Recharge systems for protecting and enhancing groundwate

TOPIC 7
MAR strategies / Sustainability of managing recharge systems 827
2
1
10
2
14 3
4
12
5
13
11
15
9
7 6
1
8
South
Göta Älv River
North
Figure 1. Map over the Dösebacka AR-plant; resistivity soundings (solid lines), drill holes (red dots),
refraction soundings (dotted lines) and wells (numbered circles). Upper case letters A-I are infiltration ponds,
and the numerals 1 and 2 are referred to in the text.
bedrock (Fig. 1), and samples were brought to the surface at every meter by air-induced flushing. The grain size
of the sediment was determined using standard sieve and hydrometer methods. Sand-grain counts and X-ray diffraction
(XRD) were used to determine the mineral content (Bryllert, 2005).
The hydrogeology and a groundwater-flow model are based on the known geology, groundwater logging, and temperature
measurements in abstraction wells once a week during 2003-2004. Flow path were generated through
numerical calculation with MIKE SHE (a product of DHI, Sweden). Residence time for abstracted water in GRP 9
was determined with a tracer experiment using NaCl that was added in Basin F (see below ‘Tracer Experiment’).
Analyses of Na + , Cl – , and electrical conductivity were performed in GRP 9. Residence time from the temperature
measurement and the tracer experiment were compared, giving dampening rates. The rates were then used for conversion
of the temperature-related residence times into probable residence time for each well.
The hydrochemistry at the Dösebacka site was analysed from water-quality data taken from 1992–2004. A Piper
diagram (Piper, 1944) was produced from the water-quality data, giving information on the geochemical character
of the groundwater in the abstraction wells. Stable isotopes ( 18 O and 2 H) and 87 Sr/ 86 Sr isotopic ratios were
analysed at three different times in 2004 to infer the mixture between surface water and different groundwater bodies.
Water-treatment efficiency was evaluated from water-quality data measured once a month during a period of
nine months from August 2003 to April 2004.
Tracer experiment
The tracer experiment was conducted using sodium chloride (NaCl). The tracer is easy to handle, harmless to
humans, cheap and the Cl – ion is regarded as conservative in the aquifer material. Furthermore, the background
Cl – content in GRP 9 is fairly low (Table 3). The amount of sodium chloride was chosen so that the water-quality
limits of 100 mg/l for Na + as well as for Cl – would not be exceeded in water produced from the wells.
The tracer experiment started March 29, 2004. A total amount of 350 kg NaCl was mixed with 4 m 3 water in a tank.
This concentrated solution was added to infiltration Basin F (Fig. 1). The water level in the basin was low (only a
few decimetres) because the infiltration-water supply had been temporarily stopped. All the NaCl-rich water in the
basin was allowed to infiltrate before the water supply to the basin was opened again.
10 – 16 June 2005, Berlin ■ 5th International Symposium ■ AQUIFER RECHARGE ■ ISMAR 2005