Figure 2). The two techniques are: (1). Surface mapping of
volcanic aquifer system on 1 : 25.000 map scale and, (2). Interpretation of physical and chemical
characteristic of water.
The first technique was carried out in order to recognize the geometry of the aquifer and the
hydraulic properties of soil (unconfined aquifer) from 10 field permeability measurements. The
observations were taken on volcanic rock exposures and spring locations.
The second technique was performed with the aim to identify the origin of groundwater and its
movement. This technique consisted of interpretation of physical and chemical properties of
groundwater samples. The samples was taken from 24 springs sites, 1 river sampling site, and 1 rain
water sample. The physical properties measurements included: temperature (oC), conductivity
(S/cm), pH; while the chemical properties measurements consisted of major elements concentration
(Ca2+
, Na+, Mg
2+, Cl
-, K
-, HCO3
-).
More detailed analysis was applied to a spesific spring, which was selected according to the high
amount of its discharges and its contribution to public water supply. In such area, the analysis was also
supported with groundwater travel time prediction as one of the basic consideration to delineate the
recharge area. Basically, the prediction is based on comparison of rainfall gauge fluctuation and the
spring discharge fluctuation. More over, the recharge area delineation also considered themorphological feature as one of the primary feature controlling the unconfined groundwater.
International Conference on Urban Hydrology for the 21 st Century
14-18th October, Kuala Lumpur
3
3. THE RESULTS
3.1 Hydrogeological conditions
A. Aquifer and Spring Characteristics
Based on the aquifer and spring observation, the springs at East slope of Mt. Ciremai (Cilimus-
Jalaksana area) can be divided into 3 spring belts based on elevation: Zone 1 100-250 masl; Zone 2
250-650 masl (largest frequency); and Zone 3 650-1250 masl. Each spring belt corresponded to
volcanic aquifers distribution:
Lahar pore space aquifer system (< 750 masl). The aquifer discharged depression and contact
springs with total spring discharge of 1063 l/sec.
Lava flows fracture aquifer system (750-1250 masl). The aquifer discharged fracture spring
with total spring discharge of 80 l/sec
Pyroclastic breccias pore space aquifer system (1250 – 3100 masl). The aquifer discharged
depression springs with total spring discharge of 18.2 l/sec of total discharge.
The overall spring discharge potential is presented in Table 1, while the 3D geological condition and
the spring types are presented in Figure 3.
B. Field permeability test
From field permeability test (Chow et.al., 19647; Miyazaki, 1993
8), it can be concluded that all types
of soil can functioned as potential recharge materials. The conclusion is confirmed by the permeable
soils that varies upon rock type. Soil derived from lahar shows the largest permeability values of 1.26 -
2.53 cm/min, followed by pyroclastic breccias soil 1.5 cm/min, and soil of lava flow 0.5 – 1.2 cm/min(see Table 2). The high field permeability value (Linsley & Franzini, 19789) indicates that the soil
material is very potential to infiltrate rain water into the aquifer.
3.2 Groundwater movement
3.2.1 Interpretation on physical and chemical properties of water
The interpretation is based on comparison between physical and chemical properties of groundwater,
rain water, and river water. This technique is supported by assumption, that naturally, the
characteristics of meteoric type groundwater is similar to rain water’s. While, the anomalous
characteristics of groundwater indicates that the water does not follow the meteoric water cycles andinterpreted to be undergo a distinct circulation as well as chemical processes.
From Table 3.1-3.3 and Piper Diagram Plot (Piper, 194410
), it can be seen that the rain water had low
conductivity and bicarbonate type water, while most of the groundwater samples were classified in to
3 types (see Figure 4):
1. Mesothermic, low conductivity, and bicarbonate type water (Dominant type)
2. Hypothermic, low conductivity, and bicarbonate type water (Cibulan spring)
3. Hyperthermic water with high conductivity, and NaK-bicarbonate type water (Sangkanurip
spring)
Based on that data and assumption, the type 1 and type 2 water is likely similar to rain water
characteristics. Both water types are included in meteoric water cycles, which the rain water directlyinfiltrate and served as the spring recharge.
International Conference on Urban Hydrology for the 21 st Century
14-18th October, Kuala Lumpur
5
4.3 Delineation of recharge area
The recharge area delineation are based on 2 approaches: theoretical and field (surface-subsurface)
observation. The theoritical approach was based on correlation of rainfall and spring discharge graph
after Todd (1984)14
. According to Todd (1984), from the correlation between rainfall and springdischarge can be obtained recharge area extent.
Based on Todd’s graph, the springs on the area are grouped in to 5 and analyzed using the graph. The
result shows range of spring recharge area extent of 50 to 1000 km2. Regarding the graph, Todd’s
theoritical approach must be supported with more field observation approach, considering that the
graph was constructed based on subtropical climate with dominant sedimentary rock.
The high amount of rain in the area (maximum of 4000 mm) are giving significant influence to spring
discharge as well to recharge area extent. Additionally, undulating morphological control has an
important control to unconfined groundwater. Moreover, the spring is fed from the layer of volcanic
breccia aquifer which is overlain by lava flow ridge. The lava flow is giving an artesian condition on
Cibulan Spring Area. The ridge geometry also controls the groundwater flow path. Furthermore, thephysical and chemical properties of water shows a local circulation, with predicted travel time is 3
months.
Based on above facts, the recharge area is delineated. The delineation is elongate following the
volcanic breccia ridge as the aquifer. The area extent is at least 3 km2
covering the laharic breccia
(Figure 9). The result is more limited if compared to Todd’s graph result because of the various
volcanic geological condition which control the hydrogeologic boundary and distinct morphological
feature.
5. CONCLUSIONS
1. The volcanic aquifer system around Ciremai Mt. can be divided in to: pore space system of
pyroclastic breccia and lahar, fracture system of lava. Each unit consists of residual soil
aquifer and fresh rock aquifer.
2. All of the aquifer units show high heterogenity of permeable and impermeable layers in detail
scale; it is indicated by limited area extent of artesian condition on Cibulan Spring.
3. Based on detailed isophreatic analysis in 2 areas, the groundwater system shows a radial flow.
Such flow is controlled by volcanic deposit geometry and volcanic deposit flow pattern.
4. Geological mapping and groundwater characterization can be used as an approach to
determine spring recharge system and to delineate spring recharge area.
5. Based on the volcanic aquifer mapping and high rainfall measurement, the spring recharge
area extent results is more limited compared to spring recharge area from Todd’s graph.6. More detailed subsurface investigation can give more support in detailing the spring recharge
area delineation.
7. The spring recharge area identification is the first step of groundwater basin management to
Bahan Volkanik dalam Upaya Identifikasi Akifer pada Sistem Gunungapi. Studi Kasus:
Daerah Pasir Jambu-Situwangi Soreang, Kabupaten Bandung, Jawa Barat”, Jurnal Buletin
Geologi, Vol 3, Tahun 2000
4Irawan, D.E. (2001). “Karakterisasi Sistem Akifer dan Pola Aliran Airtanah pada Endapan
Gunungapi Strato. Studi Kasus: Zona Mataair pada Lereng Timur Gunungapi Ciremai,Kecamatan Cilimus-Jalaksana, Kabupaten Kuningan, Jawa Barat”. Tesis Magister