From 1985 to 1990 WestGold managed a marine placer mining operation with substantial documentation concerning its submarine failings disposal (STD) system. For 5 years the operation involved the use of a floating bucket-ladder dredge with an integrated, gravity-based treatment plant to extract free particulate gold fi om the seabed gravels. Three-quarters of the throughput was disposed of at 1.5 m below sea level through two pipes, each of 0.51-m diameter. The system's design resulted from considerable trial and error and modeling studies to achieve regulated seawater conditions. The information is publicly available as a result of a very open permitting and operating process. The mining permit specified waste discharge controls and, environmental impact limits for topics of local concern: the dredge's effluents, the red king crab population (an important fishery resource), seawater turbidity, and bioaccumulation of trace metals, especially mercury (a remnant of prior beach mining). The impact on crab stock was negligible to the point that monitoring was scheduled to be abandoned in 1991 (but mining operations ceased in September 1990). An impoverished benthos remained for at least 2-3 years after dredging, with sandy areas able to recolonize to a highly variable fauna within 3-4 years. Cobble and repeatedly dredged areas recolonize more slowly. An extreme storm in 1992 has also affected the seabed.
