One possible source could be the use of fertilizers as ammonium sulfate, for example. As the concentrations are low the sulfate content could be originated from the recycling of the groundwater used in iirigation.

Potentially, suplphur may be of geothermal origin, oxidated due to some reason. Another option is that suphates come from protein decomposition. 

may be originated to the dissolution of Gypsum rocks in lagoon environment or Gypsious soil(Gypcrete). best wishes

There are many sources of sulfate in groundwater (see e.g. J.D. Hem- US Geol. Survey, Water-Supply Paper 2254, 1992). All above answers are OK. I can also add transport sulfates with rain and oxidazing suphides of metals (e.g. pyrite FeS2) dispersed in rocks (soil) even in small amounts. 

Thanks to all for sharing information -Asit

main source is  pesticides

Gypsum minerals may appear in detrital deposits not visible to the naked eye, in shales or marls. If it is not a natural source, it may be due to fertilizers or perhaps to urban waste water. It is essential to carry out a cartography of the extension of the hydrochemical anomaly so that the investigator can look for the cause.

In groundwater, 10 to 15 ppm SO4  is obvious and most reasonable. This much concentration may not  require any rich sulphate source. Only interaction of rain water with ground surface is enough as to explain this much concentration of SO4.

... apart from fertilization and organic matter (brought forward) above, reduced sulfide minerals present in the aquifer may be a source (e.g. pyrite oxidation), often coupled with nitrate reduction.

This option would be more likely if these sediments are fine/silty sand of fluviatile or estuarine genesis with lenses of organic matter and clay/silt present.

The sedimentary environment is important, in an arid environment the existence of sulphates associated with evaporation is feasible. In large sedimentary basins, different climatic conditions influence the lithological nature of the sediments and this influences the hydrochemistry of the aquifer formations.

Thanks to Dr. Robert Kringel, Dr. BP Naveen and Dr. Marc Martínez Parra for your contributions. Regards

There are two main sources of sulfate to the groundwaters of the Bengal Basin. 1] brackish connate water - estuarine water trapped in the sediments as they were laid down and now preserved in odd patches where later freshwater flushing has been poor. This is typically found at depths > 50 m. 2] Septage. That is, water leaking from pit latrines (villages) and leaking sewers (towns). As most groundwaters are anoxic, sulfate has been removed (or its concentration lessened) from much of the deeper groundwater by sulfate-reduction. See McArthur et al. Waste-water impacts on groundwater: Cl/Br ratios and implications for arsenic pollution of groundwater in the Bengal Basin and Red River Basin, Vietnam. STOTEN 437 (2012) 390–402.

Prof. (Dr.) John,

Thanks for insightful remarks on the topic. The question came to my mind about one year back when I was writing an article; the paper has been published in May, 18.Article Hydrogeochemistry and quality of groundwater in a part of Da...

The paper could have been more enriched if I had incorporated the knowledge, you extended. If you are interested, then I can send the full text of the paper.

Sir, I have read the paper, you mentioned - an excellent work. I feel lucky to interact with a renowned expert on geochemistry.

Best regards

If the result did not indicate geogenic (Natural) as you said, then anthropogenic (human) source is suspected may be through waste of sewage system. You check the correlation between Sulfate , Nitrate, Iron and Phosphate if analysed. Nitrate correlation with sulfate will answer the question.

Jamiu Abimbola Aladejana - Thanks for your valuable comments.

Primary source is monsoon rains (10-15 mg/l). Part of the water is spent to evaporation (via storage/irrigation/agriculture). So one could expect higher ground water sulphate in vicinity of water reservoir or intensive irrigated areas. Some plants could add to S accumulation, like rice and shugar cane. S-content in the crop/biomass removed versus retained...

agriculture

Another supplementary source of SO42- is the likely oxidation of pyrite (FeS2 ), which can occur in recharge areas according to the equation (Appelo and Postma, 1993):

However, anthropogenic sources related to agriculture may also contribute to this element (SO42-), farmers widely use such fertilizers based on potassium sulfate, ammonium sulfate and the sulfo-phosphate ammonium.