The subject of the joint ground water quality monitoring on the Hungarian side consists of 22 wells, from among 16 objects are ground water quality observation wells, situated in the upper layer of the gravel sediments, and 6 wells are used for drinking water supply (Tab. 4-1).

Samples were taken 4 times during the year. In the hydrological year 2004 there was one sample taken in case of the Darnózseli I drinking water well. Dissolved oxygen measurements in ground water quality observation wells were done as well.

The water quality monitoring in observation wells was carried out by the North-Transdanubian Inspectorate for the Environment Protection and Water Management, the water quality monitoring in wells for drinking water supply were carried out by Regional Waterworks Companies. Wells included in the ground water quality monitoring are shown on the Fig. 4-1.

Table 4-1: List of monitoring objects on the Hungarian territory

The ground water quality in case of four selected observation wells on the Hungarian side in 2004 was as follows.

Well No. 9327, locality: Dunakiliti

Based on long-term data seasonal, periodical variation of water quality was markedly observed in the ground water observation well. The groundwater has lower salt content, similar to the Danube water. Periodicity appears mainly in changes of water temperature, dissolved oxygen, conductivity, pH, nitrate and phosphate ion concentrations. In the same time a slight increase of sodium and chloride concentration was recorded. No substantial change occurred in the organic contamination, phosphate ion concentration and in content of nitrogen forms in comparison to the previous year. Iron and manganese in the water was detected in a concentration below the ground water quality limits, with a light increase of the iron concentration ad slight decrease of manganese concentration.

Well No. 9413, locality: Sérfenyősziget

Seasonal fluctuation was observed in pH values, sodium and chloride concentrations, as well as in iron and manganese contents. The conductivity values, which refer to the salt concentration in the water, show slight decreasing tendency. Corresponding to this the content of potassium, magnesium and chloride show decreasing tendency. The calcium concentration in 2004 reached lower values in comparison with the previous year. Concentrations of nitrogen forms, phosphate ions and concentration of organic matter are low, below the limit values. However, slight increase was observed in case of phosphate ions and slight decrease in case of ammonium, nitrite, nitrate and organic matter contents. No basic change came up in case of iron and manganese content in the ground water. The manganese content seasonally fluctuates and permanently exceeds the limit value.

Well No. 9430, locality: Kisbodak

The temperature of water with a moderate salt content showed a seasonal fluctuation, however it did not followed the fluctuation of air temperature. The continuous decrease of salt content had stopped; values were stable, similarly to the previous year. Significant increase of pH value was recorded in March, but the other values were similar as in the previous year. The organic matter content was lower in comparison with the previous year, and no significant changes were recorded in case of nitrogen forms and phosphate ion concentrations. Considering the drinking water use only the ammonium ion content could be objected, except the spring measurements. The iron concentration significantly fluctuates during the individual years, while in case of manganese a decreasing tendency can be observed in comparison with the previous year. Decreasing tendency was detected in case of sulphate ion concentrations as well, while the chloride concentrations slightly increased.

Well No. 9456, locality: Ásványráró

The conductivity values of the water with a stable, slightly seasonally fluctuating water temperature and medium salt content, in comparison with the previous year slightly increasing. The organic matter content was below the ground water quality limit values and presented a slight seasonal fluctuation; no significant changes occurred in comparison to the previous year. From among the nitrogen forms the ammonium ion concentration exceeded the limit value, with maximum in October. The ammonium ion concentration values show increasing tendency. The nitrite and nitrate contamination was not typical in this water. The iron and manganese content demonstrated a seasonal fluctuation, and the concentrations oscillated above the limit concentrations.

4.2. Slovak territory

For purposes of the Slovak-Hungarian monitoring the data of Western Slovakia’s Waterworks Enterprise (ZVS), the Waterworks Enterprise Bratislava (BVS), Slovak Hydrometeorological Institute (SHMÚ) and Ground Water Consulting Ltd. were used. Wells of Waterworks Enterprises are used for drinking water supply; the other objects are observation wells (Tab. 4-2).

Evaluation for each well included in the joint monitoring, similarly to the previous years, was done for period of twelve years (1.10.1992-31.10.2004) in the Slovak National Annual Report. The evaluation in this report is focused mainly to the ground water quality in waterworks, which are more representative because of their continuous pumping. All data from each well were interpreted in relation to the agreed limits for drinking water, which are presented in Tab. 4.3.

In the middle of the year 2004 the Waterworks Enterprise Bratislava had closed the pumping and finished the water quality observation on the object No. 116 (Kalinkovo, S-4) due to technical reasons. Since July 2004 they started to pump an alternative object (Kalinkovo, S-10), situated in the same waterworks. The well S-10 (object No. 119) had been used for drinking water supply in the period before putting the Gabčíkovo hydropower structure into operation and the pumping was finished in 1992. In the period from 1993 to July 2004 the well was not used. In the actual evaluation data for both well are presented.

 Table 4-2: List of monitoring objects on the Slovak territory

Short evaluation of the ground water quality in monitoring objects included in the data exchange according to the Agreement

In comparison to the previous year there were no significant changes observed in parameters analysed during the hydrological year 2004. The ground water quality in drinking water sources is very stable in long term and satisfies the agreed ground water quality limits. The only exceptions are the waterworks Bodíky (No. 485), where manganese concentration 22 times and ammonium concentration once (in 2001) exceeded the limit values during the whole observation period, and the waterworks Rusovce (No. 102), where sulphate concentration once (in 1992) exceeded the limit value.

The ground water quality in observation objects is more influenced by local impacts. The monitoring results show that agreed limits are exceeded in case of ammonium concentration, nitrites (primarily on objects No. 899 and 170), manganese (primarily on object No. 899), iron (primarily on objects No. 170 and 872). Sporadically occur values exceeding limit concentration for magnesium, COD_Mn and chlorides. Concentrations of all other analysed ground water quality components in observation objects satisfy the agreed limits for ground water quality.

Detailed evaluation of the waterworks and observation objects according to the limit values is given in the table “Exceedings of the Standard’s limits in ground water quality parameters” in the Graphical Appendix of the Slovak National Annual Report in 2004.

Evaluation of ground water quality at waterworks for drinking water supply.

Right side of the Danube

(Waterworks at Bratislava No. – 907, at Rusovce – No. 102, at Čunovo – No. 2559)

The water quality on waterworks at Rusovce and Čunovo is very similar after damming the Danube. Damming the Danube had a great influence on the ground water quality, primarily on waterworks at Rusovce, where the ground water flow direction had changed. After damming concentrations of cations (sodium, calcium and magnesium) and anions (chlorides, sulphates and hydrogencarbonates) significantly decreased, which subsequently resulted in the decrease of conductivity. Decrease of cations, anions and conductivity had stabilised in the period 1996-2002. At the Čunovo waterworks slight increasing tendency of pH values can be observed during the monitored period. Decrease of cations and anions was observed, similarly to the waterworks Rusovce, but in less extent (mainly in case of sodium, chlorides and sulphates). After the decrease of individual parameters, their concentrations are stabilising since 1998-1999, and the cations and anions fluctuate mostly in a narrow range. In case of calcium and magnesium there is a slight increase observed. The decreasing tendency of sulphates and hydrogencarbonates stopped in 2002. On both waterworks the nitrate concentrations decreased, however there is a slight increasing tendency observed since 2001. On both waterworks the organic contamination, expressed by COD_Mn, decreased as well. The TOC values fluctuate, but in 2003 and 2004 there is a slight increase registered on both waterworks.

The situation at the waterworks Pečniansky les – object No. 907 at Bratislava differs in comparison to the other monitored objects on the right side of the Danube. Values of respective parameters fluctuate a lot during the year, except the pH value, partially ammonium ions, nitrites and potassium. The measured values show a slight increase of calcium, magnesium, chloride, hydrogencarbonates and oxygen concentrations. Slight decrease was observed in case of manganese, sulphates, phosphates, silicates and COD_Mn. At the turn of years 2002-2003 significantly higher conductivity values occurred (65 mSm^-1 against the average value 45 mSm^-1). In the following period the conductivity values returned to the level of long-term average values. The other parameters did not showed changes against the long-term data.

Left side of the Danube

(Waterworks at Kalinkovo No. – 116, at Šamorín – No. 105, at Dobrohošť – No. 467, at Bodíky – No. 485, at Gabčíkovo – No. 103)

The ground water quality at waterworks situated on the left side of the Danube was not influenced by the damming to that extent like the quality at the waterworks on the right side of the Danube. The ground water quality at the waterworks Kalinkovo (objects No. 116 and 119) and at Šamorín (object No. 105) is similar. Some differences exist in calcium, magnesium, manganese and hydrogencarbonates concentrations and conductivity values (details are given in the Slovak National Annual Report for the year 2004). In case of nitrates content long-term decrease had been observed on both waterworks, however slight increase is registered since 2001. Concentration of sulphates decreases on both waterworks, but in 2004 an increase was detected. The concentration of silicates slightly increasing, the increase in 2002-2003 was more evident. However, in 2004 the content of silicates significantly decreased. The COD_Mn values were slightly increasing till 2001, however in the period 2002-2004 COD_Mn slightly decreased on both waterworks. TOC values at Kalinkovo increased and in 2003-2004 has stabilised, even a slight decrease have been observed. At waterworks Šamorín the increase of TOC stopped in 1999 and since 2000 the concentrations have begun to decrease slightly. In comparison to the previous period the average water temperature at Kalinkovo waterworks in the period 2001-2004 increased by 0.5-1 °C in average.

The ground water quality at Gabčíkovo waterworks differs from the ground water quality at Kalinkovo and Šamorín waterworks due to the different ground water flow direction. In case of conductivity, nitrates and sulphates concentrations increase is registered at Gabčíkovo waterworks. Concentrations of silicates are higher in comparison to waterworks Kalinkovo and Šamorín, and since 2002 there is additional slight increase, similar as at Kalinkovo and Šamorín waterworks. Further on increase of sodium, calcium and hydrogencarbonates concentrations are evident. Concentrations of phosphates, nitrites, ammonium ions, iron and manganese (except of Kalinkovo) are low and mostly oscillate at the level of detection limits. The TOC values were increasing in the period 1992-1998, since 1999 they are decreasing, similarly to the Kalinkovo and Šamorín waterworks. COD_Mn values fluctuate on each of the mentioned waterworks and in the period 1992-2001 were slightly increasing, however the values measured in 2002-2004 show decreasing tendency.

The ground water quality at waterworks No. 467 – Vojka and No. 485 – Bodíky is strongly influenced by local conditions. Although the waterworks are close to each other, based on the measurements it can be stated that tendencies in ground water quality parameters are different decrease of conductivity, calcium, manganese and sulphate concentrations at Bodíky waterworks; increase of conductivity, calcium, manganese, sulphate and hydrocarbonate concentrations at Vojka waterworks (details are given in the Slovak National Annual Report for 2004).

The water temperature at waterworks Bodíky is balanced, at waterworks Vojka slightly increases. PH values are similar; the conductivity values are higher at waterworks Vojka. The ammonium ion, iron and manganese concentrations are low at Vojka in long term, mostly at the level of detection limit, at the waterworks Bodíky these parameters fluctuate and since 1998 increase of manganese content is evident. Oxygen concentrations are low in long term on both waterworks. Nitrate concentration at waterworks Vojka decreased after the damming and it stabilises at present. At waterworks Bodíky the decrease of nitrates was lower in comparison with waterworks at Vojka and the concentrations slightly increases at present. Nitrites and phosphates concentrations in long-term mostly oscillate at the level of detection limit. COD_Mn and TOC values slightly decreased on both waterworks during last three years.

4.3. Conclusions

Based on the results from the Slovak side it can be stated that the basic physical and chemical parameters, cations, anions and oxygen regime parameters mostly satisfies the agreed ground water quality limits at all monitoring objects. The nutrient content satisfies the agreed limits in long term as well, except the nitrates in object No. 170 (during the period 1994-2000, while in 2001-2003 the situation got better), and ammonium content, particularly in object No. 899. The iron and manganese contents satisfy the agreed limit on most of the monitored objects, however manganese content frequently exceeded the given limit in objects No. 116, 485 and 899 and the iron content exceeded the limit in objects 170 and 872, occasionally in objects No. 262, 234 and 265.

Summarizing the results of the long-term water quality observations of 16 groundwater quality observation wells on Hungarian side it can be stated that the water base of Szigetköz is typically characterised by higher iron and manganese content. The iron and manganese content permanently exceeded the groundwater quality limit on most of the observed wells.

In general it can be stated that content of parameters indicating the presence of organic matter – like nitrogen forms, organic matter, presumably indicating contamination of agricultural and waste water origin – slightly decreases or it did not changed in comparison to the previous year.

An exception is the well No. 9368, situated in the inland area of Szigetköz at Rajka, where the high content of ammonium ions is typical. The well No. 9458, situated at Ásványráró is an example of local pollution of ground water by animal husbandry.

Apart from wells indicating local pollution of the ground water, it can be stated that in remaining wells, included in the monitoring, the nitrates and nitrites concentrations are lower than in the surface water. The low concentration of oxygen is typical as well. From place to place pollution by higher amount of iron or manganese occurs, which may indicate of redox processes.

Changes in ground water quality at some places reflect an integrated effect of the transformations occurred in the region, in which the changed ground water flow directions, affected by the Szigetköz water supply, also played role.

When analysing the measured ground water quality data of drinking water producing wells it is evident that the ammonium ion and organic matter contents are higher in wells at Győr region. In these wells also the iron and manganese content exceeds the drinking water quality limit values or oscillates around them. The iron and manganese concentrations are higher in wells at Győr-Révfalu water source, than in wells at Győr-Szőgye, which are pumped from bigger depth. The water quality in waterworks Dunakiliti I., Feketeerdő T2 and Darnózseli I is excellent and the ground water quality is characteristic by high stability. In general the ground water quality in drinking water producing wells – occasionally after treatment – is suitable for drinking water supply.

Limits for drinking water quality used for evaluation in the frame of joint monitoring are given in the following table:

Table 4-3: Ground water quality limits for drinking water