Recharge systems for protecting and enhancing groundwate

848
TOPIC 7
Sustainability of managing recharge systems / MAR strategies
All water bodies in Fig. 6 are pH-neutral (and calcite saturated) due to a high CaCO 3 content of the dune
and underlying beach sands. The recharged polder waters deviate from the Rhine and Meuse River waters by their
freshened and reduced character (AP FR ) already at their starting point in the upper aquifer. This is due to a primary
Na+K+Mg-excess of this surface water which receives seepage of dune groundwater displacing relict brackish
groundwaters. Their initial reduced facies is caused by very high nutrient loads which led to much sludge formation
and thus consumption of all available O 2 and NO 3 . Downgradient this AP FR water looses its primary freshened
character (positive BEX) by exchange for Ca (site 3).
The general hydrochemical evolution of Rhine River water downgradient, in the period 1980–1990, is: from
polluted (thus pH-neutral, (sub)oxic, BEX-equilibrated), to polluted and reduced, to polluted, reduced and
salinized (site 4). The salinized facies is due to displacement of fresher dune water, having relatively low Na, K and
Mg concentrations.
The evolution of Meuse River water downgradient (area 2), in the period 1980–1990, deviates from the one
for Rhine water by a freshened instead of salinized facies. This is due to displacement of saltier Rhine River water,
having relatively high Na, K and Mg concentrations.
The improved quality of Rhine and Meuse River water, notably since the early 1980s, has contributed to a significant
decrease of their pollution index WAPI. This also holds for the upper infiltrated waters in the dunes since
the 1990s, thus with a significant delay. This delay is due to (a) the slow leaching of pollutants that accumulated
in both sludges and the aquifer system, (b) abolition of the chlorination for transport (from pretreatment plant to
infiltration area) since about 1990, and (c) removal of the older, relatively polluted sludges from the basins mainly
in the 1990s.
Figure 6. Spatial distribution of hydrosomes (groundwater bodies) and their chemical facies (period 1980–1990)
along a section parallel to the North Sea coast, in between Hoek van Holland and Zandvoort
(slightly modified after Stuyfzand, 1993). For characteristics of recharge sites 1–5 see text.
The Rhine fluvial plain in the Netherlands
The spatial distribution of Rhine bank filtrate, in its fluvial plain in the Netherlands (Fig. 7), is dictated by the exfiltration
of fresh groundwater from ice-pushed hills (in between well fields 25 and 45), the pumping of groundwater
ISMAR 2005 ■ AQUIFER RECHARGE ■ 5th International Symposium ■ 10 –16 June 2005, Berlin