Metla Project 7006

Artificial recharge of groundwater: infiltration techniques, soil processes and water quality

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Duration: 1998-2002   

Objectives

The use of artificial groundwater recharge for producing high quality drinking water is increasing in Finland. At the moment 10 % of water used in Finland is artificially recharged groundwater, and by 2010 it is estimated to account for over 20 % of the total water use. The intention of this artificial recharge is to produce groundwater that is similar to natural groundwater. This is done by using as few chemicals and in as small amounts as possible, and by infiltrating surface water taken from water bodies into soil, either by means of basin infiltration, or by sprinkling infiltration.

The aim of the project is to optimise the infiltration techniques and recharge process in relation to the quantity, quality and environmental effects of artificial groundwater. This is being implemented by
  1. Determining the causal relationships between physico-chemical and microbiological soil processes and water quality as infiltrating surface water is gradually converted into artificial groundwater. Quality changes are studied in the soil surface layer, percolation water layer and groundwater layer by sampling and analysing soil, percolation water and groundwater. The effect of surface water quality (organic matter, pH, nutrients), and the need for pre-treatment is also being investigated.
  2. Determining the changes in soil processes and water quality using different infiltration techniques: basin infiltration and sprinkling infiltration: timing and duration, surface load.

  3. Determining the size, hydraulic and hydrogeological characteristics and retention times in the aquifer and to use this information, together with the water quality data, for modelling the dimensioning, capacity and control of artificial groundwater plants.

Results

Methods

Hydrogeochemical variables and hydraulic processes of the surface soil zone, percolation water zone and groundwater zone were studied at five AR groundwater supply plants in Finland. These studies included analysis of soil, infiltration water, percolation water and groundwater samples, and measurements of groundwater flow characteristics and retention time. The causal relationships between the data were observed. Groundwater flow was modelled using the data.

Results

Pre-treatment tests revealed that even the smallest quantities of solid substances, such as clay, caused clogging of the soil. Rapid filtration of water significantly reduced clogging.

One of the important research objectives, within the project, was to determine the changes in the concentration of organic cabon, as well as its quality. The studies demonstrate that, the reduction of TOC concentration was mainly restricted to the groundwater zone. Moreover, the highest molecular size fractions of dissolved organic carbon were removed from the artificially recharged groundwater more efficiently than the lower size fractions. The infiltration method - basin or sprinkling - did not noticeably influence neither this removal nor the reduction of TOC concentration.

The behaviour of bacteria and viruses during artificial recharge was investigated in a model ridge. The results demonstrate that filtration and adsorption efficiently remove bacteriophages in the ridge. The concentration and activity of micro-organisms in infiltrated lake water decreased particularly well at the initial stage of the infiltration process. Nevertheless the growth of micro-organisms in several artificial groundwater samples was quite intense, demonstrating that these waters are not fully stable from the microbiological aspect.

Knowledge about the flow conditions of groundwater was specified by pipe flow measurements. Results were used for adjusting the input parameters of the groundwater model, which - in turn - specified the final results of retention time and dilution calculations made for groundwater models. The flow conditions of the soil and the groundwater retention time significantly influenced the TOC concentration of the artificially recharged groundwater. The target TOC concentration -less than 2 mg/l - was attained with varying retention times (7-80 days) and with varying groundwater path lengths (160-1300 m).

The planning and dimensioning of an artificially recharged groundwater supply plant is controlled by the quality of infiltration water, groundwater flow characteristics such as aquifer particle size distribution and hydraulic conductivity as well as the retention time. Therefore, different AR groundwater supply plants may need infiltration areas of different sizes to produce the same water quantity and water quality. Thus, each planned AR plant requires thorough field studies beforehand.

Application of the results

Field research results, from all facilities, will be used for the specification of their groundwater models. The results of the research upgrade the planning and implementation of water delivery to waterworks. Upgrading the delivery of water to waterworks improves the general know-how within the sector, and improves the potential for businesses operating in the field, both at the domestic and the international level. Not only do waterworks, using basin infiltration and sprinkling infiltration benefit, but also businesses manufacturing related equipment also benefit directly from the results of this research. The accumulated know-how may be utilised in domestic projects dealing with the formation of artificial groundwater. Moreover, the scientific community in general benefits from the research results.

Evaluation of the project

The Water Services Technology Programme was internationally evaluated in automn 2002 (http://www.vvy.fi/2001/raportit/Water_Services_1997-2001.pdf).

The review team found that TEMU research project was " a leading, world-class scientific research. The work done in the TEMU research project was of very high scientific quality, the scientific production was good, and the mix of science, engineering and natural sciences was very beneficial to all parties. The knowledge of artificial groundwater quality changes has significantly improved in the course of the project. The research brought forward new perspectives that had not been taken into account in previous research. Procedures that have not been used in similar conditions before were introduced during the study. This project has produced considerable competence in the area of groundwater recharge and that one should consider publishing the guidebook internationally". The final report was published in automn 2003.

Participants:


Project leader: Helmisaari, Heljä-Sisko

Other researchers: Derome, John, RO (1998-2000),Kitunen, Veikko, ES (1998-2001), Lindroos, Antti-Jussi, VA (1999-2001), Smolander, Aino, VA (1998-2001)


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Updated 12.06.2012
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