In the Wairau Valley 40 km southwest of Blenheim, elevated salinities are present in the groundwater below a depth of approximately 15 m, to the north of the Wairau Fault. Saline water is present very close to the surface between the Southern Hills and the Wairau Fault. Highest concentrations are located in well O28/w/0219 with total dissolved solids concentrations approximately 31,000 mg/L. Only a few wells in the study area have intercepted the saline groundwater. A report by Taylor (2003) has identified the groundwater below the Holocene terrace surface is recharged from Southern Hills runoff, however the Wairau Fault has a significant impact on the groundwater flow on the south bank acting as a semi-permeable barrier to groundwater flow from the southern Hills streams identified by several spring which emerge on the fault trace. The scope of this investigation was to identify the extent of the saline groundwater in the Homelands area and to attempt to define the origin of the highly saline groundwater. Furthermore, to define the groundwater flow path below the upper terrace surface to recharge the Wairau Valley Aquifer. The Multi-Electrode Resistivity technique was used to define the extent of the saline groundwater. This shows the saline groundwater is ubiquitous at depth in the study area. The depth to the freshwater/saline water interface varies laterally in the resistivity profiles. A major control on the presence of the groundwater salinity is considered to be the permeability of the gravel. Gravels with a higher permeability are probably washed of any residual salinity that may have been present in the past. Investigations into the origins of the saline groundwater were completed using stable isotope analysis (¹⁸O, ²H, and ¹³C), hydrochemistry and age dating techniques (³H and ¹⁴C). Due to the complex chemistry a single source could not be identified, however two methods were identified as the most likely. This was evaporative concentration of fresh water in the Wairau Valley, or the upward migration from the Wairau Fault of formation water probably of seawater origin. The stable isotope data fits best with an evaporative concentration of freshwater within the Wairau Valley, however, ratios of chemical constituents are very similar to other formation waters found in other parts of the world. Stream gauging of streams on the south bank show no significant water loss in the reaches north of the Wairau Fault. Therefore, recharge must be crossing the Fault trace as groundwater. Boundary Creek looses all of its surface flow for most of the year upon reaching the valley floor. Bounday Creek has washed out sections of the Wairau Fault and Major terrace riser between Wr 1 and Wr 2 terrace surfaces. It is proposed that groundwater flowing in the gravels reworked by Boundary Creek is the major recharge source for the Wairau Valley Aquifer.

In the Wairau Valley 40 km southwest of Blenheim, elevated salinities are present in the groundwater below a depth of approximately 15 m, to the north of the Wairau Fault. Saline water is present very close to the surface between the Southern Hills and the Wairau Fault. Highest concentrations are located in well O28/w/0219 with total dissolved solids concentrations approximately 31,000 mg/L. Only a few wells in the study area have intercepted the saline groundwater. A report by Taylor (2003) has identified the groundwater below the Holocene terrace surface is recharged from Southern Hills runoff, however the Wairau Fault has a significant impact on the groundwater flow on the south bank acting as a semi-permeable barrier to groundwater flow from the southern Hills streams identified by several spring which emerge on the fault trace. The scope of this investigation was to identify the extent of the saline groundwater in the Homelands area and to attempt to define the origin of the highly saline groundwater. Furthermore, to define the groundwater flow path below the upper terrace surface to recharge the Wairau Valley Aquifer. The Multi-Electrode Resistivity technique was used to define the extent of the saline groundwater. This shows the saline groundwater is ubiquitous at depth in the study area. The depth to the freshwater/saline water interface varies laterally in the resistivity profiles. A major control on the presence of the groundwater salinity is considered to be the permeability of the gravel. Gravels with a higher permeability are probably washed of any residual salinity that may have been present in the past. Investigations into the origins of the saline groundwater were completed using stable isotope analysis (¹⁸O, ²H, and ¹³C), hydrochemistry and age dating techniques (³H and ¹⁴C). Due to the complex chemistry a single source could not be identified, however two methods were identified as the most likely. This was evaporative concentration of fresh water in the Wairau Valley, or the upward migration from the Wairau Fault of formation water probably of seawater origin. The stable isotope data fits best with an evaporative concentration of freshwater within the Wairau Valley, however, ratios of chemical constituents are very similar to other formation waters found in other parts of the world. Stream gauging of streams on the south bank show no significant water loss in the reaches north of the Wairau Fault. Therefore, recharge must be crossing the Fault trace as groundwater. Boundary Creek looses all of its surface flow for most of the year upon reaching the valley floor. Bounday Creek has washed out sections of the Wairau Fault and Major terrace riser between Wr 1 and Wr 2 terrace surfaces. It is proposed that groundwater flowing in the gravels reworked by Boundary Creek is the major recharge source for the Wairau Valley Aquifer.

Lidköpings kommun i Västra Götalands län tar ut en del av sitt råvatten till dricksvattenproduktion från grundvattenmagasinet Rådaås. Det görs genom tre olika uttagsbrunnar (Brunn 1, Brunn 2 och Brunn 3) som körs en i taget. På senare tid har kommunen börjat misstänka att salthalterna i uttagsvattnet ökar, och det finns ett intresse för att förstå vad problemet beror på och vad som kan göras åt saken.  Syftet med detta arbete är att undersöka förekomst och ursprung hos saltvattnet i magasinet och att undersöka hur brunnsdrift i samband med grundvattennivåer påverkar halten i uttagsvattnet. Eftersom det sedan tidigare finns misstankar om att det rör sig om relikt saltvatten utgör det en hypotes för detta arbete. Relikt saltvatten är salt grundvatten som avsatts under en tid då området varit täckt av salt hav, till exempel delar av Sverige under Östersjöns utveckling sedan den senaste istiden.   För att undersöka förekomst av saltvatten i magasinet funktionstestades och provtogs samtliga tillgängliga grundvattenrör för kloridhalt. Resultatet visar att kloridhalten ökar med grundvattenrörens djup och att de högsta salthalterna finns i en djuphåla eller ränna i berggrunden strax under Brunn 1 och 2. För att undersöka ursprunget hos det salta grundvattnet provtogs några av grundvattenrören och samtliga uttagsbrunnar för jodid. Med hjälp av jodid-/kloridkvoten kunde det fastställas att saltvattnet är av relikt ursprung.  För att undersöka hur brunnsdrift påverkar salthalten i uttagsvattnet togs start- och slutprover på kloridhalt i början och slutet på varje driftsperiod och brunn under tre månader. Mönstret i kloridhalt jämfördes med grundvattennivåer. Resultatet visar att kloridhalterna i uttagsvattnet ökar under driftsperioden för samtliga brunnar, men återhämtar sig då brunnen är vilande. Generellt är salthalten högst för Brunn 2 och lägst för Brunn 3. Det kan bero på att Brunn 2 ligger sist av de tre brunnarna i grundvattnets strömningsriktning medan Brunn 3 ligger först samt längst bort från rännan i berggrunden.  Resultatet från detta arbete visar också på att grundvattenuttaget ur Rådaåsmagasinet sedan 1990-talet har orsakat en höjning av salthalterna i råvattnet. Rekommendationer som ges till Lidköpings kommun för att minska eller bibehålla nuvarande salthalt är att installera kontinuerlig övervakning av konduktivitet i uttagsbrunnarna och av grundvattennivå i de två rör som ligger brunnarna närmast. Detta för att i realtid kunna följa hur uttagssätt och grundvattennivå påverkar salthalten. En idé är också att strategiskt placera ut en eller flera nya uttagsbrunnar och på så sätt undvika saltansamlingar i djupa jordlager. / Lidköping municipality in Västra Götaland county, Sweden, extracts some of its raw water for drinking water production from Rådaås aquifer. It is done by using three different pumping wells (Well 1, Well 2 and Well 3) which are run one at a time in a cyclic manner. Recently, the municipality personnel have started to suspect that the salinity of the raw water is increasing. They are therefore interested in understanding the cause of the problem and what could be done to mitigate it.  The purpose of this study is to investigate the occurrence and origin of saline groundwater in the Rådaås aquifer and to determine how operation of the pumping wells along with groundwater levels affect the salinity in the raw water. Since there is already a suspicion of the saline water being relict salt water, that is a hypothesis for this study. Relict salt water is saline groundwater deposited during times when an area was covered by marine water, for example some areas of Sweden during the development of the Baltic Sea since the latest ice age.    To investigate the occurrence of saline groundwater in the aquifer, all available piezometers were tested for functionality and sampled to analyse chloride concentration. The results show that the chloride concentration increases with the depth of the piezometer and that the highest concentrations are found in a depression or furrow in the bedrock just below Well 1 and 2. To investigate the origin of the saline groundwater, some of the piezometers and all pumping wells were tested for iodide. Using the iodide/chloride ratio, it was concluded that the salt water is relict. To investigate how operation of the pumping wells affect the salinity of the raw water, samples of chloride concentration were extracted in the beginning and in the end of each pumping period and well during three months. The resulting pattern of chloride concentration was compared to groundwater levels. The results show that the chloride concentrations in the raw water increase during the pumping periods for all wells, but recover when the well is resting. In general, Well 2 shows the highest salinity and Well 3 shows the lowest. The reason may be that of the three, Well 2 is located last in the groundwater flow direction, while Well 3 is located first and is also furthest away from the furrow in the bedrock.    The results of this study also show that groundwater withdrawal from Rådaås aquifer since the 1990’s has caused an increase of salinity in the raw water. Recommendations given to Lidköping municipality to reduce or maintain the salinity of the raw water are to install continuous surveillance of conductivity in the pumping wells and of groundwater levels in the two most adjacent piezometers. This is to enable live monitoring of how operating the pumping wells along with groundwater levels affect the salinity. Another idea is to strategically place one or more new pumping wells to insure that they avoid deep layers of soil where salt water is accumulated.