HomeMy WebLinkAboutWPO201400008 Review Comments 2015-06-22Short Review Comments Report for:
WPO201400008
SubApplication Type:
Crozet GAC Updates
Stormwater Management/BMP Plan
Erosion and Sediment Control Plan
Date Completed:03/26/2014
Reviewer:Michelle Roberge CDD Engineering
Review Status:Requested Changes
Reviews Comments:
Division:
Date Completed:03/26/2014
Reviewer:Michelle Roberge CDD Engineering
Review Status:Requested Changes
Reviews Comments:
Division:
Date Completed:06/18/2014
Reviewer:Michelle Roberge CDD Engineering
Review Status:Approved
Reviews Comments:
Division:
Date Completed:06/18/2014
Reviewer:Michelle Roberge CDD Engineering
Review Status:Approved
Reviews Comments:
Division:
Date Completed:05/14/2015
Reviewer:Max Greene CDD Engineering
Review Status:No Objection
Reviews Comments:
Division:
Date Completed:05/14/2015
Reviewer:Max Greene CDD Engineering
Review Status:No Objection
Reviews Comments:
Division:
Date Completed:06/22/2015
Reviewer:Ana Kilmer CDD
Review Status:Approved
Reviews Comments:6/4/2015- swa submitted to county
6/5/2015 - swa forwarded to CAO. CAO approved swa
6/5/2015 - swa forwarded to County Executive
6/22/2015 - swa recorded at Clerk's Office. Deed Book 4637, Page 523
Division:
Page:1 of 1 County of Albemarle Printed On:February 13, 2017
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: Crozet GAC Updates
Plan preparer: Hazen and Sawyer [Bret Edwards, bedwards @hazenandsawyer.com]
Owner or rep.: Albemarle County Service Authority [Justin Weiler, jweiler @rivanna.org]
Plan received date: 21 May 2014
Date of comments: 11 Jun 2014
Reviewer: Michelle Roberge, Glenn Brooks
The erosion & sediment control plan and stormwater management plan (WP0201400008)
submitted on May 21, 2014 is approved.
We asked the applicant to satisfy MS -19 from 9VAC25- 840 -40: 1) Either show the downstream
channel is adequate or 2) demonstrate that water is detained on -site to meet code sections 9VAC25- 840 -40
and 9VAC25- 870 -66. The computation package from Hazen and Sqawyer does not demonstrate
compliance as per item (2) above, which was the agreed upon approach discussed in the meeting of May
8ffi, 2014. (It is noted that Mr. Edwards, who submitted the report, was not at the meeting.) Instead, it once
again states the channels are adequate in a narrative within the sealed package, even though it also notes
that erosion is evident at station 1 +59, and the channel is simply a backyard swale. We strongly
recommend you address the channel, or lack of a channel, with downstream residents.
Please pay the Lickinghole Basin Fee of $508.51. Also, the forms and instructions to request the
Water Protection Ordinance bond amount can be found on the Community Development Department
website shown below. You may contact Ana Kilmer (Albemarle County Department of Community
Development) at ext. 3246 for further information on bonding procedures.
hqp: / /www.albemarle.org/upload/ images / forms _center /departments /Community Development/forms /bond
sBond_ Estimate _Request Form.pdf
Once the E &SC and SWM bond has been posted, you may contact the Department of Community
Development to arrange a pre - construction meeting with a County Erosion & Sediment Control Inspector.
Should the County Inspector find the limits of disturbance increased or the need for additional control
measures required to protect the site, additional fees will be required.
Sincerely,
Michelle Roberge
May 12, 2014
Erosion Control &Stormwater Review
County of Albemarle
Department of Community Development
401 McIntire Road
Charlottesville, VA 22902-4596
Attn: Michelle Roberge
Re: Crozet Water Treatment Plant GAC
Upgrades—WP0201400009
Response to comments
Dear Ms. Roberge:
Please find below response to comments made for the Crozet Water Treatment Plant. Also attached in
this submittal are updated drawings, updated stormwater and E&S calculations, and figures.
In response to comments made by Albemarle County, Hazen and Sawyer offers the following on behalf of
the Rivanna Water and Sewer Authority.
E&S Comments from Engineering 3-24-14 Michelle Roberge
1. Label LOD acreage on C-1 sheet in notes.
Response: The Limits of Disturbance acreage has been added to the notes on sheet C1.
2. At the time of approval, an original signature and date shall be shown on plans.
Response: Comment noted.
3. Include in notes the name of watershed: Lickinghole Creek Watershed.
Response: The project's watershed, Lickinghole Creek Watershed, has been added to the
notes on sheet Cl.
4. It appears that there is a swale near the main entrance. Please verify if swale is actually there.
Verify if there is any runoff to Beaver Creek Reservoir and include in notes under watershed.
Response: There is a swale on the property along Three Notched Road that collects and
routes runoff towards the south west portion of the site and ultimately into the Lickinghole
Watershed. As can be seen on sheet C42 this swale will be continued in the post proiect
conditions. The existing swale along Three Notched Road prevents water from crossing the
road and into the Beaver Creek Reservoir. Hazen and Sawyer conducted a field visit on 4/10/14
and was able to verify.
5. Change title to include SWM & E&S Plan.
Response: The title sheet has been updated as well as the title block on each sheet.
6. Provide RWD (gravel mound)at new entrance to divert runoff to swale.
Response: A temporary gravel RWD has been added to divert runoff to the swale at the new
entrance and is shown on sheet C41.
7. Also show paved construction entrance in detail section.This allows inspector to enforce paved
construction entrance if gravel entrance does not work.
Response: A paved gravel construction entrance detail per Albemarle County Design
Standards has been added to sheet D1.
8. Address MS-19. There is a subdivision west and south of site.We need to ensure adequate
channels.
Response: The narrative has been revised to reflect updated figures and calculations
addressing MS-19.
Stormwater Comments Engineering 3-24-14 Michelle Roberge
1. If all runoff eventually drains into Lickinghole Basin provide pro-rated share payment for quality.
We can calculate when plan is ready to approve.
Response: Comment noted.
2. It appears there will be future development on this site. I recommend planning for future buildout
and situating the biofiter in an area that would satisfy the full build-out conditions.
Response: The biofiters have been sized based on the proposed improvements for this
project and are located on the only available and practice areas onsite. Your recommendation
is appreciated; however,future development at the WTP is years away and the locations of
any proposed structures at this point would only be a guess. It is not feasible at this time to
locate stormwater BMPs for this project to satisfy build-out conditions for the future.
3. Removal rate reduction calcs should only analyze the area being developed.
Response: The removal rate reduction calcs have been revised to analyze the limits of
disturbance.
4. More runoff from traveiway needs to be captured. We look for, at a min, 90%capture for the
additional impervious area. Also, site runoff should not drain into street.
Response: The proposed improvements for this site will reduce the total impervious at the
Water Treatment Site, therefore no"additional" impervious area is anticipated. The proposed
traveiway surface is gravel and 0.12 acres of this gravel surface will travel via sheet flow to the
fproposed Bioretention Cells (out of a total 0.26 acres replaced). Additionally,there are areas
V on site where existing gravel will be removed and restored to maintained grass (0.17 acres).
The gravel entrance road has been modified so that no runoff will drain into Three Notched
Road.
5. Use SCS method instead of Rational Method.
Response: Bioretention design calculations have been changed to the SCS Method.
6. Show stormwater management easements and access easements to SWM facilities. Easement
needs to encompass the 100 yr high water mark.
Response: Stormwater management easements and access easements have been provided
on the drawings. There is no 100 yr high water mark for the Biorention cells as they were
designed to capture only the first inch of runoff from the impervious area as per the
requirements of the Virginia Stormwater Management Handbook.
New*, Name
7. SWM details and cross-sections need to be to scale.
Response: The SWM details and cross-sections have shown to scale and can be seen on
sheet C43.
8. Provide Albemarle SWM notes from our design standards.
Response: SWM notes per the Albemarle County design standards have been added to sheet
C43.
9. Clarify no utilities are under SWM facilities.
Response: Sheet C411 has been provided to show that there are no existing or proposed
utilities under the proposed SWM facilities.
10. Show forebays for all basins.
Response: Forebays have been added to all basins.
11. Show access to cleanouts of SWM facility.
Response: A stormwater access easement has been provided on he plans,
12. Show underdrains in biofilter plan view.
Response: Underdrains are now shown in plan view.
13. Label Tc&CN values on drainage area map.
Response: Tc and CN values have been added to the Drainage Area Maps.
14. For biofilter#1, maintain 643.5 elevation around facility.
Response: Elevation 643.5 has been maintain around the entirety of biofilter#1.
15. For biofilter#2, maintain 649 elevation around facility.
Response: Elevation 649 has been maintain around the entirety of biofilter#2.
Two(2)copies of the modified drawing set and modified calculations have been provided, illustrating
the responses above. We trust this information will allow you to complete your review of the WPO and
SWM applications. Please do not hesitate to contact me with any questions or concerns.
Sincerely,
HAZEN AND SAWYER, P.C.
Bret T. Edwards, P.E.
Principal Engineer
ifed
COUNTY OF ALBEMARLE
Department of Community Development
'_ Lo D (11 $t.�c 401 McIntire Road
[[ cites Charlottesville,Virginia 22902
WPO Plan Review
Project: Crozet GAC Updates Plan submittal date: 12 Feb 2014
Number: WPO201400009
Date: 24 Mar 2014
Reviewer: Michelle Roberge Phone: 434-296-5832
This is an abbreviated review comment notice. County engineering staff is available every Thursday
afternoon to discuss details of review. To schedule,please call your reviewer for an appointment.
Erosion & Sediment Control: Adequate
(Code Chapter 17,Article II) X Not Adequate
Y N
x State standards followed, and Design Standards Manual notes and details
x Adequate limits and perimeter measures out of work areas
x All stages protected adequately
x Adequate channels
v -Label LOD acreage on C-1 sheet in notes. . ?Lig. .
-At the time of approval,an original signature and date shall be shown
on plans.
\,, -Include in notes the name of watershed: Lickinghole Creek
Watershed.
-It appears that there is a swale near the main entrance. Please verify if
swale is actually there.Verify if there is any runoff to Beaver Creek
Reservoir and include in notes under watershed.
-Change title to include SWM&E&S Plan.
!� -Provide RWD(gravel mound) at new entrance to divert runoff to
swale.
-Also show paved construction entrance in detail section. This allows
inspectors to enforce paved construction entrance if gravel entrance
oes not work.
-Address MS-19.There is a subdivision west and south of site.We need
to ensure adequate channels.
Stormwater Management:
(Code Chapter 17,Article III) n/a Adequate
Not Adequate
Y N
x Enough capture and treatment for on-site areas
x Enough detention storage for on-site areas G/e t 014-
Sealed
-Sealed hydrologic and hydraulic computations provided. tior
-If all runoff eventually drains into Lickinghole Basin provide pro-
rated share payment for quality. We can calculate when plan is ready
to approve.
-It appears there will be future development on this site. I recommend
planning for future buildout and situating the biofilter in an area that
would satisfy the full build-out condition.
[17-20411 An application for an erosion and sediment control plan that requires modifications,terms,or conditions to be included in order for it to
be approved shall be deemed to be withdrawn if the owner fails to submit a revised plan addressing the omitted modifications,terms or conditions
within six(6)months after the owner is informed of the omitted information as provided under paragraph(B).
-Removal rate reduction calcs should only analyze the area being
developed.
r-More runoff from travelway needs to be captured.We look for,at a
min,90% capture for the additional impervious area. Also,site runoff
should not drain into street.
s/' -Use SCS method instead of Rational Method.
-Show stormwater management easements and access easements to ,w uait/ ,
SWM facilities. Easement needs to encompass the 100 yr high water r,Y r /
mark.
/-SWM details and cross-sections need to be to scale.
✓'-Provide Albemarle SWM notes from our design standards.
v"-Clarify no utilities are under SWM facilities.
v -Show forebays for all basins.
-Show access to cleanouts of SWM facility.
-Show underdrains in biofilter in plan view.
v'-Label Tc& CN values on drainage area map.
v-For biofilter#1,maintain 643.50 elevation around facility.
ix-For biofilter#2,maintain 649 elevation around facility.
Mitigation: Adequate
(Code Chapter 17,Article III)
X Not Adequate
Y N
Buffers and disturbed areas adequately shown
Adequate plantings at 2:1,or other mitigation provided
-Provide mitigation for disturbance within the WPO buffer.
/0174 / /IQ.CesS'aiW S"Ce
cSi /dL nZobiller
This review attem is to �'
p encompass the larger compliance questions. County staff does not assume
responsibility for any calculation or plan details, and cannot cover the intricacies of every plan submitted. L..- s,s WPO
Each plan and calculation must have a professional seal and signature to assume these responsibilities. ./r"5 'I
� �
/4GOrfec /X
This plan is Approved (please see attached Approval Fact Sheet) J
X Not Approved
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[17-204.f] An application for an erosion and sediment control plan that requires modifications,terms,or conditions to be included in order for it to
be approved shall be deemed to be withdrawn if the owner fails to submit a revised plan addressing the omitted modifications,terms or conditions
within six(6)months after the owner is informed of the omitted information as provided under paragraph(B).
A
�RGICn4'
Project: Crozet GAC Updates
Number: WP0201400009
Date: 24 Mar 2014
Reviewer: Michelle Roberge
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902
WPO Plan Review
Plan submittal date: 12 Feb 2014
Phone: 434 - 296 -5832
This is an abbreviated review comment notice. County engineering staff is available every Thursday
afternoon to discuss details of review. To schedule, please call your reviewer for an appointment.
Erosion & Sediment Control: Adequate
(Code Chapter 17, Article II) X Not Adequate
Y N
State standards followed, and Design Standards Manual notes and details
Adequate limits and perimeter measures out of work areas
All stages protected adequately
Adequate channels
-Label LOD acreage on C -1 sheet in notes.
-At the time of approval, an original signature and date shall be shown
on plans.
- Include in notes the name of watershed: Lickinghole Creek
Watershed.
-It appears that there is a swale near the main entrance. Please verify if
swale is actually there. Verify if there is any runoff to Beaver Creek
Reservoir and include in notes under watershed.
- Change title to include SWM & E &S Plan.
- Provide RWD (gravel mound) at new entrance to divert runoff to
swale.
-Also show paved construction entrance in detail section. This allows
inspectors to enforce paved construction entrance if gravel entrance
does not work.
- Address MS -19. There is a subdivision west and south of site. We need
to ensure adequate channels.
Stormwater Management:
(Code Chapter 17, Article III)
Y N
n/a Adequate
Not Adequate
Enough capture and treatment for on -site areas
Enough detention storage for on -site areas
Sealed hydrologic and hydraulic computations provided.
-If all runoff eventually drains into Lickinghole Basin provide pro-
rated share payment for quality. We can calculate when plan is ready
to approve.
- It appears there will be future development on this site. I recommend
planning for future buildout and situating the biofilter in an area that
would satisfy the full build -out condition.
[17- 204.f1 An application for an erosion and sediment control plan that requires modifications, terms, or conditions to be included in order for it to
be approved shall be deemed to be withdrawn if the owner fails to submit a revised plan addressing the omitted modifications, terms or conditions
within six (6) months after the owner is informed of the omitted information as provided under paragraph (B).
- Removal rate reduction calcs should only analyze the area being
developed.
-More runoff from travelway needs to be captured. We look for, at a
min, 90% capture for the additional impervious area. Also, site runoff
should not drain into street.
-Use SCS method instead of Rational Method.
-Show stormwater management easements and access easements to
SWM facilities. Easement needs to encompass the 100 yr high water
mark.
-SWM details and cross - sections need to be to scale.
- Provide Albemarle SWM notes from our design standards.
- Clarify no utilities are under SWM facilities.
-Show forebays for all basins.
-Show access to cleanouts of SWM facility.
-Show underdrains in biofilter in plan view.
-Label Tc & CN values on drainage area map.
-For biofilter #1, maintain 643.50 elevation around facility.
-For biofilter #2, maintain 649 elevation around facility.
Mitigation:
(Code Chapter 17, Article III)
Y N
Adequate
X Not Adequate
Buffers and disturbed areas adequately shown
Adequate plantings at 2:1, or other mitigation provided
- Provide mitigation for disturbance within the WPO buffer.
This review attempts to encompass the larger compliance questions. County staff does not assume
responsibility for any calculation or plan details, and cannot cover the intricacies of every plan submitted.
Each plan and calculation must have a professional seal and signature to assume these responsibilities.
This plan is
Approved (please see attached Approval Fact Sheet)
X Not Approved
[17- 204.f1 An application for an erosion and sediment control plan that requires modifications, terms, or conditions to be included in order for it to
be approved shall be deemed to be withdrawn if the owner fails to submit a revised plan addressing the omitted modifications, terms or conditions
within six (6) months after the owner is informed of the omitted information as provided under paragraph (B).
LIS>Administrative Code> •VAC25-840-40 /40/1401/4 —71640 .5 #° Page 1 of 6
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9VAC25-840-40. Minimum standards. 1 • Se, c Vrti
A VESCP must be consistent with the followingcriteria, techniques and methods: �E�
q
1. Permanent or temporary soil stabilization shall be applied to denuded areas within seven days
after final grade is reached on any portion of the site. Temporary soil stabilization shall be applied
within seven days to denuded areas that may not be at final grade but will remain dormant for
longer than 14 days. Permanent stabilization shall be applied to areas that are to be left dormant
for more than one year.
2. During construction of the project, soil stock piles and borrow areas shall be stabilized or
protected with sediment trapping measures. The applicant is responsible for the temporary
protection and permanent stabilization of all soil stockpiles on site as well as borrow areas and soil
intentionally transported from the project site.
3. A permanent vegetative cover shall be established on denuded areas not otherwise permanently
stabilized. Permanent vegetation shall not be considered established until a ground cover is
achieved that is uniform, mature enough to survive and will inhibit erosion.
4. Sediment basins and traps, perimeter dikes, sediment barriers and other measures intended to
trap sediment shall be constructed as a first step in any land-disturbing activity and shall be made
functional before upslope land disturbance takes place.
5. Stabilization measures shall be applied to earthen structures such as dams, dikes and
diversions immediately after installation.
6. Sediment traps and sediment basins shall be designed and constructed based upon the total
drainage area to be served by the trap or basin.
a. The minimum storage capacity of a sediment trap shall be 134 cubic yards per acre of
drainage area and the trap shall only controi drainage areas less than three acres.
b. Surface runoff from disturbed areas that is comprised of flow from drainage areas greater
than or equal to three acres shalt be controlled by a sediment basin. The minimum storage
capacity of a sediment basin shah be 134 cubic yards per acre of drainage area. The outfall
system shalt, at a minimum, maintain the structural integrity of the basin during a 25-year storm
of 24-hour duration. Runoff coefficients used in runoff calculations shall correspond to a bare
earth condition or those conditions expected to exist while the sediment basin is utilized.
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LIS > Administrative Code > 9VAC25-840-40 Page 2 of 6
7. Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion.
Slopes that are found to be eroding excessively within one year of permanent stabilization shall be
provided with additional slope stabilizing measures until the problem is corrected.
8. Concentrated runoff shall not flow down cut or fill slopes unless contained within an adequate
temporary or permanent channel, flume or slope drain structure.
9. Whenever water seeps from a slope face, adequate drainage or other protection shall be
provided.
10. All storm sewer inlets that are made operable during construction shall be protected so that
sediment-laden water cannot enter the conveyance system without first being filtered or otherwise
treated to remove sediment.
11. Before newly constructed stormwater conveyance channels or pipes are made operational,
adequate outlet protection and any required temporary or permanent channel lining shall be
installed in both the conveyance channel and receiving channel.
12. When work in a live watercourse is performed, precautions shall be taken to minimize
encroachment, control sediment transport and stabilize the work area to the greatest extent
possible during construction. Nonerodible material shall be used for the construction of causeways
and cofferdams. Earthen fill may be used for these structures if armored by nonerodible cover
materials.
13. When a live watercourse must be crossed by construction vehicles more than twice in any six-
month period, a temporary vehicular stream crossing constructed of nonerodible material shall be
provided.
14. All applicable federal, state and local requirements pertaining to working in or crossing live
watercourses shall be met.
15. The bed and banks of a watercourse shall be stabilized immediately after work in the
watercourse is completed.
16. Underground utility lines shall be installed in accordance with the following standards in
addition to other applicable criteria:
a. No more than 500 linear feet of trench may be opened at one time.
b. Excavated material shall be placed on the upnii: side of trenches.
c. Effluent from dewatering operations shall be filtered or passed through an approved
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• LIS >Administrative Code> 9VAC25-840-40 Page 3 of 6
sediment trapping device, or both, and discharged in a manner that does not adversely affect
flowing streams or off-site property.
d. Material used for backfilling trenches shall be properly compacted in order to minimize
erosion and promote stabilization.
e. Restabilization shall be accomplished in accordance with this chapter.
f. Applicable safety requirements shall be complied with.
17. Where construction vehicle access routes intersect paved or public roads, provisions shall be
made to minimize the transport of sediment by vehicular tracking onto the paved surface. Where
sediment is transported onto a paved or public road surface, the road surface shall be cleaned
thoroughly at the end of each day. Sediment shall be removed from the roads by shoveling or
sweeping and transported to a sediment control disposal area. Street washing shall be allowed
only after sediment is removed in this manner. This provision shall apply to individual development
lots as well as to larger land-disturbing activities.
18. All temporary erosion and sediment control measures shall be removed within 30 days after
final site stabilization or after the temporary measures are no longer needed, unless otherwise
authorized by the VESCP authority. Trapped sediment and the disturbed soil areas resulting from
the disposition of temporary measures shall be permanently stabilized to prevent further erosion
and sedimentation.
19. Properties and waterways downstream from development sites shall be protected from
P 1 sediment deposition, erosion and damage due to increases in volume, velocity and peak flow rate
1,0
`;I
of stormwater runoff for the stated frequency storm of 24-hour duration in accordance with the
Nei I
0fr following standards and criteria. Stream restoration and relocation projects that incorporate natural
channel design concepts are not man-made channels and shall be exempt from any flow rate
capacity and velocity requirements for natural or man-made channels:
a. Concentrated stormwater runoff leaving a development site shall be discharged directly into
an adequate natural or man-made receiving channel, pipe or storm sewer system. For those
sites where runoff is discharged into a pipe or pipe system, downstream stability analyses at
the outfall of the pipe or pipe system shall be performed.
b. Adequacy of al! channels and pipes shall be verified in the following manner:
(1) The applicant shall demonstrate that the total drainage area to the point of analysis within
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' LIS > Administrative Code> 9VAC25-840-40 Page 4 of 6
the channel is one hundred times greater than the contributing drainage area of the project in
question; or
(2) (a) Natural channels shall be analyzed by the use of a two-year storm to verify that
stormwater will not overtop channel banks nor cause erosion of channel bed or banks.
(b) All previously constructed man-made channels shall be analyzed by the use of a ten-year
Vet 5
storm to verify that stormwater will not overtop its banks4nd by the use of a two-year storm to
_ s
demonstrate that stormwater will not cause erosion of channel bed or banks; and
oferoded
(c) Pipes and storm sewer systems shall be analyzed by the use of a ten-year storm to verify o' I+Si
that stormwater will be contained within the pipe or system. 2-f-5 o;
x'10/ os J h
c. If existing natural receiving channels or previously constructed man-made channels or pipes fiyrPro& ,
are not adequate, the applicant shall: GZ(sb4u6✓ilW
4A(( /mitt Will n o.-
(1) Improve the channels to a condition where a ten-year storm will not overtop the banks and a WAr)er
two-year storm will not cause erosion to the channel, the bed, or the banks; or ! f 9(
cA'0,55'-5 s ee
ms.
(2) Improve the pipe or pipe system to a condition where the ten-year storm is contained within
the appurtenances;
(3) Develop a site design that will not cause the pre-development peak runoff rate from a two-
n/P
year storm to increase when runoff outfalls into a natural channel r will not cause the pre-
development peak runoff rate from a ten-year storm to increase when runoff outfalls into a man-
made channel; or
(4) Provide a combination of channel improvement, stormwater detention or other measures
which is satisfactory to the VESCP authority to prevent downstream erosion.
d. The applicant shall provide evidence of permission to make the improvements.
e. All hydrologic analyses shall be based on the existing watershed characteristics and the
ultimate development condition of the subject project.
f. If the applicant chooses an option that includes stormwater detention, he shall obtain
approval from the VESCP of a plan for maintenance of the detention facilities. The plan shall
set forth the maintenance requirements of the facility and the person responsible for performing
the maintenance.
Outfall from a detention, facility shall be discharged to a receiving channel, and energy
dissipators shall be places at the outfall of all detention facilities as necessary to provide a
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LIS > Administrative Code > 9VAC25-840-40 Page 5 of 6
stabilized transition from the facility to the receiving channel.
h. All on-site channels must be verified to be adequate.
i. Increased volumes of sheet flows that may cause erosion or sedimentation on adjacent
property shall be diverted to a stable outlet, adequate channel, pipe or pipe system, or to a
detention facility.
j. In applying these stormwater management criteria, individual lots or parcels in a residential,
commercial or industrial development shall not be considered to be separate development
projects. Instead, the development, as a whole, shall be considered to be a single development
project. Hydrologic parameters that reflect the ultimate development condition shall be used in
all engineering calculations.
k. All measures used to protect properties and waterways shall be employed in a manner which
minimizes impacts on the physical, chemical and biological integrity of rivers, streams and other
waters of the state.
I. Any plan approved prior to July 1, 2014, that provides for stormwater management that
addresses any flow rate capacity and velocity requirements for natural or man-made channels
shall satisfy the flow rate capacity and velocity requirements for natural or man-made channels
if the practices are designed to (i) detain the water quality volume and to release it over 48
wk f; il hours; (ii) detain and release over a 24-hour period the expected rainfall resulting from the one
gi'
�� 01t t year, 24-hour storm; and (iii) reduce the allowable peak flow rate resulting from the 1.5, 2, and
lt 10-year, 24-hour storms to a level that is less than or equal to the peak flow rate from the site
C
V assuming it was in a good forested condition, achieved through multiplication of the forested
�0 ;\
)\ 0 1b�� 9� peak flow rate by a reduction factor that is equal to the runoff volume from the site when it was
. 1�(S Q Oft � in a good forested condition divided by the runoff volume from the site in its proposed condition,
��
, ` t�k and shall be exempt from any flow rate capacity and velocity requirements for natural or man-
ap� it made channels as defined in any regulations promulgated pursuant to § 62.1-44.15:54 or 62.1-
(�e)1' 44.15:65 of the Act.
403‘t m. For plans approved on and after July 1, 2014, the flow rate capacity and velocity
requirements of§ 62.l-44.15:52 A of the Act and this subsection shall be satisfied by compliance
with water quantity requirements in the Stormwater Management Act (§ 62.i.-44.15:24 et seq. of
the Code of Virginia) and attendant regulations, unless such land-disturbing activities are in
accordance with 9VAC25-870-48 of the Virginia Stormwater Management Program (VSMP)
https://leg 1.state.va.us/cgi-bin/legp504.exe?000--reg+9 VAC2 5-840-40 6/10/2014
LIS> Administrative Code > 9VAC25-840-40 Page 6 of 6
Regulations.
n. Compliance with the water quantity minimum standards set out in 9VAC25-870-66 of the
Virginia Stormwater Management Program (VSMP) Regulations shall be deemed to satisfy the
requirements of subdivision 19 of this subsection.
Statutory Authority
§ 62.1-44.15:52 of the Code of Virginia.
Historical Notes
Former 4vAC50-30-40, derived from VR625-02-00 §4; eff September 13, 1990; amended, Virginia Register
Volume 11, Issue 11, eff. March 22, 1995; Volume 29, Issue 4, eff. November 21, 2012; amended and
renumbered, Virginia Register Volume 30, Issue 2, eff. October 23, 2013.
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