Abdul Wahab Khan
Panaji
A study conducted by the Central Ground Water Board (CGWB) has sounded an alarm on the fragile groundwater system in North Goa’s coastal villages of Candolim, Calangute and Anjuna, which are popular tourist areas.
The research findings suggest an urgent need for real-time surveillance and management strategies to safeguard the coastal aquifers. The researchers have warned that unchecked development could push the delicate balance beyond recovery. Natural tidal forces and human activity are jointly reshaping Goa’s groundwater system, states the study.
With an aim of assessing the extent of saline water intrusion, chemical imbalances and human-induced contamination in one of the state’s most densely developed coastal areas, the researchers examined the groundwater quality across multiple seasons between September 2022 and March 2023. Thirty monitoring wells were deployed, with the researchers drawing samples during rainy season, post-monsoon regression and pre-monsoon phases.
“Goa’s coastal aquifers are increasingly vulnerable to both, anthropogenic pressures and tidal influences,” the report says, further stating that “a discernible degradation in groundwater quality was notably observed during the post-monsoon period, with nitrate levels in Calangute soaring up to 98.05 mg/l (milligrams per litre) – well above the safe limit of 45 mg/l”.
The study attributed the nitrate surge in groundwater to a combination of factors, including heavy inflow of tourists, organic waste generation and improper disposal practices. Researchers have warned that nitrate contamination in groundwater poses serious health risks ranging from abdominal disorders and hypertension to birth defects and cancers.
Hydrochemical analysis revealed striking seasonal shifts. Gibbs plots indicated that while pre-monsoon samples were dominated by rock-derived elements, post-monsoon samples showed seawater influence, a result of tidal influx into aquifers. A Gibbs plot is a hydrogeochemical tool used to identify the main hydrogeochemical processes like evaporation, precipitation and rock-water interaction that control the chemical composition of surface water and groundwater.
Similarly, Piper trilinear plots revealed a transition from magnesium bicarbonate-type facies (hard water) in pre-monsoon phase to mixed calcium magnesium carbonate and sodium chloride post monsoon – a clear evidence of saline water intrusion into the groundwater.
Electrical conductivity (EC), a key indicator of salinity, mostly remained within 750 mS/cm (MilliSiemens per centimetre), but spiked alarmingly to 1,600 mS/cm near the Calangute creek. The report attributed this to tidal influx and possible localised preservation of paleo-seawater in Baga and Anjuna.
Total Dissolved Solids also reflected seasonal variations, with levels exceeding 500 mg/l in certain inland locations such as Mazal Waddo in Anjuna before subsiding after monsoon recharge.
The research was conducted by Sangita P Bhattacharjee (Scientist-D&OIC, Central Ground Water Board [CGWB] Belagavi), Sushant S Navarat (Assistant Hydrogeologist, CGWB Belagavi) and Jyothi Kumar Nalli (Regional Director, CGWB Bengaluru).
