2025-04-09_PERMIT FILE - C1981019 ‎(2)‎

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 4/9/2025
• Section_Exhibit Name: Exhibit 07 Methodologies & Assumptions for Sedimentation Pond Design Evaluations
• Media Type: D
• Archive: No

Exhibit 7 Page 8 Revision Date: 4/9/25
Revision No.: MR-261
adequate freeboard to prevent overtopping were also evaluated. The TR-60 discharge criteria used in the
emergency spillway capacity and freeboard evaluations are as follows:

 Discharge flow basis for emergency spillway capacity evaluation (for a Class B pond):
 100-yr, 6-hr peak flow + 0.12 (PMP, 6-hr peak flow - 100-yr, 6-hr peak flow)
 Discharge flow basis for impoundment freeboard evaluation (for a Class B pond):
 100-yr, 6-hr peak flow + 0.4 (PMP, 6-hr peak flow - 100-yr, 6-hr peak flow)

TABLE 5
IMPOUNDMENT HAZARD ANALYSIS SUMMARY

IMPOUNDMENT

HAZARD
CLASSIFICATION/BASI
S

SPILLWAY
CAPACITY
EVALUATION
BASIS1/RESUL
T

FREEBOARD
EVALUATION
BASIS1/RESULT/
FREEBOARD
Work Area Pond A/Agricultural Land Class B/Ok Class B/Ok/1.55’
Gossard Pond A/Agricultural Land Class B/Ok Class B/Ok/6.46’
Stoker Siding Pond A/Agricultural Land Class B/Ok Class B/Ok/3.64’
Rail Loop Pond A/Agricultural Land Class B/Ok Class B/Ok/1.82’
Prospect Pond B/Proximity to State
Highway 13
Class B/Ok Class B/Ok/0.61’
West Pit Pond A/Agricultural Land Class B/Ok Class B/Ok/2.47’
Section 16 Pond B/Proximity to State
Highway 13
Class B/Ok Class B/Ok/0.96’
East Taylor Pond A/Agricultural Land Class B/Ok Class B/Ok/0.76’
Taylor Pump
Holding Pond
A/Agricultural Land Class B/Ok Class B/Ok/0.91’
Notes: 1 Spillway capacity and freeboard for all ponds were evaluated for a uniform worst-case
hazard classification (Class B)

The results of the WWC impoundment hazard analysis indicate that emergency spillway capacities and
available freeboard for all existing ponds are adequate to affect full compliance with applicable
requirements under the guidelines of TR-60, based on the applicable hazard classifications. Given this
confirmation of compliance, no modifications to the existing emergency spillway structures are required.

5.0 POND DESIGN EVALUATION RESULTS
The supporting SEDCADTM4 analyses and watershed maps are presented as attachments in each of the
individual pond design sections