GENERAL31326

• Permit No: C1980005
• IBM Index Class Name: General Documents
• Doc Date: 6/6/1997
• Doc Name: PROPOSED DECISION AND FINDINGS OF COMPLIANCE FOR RN3
• Permit Index Doc Type: FINDINGS
• Media Type: D
• Archive: No

grazing and wildlife utilization of the reclaimed azea. Exhibit 7-7, Surface
Hydrology Map, depict the existing and proposed stock tanks.
C. Sedimentation Ponds
Seneca Coal Company will primarily use sediment ponds to prevent additional
contributions of sediment to streamflow or runoff outside the permit area 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 regazding [he
designs of the ponds and diversions is provided in Tab 7 of the permit application.
Wadge Impoundment (002) 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
area flows into Little Grassy Creek, a tributary of Grassy Creek. A large sediment
pond, the Wadge Impoundment, is located near the mouth of Little Grassy Creek and
controls runoff and sediment from a 2100 acre area of which 860 acres aze to be
disturbed by mining. This pond was permitted as a permanent impoundment, that
has been designed with a large permanent pool of 267 acre-feet. Runoff from the
10-year, 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 [he
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 not provide at least 24
hours detention time, the following finding 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 characteristics 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 discharge from a truck washing facility after the water has been treated. An
increase of total dissolved solids on the order of 1500 mg/I (from 1500 to 3000) was
to