Water4Coast. Evaluation of water quality issues before application of managed aquifer recharge in a coastal chalk aquifer

Klaus Hinsby, Anders R. Johnsen, Sebastian R. Sørensen, Dieke Postma

Publikation: Bog/rapportRapport (offentligt tilgængelig)

Abstrakt

This report is one out of three reports assessing the potential for application of managed aquifer recharge to control salt water intrusion on the Southern part of the Falster Island, Denmark. The two other reports by Rasmussen et al., 2015 and Hinsby et al. 2015 consider the model simulations of injection into the Chalk aquifer and efficient data acquisition, transfer and management for the development of advanced Supervisory Control and Data Acquisition (SCADA) systems, respectively. This report considers water quality issues related to aquifer storage and recovery e.g. by using either groundwater or treated surface water (drainage water) for e.g. injection during the wet wintertime and retrieval again in the dryer summer period in order to reduce and control salt water intrusion in the region and protect subsurface drinking water resources. The report evaluates the risks of using aerobic and anaerobic groundwater as well as aerobic drainage water for injection into the Chalk aquifer.

It is concluded that anaerobic groundwater from the water works connected pipelines may be used for injection without any treatment. Analyses from all the water supply wells show that they generally contain very similar anaerobic groundwater older than 75 years without any measurable human impact or contamination. Hence, this water type can be infiltrated without initiating problematic geochemical reactions and jeopardizing the quality of the high quality groundwater in the Chalk aquifer.

In contrast the drainage waters in the drainage canals contain elevated concentrations of both pesticides (MCPA-), industrial chemicals (PFOS), and at one point also high numbers of faecal bacteria (E.coli). Furthermore, a wide range of pharmaceuticals used for a variety of diseases have been found in rather high concentrations in the effluent from a waste water treatment plant discharging to the drainage canal. Hence, if these waters have to be used for injection, strict quality control and/or an intensive treatment and dilution e.g. with pristine groundwater pumped from the Chalk aquifer, will be required to ensure that contamination is not introduced at unacceptable levels into the pristine high quality groundwater of the Chalk aquifer in the area.

Furthermore, the injection of aerobic water containing oxygen and/or nitrate into the anaerobic groundwater will induce oxidation of reduced minerals (Iron sulphides) and organic matter, which may lead to on one hand both technical problems with clogging of wells screens by iron oxides and water quality issues with elevated concentrations of some trace elements and metals, but on the other hand also positive side effects such as removal of nitrate in the subsurface and reduced nitrogen loadings to the coastal waters of the western Baltic Sea.

The results from the preliminary investigations and assessments clearly show that further investigations of the geochemistry and the hydraulics of the Chalk aquifer are required in order to better assess positive and negative effects and the feasibility of injecting anaerobic groundwater or treated aerobic drainage water into the fractured Chalk aquifer to protect subsurface water resources used for water supply on Southern Falster.
OriginalsprogEngelsk
UdgivelsesstedCopenhagen
ForlagGEUS
Antal sider38
Vol/bind2015
DOI
StatusUdgivet - 4 maj 2018

Publikationsserier

NavnDanmarks og Grønlands Geologiske Undersøgelse Rapport
ForlagGEUS
Nr.93
Vol/bind2015

Emneord

  • Denmark

Programområde

  • Programområde 2: Vandressourcer

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