PERMFILE61006

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 9/2/2004
• Section_Exhibit Name: Exhibit 07 Letters on Ponds from WWC Engineering
• Media Type: D
• Archive: No

Mc Crellin Scott
July 30, 2002
Page 2 of 3
5. Section 16 Watershed SEDCAD 4 Model Input. These sheets provide a summary
of the input data into the new SEDCAD 4 model of the Section 16 watershed.
6. CN Breakdown. This color figure shows the curve number breakdown for the
watershed. Dark green is undisturbed (CN=47), green is reclaimed 3+ year growth
(CN=56), blue is reclaimed 1 to 2 year growth (CN=61), and red is reclaimed
topsoiled and seeded (CN=86). This figure represents the watershed immediately
after the pit is backfilled and is considered the worst-rase scenario. Prior to that time.
the pit intercepts a large portion of the watershed. Curve numbers were obtained
from "Methodologies and Assumptions for Sedimentation Pond Evaluations" of the
approved permit (Volume 2C).
7. Section 16 Sedimentation Pond Summary. This table provides a quick reference to
the differences between the current model of the Section 16 watershed and earlier
versions. The summary sheet indicates that although the drainage area increased 65.3
acres between 1998 and 2002, discharge parameters for the ]0-year and 25-year
storms generally decreased. The pond summary sheet also predicts the Section 16
Pond has 2.5 years of sediment storage.
8. SEDCAD 4, Section 16 10-year, 24-hour Model. This is the printout of the ] 0-year,
24-hour design storm. This model demonstrates that using the design storm the
Section 16 Pond is in compliance with an effluent discharge of less than 0.5 ml/1
settleable solids and no discharge in the emergency spillway.
[.
9. SEDCAD 4, Section 16 25-year, 24 hour Model. The spillway is adequate.
10. SEDCAD 4, Section 16 100-year, 24-hour Model. The spillway is adequate.
1 1. SEDCAD 4, Section 16 TR-60 Emergency Spilhvay Evaluation. The Section 16
Pond was assumed to be a Class B pond for a TR-60 emergency Spilhvay evaluation.
The rainfall amount used for this model was the 100-year. 6-hour amount plus 0.12
times the difference between the probable maximum 6-hour amount and the 100-year.
6-hour amount. The model shows the Spilhvay is adequate to meet the TR-60 criteria
for a Class B structure. The probable maximum precipitation was determined from
HMR 49.
13. SEDCAD 4, Section 16 TR-60 Emergency Spilhvay Freeboard Evaluation. The
Section 16 Pond was assumed to be a Class B pond for a TR-60 emer~~enc~ s'pilh~a~
freeboard evahiatiai. The freeboard is adequate to withstand the runoff from the ] 00-
~~ear. 6-hour rainfall plus 0.4 times the difference between the PivIP-6-hour and the
W
WC Engineering