OR/14/068 Results

Lapworth, D J, Gopal, K, Rao, M S, and MacDonald, A M. 2014. Intensive groundwater exploitation in the Punjab — an evaluation of resource and quality trends. British Geological Survey Internal Report, OR/14/068.

Long-term changes in groundwater level

The long-term trends in groundwater levels for the 43 CGWB monitoring sites, with data covering 20 years or more, can be found in Appendix 1. Figure 7a shows a map of the trends in groundwater decline across the catchment, 8b the current pre monsoon groundwater level It can be seen that the sites with no long-term water level decline are found in the Kandi region or in close proximity to the R Beas and Satluj, sites with moderate or high levels of groundwater decline are located away from the rivers or close to the foothills. There is an overall increase in the rate of groundwater level decline across plain towards the confluence (Figure 7a), which coincides with an absence of the canal distribution system. There is one noteworthy anomaly, Udhopur, to the south of Jalandhar 3, which has a shallow water table and which has no long-term decline in water level. This site is in close proximity to a large perennial tributary of the Satluj (see Figure 4) and the trends and groundwater levels at this site probably reflect hydraulic connectivity with this alluvial aquifer in close proximity to the river channel.

In the northern corner of the catchment groundwater levels are shallow and show no long-term trends (see Figure 7), this reflects the topography of the region and perhaps the sustained discharge from the Pong Dam (Himachal Pradesh) which maintains river/canal flow and groundwater levels in this region. Sites with the deepest groundwater levels (pre monsoon) are found in the Kandi region and in the central and SW region of the plains, this reflects the incised topography of the Kandi belt and the high level of abstraction within the shallow plains aquifer for irrigation. The region considered as the recharge zone for the plains aquifer, where there is a change in slope from the Kandi belt, generally have shallow groundwater levels and only moderate long-term declines in pre-monsoon groundwater levels.

Figure 7 Spatial variation in (a) long-term (20 years) decline in pre monsoon groundwater level (b) pre monsoon groundwater level in 2010. Source: CGWB.

Stable isotopes

Figure 8 (a–c) shows the stable isotope results in relation to the regional meteoric water line (RMWL) from Kumar et al. (2010), and calculated robust regression lines, from this study for shallow and deep sites under pre and post monsoon conditions. Figure 9 shows a plot of all the data in relation to previous studies of shallow and deep groundwater stable isotope results published by Rao et al (2014). Figure 10 shows a plot of spatial variation of stable isotope results across the Bist-Doab region.

Overall the shallow and deep values obtained in this study are consistent with those found by Rao et al (2014) in the same catchment (see Figure 8) with the exception of a few enriched outliers. There is a generally consistent result across the catchment which shows enriched samples in the shallow groundwaters compared to deep sites (see Figure 8 and 10) due to a greater component of relatively depleted recharge sources in deep sites from recharge zones up-gradient due to a the effects of the continental Raleigh distillation processes as the monsoon air masses track across India from the Bay of Bengal. The deep sites show no significant changes under pre and post monsoon conditions in all but one site (Hariana) which is found in the recharge zone.

The shallow boreholes at Amritpur (7.6 mbgl), in close proximity to the River Beas, show particularly depleted values for δ¹⁸O and δ²H, suggesting that there is significant surface water- groundwater connectivity in this location. At this site the shift in δ¹⁸O from -9.5 to -8.9 between pre and post monsoon conditions suggests that this process is highly dynamic and operating within a sub 4 month time frame in response to post monsoon recharge from the Beas to the adjacent shallow alluvial aquifers. In contrast, the deep site at Amritpur (76 mbgl) showed no changes (-6.9) both pre and post monsoon. The highly enriched δ¹⁸O values at Arjanwal in the shallow groundwaters (-2 and -4.8, See Figure 10) suggest that there are significant sources of shallow recharge water at this location exhibiting signs of evaporative fractionation prior to recharge.

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  Figure 8 Stable isotope results (δ¹⁸O vs δ²H) for (a), shallow sites pre monsoon (b), deep sites pre monsoon (c) shallow sites post monsoon and (d). deep sites post monsoon. Solid line shows the RMWL and dashed line the robust regression line for the data.

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  Figure 9 Stable isotope results (δ¹⁸O vs δ²H) for all data in comparison with published regression lines for shallow, deep groundwater across the catchment and surface waters. * Regression lines from Rao et al., (2014).

Figure 10 Spatial and temporal variation in stable isotope results (δ¹⁸O) across the Bist-Doab.

Dissolved gases (cfc-12 and cfc-11)

Table 3 shows the results for CFC-11 and CFC-12 concentrations in groundwaters, modern fractions and estimated (PFM) MRTs for sites using CFC-12 data. A recharge temperature of 26°C was used to calculate MRTs, the average value obtained from field observations. Figure 11 and 12 shows the CFC-12 and CFC-11 results, presented as the fraction of modern water, for all the sites in this study. It can be seen that only a handful of samples show signs of significant CFC-12 contamination compared to CFC-11. Figure 13 shows the model mean residence times (MRT) for groundwater estimated using CFC-12 data and a piston flow model, samples that had a modern fraction >1.1 were excluded from this analysis due to likely contamination.

Figure 11 CFC-12 results presented as the fraction of modern water. Hydrogeological setting for sites; Amia M.-Malikpur (Zone 1, Kandi); Ajnoha-Mehli (Zone 2, Plains); Saidpur — Phillaur (Zone 3, floodplain/confluence). Data missing from Hoshiarpur and Amritpur.

Figure 12 CFC-11 results presented as the fraction of modern water. Hydrogeological setting for sites; Amia M-Malikpur (Zone 1, Kandi); Ajnoha-Mehli (Zone 2, Plains); Saidpur —  Phillaur (Zone 3, floodplain/confluence). Data missing from Hoshiarpur and Amritpur.

Table 3    CFC-12 and CFC-11 concentrations, modern fractions and mean residence times

	Shallow CFC-12 pmol/L	CFC-11 pmol/L	CFC-12 Mod. Fr.	CFC-11 Mod. Fr.	CFC-12 MRT* -Years	Deep CFC-12 pmol/L	CFC-11 pmol/L	CFC-12 >Mod. Fr.	CFC-11 Mod. Fr.	CFC-12 MRT -Years*
Pre-monsoon
Aima Mangat	1.75	2.23	1.19	0.95	0	1.66	1.29	1.12	0.55	0
Hariana	0.09	0.15	0.06	0.07	54	0.13	0.15	0.09	0.07	51
Hoshiarpur	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
Mailli	1.58	2.95	1.07	1.26	0	0.05	0.08	0.03	0.03	59
Malikpur	0.81	3.94	0.96	1.32	22	0.00	0.00	0	0	68
Ajnoha	N/A	N/A	0.51	N/A	18	0.09	0.23	0.06	0.1	54
Arjanwal	1.51	0.77	1.02	0.33	0	0.07	0.21	0.05	0.09	55
Banga	0.23	0.58	0.16	0.26	47	0.96	0.51	0.67	0.22	32
Boot	0.60	0.09	0.41	0.04	39	0.50	0.63	0.34	0.27	41
Garhshankar	1.27	0.14	0.89	0.06	26	0.03	0.29	0.02	0.13	63
Jandiala	23.57	163.58	16.01	69.66	>Mod	1.44	9.63	0.98	4.1	22
Nawanshahr	1.37	2.73	0.93	1.16	24	0.84	1.00	0.57	0.42	34
Nussi Pind	0.00	0.00	0	0	68	0.12	0.08	0.08	0.03	52
Mallian Kalan	1.32	3.06	0.9	1.3	25	0.05	1.16	0.03	0.49	59
Mehli	1.41	0.77	0.95	0.33	23	0.28	0.21	0.19	0.09	46
Saidpur	2.16	0.18	1.47	0.08	>Mod	0.51	0.20	0.34	0.08	41
Amritpur	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
Bussowal	0.00	0.00	0	0	68	1.90	2.39	1.29	1.02	0
Phillaur	1.96	8.23	1.33	3.5	>Mod	0.26	3.18	0.18	1.35	46
Mean	2.5	11.8	1.6	5.0	29.6	0.5	1.2	0.4	0.5	42.5
Median	1.3	0.8	0.9	0.3	24.5	0.3	0.3	0.2	0.1	46.0
Post-monsoon
Aima Mangat	1.35	4.18	0.92	1.78	24	1.62	1.47	1.10	0.62	0
Hariana	0.11	0.14	0.08	0.06	52	0.18	0.11	0.12	0.05	48.5
Hoshiarpur	0.38	0.17	0.26	0.07	43	0.80	0.82	0.54	0.35	35
Mailli	1.39	2.61	0.94	1.11	23.5	0.06	0.37	0.04	0.16	57
Malikpur	2.20	2.26	1.50	0.96	>Mod	0.00	0.14	0.00	0.06	68
Ajnoha	0.64	0.19	0.44	0.08	38	0.05	0.12	0.03	0.05	58
Arjanwal	1.74	0.28	1.18	0.12	0	0.58	0.65	0.39	0.28	39
Banga	0.00	0.15	0.00	0.06	68	0.32	0.33	0.22	0.14	44
Boot	0.51	0.32	0.35	0.13	40	0.45	0.46	0.31	0.20	41.5
Garhshankar	1.34	0.03	0.91	0.01	24	0.07	0.14	0.05	0.06	56
Jandiala	11.58	107.79	7.86	45.90	>Mod	1.62	3.46	1.10	1.47	0
Nawanshahr	1.72	3.37	1.17	1.44	>Mod	0.77	0.71	0.52	0.30	35.5
Nussi Pind	0.13	0.23	0.09	0.10	51	0.09	0.12	0.06	0.05	54
Mallian Kalan	1.12	0.44	0.76	0.19	28	1.19	1.95	0.81	0.83	26.5
Mehli	2.06	3.73	1.40	1.59	>Mod	0.29	2.63	0.20	1.12	45
Saidpur	1.05	0.11	0.71	0.05	29.5	0.44	0.29	0.30	0.12	41.5
Amritpur	1.80	0.65	1.22	0.28	0	0.23	0.82	0.16	0.35	46.5
Bussowal	0.38	0.30	0.26	0.13	43	2.10	2.65	1.43	1.13	>Mod
Phillaur	1.61	4.12	1.09	1.76	0	0.14	0.15	0.09	0.06	50.5
Mean	1.6	6.9	1.1	2.9	30.9	0.6	0.9	0.4	0.4	41.5
Median	1.3	0.3	0.9	0.1	29.5	0.3	0.5	0.2	0.2	44.5

* Piston flow model used to estimate MRT. Mod. Fr = modern fraction

Table 3 and Figures 11 and 12 show that for most locations the shallow boreholes had significantly higher CFC concentrations and corresponding modern fractions. Shallow groundwaters were shown to have significantly younger MRTs compared to deep groundwater samples (Figure 13). Median MRTs were comparable for deep sites pre and post monsoon, while for shallow groundwaters MRTs were shifted towards younger residence times during post monsoon sampling, although this is not statistically significant (p=0.05).

Figure 13 Notched box-plot of CFC-12 piston flow model Mean Residence Time (MRT) grouped by borehole depth and pre/post monsoon conditions.

Figure 14 Spatial variation in CFC-12 modern fractions and MRTs.

Figure 14 shows that there is no clear spatial relationship across the catchment for MRT in deep groundwaters, however it is noteworthy that the sites with the youngest deep groundwaters were found in the region of rapidly declining groundwater levels (e.g. Jandiala with MRTs between 0–22 years) and in the recharge area (Amia Mangat) which gave modern recharge values. Overall the deep groundwaters have median MRTs of 45 years, while the shallow groundwaters have median MRTs ca.30 years. Some locations in the region of rapidly declining groundwater levels (e.g. Bussowal, Mallian Kalan Jadiala and Arjanwal) had deep groundwaters that showed significantly younger MRTs post monsoon (43, 27, 0 and 39 years respectively) compared to pre monsoon (68, 59, 22 and 55 years) suggesting rapid pumping induced vertical leakage of modern water to depth during the monsoon.

Nitrate, chloride and sec

A complete table of summary statistics for major and trace elements is given in Appendix 1. Figure 15 shows box-plots for nitrate, chloride and SEC data grouped by borehole depth and pre/post monsoon conditions. Figure 16 shows cross-plots of total borehole depth vs NO₃, Cl, SEC and MRT. There is a consistent trend of significantly lower SEC and lower concentrations of Cl and NO₃ in the deep groundwater, this is strongly suggestive of anthropogenic sources of contamination within the shallow aquifers, and migration to depth at some locations. Overall, median concentrations are below 50 mg/L (WHO drinking water limit), however, there are a few sites where this is exceeded in both the shallow and deep sites. Median values for all three parameters in the shallow groundwater, were lower post-monsoon compared to pre-monsoon. This suggests a dilution effect in the shallow groundwater due to rapid meteoric monsoon recharge. While median concentration of nitrate in the deep groundwater are low, <5 mg/L, there are a significant number of sites which show concentrations >10 mg/L, which suggests that contamination from shallow sources may be mobilised and flushed to depth within the aquifer. A significant proportion of shallow sites have low nitrate concentrations and high SEC, this point to natural attenuation of nitrate in shallow aquifers in some situations, likely linked to redox controls and availability of DOC in the shallow aquifers. The low SEC in most of the deeper sites also indicates the lack of evidence for saline groundwater at depths of 150 m within this Doab.

Figure 15 Notched box-plot of a) NO₃, b) Cl and c) SEC grouped by borehole depth and pre/post monsoon conditions.

Figure 16 Cross-plot total borehole depth vs a) SEC, b) NO₃, c) Cl and d) MRT.

Trace elements

Figure 17 shows box plots for selected trace elements of particular significance in terms of drinking water quality (e.g. As, F, Se, U, Fe and heavy metals) and groundwater residence times/geochemical evolution due to mineral dissolution processes (e.g. As, Mo, U). All groundwater samples in this study had dissolved As and F concentrations below 10 μg/L and 1.5 mg/L (WHO drinking water guideline values). Iron concentrations were generally below 500 μg/L except for some shallow sites, where overall Fe concentrations were significantly higher during post monsoon conditions and were >2000 μg/L in a few instances. Selenium concentrations were <10 μg/L in deep sites, however there were significantly higher concentrations in shallow groundwater, occasionally exceeding concentrations of 20 μg/L. Median concentrations of Cd, Pb, Cr, Cu, Ni and Zn were all significantly higher in shallow sites compared to deep sites, suggesting an anthropogenic source of contamination. Lead concentrations were generally below 10 μg/L, however there were 5 occasions where concentrations in shallow groundwater exceeded 20 μg/L. The heavy metals and Se appear to have a shallow source, anthropogenic contamination from waste water is a likely source for the former while perhaps enhanced Se concentrations in soils may be the source of enhanced Se in shallow groundwaters (Dhillon and Dhillon 2003).

Figure 17 Notched box-plots of selected trace elements a) As, b) Fe, c) F, d) Se, e) Mo, f) U, g) Pb, h) Cd, i) Cr, j) Cu, k) Ni, m) Zn grouped by borehole depth and pre/post monsoon conditions.

Median concentrations of U, Mo and As were higher in the deeper sites compared to the shallow sites. Median concentrations for uranium in deep sites are >15 μg/L (WHO provisional guideline value is 30 μg/L). This guideline value for U is based on daily water consumption of 2 L/day which may not be realistic for NW Punjab, particularly during the hot season. These trace elements and others (e.g. Sr, Li, Rb) can be used as traces of groundwater evolution due to mineral dissolution processes and are therefore tracers of groundwater residence times (e.g. Edmunds et al., 2003). These results suggests that a major control on trace element concentrations, for elements which are not limited by mineral saturation, is groundwater residence time and water-rock interactions, however, anomalous high concentrations for U, Se and Mo in some shallow groundwaters also suggests a redox controls on element concentrations may also be important in some instances. Figure 18 shows a cross plot of MRT vs four common chemical indicators of groundwater residence time (Mo, NO₃, Mg/Ca and Sr). There is a general trend of increasing Mo, Sr and Mg/Ca with increasing MRT and a decreasing trend in NO₃ with increasing MRT, together these highlight residence time controls on natural trace element compositions and anthropogenic contamination in groundwater. The variation in trace element composition (i.e. the noise in the trend) for samples with a given MRTs also suggests that mixing processes occurring at sites are important in controlling chemical compositions of groundwater and may reflect anthropogenic induced mixing due to intense pumping.

Figure 18 Cross-plot of MRT vs a) Mo, b) NO₃, c) Mg/Ca and d) Sr.