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The DME was advised by Vista Gold of the overflow of Retention Pond 2 (RP2) at 1210 hours, Friday 22nd February. Two members of DME’s Environmental Monitoring Unit (EMU) and the Labtruck were immediately despatched to site to investigate the report and collects samples.
EMU arrived at site at approximately 1730 hours and immediately commenced sample collection. Five samples were collected that evening and a further nine collected the following day. The samples were prepared for despatch to the laboratory during Sunday and delivered to the laboratory Monday morning, 25th February. Preliminary results were received late Tuesday afternoon 26th February.
When EMU arrived at site they observed that as well as RP2 overflowing, RP5 was also overflowing via its spillway directly into Batman Creek. RP2 is a small pond on the northern side of the plant area that collects runoff from the low-grade stockpiles; its water quality is generally similar to that in Batman Pit (RP3) and RP1. RP5 collects runoff from the general plant area, water quality in RP5 is generally better than that in RP2.
Following a site inspection and discussions with Vista Gold, DME concluded that the contributing factors to RP2 overflowing were a number of electrical failures over the preceding days, and then a pump/pipeline failure on Friday. RP5 could only be pumped to RP2, so they were unable to start pumping from RP5 until RP2 had been pumped down sufficiently.
Vista have subsequently modified pipeline infrastructure to allow for both RP2 and RP5 to be pumped concurrently to either Batman Pit or the Tailings Dam.
A review of the field measured parameters - Electrical Conductivity (EC) and pH – and the laboratory data for each of the samples collected clearly shows that there was no measurable impact detected in the Edith River.
Below are two maps that show the locations where the samples were collected and the results.
Click on each image to see larger version.