Site Description

The Helen Mine is situated in the Mayacmas Mining District near the headwaters of Dry Creek. The mine is the southernmost working of three mercury mines in the area and is primarily a patented claim. However GPS readings taken in August, 2000 show that the mine effluent and lower portal are on BLM land (Image #1).  According to historical records the mine was located about 1860 and was intermittently active up to 1966.  Total production over the life of the mine is estimated at nearly 11,000 flasks.  Total development consists of about 6000 feet of tunnels on three principal levels, much of which is patented.   The site is actively releasing brown effluent onto BLM land and into Dry Creek.  The white precipitate content is uncertain but is seasonably dissolved and washed into the creek.  The main adit, although caved at the portal may be accessible via an open cave about 100 feet south of the portal..        

Environmental Assessment

A GPS survey of the mine features were was undertaken during FY2000. Sampling of storm water flows of the mine effluent, stream water and sediment downstream occurred during FY2001-2. Biota mercury sampling occurred during FY2003. Elevated levels of total and methyl mercury were detected in the calcine mine waste dumps. adjacent to the mine portal.

CERCLA Actions

CERLCA cleanup actions are proposed during the FY2006-13 period, depending upon the BLM AML statewide CERCLA remediation schedule and available funding for priority, impaired watersheds.

Photo 1: Mine effluent from main adit portal located to the left of photo.  The brown sediment extends about 100 feet from the portal where it enters an erosional gully on route to Dry Creek.  The content of the white precipitate has not yet been determined.  During the late summer season, a whitish mineral precipitate forms on the surface of the mine tailings and then is subsequently washed away by winter storm events into Dry Creek, an ephemeral stream tributary of Upper Putah Creek.

Photo 2:  Iron-oxide rich effluent seeping from the toe of the lower mine dump. The material, including the white precipitate is the same as the effluent flowing from the main portal (Photo #1).  Dry Creek is about 300 feet downslope in the upper right of the photo (Image #1). 

Helen Mine Map #1:  Arcview  plot of GPS readings in the Helen Mine area. Note the mine area, the adit portal, and mine effluent and seep are all on BLM-managed lands.