OR/14/068 Conclusions

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.

This report summarises initial findings from a hydrogeological case study focussed on investigating the response of groundwater resources in Punjab State, India to sustained long-term (>30 year) abstraction. The report covers a basic analysis of the long term groundwater level data (available from GWDB) in the region as well as the initial analysis and interpretation from a hydrochemical investigation carried out using a suite of environmental tracers (including dating tools and stable isotopes) to understand the sources of shallow and deep groundwaters in the Bist-Doab region of northern Punjab. Pre and post monsoon samples were collected across the Bist-Doab from paired shallow and deep sites and analysed by BGS. The findings from this case study have broad relevance across a large geographical area since broadly similar groundwater typologies extend across Indian Punjab, northern Rajasthan in the west, and upper Pakistan Punjab, as well as into neighbouring Indian states of the Ganges Basin in the east (e.g. Haryana).

Preliminary conclusions:

• Evidence from long-term groundwater monitoring shows declining trends in shallow pre- monsoon groundwater levels across a large part (20–25%) of the Bist-Doab.
• This is leading to enhanced recharge during the monsoon. For the most affected region of the Doab, declining post monsoon water levels suggest that abstraction for irrigation is outstripping the enhanced recharge potential.
• If the current situation is allowed to continue, in the long-term this will lead to a continued decline in shallow groundwater levels pre-monsoon, currently commonly found to be >20 mbgl, with future implications for irrigation.
• CFC groundwater age tracers show that median shallow groundwater MRTs of 25 years and 30 years under post-monsoon and pre-monsoon conditions. Deep groundwater (>100 mbgl) had median MRTs of 45 years irrespective of recharge conditions. Modern tracers were detected in all of the deep sites.
• Deep groundwater MRTs are much younger than would be expected under natural groundwater flow regimes. The region with long-term declining groundwater levels shows evidence of enhanced modern recharge in both shallow and deep groundwater, suggesting that there is a significant component of vertical leakage to deeper aquifers induced by long-term intensive pumping.
• Some of the shallow groundwaters have SEC >1500 μS/cm, with potential implications for the use of this water for irrigation in the long-term due to the build-up of salts in the unsaturated zone.
• There is evidence of nitrate breakthrough from the shallow groundwater to depth and this is likely to be enhanced in the future if the current increases in pumping from the shallow and deep aquifers continue. This has implications for future contamination of deep sources of drinking water from other anthropogenic contaminants such as pesticides.
• The naturally occurring contaminants arsenic and fluoride were present in concentrations below WHO guideline drinking water limits for all sites and median concentrations were below 2 μg/L and 0.4 mg/L respectively.
• Uranium concentrations in deep groundwater are significantly higher (p<0.05) compared to shallow groundwater, median values >15 μg/L, as a result of long residence times and mineral dissolution. There may be implications for elevated radon in deep groundwater, and this should be investigated.