1999-11-15_HYDROLOGY - M1977378 ‎(2)‎

• Permit No: M1977378
• IBM Index Class Name: HYDROLOGY
• Doc Date: 11/15/1999
• Doc Name: Project Completion Insp., Upland Hydrologic Control Project
• From: DMG
• To: CDPHE-WQCD
• Permit Index Doc Type: Hydrology Report
• Media Type: D
• Archive: No

Project Completion Inspection 2 November 11, 1999
Upland Hydrologic Control Project CDPS No. CO-0044768
Consent Decree 94CV5459 DMG File No. M-77-378
rock and soil layer. Construction of the ditch appeared complete, ditch capacity appeared
sufficient to function as designed. Ditch appeared stable, no evidence of slumping,
excessive erosion or sediment deposition. Water was entering the ditch from the outlets
of upland diversions A and B.
A second upland diversion ditch had been constructed along the north and east sides of
the Mayflower Mill and associated access roads. The ditch begins at the topographic rise
which creates a drainage divide near the NE end of Tailings Pond 1 . Drainage on the west
side of the topographic rise is conveyed within the ditch for Tailings Pond 1 , described
above. Drainage for the east side of the topographic rise is conveyed around the
Mayflower Mill facility and access roads and is discharged downslope of the facility to a
talus slope. The upland diversion ditch for the Mayflower Mill facility receives flow from
upland diversion C as well as upland surface runoff. The diversion ditch is an open
channel, lined with heavy black plastic and surfaced with rock and soil layer. Construction
of the ditch appeared complete, ditch capacity appeared sufficient to function as designed.
Ditch and ditch outlet to the talus slope appeared stable, no evidence of slumping,
excessive erosion or sediment deposition. Water was entering the ditch from the outlet of
upland diversion C.
Upland Diversion A is located in an upland drainage and directs shallow subsurface flow
and surface runoff to the upland diversion ditch for Tailings Pond 1 . Diversion A was
constructed within a pre-existing drainage channel and therefore minimized new
disturbances created by culvert installation. Diversion A is a buried 24" diameter culvert,
approximately 700' long. The culvert material is a double walled black plastic pipe, the
outer wall is annular, the inner wall is smooth. Two 48" diameter manholes were set in
the bottom of concrete lined catchment bowls to direct drainage into the culvert inlet.
Uppermost of the two manhole drains was backfilled with rock cover. The manhole covers
safeguard the drop structures and serve as debris guards for the culvert inlet. Water could
be heard entering the culvert. Discharge from the outlet of diversion A appeared
consistent with inflow, little more than a trickle. Large rock were appropriately placed at
the culvert outlet as energy dissipators. Construction of upland diversion A appeared
complete, affected areas had been graded to blend with surrounding topography. Operator
indicated that areas affected by construction had been seeded with reclamation species,
evidence of seeding was observed. Affected areas appeared stable, no evidence of slope
movement or excessive erosion was observed.
Upland Diversion B is located on a talus slope and directs shallow subsurface flow and
surface runoff to the upland diversion ditch for Tailings Pond 1 . Diversion B was
constructed on a talus slope and therefore minimized disturbances to native vegetation
during culvert installation. Diversion B is a buried 24" diameter culvert, approximately
400' long. The culvert material is a double walled black plastic pipe, the outer wall is
annular, the inner wall is smooth. Two 48" diameter manholes were set in the bottom of
concrete lined catchment bowls to direct drainage into the culvert inlet. Uppermost of the