Abstract

The main objective of managed aquifer recharge (MAR) in Finland is the removal of natural organic matter (NOM) from surface waters. A typical MAR procedure consists of the infiltration of surface water into a Quaternary glaciofluvial esker with subsequent withdrawal of the MAR treated water from wells a few hundred meters downstream. The infiltrated water should have a residence time of at least approximately one month before withdrawal to provide sufficient time for the subsurface processes needed to break down or remove humic substances. Most of the Finnish MAR plants do not have pretreatment and raw water is infiltrated directly into the soil. The objectives of this paper are to present MAR experiences and to discuss the need for and choice of pretreatment. Data from basin, sprinkling, and well infiltration processes are presented. Total organic carbon (TOC) concentrations of the raw waters presented here varied from 6.5 to 11 mg/L and after MAR the TOC concentrations of the abstracted waters were approximately 2 mg/L. The overall reduction of organic matter in the treatment (with or without pretreatment) was 70%-85%. Mechanical pretreatment can be used for clogging prevention. Turbidity of the Finnish lakes used as raw water does not necessitate pretreatment in basin and sprinkling infiltration, however, pretreatment in well infiltration needs to be judged separately. River waters may have high turbidity requiring pretreatment. Biodegradation of NOM in the saturated groundwater zone consumes dissolved oxygen. Thus, a high NOM concentration may create conditions for dissolution of iron and manganese from the soil. These conditions may be avoided by the addition of chemical pretreatment. Raw waters with TOC content up to at least approximately 8 mg/L were infiltrated without any considerations of chemical pretreatment, which should be evaluated based on local conditions.

Highlights

  • IntroductionWater resources are abundant in terms of surface area; the inland waters cover around 10% of the total area of the country and there are about 56,000 lakes in Finland

  • The aim of this paper is to present experiences of in drinking water production with a special emphasis on raw water quality and pretreatment

  • managed aquifer recharge (MAR) in unconfined esker aquifers is used for natural organic matter (NOM) removal from humic lake and river waters in Finland

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Summary

Introduction

Water resources are abundant in terms of surface area; the inland waters cover around 10% of the total area of the country and there are about 56,000 lakes in Finland. A volume of 5.8 million m3 /day could theoretically be abstracted from the Finnish. A volume of 5.8 million m3/day could theoretically be abstracted from the Finnish groundwater [1]. Groundwater has been preferred as drinking water.

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