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Contamination of Village Wells

origin and consequences

part 1  - nitrate (English version below and Russian version)

part 2  -  pesticides)

 

2nd photo: village well, Kiev Oblast

The photo shows a typical village well.  About 11 million Ukrainian people drink water from such wells. Only 9 % of those villages have a canalisation. For the cities, this figure is 91 %.  Clean water however can only be expected if the area around (mainly groundwater upstream) is unused,  not cultivated  or otherwise contaminated. About consequences for human health and animals a few hints are given in  NO3-article. Polluted  wells can quickly be detected through electrochemical measurements. For more explanations see here. About methods - view overview!
 

Introduction

In villages and sometimes in smaller towns as well,  people are dependent on water from shallow wells. These wells, as shown on the photos,  can be found in streets and gardens. They contain water from the groundwater surface about < 1 m to >10 m below the soil surface. In most cases, the water is clear and tasty. Sometimes the population can get water from a deep well through a new distribution system, but it is possible that they refuse it because it is less tasty. The reason for this can be a higher concentration of iron.

Usually, people are not aware of the risk connected to the quality of their well water. First of all, babies are endangered because high nitrate concentrations are frequent. They lead to high nitrite levels that inhibit the oxygen transport in the blood. This is known as "blue-baby syndrome" and was reported to occur in the Poltava region; (10-15 cases according to official statistics, citied in /1/). Only if humans or animals die because of a high contaminant level, people start caring about.

The main contaminants of village well water are nitrate, pesticides, microbiological contamination and radon. Microbiological contamination is controlled by the Sanitary-Epidemiological Service (SES) and if necessary it is reduced by high doses of inorganic chlorine. In these cases, usually organic matter is also present in higher concentrations leading to the formation of dangerous chlororganic compounds.

Other types of pollution are mostly of local importance. To understand where the contaminants come from, what the reasons are and what can be changed, it is necessary to know the flow direction of the groundwater as shown in fig. 1.

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Fig. 1: Simplified scheme showing the pathway of water from the soil surface through the aquifer into the next river. Abbreviations: A1 and B1 are places where pollutants are deposed off or digged in the underground; A2 is a village well reaching the groundwater surface, B2 is another type of well as often found in private gardens. Water tubes usually reach deeper layers.

 

Origin of contaminants

Groundwater resources are refilled from rain water and smelting snow. It lasts several years until water from the soil surface reaches the groundwater surface. The time depends from the rain quantity, evapotranspiration, water level distance and soil characteristics. Then the water moves towards the deepest point of the groundwater table. This is usually the direction towards the next river that drains the river catchment area. On its way through the soil and the aquifer, clean water can solve natural compounds (as carbonates, fulvic acids) and anthropogenic contaminants (as organic pollutants, nitrate, pesticides).  Water that humans have contaminated with organic matter can be cleaned through filtration, biodegradation etc. A scheme of bacterial degradation is shown in figure 2. In reality, much more physical, chemical and biological reactions, influencing each other, participate in this process. One of the end-products of this self-purification process is nitrate. Nitrate can only be built in the presence of oxygen. Bacteria use oxygen for nitrification of ammonia, which is a degradation product of amino-acids.

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Fig. 2. Biodegradation of organic matter depending on the presence of oxygen and the degradation end products; at the left hand side (circle) typical anions in well water.

If the organic mater (in water or soil) is not depleted, degradation can go on nevertheless because bacteria can use oxygen bound in anions as nitrate. For this purpose nitrate and other compounds can be reduced: nitrate is reduced mainly to N2, iron III to iron II, sulphate to H2S, CO2 to CH4 and so on. Water containing high nitrate concentrations has only low amounts of iron and is therefore more tasty than water free of nitrate with high amounts of iron that makes water brownish and its taste strong. These facts and observations are only very shortly explained here for water users who are not yet familiar with them.

Investigation results

Village wells have been investigated in several regions of the central part of North Ukraine (Kiev Oblast, Chernigov Oblast: map, fig. 3).

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Fig. 3: Map showing roughly the main locations of sampling points (and results of measurements)

In more than half of the samples the Ukrainian standard for drinking water (45 mg/L = 10 mg/L N) is exceeded. Fig. 4 shows a comparison with other water types as small streams , tap water, artesian wells in Kiev and source water. Maximum values reach several hundred mg/L NO3 (up to 800 mg/L was measured and several thousand was orally reported from other sources but not yet verified).

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Fig. 4: Nitrate (NO3-N) concentrations (median on y-axis) in various types of water in and around Kiev: I = small rivers in Kiev, II = Kiev tap water, III = artesian wells in Kiev, IV = natural sources of small streams in and around Kiev, used for drinking water, V = village wells in northern Ukraine ; limit for drinking water ~ 10 mg/L (N).

The next figure (5) gives an overview on other relevant parameters (el. conductivity, organics and chlororganics.). High AOX values are probably the consequence of disinfecting.

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Fig. 5: Minimum, maximum, 25 %, 75 % and median value of el. conductivity (EC in mS/m), nitrate (NO3-N in mg/L N), organic compounds (SAC_254 in 1/m) und sum of chlororganics (AOX in ug/L).

Further investigations have been started to find out if soils near the well (in the upstream direction of ground water flow) are significantly polluted in case of high nitrate concentrations in the well water. This was obvious in a few cases of extreme pollution (dung heap, hotbed, pig breeding). In most other cases this was not visible, but the comparison of results from soil and water analyses point in this direction. Fig. 6 and 7 show results. Organic pollution is difficult to quantify and to distinguish from natural humus. It is assumed that anthropogenic organic matter has a higher oxygen demand than humus. Therefore, in a 1st approach, pollution has been quantified by  measurements of the biochemical oxygen demand of 1 g sample per 1 day (BOD1) and alternatively by BOD1/IL. IL is the loss of weight after heating the sample at 550 oC for several hours.

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Fig. 6 and 7: Influence of anthropogenic soil pollution on nitrate level in the well water.

Consequences

High nitrate concentration in village wells are not a consequence of industrialised high intensity agriculture as is the case in Western Europe. The reason is soil contamination nearby the wells itself. Main contamination sources are

  • spreading of waste water in gardens (if canalisation is lacking) and toilets

  • use of fertilisers in private gardens

  • livestock breeding

 

 

Considering the enormous amount of contaminated wells and huge number of people using its water, counter measures should have highest priority. It is recommended to identify those wells asap, inform the population on health hazards and to organise counter measures as far as possible. The focus should be on the areas nearby, upstream the (shallow) wells as shown in fig.8.

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Fig. 8: Areas (A 1, B 1) where well water (A 2, B 2) infiltrated the underground as explained in fig.1. Abbr.: A 2 = shallow village well, B 2 deeper well .

The relevant places should be controlled, cleaned and kept clean as far as possible. Otherwise the use of the well should be given up.

The relevant soil area for deep wells is more difficult to find needing further investigation or information. In general, the place of contamination is at a bigger distance upstream of the well (fig.8) and thus, filter distance and time to reach the well are bigger.

But how to control thousands of village wells?

simply constructed shallow well in a village street  -  64 kB

Almost always, polluted wells can be identified within seconds by measuring the electrical conductivity (EC) on-site. In those cases, the concentrations of chloride and sulfate are increased leading to a good correlation with EC:
   
    r_Cl = 0,85  and r_SO4 = 0,91; (p<0,01 in both cases).

Nitrate too correlates with EC (r_NO3-N = 0,55; p<0,01) and even AOX (r_AOX = 0,71; p<0,05). The EC can therefore be used as an indicator for ground water pollution. If EC is higher than 50 mS/m (500 microS/cm), pollution should be expected and people should be informed about this. To minimise the amount of analytical work later in the laboratory, it is recommended to take a sample and to analyse the pollution with nitrate and the organic load using the known ultraviolet absorption methods (see also extract from method data bank). Which other analyses are necessary to perform should be decided by the responsible water expert!!! Unfortunately, there is one obstacle. The 2 mentioned  express methods (EC and UV determination of nitrate) are not certified in Ukraine, but they are recommended here as necessity indicators for further "official" measurements.

Two more graphics show the correlation between nitrate and electrical conductivity  based on two investigation series in different regions, Zhytomir, 140 km west of Kiev and data from the 2nd graphic (below) are from Sokolovka, about 100 km north of Kiev.

Another factor influencing the EC is related to the soil type and the geological background. Examples show that this background has to be taken into account to reach a better prognosis security. The relationship between organic soil load and nitrate in the groundwater are highlighted here.

Literatur:

/1/ TSVETKOVA, A. (2002): Drinking Water in Ukraine: Communication and Empowerment for Local and International Action - Mama 86 (edit.), Kiev, 42 p.     

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last update Jan. 2017
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