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upward sequence of the Quaternary sediments indicates a fluvio-deltaic depositional environment. Occurrence of peat in the upper horizons of the sediments and occurrence of marsh or salt lakes at the northern part of the area indicate that bog and marshy conditions prevailed during the close of sedimentation. fluvio-deltaic depositional environment. Occurrence of The yellow colour of the sand (at a depth range of 24— 76 m) is thought to be due to oxidation of the sediments generated from the Archean terrain of the Chotonagpur Plateau and brought down by the rivers flowing from the west. The grey to light grey colour of overlying sediments

Figure 2 upward sequence of the Quaternary sediments indicates a fluvio-deltaic depositional environment. Occurrence of peat in the upper horizons of the sediments and occurrence of marsh or salt lakes at the northern part of the area indicate that bog and marshy conditions prevailed during the close of sedimentation. fluvio-deltaic depositional environment. Occurrence of The yellow colour of the sand (at a depth range of 24— 76 m) is thought to be due to oxidation of the sediments generated from the Archean terrain of the Chotonagpur Plateau and brought down by the rivers flowing from the west. The grey to light grey colour of overlying sediments

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Fig. 1 Location of study area
Fig. 1 Location of study area
Table 2 Status of the piezometric surface of the present study area in 2005 (Fig. 3b) is more or less similar to that of post- monsoon in 2004 except for a general recession of the piezometric surface of 2-4m. The striking difference between the contours of these two periods is the absence of two local groundwater mounds within Kolkata, one at Beleghata and the other near Ballygunja during pre-mon- soon period of 2005. indicates a reducing condition of deposition and brought down from the Himalayan domain during the late Quater- nary period (Sikdar 2000).
Table 2 Status of the piezometric surface of the present study area in 2005 (Fig. 3b) is more or less similar to that of post- monsoon in 2004 except for a general recession of the piezometric surface of 2-4m. The striking difference between the contours of these two periods is the absence of two local groundwater mounds within Kolkata, one at Beleghata and the other near Ballygunja during pre-mon- soon period of 2005. indicates a reducing condition of deposition and brought down from the Himalayan domain during the late Quater- nary period (Sikdar 2000).
Fig. 3. a Contour map showing the elevation of piezometric surface (with respect to mean sea level) during post monsoon, 2004. b Contour map showing the elevation of piezometric surface (with respect to mean sea level) during pre-monsoon, 2005 Fourth degree trend surface map of pre-monsoon, 2005 (Fig. 4a) indicates that the regional flow of groundwater is from east to west. The map indicates that there is a groundwater mound near the south-eastern corner of area near Pratapnagar region. From this mound, groundwater flows in all directions. At northeastern corner of the study area, there is another groundwater mound near Hatisala region. From this high, groundwater moves towards southwest and near Gangapur region the flow direction takes a bend and flows towards west. This map also reveals that a depression of 13.7 m from mean sea level near Entali triggers groundwater flow from wetland in the east to Kolkata in the west. The trend surface map of post-monsoon Kolkata in the west. The trend surface map of post-monsoon Groundwater elevation contours of post-monsoon in 2004 (Fig. 3a) reveal that a groundwater trough exists within the wetland near Dhapa—Manpur region and the groundwater moves towards this depression from the sur- rounding region. Troughs are also observed at places such as Ghasiara and Arapanch, Ushpara of Bhangar-I block and near Entali and Bagbazar of Kolkata. Local groundwater mounds, from which groundwater moves away in all directions (Fig. 3a). Groundwater contours of pre-monsoon directions (Fig. 3a). Groundwater contours of pre-monsoon
Fig. 3. a Contour map showing the elevation of piezometric surface (with respect to mean sea level) during post monsoon, 2004. b Contour map showing the elevation of piezometric surface (with respect to mean sea level) during pre-monsoon, 2005 Fourth degree trend surface map of pre-monsoon, 2005 (Fig. 4a) indicates that the regional flow of groundwater is from east to west. The map indicates that there is a groundwater mound near the south-eastern corner of area near Pratapnagar region. From this mound, groundwater flows in all directions. At northeastern corner of the study area, there is another groundwater mound near Hatisala region. From this high, groundwater moves towards southwest and near Gangapur region the flow direction takes a bend and flows towards west. This map also reveals that a depression of 13.7 m from mean sea level near Entali triggers groundwater flow from wetland in the east to Kolkata in the west. The trend surface map of post-monsoon Kolkata in the west. The trend surface map of post-monsoon Groundwater elevation contours of post-monsoon in 2004 (Fig. 3a) reveal that a groundwater trough exists within the wetland near Dhapa—Manpur region and the groundwater moves towards this depression from the sur- rounding region. Troughs are also observed at places such as Ghasiara and Arapanch, Ushpara of Bhangar-I block and near Entali and Bagbazar of Kolkata. Local groundwater mounds, from which groundwater moves away in all directions (Fig. 3a). Groundwater contours of pre-monsoon directions (Fig. 3a). Groundwater contours of pre-monsoon
Fig. 4 a Fourth degree trend surface map of pre-monsoon, 2005. b Fourth degree trend surface map of post monsoon, 2004
Fig. 4 a Fourth degree trend surface map of pre-monsoon, 2005. b Fourth degree trend surface map of post monsoon, 2004
Fig. 5 a Graph showing east-west cross section. b Graph showing north-south cross section analyses of the groundwater and the percent compliance with the Indian Standard (BIS 10500 1991) and WHO (1993) are summarized in Table 3.
Fig. 5 a Graph showing east-west cross section. b Graph showing north-south cross section analyses of the groundwater and the percent compliance with the Indian Standard (BIS 10500 1991) and WHO (1993) are summarized in Table 3.
Detection limit for copper 0.002, arsenic 0.003, lead 0.01, chromium 0.008, cadmium 0.001, phosphate 0.005, selenium 0.001, fluoride 0.005. A values in mg/l BDL below detection limit Table 3 Comparison of groundwater quality with drinking water standards, Indian and WHO
Detection limit for copper 0.002, arsenic 0.003, lead 0.01, chromium 0.008, cadmium 0.001, phosphate 0.005, selenium 0.001, fluoride 0.005. A values in mg/l BDL below detection limit Table 3 Comparison of groundwater quality with drinking water standards, Indian and WHO
groundwater of this area possibly represents a remnant of ocean water entrapped in the sediments during their deposition under marine conditions, which has later undergone some modification during its period of con- finement (Sikdar et al. 2001). Later the confined ocean water was progressively diluted by influxes of freshwater from (i) the recharge area lying far north of the study area (Fig. 1), and (ii) infiltration of meteoric water through small pockets in the eastern region of study area where the undergone some modification during its period of con-
groundwater of this area possibly represents a remnant of ocean water entrapped in the sediments during their deposition under marine conditions, which has later undergone some modification during its period of con- finement (Sikdar et al. 2001). Later the confined ocean water was progressively diluted by influxes of freshwater from (i) the recharge area lying far north of the study area (Fig. 1), and (ii) infiltration of meteoric water through small pockets in the eastern region of study area where the undergone some modification during its period of con-
* Variables with significant loading Table 8 Principal component analysis using 40 groundwater samples
* Variables with significant loading Table 8 Principal component analysis using 40 groundwater samples
* Statistically significant correlation between variables at 99.9% confidence level ** Statistically significant correlation between variables at 97.5% confidence level Table 7 Correlation coefficient matrix of chemical parameters of 40 groundwater samples
* Statistically significant correlation between variables at 99.9% confidence level ** Statistically significant correlation between variables at 97.5% confidence level Table 7 Correlation coefficient matrix of chemical parameters of 40 groundwater samples
Fig. 9 Plots of PC scores for PC I versus PC II
Fig. 9 Plots of PC scores for PC I versus PC II
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