FR Bannu an area in KPK Pakistan, where in an area of almost 4 sq. km we have two diff quality underground water. One is totally undrinkable and the other one is drinkable. One extra point that Kohat Salt zone is present in the North of this area. We have evaporites in the vicinity, but why we have drinkable water over there then?
I have one/two points regarding its answer but Let me know yours first.
Both soft and hard rock formations have the quality of an aquifer. The hard rock possesses secondary porosity and hence occurrence and movement of groundwater depends on connectivity of joints and fractures.
There is a possibility of different aquifers existing or shallow and deeper aquifer or else existence of perched water body in that area. More details could be possible after hydrogeological evaluation of the study area.
With knowledge of tomography, or the approximate position and power of salt releasing strata like marine clays or salt pits and lumps there could be heterogeneity in ground waters
You may want to consider geological substrate and separation possible by aquifer. Freshwater is heavier than salt water, so rainwater infiltration or undeground flow pattern could be diluting deeper waters. I will send paper by Toth, and his theories of underground flow path may be useful. If you have geological mapping of substrates, it may become evident. A geologist or hydrogeologist may be helpful if trying to characterize the specifics, and may help to understand and protect your drinking waters from damage and assess how sustainable they are under the circumstances and all uses of water.
This may suggest some of the complexities of how groundwater can circulate as an example, not necessarily specific to your circumstance.
Both soft and hard rock formations have the quality of an aquifer. The hard rock possesses secondary porosity and hence occurrence and movement of groundwater depends on connectivity of joints and fractures.
There is a possibility of different aquifers existing or shallow and deeper aquifer or else existence of perched water body in that area. More details could be possible after hydrogeological evaluation of the study area.
@Bhavana Umrikar I also suggested your perched aquifer concept... thnaks
Having salty or briny water at some depths while also having nicely fresh water at other depths is very common in the western US, so I'm not surprised to hear that you have such an occurrence in Pakistan too. You didn't give us any information regarding the depths at which these varying water qualities occur, but in looking at a map of the area around Bannu, Pakistan I see that surface waters are relatively abundant in the area, shedding off from the Karakoram range. I also see a reservoir. From this it is easy to imagine that some aquifers are being recharged from local precipitation, some are being recharged from distant precipitation, some are being recharged from flowing surface waters, and some are being recharged from surface waters impounded in the reservoir(s). These widely varying pathways, as well variations in the host rock/sediments of the aquifers, will give wildly varying water qualities. Salinity being just one of many water quality parameters that likely vary between aquifers. If any of the aquifers have been heavily exploited by pumping, then this will be adding additional complications to the puzzle.
If we are only talking about shallow ground water, then I would surmise that the evaporites you mention being in the area have "contaminated" different aquifers and areas to varying degrees as influenced by the dramatic tectonic deformation that is actively occurring in the region.
The short answer is that what you are observing is a very common phenomena. In my local area, one person's well may have very sweet water while the neighbor's well might be loaded with iron and sulfides causing it to taste awful and leave stains on plumbing fixtures. Theses shallow waters are being pumped from host materials that react with the water. Residence times in the host material can also be very different.
Co Existence of saline water and fresh water examples can be seen in various locations of Krishna and Godavari delta regions of southern part of India and closer to Bay of Bengal. In few cases upper layer with fresh water and below saline water ,and in some cases just reverse. hydro geological and hydro chemical investigations resulted to delineated interface boundaries which probably due to under ground water channels and caused to be ingress process. The detail study is available on line.
Variation in groundwater quality can occur even within less than 100meters separation due to inherent heterogeneity characteristic of the earth. Hence, unpredictable random variation in recharge/discharge processes and hydrodynamic dilution and dissolution can occur. Stratigraphic positions of the aquiferous rock units can also influence water quality in a given enclosure.
- Badges
- Science topic
- Similar topics
- Geoscience
- Hydrology