1. NON-PURGING GROUNDWATER BOREHOLE SAMPLING TECHNIQUE PRACTICED IN A COAL FIRED POWER STATION ENVIRONMENT
Test & Measurement Conference_2017
Saint George Hotel & Conference Centre, Pretoria
Presented by: Gundo Mathoho
Date: 31 July 2017

2. Contents
Introduction
Groundwater monitoring at Eskom sites
Groundwater Sampling Depth: EC Profiling
Groundwater Sampling: Bailing method
Case Study: Komati Power Station
Conclusions

3. Introduction
Groundwater sampling for years has been done across Eskom sites mainly for evaluating the water quality of underlying aquifers
Water qualities from these aquifers is used to understand the natural processes governing groundwater chemistry changes, as well as potential impacts due to anthropogenic influences occurring at the surface
Eskom employs two non-purging groundwater sampling techniques for optimal interval sampling of the representative sample at a particular depth
Solinst Discrete sampler and a double valve bailer are used at Eskom

4. Groundwater Monitoring at Eskom sites
Groundwater resource and its usage is protected and regulated under the National Water Act (Act 36 of 1998) of South Africa
Eskom is obligated to conducting groundwater monitoring at all its Power Stations as part of the Water Use License (WUL) conditions
Surface & groundwater monitoring at Eskom sites has been taking place since the 1980’s.
Monitoring sites per site: (boreholes) & 10 – 70 (surface)
Annual Cost of monitoring: ± R per site

5. Cont.
The bulk of the work that Eskom and contracted consultants undertakes is mainly seasonal monitoring program which includes:
Collection of groundwater samples
Laboratory chemical analysis of samples
Interpretation of results and reporting to Department of Water and Sanitation (DWS)

6. Groundwater quality potential impacts

7. Cont. Over 90% of SA’s aquifers fractured
Fractures form conduits through which groundwater and pollution can move
Rock matrix stores water
Boreholes intercepting fractures can have high yields

8. Cont.

9. Cont.
Recommended sampling depth= 7mbgl
Gomo et al 2017

10. Discrete Groundwater sampling: Bailing Method
A bailer is non-invasive grab sampler used in groundwater monitoring boreholes to collect a groundwater sample below the ground surface
Typically, a bailer consist of a hollow tube with two or one valves and a handle at the top to attach either or both the anchoring and valve regulating line.

11. Cont.
Rinse the sampler on surface and make sure that everything works well.
Lower the sampler to a predetermined depth of the borehole
Collect the water sample
Fill sample bottle
Immediately measure and record physicochemical parameters
Preserve sample according to laboratory instructions

12. Case Study: Koamati Power Station
Komati Power station is located South of Middleburg
The site forms part of the Highveld Coalfield
The main water bearing aquifers in the vicinity of the power station are fractured rock aquifers
Groundwater monitoring at Komati power station is done according to relevant environmental permit conditions
EC profiling was perfomed using a calibrated Solinst TLC meter on three monitoring boreholes located at the ashing area
Selected boreholes are AB01, AB04 and AB07, the maximum penetrated depth during drilling was 40mbgl for all boreholes

13. Komati Power Station

14. Logs vs. EC profiles

15. Cont.

16. Cont.

17. Cont.
No preferential pathways for groundwater migration and contaminant migration can be identified.
It is recommended that sampling be continued at this depth.
It should be noted that all boreholes were drilled to a depth of 40 metres but has since silted up to a depth of around 37 metres.

18. Conclusions
Groundwater monitoring boreholes at Eskom sites are purged using a borehole submersible pump at least twice a year as good practice
This ensures relative fresh groundwater ingress into the borehole to avoid stagnation of water, especially in low yielding boreholes.
During the EC profile investigation no preferential pathways were identified in the boreholes along which groundwater contaminant flow can take place
Previous sampling depth might have been determined on the basis of drilling information, in particular, the water strike with the highest blow yield
The current sampling depths are therefore recommend as future sampling depths
Future work = Comparative study,

19. Thank you Gundo Mathoho - Hydrogeologist Research Testing and Development Lower Germiston Road Rosherville Gauteng Private Bag Cleveland 2022 SA Tel: Cell:

20. Backup slides

21. The order of sampling must be from the (expected) least contaminated boreholes to the most contaminated holes.
Record borehole number, time, date and any other relevant observations on the sampling form.
Remove the borehole cover carefully, inspect the borehole and record abnormalities observed
Measure and record the collar height of the borehole above general ground level
Measure the depth of the static groundwater level to an accuracy better than one cm. (Water levels should be recorded from the collar height – unless specified otherwise)
Clean all sampling equipment if necessary.

22. Lower the bailer to the prescribed depth and grab the sample in the appropriate way as described for the specific bailer.
Raise the bailer to the surface and rinse the sample bottle, with some of the sampled groundwater. Carefully fill the sampling bottle with the sampled water, ensuring that the bottle is filled to the brink with no air trapped.
In the case of sampling for metal analysis, it is essential that the sample bottle is only opened when ready to fill and not emptied or rinsed as it contains preservative acid. While filtering fill the sampling bottle with the sampled water ensuring that the bottle is filled to the brink with no air trapped. All samples collected for metal analysis should be filtered and preserved, unless otherwise specified by the project leader.
Should samples be taken for bacteriological analysis, the appropriate preserved sample bottles should be used.

23. Replace the cap and dry the bottle with clean absorbent paper/cloth.
Take field measurements such as pH, EC, Temperature and DO
Attach a clean label to the bottle and write the following information on the label using legible capital letters:
Site and project name
Sample (borehole) number
Date
Constituent to be analysed
Name of the project manager

24. Preserve the sample on ice or in a cooler box.
Laboratory to analyse samples
Sample depth
The sample label should be covered with sello-tape to prevent damage to the label.
Preserve the sample on ice or in a cooler box.
Complete the chain of custody, leaving no blanks.
Rinse the bailer with clean water.
Carefully repack all equipment, ensuring that it is not contaminated during travel.
Replace the borehole seal.

25. Ensure that the site is in good order before leaving.
Return all samples to the lab as soon as possible, preferably never more than three days after sampling. All samples collected for bacteriological and chrome VI analysis should be submitted to the laboratory within 24 hours.