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

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

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

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: 20 - 50 (boreholes) & 10 – 70 (surface) Annual Cost of monitoring: ± R 1 000 000 per site

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)

Groundwater quality potential impacts

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

Cont.

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

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.

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

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

Komati Power Station

Logs vs. EC profiles

Cont.

Cont.

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.

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,

Thank you Gundo Mathoho - Hydrogeologist Research Testing and Development Lower Germiston Road Rosherville Gauteng Private Bag 40175 Cleveland 2022 SA Tel: +27 11 629 5643 Cell: +27 72 501 4020 E-mail: Mathohg@eskom.co.za

Backup slides

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.

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.

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

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.

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.