2019-07-17_REVISION - C1981035

• Permit No: C1981035
• IBM Index Class Name: Revision
• Doc Date: 7/17/2019
• Doc Name: Adequacy Review #2
• From: DRMS
• To: GCC Energy, LLC
• Type & Sequence: TR27
• Email Name: RDZ
• Media Type: D
• Archive: No

Tom Bird,GCC Energy, LLC
Page 2of3
17 July 2019
c. Additionally, it appears that the underdrain in the Trautner report is designed as an
independent underdrain. In TR-27,the underdrain proposed is an extension to the existing
underdrain of the Refuse Pile. Please explain if the design in TR-27 takes into account
the addition of potential groundwater flow from the current underdrain of the Refuse
Pile into the Lower Refuse Pile.
Appendix 11
7. No additional response required.
8. In "Revision 5,"please add a discussion on the ponds,including the comment on how the
contributing area will be decreased with the new plan in TR-27, and explain how no other
changes caused by the TR-27 proposal to the watershed would impact the volume of water
and sediment flowing into the two ponds. In particular,the new design for the refuse pile is
very steep at the north end of the pile; how will this impact the sediment load to the ponds
and the frequency of cleaning the ponds?
9. No additional response required.
10. No additional response required.
11. No additional response required.
12. The Division has the following follow-up comments.
a. In Section 2.05.6(page 1),GCC says that a vegetated channel will hold up to a 10-
year storm (will not erode). Where does "10-year" come from? The channels are
designed for 100-year storm. Can GCC site an applicable rule?
b. In the "Revision 5" document, GCC should provide a discussion of Reach 1, namely
how the newly configured channel will be armored sufficiently for the reach where
the new channel slopes down to the existing channel(slope of approximately 30%).
c. In the "Revision 5" document,Item#2 mentions an armored stilling basin. This
should be shown on the Drainage Plan Schematic.
d. In the "Revision 5" document, GCC should discuss how erosion control and
sediment control practices will be used on the steep slopes of the lower Refuse Pile.
e. In the "Revision 5" document,Item#4 should discuss the sizes and materials (CMP,
RCP, or other) of the culverts.
f. In the "Revision 5" document,the last item(#6) should indicate that flows from
both Reach 7 and Reach 10 flow into Reach 8.
g. The Drainage Plan Schematic legend should include all features on the map. For
example, GCC should add a legend item for the curved line with triangles that is
southwest of the Burnwell structures.
h. SEDCAD model for Clear Water
i. In"Revision 5,"please add a map showing SWS areas.
ii. Please check the design and calculations for Structure 1 of the West Clear
Water Ditch model. For the discharge(23.19 cfs) and area(0.83 sq ft)in the
SEDCAD run,the average velocity would be approximately 28 feet per
second,which is very high and could lead to instability of the riprap.
iii. For Structure 2 of the West Clear Water Ditch model,larger riprap than in
the SEDCAD model(D50=9 inches)is advised, given the channel steepness
and average flow velocity of approximately 13 ft/s.