HomeMy WebLinkAboutWPO202000037 Correspondence 2020-09-22SHIMP ENGINEERING, P.C.
Design Focused Engineering
September 21, 2020
John Anderson, PE
County of Albemarle
Department of Community Development
401 McIntire Road, North Wing
Charlottesville, Virginia 22902
RE: Response Letter #1 for WP0202000037 Galaxie Farm VSMP
Dear John,
Thank you for your review of the Road Plans for Galaxie Farm Subdivision. This letter contains
responses to County comments dated August 18, 2020. Our responses are as follows:
A. Stormwater Pollution Prevention Plan (SWPPP)
SWPPP: Provide. Please use SWPPP template, link:
https://www.albemarle.org/home/showdocument?id= 166.
SWPPP provided.
B. Pollution Prevention Plan (PPP)
1. Provide PPP Exhibit (SWPPP Sec. 6A) that identifies preliminary location of:
a. Rain gauge
b. Portable sanitary facilities
c. Covered non -hazardous solid waste dumpster
d. Concrete wash -out draining to trapping device
e. Paved construction entrance w/ spray wash
f. Paint /Stucco /Solvent storage
g. Lined (10ml) on -site fuel storage containment sized for fuel volume + 10-yr storm event x
1.1
These items are included in the PPP.
C. Stormwater Management Plan (SWMP)
1. Any Forest and Open Space used in the VRRM worksheet as a Post -Development land cover will
need to be shown on the plans and labelled as 'SWM Forest and Open Space'. The following note
will need to be placed on the plan: "The SWM Forest and Open Space Easement is subject to the
guidance set forth by DEQ in the Virginia Stormwater Management Program. The areas will
remain undisturbed in a natural, vegetated state, except for activities as approved by the local
program authority, such as forest management, control of invasive species, replanting and
revegetating, passive recreation (e.g., trails), and limited bush hogging to maintain desired
vegetative community (but no more than four times a year)."
Note added to cover sheet.
912 E. High Sr. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com
Note to reviewer. there were 2 comments labeled as "l. "— in this response I changed the
second "l."to "2."for easier tracking.
2. Pg. 1 and 2 of SWM calculation packet reference design intent to restore degraded sections of
Cow Branch to comply with 9VAC25-870-66(B) without submitting design for stream
restoration. Plan appears to lack any referential design data for riffle /run sections, sinuosity,
stream bed, analysis of existing stream data, or plan /profile information for proposed revised
stream centerline or any in -stream structures required to effect natural stream restoration.
Albemarle has direct experience contracting with design and construction firms to restore
degraded streams, and anticipates revised SWM plan that furnishes requisite natural stream
design methodologies. Note: stream bank plantings alone are not natural stream restoration. FES
[Water Resources will be invited to review and comment on natural stream restoration elements
of design. Note on sheet C5: `Restore channel between culverts B and G per natural design
standards in accordance with 9VAC25-870-66-B(2)' is a statement that references, requires and
depends on design.
The storm system outfall location has been changed. This is due to several reasons,
primarily being that a revised routing which changes the location of POA 1 to be at the
current point where local runoff hits Cow Branch is easily achievable without having to
perform channel restoration and without major revision to the subdivision design. So for
the current design, no restoration is proposed, and all references to this have been removed
from the plans.
3. Additional comments possible, relative to item 2, above.
Acknowledged
4. Revise per (related) preliminary plat or road plan review comments.
All changes related to Road Plan & Prelim. Plat review comments are included in this
submittal.
5. Remove all portions of Lots 57, 58, 59 from 100' stream buffer (Also: Engineering preliminary
plat and road plan review comments).
All portions of Lots 57-59 removed from stream buffer (this had happened with Road Plan
submittal 2).
6. C5, CT Show all portions of property. SSW corner of development does not appear to be visible
on these, and perhaps other sheets. A match -line inset of developed areas not yet shown is an
acceptable approach.
Matchline inset has been added to show this area.
7. C19
a. Show multiple inlets to single structure, graphically; for example:
i. Sir. E6
ii. Sir. E7
Multiple inlets to single structure now shown graphically.
b. Label MHs with 4' vertical interval between INV IN and MH floor to receive 1/2" steel
slab.
1/2" Steel plate was required for E7 and is now added to profile.
c. Label Sir. requiring VDOT SL-1 (safety slab; lat. >12').
SL-1 was required for E7 and E7A and is now added to profile.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
8. Revise Runoff Quality Narrative (p. 2 calc. packet) to reflect post -developed 2.80 Ac. Forest
/Open space land cover condition (p. 84). Also:
a. Final plat must include metes and bounds that establish 2.80 Ac. forest /open space
easement
Noted. We have already hired Roger W. Ray & Associates to complete the final
subdivision plat, they will prepare this using our AutoCAD tinework as well as Road &
VSMP plans.
b. Revise 0.58 Ac. SWM Forest /open space easement to exclude a portion proposed FOS
easement immediately east of sidewalk, and Lot 65. Galaxie Farm HOA, owner of Lot
65, and maintenance crews cannot be expected to understand, appreciate or abide limits
on maintenance of FOS area proposed to approach within F of sidewalk. Engineering
cannot approve west boundary of 0.58 Ac. FOS area, until revised to allow reasonable
buffer for normal subdivision maintenance of open space. In other words, HOA will bush
hog areas adjacent to sidewalk more than 4 times per year; and will likely maintain areas
within 25' of sidewalk in lawn or turf condition. Revise, and adjust VRRM and on -site
SWM design and nutrient credit purchase proposals, as needed.
Noted. Easement shifted 5' away from both ROW adjacent to sidewalk and from Lot
65.5' gap between these areas will provide an adequate buffer for regular lawn
maintenance - this is plenty of width for an industrial riding law tmover to pass in a
stripe alongside this area. Anecdotally, having worked in landscaping firms for similar
subdivisions in my youth, in my experience landscapers gladly accept limits to the extent
of their service area - since maintenance is contractual and not hourly. A 25' wide
buffer area is not necessary - as the maintenance crews have no desire to do more work
than is required. This revision has reduced the FOS easement by 0.02 acres - this has
been updated in the VRRM spreadsheet and throughout the VSMP plans.
9. VSMP Plan SWM Calculation Packet
a. Pg. 1 -Revise ref. to POA A to POA 1, consistent with terminology elsewhere in packet.
POA A corrected to reference POA 1.
b. Pg. 4 - 8 appear to be section dividers. Please align dividers with corresponding packet
contents. Relocate divider pages to sections of the calculation packet that follow /present
listed information. Otherwise, packet sections are indistinguishable with data difficult to
locate, trace, or review.
This was my error in creating the PDF and has been corrected - dividers should have
been placed at proper sections throughout packet. Now corrected.
c. Pg. 12 -Revise POA 2 label text color to black /similar, so readable.
POA 2 label revised for readability.
Cl. Pg. 13 v. Pg. 85: It is difficult to reconcile table values (p. 13) listing on- /offsite turf
/impervious areas that rout to BMP 1 (via Str. F2) with VRMM.xls 4.60 Ac. /1.60 Ac.
turf /impervious area values (pg. 85, DA A) that route to Mfr. Treatment. Please clarify.
Video -call may be helpful.
Noted, this was not well detailed. This has been revisited and clarified.
One note - after additional review of upstream areas - we found that the Albemarle
Health & Rehabilitation Center (noted in the packet as MFA @ Mill Creek) drains into
a biotilter, which drains into the Galaxie Stormtech BMP. In -2015, Shimp Engineering
had completed the site plan and as-builts for the MFA @ Mill Creek design. Thus, to
most accurately account for that drainage area, we have imported the old HydroCAD
design for MFA which includes this offsite biofdter into our Predev and Postdev SWM
analysis. In reviewing this old design, we found that the MFA biofdter provides a 65%
nutrient removal. So to account for this treatment, we only accounted for the remaining
untreated nutrient load in the VRRM spreadsheet. This was the difference in total area
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shimp-engineering.rom
(100%-65%=35%): so the equivalent of 35% of the MFA site area is untreated area
which could be claimed as new treatable area in the VRRM spreadsheet. The physical
design of the BMP still incorporates the full MFA site area (refer to HydroCAD
modelling) — but we have now ensured this BMP does not "double -dip" nutrient
removal. We also confirmed that there are no other upstream BMP's which drain into
the Galaxie Stormtech BMP. Thus, the VRRM spreadsheet now accurately represents
the treatment provided by the new BMP.
e. Pg. 81: this table is difficult to evaluate; please:
i. PDA 3 (Entire site runoff) 10-year Q pre/post <10cfs, while POA 1 and PDA 2
onsite runoff 10-year Q pre/post are orders of magnitude higher. Please clarify.
Clarified with narrative.
ii. For every Q 1-yr, 10-yr value in any table on pg.-81, please list corresponding
HydroCAD letter descriptor and pg. #. Additional comments possible, once
correlation provided. Albemarle commends sophistication, elegance, detail, and
accuracy of design, but cannot trace it with ease to the point we are able (yet) to
confirm compliance with 9VAC25-870-66.
Notation has been clarified.
iii. Section of Cow branch between POA 1 and PDA 2 proposed to be restored
assumes certain channel capacity /ability to absorb additional Q 1-year post -
developed flow (12.00cfs). Provide natural method stream design for this section
of Cow Branch that proves the point, computationally.
Design has been revised so that this is now not needed.
iv. Storm pipe capacity (LD-229): Ensure flow does not exceed stone pipe capacity.
Also, please ref. Engineering preliminary plat and road plan review comments re.
pipe capacity.
Noted. This has been accomplished with recent revisions.
10. C5 includes label `slopes surveyed <25%'. Submit survey for Engineering review.
All Preserved Slopes disturbance removed.
It. Revise grayscale text across all plan sheets to print black, rather than grayscale. It is difficult to
review and recognize labels, notes, dimensions, etc.
Gryscale teat fixed.
12. Revise C8 and C20 , and elsewhere as needed, StormTech stone invert elevations for consistency;
for example, bottom of stone is given in labels, notes or table on these sheets as: 474.00, 474.75,
475.00.
Consistent and final BMP design has now been provided.
13. C20
a. Revise to resolve weir /stair 2 conflict.
Revised to provide adequate clearance for personnel access. For greater benefit to public
safety, a single manhole lid has been provided with stair that splits to both sides of the
concrete weir. See updated details. Since the manhole base is 7' diameter, there will be
adequate space.
b. Detail 3: show 6" solid PVC underdrain to Sir. E6 in plan view (C7) and in pipe profile, C19.
Design revised to route 6" PVC into Str. E6Z after weir. 6" PVC shown in details and
profiles. Main BMP outlet profile (E6-E6Z) copied onto C20 for ease of reference.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
c. Supplement Stormtech BMP profile with SWM facility overall L x W dimensions in plan
views (to aid review, construction inspection, As -built review, and bond estimate -reduction -
release).
Noted, dimensions added to plan view. Section detail added to sheet. Additional Str. E6Z
details added for additional review, manufacturing, and construction clarity.
d. Weir E3 details:
i. Label weir plate thickness. If weir plat is precast, indicate with label.
Noted. Weir is a 4" precast, as now noted on plans.
ii. Provide 18" x 30" trash rack detail.
Trash Rack Removed. Rationale:
1. A trash rack is unnecessary for an opening this large — as debris large enough to
obscure or clog this orifice is unlikely to float, and unlikely to enter the BMP anyway.
2. With the exception of large storms, most debris will be intentionally caught in the
Isolator Row (that is its function). Regular debris is not anticipated around the
weir/orifice.
3. Even with debris, a trash rack would cause more of a maintenance burden, as it
could hinder debris such as grass clippings, leaves, small branches from passing
through this orifice, and trap it in the manhole whereas without a trash rack it could
pass through. The above mentioned debris would not prevent a downstream nuisance,
as the larger downstream storm sewer has more cross sectional area than the orifice.
4. Additional space for maintenance activity in the manhole will provide better benefit
to the function of the BMP than a trash rack.
Thus, these considerations dictate that trash rack be removed from this orifice.
iii. Resolve ladder /trash rack conflicts, if any.
Ladder/trash rack conflicts removed. See response to d.ii, above.
iv. Labels ref. E7Z and E7, which is confusing. Revise to reference single structure.
Erroneous structure labels have been corrected — these details are for E6Z.
14. This item does not request revision but notes that USGS StreamStats peak flow (a regression
methodology) predicts significantly higher peak flow than the Southern Piedmont Rural
Regression Equation methodology referenced in the calculation packet (Link:
https:Hstreamstats.usgs.gov/ss/ ) An online pipe capacity calculator appears to indicate dbl. line
culverts A and B have capacity for peak flow predicted by USGS StreamStats. Were this not the
case, review would request design revision. (IMAGES OMMITED FROM RESPONSE)
Noted, the USGS StreamStats website is a useful resource, we appreciate you sharing it.
Since Southern Piedmont Rural Regression Method is a standard accepted by VDOT for
computing peak runoff, and since it produces similar computation results as the HydroCAD
peak flow, (added to packet) we will not replace the contents of the packet, but appreciate
the additional redundancy in calculation.
D. Erosion and Sediment Control Plan (ESCP)
1. CIO-C13 a. Revise LOD to show no disturbance within stream buffer, except minimal grading
needed to construct stream crossings ( x 2) or to install drainage structures, or pipes. Disturbance
within stream buffer is constrained by ordinance, and LOD shown appears to exceed minimal
required disturbance within the stream buffer.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
LOD slightly revised to be as small as possible within the stream buffer area. LOD may
appear excessive on some sheets due to the disturbance required to remove the existing
Galaxie Farm Lane pavement, as well as to allow enough room to install Cow Brainch
culverts & Rip -rap. The best graphical description which dictates the LOD required is
shown on C10 — Phase 1B.
2. C5 or C7: On either sheet, dimension riprap at all pipe outfalls (L x W x D). Labels are helpful,
but additional detail is needed for review, bond estimate, construction inspection, etc.
Dimensions added to detail on C15.
3. C7, C8 Provide additional proposed contour labels.
Additional contour labels added.
4. Wherever proposed lot grading falls toward a street (Road B 1 or D, for example) provide
collection behind curbing (yard inlets, for example) to convey runoff into piped storm
conveyance. As -built grading does not admit lot runoff to cross back of curb to gutter. Recall, for
example, multiple low areas behind curb during recent bond inspection at Riverside Village.
Design is theoretical, but for cross -lot runoff to actually reach in -street storm lines, provision
must be made for runoff to cross beneath curb to reach the in -street system. Note: Pg. 13 of Cale.
packet makes clear that offsite runoff (via multiple TOC pathways /Str. F2) reaches BMP 1.
Design must ensure these runoff pathways exist (as designed) in the post -developed (As -built)
condition.
We appreciate Engineering's concern for ensuring the goals of the plan translate to
effectiveness in the field, however, if poor grading or unfinished lot delivery causes issues
that prevent runoff from following plan design, these items must be corrected in the field. If
as -built inspections require regrading to achieve design objectives, then that must be
accomplished. I have not been involved with the Riverside Village as-builts, but it sounds to
me like a construction issue that should have been fixed by the contractor earlier in the
process. Additional conveyance will not be provided behind curbs since this would be
redundant infrastructure with undue cost burden for both initial construction and long
term maintenance. Also, the VDOT road calculations show that the existing road
infrastructure can readily achieve the drainage objectives of this plan.
5. C9: Project Description Notes:
a. Note 1: Owner /developer submits application for and obtains an approved plan, unless
contractor is a licensed surveyor, or professional engineer.
You are correct — that note was misleading, revised to state "shall ollow all ... permitting
requirements"
b. Note 2: revise to read `Installation of temporary erosion and sediment.
Note 2 revised as requested.
c. Ref. comments for C 10 — C 13, and revise C9 sequence notes, as needed.
Noted.
C10
6. Label ST1, ST2 weir outfall dimensions (L x L).
Outfall dimensions added.
7. Provide demolition Note/s, Phase IA. (Ex. building, Ex. drive: TBR).
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
"Demo" leader notes added.
8. Coordinate with USACE for permit coverage (work in a live stream, cofferdam, structure
installation, stream impact /loss of stream reach). Provide evidence of USACE NW permit
issuance.
Per attached email with Vinny Pero at USACE, this project falls under nonreporting
Nationwide Permit 18.
9. Estimate /report live stream reach loss (LF).
We have attached the plans that were sent to Vinny which calculates the loss and fill within
the stream. Loss of live stream reach: 145 sf.
C10
C11
10. Provide notes, details re. Ex. well abandonment. Provide copy of coordination with VDOT on
topic of well abandonment within future VDOT ROW (Road A).
Acknowledged, directive notes, and Well Abandonment State Code notes added to Sheet
C2. Coordination with VDOT forthcoming.
It. Provide ESC Legend: Line -type symbols /meaning can be discerned, but legend is needed for
clarity, for stream diversion, DD, RWD, SF, tree protection, etc.
Missing legends added to all ESCP sheets.
12. Provide Note or revise Phase IA sequence to eliminate apparent STl — Ex. driveway conflict.
Trap moved to avoid conflict.
13. Revise sequence Note 6 (phase 1B) to reference Road A, rather than Road 1.
Revised as requested.
14. Revise sequence Note 5 (phase IA) to reference culverts A and B.
Revised as requested.
15. Revise sequence Note 6 (phase 113) to reference culverts A and B.
Revised as requested.
16. Remove storm line D from Phase IA /113 unless installed with Phase 1.
Storm line D will be installed in this phase, it is not specifically mentioned as installation
time is flexible, and dependent on the other items listed in the sequence.
17. If storm line D is installed with Phase 1, show ST2 in storm line D profile.
Noted, this is now shown in the profile.
18. Label Rt. 20.
Acknowledged.
19. Provide ESC legend.
Acknowledged.
20. Remove storm line D unless installed with Phase 2.
912 E. High St. Charlottesville, VA 22902 1434.227,5140 1 shimp-engineering.com
It was installed in Phase 1, so it is shown intentionally.
21. Provide SF (DD, or similar) behind upslope curb to protect surface of roads A, B, C, D from silt
/sediment deposition.
Acknowledged, thank you.
22. PCE at Rt. 20 may be removed, once Road A is paved.
Noted, we have moved this location for phase 2 & beyond.
23. Show relocated stone /paved construction entrances at points construction vehicles may leave
paved development road surface and enter graded earth areas.
Noted, see new locations.
24. Label SB riprap outfall dimensions in this, or other view (L x W).
Outfall dim. Labelled in both views.
25. Provide temporary rock -lined SCC upslope of and parallel with FD that receives runoff from DD
and DV shown along south edge of parcel, south of Road C. Momentum and volume of sediment -
laden runoff exiting DV for FD will likely cause recurrent erosion issues unless rock -lined SCC
conveys runoff to SB.
Noted, this is provided.
26. If runoff from partially -stabilized graded slopes is meant to sheet across Road A to reach the SB,
this cannot be approved. Once Road A curb and gutter is installed, sediment -laden runoff that
reaches the base -asphalt surface of Road A will be confined by C&G. Revise ESC Phase 3 so
runoff from all areas intended to be controlled by the sediment basin, reaches the SB. Ensure curb
inlets, once constructed, are protected adequately during all phases of construction.
Runoff is not intended to flow across street, error in linework has been corrected.
C13
27. Revise proposed permanent DV along south edge of development to underground piped storm
conveyance. Also, ref. Engineering review comments on road plan, and preliminary plat.
Noted, DV will be replaced with piped system during Phase 4. Shown on C13.
28. Provide sequence /narrative /symbols /linework for coffered work area required to construct Road
F.
Since Road F was removed this is no longer required.
29. Provide PCE at Int. Road F and Rt. 20, whether it is intended to be used or not. It will likely be
used as a site entrance, despite design intent. Albemarle County inspector may, at his discretion,
not require a paved construction entrance at this location, but Road F is to be paved, so a paved
CE is appropriate.
Since Road F was removed this is no longer required. Ex. Avinity fire access road cannot be
used for construction (since it is offsite property), so none will be provided for this either.
30. Provide SF, diversion, etc. to protect surface of road E, once constructed, until upslope DA is
stabilized.
Silt fence will be sufficient, and is now provided.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom
31. Include narrative sequence (Note 9), symbols, measures that outline/describe stream channel
restoration activities in adequate detail, and offer adequate stream protection during this phase of
the project.
Stream channel restoration no longer proposed.
E. Mitigation Plan
32. C17, Mitigation Plan:
a. Please provide source of Mitigation Option A (channel restoration) requirements. Although
used in the past, Crozet Court subdivision, for example, reviewer needs to identify source of this
option.
This came from an old Albemarle County E&S guidance document, however channel
restoration is no longer proposed.
b. Math: Since only 1.32 Ac. of unforested buffer appears available for mitigation plantings, the
proposed 1600 bare root seedlings at 1,210 stems /Ac. ( planted 6' x 6' OC) appears to represent
a maximum, but (related to a., above) were this not the case, the 2:1 plantings : area of buffer
impact ratio would apply to 1.26 Ac. area disturbed within stream buffer. Table narrative on C 17
credits 1 LF channel restoration as offset for 100sf disturbed buffer. Again, reviewer not familiar
with source of channel restoration buffer impact offset credit. Also, please note that 1,210
seedlings option (Option C, Table B, DCR Riparian Buffers Guidance Manual, p. 95) requires
applicant to enter into a 5-year maintenance and performance guarantee, which will also stipulate
minimal survival required after two growing seasons of 600 plants per Ac. Provide 5-year
maintenance and performance guarantee as condition of V SMP /WPO plan approval.
Math updated to reflect strategy revision. DCR source listed. 5-yr maintenance and
performance guarantee noted (guarantee documents will be handled by Nicole Scro).
Additional notes added.
c. Providc planting pattcrn ( 6' OC).
Planting pattern added.
d. Provide list /table of proposed mitigation plant species (type /count) from Albemarle County
Approved planting list (to be evaluated by Water Resources staff).
List provided.
e. Channel Restoration Instructions is inadequate. Also, see comments elsewhere. Natural stream
restoration design is required for plan approval to support 9VAC25-870-66 compliance.
Stream channel restoration no longer proposed.
If you have any questions or concerns about these revisions, please feel free to contact me at
keane@shimp-en 'ngi eering corn or by phone at 434-227-5140.
Regards,
Keane Rucker, Err
Shimp Engineering, P.C.
912 E. High St.. Charlottesville, VA 22902 1434.227.51401 shlmp-engineenrig.rom