Geoscience Reference
In-Depth Information
Table 1.
The basic characteristics of all aquifers in the study area.
SWG
∗
Thickness
(m
3
/day)
Aquifer
Time
(m)
Composition
Phreatic
aquifer
Holocene
5-20
Fine sand, silt, and clayey silt
<
319.5
I-aquifer
Late
Pleistocene
6-15
Silty fine sand, silt
500-1000
II-aquifer
Late
Pleistocene
20-40
Fine sand, gravel medium to
fine sand
3000-5000
III-aquifer
Middle
Pleistocene
20-30
Silty fine sand, medium to fine
sand and sandy gravel
3000-5000
IV-aquifer
Early
Pleistocene
30-50
Fine sand, coarse to medium
sand, sandy gravel
100-3000
V-aquifer
Early
Pleistocene
10-50
Coarse to medium sand, sandy
gravel
100-3000
∗
SWG is the specific well discharge.
range of several wells or small area, and ground subsidence due to ground-
water overdraft. Little has been known for regional dynamic and chemical
evolution under natural condition and human activities. The present study
emphasizes particularly on groundwater chemical analyses, combining with
water flow modeling, to reveal the ways of hydrochemical evolution and the
change of groundwater flow field affected by human activities.
2. Database and Methodology
The database used for hydrochemical and hydrogeological analyses is estab-
lished on the basis of 78 Quaternary hydrological boreholes, which were
drilled during 1958-1985 by the Geology and Mineral Bureau of Shanghai
(GMBS). Totally, 259 water samples were collected from five confined
aquifers, of which 31 samples were from I-aquifer, 70 from II-aquifer, 53 from
III-aquifer, 70 from IV-aquifer, and 35 from V-aquifer. The concentra-
tion of K
+
,
Na
+
,
Ca
2+
,
Mg
2+
,
NH
4
,
Al
3+
,
Cl
−
,
HCO
3
,
CO
2
3
, and SO
2
4
in
groundwater samples were analyzed by the chemical analysis laboratory of
GMBS, and the values of pH and temperature were also measured.
To describe the variety of groundwater flow influenced by human activ-
ities, a quasi-three-dimension numerical model is established using MOD-
FLOW software of US Geological Survey.
3
The phreatic aquifer and aquifers
I-III were included in the model. So a great deal of information about
hydrogeology of four aquifers are collected, together with water heads in
157 observation wells and the yields of 1,527 artificial discharge/recharge
wells in 1980-1990.
