APPCOR10278

• Permit No: C1994082
• IBM Index Class Name: Application Correspondence
• Doc Date: 3/14/1995
• Doc Name: RESPONSE TO DMG 1/20/95 AND 1/24/95 ADEQUACY LETTERS
• From: SCC
• To: DMG
• Media Type: D
• Archive: No

Yoast Mine area. The k factor and hydrologic grouping values
were derived from information preseni:ed in Tab 9. •
34. If SCC were to make any changes to the mining sequence or
total disturbance areas, appropriate revisions will be
submitted to the Division, provided they have an affect on the
sediment comtrol structures.
35. Addendums 1 and 2 are identical. Therefore, Addendum 2 will
be eliminated. The title to Addendum 1 has been revised to
include ditches and culverts.
36. This question has not yet been addressed.
37. Material in the ponding area of the pond has a high natural
moisture content, making this material hard to work with. It
would first have to be dried to accept:able limits prior to use
as embankment material. The statements on using this material
have been deleted from the design narrative.
38a. SCC revised +;.he SEDCAD runs incorporz:ting CDMG's CN values of
85 for the spoil area and 52 for the undisturbed area. This
did result i.n a much higher runoff and sediment yield from
SWS2 (as shown in CDMG's map). There were two soil types (2D,
2E) and (12C, 12D) that should have a D type hydrologic
grouping in this area. This may ~~hange the curve number
slightly in the spoil area. Rather than change this CN, SCC •
used the CN of 85 suggested by CDMG. SCC also used the higher
precipitation values suggested by CDMG.
Entry of the above changes should provide a pond, and
associated :structure design, that is on the conservative
(high) side. As CDMG is aware, this assumes a worst case
situation; t:he mining area being totally disturbed at one
time. The SEDCAD model, in this case, does not take into
account that some of the runoff does not make it to the pond.
Much of the runoff will get trapped in the spoil area and
either get soaked into the spoil or end up in the pit.
Basin trap efficiency fell below 100 percent for the 10-yr,
24-hr storm at both Ponds 10 and 11 using the revised runoff
numbers. This information was discussed with CDMG personnel
on 2/15/94. Per CDMG, as long as i:he value listed as Peak
Settleable Concentration (SEDCAD) was below 0.5 ml/1, the
design met the water quality requirements. Both Ponds 10 and
11 are well below this value.
b. SCC also came to the same conclusion as CDMG that breaking
Watershed 9 up into several subwater~:heds had no impact on the
runoff. Watershed 9 remains the same as the original design.
c. SCC modeled both particle size distributions, those used by
CDMG and SC'C. The end result wa:; that, given all other
parameters remaining the same, it had no effect on the
sediment yield whether the top few particle sizes were thrown •
out or not. SCC used particle siz~a distributions based on
8