River Bank Filtration

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?

Taxonomy

• Groundwater Modeling
• Groundwater Mapping
• Surface-Groundwater Interaction
• River Engineering
• Groundwater Resource

10 Answers

1. 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..

2. 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.

3. 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.

4. 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.

5. 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.

6. Surely there must be some info with regards to local hydrogeology that you can consult: geological investigations, borehole records, hydrogeological reports, hydrogeological maps? I d consult national and regional archives from your country's department or body responsible for geological research etc.

   250 m is quite close to a river and if the river is groundwater fed, then there will be an impact on the river almost certainly. If your river has sand banks then it may be running on top of sandstone. However, the river may be running on top of an aquitard (for example clays), so it could be partially or totally confined, with low baseflow index (indicating no to little inputs from aquifer).

   Normally you'd test the connectivity between your borehole and river properly, before you decide where to abstract - I'm not sure if your borehole is a test one but it sounds like it's not. This study may help you decide how to proceed best. Whatever you do, you will have to gather data over several months to understand what is going on, as interactions between groundwater and rivers can be complex.

   It is crucial you understand what if any impact your abstraction has on the river, as a large decline in flows can cause ecological damage, especially during very low flows and can affect downstream abstractors whose livelihoods may depend on the water available to them. You may breach some environmental legislation too, which can lead to fines etc.

7. Dear V S.

   
   
   

   Pl indicate how much water in kl per day, will be extracting and for what purpose.

   
   
   

   Is the river ever flowing or perenial in what months, Etc.

   
   
   

   If you are drawing water what provisions, will you do for rain water harvest/ charging your aquifer in use.

   
   
   

   If waste water is being generated, will your outflow of effluents be processed and sent back to river in compliance to local pollution rules / standards Etc.

   
   
   

   As you are drawing water, an important natural resource, you need to give back to the communities by doing woodland development on river banks, aptly ie planting native and desired trees saplings. 

   
   
   

   With well wishes for doing good to communities.

   
   
   

   Prof Ajit Seshadri.

   
   
   

   Chennai. INDIA.

8. In addition to runoff, rivers receive groundwater from adjacent soil, which moves into the river channel. This is called "base flow".  A well that is located close to a river may reverse this flow and draw water from the river. Thus, it is likely that at least some of the water that is flowing into your well comes from the river, particularly in cases of sandy soil. Lab tests are not the best way to determine this, but there are other ways of estimating the effect of the nearby river on a well. Look up a groundwater hydrology text or the USGS website.

9. I agree with Ken Isakson's answer. The main criteria are highest efficiency of water pumping from its source, i.e. maximum water flow at minimal cost of equipment. The higher the source of the water the easier it is to transfer it to the source (relying more on share of gravity than the work of the pumps- which raises the cost). 

10. There are lots of expensive ways to get at this answer that involves modeling and geochemistry.  However, the simplest way may be to measure the depth to water at the well compared with the average surface elevation of the water at the river.  If the static elevation of water in the well is significantly above the surface elevation of the river, then you are likely drawing from groundwater that flows to the river.  If there is only a slight difference above or if the static elevation Is below the surface of the river, you are likely drawing water from the river.  Without further investigation, that's the best I can come up with.