Artificial recharge of groundwater for public water supply : potential and limitations on boreal conditions

Sammanfattning: It is motivated by the intentions of Agenda 21 to findalternatives to the increasing dependence on chemical treatmentin the production of public water. Conventional waterworkscommonly include chemicals for removal of organic compounds,for reduction of corrosiveness and for disinfection. Thispractice has drawbacks which may be lessened or avoidedaltogether with the use of artificial groundwater recharge.However, the mechanisms active in the quality change of thewater during artificial groundwater recharge are not fullyunderstood. In this thesis the factors which affect theretention of natural organic matter (NOM), iron, manganese andsuspended and colloidal matter were studied. The extent andlocation of their retention in infiltration ponds wasinvestigated. Furthermore, the potential for using limestonefilters in infiltration ponds for increasing hardness andalkalinity of the water was investigated. The water quality wasmonitored over time periods between 7 months and 5 years andthe filter sand was examined before and after study periods.The studies were carried out at field sites or in columns atpublic waterworks in Sweden. It was found that retention of NOMwas affected by climatic variations. The highest eliminationrate was found in the uppermost part of the porous media andduring the late summer. The retention of iron and manganese wasnot affected by climatic variations. This retention took placeto a greater extent and at shallower levels than that for NOM.Unsaturated flow conditions were found to be more effective forremoval of suspended and colloidal matter, thansaturated flowconditions. Limestone filters embedded in the filter sand werefound to increase the pH, alkalinity and hardness in thepercolating water. The degree of the effect on this water wasdependent on the infiltration rate, the specific surface areaof the limestone and the specific dose of limestone, as well ason the degree of undersaturation of calcite in the infiltrationwater. These findings contribute to the knowledge andunderstanding of the processes involved in the water qualitychanges during artificial groundwater recharge. They may enablewell adapted adjustments of the design and operating conditionsat artificial groundwater recharge schemes.Keywords:drinking water, NOM, TOC, iron, manganese,calcium carbonate, alkalinity, colloids, infiltration ponds,Sweden.