Surface Water and Groundwater Quality Evaluation in a Mining Area

This paper presents a monitoring of groundwater and surface water in the mining area Tg. Ocna, by analyzing 16 physico-chemical parameters (pH, turbidity, dissolved oxygen, Pb, Ni, Cu, Fe, Mn, Zn, Cr, Mg, SO4 , Al, NO2 , NO3 , NH4 ), from three rivers Slanic, Trotus and Valcele, a small lake Groapa Burlacu, a fountain and three monitoring drilling wells (F11, F16 and F17). Studies on the quality of surface water and groundwater in areas near mines are important due to extraction and exploitation of salt. The samples were collected in April 2019. Following the analyzes, their results are included in the following concentration ranges: pH 7.21 to 8.46 unit. pH, turbidity 0.54 to 169 NTU, dissolved oxygen 6 to 8.59 mg/L, Pb 0.075 to 0.095 mg/L, Ni 0.026 to 1.05 mg/L, Cu 0.088 to 0.809 mg/L, NO2 0.001 to 0.037 mg/L and NO3 0.290 to 4.34 mg/L. The pH, turbidity and dissolved oxygen were measured in situ using portable equipment’s. As for the other parameters, they were analyzed in the water laboratory from Vasile Alecsandri University of Bacau by using spectrophotometry. Some concentrations of the physico-chemical indicators of the water samples analyzed were found to be more than the water quality classes.

Regarding the quality of the groundwater, the physical-chemical properties monitoring can be the best methods for punctual or global quality evaluation. Besides these properties there are other parameters that can change the quality of groundwater, for example metals. The main sources of pollution with metals of the water are the untreated wastewater discharges, the industrial and mining activities, the agricultural activities etc. [32][33][34][35][36][37][38][39][40][41][42][43][44][45].
The mining exploitation, in most countries, is an important economic activity essential to supply raw materials for human activities. Within this activity, the operations used can produce large

Study Area
The city of Targu Ocna is in the southwest of Bacau county, on the banks of the Trotus river, where it receives the waters of the Slanic and Valcele affluent. The geographical coordinates of the study area are 46.2876°N 26.6034°E. The studied area is near the Targu Ocna salt mine, which includes a salt solution section exploitation area. Since the area is located between mountains and hills, the thermal regime is a moderate one with mild winters with early spring and cool summers with an average annual temperature of 9.3°C.
Surface water and groundwater samples ( Figure 1) were collected from 11 different points within the Slanic River, upstream and downstream (RSU and RSD), the Trotus River, upstream and downstream (RTU and RTD), the Valcele River, upstream and downstream (RVU and RVD), a fountain, and three drilling monitoring points (F11, F16, F17), from the city of Targu Ocna. The monitoring points were chosen for a good water quality evaluation before and after mining area.

Sampling and analysis
The collection of samples was carried out in April 2019 in 500 mL polyethylene (PET) bottles and stored at proper temperature. The equipment's used for parameters evaluations are presented in Table  1.
Physico-chemical parameters measured in-situ were pH, turbidity and dissolved oxygen performed by using portable WTW equipment's. The rest of parameters were evaluated in the Vasile Alecsandri  [47,48,49]. Regarding the analysis of rest of the parameters, were used certified methods, recommended by VIS DR 3900 spectrophotometer HACH producer.

Evaluation of the parameters performed in situ
The parameters analyzed in situ were pH, turbidity and dissolved oxygen ( Figure 2). As can be seen in Figure 2a  The turbidity values (Figure 2b) of groundwater varies from 0.54 to 55 NTU recorded at measurement point F17, and the values recorded within surface waters varies from 0.73 to 169 NTU. The highest values are recorded upstream for the RSU measurement point and the lowest values are recorded at the RVU measurement points and in the fountain. The high values recorded for turbidity can be a consequence of the high precipitation level from that period.
The highest values of dissolved oxygen (Figure 2c) for surface waters are recorded in the upstream of RSU and RTU, except for the sample taken from the River Valcele where the highest value is recorded downstream. The value recorded in the measuring point Groapa Burlacu was 6.77 mg/L. Regarding the measurement points taken from the groundwater, the highest values were recorded in points F16 and F11.

Evaluation of the parameters performed in laboratory
Thirteen indicators (Figures 3 and 4) Ni, NO3 -, Cu, Fe, Mn, SO4 2-, Pb, NO2 -, Zn, Cr, NH4 + , Al and Mg were analyzed from the samples of the groundwater and surface water in the Vasile Alecsandri University of Bacau laboratory.  The concentrations of the NO3values were between 0.290 mg/L to 2.85 mg/L. The high value of the NO2and NO3concentration were recorded in the point RSU. This point is in the incidence of the possible waste and wastewater from near households.
The surface water analyzes results indicate high level of SO4, 167 mg/L to 30.2 mg/L. These values indicate that the water samples are included in the II and III quality class. The samples analyzed from the sampling points RSU, RSD, RTU, RTD and Groapa Burlacu belong to quality class II, and the sampling points RVU and RVD belong to II quality class [50]. In

Conclusions
The study presents a monitoring of groundwater and surface water in the mining area of Targu Ocna, Bacau county.
Following the results, the parameters that were measured for the water quality study show that the maximum pH value was recorded at the measuring point Groapa Burlacu indicating an alkaline pH.
Domestic activities, waste, weather conditions within the study area may influence the chemical composition of surface and groundwater within the studied area.
The present study evaluates a monitoring of the contamination level of the water sources around the studied area. The results of the analyzed indicators (Pb, Ni, Cu, Fe, Mn, Zn, Cr, Mg, SO4 2-, Al, NO2-, NO3-and NH4 + ) in the surface and groundwaters vary from sample to sample. The highest concentrations of the analyzed indicators are found in the samples taken from the surface waters, except for the SO4 2indicator.