Quality and Chemical Type of Groundwater in Gringsing District, Batang Regency

Water quality is an aspect that is increasingly being considered in water management efforts. This is caused by the increasing frequency of water pollution problems. The purpose of this study was to analyze the quality and chemical type of groundwater in Gringsing District. Water quality analysis used in this study is a quantitative descriptive analysis by comparing the results of water quality analysis with water quality standards. To determine the chemical type of groundwater, the Stuyfzand method was used through analysis of the concentration of the dominant ions of groundwater, i.e. Ca2+, Mg2+, Na+, K+, HCO3− , SO42− and Cl-. The results showed that in general the quality of groundwater in the study area is suitable for use as a source of drinking water. There were only 4 water samples whose concentration did not meet the quality standards. The chemical type of groundwater in the study area varies greatly. There was only 1 type of groundwater found in the 2 samples, i.e. type F/0/Ca2+/HCO3 -/+, namely groundwater with a chloride content of less than 150 mg/l or fresh water, the dominant ion being calcium and bicarbonate and the addition of fresh water. and balanced saltwater.


Introduction
Water is a very important resource to support human life.However, from time to time problems related to water are increasingly complex.In addition to the increasingly limited amount, the quality of the water is also declining.Aspects of water quality are also increasingly being considered in relation to the management of water resources, due to the increasing water problems associated with these aspects [1,2,3].
Chemically, indeed the chemical concentration in water is not always the same from one place to another, depending on environmental factors that affect the water in the area concerned.Water as a component in the hydrological cycle, will also experience changes in chemical composition, either in the form of adding or reducing the concentration of chemical elements [4].
For groundwater, rock is an important factor that can distinguish the quality of groundwater in one area from another, because each rock has its own mineralogy composition which will affect the chemical properties of the groundwater contained therein [5].Groundwater is also inseparable from other environmental influences such as climate change and pollution [6,7].Groundwater contamination has occurred in many places, especially in big cities that are densely industrialized and residential.In general, the main sources and causes of groundwater pollution come from domestic, industrial and agricultural activities [8].
Gringsing District is one of the districts in Batang Regency which is close to the transportation route from the mobilization of the northern coast of Java Island.This district is also part of the IOP Publishing doi:10.1088/1755-1315/1313/1/012032 2 development of the Batang Integrated Industrial Zone as well as the potential for agro-industry, agrotourism and agribusiness.It is also possible that the development of Gringsing District with the development of the Batang Integrated Industrial Estate will also affect population growth, increased water demand, land use, and other follow-on needs.Increased utilization of groundwater in Gringsing District has the potential to cause over-exploitation, especially in the north coast area which is densely populated and industrialized.This synergizes with the potential for seawater intrusion which can then affect groundwater quality [9].

Groundwater Sampling
To determine the quality of groundwater in the study area, water samples were taken at 17 sample points.Determination of sample points was carried out by purposive sampling taking into account the distance from the shore and its distribution.Groundwater sampling locations are shown in figure 1.

Determination of Groundwater Chemical Type
To determine the chemical type of groundwater, it is necessary to know the concemtration of the dominant ions of groundwater, i.e.Ca 2+ , Mg 2+ , Na + , K + , HCO -, SO 2-and Cl -.The chemical type of 3 4 groundwater is determined by the Stuyfzand Classification [11].The division of this system is shown in table 1

Sub-Type
The dominant cation and anion (in units of meq/l) were used as the basis for division of the type into based sub-types.The concentration of cations and anions were plotted on an equilateral triangle based on the percentage, as could be seen in Figure 2.

Groundwater Quality
The results of research showed that the quality of groundwater in the study area was quite varied, indicated by the varying values and chemical concentration of each water quality parameter (Table 3 and Table 4).Looking at Tables 3 and 4, it can be seen that in general the quality of groundwater in the study is suitables for use as a source of drinking water.There were only 4 water samples whose concentration did not meet quality standards, namely sample number 6 in Sidorejo District and samples 7, 8, 10 and 11 in Yosorejo District.
Groundwater in sample number 6 in Sidorejo is not suitable for use as a source of drinking water because the concentration of sodium and chloride exceed the quality standards.Groundwater in sample number 8 in Yosorejo is groundwater with the worst quality because there are 6 parameters that do not meet quality standards, namely electrical conductivity, Total Dissoved Solids (TDS), hardness, calcium, sodium and chloride.For groundwater in samples 10 and 11, only the sodium concentration exceeded the quality standard.

Chemical Type of Groundwater
As previously stated, in the Stuyfzand classification the chemical types of water are divided into main types, types, sub-types and classes.The following shows the calculation for each of these divisions.

Main type
The main types are determined based on the concentration of chloride ions in groundwater in units of mg/l (Table 5).Based on Table 5, it is known that sample number 5 has a chloride concentration of 160 mg/l, while samples number 6 and 8 have a chloride concentration of more than 600 mg/l.Groundwater with a chloride concentration of 150-300 mg/l belongs to the chemical type Fb or freshbrackish water, while groundwater with a chloride content of 300-1000 mg/l is classified as chemical type B or brackish water.

Sub-type
Sub-types are determined based on the concentration of the dominant cation and anion in units of meq/l.In determining this sub-type, Fe 2+ is not considered because its concentration in groundwater is very small compared to the concentration of other dominant ions.Table 7 shows the results of determining sub-types based on these criteria.Based on Table 7, it can be seen that 8 samples belong to the Ca 2+ /HCO -, 3 samples belong to the Na + /Mix, 2 samples belong to the Na + /Cl -and Ca 2+ / Cl -and then 1 sample each belongs to the the Na + /HCO -and Ca 2+ /Mix sub-types.

Classes
For each sub-type it is divided into three classes according to the number of cations Na + , K + and Mg 2+ (Table 8).Looking at  Observing Table 9, it can be seen that of the 17 groundwater samples taken, almost all of them had different types of groundwater chemistry, indicating that the chemical types of groundwater in the study area varied greatly.There was only 1 type of groundwater found in the 2 samples, namely type F/0/Ca 2+ /HCO -/+ which was found in samples number 11 and 15.Groundwater with chemical type F/0/Ca 2+ /HCO -/+ is groundwater with a chloride concentration of less than 150 mg/l or fresh water, the dominant ions are calcium and bicarbonate and there is a fresh water encroachment.
Although there is a tendency for groundwater near the coast to taste brackish with the main types Fb and B, this does not occur for all groundwater near the coast.However, it can be said that water samples located far from the coast have groundwater that tastes fresh, indicated by the main type of water F.

Conclusion
1.In general, the quality of groundwater in Gringsing District area suitable for use as a source of drinking water.There were only 4 water samples whose concentration did not meet quality standards, i.e. sample number 6 in Sidorejo District and samples 7, 8, 10 and 11 in Yosorejo District.2. The chemical type of groundwater in Gringsing District area varies greatly.There was only 1 type of groundwater found in the 2 samples, namely type F/0/Ca 2+ /HCO -/+ which was found in samples number 11 and 15.Groundwater with chemical type F/0/Ca 2+ /HCO -/+ is groundwater with a chloride concentration of less than 150 mg/l or fresh water, the dominant ions are calcium and bicarbonate and there is fresh water encroachment.

Figure 2 .
Figure 2. Determination of sub-type (source : [11] with modification) of the Minister of Health of the Republic of Indonesia Number 492/MENKES/PER/IV/2010 b) Regulation of the Minister of Health of the Republic of Indonesia Number 32 of 2017 c) Government Regulation of the Republic of Indonesia Number 82 of 2001 d) According to D.K.Todd dan L.W.Mays

Table 2 .
. Determination of the main types, types and classes is shown in table 2, while the determination of the sub-types is shown in figure2.Determination of main type, type and class

Table 3 .
Analysis result of physical properties, pH and hardness a) Regulation of the Minister of Health of the Republic of Indonesia Number 32 of 2017 b) Government Regulation of the Republic of Indonesia Number 82 of 2001 c) Field observations

Table 4 .
Analysis result of dominant ions in groundwater

Table 5 .
Determination of main type The chemical type of groundwater is determined based on the concentration of hardness caused by Ca2+and Mg 2+ ions in mmol/l (Table6).From Table6it can be seen that 2 samples are classified as very hard, 2 samples are classified as hard, 4 samples are classified as moderatory hard, 6 samples are classified as soft and 3 samples are classified as very soft.

Table 7 .
Determination of sub-type

Table 8
is greater than seawater and 3 samples belong to class (0) or have additional fresh and sea water in balance.Furthermore, based on the results of determining the main types, types, sub-types and classes, the chemical type of each water sample can be determined as shown in Table9.
, it can be seen that 14 samples belong to class (+) or have additional

Table 8 .
Determination of classes

Table 9 .
Groundwater chemical type in each samples Ca 2+ /HCO3 -/0 Fresh water with very hard hardness, dominant ions are calcium and bicarbonate, equilibrium