Analysis of The Potential of Volcanic Aquifers in Supporting The Development of Groundwater Resources in Bogor District, West Java

: This research is crucial for understanding the aquifer potential of volcanic deposits as a sustainable groundwater source, especially in regions experiencing rapid urbanization and agricultural expansion. It aims to analyze the aquifer potential of volcanic deposits in Bogor Regency, focusing on the Bogor Groundwater Basin, the upper Cisadane watershed, the eastern slopes of Mount Salak, and the western slopes of Mount Pangrango. The methods used include secondary data collection from regional geological maps and primary data collection through field surveys, geological mapping, and hydrogeological mapping. The results show that the volcanic rock units in this area, consisting of stony tuff, tuff breccia, lava, and andesite lava, have unique characteristics with significant potential as aquifers. Detailed geomorphological and hydrogeological mapping revealed different types of springs and physical properties of water that support the sustainability of groundwater resources. These findings contribute significantly to the development of better groundwater management policies, effective water infrastructure development, and environmental conservation strategies in Bogor District, ensuring clean water availability for the future.


INTRODUCTION
Hydrogeology is a branch of geology that studies the distribution and movement of underground water in soils and rocks in the Earth's crust, with a focus on the interaction between groundwater and its geological environment (Fetter, 2018).One important aspect of hydrogeology is aquifer potential, which is a layer of rock or sediment capable of storing and delivering large amounts of water (Todd & Mays, 1980).Aquifer potential is strongly influenced by the porosity and permeability of rocks, which determine the storage and flow capacity of water (Cartwright & Weaver, 2005).Aquifers with these characteristics serve as important natural reservoirs for wells, springs and rivers, making them vital water sources for domestic, agricultural and industrial needs (Irawan et al., 2009).Evaluation of aquifer potential by hydrogeologists through drilling methods, geological mapping and geophysical techniques helps in managing water resources sustainably, ensuring water availability for various needs and protecting groundwater quality from contamination (Endyana et al., 2016).
Groundwater plays a vital role for both residents and industries, especially in areas such as Bogor Regency.For residents, groundwater is the main source of clean water used for daily needs such as drinking, cooking, bathing and washing.In addition, groundwater also supports local agriculture by providing consistent irrigation, which is crucial for the food security and economy of local communities.For the industrial sector, groundwater provides essential raw materials for various production processes, from manufacturing to food and beverage processing.This dependence makes sustainable groundwater management a top priority, in order to continue supporting community life and industrial activities without damaging ecosystems and depleting existing resources (Mulyanti, 2022).
Bogor District faces many challenges in meeting its clean water needs, including increasing population, urbanisation, climate change, and human activities that damage the balance of groundwater resources.Rapid population growth and urbanisation significantly increase the demand

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Analysis Of The Potential Of Volcanic Aquifers In Supporting The Development Of Groundwater Resources In Bogor District, West Java for clean water, while water management infrastructure is often unable to keep up.Climate change exacerbates the situation by causing uncertainty in rainfall patterns, which impacts aquifer recharge and surface water availability.In addition, human activities such as overuse of groundwater for agriculture and industry, as well as deforestation and land use change, contribute to the decline in groundwater quantity and quality.The combination of these factors poses a major challenge for Bogor District in ensuring sustainable availability of clean water for all its citizens (Sarie et al., 2023).
In recent years, the high reliance on conventional groundwater sources in Bogor District has raised serious concerns regarding the decline in clean water availability.Over-exploitation has led to a decline in groundwater discharge, which threatens the sustainability of water supply for domestic, agricultural and industrial needs.Conventional groundwater sources, which generally originate from shallow aquifers, are increasingly unable to fulfil the growing demand (Juwono & Subagiyo, 2018).Therefore, attention is turning to groundwater sources from volcanic deposits, which are considered to have greater potential and better quality.Further investigation into these sources is expected to provide a more sustainable alternative, reduce pressure on conventional aquifers, and ensure sufficient clean water supply for all communities in the future.
This research aims to analyse the potential of volcanic sediment aquifers as potential groundwater sources in Bogor District in the hope of providing new insights and important contributions to the management of groundwater resources in Bogor District.The relevance of this research is significant in the context of groundwater management policy development, water infrastructure development, and environmental conservation in Bogor District.The results of the research are expected to serve as a basis for better decision-making in groundwater resource management, supporting appropriate policy formulation, infrastructure development that is responsive to clean water needs, as well as more effective environmental conservation strategies, thus ensuring sustainable clean water availability for the future.

RESEARCH METHOD
This research will be conducted in the Bogor Groundwater Basin, the upper Ciliwung watershed, the eastern slope of Mount Salak, and the western slope of Mount Pangrango.The research method involves secondary and primary data collection.Secondary data will mainly include surface geological data such as lithology and geological structure obtained from the 1:100,000 scale regional geological map.Furthermore, primary data collection is conducted through geological and hydrogeological surveys and mapping.
Geological mapping will include observations of geomorphology, rocks, and geological structures.Geomorphological observations will use remote sensing data such as satellite imagery through analysis of Shuttle Radar Topography Mission (SRTM) and Digital Elevation Model (DEM) data with a spatial resolution of 30 metres, as well as interpretation of Landsat imagery.The mapping involves identifying and mapping the landscape and surface characteristics of the study area.
Hydrogeological mapping will focus on observing springs in the field to determine the type of spring and the physical properties of the water.These observations include mapping spring locations, measuring elevation, determining groundwater type, and measuring physical water properties such as pH, electrical conductivity (DHL/Ec), and total dissolved solid (TDS).In addition, chemical analysis of ions and cations will be conducted in the laboratory to complement the hydrogeological data.
The combination of geological and hydrogeological mapping will provide a comprehensive picture of the potential of volcanic sediment aquifers as groundwater sources in Bogor Regency, so that it can be used as a basis for better and sustainable water resources management.

RESULT AND DISCUSSION
Bogor Regency has complex and diverse geological and hydrogeological conditions, influenced by the presence of volcanoes such as Mount Salak and Mount Pangrango.The geology of the area is dominated by volcanic deposits, including lava, tuff, and breccia, which form potential aquifers for groundwater sources.The varied geological structure, with numerous faults and folds, also affects the distribution and availability of groundwater.The hydrogeology of Bogor District is characterised by groundwater flow systems that recharge aquifers from surface runoff and rainwater infiltration, especially in mountainous areas.Natural springs are found on the mountain slopes, providing a source of clean water for the local population.The combination of rich geological conditions and dynamic hydrogeological systems makes Bogor District an important area for further research to ensure the sustainability of groundwater resources.

Geomorphology Figure 1. Geomorphological Map of Cisadane Watershed
Based on image analysis and its origin, geomorphology in the Cisadane Watershed can be classified into seven units according to (Mawardi et al., 2019).The following is an explanation of each geomorphological unit:

Formation of Volcanic Origin
This unit is formed from volcanic activity.Its characteristics include the presence of volcanic cones, lava flows, and pyroclastic materials.Due to volcanic deposits, this area usually has a rough topography with steep slopes and fertile soil.

Formation of Denuded Volcanic Origin
These areas were originally formed from volcanic material, but have undergone a significant denudation process.Denudation is the process of weathering, eroding and transporting material by water, wind or ice, which causes these volcanic-origin formations to become smoother and lower.

Formations of Volcanic Fluvial Origin
These are the result of the interaction between volcanic activity and fluvial (river water) processes.Here, river flow has influenced and altered volcanic deposits, resulting in river valley-like formations formed from eroded and re-deposited volcanic material.

Denuded Structure Origin
These formations originate from uplifted geological structures (e.g.folds or faults) that have undergone denudation.The result is a landscape with relief patterns influenced by the original geological structure, such as hilltops and valleys parallel to the structure.

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Analysis Of The Potential Of Volcanic Aquifers In Supporting The Development Of Groundwater Resources In Bogor District, West Java

Dissolution Origin Formation
This unit is formed by the dissolution of rocks, especially carbonate rocks such as limestone.The dissolution process creates distinctive forms such as caves, sinkholes and dolines.These areas are usually found in areas that have a rock composition that is easily dissolved by water.

Denuded Structure Origin
These formations originate from uplifted geological structures (e.g.folds or faults) that have undergone denudation.The result is a landscape with relief patterns influenced by the original geological structure, such as hilltops and valleys parallel to the structure.

Dissolution Origin Formation
This unit is formed by the dissolution of rocks, especially carbonate rocks such as limestone.The dissolution process creates distinctive forms such as caves, sinkholes, and dolines.These areas are usually found in areas with a rock composition that is easily dissolved by water.
Each geomorphological unit in the Cisadane watershed exhibits a distinct geological history and natural processes, which can be seen through image analysis and field studies.These forms reflect not only past geological activity but also processes that are still ongoing today.
The observation site is located in the northeastern region of Mount Salak and has an altitude of 400 -2000m above sea level.Morphological expressions in the investigation area show morphological forms of volcanic cones, pyroclastic flow ridges, and undulating plains formed by deposits of lava flows and lahars (Figure 3).The young-mature geomorphological stage is expressed by the shape of hills and plains that are still medium -coarse-textured, and exogenic processes are not yet intensive.Some slope forms in the investigation area have undergone engineering (terracing) for agricultural purposes and residential areas, while others are still pristine.The height difference between the lowest and highest elevation is ± 1725 m.From the results of analysis using ArcGIS software, the investigation area has a flat to steep slope or 2 to > 30%.

Figure 2. Geomorphological map of the Northeast area of M. Salak
The geomorphology of the western slope of Pangrango has an altitude of 500 -1800m above sea level.Morphological expressions in the investigation area show morphological forms of volcanic cones, pyroclastic flow ridges, and undulating plains formed by lava and lahar flow deposits (Figure 3.5).The young -mature geomorphological stage is expressed by the shape of hills and plains that are still medium -coarse textured and exogenic processes are not yet intensive.Some of the slope forms seen in the investigation area have undergone engineering (terracing) for agricultural purposes and residential areas, while others are still pristine.The height difference between the lowest and highest elevation is ± 1725 m.From the results of analysis using ArcGIS software the investigation area has a flat to steep slope or 2 to > 30% (Figure 3).The investigation area with slopes from flat to steep (about 2 to more than 30%) has a significant relationship with aquifer potential in groundwater development.Flat slopes tend to have greater groundwater accumulation due to higher water retention.On the other hand, steep slopes can drain water faster, increasing the opportunity to recharge aquifers located below.Therefore, areas with diverse slopes can provide favourable conditions for sustainable groundwater development (Akbar, 2023).An understanding of the relationship between slope and aquifer potential allows for more efficient and effective water resources management planning in utilising groundwater potential across a range of topographic conditions.

Stratigraphy
The rock units located in the Ciliwung watershed consist of several rock units, namely the Old Volcano Rock Unit, Pangrango Volcano Rock Unit, and Salak Volcano Rock Unit.
The Old Volcanic Rock Unit consists of stony tuff and volcanic rocks found in the Cigombong and Cikereteg areas.These rocks are grey, brown, and black, in the form of weathered tuff breccia with andesitic igneous rock components measuring 0.5 cm -3 cm, dominantly 0.5 cm, angular to oblique, open packed, and medium sorting.
The Mount Pangrango Volcanic Rock Unit is composed of andesite bedded lava (Qvpy) and lahar and andesite basalt lava (Qvpo) originating from Mount Pangrango.This unit is found in Pasirbuncir Village and is in the form of uncompacted sand, black grey to black in colour, medium to coarse grained, angular to rounded.
The Salak Volcano Rock Unit is composed of lava flows, lava, tuff breccia, and lapilli and stony tuff.The oldest rock is the stony tuff (Qvst) covered by lava, tuff breccia and lapilli (Qvsb).Rock outcrops are found in Cileungsir and Cibandawa rivers, in the form of weathered volcanic breccia, brown in colour, matrix-supported, with coarse to very coarse tuff matrix, angular to oblique igneous rock components, 2 cm -3 cm in size and locally 5 cm in size, with poor sorting and open packing (Hadian et al., 2016).
Stratigraphic columns in several places show various rock facies, as found in geomorphological research and volcanic facies characteristics in the Cihideung and Ciparikalih Rivers, Cibadak Sub Watershed (Natasia et al., 2018), which identified several facies, namely lapilli facies, lapilli tuff facies, tuff breccia facies, and lava facies.
Meanwhile, the results of stratigraphic measurement observations in the study area on the eastern slope of Mount Salak in the Cihideung River track, and the Cigombong River on the western slope of Mount Pangrango in the Cisalopa River and Ciherang River track, also identified the existence of distal facies, medial facies, and proximal facies, with a lithological arrangement that is almost the same as the results of the research by Natasia et al.The Old Volcano, Mount Pangrango and Mount Salak Rock Units reflect geological formations rich in volcanic materials, including stony tuffs, tuff breccias, lavas and lahars.The potential of aquifers in groundwater development is closely related to the se formations' physical and hydrogeological propertie.Pumiceous tuff rocks tend to have high porosity and the ability to store groundwater in cracks and pores.Tuffaceous and lapillary breccias can also contribute to the formation of good aquifers, especially if they have a weathered and permeable structure.Lava and lava flows, although perhaps less porous, can provide an overburden that restricts groundwater flow, allowing the accumulation of water underneath (Irma Lusi & Annisa Salsabilla, 2020).

Hydrogeology Aquifer system
The aquifer system of the study area was identified through surface geological mapping of the study area which covers most of S. Cihideng, the eastern part of the slope of G. Salak and S. Ciherang on the slope of G. Pangrango.The cross-section of aquifer layers resulting from the correlation of outcrop data, geoelectric data and drill logs shows layers: -Free aquifer (0-20/30 metres): pyroclastic rock (volcanic breccia).
-Impermeable layer (20 -30 metres): dense very fine tuff, aquitar layer -Semi-suppressed and suppressed aquifers (30 -120 metres): lapilli, lapilli tuff, pyroclastic breccia and laharic.impermeable layer of igneous rocks.-  Cross section of aquifer layers resulting from correlation of outcrop data, rock layers -Free aquifer: Pyroclastic breccia layer with a thickness of 10 -50 metres, inter-grain cavity aquifer system and some fracture systems.-Impermeable layer: Andesitic lava aquifug layer, and secondary aquifers, fracture system.-Free and semi-suppressed aquifers: Layers of tuff, lapilli, breccia are found in the sloping areas at the foot of the volcano, 12 -45m thick.Surface, subsurface geological data (geoelectric and drill log data), can provide an overview of geological and hydrogeological conditions ranging from the summit slopes to the foot of the volcano.On the summit slope: surface mapping results at elevations of 750 m to 1250 m, igneous rocks as aquifug layer and fracture-type secondary aquifer, massive pyroclastic breccia, primary aquifer layer of intergranular cavity type and fracture type, and unconfined aquifer type.
The results of surface mapping show an elevation of 550 m above sea level to 750 m above sea level on the slopes of the volcano body.Proclastic rocks are in the form of breccias and lapilli breccias, layers of lapilli and lapilli tuffs, tuffs, aquifer layers, aquitards, and a small portion of fracture-type secondary aquifers in breccias.The tuff layer is dense, forming an aquiclude layer as an insulating layer.
All rock layers in this zone form a multilayered aquifer with an unconfined aquifer system and a semi-suppressed aquifer.Changes in aquifer layers occur laterally which will affect hydraulic changes to form anisotropic aquifers.
On the lower slope (the foot of the volcano) at an altitude of 300-550m above sea level, drill log data, depth 70-120mbmt, vertical sequence shows a mixture of volcanic rocks (lava flow) in the form of breccia, tuff, lapilli tuff.From the drill data, lapilli tuff, tuff and breccia are found.The intersection between layers of lapilli tuff, lapilli and breccia is the rock forming the aquifer layer.While the tuff layer forms an impermeable layer, so that the lithological variations at the foot of the two volcanoes at a depth of > 80 m form an aquifer system, free, semi-pressured and suppressed.
From the results of surface mapping and drilling data, it can be illustrated that on the two slopes of the volcano form a free aquifer layer on the slopes of the peak, on the body of the volcano consists of free and semi-suppressed aquifers.At the foot of the volcano/valley between the two volcanoes, from geo-electrical data and drill logs, it can be seen that the lithological variation is increasing, in the form of intersections, laharic breccia, pyroclastic breccia, lapilli and tuff, forming a free aquifer system at the top and a suppressed aquifer at the bottom.Hydrogeologically, these groundwater quality characteristics can provide an idea of the potential of aquifers in groundwater development in the Bogor District area.Water quality that has a neutral to slightly alkaline pH and moderate to low TDS content indicates the potential for relatively good groundwater development.(Hertika et al., 2022).

Figure 10. Histogram of pH frequencies, in relation to lithological assemblages
The pH values ranged from 6-9 with an average of 7.1, the most frequent values being 7 to 7.2.The figure shows that groundwater in the Breccia has the highest pH of 8.5-9, which is 6.7.Hydrogeologically, relatively neutral to slightly alkaline pH values may indicate the potential for good groundwater development.Water with a pH in this range tends to have a good ability to hold various types of chemicals required by plants and living organisms.However, particularly for high pH waters The histogram of Ca²⁺ concentration in meq/L in the aquifer system of volcanic deposits, including lahar breccia, lapilli, pyroclastic breccia, tuff, and lapilli tuff, shows the variation of calcium content in groundwater.From the analysis, the highest average calcium content was found in the lahar breccia with a value of 13.75 meq/L, while the lowest was in the lapilli tuff with a value of 9.7 meq/L.
These variations indicate differences in aquifer characteristics in each rock formation, which may affect the potential for groundwater development in the area.For example, a higher calcium content in the lahar breccia may indicate the potential for harder groundwater or higher mineralisation, while a lower calcium content in the lapilli tuff may indicate a purer groundwater source or less affected by mineralisation processes (Purnama, 2019).

Mg Vs Lithology Figure 13. Histogram of Ca cation chemistry parameters in relation to lithological type
The concentration of Mg²⁺ in meq/L in the aquifer system of volcanic deposits, including lava breccia, lapilli, pyroclastic breccia, tuff, and lapilli tuff, shows variations in magnesium composition.The average magnesium composition in the groundwater samples ranged from 4.7 to 5.9 meq/L, with the highest value of 5.9 meq/L in the lahar breccia and the lowest of 4.7 meq/L in the pyroclastic breccia lithology.
These variations indicate differences in the chemical characteristics of the aquifers in different rock formations, which may affect the potential for groundwater development in the area.For example, higher magnesium concentrations in the lahar breccia may indicate the potential for harder groundwater or higher mineralisation, while lower concentrations in the pyroclastic breccia may indicate a purer groundwater source or less affected by mineralisation processes (UTAM, 2021).Na  The concentration values of Na²⁺ in meq/L in the aquifer system in lava breccia, lapilli, pyroclastic breccia, and lapilli tuff rocks show uneven frequency of occurrence in all groundwater samples.The average sodium content in groundwater for each lithological type ranged from 6.7 to 18.59 meq/L, with the highest values found in the lahar breccia.
This variation indicates differences in the chemical characteristics of the aquifers in different rock formations, which may affect the potential for groundwater development in the area.For example, the higher sodium content in the lahar breccia may indicate the potential for groundwater to be more affected by mineralisation processes or infiltration of chemicals from the surrounding environment (Purnama, 2019).

K Figure 15. Histogram of cation chemistry parameter K about lithological type
The Na²⁺ concentration values in meq/L in the aquifer system in lava breccia, lapilli, pyroclastic breccia and lapilli tuff rocks show significant variations.The frequency of sodium content is considerable, with the average of each rock type ranging from 1.44 to 2.85 meq/L.The highest value was found in the lava breccia with a concentration of 2.85 meq/L.This variation indicates differences in the chemical characteristics of the aquifers in the various rock formations, which may affect the potential for groundwater development in the area.Higher sodium concentrations, especially in the lahar breccia, may indicate the influence of geological processes or human activities that could affect groundwater quality (Purnama, 2019).This variation in concentration indicates differences in the chemical characteristics of groundwater in different rock formations, which may affect the potential use of groundwater for various purposes, including human consumption and agriculture (Gumilar, 2023).In this facies, it is suspected that the dominant Ca content comes from rocks containing Ca Plagioclase such as andesite, the dominant HCO3 is suspected of mixing with percipitation water (rainwater).This is evidenced by the low EC values of 26 to 135 µS/cm and TDS values of 19 to 110 mg/litre, so it is estimated that this groundwater comes from local groundwater flow.2. Na, K, Mg HCO3 (Sodium, Potassium Magnesium Bicarbonate) Facies This facies is found in samples from deep wells in depressed aquifers (artesian).The appearance of the Na element in this facies is thought to be water through rocks containing Na Plagioclase such as labradorite andesin rocks, the K (Potassium) element is thought to come from rocks containing K -Feldspar.Elemental Mg (magnesium).The water in this well comes from an old stream of water from a regional groundwater flow, characterised by a TDS value of 305 mg/litre.Springs in this facies are interpreted through rocks containing pyroxene and olivine.These springs are intermediate in nature as evidenced by Ec values of 115 to 145 µS/cm and TDS of 77 to 99 mg/litre and emerge through contact and compression type springs.It is estimated that this groundwater originates from intermediate groundwater flow characterised by TDS values of 62-89 ppm. 3. Na, K, Mg HCO3 (Sodium, Potassium Magnesium Bicarbonate) Facies This facies is found in samples from deep wells in depressed aquifers (artesian).The appearance of the Na element in this facies is thought to be water through rocks containing Na Plagioclase such as labradorite andesin rocks, the K (Potassium) element is thought to come from rocks containing K -Feldspar.Elemental Mg (magnesium).The water in this well comes from an old stream of water from a regional groundwater flow, characterised by a TDS value of 305 mg/litre.

CONCLUSION
Based on the observations, this research shows that an in-depth understanding of the geological and hydrogeological conditions in Bogor Regency, particularly regarding the aquifer potential of volcanic deposits, is essential to ensure the sustainability of groundwater resources.The old volcanic rock units, Mount Pangrango and Mount Salak, with various types of volcanic rocks, have unique characteristics that affect the distribution and quality of groundwater.Through detailed geological and hydrogeological mapping, including stratigraphic analysis, this research provides a strong scientific basis for the development of groundwater management policies, water infrastructure development,

Figure 3 .
Figure 3. Geomorphological map of the Western slope area of M. Pangrango

Figure 4 .
Figure 4. Stratigraphic column of eastern slope of M. Salak R. Cihideung and R. Cigombong

Figure 7 .
Figure 7. Cross-section of aquifer-forming lithological layers on the western slope of M. Pangrango

Figure 9 .
Figure 9. Frequency histogram of physical properties parameters, temperature, pH, eC and TDS/ZPT.The average groundwater temperature in Bogor District is 24.5°C, with the most frequent temperature range between 22.5 and 25°C.Groundwater pH values were almost evenly distributed from 5.5 to 9, with an average pH of 7.2 and dominance in the range of 6.5 to 7.5.Total Dissolved Solids (TDS) values ranged from 13 ppm to 305 ppm, with dominant values between 70 ppm to 80 ppm, and the highest TDS recorded at 305 ppm.The distribution pattern of TDS is very similar to the distribution of electrical conductivity (eC), as eC values are strongly influenced by TDS concentrations.Hydrogeologically, these groundwater quality characteristics can provide an idea of the potential of aquifers in groundwater development in the Bogor District area.Water quality that has a neutral to slightly alkaline pH and moderate to low TDS content indicates the potential for relatively good groundwater development.(Hertika et al., 2022).Correlation of pH and Lithology Figure 11.Histogram of TDS/ZPT frequencies, about lithological assemblages Potential Of Volcanic Aquifers In Supporting The Development Of Groundwater Resources In Bogor District, West Java

Figure 14 .
Figure 14.Histogram of Na2+ cation chemistry parameters in relation to the lithological type

Figure 16 .
Figure 16.Histogram of anion chemical parameters Potential Of Volcanic Aquifers In Supporting The Development Of Groundwater Resources In Bogor District, West JavaGroundwater facies East slope of Mount Salak and West slope of Mount Pangrango West Slope M. Pangrango East Slope M.Salak Figure 17.Groundwater facies of eastern slopes of M. Salak and western slopes of M. Pangrango Pipper Plot results of major ion concentrations resulted in 3 facies (IRIANTO, 2022): 1. Ca, Mg, HCO3 (Calcium, Magnesium bicarbonate) facies.