GENERAL46097

• Permit No: C1980005
• IBM Index Class Name: General Documents
• Doc Date: 12/6/2002
• Doc Name: Proposed Decision & Findings of Compliance for RN4
• Permit Index Doc Type: Findings
• Media Type: D
• Archive: No

extended to January 13, 2003. At this time and until approval of TR-35, all of the
stock ponds are considered to be temporary structures.
C. Sedimentation Ponds
Seneca Coal Company will primarily use sediment ponds to prevent additional
contributions of sediment to streamflow or runoff outside the permit azea due to
mining disturbances. Existing sediment ponds include Wadge Impoundment
(NPDES 002), Northwest Impoundment (NPDES 003), Pond 004 and Pond 008,
PeCoCo Impoundment and Spill Control Pond #2. Information regarding the
designs of the ponds and diversions is provided in Tab 7 of the permit application.
Wadge Impoundment f002) A major portion of the Seneca II Mine is located within
the Grassy Creek basin. Surface runoff originating in the western part of the permit
azea flows into Little Grassy Creek, a tributary of Grassy Creek. A lazge sediment
pond, the Wadge Impoundment, is located near the mouth of Little Grassy Creek and
controls runoff and sediment from a 2100 acre area. This pond was permitted as a
permanent impourdment, that has been designed with a large permanent pool of 267
acre-feet. Runoff from the 10-yeaz, 24-hour design storm is 12 acre-feet.
Information in the permit application demonstrates the pond is an efficient sediment
control structure, although, less than 24 hours of detention is provided given the
principal spillway design. The pond receives inflow from up slope spoils aquifers
which have developed in the old Wadge spoils. Surface runoff detained in the pond
is considered to dilute the concentrations of total dissolved solids (TDS) in spoils
inflow and may serve to improve water quality in general. This pond is in
compliance with the requirements of Rule 4.05.6 and continues to meet National
Pollution Dischazge Elimination System (NPDES) effluent limitations. Since the
pond does notprnvide at least 24 hours detention time, the following"fmding is in
order;
Alternative design criteria have been approved for use in sediment pond design
and/or construction. This decision is based on a thorough analytical demonstration
by a qualified professional engineer that the resulting pond will be as
environmentally sound and structurally stable taking into consideration physical,
climatological and other chazacteristics of the site. (4.05.6(11)).
Northwest Impoundment (003) A second pond is located in the Grassy Creek basin
and serves to control runoff and sediment from the shop and office area. The
Northwest Impoundment was permitted as a permanent impoundment which drains
an area of 30.5 acres and has a permanent pool of 5.1 acre-feet. This pond also
receives dischazge from a truck washing facility after the water has been treated. An
increase of total dissolved solids on the order of 1500 mg/1(from 1500 to 3000) was
observed between 1983 and 1991 in the effluent from this pond. This increase is
attributable to the truck-wash facility. A review of the pond performance indicated a
reduction in the size of the principal spillway to a 6 inch orifice was necessary to
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