Abstract

Three tracer tests were carried out by slug injection of fluorescein, amino-G-acid, and bromide at piezometers with 0.4 m long intake zones located 5 m distant from an 80 m deep pumping borehole. The piezometer intake zones were about 2 m (Tests 1 and 2) and 18 m below static water level, and the pumping borehole was sealed using a packer at about 11 m (Tests 1 and 2) and 19 m below static water level. Analytical expressions were used to interpret the data. Test 2 was unsuccessful.

Four pathways were discernible from the Test 1 tracer breakthrough curves. These pathways were interpreted as being due to three dominantly fracture routes and one dominantly intergranular flow route. The earliest (sharp) peak arrived after a few hours, and the last (broad) intergranular flow peak arrived after around 40 hours. Fluorescein was delayed slightly (retardation factor = 1.4) relative to the other tracers. In the deeper Test 3, three pathways were discernible, with concentration peaks at about 9, 25, and 78 hours. Fluorescein was delayed relative to amino-G-acid (retardation factors = 1.25 and 1.5) in the second and third pathways. As with the first test, the last peak was very broad, suggesting a variety of intergranular routes through the rock, and possibly the effect of diffusion.

The tests clearly demonstrate the importance and complexity of fracture flow over short distances in the Triassic sandstones, the complexity of the intergranular flow routes, and that different retardation factors can be associated with different pathways.

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