Water Quality for Geotechnical Drilling

[Patgeotech]

Greetings,

We are currently undertaking a borehole investigation in a drought affected area in South Africa, so our water usage is important. We will be doing extensive laboratory testing on the recovered samples (geotechnical and chemical tests). We have been asked why we cannot use recycled water or water from a treatment plant. We tested the treated/recycled water and compared the results to clean/potable/drinking water - the results showed the treated/recycled water to be 5 times higher than acceptable drinking water standards. Does one allow the use of these treated/recycled water sources? or do we stick to our normal drinking water standards for borehole drilling. I feel that the treated/recycled water will definitely affect the accuracy of our test results - but cannot say for sure by how much, which brings in a degree of uncertainty to our test results. Is there a water quality standard/specification for borehole drilling? Would appreciate your comments on the matter.

 

[fattdad]

What tests are you running that could be affected by water quality? I'd think that soil strength and classification tests would be unaffected. If you are considering soil or water chemistry, then hollow stem augers may be an option, depending on the geology and the depth of the field exploration.

f-d

¡papá gordo ain’t no madre flaca!

 

[cvg]

the results showed the treated/recycled water to be 5 times higher than acceptable drinking water standards

What is 5 times higher? pH, nitrates, TDS, - what? Also consider that you are in effect "injecting effluent into a well". Will that be considered to contaminate the aquifer? Will the relevant water authority allow it? Highly unlikely it would be allowed in the states.

 

[Patgeotech]

Further to your comments,

We will be undertaking chemical testing on soil and water samples. In terms of water samples, one can purge the boehole to remove the excess treated water, so we do not regard that as a problem.

What does concern me, is if we use recycled/treated water to recover our softer versions of mudstone/siltstone samples, the treated water will influence the soil moisture content (we are drilling without drilling liners), so other foreign constituents will bind with the clay/silt particles. If the drilling water is kept the same or as near to the natural groundwater, then I would expect no adverse changes to the soil geochemistry, but if drilling water with a concentration of chloride or total dissolved solids of 5 to 10 times higher than the natural or potable drilling water is used, then there must be same changes to the geochemistry of the soil fabric. Soil conductivity and resistivity tests would be affected and possibly hydrometer tests. Water quality is something that clearly has not be researched in terms of the possible chemical changes to moisture sensitive soils.

In terms of this investigation, we are trying to extract as much soil/rock core as we can to extract sample.

In terms of the water quality tests, we undertook a few preliminary tests to compare against potable/clean water. All test results indicated higher test results compared to the clean water sample. We tested a borehole water sample that is located in the area and it gave similar results to that of clean water sample - so would have been a good water source, however because of the severe drought in the area, the borehole has subsequently dried up and we have started drilling.

The tests we undertook were typical of our drinking water standard without any metal testing though (we needed quick results-the usual time related problems). Yes, using the recycled/treated water would 'contaminate' the ground - as we do not have sufficient test results, I do not wish to use this water for that very reason - I cannot say for sure what the level of contamination would be. It is much higher in terms of every test we undertook and to me that is unacceptable to put into the ground without adequate testing. Things are done a bit differently in Africa - would provide good experience for sustainable and practical engineering.

I have been asking quite a few fellow geotechs across the world spectrum and there seems to be a degree of uncertainty in terms of water quality for soil testing - makes for some interesting research topics.

Your thoughts on the matter?