1999-02-24_INSPECTION - M1981302

• Permit No: M1981302
• IBM Index Class Name: Inspection
• Doc Date: 2/24/1999
• Doc Name: MINERALS PROGRAM INSPECTION REPORT
• Inspection Date: 2/18/1999
• Media Type: D
• Archive: No

• • (Page 21 •
MINE ID # OF PROSPECTING ID k M-81-302
INSPECTION DATE 2/18/99 INSPECTOR'S INITIALS ACS
OBSERVATIONS
On February 1, 1999, the citizens group Neighbors for a Livable Boulder (NLB) submitted a written
request to the Division of Minerals and Geology (DMG) to conduct an inspection of the Deepe Farm Pit,
Permit No. M-B1-302. In the NLB submittal, concern was expressed about leakage through the Deepe Farm
Pit perimeter levee and development of wetlands at the site. In follow-up correspondence dated
February 16, 1999, NLB requested that DMG address the following list of issues relative to the levee:
1. Criteria for construction of the berm.
2. Was the berm constructed according to regulations?
3. State performance standards for the berm.
9. Particulars of slope, freeboard, seepage, and levee fill.
DMG policy specifies that all written requests for inspection be addressed within 30 days. In
accordance with this policy, the Deepe Farm Pit was inspected on February 18, 1999. The following
individuals were present for the inspection:
• Allen Sorenson and Gregg Squire of the DMG.
• Tom Browning, Water Conservation Board, Floodplain Management Section.
• Ed Smelko, City of Boulder resident.
• Alan Taylor, City of Boulder, Floodplain and Wetlands Coordinator.
• Mike Hart, consultant to Western Mobile Boulder.
The two primary areas of seepage at the toe of the reclaimed gravel pit inslope were inspected. These
seeps are located on the land-side of the levee, and appear to be issuing from the in-situ material
well below the levee fill. The apparent source of the seepage is Dry Creek Ditch No. 2 that is located
at the stream side toe of the levee. The ditch was flowing at the time of the inspection and
apparently flows year round. The areas of seepage on the land side of the levee were observed during
the DMG's 4/13/98 inspection of the Deepe Farm Pit and are described in the report of that inspection,
a copy of which is attached. The seeps were flowing clear at the time of both inspections. Based on
qualitative observation, the seepage rate was greater on 9/13/98 than on 2/18/99. The "secondary
lateral ditch" referenced in the 4/13/98 report has been installed.
Several areas of seepage were observed flowing into the pit at its western perimeter. These seeps do
not appear to be related to flow in irrigation ditches, and are most likely the natural expression of
ground water present beneath the undisturbed pasture to the west of the pit. The South Boulder and
Bear Creek Ditch was not flowing at the time of the inspection.
Wetlands vegetation was observed at all of the seepage areas inspected. Woody vegetation that was
expressing itself had been recently cut down in accordance with good levee maintenance practices.
Overall the levee is well maintained and in excellent condition, as discussed in the memorandum
provided by the Water Conservation Board, a copy of which is attached.
It was discussed at the site among the inspection attendees that public confidence in the stability of
a structure such as the Deepe Farm Pit levee is important, and it was decided thaC the best course of
action to evaluate the effect of the seepage on the stability of the structure is the conduct a piping
analysis. This recommendation is included in the attached Water Conservation Board memo. The DMG
suggests [hat Co evaluate piping potential, flow nets should be developed for the two locations where
seepage has been observed below the levee and hydraulic gradients calculated at the discharge points.
The flow nets should be based on the water surface elevations that would be present during the 100-year
flood. If any exit gradients approaching 1.0 are calculated, then measures Co prevent piping may be
required. (Reference, Freeze and Cherry, Groundwater, 1979, Prentice-Hall, Inc., New Jersey, pages
982-983). As an alternative to piping analysis for the two seepage locations, the operator may chose
to construct a flow net for a composite cross-section considering maximum levee height, maximum gravel
pit depth, and minimum levee width, as this would provide a worst-case analysis for a single flow net.
If the operator chooses to conduct some different type of piping analysis than that recommended here,
the DMG should be contacted for approved of the method of analysis proposed. See P8-1 on the last page