HomeMy WebLinkAboutWPO201100071 Correspondence 2012-06-21 us:
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville,Virginia 22902-4596
Phone(434)296-5832 Fax(434)972-4126
Project: WPO-2011-00071, RE-Store'n Station SWM Plan
Plan preparer: Mr.Nat Perkins,PE;NP Engineering
Owner: Jefferies II,LLC
Owner's Rep.: Mrs.Jo Higgins;Project Development Limited
Date received: 12 September 2011
(Rev. 1)14 February 2012
(Rev.2)30 April 2012
Date of Comment: 8 November 2011
(Rev. 1)2 March 2012
(Rev. 2)21 May 2012
Engineer: Phil Custer
The second revision to the SWM plan for the RE-Store'n Station (WPO-2011-00071),received on 30
April 2012,has been reviewed. The plan can be approved after the following comments have been
addressed:
1. Please provide an approval letter from Filtcn-a that the current layout and grading plan is
acceptable to them. I have concerns with the `grading plan not allowin`e any water to sonic
structures. For instance, the contours are pitched assay from the curb that F-I is placed on.
(Rev. 1) Comment has been addressed. SFF
2. Please provide an approval letter from ACF Environmental that the current layout is accepta e
for the use of the modular Raintank system.
(Rev. 1) The raintank system has been replaced in this submittal with a Contech detention facile
and the applicant has provided an approval letter from this supplier. However, changes to the
system are required and an updated letter will be necessary.
(Rev. 2) Comment has been addressed. Though,please provide an updated letter after
modifications to the system design, detailed below,are completed.
3. This application will require that a Stormwater Management Facility Maintenance Agreement he
recorded. Please complete this form and submit it to Ana Kilmer with a$17 recordation fee after
reading the instructions online. Please include all parcels contained in this site plan on this
agreement.
(Rev. 1) Pity has beet(pr('i kited and es ' r,r'en?1%l' ,r'C C1I ,,r'!rice ced h r Ann Kilmer.
(Rev. 2) Comment has been addressed.
4. The modified simple spreadsheet must analyze the watersheds for each stormy,ater quality facility
proposed on site and should not analyze a wateished including offsite water. By doing so. you
are obligating yourself to treating that offsite water to that removal rate, which the current plan is
not doing and is also not desirable. Please update the modified simple spreadsheet for only the
drainage areas to the detention facility and to the cistern.
([lei'. I)A modified simple spreadsheet has been /'rm ided jbr the areas drafiii711 ' to the fll r'i'iTi,
Howe'er, no modified simple spreadsheet has been p1'('1 idea for the (ictetti (please see the
lolfoir n' comment).
(Rev. 2) Comment has been addressed. The county will consider only Fi/terra 9 as a
stormwater facility. The cistern is nut a stormwater facility covered bv this plan.
5. If removal credit is desired for the.cistern,the four pages of the state's Cistern Design
Spreadsheet in Appendix C should be included in the Stormwater report in full so it can he
evaluated. Page 4 is impossible to read and the first three pages are 'c:ry difficult to read. Please
indicate in the stormwater report w hat the removal rate of the cistern is and pro\ide justification
in the calculations. it the removal rate of the .intern does not meet the rc:cluired rate after the
modified simple spreadsheet is anleaded per comment 4, the cistern must he1,otnc lareer. toilets in
the gas station iilU5t use water-Flom the cistern, or another BMP facility (upstream or
downstream) must he provided.
n,
(Rev. I) Rather than addressing !hit'COPilne`rit, the applicant has chosen to state that the cistern
has not been provider!as a sworn.;ate!'/<'1C71ir', but no other water quality measure is provided
for the runoff tl'o,n the canopy and store roof as mentioned in the initial comment. Please either
de•Sivi this cistern (iS a water quality measure (in It•111c.11 case you will likely need to provide year
round usage)and provide the calculations referred to in the (00117ients from the first submittal or
prov
ide IC fd('an Cl1?plopi7crte welter quality measure above o1"below this Y;'SIc'rTl..
(Rev. 2) Filterra 9,provided upstream of the cistern, is providing the water quality treatment
for this watershed. The cistern is not a stormwater facility part of this stormwater management
plan. Comment has been addressed.
6. Please provide pre-treatment and screening for the drainage system upstream of the cistern per
VA DCR Stormwater Design Specification No. 6.
(Rev. I) A rnitcchs unit is rejerred to in the approval letter, but no details or alignment is
prov'idded in the resubmittal. Details and placement of the system is required 1/the cistern is
designed as a stormwater quality tlllit. (Please see the previous comment.) If no other water
quality unit is provided up or downstream of the cistern. the cistern mist be designed to meet the
required removal late.
(Rev. 2) Filterra 9,provided upstream of the cistern, is providing the water quality treatment
for this watershed. The cistern is not a stormwater facility part of this stormwater management
plan. Comment has been addressed,
7. The pioximit}' of the Raintank 2 and one of the drainfields is a concern of the county. I'm not
certain that the two systems are far enough apart not to affect each other and i hai\.e contacted the
Vuginia Health Depaitmeni regarding this issue. An impers.ious liner may he required on this
system to make sure septic effluent does not find its way into the detention system and that the
detention system does not affect the efficiency of the drainlield.
(Rev. 1) The Virginia Department of Health has concluded that the two underground systems
should not affect each other's performance.
8. Detention requirements have been met: the 2 and 10 year discharges for the 1.49 acre post-
development watershed has been reduced to the pre-development rates. For all other projects
submitted to this county,the updated IDF curves found in the Design Manual must be used. For
this project,you do not need to use the updated IDF curves because the routings are acceptable.
(Rev. 1)A new detention system has been provided in this submittal. An independent analysis of
the system has confirmed that detention rates have still been met. Please be aware that future
submittals to the county will require the applicant to model the critical storm duration for all
design storms. Please make the following corrections to the plan which are necessitated because
of the modified design:
a. All changes in direction and slope for pipes require a manhole. Please provide at least
one manhole in the outlet pipe from the detention system. The Contech detention system
shows a 15"stub out at the bulkhead. If this stubout cannot be constructed at the
required—25 angle, a second manhole will be required. Please either provide this
manhole or modify all contech details to show this stubout at the proper angle.
• (Rev. 2) The design of the outlet was modified but the outlet profile was not altered
accordingly. Please update the profile of the pipe out of the facility. Please make sure
the pipe between the facility and the manhole has a 0.5%minimum slope on it. Please
also make sure the invert out of the manhole is at least 0.lft below the invert in.
b. Please modify all Stormwater;a etc gement notes on sheet SW-2 .Since the 1. refhr to the
Ruin tank system. which Ic as removed between the f rst and cecceud submittals. Please
make Sure these revised notes include the 3 counts.gei'teral notes for Stormwater
;l-Iraingeillent pled:,; found in the latest edition of the desi,euI nt(lllrt.,'1.
(Rev. 2) Comment has been addressed.
c. In the plan ana profile of the system, show the grading required to provide the minimum
cover stated in the notes. It seems that the system could be dropped 3ft rather and the
need for fill would be eliminated. This would also place the outlet of the pipe closer to
the bottom of the stream which would help prevent future erosion at the headcut. Please
also show the proposed grading of the area above the facility, since existing grades will
be destroyed with the sediment basin construction.
(Rev.2) The grades drawn by the applicant do not match the note requiring at least two
. � feet of fill over the facility. The pipe stubout with the weir wall and the top portion of
the southern edge of the facility will be exposed. The outlet pipe through the
S.451' .... Z vaias. downstream property is proposed too high in the ground;it cannot be constructed with
Ift of cover that close to the new channel. The grading plan also demonstrates that the
I40Y%b 14 2..TV 15( soil between the southern end of the facility and the downstream face of the
ANDS -2.,, embankment does not come close to meeting the standards of VSMH 3.01 especially
• considering the design of the swale at the base of the embankment. Please modify the
grading for the swale and the embankment to show the fill required to provide the
necessary cover for the facility while also providing an adequate slope(3:1)on the
downhill side of the embankment. It seems the pipe detention system must shift at least
15ft to the north and/or be lowered to achieve these requirements.
d. The contech plan view detail does not match the layout of the facility on Sheet SW-3.
>- Please correct.
Co Zq —'r� (Rev.2) The length of the stubout that contains the weir plate is inconsistent between
the detail and SW-3.
e. Is the line above the 6"orifice in the Orifice Plate Derail a spillway? If so, please
specify it.s length and elevation. If not, please provide more clarification in the detail as
to what the line is.
(Rev. 2) Comment has been addressed.
f The slope of the pipe into the detention system has been incr-eased.from 15.99° to
I5.52 0C. The increase in slope above 16% requires that an,hor No,k are required on
every other pipe joint. Please refer to %'DOT Special Design Di awing A-73 and MA-73
for AnchorDetails for Concrete Pipe. Alternatively, the plan can /ede.si n the s_sstem so
no slope greater than 16c%i.is proposed.
toaAt, .��b (Rev.2) Comment has been addressed.
'RE�IAD ai awe.* g. (Rev. 2)For many of the routing reports, the inputs for the design of the stormwater
facility do not match what is shown in the plan. Please make sure all stormwater
•5Cfj�V(11.7)4 big- calculations are consistent with the final design of the stormwater facility.
9 e control structures for the detention system must be accessible for inspection and
oba..." et• maintenance. The current design of the facility has the potential for clogging at the inlet end of
the pipe inside the facility where maintenance would be difficult. The control structure must have
a trashrack placed overtop of it that meets state minimum standards. I also recommend placing
some sort of screening or filter upstream of the detention system to prolong the life of the facility.
This last suggestion is not a requirement.
(Rev. 1) On sheet SW-3,please show all access points to the facility and provide a top elevation
for the rim of each structure. Please also sl'ecity in all Contech details the,. .1ST-
, I, or equivalent, rnt/st be provided in all risers into the facility.
Z' IY,(J .- (Rev. 2)Comment has not been addressed. The rim elevations on the detail also do not work
with hthe grades proposed on SW-3.
10. Please use a minimum of 15"diameter pipes in the stormwater facility to decrease the likelihood
of clogging.
(Rev. 1) Comment has been addressed.
11. An analysis of the downstream channel per Minimum Standard 19 was not provided with the
SWM or ESC plan. Please refer to page 7(of 35)of the County's Design Manual and the
Virginia Erosion and Sediment Control Handbook for what the county expects for an analysis of
downstream channels. Per state law,this analysis must be performed using the 24-hour storm.
According to DCR's Technical Bulletin#1,detention does not constitute compliance with MS-19
because total volume of runoff is increased and poses a potential threat to downstream properties.
(Rev. 1) Comment has not been addressed. A downstream channel analysis is required in any
situation where the velocity,peak rate, or volume of runoff is increased in a development.
Normal detention does not eliminate the requirement for the applicant to check downstream
channels because volume is increased unless a significant amount of infiltration is provided. If
an analysis cannot be performed, the applicant must proceed as if an inadequate channel is
present and provide over-detention meeting State Code Section 10.1-561.
�to .E,it (Rev.2)In a meeting with the applicant,I agreed to consider MS-19 addressed if the 2-year
SCS storm was completely routed through the 3"orifice(smallest achievable)because of the
size of the contributing drainage area and size of the existing channel. However, this
requirement was not fulfilled. The applicant's calculation clearly indicates that the 6"orifice is
b" MtErEC> r7 activated during two year SCS storm. It seems that if the 6"orifice was eliminated, the system
would be approvable.
12. To receive a bond estimate,please provide a completed Bond Estimate Request Form to the
County Engineer after all comments have been addressed.
(Rev. 1) WPO bond amounts will be calculated after plan approval.
(Rev. 2)Please provide me with the supplier's price for the underground detention system, so
N��1 that a bond can be calculated after the few remaining comments are addressed. A price for the
cistern should be excluded.
E?_sam_PFiC_WP0-201 I-00071 RE-Siore'n Siauon SWIV7 Plan doe
Shkrili‘A
WAIN
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville,Virginia 22902-4596
Phone(434)296-5832 Fax(434)972-4126
Project: WPO-2011-00071,RE-Store'n Station ESC Plan
Plan preparer: Mr.Nat Perkins,PE;NP Engineering
Owner: Jefferies II,LLC
Owner's Rep.: Mrs.Jo Higgins;Project Development Limited
Date received: 31 August 2011
(Rev. 1) 14 February 2012
(Rev. 2)23 April 2012
Date of Comment: 15 October 2011
(Rev. 1)2 March 2012
(Rev. 2)21 May 2012
Engineer: Phil Custer
The second revision to the ESC plan for the RE-Store'n Station(WPO-2011-00071),received on 23 April
2012,has been reviewed. The plan can be approved after the following comments have been addressed:
1. It appears that the ESC Plans were all printed at 30scale, not 40. If this is correct, please replace
all references to 40 scale with 30 scale.
(Rev. 1) Comment has been addressed.
2. On all three phases, please clearly show and label the limits of disturbance boundary.
(Rev. I) In phases I and 2. extend the limits of disturbance around the outlet protection below the
sediment basin. In phase 2, show the limits into the IIDOT ROW. In phase.3, shout'limits of
disturbanu'a.
(Rev. 2) Comment has been addressed.
3. Please show all proposed grading on Phase 2 and Phase 3. It is difficult to evaluate the adequacy
of these phases without proposed contours. Additional comments may be necessary because the
plan was not able to be fully evaluated.
(Rev. 1)In phase 3,please show the proposed grade lines.tor the.fill required to provide the
proper corer over the detention facility and the final proposed grading in the area of the
sediment basin after it is removed. An adequate channel will need to be provided in the area
previous disturbed by the sediment basin.
Q • Rev. 2) Two 90 degree turns for this channel is unrealistic. Please revise. Also, the current
ADDED -"1 grading of the channel results in substandard grades for the SWM facility embankment.
et (�i p..s, Please see SWM comment 8c for more information.
- 4. Related to the previous comment,the sediment basin and sediment trap should be sized for the
largest watershed each facility will likely experience as the site is filled in. For instance,the site
will likely be tipped towards the sediment basin, since the stormwater facility is located in the
vicinity,so its drainage area will increase as the earthwork progresses.
(Rev. 1) The sediment trap drainage area is larger than the watershed shown in the plan. Free
Town Lane does not divert water away from this trap as the map implies.
t.
., fr:,' r ,,, .�, .'"tr t?r?;Ct,`i-+l, vlriiGCiire 7u Il'aS it l7 ,.`:Llti:a.'e':c L1 1,71:c'r li'C1ti'i"Gli Cti 70 the
tit(11 dent ba`.in than designed. Plea re aC(0ililt tin-tills acreage in the ta/etilatiorts.
:ul s0. when the rlevigil of the sediment basin it as mortified, an error was made with regard to the
crnbankment. :Accoratrr to the calculations. the top of embankment must be 691, but the plan is
Si Te.gp Lc m!:uGLe? To t:.o w uii embarkment top of 6�l'.t. Pic c::'H . r n! .'ktuen iJrh ';f at lea3t hti
i.
1�1h15E1)• ? SE. t (Rev.2) The sediment trap is too small for the drainage area during the first weeks of
IS 0 8S AC., construction. The previously used drainage area of 0.85 acres is required for this trap. The
Puy. 2 is cleanwater diversion requires instant stabilization. Please provide either sod or riprap on this
hannel. Also, the volume calculations for the sediment basin are incorrect. The location of
D.35 oiv. the dewatering orifice will need to be revised once the volume calculations are corrected.
:Es A•t1 C.1460 . Silt fence is frequently proposed perpendicular to contour lines in this plan which is not allowed
Sat6els per state guidelines. In these instances,water will not travel through the fence but will be
redirected downhill,like a diversion. Please replace the silt fence on the east side of the property
line with a diversion from the northeast corner to the sediment trap. On the west end of the
property,please simply remove the silt fence. If a visual boundary is desired by the applicant,I
recommend a type of safety fence.
(Rev. 1) Comment has been addressed, though the first step in the construction sequence was not
modified accordingly. It seems step 3 can refer to silt fence. Similarly, the construction sequence
still refers to raintanks, which have been eliminated with this application. The contech structures
should be installed after the site has been stabilized, in phase 3.
C-`)"SEb -- (Rev.2)Please remove step one from the construction sequence and add"and silt fence as
shown"to the end of step 3 of the construction sequence.
6. Please remove the silt fence from directly below the outlet of both settling facilities. Silt fence
cannot receive concentrated flow.
(Rev. 1) Comment has been addressed.
7. During the review of the preliminary site plan, the Chief of Current Development,Bill Fritz.
appro\cd the disturbance of a 20ft wide section of the undistui bed buffer to the south. Please
show the area of the buffer that was approved for disturbance. It appears that the area shown on
this submittal does match the area approved by Bill. If the area proposed for disturbance is. in
fact, different, another uuaiver of this disturbance may need to be processed.
(Rev. 1) In this ESC application, the center of the 20ft of allowable disturbed buffer is 99ft
from the property corner. In the approved preliminary plan, the center of the 20ft buffer is
7 I.5 ft frorn the property corner. The disturbed area of this buffer was moved. However. Bill
Fritz, has determined that this cftartne does not negatively a 'ect the reviorts apj royal and the
revised location is acceptable.
8. The embankment of the sediment basin ties into existing grade within the undisturbed buffer(see
where the 676 contour line would be). Please modify the plan to make sure no disturbance to the
undisturbed buffer occurs, other than the area previously authorized.
(Rev. I) Comment has been addressed.
9. In plan view,please draw the sediment basin bottom as 671.
(Rev. 1) Comment has not been addressed. Please draw the 671 contour line in the sediment
basin and modify the bottom dimensions to meet this contour line. Update the sediment basin
sSCD bottom dimension reference in the embankment detail accordingly.
`� (Rev. 2) The note adjacent to the sediment basin on sheets EC-4 and EC-5 still mentions a
bottom elevation of 672.
1 U. Please,how Permanent Seeding (PS) symbols throughout the plan \A here necessary.
(Rev. I} Comment has been addressed.
I I. Please include the county's payed. wash rack detail in this sheet set. This detail can be found in
the county's design n_t�intial on page 28 of 35.
(Rev. I) Comment has been addressed.
12. The county has updated its standard ESC Note set. Please use the latest s ersion found in the
county's design manual.
(Rev. I) Comment has been addressed.
13. An analysis of the downstream channel per Minimum Standard 19 was not provided with the
ESC plan. Please refer to page 7(of 35)of the County's Design Manual and the Virginia Erosion
and Sediment Control Handbook for what the county expects for an analysis of downstream
channels. Per state law,this analysis must be performed using the 24-hour storm.
(Rev. 1) Comment has not been addressed. A downstream channel analysis is required in any
situation where the velocity,peak rate, or volume of runoff is increased in a development.
Normal detention does not eliminate the requirement for the applicant to check downstream
1c.... channels because volume is increased unless a significant amount of infiltration is provided. If
an analysis cannot be performed, the applicant must proceed as if an inadequate channel is
2 "le-, L'i r Q_ present and provide over-detention meeting State Code Section 10.1-561.
S-�tz-,....C LCS Rev.2) The applicant intends on addressing this requirement through over-detention. Please
\ "O e • refer to SWM comment#11.
14. Please provide the cross-sections and calculations(2-year velocity and 10-year capacity)for the
new VDOT ditch. Please specify any liner,if necessary.
(Rev. 1) Comment has not been addressed. The response to this comment in the applicant's letter
� •� � �` refers to the placement of north arrows on the plan.
(Rev.2) The assumed slopes in the calculations for the new channel around the stormwater
C-A LGS cility do not matched the proposed grades. Also, it's difficult to accurately review these
calculations because these channels are not stationed in any sheets submitted to county
engineering.
15. To receive a bond estimate,please provide a completed Bond Estimate Request Form to the
County Engineer after all comments have been addressed. All owners of properties disturbed
with this application must sign this document and be party to the bond unless all offsite
easements are recorded. The easements must be written in a manner that allows the county and
its assigns to the construction site.
(Rev. 1) WPO bond amounts will be calculated after plan approval.
(Rev. 2)Comment remains unchanged.
605 Global Way,Suite 113
•��; : r-L�r. Linthicum,MD 21090
Ir�i n n www.contech-cpi.com
CONSTRUCTION PRODUCTS INC.
Nat Perkins, P.E. June 215T, 2012
NP Engineering
680 Ivy Farm Drive
Charlottesville,VA 22901
RE: Review of stormwater management design for Re-Store'N Station,Albemarle County,Virginia
The purpose of this letter is to document for Albemarle County and VA DCR our review of the plans and the
proposed application of the water quality treatment structures at this site as you have requested.
CONTECH has reviewed stormwater management designs for both the rainwater harvesting system and the
underground detention pond.
Rainwater Harvesting System
Based on the catchment area of 7,300 sf (gas station canopy) and irrigation requirements, CONTECH
recommends a 72" diameter SPRE cistern with a total length of 74If. This tank will provide a storage volume
of approximately 15,000 gallons and a runoff reduction of 78%. The system is designed to irrigate 18,000 sf
from April to October with an average depth of 0.785" per week(varies by month).
Underground Detention System
Perforated 72" diameter CMP was selected to minimize the overall footprint. The dimensions of the system
are 44'x86' including a 1' stone perimeter. The system has a total of (4) 36" access risers including one
downstream of the outlet control weir plate.
In summary, both the rainwater harvesting system and underground detention system are expected to
operate in accordance with CONTECH Construction Products' design intent.
Please feel free to contact me if you have any questions or concerns.
Sincerely,
Aaron M. Lowell
Design Engineer—Stormwater Products
CONTECH Construction Products Inc.
lowella@contech-cpi.com
www. contechstormwater. corn
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