20100063 Ver 1_Staff Comments_20100512

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DWQ#
Triaged By:
Reviewer 1
Reviewer 2
Reviewer 3
Triage Comment Sheet
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SATriage FormsUriage Issue Sheet.doc
PLEASE PRINT CLEARLY
Date: I
Date: 1
Date:
10-0063 Franklin County HUB
AML Comments
May 12, 2010
1. The DWQ does not accept the proposed method for addressing the stormwater management
plan as stated in Mr. Hammerbacher's undated letter: limiting the overall development to a
maximum impervious surface area of less than 24 percent. As was discussed in the meeting
held on February 23, 2010, the DWQ will allow the development to be limited to less than 24
percent on a lot-by-lot basis with vegetated conveyances only (and no stormwater collection
systems) as a conceptual method of addressing the stormwater management. As the lots are
developed, the site plans for the lots, a Low Density Supplement Form, and a Diffuse Flow Plan
will need to be provided to the DWQ for review and approval.
2. All DF plan sheets must show one foot topographic lines throughout the entire sheet to assist
the DWQ with its review.
3. At all outlets, drainage from the both sides of the road must be conveyed to a BMP or diffuse
flow device.
4. The drainage areas of outlets #1, #4, #8 and #9 include large areas of currently undeveloped
land. Per the BMP Manual, all BMPs must be design for future built-out conditions. Please
either redesign the BMPs that serve these drainage areas to handle the expected future built-
out condition or propose another workable solution. These BMPs will need to be protected
from sediment during the construction process.
5. At outlet #3, please provide a level spreader to diffuse the stormwater runoff from both sides of
the road from stations 21+30 to 24+00.
6. At outlet #4, please move the 24" RCP further downslope to convey a greater portion of the
roadway drainage from the east side of the road to the bioretention area (this will remove most
of the flow from outlet #5). Please adjust the design of the bioretention area accordingly.
7. At outlet #7, the flow bypass structure will pass the drainage through the vegetated filter strip,
which is not allowed per the BMP Manual.
8. For the 18" RCP at station 49+35, please provide an appropriate diffuse flow device.
9. Outlets #8 and #9 discharge too far away from a riparian buffer to prevent flow reconcentration
before the stormwater reaches the receiving stream. Please redesign such that flow will be
discharged adjacent to a riparian buffer through an appropriate diffuse flow device.
10. Please address the following design issues with the bioretention cells:
a. Appropriate pretreatment devices must be included.
b. A detail with elevations for the outlet weirs must be included.
c. A planting plan for the sod that specifies the species that will be used, the source, and
the fertilizer and watering requirements must be provided.
d. A soils test that includes borings within the footprints of the proposed bioretention
areas to document the level of the Seasonal High Water Table must be provided.
e. A calculation of the drawdown time for each cell must be provided.
f. Clean-out pipe locations must be shown.
g. The P-value for the media must be specified.
h. All operation and maintenance plans must be signed and notarized.