Determination of groundwater conservation zones study by considering groundwater recharge changes

This paper aims to find a new groundwater conservation zone concept in Indonesia by improving groundwater zoning by considering groundwater recharge changes. The previous zoning criteria only used groundwater level decrease and selected groundwater quality parameters. The ideas of this new concept are related to actual conditions, in terms of groundwater recharge changes due to global climate changes that control the precipitation frequency and in terms of land use changes that control groundwater recharge quantity. The changes are dynamically altered due to anthropogenic interactions. Based on Decree No. 31 2018, the groundwater conservation zone is based on three criteria: the decline of the groundwater table, the groundwater’s physical quality, and the apparent effect on the environment. This research will improve the criteria by suggesting some improvements to that approach: firstly, the application of modeling in calculating the groundwater decline rate, secondly the investigation of the effect of recharge decline due to land use change, and lastly to include recommendations on each zone in the groundwater conservation zone. This new concept is expected will revise the previous Decree that according to the consensus approach is not a scientific approach


Introduction
Water is one of the most fundamental human needs.The history shows that the thriving of civilization is highly correlated with the presence of water, be it surface or groundwater.Surface water is all water that is present on the surface, including streams, lakes, and rivers.Groundwater, on the other hand, is water that is present in the saturated zone in the subsurface.Although the presence of groundwater is 'invisible' to the naked eye, nearly 99% of liquid freshwater is available in the form of groundwater.The potential of groundwater prospects could be mapped by using the GIS technique [1] [2] which can be applied to analyzing the determination of groundwater conservation zones.
Groundwater is a part of the hydrologic cycle.Groundwater recharge happens as the water from the surface infiltrates soil to reach the groundwater table.There are several parameters that could affect groundwater recharge, including precipitation value, evapotranspiration, climate, land use, geological conditions, topography, and vegetation [3].The quality and quantity of groundwater are correlated with its interaction with human activities [4].The human activities and negative impacts are harder to mitigate in groundwater compared to surface water due to its behavior in aquifers.Due to that, it is imperative to monitor groundwater and protect it from degradation in quality and quantity.The groundwater quality could be measured by its chemical characteristics [5].To protect groundwater systems, the Indonesian government is trying to implement a conservation strategy by issuing the Ministry of Energy and Mineral Resources Decree number 31 in 2018 about the guidelines for groundwater conservation zone determination.The groundwater status condition in the conservation zone is determined by the following parameters: the lowering groundwater table, the value of total dissolved solids (TDS), or electrical conductivity and land subsidence [6].
The implementation of the decree above helped protect groundwater from further degradation.However, improvement could be made to improve the determination of groundwater conservation zones.This research focuses on the possibility of extending the parameters mentioned in the decree by the addition of integration of the groundwater recharge zone into the groundwater use zone, the addition of groundwater recharge parameter, and the integration of heavy metals into the determination of condition in the groundwater use zone.
The purpose of this research is to find a new groundwater conservation zone concept by improving the groundwater zoning considering groundwater recharge changes.The previous zoning criteria based on Decree No. 31 Year 2018 only use groundwater level decrease and selected groundwater quality parameters and will be revised by actual conditions: groundwater recharge changes and land use changes.

Literature Review
Based on the Indonesian Ministry of Energy and Mineral Resources Decree Number 31 in 2018 about the guidelines for groundwater conservation zones determination, groundwater conservation is an effort to protect the presence, nature, and use of groundwater to ensure that it has sufficient quality and quantity for current and future use.Groundwater conservation zones could be divided into two main zones: groundwater protection zones and groundwater use zones.

Groundwater Protection Zone.
Groundwater recharge zone and spring protection zone are a group of this zone.The delineation of groundwater recharge zones is important in saving and protecting groundwater resources and aquifer management [7].The delineation of the spring protection zone is much simpler, simply the radius of 200 m from springs.

Groundwater Use Zone.
The groundwater use zone could be divided into four zones that indicate the groundwater conditions in the particular zone.The groundwater conditions are determined by the quality, quantity, and environmental damage from groundwater abstraction.The groundwater quantity is represented by the decline in the groundwater table, the water quantity by the change in its TDS or EC value, and the environmental damage by land subsidence.The presence of heavy metals is an indicator that the groundwater conditions are damaged, although this presence could be theoretically the result of natural processes.
Safe, vulnerable, critical, and damaged are the four zones in the groundwater use zone.The groundwater use zone classification is classified using the matrix for groundwater quality and quantity as seen in Figure 1.The calculation of groundwater table decline uses the formula in equation 1 with S as groundwater decline rate (in %), d is the initial groundwater table (m) and ρ is groundwater decline after usage (m).Graphical representation can be seen in Figure 2.

𝑆 = × 100%
(1) Groundwater recharge is the process of water percolation from the surface to the groundwater table through soil columns [3].There are several methods to calculate groundwater recharge [3]: A. Water Balance method This method simply uses a hydrological cycle to calculate the possible groundwater recharge value with D as recharge (mm), P as precipitation (mm), ET as Evapotranspiration, ΔS the change in storage (mm), and R off as surface runoff.This method itself should be used for water investigation in general to gain insight into a hydrological cycle in the study area.
Equation 2 above needs to be modified to calculate recharge in cities or big human settlements due to human activities [9].Thus, the formula above could become equation 3 and equation 4 with  as rain that falls into the impervious surface (mm/y),  perv as rain that falls into the pervious surface (mm/y),   is the percentage of pervious surface, P is precipitation (mm/y),   is the percentage of surface runoff,   is the percentage of rainfall on the impervious surface that infiltrate the soil,   is the actual evapotranspiration from the pervious surface (mm/y) and   is the actual evapotranspiration from the impervious surface (mm/y): The physical method could be divided into two main methods based on the aquifer types: a method for an unsaturated zone and a saturated zone.For unsaturated zones, the zero-flux plane, the Darcy method, and the use of lysimeters are common methods used.This method is quite costly but could determine groundwater recharge with precision.On the other hand, the physical method to calculate groundwater recharge is the groundwater table fluctuation method which simply uses groundwater table data.

C. Tracers method
The tracers method could be used to collect important information for groundwater recharge studies, including the recharge quality and quantity, the source of recharge, and travel time from the source to determine the solute transport.There are three types of tracers that could be used: natural tracers (chloride, hydrogen, oxygen), anthropogenic tracers (tritium, CFC), and artificial tracers (fluorescent dyes)

Groundwater Modeling.
The groundwater model is a physical process that was modeled mathematically from the Darcy equation and the law of conservation of energy to get the groundwater flow formula for steady state (equation 5) and transient state (equation 6) [10] where K xx , K yy , K zz is hydraulic conductivity values in x, y, and z-axis (m/s), h is groundwater table (m), W is volumetric flux per unit volume (s -1 ), Ss is the specific storage (m -1 ) and t is time (s).This mathematical equation could be modeled by using finite element, finite difference method, or a mix of the two.One famous example of a modeling tool using finite difference is mudflow.
Mudflow is a three-dimensional groundwater numeric tool that uses finite differences to simulate groundwater flow in a saturated zone.The simulation was performed by using a grid and precisely using the middle point of grids (Figure 4).The advantage of mudflow is its ability to simulate the groundwater flow and conditions in variable physical and geometrical properties.The policy for groundwater conservation zones is highly dependent on the condition of the groundwater in each zone, as seen in Table 1 [6].

Research Location
The research locations are located on two groundwater basins in Indonesia, namely Randublatung Groundwater Basin and Karanganyar-Boyolali Groundwater Basin.

Randublatung Groundwater Basin.
Randublatung Groundwater Basin is located on the Ngawi geological map with the alluvial deposit lithology consisting of clay, sand, granules, and pebbles (Figure 5).Aquifers in Randublatung Groundwater Basin is dominated by productive aquifer (Figure 6).The period for granting an extension of the Groundwater Exploitation Permit is a maximum of 4 (four) years.
The period for granting groundwater exploitation permits is no longer than 3 (three) years.Karanganyar-Boyolali Groundwater Basin is located on volcanic and alluvial deposit that consists of mud, clay, sand, granule, pebble, and cobble (Figure 7).Aquifer productivity is variable (Figure 8).

Methods
The main methodology for this research is the use of Geographic Information System (GIS) and mudflow.The groundwater model creation starts with data collection and interpretation before analysis to get the results of this research.The first step was to collect both primary and secondary data before calculating groundwater recharge for the last 30 years.Additionally, the groundwater condition changes for the last 30 years will be analyzed.The next step is to analyze the linkage between the groundwater condition and groundwater recharge calculations.The final step is to create a groundwater conservation map with respect to groundwater recharge changes.

Randublatung Groundwater Basin.
Total Dissolved Solids values range from 108 mg/L to 632 mg/L (Table 2).This value could be considered a safe groundwater use zone [6].
The initial groundwater level data was data used from 1993-1999 compared to the data from 2020.Groundwater Conservation Zone Map was a product of groundwater quality and quantity data.Randublatung Groundwater Basin is dominated by a damaged zone with an area of 169,37 km 2 or 61% of the total area.Safe zone, on the other hand, is only 0,2% of the total area with an area of only 0,53 km 2 (Figure 9).Similarly, TDS and EC values were obtained during the field inspection in 2021 from 24 wells all across the Karanganyar-Boyolali Groundwater Basin.TDS value ranges from 150 -597 ppm and EC value 226 -898 µS/cm (Table 3).The TDS and EC value shows that it is still in the safe zone.The groundwater conservation zone is dominated by a safe zone (pink area) as shown in Figure 10.utilization zones (safe, vulnerable, critical, and damaged) can be prepared for the two CATs.Based on the area of CAT Randublatung and CAT Karanganyar Boyolali, CAT Randublatung has a smaller area than CAT Karanganyar Boyolali.The distribution of data on CATs with smaller areas tends to be spread evenly, however, for large and wide CATs it requires a complete data distribution so that the data is not spread evenly.
Groundwater conservation zoning in the Randublatung Groundwater Basin consists of safe, vulnerable, critical, and damaged zones and is dominated by damaged zones.On the other hand, the groundwater conservation zoning in the Karanganyar-Boyolali CAT consists of safe, vulnerable, critical, and damaged zones and is dominated by the safe zone.
Recommendations as a form of groundwater conservation efforts in damaged zones include the addition of Green Open Space (RTH), the addition of injection wells or recharge wells and the implementation of groundwater management policies in the form of reducing excessive pumping by providing alternative sources of raw water other than groundwater.
Based on the understanding and comparison of the two Groundwater Basins, we can infer that the result of this research is the improvement of groundwater management in the groundwater conservation zone (Table 4).

Conclusion
This paper concludes the ideas of improving the groundwater zoning considering groundwater recharge changes is related to actual condition, in terms of groundwater recharge changes due to global climate changes that control the precipitation frequency and in terms of land use changes that control groundwater recharge quantity.This is a new groundwater conservation zone concept in Indonesia compared to the previous zoning criteria that only use groundwater level decrease and selected groundwater quality parameters.
Concluding from the understanding and comparison from Randublatung and Karanganyar-Boyolali Groundwater Basin, there are three novelties of recommendation to revise groundwater zoning: The groundwater recharge zone is integrated into determining the condition of the groundwater utilization zone, there is a parameter value of groundwater recharge, integrating the value of heavy metal content into determining the condition of the groundwater utilization zone Expectantly, this new concept will revise or improve the Decree No. 17/2018 to be more scientific and actual approach.

Figure 4 .
Figure 4. Schematic of grid use in mudflow [11] 2.1.5Groundwater Conservation Zone Policy.The policy for groundwater conservation zones is highly dependent on the condition of the groundwater in each zone, as seen in Table 1[6].

Figure 9 .
Figure 9. Groundwater Conservation Map and Groundwater Recharge Map of Randublatung Groundwater Basin 3.1.2Karanganyar-Boyolali Groundwater Basin.Initial groundwater level was obtained through a literature study with the data from 1993-1999.The primary data was obtained during the field campaign in 2021.Similarly, TDS and EC values were obtained during the field inspection in 2021 from 24 wells all across the Karanganyar-Boyolali Groundwater Basin.TDS value ranges from 150 -597 ppm and EC value 226 -898 µS/cm (Table3).The TDS and EC value shows that it is still in the safe zone.The groundwater conservation zone is dominated by a safe zone (pink area) as shown in Figure10.

Table 2 .
TDS value for Randublatung Groundwater Basin

Table 4 .
The result of this research, compared to the existing groundwater conservation zone