Section 7. MINING WASTES
MODIFICATION OF SEDIMENT CONTROL PONDS
Charles R. Jenkins, Professor
Department of Civil Engineering
West Virginia University
Morgantown, West Virginia 26506
James F. Pankanin, Environmental Engineer
U.S. Environmental Protection Agency
Chicago, Illinois 60604
INTRODUCTION
Sediment ponds are constructed at surface mine sites to prevent undesirable deposition
of silt, sediment and other detritus in any area outside the active mining site. Prior to
1978 in West Virginia, a sediment pond was required to have a minimum capacity to
store 0.125 ac-ft per acre of disturbed area (3048 m3 /ha) in the watershed [ 1 ]. The
sediment pond was to be cleaned out when the sediment accumulation approached 60%
of the design capacity. An Environmental Protection Agency report stated that sediment
control ponds as then designed and constructed were only marginally effective in reducing
suspended solids discharge [2].
Proposed rules for regulating the Surface Mining Control and Reclamation Act of 1977
were published in the Federal Register in September, 1978 [3]. These rules require ponds
to have a sediment storage volume equal to the accumulated sediment volume from the
drainage area to the pond for a minimum of three years or 0.1 ac-ft per acre (2438 m3/ha)
of disturbed area in the watershed. The ponds shall also provide a 24-hr detention time
for the runoff entering the pond from a 10-yr, 24-hr precipitation event. Regulatory
authority may in some instances reduce these requirements slightly. Sediment shall be
removed when the volume accumulates to 60% of the required sediment storage.
Effluent limitations are shown in Table I.
Table I. Effluent Limitations
Average of Daily Values for
Characteristics Maximum Allowable 30 Consecutive Discharge Days
Iron, Total (mg/l) 7.0 3.5
Manganese, Total (mg/l) 4.0 2.0
Total Suspended Solids (mg/l) 70.0 35.0
pH (within range) 6.0-9.0
Sediment ponds work by reducing the velocity of water so that gravitational settling
will clear the water before discharging into receiving streams. Short-circuiting across the
pond will result in a decreased detention time and a lower quality effluent. This is a common problem of sediment ponds.
This study was designed to (1) evaluate the operational efficiency of two similar surface mine sediment ponds during storm flows; (2) consider, build, and install modifications
for each pond; and (3) evaluate performance during storm flows with the modifications
installed to determine the effectiveness of the various modifications.
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