River Bank Filtration

Question

I am drawing water from the ground at a distance of 250 m from a river bank.  I need to establish the source of the water being drawn: a) is the source the river, whose water would have seeped through the sand on its banks, or b) is the source an underground aquifer.  What tests (chemical / physical) tests can I perform to ascertain this?

Omeje Maxwell · Answer

You can simply use the  integrated geophysical approach to evaluate the ground water source or if there is inter connectivity  between the two. Such could be the integration of Electrical Resistivity Tomography  and Electromagnetic  Methods. The compatibility  of these two geotecnical tools I feel will address the issue you raised here..

V SOAMIDAS · Answer

I thank all persons who have responded to my query.  
 
Based on the responses, here is some more data:
1. The river is a perennial river (River Yamuna), fed from melting snow in the Himalayas and rain in its catchment.
2. The loacation is Agra, Uttar Pradesh, India
3. The water being drawn is further being filtered in a slow sand filter to obtain potable water.   There is no waste water being produced.  Regarding RWH, the location is open, with no buildings close by.  The ground is sandy and there is almost no runoff here unless very heavy rains occur for a long duration (which i have personally seen only twice in the past 25 years).
4. Quantity proposed to be drawn is 100 kilo liters per day, to be supplied to nearby villages.  (The facility will be activated soon)
5. Giving back to the community has a very high priority in the scheme of things at my organisation.  Tree plantation is done regularly on every possible occasion (Independence Day, Republic Day, Lorhi, Holi, Deepawali, ...)  Large swathes of barren areas have been covered with greenery over the years by sustained plantation and care.
6. The water level has been determined in two bores, near the river.  These levels are as follows:
RL at River bank - 100 m
RL at the bore on RBF site 250 m from river bank - 99.565 m
RL at a bore 500 m from river bank - 102.31 m
 7. Chemical analysis of water samples from these locations has not yet been done.  As suggested by Ian Pearson, I will try to analyse for chlorides and nitrates.
8. At present there are no bores between the river bank and the RBF bore.  I will have to put in bores for this purpose.  Will try out shortly.
9. The bore has already been drilled, but if required, another one at a more appropriate location can be made.  The existing one can be dismantled.
 
Again I thank all for your suggestions.  
Based on your suggestions, at present the option of drilling wells between the River and the RBF well and finding out the RL of water in these seems to a good way to proceed.  Further, Chloride and Nitrate estimation in the water from these wells could also provide an answer to my query.
 
If any further comments / suggestion can be made based on the above information, please do post the same for me.
Thank you.

Ian Pearson · Answer

In addition to Ken Isakson's comment, remember that the static level in the borehole or well is likely to be above the stream level, implying that the aquifer will be feeding the stream.  However when you pump, you will draw down the level in the well, which may result in a sufficient back-flow from the stream to the well.  So try to check both the static level without pumping, and again when you have been pumping for some time.
In terms of the chemical tests you could carry out, test the chloride in the stream and in the well, or even just the TDS.  If possible also try to get a sample to test from a well which is further from the stream but probably drawing from the same aquifer.  The results will indicate the approximate source of the water.  However as indicated above, try to get at least 2 samples from the well - i.e. after there has been no pumping for some hours, and then again after pumping has taken place for a period.
If the chloride or TDS values don't help you, try a non-conservative water quality parameter such as nitrates.

Vasudev Shirahatti · Answer

The question here whether the well yield is from the river or from the acquifer. River could be influent 
or effluent depending on the relative River stages and the phreatic surface elevation. Best way to determine is to put couple of boreholes between the river and the well and measure the water surface in the boreholes.

Vasudev Shirahatti · Answer

The question here whether the well yield is from the river or from the acquifer. River could be influent 
or effluent depending on the relative River stages and the phreatic surface elevation. Best way to determine is to put couple of boreholes between the river and the well and measure the water surface in the boreholes.

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