Definition of natural background levels and threshold in the Joniskis groundwater body (Lithuania)

Definition of natural background levels and threshold in the Joniskis groundwater body (Lithuania)

K. Kadunas, R. Giedraitis, J. Arustiene Geological Survey of Lithuania, Vilnius SUMMARY

Joniskis GWB (original code – LT00102) belongs to Lielupe – Musa river basin district. It lies in the Northern part of Lithuania at the border with Latvia. The boundaries of groundwater body are conditional and based on intensity of water use. The main aquifers, used for water abstraction in the region, are deep Devonian aquifers, some of them rich in gypsum deposits. Shallow ground water use is limited due to poor geological conditions. Due to high gypsum content in Devonian aquifers, intensive water use originates increased sulphate concentration in drinking water. As a result of characterization which was carried out according requirements of the Directive 2000/60/EC, the Joniskis groundwater body has been attributed to groundwater bodies at risk. The threshold value for sulphate has to be established for this groundwater body.

For Joniskis GWB natural background levels for substances not only were making body “at risk” have been evaluated. For evaluation of NBL the methodology proposed in BRIDGE project was used, that is:

groundwater samples with NO3 concentrations above 10 mg/l (shallow aquifers only) were excluded and the concentration at the 90 – percentile was used. For shallow Quaternary groundwater NBL was computed for loamy and sandy soils.

Evaluation of threshold values (TV) for the toxic components (Cr, Zn, Cu) and indicator parameters (NH4+

, Na⁺, Cl^-, SO42-

) that are limited by the drinking water standard (DWS) have been performed using proposed methodology which is binding the threshold values (TV) with Maximum permissible concentrations limited by the Hygiene Norm (further referred as REF) and natural background values according to 90% percentile (NBL). For water table aquifer the REF value is ecological standard stated for groundwater. For calculation of threshold values the dilution and attenuation factors were not been taken into account.

Following the results of derivation of threshold values, the water table aquifer has good chemical status according concentrations of Cr, Cu, Cl and SO4. Concentration of these parameters only in several cases exceeds established TV. More detailed evaluation of chemical status is required for parameters as NH4, PO4 and Zn, content of which exceeds TV and enlarged concentrations them can be result of both – human activity and of natural origin.

For main aquifers used for drinking water abstraction TV was derived for three aquifers composing hydrodynamically connected system of aquifers. Different values for indicator parameters were computed.

However the use of proposed methodology and compliance testing showed that computation of threshold concentrations, evaluation of natural background levels or use of reference concentrations require refinement to answer questions which can be important managing groundwater resources and not

“over protect” them avoiding unjustified expenses.

1. Introduction

Joniskis groundwater body (GWB) is one of 22 bodies delineated in the process of characterization of the river basin districts, human impact and economic analysis of water use.

The boundaries of groundwater body are conditional and based on intensity of water use. The main aquifers, used for water abstraction in the region, are deep Devonian aquifers, some of them rich in gypsum deposits. Shallow ground water use is limited due to poor geological conditions (loamy, morainic deposits). It is used only by rural population for domestic purposes.

Due to high gypsum content in Devonian aquifers, intensive water use originates increased sulphate concentration in drinking water. The concentration of sulphate two – three times exceeds drinking water limit. In large waterworks of the region upward trends of sulphate concentrations are dependent on the yield. As a result of characterization, the Joniskis

groundwater body has been attributed to groundwater bodies at risk. The threshold value for sulphate has to be established for this groundwater body.

2. CHARACTERISATION OF THE GROUNDWATER BODY (OR GROUP OF GROUNDWATER BODIES)

2.1 Physical and hydrogeological description

2.1.1 Geographical boundaries

Joniskis GWB (original code – LT00102) belongs to Lielupe – Musa river basin district. It lies in the Northern part of Lithuania at the border with Latvia (Fig. 1). The area of GWB is 509 km², centre coordinates in ETRS89 system are: longitude – 23.71921633; latitude – 56.25671019.

Figure 1. Joniskis groundwater body

Groundwater body covers Joniskis (463 km²) and Pakruojis (46 km²) administrative districts with approximate number of population 19500 people. Inhabitants concentrate in Joniskis district (18700), the largest city with population of 11300 is administrative centre Joniskis.

The groundwater body is highly drained by surface water sources. Eleven streams flow across the body, and ponds occupy 0.79 km². Botanical conservation area Laumekiai is located within the groundwater body.

The surface of groundwater body has been moulded by the last glaciation therefore the terrain is very smooth. Prevailing absolute elevations (66 %) vary between 40 – 50 m., only 25 % of the landscape is higher than 50 m. above see level. Land surface is composed of moraine clay (78%), sandy (20.41%) and peat (1.46%) sediments. Fertile soil is the reason for agriculture development. Arable lands, grass lands and orchards occupy more than 84% of the area. Forests (11.57%), water courses (0.16%) and urban areas (4.1 %) cover remaining part of the territory.

2.1.2 Climate

Mean annual temperature is 7.3⁰C. August is the warmest month with average temperature of 19,5^oC and the January is coldest month (-8,3^oC, Table 1).

Table 1. Average monthly temperatures, t^oC

According to data from nearest weather stations average annual rainfall varies from 590 to 605 mm (Table 2).

Table 2. Average annual rainfall, mm

2.1.3 Water balance

Due to geological structure (clay, loam, etc.), from average annual rainfall of 600 mm, about 420 – 450 mm (average – 435 mm) evaporate (72.5%) and 140 mm forms surface runoff (Table 3). Groundwater is recharged by only about 4.2% of annual rainfall.

Table 3. Annual average water balance, mm

Mean annual precipitation on the area of groundwater body (509 km²) reach about 305.4×10⁶ m³, of which 221,415×10⁶ m³ evaporate and 72,233×10⁶ m³ comprise surface runoff. Very approximate evaluation shows (no detail investigation has been performed), that shallow groundwater recharge is 12,827×10⁶ m³ per year. Part of recharged water is replenishing groundwater reserves of deep aquifers.

2.1.4 Geology

Area of Joniskis groundwater body is covered by comparatively thin Quaternary deposits. In geological cross-section silt and sandy loams are prevailing. Very rarely lenses and threads of glaciofluvial or alluvial sands have been discovered. Thickness of Quaternary deposits varies in range of 3 – 38 m. with median value of 6 m. Silt and sandy loams, glaciolacustrine clay in 78%

of the area are exposed on land surface, the sandy deposits cover 8.5% of the surface.

Below Quaternary sediments, weathered surface of upper Devonian deposits was discovered (Fig. 2). Upper part of Upper Devonian strata includes Famenian (D3fm), Upper Frasnian (D3fr³) and Frasnian (D3fr) aquifers, comprised of layers of fractured dolomite, marlstone, dolomitic marlstone, silt and siltstone. For Frasnian sediments the threads of gypsum are typical.

Bellow upper Devonian strata main aquifer of Upper – Middle Devonian (D3-2) occurs. It consists of sand, sandstone, clay and marlstone layers.

Figure 2. Geological cross-section of the groundwater body

The lower part of this hydrodynamically connected system is underlain by the regional Middle Devonian aquiclude.

2.1.5 Hydrogeology

2.1.5.1. Delineation and type of groundwater body

Fresh groundwater accumulates in Quaternary and Devonian deposits. Quaternary strata consist mainly of loam and sandy loam with thin and local inter-layers of sand with low water bearing capacity and they are not used for public water supply. Shallow Quaternary aquifers are used only for individual consumption in settlements where water supply and sewerage systems are not developed. Usually shallow groundwater levels occur at the depth of 1 – 2.5 m.

below surface and it discharge into surface water courses.

For water supply in Joniskis groundwater body the following Pre-Quaternary aquifers are used:

Upper Famenian (D3fm) water bearing complex (7 stages);

Upper Frasnian aquifer (D3fr);

Middle Frasnian (D2fr) water bearing complex (4 stages);

Upper – Middle Devonian (D3-2) water bearing complex.

Main characteristics of Pre-Quaternary hydrogeological complex are presented in table 4.

Table 4. Main characteristics of Pre-Quaternary hydrogeological complex

Famenian water bearing complex consists of inter-bedded stratum of fractured dolomite, marlstone with clay and silt. Due to poor hydrogeological features, it’s use is limited.

Famenian deposits are underlain by Upper Frasnian (D3fr³) aquiclude consisting of inter- layers of clay, sandstone and dolomite with gypsum interbeds. Below Upper Frasnian to Upper – Middle Devonian (D3-2) aquifer two aquicludes of Middle and Lower Frasnian have been discovered.

Geological cross – section, finalizing Upper – Middle Devonian (D3-2) water bearing complex (aquifer), consist of sandstone and sand inter-bedded with thin layers of clay and marlstone.

Bellow low permeable dolomitic marlstone and clay form regional aquifuge.

2.1.5.2. Hydrodynamics

The hydrodynamic situation of the Joniskis groundwater body depends on groundwater withdrawals in the area and, particularly, on water abstraction in Joniskis well-field. In natural conditions pjezometric level of Upper – Middle Devonian aquifer was approximately 44 m of absolute height. In 1989 – 1992, when water use in Joniskis well-field reached in average 3000 m³/d, groundwater level has dropped by 28 m (8 m. above see level) and have formed large cone of depression which covered about 2/3 of the area (Fig. 3).

Figure 3. Potentiometric map of the study area with rivers and main groundwater flow directions (blue arrows)

Distribution of groundwater levels of different aquifers (table 1) demonstrates vertical movement of groundwater and hydrodynamical interaction of the aquifers.

Table 5. Main hydraulic properties of the groundwater body

2.1.5.3. Hydrogeochemistry

The hydrogeochemical situation of the aquifers is determined by geological composition of water bearing strata and their recharge conditions. Recharge area of Middle-Upper Devonian aquifer is situated far to the East from Joniskis GWB. The average concentration of total dissolved solids, HCO3

-, NH4

+, Ca²⁺, Cl^-, Mg²⁺ does not exceed standard for drinking water with the exception of high concentration of total iron (Table 6). However inflow of water from overlying Frasnian aquifer, which is rich in gypsum deposits, caused increased concentrations of sulphate. High maximal concentrations of Na⁺ ir K⁺ in several parts of the body prove inflow of mineral water through faults in regional aquifuge.

Table 6. Chemical composition of groundwater

Sulphate concentration is also lower in Eastern part of the body comparing to Joniskis well field (Fig. 4). In the well field sulphate content 2 – 3 times exceeds drinking water norm. Water abstraction causes rising of sulphate concentration in drinking water of the Central and Western part of the body.

Figure 4. Sulphate concentration in upper – middle Devonian aquifer

Because Frasnian aquifer contains gypsum deposits the concentration of many water quality indices are higher than observed in Middle-Upper Devonian or Frasnian aquifer. The data of hydrochemical investigations show that water composition is subject to water – sediment interaction, but upward trend of sulphate in abstracted water is the evidence of anthropogenic impact.

2.1.5.4. Groundwater receptors

Although shallow groundwater is discharging into surface streams due to geological structure (loam, loamy sand) groundwater recharge is very small and its quality have no impact to groundwater dependent aquatic and terrestrial ecosystems and protected areas.

Deep aquifers, used for water supply, contain elevated concentrations of sulphates and increased water abstraction invoke upward sulphate trend.

2.2 Identification of pressures 2.2.1 Groundwater abstraction

In 2005 in Joniskis GWB 26 well fields operated and supplied drinking water for population. 7 well fields provided water from Famenian aquifer, 10 – from Frasnian, 2 – from Famenian and Frasnian and 7 from Upper – Middle Devonian aquifer (Fig. 5). In average about 200 000 m³/year is abstracted from Famenian aquifer, 90 000 m³/year from Frasnian and about 300 000 m³/year, including the largest Joniskis well field, from Upper – Middle Devonian water bearing complex.

2.2.2 Artificial recharge

There are no artificially recharged aquifers in the area

2.2.3 Pollution

2.2.3.1 Diffuse sources

Diffuse pollution can be related to intensive agriculture (arable lands), urban complexes, industrial or commercial units. However concentrations of nitrates and pesticides in shallow groundwater are below allowable limits.

2.2.3.2 Point sources

In the process of characterization of Joniskis groundwater body 183 potential groundwater point pollution sources have been identified. From this number 65 dairy and pig farms, 73 locations of storages of oil products and 19 former pesticide and fertilizer storages have been detected. Available information shows existing groundwater pollution on the territories of petrol stations and in vicinities of former pesticide and fertilizers storages. However impact of contaminated sites to possible receptors has not been investigated.

2.3 Conceptual model

Joniskis groundwater body is a complex hydrodynamical system consisting of three aquifers used for water supply. Upper part of the GWB comprise thin layer of Quaternary loamy clay and loamy sand, which cover main aquifers. Above – mentioned aquifers are separated by local aquitards, and the regional aquifuge of Middle Devonian deposits plays the role of lower hydrodynamical boundary. In major part of the body, distribution of heads of aquifers show downward movement of infiltrated water.

Recharge area of Famenian water bearing complex co-insides with the area of occurrence of Famenian deposits. Famenian aquifer “feed” the major rivers of area (Fig. 6). The water balance of the aquifer is formed by inflow from Quaternary deposits and Frasnian stratum, small part of resources are used for water supply.

Figure 5. Conceptual model

Frasnian and Upper – Middle Devonian aquifers, within the boundaries of the body, play role of transit zone. Water resources inflow to the body from recharge area situated towards East and South - East. However, due to permeability of local aquitards, inflow from Famenian and Upper – Middle Devonian aquifers take place. Inflow from deeper geological units is unpredictable and can be observed only in fault areas of regional aquifuge.

Chemical composition of groundwater depends on time of interaction between sediments – water (transit zone) and solution of gypsum sediments in groundwater during the resources formation process. As a result, due to seepage through carbonates, rich in gypsum sediments, water of Famenian and Frasnian aquifers has similar chemical composition. As Upper – Middle Devonian aquifer consists of silicate deposits (sand, sandstone) its chemical composition differs from overlying aquifers. Only intensive groundwater abstractions accelerate inflow of sulphate to the aquifer.

2.4 Existing natural background levels

2.4.1 National/regional method used for deriving natural background levels

There is no national methodology approved to define NBL in Lithuania, but depending on tasks such levels for different compounds and different aquifers in practise are determined using same common principles. It is based on statistical determination of hydrochemical background.

Statistically calculated value of upper limit (95% or 99%) of hydro-chemical background for the compound of interest is usually treated as NBL.

The hydrochemical background is defined as the average amount of element established by observing its natural variability in a natural object, which is homogenous from the hydrogeochemical point of view. Its value depends on the selected estimation of the central (arithmetical mean, geometrical mean, logarythmic mean, median) value, of the probability distribution model and homogeneity of the samples. Under normal low, background distribution shall be distribution of the concentration of elements within the

interval , where

⎥⎦⎤

⎢⎣⎡Y⁻−

1 , 96

;

1 , 96

−

Y is estimation of the central position of data (average), is estimation of standard deviation , and values outside this interval shall be regarded as abnormal. When the available data or their (transformed) logtransformed values correspond to normal distribution, 95 % of the values of the samples fall in this interval. The statistically validated upper background limit of the macro-component composition of groundwater corresponds to the statistically validated (p≥5%) interval of distribution model . Such approach was approved by special order to be used in Initial characterization of groundwater bodies under WFD requirements (Minister of Environment order No 719 on Approval of Methodological Guidelines for Characterisation of Groundwater Bodies and Assigning of Groundwater Bodies to River Basin Districts of 24 December 2003.)

SY σ_Y

⎥⎦⎤

⎢⎣⎡ +Y⁻

1 , 96

Quite common is to calculate upper boundary of background as .

⎥⎦⎤

⎢⎣⎡ +Y⁻

2

Upper background limit usually is determined based on one from three data sources:

Based on long-term National groundwater monitoring data;

Based on data of temporary sampling of productive wells;

Based on special case studies in which determination of NBL is one of the topics.

Determination of NBL usually includes such procedures:

Verification and validation of data set;

Calculation of statistical parameters (min, max, STD, average, quartiles, percentiles);

Graphical analysis (Histograms of distribution of elements; peak analysis);

Additionally:

Hydrochemical analysis (special diagrams, equilibrium equations) Factor analysis

2.4.2 National/regional natural background levels of selected substances

For Joniskis GWB natural background levels for substances not only were making body “at risk” have been evaluated. For evaluation of NBL the methodology proposed in BRIDGE project was used, that is: groundwater samples with NO3 concentrations above 10 mg/l (shallow aquifers only) were excluded and the concentration at the 90 – percentile was used. For shallow Quaternary groundwater NBL was computed for loamy and sandy soils. Table 7 presents the results of NBL evaluation.

Table 7. Existing natural background levels, mg/l

For the evaluation of NBL of Devonian aquifers data from existing water abstraction and other wells has been used. This NBL should be used as regional NBL only for Joniskis GWB. As no national shallow groundwater monitoring network exists in the Joniskis GWB area, the natural

background level for shallow groundwater was computed from the data of national monitoring wells established in different geological environment.

2.5 Review of impacts

2.5.1 Monitoring networks (groundwater and surface water)

In the area of GWB surveillance monitoring network for groundwater has not been established. For characterisation purposes only data from drinking water abstraction points was used. At present operational water monitoring is implemented in Joniskis well field, where groundwater quantitative and raw water qualitative statuses are monitored. In 2006 operational monitoring in other water abstraction wells is foreseen.

2.5.2 Effects of abstraction on groundwater quantity

The highest amount of groundwater (509 thous.m³/year, 1394 m³/d.) is permitted to abstract from the Upper-Middle Devonian aquifers. In 2004 groundwater abstraction from these aquifers reached 329 thous. m³/year, (1394 m³/d.). This makes 63,65% of annual norm and 64,49% of permitted daily amount (Table 8). The system of aquifers is exploited by 3 largest well fields of the GWB.

Table 8. Groundwater abstraction from the system of aquifers in 2004

Upper Frasnian aquifer is the second important aquifer of the GWB. Upper Famenian has lowest abstraction (Table 8).

The largest water user is Joniskis well field producing Upper-Middle Devonian aquifer system. In 2004 m. the well field has used 77,8 % of total production from the Upper-Middle Devonian aquifers and about 40% of water abstracted from all three groundwater aquifers.

Fluctuation of groundwater levels in Famenian and Stipinai aquifers was not measured therefore information on pjezometric levels and groundwater availability in the aquifers is scarce. Pjezometric levels of Upper-Middle Devonian aquifers are measured only in Joniskis well field since 1987 and territorial hydrodynamic picture of the aquifer is also unknown.

Rough analysis of water levels in the water bearing system during the maximum exploitation has been performed for the period of 1989 – 1992, when the yield exceeded 3 thous. m³/d.

Water level in the well field then has dropped by 28 m reaching 8 m ASL and wide depression cone was formed in the water bearing system. Such a high depression in Upper-Middle Devonian aquifer system should have influenced changes of water levels in Famenian and Frasnian aquifers.

2.5.3 Effects of abstraction on groundwater quality

At the moment information on groundwater abstraction rates and changes of water chemistry in the Upper-Middle Devonian aquifer system is collected in the Joniskis well field only.

Available information demonstrates that increase of groundwater abstraction results in growth of sulphate concentration in water. During the period of maximum exploitation in 1987 – 1992 sulphate content in majority of water samples has exceeded upper limit of natural background values for this component (612 mg/l.) (Fig. 6).

Figure 6. Fluctuation of sulphate concentration in 1978 - 1991

Decrease of groundwater consumption leads to reduction of sulphate concentrations in water samples. (Fig. 7). Presently sulphate concentration in groundwater is below the upper limit of background values and is close to median– 365 mg/l.

77-12 79-12 81-12 83-12 85-12 87-12 89-12 91-12 0

200 400 600 800 1000 1200 1400

Date

mg/l

87-05 89-11 92-05 94-11 97-05 99-11 02-05 04-11 07-05 0

200 400 600 800 1000 1200 1400

date

mg/l

Figure 7. Fluctuation of sulphate concentration in 1987 – 2005 2.5.3.2 Changes in redox conditions

pH index of the groundwater extracted from the Joniskis wells varies from 6,83 to 7,83, while the roof value of natural background in the Upper- Middle Devonian aquifers is 7,79. During the period of maximum exploitation pH indices were higher fluctuating between 7,7 and 7,87.

With decrease of pumping rate groundwater became more acid and according to last available data in 1999 pH was below 7,6.

Redox (Eh) index in the well field has been measured during the time interval between October 1995 to May 1999, i.e. during the period of decrease of groundwater abstraction. Eh values varied between -107 and 68, while the roof Eh value of natural background was 38.

Highest Eh indices (0-68) have been observed in 1995, whereas in mid-1999 they have dropped to -63 ~ -45, i.e. decrease of groundwater pumping rate created reducing environment in the aquifer system.

2.5.4 Effects of abstraction on dependent ecosystems

Up to the moment groundwater dependent aquatic and terrestrial ecosystems and level of their dependency have not been distinguished. Lowering of water table during the exploitation and groundwater inflow from the neighbouring aquifers can impact dependent ecosystems. The highest impact is possible due to groundwater production from the Famenian aquifer. But development of these aquifers is not intense, and therefore the ecosystems are most probably not influenced.

2.5.5 Effects of artificial recharge

There are no artificially recharged aquifers in the area.

2.5.6 Effects of pollutant pressures on groundwater quality

Surface pollution has an influence on shallow groundwater quality and through it may affect the quality of Famenian aquifer. Heavily polluted shallow groundwater can penetrate into deeper aquifers but this was not the case until now.

2.5.7 Effect of groundwater induced pollutant pressures on dependent ecosystems

3. GROUNDWATER STATUS EVALUATION BY THRESHOLD VALUES

3.1 Application and evaluation of proposed threshold methodology

Evaluation of threshold values (TV) for the toxic components (Cr, Zn, Cu) and indicator parameters (NH4

+, Na⁺, Cl^-, SO4

2-) that are limited by the drinking water standard (DWS) have been performed using proposed methodology which is binding the threshold values (TV) with Maximum permissible concentrations limited by the Hygiene Norm (further referred as REF) and natural background values according to 90% percentile (NBL). For water table aquifer the REF value is ecological standard stated for groundwater. For calculation of threshold values the dilution and attenuation factors were not been taken into account.

Three cases have been analysed:

1^st – NBL<REF: then according to proposed methodology, TV=(REF+NBL)/2.

2^nd – NBL<REF/3: then TV=2×NBL.

3^rd – NBL>REF: then, TV=NBL.

In shallow aquifers distribution of NH4, Zn and Cu meets requirements of case 1, Cl, SO4, PO4 and total Cr – case 2. Results of estimation threshold values for toxic and indicator parameters in water table aquifer are presented in table 9.

Table 9. Threshold values for water table aquifer, mg/l (data from national monitoring network)

Distribution of Na⁺, Cl^- in Devonian water bearing sediments meets requirements of the 2^nd case in all aquifers. Due to high natural concentrations, fluctuation of NH4

+ and SO4 2-

corresponds to the 3^rd case in all aquifers.

Results of derivation of threshold values (TV) for Devonian aquifers are presented in tables 10 - 12.

Table 10. Threshold values for upper Devonian famenian aquifer, mg/l

Table 11. Threshold values for upper Devonian frasnian aquifer, mg/l

Table 12. Threshold values for middle – upper Devonian aquifer, mg/l

3.2 Results and compliance testing

As was mentioned above, the monitoring data about shallow ground water quality in Joniskis groundwater body in not available due to absence of monitoring network. However, methodology of estimation of threshold values could be applied using national monitoring data from other, similar to land use and geology, sites of the country. Results of derived threshold values allow to evaluate status of shallow groundwater of other groundwater bodies and relatively to apply them for Joniskis body. Following the thresholds presented in table 9, the water table aquifer has good chemical status according concentrations of Cr, Cu, Cl and SO4. Concentration of these parameters only in several cases exceeds established TV. More detailed evaluation of chemical status is required for parameters as NH4, PO4 and Zn, content of which exceeds TV and enlarged concentrations them can be result of both – human activity and of natural origin.

Ammonia concentration in shallow groundwater in 9% of cases is higher than TV established applying 1^st case. TV for phosphate concentration was derived applying 2^nd case (NBL<REF/3:

then TV=2×NBL) and 5% of samples go beyond TV.

For main aquifers used for drinking water abstraction TV was derived for three aquifers composing hydrodynamically connected system of aquifers (table 10 – 12). Different values for indicator parameters were established.

In all aquifers concentrations of Cl^- and Na⁺, with exception of 1 – 2 samples, do not exceed REF, NBL and TV. Therefore groundwater quality is good with respect to above mentioned chemical parameters.

However derived TV for sulphate and ammonia differs from aquifer to aquifer and become difficult to evaluate chemical status of the groundwater body.

The third TV derivation case, when NBL>REF and TV=NBL, and same time >REF, in all hydrogeological systems 50% water samples contain SO4

2- concentrations >REF and in up to 10

% water samples they exceed TV. Thus with respect sulphate, 50% of water samples contain water of poor chemical status according to REF and only up to 10% of samples contain poor water according to TV.

NH4

+ concentrations in 25% water samples collected from Famenian and Frasnian hydrogeological systems exceed REF and up to 10 % samples exceed TV. Consequently 25% of water is of poor quality according to REF and 10 % of samples contain poor water with respect to TV. In 25% of water samples from Upper-Middle Devonian aquifers NH4

+ concentrations are

above REF and up to 10 % – above TV, i.e. in 25 % of samples water is poor with respect to REF and in 10 % samples with respect to TV.

4. CONCLUSIONS

Joniskis groundwater body (GWB) is one of 22 bodies delineated in the process of characterization of the river basin districts, human impact and economic analysis of water use.

The boundaries of groundwater body are conditional and based on intensity of water use. The main aquifers, used for water abstraction in the region, are deep Devonian aquifers, some of them rich in gypsum deposits. Shallow ground water use is limited due to poor geological conditions (loamy, morainic deposits). It is used only by rural population for domestic purposes.

Due to high gypsum content in Devonian aquifers, intensive water use originates increased sulphate concentration in drinking water. The concentration of sulphate two – three times exceeds drinking water limit. In large waterworks of the region upward trends of sulphate concentrations are dependent on the yield. As a result of characterization, the Joniskis groundwater body has been attributed to groundwater bodies at risk. The threshold value for sulphate has to be established for this groundwater body.

The use of proposed methodology and compliance testing showed that computation of threshold concentrations, evaluation of natural background levels or use of reference concentrations require refinement to answer questions which can be important managing groundwater resources and not “over protect” them avoiding unjustified expenses.

Whereas derivation of threshold concentrations is based on evaluation of natural background concentrations and quality standards (REF), the methodology should in generally clarify:

a) Which period of monitoring data should be used for derivation of NBL. As an example of saline water intrusion due to intensive water use of deep aquifers: in Joniskis groundwater body intensive water abstraction was till 1991. In that time upward trend of sulphate was observed.

Due to economic circumstances from 1991 to 2005 water use decrease and monitoring data show downwards trend of sulphate in abstracted water. In both cases values of natural background and, respectively, threshold values will be different. From other hand, derivation of threshold’s using equation, when NBL>REF: then, TV=NBL, do not allow any human activity because it can cause trend increment. Management of water use in such cases can be impossible because of lack of other drinking water sources.

b) Groundwater body can consist of aquifer or aquifers (WFD, art. 2-12). In Joniskis groundwater body three aquifers make hydrodinamically connected system of aquifers. The use of one of them can invoke groundwater quality changes in all system or in one or another aquifer. The derivation of threshold’s for sulphate values in Famenian, Frasnian and middle- upper Devonian aquifers show that value can vary from 580 to 1590 mg/l. Which value should be used to avoid “over estimation” of chemical status of groundwater body?

c) Whereas, in prevailing cases, use of deep aquifers can not influence surface/terrestrial systems, the establishment of threshold values for substances indicators of intrusion could be optional even upward trend is observed. Hence, upward trends of indicators of intrusion can not be treated as “pollution” and regarded as intrusion. In such circumstances only Drinking Water Directive and prescribed restriction of water use could be applied.

d) The methodology of derivation of natural background values for water table aquifer seems shifting to derive “native” values. Proposal to exclude samples with values of nitrates more 10 mg/l or values of potassium more 5 mg/l can twist the sense of derived background. This approach could be applicable for protected areas only. From one hand, presence of nitrogen compounds in groundwater can activate biodegradation of organic pollutants and excluding some sets of samples from derivation process can affect derivation of threshold values of other pollutants. From another hand, why not exclude only samples where nitrate concentration exceeds 25 or 37.5 mg/l (75% of standard making body “at risk”)?

e) Computation of threshold values is based on reference values. In fact these values should be part of country legislation. However when part of body (or body) is used for drinking water abstraction reference value for shallow groundwater should be equal drinking water standard (DWS). These standards usually are consentient for many countries. Use DWS as reference values definitely can make established thresholds comparable round the EC countries. However countries legislation usually set other ecological standards, which limiting concentrations of pollutants in surface or in groundwater. Different values can be applied when groundwater can be used for abstraction or it not intended to be used, but pollution can affect other ecosystems.

In Joniskis case study, threshold values for shallow groundwater, presented in table 9, derived applying ecological standard for groundwater which can be used in future. Only 5 – 9 % of samples are higher threshold concentrations. But, if for derivation of thresholds the ecological standard for groundwater as non portable water source or ecological standard for surface water would be applied, the threshold values for several indicator parameters can be 50 – 70 % higher or lesser respectively. Recommendations or attempts to find common for EC reference concentrations, from our point of view, can help to compare established thresholds and to manage groundwater protection in Europe.

f) Evaluation of natural background concentrations for substances as heavy metals would require description of sampling procedures. Sampling of monitoring wells for evaluation of heavy metals in groundwater includes sample filtering procedure (Lithuania). Different approaches used in sampling procedures can directly affect results of computation of threshold values.

5. REFERENCES

1. Order of the Director of Geological Survey regarding collection of information and inventory of discharge of dangerous substances into groundwater, 3 February, 2003 No. 1-06.

2. Hygienic norm HN 24: 2003 Requirements for drinking water safety and quality. Order of the Minister of Health Protection, July 23, 2003, No. V-455.

3. Regulation on reduction of water pollution by dangerous substances. Order of the Minister of Environment, December 21, 2001, No. 624.

4. Fresh groundwater status characterization for water management in River Basin Districts according requirements of Directive 2000/60/EC of the European Parliament and of the Council. Vol. II. Status of Middle – Upper Devonian groundwater body (LT001).

Annexes: Tables

Table 1. Average monthly temperatures, t^oC

Month I II III IV V VI VII VIII IX X XI XII

t

C -8,3 0,2 3,2 8,7 9,5 12,5 16,7 19,5 13,6 7,9 -0,7 -3,2

Table 2. Average annual rainfall, mm

Month I II III IV V VI VII VIII IX X XI XII Avera ge

Birzai station 32 24 34 40 52 58 77 71 64 55 52 45 605 Kyburiai

station

32 25 29 43 50 60 75 78 61 57 45 39 595

Table 3. Annual average water balance, mm

Precipitation Evaporation Surface runoff Groundwater recharge

600 (100%) 435 (72,5%) 140 (23,3%) 25 (4,2%)

Table 4. Main characteristics of Pre-Quaternary hydrogeological complex

Top Bottom Aquifer/Stage

Depth, m Abs. height, m Depth, m Abs. height, m

D

fm (aquifer) 3÷29,5 18,4÷58,0 20,0÷140,0 44÷89,6 8,0÷137,0

D3fr³ (aquiclude)

20,0÷140,0 44,0÷89,6 41,0÷158,5 -107,5÷7,48 4÷39

41,0÷158,5 -107,5÷7,48 46,0÷175,0 -117,2÷2,48 <15

46,0÷175,0 -117,2÷2,48 101,8÷183,0 -125,2÷123,6 3÷49

101,8÷183,0 -125,2÷123,6 170,5÷218,5 -166,6÷-123,6 17÷103

170,5÷218,5 -166,6÷-123,6 177,0÷222,0 -129÷-170,6 3÷15(?)

D3-2 (aquifer)

177,0÷222,0 -129÷-170,6 ~ 400 ~ - 360 ~190

D2nr (aquifuge)

~ 400 ~ - 360 ~ 500 ~ - 460 ~190

Table 5. Main hydraulic properties of the groundwater body

D3fm D3fr D3-2

Depth to groundwater, m 0-25,64 0-21,0 0-48,0 Pjezom. level, m above see level 25,64-69,1 23,4-54,0 11,4-44,8

Hydraulic conductivity, m/d 0,5-20,0 2,0-40,0 2,0-15,0

Permeability, m²/d 10-700 20-600 50-600

Specific yield , l/s 0,15-6,0 0,2-3,0 0,5-3,0

Table 6. Chemical composition of groundwater

Min Average Median MAX H N:24

H or. D3fm D3fr3 D3-2 D3fm D3fr3 D3-2 D3fm D3fr3 D3-2 D3fm D3fr3 D3-2 Norma

BM 203,36 554,85 315,35 811,88 1588,77 807,47 752,61 1367,47 750 1708,21 3491,4 1612,8

BK 4,3 2,56 0,96 15,68 21,63 11,58 12,75 20 10,43 66,1 39 36,7

PI 0,96 0,1 0,07 4,65 4,81 2,12 4,32 4 1,76 13,12 14,64 9,6 5

250

348,22 878,76 410,95 287,5 810,3 365 1056 2200 1128 250

1,5 0,72 1,5 0,5

50

0,51 0,94 0,52 2,94 7,62 2 0,5

325 200

0,77 0,73 1,18 0,5 0,49 0,91 4,2 2,4 5,78 0,2

2,8 6,4 3,55 22,91 45,49 32,82 18 35,5 33 91 355 71

7,2 65,2 40,67

51,4 170,8 122 336,63 310,41 246,45 348 311 238 488 427 489

0 0 0 0,14 0,08 0,07 0 0 0,01

0 0 0 0,7 0,15 0,76 0 0 0 7,7 2 22

0 0 0 0,32 0,29 0,21

11,54 20,88 8,9 15,01 30,03 37,97 14,46 31,8 34 35 36,6

5 6,25 0,96 10,25 13,34 16,51 10,65 10 13,33 16,83 21,16 137

5 2,75 58 139,29 308,53 136,18 135,14 280,56 119 380,7 605 318

1,62 42,56 12 57,62 81,73 57,76 58 74 55 126,88 167,81 104,92

0 0 0

Cl ^-

SO₄^2-

HCO₃ ^-

NO₂ ^-

NO₃^-

NH₄+

Na+

K +

Ca₂⁺ Mg₂⁺ Fe_t

Table 7. Existing natural background levels, mg/l Aquifer Cl^- SO42-

NO3-

NH4+

Crtotal Zn Cu PO42+

Q loamy 19 33 4 4.6 0.003 0.03 0.015 0.06

Q sandy 25 60 2 0.6 0.001 0.02 0.0015 0.14

Q loamy+sandy 46 82 3.2 1.4 0.002 0.04 0.0044 0.22

D3fm 36 710 2 1.22 ND ND ND ND

D3fr 43 1582 0 1.56 ND ND ND ND

D3-2 45 579 2 0.7 ND ND ND ND

ND – no data

Table 8. Groundwater abstraction from the system of aquifers in 2004

Limit of

abstraction, thous. m³/year

Limit of abstraction,

m³/d

Number of wells Abstracted thous. m³/year

Abstracted m³/d

D3fm 296 818 12 219 599

D3fr 133 364 13 91 249

D3-2 509 1394 22 329 899

Table 9. Threshold values for water table aquifer, mg/l (data from national monitoring network)

Parameter REF

Number of samples (N) after plausibility check

Number of samples (N) and NBLs according to simplified preselection approach

TV

Number of samples from N for which the TV is exceeded

Cl^- 350 523 N = 398 NBL = 46,1 92,2 0

SO4

2- 450 523 N = 398 NBL = 81,5 163 1

NH4

+ 2,0 521 N = 344 NBL = 1,1 1,55 32

Cr tot. 0,05 47 N = 33 NBL = 0,002 0,004 1

Zn 3,0 47 N = 33 NBL = 0,036 0,068 4

Cu 0,1 45 N = 31 NBL= 0,0044 0,0072 1

PO4

+ 0,7 219 N = 144 NBL = 0,22 0,44 7

REF – ecological standard for groundwater

Table 10. Threshold values for upper Devonian famenian aquifer, mg/l

REF

Number of samples (N) after plausibility check

Number of samples (N) and NBLs according to simplified preselection approach

TV

Number of samples from N for which the TV is exceeded

Cl^- 250 60 51 NBL = 35,5 71 1

SO4

2- 250 52 48 NBL = 710 710 5

NH4

+ 0,5 52 50 NBL = 1,22 1,22 5

Na⁺ 200 14 12 NBL = 17,14 34,28 1

REF – drinking water standard

Table 11. Threshold values for upper Devonian frasnian aquifer, mg/l

REF

Number of samples (N) after

plausibility check

Number of samples (N) and NBLs according to simplified preselection approach

TV

Number of samples from N for which the TV is exceeded

Cl^- 250 30 25 NBL = 43 86 2

SO4

2- 250 29 25 NBL = 1582 1582 4

NH4+

0,5 26 24 NBL = 1,56 1,56 3

Na⁺ 200 8 6 NBL = 34,8 69,6 0

REF – drinking water standard

Table 12. Threshold values for middle – upper Devonian aquifer, mg/l

REF,

mg/l

Number of samples (N) after

plausibility check

Number of samples (N) and NBLs according to simplified preselection approach

TV

Number of samples from N for which the TV is exceeded

Cl^- 250 45 42 NBL = 45 90 0

SO4

2- 250 45 43 NBL = 579 579 5

NH4

+ 0,5 40 37 NBL = 0,7 0,7 5

Na⁺ 200 30 26 NBL = 37 74 0

REF – drinking water standard