20080067 Ver 3_Staff Comments_20110308

08-0067v3 Alston Pond
AML comments
March 8, 2011
1. There were significant inadequacies in the stormwater management plan. Please be advised
that ALL of the following requests must be provided in your resubmittal or the project will be
returned.
Along with the Supplement Forms, please provide one Required Items Checklist for each
proposed wet detention basin. Please provide ALL information that was omitted in the most
recent submittal. These items include, but are not limited to, a soils report that documents the
level of the seasonal high water table at each proposed BMP (via a soil boring done within the
footprint of each BMP), the boundaries of the drainage areas for the BMPs, the maintenance
access and the boundaries of the drainage easements for the stormwater devices.
3. You must completely fill out each Supplement Form (both Wet Detention and LS-VFS Forms) and
correct all known errors in design.
4. Please provide actual calculations of the average depth. Assuming an average depth is not
sufficient.
5. Please provide actual calculations of the drawdown time. Reporting 2.00 days in each Wet
Detention Basin Supplement Form is not sufficient.
6. Please provide a hardened emergency spillway for each proposed Wet Detention Basin.
7. Please provide specifications for the anti-seep collars on the outlet barrels and please check to
see if one anti-seep collar will be sufficient based on the length of the barrels.
8. The planting plans should show how the different plant species are to be distributed on the
vegetated shelf.
9. You must sign and seal all plan sheets and the calculations booklet.
10. Please provide a minimum of one foot of freeboard for each proposed wet detention basin.
11. The LS-VFS Required Items Checklist states that a plan detail at a scale of 1" = 30' or larger has
been provided but DWQ was unable to find them on Sheet 28.
12. In addition to the above, please address the following issues specifically associated with BMP
#1:
a. It appears that the forebays comprise more than 20% of the overall volume of the wet
detention basin. Please calculate the volumes and adjust as needed.
An LS-VFS is required at the outlet of this device. Please provide an LS-VFS design, a
Supplement Form and a Required Items Checklist with all required items. Please be sure
that the LS-VFS is designed in accordance with Chapter 8 of the BMP Manual.
13. In addition to the above, please address the following issues specifically associated with BMP #2
and its associated level spreader:
a. A level spreader may not be used adjacent to the riparian buffer in the proposed
location because the slope exceeds five percent.
b. An LS-VFS is required at the outlet of this device. Please provide an LS-VFS design, a
Supplement Form and a Required Items Checklist with all required items. Please be sure
that the LS-VFS is designed in accordance with Chapter 8 of the BMP Manual.
14. In addition to the above, please address with following issues specifically associated with BMP
#3:
a. The flow path for this device is inadequate, particularly for the stormwater entering via
FES 300. Please redesign this device to provide a flow path of at least 3:1.
An LS-VFS is required at the outlet of this device. Please provide an LS-VFS design, a
Supplement Form and a Required Items Checklist with all required items. Please be sure
that the LS-VFS is designed in accordance with Chapter 8 of the BMP Manual.