Read/Download - SKB

1601009080701401201008060504030604020004-27 05-02 7 12 17 22 27 06-01 6 11 16 21 26START :05/04/26 06:00:00 INTERVAL: >= 1 Hour STOP :05/06/30 17:59:59Figure 5-11. Groundwater table (red), flushing water flow rate (yellow) and return water flow rate(green) versus time during core drilling of borehole KFM06C.month-dayAs the upper 100 m of the borehole are cased and cement grouted, there was no return waterinflow above the core drilled part of the borehole. Shortly after core drilling started, the returnwater flow rate was c. 40 L/min, indicating water yielding fractures just below 100 m. Whencore drilling commenced, the water inflow increased simultaneously as the groundwater tabledraw-down was larger. However, after the summer holidays both the return water flow rate andthe draw-down stabilized. The results indicate absence of major groundwater inflows to theborehole at larger depths.Uranine content of flushing water and return water – mass balanceDuring the drilling period, sampling and analysis of flushing water and return water for analysisof the content of Uranine was performed systematically with a frequency of approximatelyone sample per every fourth hour during the drilling period, see Figure 5-12. Like in boreholesKFM02A, KFM03A, KFM04A KFM05A and KFM06A, a dosing feeder controlled by a flowmeter was used for labelling the flushing water with Uranine to a concentration of 0.2 mg/L.A mass balance calculation of the accumulated volumes of flushing water and recovered flushingwater in the return water suggests that minimum 115 m 3 of flushing water was lost in theborehole. According to notations in the log book, the amount of Uranine added to the boreholewas 238 g. If the averages of the Uranine concentration values in the flushing water and inthe return water are used to calculate the amount of Uranine added to and recovered from theborehole, the calculations give 238 g and 227 g respectively.Flushing water pressureThe flushing water pressure measured during drilling of borehole KFM06C is exposed inFigure 5-13. Like in boreholes KFM02A, KFM03A, KFM04A, KFM05A, KFM06A, KFM07Aand KFM08A the borehole diameter was 77.3 mm, i.e. increased c. 1 mm compared to inborehole KFM01A. This resulted in lower flushing water pressure than in KFM01A.38