IMPLEMENTATION OF INTERNATIONAL TECHNOLOGIES AND KNOW-HOW FOR IMPROVEMENT OF WATER SUPPLY IN ALYTUS, LITHUANIA
B. Paukstys*, E. A. Hansen** and Rimantas Mockus***
*Hydrogeological Company “Grota”, Eisiskiu plentas 26, LT-2038 Vilnius, Lithuania, e-mail:
** DHI Water and Environment, Agern Alle 11, Copenhagen, Denmark, e-mail:
*** Company "Dzukijos vandenys", Pulko street 75, LT-5840 Alytus, Lithuania
ABSTRACT
This paper describes preliminary results of an international project, conducted in co-operation between Denmark and Lithuania to solve complicated municipal drinking water supply problems. A decrease in industrial production has led to a drastic drop in water consumption, and previously designed water supply and treatment facilities are too large. Natural hydrogeological conditions cause clogging and shorten the lifespan of groundwater extraction wells. Ways to optimise water supply and improve water quality in the city are sought. International experience and funding are used to address these and many other issues.
KEYWORDS: Groundwater, leakage, water supply, international co-operation, well field.
INTRODUCTION
Groundwater is a sole source of potable water supply in Lithuania. There are 94 municipal well fields that supply groundwater to 54 major cities. Alytus city of southern Lithuania representing a complicated set of natural and human induced environmental problems has been selected as a pilot site for international project.
Hydrogeological Company "GROTA", Lithuania initiated a project "Improvement of Alytus Water Water Supply, Lithuania" in 1998, in co-operation with DHI Water and Environment, Denmark. The project is financed by the Danish Environmental Protection Agency, Danish Co-operation for Environment in Eastern Europe.
The following five main outputs with a range of activities for achieving immediate objectives of the project have been defined:
1. Well field management plan;
2. Plan for rehabilitation of water supply network;
3. Action plan for water saving at main water consumers;
4. Evaluation of existing drinking water treatment facilities and preparation of rehabilitation plan;
5. Pre-assessment of the sewer system and an action plan for inventory of the system.
Preliminary results of two first outputs are discussed in the paper. More results will be achieved in the project and presented during the conference.
THE PROBLEM
Alytus, the sixth largest city by the number of inhabitants in Lithuania (77 thousand) is supplied by potable groundwater from 3 well fields: Vidzgiris, Radziunai and Strielciai with approved by the State Commission groundwater resources of 66.3 thous. m3/d. 93,7 percent of population or 72221 people are connected to the central water supply and almost the same amount (71601) to wastewater collection network.
Water supply and water distribution system in the city has been designed to be able to safely supply with water the growing industrial city for a perspective of year 2005. Unpredicted political-economical changes in the country 10 years ago imposed, however, serious corrections of the water supply sector. After the re-establishment of independence in 1990 economical production and groundwater consumption over all Lithuania, including Alytus City, has dropped down drastically (figure 1).
Figure 1. Groundwater consumption changes in Alytus.
The reasons for such a drop of water consumtion are two-fold:
- Decrease of industrial production and
- Installation of water meters in the houses and flats
All three well fields are located in the valley of the river Nemunas. Half of water is estimated to be infiltrated surface water. The Nemunas River is highly polluted with an upstream catchment area extending into the Beylorussia.
Geological and geochemical situation of the well fields is favourable for well screen clogging. In 30 years of exploitation of the main Alytus well field more than 100 wells have been re-drilled. In some places wells were re-drilled 4-5 times. The durability of the wells varies from several months to 14 years, average being 4-6 years.
The main water supply problem today is high operation costs due to a short lifetime of the wells and water leakage from the distribution network.
DESCRIPTION OF THE WELL FIELD
Strielciai well field is the main well field of the city where well clogging problems cause serious economical problems of groundwater production. The project therefore is focusing on this well field when solving well clogging issues. The well field is located 3 km north from Alytus in the valley of Nemunas River on the right bank. Total length of the well field reaches 3200 meters. There are 22 production wells in the well field, which produce 8-10 thousand m3/d of groundwater. Exploitation of Strielciai well field strated in 1979.
Geological – hydrogeological conditions
Quaternary sand and gravel aquifer (Zemaitijos-dainavos, agII-I zm-dn) located along the valley of the Nemunas river is main production aquifer in Strielciai well field (Figure 2). Water bearing sediments are formed by grey and greenish gray multi-grained sand, sand-gravel and gravel-pebble sediments. Coarse-grained fractions prevail in the section. The aquifer is underlained by Dainavos moraine till (agIdn) or paleogenic clay and silt. Sporadic distribution and low thickness clay (up to 13 meters) influences hydraulic connection of aquifer with the upper Cretaceous confined layer located on the lower level.
Before the start of the well field exploitation piezometric level of aquifer was in depth of 0.4-21.1 meters. Water level in wells during dry season stabilizes at 2-6 meters above river water level. Seasonal fluctuations of water levels in wells reach 1.8 meters.
The aquifer is confined on all territory of the well field. Water pressure varies from 12.6 m to 43 meters. Specific capacity of wells is 1-3 l/s and sometimes reaches 8 l/s.
Figure 2. Geological cross-section of Strielciai well field
Groundwater quality
Water from production aquifer is fresh, with main cations and anions not exceeding maximum permissible concentrations (MPC) of drinking water standard. In average total dissolved solids in wells reaches 370 mg/l, in water mixture – 403 mg/l. The average pH values are 7.3-7.5. Permaganate index is very different and fluctuates from 1.2 to 22.9 mgO/l in wells, in average making 3.84 mgO/l. Predominant permanganate indices (moda) in wells is 3.36 mgO/l and do not exceed MPC for good quality water. The maximum permanganate indices in water mixture reach even 47.6 mgO/l as recorded in 1992, although average and predominant values of indirect organic material index do not exceed set limits for good quality water.
Increased concentrations of iron are detected in Strielciai as well as in other well fields. Amount of Fe2+ and Fe3+ in wells fluctuate from 0 to 7.7 mg/l. Limits of iron concentrations in wells set by standards are 0,3 mg/l. Mediana and moda of iron compounds reaches 3.21 mg/l and more than 10 times exceeds MPC. Similar situation is observed in water mixture where average values of total iron is 3.7 mg/l, and mediana 4.1 mg/l. Water of such quality could not be used for drinking purposes without de-ironing.
Well clogging
It was concluded that the main reasons for well filter clogging in the well field are as follows:
- Clogging starts from mechanical silting followed by the chemical and bacterial clogging in a course of exploitation.
- The lithology of water bearing sediments at the well fields is heterogenous vertically and horizontally. This creates different filtration conditions in the aquifer and makes difficult selection of gravel pack.
- Filter type also influences well clogging. The lowest reduction of specific capacity is observed in the wells with rod-wire type of filters. Worst filters are those made of stainless steel or brass net. Average working period of rod-wired filters is 6.5-10 years while net filters last for 3-6 years. Well aging also depends on filter diameter and length. Larger diameter filters work longer.
- Mixing of water with different chemical and gas composition contributes to chemical and biochemical clogging of filters. The reason of clogging is changes of chemical equilibrium due to aquifer aeration and iron bacteria and algae activities. Eh and pH fluctuations influence direction of chemical reactions.
- Chemical clogging of near filter zone is accelerated by biological activity of iron bacteria. Several types of iron bacteria was detected in Alytus well fields, namely Leptotihrix ochracea, Gallionella and Siderocapsa. Biological analysis of water samples detected from few to 0.2 million bacteria per liter in Strielciai well field. In some water samples also algae has been detected.
Intervention of international project
Drilling works
The drilling works includes drilling of monitoring wells and a demonstration well in the Strielcai well-field and also pulling of an existing filter for examination for clogging and rehabilitation of existing clogging wells. The demonstration well is established with non-corrosive 10” PVC-casing. The filter is the stainless steel Johnson-filter to provide maximum open area of the filter and to give good possibility to future filter maintenance. Sorted gravel pack (diameter 1-2,5 mm) is used. The results of preliminary pumping test show that the flow rate of the well is 28 l/sec with a drawdown of 17 m and specific capacity of the well is 1,65 l/sec for 1 m of drawdown
For inspection and sampling of material from a clogging filter the old filter from the existing well was pulled out. The filter was examined visually, samples of filter material collected and sent to laboratories in Lithuania and Denmark.
TV-inspection
TV-inspections of 7 production wells at the well field were performed with the assistance of the Danish TV-inspection company LMJ A/S. In two of the wells visibility was very poor. Apart from this the inspection was successful. TV inspection shows clearly the degree of filter and pipe hole clogging.
REHABILITATION OF WATER SUPPLY NETWORK
The water supply distribution network in the Alytus City is old and corroded. This leads to large water and energy losses in the distribution system and also brings brown colour groundwater to the tap of the consumers. The estimated leakage from the supply system is 30%.
In 1999 the total length of water supply pipelines was 106 km. 85 percent of pipelines are of satisfactory quality, 9% (or 8.5 km) of pipes requires renovation and 6% (5.6 km) should be changed as soon as possible. It is estimated that for 1 km of pipeline 0.6 accident happens annually. The reasons for accidents are:
78% - damage (corrosion) of pipes
26% - damage of pipe connections
6% - damage of valves.
Figure 3. Accidents in water supply network
Leak detection
The project has purchased DANTEC leak detection equipment. The equipment consists of DANTEC Leak Locator Type 10S, hydrophones for plastic pipes, spindle-locator and cable & pipe locator. The equipment was delivered in June 2000 and theoretical and practical training for the use of the equipment was organized. Two teams of operators from the Alytus Water Company were trained.
The leakage detection in the water supply net was made in two steps:
· Mapping. In this step each valve-well in the streets was visited.
· Pinpointing. In this step the leak detection team investigated the areas for possible leaks using the full leak detection equipment.
75 places for potential leaks were detected and 39 leaks repeared during the programme. It is planned that the employees of Alytus Water company will perform leakage detection on permanent basis.
Night flow measurements
The measurements of night flows is one of the widely used actions that can be taken to identify leakage problems. The minimum night flow is usually found to occur between midnight and 4 am when the consumption in the network is at its lowest. The assessed night water use can be split into three components:
- domestic night use
- non-domestic use
- large users
Normal domestic night water use represents predominantly water used in the toilets. Water used for making coffee or tea makes a small portion and is usualy ignored. Non-domestic water users from unmanned fire/police stations, banks, churches, shops, offices to hotels, hospitals, public toilets, etc. All these users were counted in Alytus in order to exclude them from the total night water consumption.
Night flow measurements were performed in July- October, 2000 and some control measurements were continued during the October. During this time full town has been covered.
Figure 4. Total night flow in July-October, 2000
Increasing rate of nightflow could be explained by the fact that more people return to their flats after the summer holiday and night water consumtion increases.
Water metering in the flats
In 1992-1993 inhabitants of Lithuania had a possibility to privatise their flats buying them from the state. The appartment privatization process was immediately followed by the installations of water metering devices in the flats. This process had both positive and negative results. Positive was that:
- water users became independent from the bad quality, leaking pipes and pay only for water they use;
- water consumption can be regulated by the consumers;
- smaller water meters can more accuratelly measure small water consumption;
- dripping water taps and leaking toilet tanks are repaired.
Negative consequencies are:
- there was no economical benefit of meter installation in the flats because the installation and checking costs are higher than water which is saved;
- large number of meters (sometimes several in one flat) substantially increased cost of their maintenance and reparation;
- there is no procedure for checking the accuracy of water meters in the flats;
- the meters are not protected from the impact on readings.
The individual water meters are only duplicating the readings of house-inlet meters which are installed in all multistory houses. Water supply company is metering the supplied water only by inlet meters. The evaluation carried out by the Vilnius Technical University shows that the difference between the readings of inlet meter and sum of the flat meters is 32 per cent in favour of inhabitants. Inhabitants pay for water according to readings of their flat meters.
Today Water Supply Company has to cover difference between the inlet meter and sum of flat meters. The company is trying to convince local and national authorities and inhabitants that they have to pay for water according to calibrated inlet meters. But this is more political issue.
CONCLUSIONS
The long term purpose of the international project "Improvement of Alytus water supply, Lithuania" is to create an integrated water supply and energy management system, strengthen the institutional capacity, improve water supply infrastructure, reduce significantly groundwater losses, save energy and reduce groundwater pollution. These problems are an important issue not only in Alytus City, which was chosen as a pilot area for the project but all over the country. Therefore it is expected that results of the project will be useful for soving similar tasks in other places.