HomeMy WebLinkAboutWPO202000042 Correspondence 2020-10-26® ROUDABUSH, GALE & ASSOC., Inc.
A PROFESSIONALCORPORATION Serving Virginia Since 1956
October 23, 2020
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902-4596
ATTN:John Anderson
RE: WP0202000042 2435 Gobbler's Ridge Pond VSMP Plan Review
John,
Please see our responses to your latest review comments of WP0202000042 Gobbler's Ridge
VSMP below.
A. Stormwater Pollution Prevention Plan (SWPPP)
The SWPPP content requirements can be found in County Code section 17-405. A SWPPP must
contain (1) a PPP, (2) an ESCP, (3) a SWMP, and (4) any TMDL measures necessary.
1. Submit 2019 VPDES Permit Registration, Sec. 1, SWPPP. Link, below.
Response: Please see VPDES Permit Registration included with this submission
(also included in SWPPP)
2. Revise SWPPP (12-section county template). Note: LOD Z1.43 Ac. Link, below.
a. Revise SWPPP title pg: Identify project, preparer, date, include ref to plan title (2435
Gobblers Ridge Pond), and WPO202000042.
Response: The SWPPP title is revised with this submission.
b. Revise SWPPP Sec. 1, 2, 3 of SWPPP. Project is not exempt. Please call if any questions.
Response: Section 1, 2, and 3 are revised with this submission.
c. Provide update to Sec. 4 of SWPPP, once all ESC Plan comments addressed.
Response: The updated ESC plan within the SWPPP is updated.
SUBJ: WP0202000042 2435 Gobbler's Ridge 1' Revision Comment Response
d. Provide Sec. 5, SWM Plan.
Response: The SWM plan is now included within the SWPPP.
e. Sec. 6.A.: Provide I F X 17" PPP Exhibit.
Response: An 11x17 PPP Exhibit is included in section 6A of the updated SWPPP.
f. Sec. 6.E. — provide complete contact information. Only a name is listed. Provide address, tele.,
email, etc. (Note: Sec. 8 lists tel. # ; if this is tele.# of C. W. Dabney, list this tel.4 at 6.E.)
Response: Section 6E is updated with complete contact information for C.W. Dabney.
g. Sec. 9 /SIGNED CERTIFICATION: Sign certification.
Response: The certification in section 9 is now signed.
h. Sec. 11: Include 2019 VPDES CGP in SWPPP, since CGP applicable.
Response: The 2019 VPDES CGP (26 Pages) is now included in the SWPPP.
B. Pollution Prevention Plan (PPP) — Also, item 2.e. above.
The PPP content requirements can be found in County Code section 17-404.
3. Provide I I" X 17" PPP Exhibit to include:
a. Rain gauge.
b. On -site fuel storage for construction grading equipment, if proposed (defer to design
judgement). If shown, provide secondary (berm) containment with impermeable liner with
volume sufficient to accommodate volume of stored fuel + 10-yr. storm event (vol.) X 1.1.
c. Stone construction entrance.
Ex. pond dewatering device.
e. Porta-john.
Response: 11x17 PPP Exhibit is included in the SWPPP and includes all items requested in
comments 3a: e. Please note that there will be no fuel storage for the project on -site.
SUBJ: WP0202000042 2435 Gobbler's Ridge 1' Revision Comment Response
C. Stormwater Management Plan (SWMP)
Project does not qualify for any VSMP exemption listed at Sec. 17-303, A.-H., and is
subject to the VSMP (Sec. 17-302.A.). This item discussed with and confirmed by
County Engineer.
Response: Acknowledged.
2. Revise sheet 1 plan title to read VSMP plan for 2435 Gobblers Ridge Pond. Include
reference to WPO202000042.
Response: The title sheet is updated with the above information.
Submit VSMP Application with appropriate fee. The fee for small construction activity
or land clearing that is equal to or greater than 1 acre and less than 5 acres is $2,700 (17-
208). Note: this land -disturbance occurs on a single-family parcel, but land disturbance
does not involve construction of a sole single-family detached dwelling. Project is
ineligible for Agreement in lieu of a SWM Plan.
Response: The appropriate fee is included with this submission.
4. $300 received for VESCP may be applied to the VSMP permit fee.
Response: Acknowledged.
5. Since half the $2,700 fee is due with initial application, balance pending is $1,035.
Engineering will notify Intake staff of this circumstance.
Response: Acknowledged.
6. This project requires and will receive a 2019 CGP.
Response: Acknowledged.
7. Provide required VSMP stormwater quantity and quality compliance calculations. Submit
VaRRM.xls.
Response: See quantity and quality analysis on sheet 7 of the attached VSMP.
SUBJ: WP0202000042 2435 Gobbler's Ridge I' Revision Comment Response
8. Note: Engineering has considered stormwater quality (sample VaRRM.x1S, Attached) and
quantity.
a. SWM water quantity control should be relatively straight -forward: post -developed
sheet flow that meets 9VAC25-870-66.D. Engineering accepts this provided plan demonstrates
rill erosion unlikely. Also, ESCP review item 47, below.
Response: Acknowledged and thank you for the provided VRRM. Please see analysis on
sheet 7 that shows rill erosion unlikely due to intentional grading patterns.
b. SWM water quality phosphorus reduction requirement is -0.09 lb. ( $0) if use re -development
worksheet (D soils, accurate for site), and 0.2 Ac. impervious ( pre -developed; pond surface);
that is, no SWM facility or water quality compliance measures required. Engineering accepts
this.
Response: See updated VRRM excel file included with this submission. Note the limits of
disturbance is expanded to allow proper room for grading operations.
c. Recommend include USDA Websoil survey data with plan re -submittal (data attached).
Response: USDA web soil survey data is included within the erosion control narrative. The
soils data map is included on existing conditions.
D. Erosion and Sediment Control Plan (ESCP)
Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP.
This plan is disapproved for reasons listed, below. The erosion control plan content requirements
can be found in County Code section 17-402.
Sheet 3
1. Sediment Trap
a. ST Calculation table provides dimensions, which is helpful. Please also include ST
floor dimension in plan view.
Response: ST floor dimensions have been added to the plan view on sheet 3.
b. Revise contours at ST weir, consistent with ST Calc. table.
Response: ST contours have been updated to be consistent with the calculation table.
c. Provide dimension label for weir (L X W) and riprap downslope of weir ( L x W X D).
Response: Dimension labels are now shown for the sediment trap outlet weir. No riprap is
proposed downslope of the sediment trap weir.
SUBJ: WP0202000042 2435 Gobbler's Ridge 1' Revision Comment Response
2. Provide TSD (VESCH 3.15, to be abandoned once grading complete) to convey slope
runoff since proposed grading eliminates existing permanent drainage channel. During
construction, concentrated runoff conveyance, top to toe of slope, is required. This may outlet at
the temporary ST and be covered in place with final stage of construction if inlet at top of slope
is permanently closed. Albemarle is not directing design, but requests design consider and
accommodate loss of existing permanent drainage feature that presently feeds the pond. Post -
construction design proposes sheet runoff. It is grading phase operations that require temporary
conveyance of storm runoff across and down the site, else periodic storm runoff may erode
newly graded slopes.
Response: A TSD is proposed for erosion control phase I until final grading is achieved
and slopes are stabilized.
3. Sheet 3, or 4: Provide topsoil note describing design intent (topsoil limits, depth) such
that final graded slopes support permanent vegetation. Import does not need to be entirely
topsoil, but suitable fill. Final graded slopes require topsoil to support permanent vegetation, and
limit potential for downslope off -site impacts.
Response: A note has been added on Sheet 4 to ensure that the top layer of fill is 24" of
topsoil to ensure vegetation establishment in accordance with VESCH specification 3.30
Topsoiling.
4. If pond floor sediment or sediment trap floor sediment is to be wasted on -site, discuss
and show areas this saturated material will be wasted, or where and how it will be placed (on
native, poor hydric, D soils) to drain sufficiently to support overlying layers of soil, without
failure.
Response: The pond floor sediment is to be dried and spread with the topsoil layer in order
to ensure the soil is not used in a loadbearing manner. A note has been added to sheet 3 to
this effect.
Sheet 4
5. Show proposed contours 384' 388'.
Response: There is no proposed 384 contour on the final grading plan. The existing 388'
that represents the top of the downslope side of the dam is now shown as proposed in
the final grading plan (ESC phase II). The intent is that when the weir is removed the
grade is restored to existing in that location.
6. Display graphically outlet for water pumped from pond.
Response: See inset detail on sheet 3.
SUBJ: WP0202000042 2435 Gobbler's Ridge 1" Revision Comment Response
a. Evaluate natural channel to receive pond pump water.
Response: See flow rate calculation in same inset referenced above. The contractor
provided a data sheet from the pump he plans to use. The max flow rate of 170gpm is
equivalent to 0.38 cfs. The flow rate is expected to be even lower given the flowpath
through the dewatering bag, modified straw bale pit, and rip rap outlet. Additionally, the
flow rate from the pump is significantly smaller than the existing 1 year peak flow rate to
the same location.
b. Ensure volume and velocity of water thru natural receiving channel will not cause damage or
exceed drainage capacity or contribute to downstream erosion or flooding. Note: Nearly
immediately, pond pump water will discharge to neighboring property.
Response: See note above.
c. Provide downstream and off -site ESC measures, as needed, to ensure even short duration
effects of pumping cause no downstream /off -site erosion.
Response: See measures added on sheet 4 inset detail.
d. Show temporary ESC measures, as needed, in conjunction with a, b, c, above.
Response: See note above.
e. Provide detail for dirt bag, or similar pond pump -water filtering device.
Response: See note above.
f Provide detail for dewatering measure, or measures.
Response: See note above.
g. Silt -laden pond pump -water may not be discharged directly to natural receiving stream
or drainage feature. Provide narrative and propose measures to aid review, and compliance
during construction phase, especially compliance with ESC Min. Std. 19, listed on sheet 5.
Response: See measures proposed on sheet 4.
SUBJ: WP0202000042 2435 Gobbler's Ridge 1' Revision Comment Response
7. Evaluate post -development design storm runoff event. Ensure runoff from proposed
grading is sheet runoff that will not likely cause or develop rill erosion.
Response: See analysis added on sheet 7. Proposed grading encourages sheet run-off.
8. Identify off -site borrow area, if borrow area known.
Response: Off -site borrow area is not currently known. The operator is unable to
identify a borrow area prior to plan approval.
9. Provide ESC plan for off -site borrow area, if required.
Response: A note has been added on sheet 1 that any offsite borrow must come from a
location covered under an approved ESC plan.
10. Sheet 5: Provide brief narrative project description. Identify borrow location.
Recommend estimate volume of import required.
Response: See the expanded project description on sheet 5. The borrow location is not
currently known. An estimated volume of import is provided in the description
(15,000CY).
Please let us know if you have any questions.
Respectfully,
Logan O'Day, EIT
Roudabush, Gale, and Associates