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HomeMy WebLinkAboutSUB201200002 Review Comments Minor Amendment 2012-03-09 ........ ,......, v4 ENGINEERS SURVEYORS PLANNERS ASSOCIATES March 9,2012 Mr. Philip Custer, P.E. Civil Engineer I Albemarle County Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 Re: Stonefield Blvd. Road Plan Amendment WPO-2012-00001 and SUB-2012-00002 WWA Project No. 208026.02 Dear Mr. Custer: This letter is to document and respond to your review comments dated February 22, 2012. Our responses are as follows: A. Stormwater Management Review Comments (WPO-2012-00001) 1. Comment: The 7.5ft retaining wall so close to the roadway presents a considerable safety issue. If the wall cannot be eliminated or reduced significantly, this design change may not be approved by county staff or guardrails around half of the facility will be needed. It seems that there are two design changes that led to the addition of the wall: the lowering of the invert of structure 46 and a dramatic increase to the size of the BMP. In the original design of structure 46, the pipe seemed to be at a sufficient depth below the pavement at the Sperry entrance. There also appears to be plenty of fall in the system to allow the outlet to be raised and still meet minimum slope requirements. The desire to have a larger footprint for the increased watershed is understandable, but please note that the county accepts 4% of the impervious area as the biofilter bed, as opposed to 5%shown in the calculation (the VSMH specifies both). Additionally, there seems to be room to stretch the biofilter to the north and minimize the wall height on the west side. (Rev. 1)A seven foot retaining wall is an unnecessary safety hazard this close to the roadway. The necessary footprint of 4700sf can be achieved by locating the wall about 18ft from the back of curb, grading from the back of curb down to the top of wall at a 3:1 slope, and extending the wall 20ft to the north. I only needed a wall of 2ft on the west side of the biofilter to achieve this. The guardrail would still be needed on the south side of the biofilter. Please specify end sections for the guardrail that remains. 3040 Avemore Square Place•Charlottesville,Virginia 22911 Telephone(434)984-2700 •Fax(434)978-1444 Charlottesville•Lynchburg Response: The grading has been revised along the roadway to provide a 3:1 slope from the back of the curb in order to reduce the height of the retaining wall to 2ft. GR-11 end treatment has been specified for the remaining guardrail. Please refer to Dwg. C-22 for details. 2. Comment: Please update all drainage area maps and calculations to include the proposed changes to the Regal Cinema plan. The calculations for the system downstream of 46.4 seem to account for the parking lot water, but the map does not match the calculations. The biofilter calculations and map do no include this area; only a note references the reason for the increased size of the facility. (Rev. 1) Comment has been addressed. 3. Comment: Biorention facilities, as well as most BMPs in the Virginia Stormwater Management Handbook, are volume-based facilities and achieve their specific removal rates by capturing the first flush (1/2" or 1", depending on RR) of storm events. The full first flush volumes cannot be caught with current configurations of structures 39.1 and 46.1. For the Sperry facility, if you wish to provide a bypass pipe for larger storms,please size all pipes to the biofilter (no restrictor plates)for the full discharge, add a structure just south of the biofilter wall, move the bypass pipe to the newly added structure, and set the elevation of the bypass pipe at Ift above the bed elevation. A similar arrangement will need to be made for the northern biofilter. (Rev. 1) The current configuration is acceptable if IS-1 is proposed on this manhole and the bypass pipe is raised 6"so it is the same elevation of the top of the pipe going to the biofilter, as it had been proposed in the first submittal. Response: Str. 46.1 has been revised to show VDOT Std. IS-1. The invert of the high flow bypass pipe was set at the elevation shown on the plans to ensure that the first flush will enter the biofilter. In addition,the high flow bypass pipe has been installed by the contractor at the inverts shown and has not been revised per your comment. We respectfully request your approval of this design. 4. Comment: Sediment forebays are required on all SWM quality facilities. Biofilter forebays should be between 10%and 20% of the biofilter floor area. (Rev. 1) Comment has been addressed. 5. Comment: Please specify the rim elevation of Structure 42.1 in the biofilter details. (Rev. 1) Comment has been addressed. 6. Comment: Please provide details of the retaining wall in this set. The set of details should include a typical cross-section and specific details for the pipes through the wall. The pipe om the facility is likely designed through the wall's footer or base. 3040 Avemore Square Place■Charlottesville,Virginia 22911 Telephone(434)984-2700 •Fax(434)978-1444 Charlottesville•Lynchburg Page 2 of 5 (Rev. 1) Comment has not been addressed. Response: Typical details have been provided for the pipes passing through the retaining walls. Please refer to Dwg. C-22. 7. Comment: What material are the walls made out of? Will the walls be permeable? Is it possible for the drain behind the wall to be a point that ponded water from the biofilter can bypass the treatment media? The wall will need to be watertight up to the rim of the grate. (Rev. 1) Watertight specifications should be extended to the bottom of the facility as well especially since a permanent water pool will existing in the stone layer. Response: The wall has been specified to be watertight from the base of the wall to an elevation of 483 per our discussion. 8. Comment: The invert out of the drop inlet is only 2.5ft below the bed elevation. A typical biofilter design sets this elevation at 3.5ft to 4ft below the bed elevation because of the underdrain. Please address this oversight. The underdrain cannot be placed in the biofilter media mix. The bed must be raised at least 1 ft, the outlet pipe and structure must be dropped at least 1 ft, the underdrain must be eliminated with soil tests supporting an acceptable infiltration rate, or the applicant must design elbow fittings on the underdrain so that a permanent pool of water exists inside the facility as long as the water elevation is at least 18" below the top of the bed elevation (Internal Water Storage). (Rev. 1) Comment has been addressed. 9. Comment: This application will require that a new Stormwater Management Facility Maintenance Agreement be recorded. Please complete this form and submit it to Ana Kilmer with a$17 recordation fee after reading the instructions online. The applicant should wait until they are sure they are going forward with this application to record this agreement. (Rev. 1) Comment has been noted. Response: A new Stormwater Management Facility Maintenance Agreement will be recorded by the applicant if necessary. 10. Comment: The SWM bond will increase with this revision. Before any road plan amendment is authorized for construction, a SWM bond will need to be posted under this application, WPO-2012-00001. The SWM bond with WPO-2011-00036 can then be released. Please provide a completed Bond Estimate Request Form to the county engineer to receive a new SWM bond. (Rev. 1) Comment has been noted. 3040 Avemore Square Place•Charlottesville,Virginia 22911 Telephone(434)984-2700•Fax(434)978-1444 Charlottesville•Lynchburg Page 3 of 5 11. Comment: (Rev. 1)Another$180 fee is needed for the review of this SWM plan amendment. Response: The $180 fee has been provided with this submittal. 12. Comment: (Rev. 1)Please refer to the separate SWM memo provided at the same time as this comment letter. Response: The North Biofilter has been removed from these plans. The comments in the SWM memo will be addressed in detail as part of the Stonefield Towncenter. Please refer to the Stonefield Towncenter Final Site Plan Amendment for further information. B. Road Plan Review Comments (SUB-2012-00002) 1. Comment: A fee of$400 is required for this private street review. [14-203] (Rev. 1) Comment has been addressed. 2. Comment: Please see comments A.1, A.2, and A.3. 3. Comment: Major deviations from the public street plans such as the reduction of clear zones, restriction of entrance widths, removal of gutter pans, and addition of the 4-way stop have been reviewed by the county engineer in conjunction with ZMA- 2011-00007. The plan cannot be approved until it is consistent with the plan/proffers approved by the Board of Supervisors. (Rev. 1) Comment has been noted. 4. Comment: One of the items not identified in the staff report is the southern median at the intersection of District Avenue and Bond Street. County engineering staff does not approve of the extension of the median to the curb line tangent of Bond Street. The plan does not have to meet the median design approved by VDOT, but County engineering staff will require the median to be moved at least 10ft from the tangent line. [14-412B] (Rev. 1) Comment has been addressed. 5. Comment: Street furniture must be shown on District Avenue as designated by Appendix B of the Code of Development. (Rev. 1)As recommended by the applicant, this will be reviewed with the Towncenter site plan amendment. 3040 Avemore Square Place•Charlottesville,Virginia 22911 Telephone(434)984-2700•Fax(434)978-1444 Charlottesville•Lynchburg Page 4 of 5 -.w I trust that the above responses and plan changes properly address the outstanding issues. If you have any questions, please contact me. Sincerely, WW Associates, Inc. A119:414( / .ah,,.............._/110111 — John D. Beirne, Jr., P.E. Senior Project Engineer cc: Thomas R. Gallagher, Edens 3040 Avemore Square Place•Charlottesville,Virginia 22911 Telephone(434)984-2700•Fax(434)978-1444 Charlottesville•Lynchburg Page 5 of 5 Philip Custer From: Philip Custer Sent: Wednesday, February 22, 2012 5:06 PM To: 'Tom Gallagher; hwhite@wwassociates.net Cc: Glenn Brooks; Mark Graham; Christopher Perez; Bill Fritz Subject: Engineering Review of Stonefield Amendments Attachments: Stonefield_SWM_22Feb2012.doc; E1mia_PBC_sdp-2012-00005 Regal Cinema Minor Site Plan Amendment.doc; E1_mia swm_P_BC_sdp-2012-00001 wpo-2011-00059 Town Center Amendment.doc; E2_swm rp_PBC_wpo-2012-00001 sub-2012-00002 Stonefield Blvd. Plan Amendment.doc Good evening, Attached are the engineering memos from the review of the first submittal of the Stonefield Towncenter and Regal Cinema amendments as well as the second submittal of the road plan amendment. I have also attached a summary memo regarding the stormwater changes at Stonefield. Other than a few minor site plan comments,all remaining issues have to do with the proposed SWM changes. Please let me know if you have any questions. Thanks, Phil 296-5832 x3072 1 o o A "roe o$^r"illy �'IRGII�IP COUNTY OF ALBEMARLE Department of Community Development 401 Mclntire Road Charlottesville,Virginia 22902-4596 Phone(434)296-5832 Fax(434)972-4126 Project: Stonefield SWM Plans(WPO-2012-00001, WPO-2012-00004, WPO-2012-00009) Plan preparer: Mr. Herb White,PE; W&W Associates Owner or rep.: Albemarle Place EAAP LLC Date received: 28 December 2011, 24 January 2012 Date of Comment: 22 February 2012 Engineer: Phil Custer and Glenn Brooks The stormwater treatment system for Stonefield has been provided in 5 separate applications and has become very hard to follow. After much analysis of all plans approved since WPO-2010-00023 and the recently proposed amendments to those plans, staff has found some concerns with the proposed changes to the stormwater treatment methods at Stonefield. In our opinion the proposed amendments do not meet the requirements of the Water Protection Ordinance, but with some modification they should. This plan relies on multiple levels of treatment. The first and second tiers are in the filteras and biofilters. The third is in the underground vaults. Each has a theoretical removal rate. However, even when crediting the inflated claims of the manufacturers,there is a practical limit to the removal rate that can be achieved. The industry data seems to draw the line around 70%. Beyond this,the technology is simply ineffective, no matter how many facilities you add. Redundancy still has value, as we know these systems sometimes have a high failure rate due to poor maintenance, but over-redundancy has less value. As we understand it,the proposed amendment relies on more treatment in the northern watershed, and less than previously approved in the southern watershed. By our analysis,this makes the southern discharge non-compliant. Because of the limitations discussed above,we do not fully credit"over-treatement"in the northern watershed. In order to achieve compliance,there needs to be more second tier coverage in the southern watershed, approximately 5 acres more. By the same token,there can be less third tier coverage in the northern watershed by removal of filterras, assuming the proposed biofilters achieve a 50%removal rate. Alternatively,the originally approved SWM plans can be maintained. ,, of1AL o®rar ®�-� COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville,Virginia 22902-4596 Phone(434)296-5832 Fax(434)972-4126 Project: Stonefield Blvd. Plan Amendment; WPO-2012-00001 & SUB-2012-00002 Plan preparer: Mr. Herb White,PE; W&W Associates Owner or rep.: Albemarle Place EAAP LLC Date received: 28 December 2011 (Rev. 1)31 January 2012 Date of Comment: 20 January 2012 (Rev. 1)22 February 2012 Engineer: Phil Custer The second submittal of the SWM and road plan amendments for Stonefield Blvd. (WPO-2012-00001 and SUB-2012-00002),received on 31 January 2012, have been reviewed. The plans can be approved after the following comments have been addressed: A. Stormwater Management Review Comments (WPO-2012-00001) 1. The 7.5ft retaining wall so close to the roadway presents a considerable safety issue. If the wall cannot be eliminated or reduced significantly,this design change may not be approved by county staff or guardrails around half of the facility will be needed. It seems that there are two design changes that led to the addition of the wall: the lowering of the invert of structure 46 and a dramatic increase to the size of the BMP. In the original design of structure 46,the pipe seemed to be at a sufficient depth below the pavement at the Sperry entrance. There also appears to be plenty of fall in the system to allow the outlet to be raised and still meet minimum slope requirements. The desire to have a larger footprint for the increased watershed is understandable,but please note that the county accepts 4% of the impervious area as the biofilter bed, as opposed to 5% shown in the calculation(the VSMH specifies both). Additionally,there seems to be room to stretch the biofilter to the north and minimize the wall height on the west side. (Rev. 1)A seven foot retaining wall is an unnecessary safety hazard this close to the roadway. The necessary footprint of 4700sf can be achieved by locating the wall about 18ft from the back of curb,grading from the back of curb down to the top of wall at a 3:1 slope, and extending the wall 20ft to the north. I only needed a wall of 2ft on the west side of the biofilter to achieve this. The guardrail would still be needed on the south side of the biofilter. Please specify end sections for the guardrail that remains. 2. I` u. c ;Ps€. t. G, t,e area xaad S and li.:/ inti ?n1 i tzi o At 4l ang t, all. STi£g "i tt , c=C #iuiii:ll4 !ar til syt4 tl?Llow.nstr,;s.at'a .>46 4 s,t, ?aCCOtilll :I°thz :)Hilal lot v,atGr., but the i"iiltl7€.l€ €?€)' match:',1,i:a. a°sila liisl it,ti , r he biotilipr alvi map iiia#, 4' at area:{s, note €' x "1'i L ti 21ti€?1"i .1€?i'tile inct ea, iZ.. (tithe sett 3. Biorention facilities, as well as most BMPs in the Virginia Stormwater Management Handbook, are volume-based facilities and achieve their specific removal rates by capturing the first flush (1/2"or 1", depending on RR) of storm events. The full first flush volumes cannot be caught with current configurations of structures 39.1 and 46.1. For the Sperry facility, if you wish to provide a bypass pipe for largetaisforms,please size all pipes to the biofilter(Tm"restrictor plates)for the full discharge, add a structure just south of the biofilter wall, move the bypass pipe to the newly added structure, and set the elevation of the bypass pipe at 1 ft above the bed elevation. A similar arrangement will need to be made for the northern biofilter. (Rev. 1) The current configuration is acceptable if IS-1 is proposed on this manhole and the bypass pipe is raised 6"so it is the same elevation of the top of the pipe going to the biofilter, as it had been proposed in the first submittal. 4. m.° :vs ,imd on all SW M qmmi rat:Uh._ is .,.€ r, ween and 20th of the bio Per floor area. f . cannten,hasbeta,- use 5. katw., i the rim elev t€: Slam: Hi: .ei riettins, 6. Please provide details of the retaining wall in this set. The set of details should include a typical cross-section and specific details for the pipes through the wall. The pipe from the facility is likely designed through the wall's footer or base. (Rev. 1) Comment has not been addressed. 7. What material are the walls made out of? Will the walls be permeable? Is it possible for the drain behind the wall to be a point that ponded water from the biofilter can bypass the treatment media? The wall will need to be watertight up to the rim of the grate. (Rev. 1) Watertight specifications should be extended to the bottom of the facility as well especially since a permanent water pool will existing in the stone layer. 8. 1'ti invert Y tiat wt= :;i i only. M.511 bet itie bird aotilter tiesUiti this e€. aim ital itt .1. `. belumv the bed elevation Pecan: the taa e ba.i_,e address oversight, t Ie unit. .... ..!¢ cannot be placed in the biolilitor media miu. ,., must s"' i be rinse( al least III, the outlet pipe and structure must be dropped at least it the un erdra n mum be eliminated with soil 'mists s upporiiup an rrittable infiltration rate, or the applicant must dealgt:1 i-itt i so �?w : tin the EariCte'1'Y�riA.7? that . ;'ri. pool t>i ts:itm'1 exists inside £ i�, .'t' e: £ s as time withir elevation i' ri least w f ( j below ft€r: the bed t i'�-;�ti£)m7 ��€ Conn/lent ,•'Ewen a dr ft. 9. This application will require that a new Stormwater Management Facility Maintenance Agreement be recorded. Please complete this form and submit it to Ana Kilmer with a$17 recordation fee after reading the instructions online. The applicant should wait until they are sure they are going forward with this application to record this agreement. (Rev. 1) Comment has been noted. 10. The SWM bond will increase with this revision. Before any road plan amendment is authorized for construction, a SWM bond will need to be posted under this application, WPO-2012-00001. The SWM bond with WPO-2011-00036 can then be released. Please provide a completed Bond Estimate Request Form to the county engineer to receive a new SWM bond. (Rev. 1) Comment has been noted. 11. (Rev. 1)Another$180 fee is needed for the review of this SWM plan amendment. 12. (Rev. 1)Please refer to the separate SWM memo provided at the same time as this comment letter. B. Road Plan Review Comments(SUB-2012-00002) 1. A , l t, is —tore,. ,or this private streetreview. 11,1.-2031 '>y rB i ,-at hoc been e ildresl 2. 3. Major deviations from the public street plans such as the reduction of clear zones,restriction of entrance widths,removal of gutter pans, and addition of the 4-way stop have been reviewed by the county engineer in conjunction with ZMA-2011-00007. The plan cannot be approved until it is consistent with the plan/proffers approved by the Board of Supervisors. (Rev. 1) Comment Itmebeen noted. 4. rlens 1 JCJ Hi] and bond Street, rn ering sLt, •LKO: apptOVC Ot , . the rniedian to the curb line t' ae t treet. The plan d not have meei nc design tipphisi.sed by VD(11. but Lawny tedgad:texigtit staff require ihe diddid os de mf.)-v,--;,,u at; least Oft flow the tangent line, 14-41213 (Rca I) Comment h been addressed. 5. Street:tbrniaire ninsi he shown on Dititriet A nun w desit;thitted by Appendix H of the(lotliti oil Developihera, (Rev,. I).48-recommended by the aliplicant,this vll he reviewed)vilh the nnyncenhw bile plan ametlanient, Filo;E2 ip PBC v,..po-2fli 2-00001 0002 n;, , O4 a an Anon hnont.do(' s ENGINEERS SURVEYORS PLANNERS ASSOCIATES January 27,2012 Mr. Philip Custer, P.E. Civil Engineer I Albemarle County Department of Community Development 401 McIntire Road Charlottesville, Virginia 22902 Re: Stonefield Blvd. Plan Amendment WPO-2012-00001 and SUB-2012-00002 WWA Project No. 208026.02 Dear Mr. Custer: This letter is to document and respond to your review comments dated January 20, 2012. Our responses are as follows: A. Stormwater Management Review Comments (WPO-2012-00001) 1. Comment: The 7.5ft retaining wall so close to the roadway presents a considerable safety issue. If the wall cannot be eliminated or reduced significantly, this design change may not be approved by county staff or guardrails around half of the facility will be needed. It seems that there are two design changes that led to the addition of the wall: the lowering of the invert of structure 46 and a dramatic increase to the size of the BMP. In the original design of structure 46, the pipe seemed to be at a sufficient depth below the pavement at the Sperry entrance. There also appears to be plenty of fall in the system to allow the outlet to be raised and still meet minimum slope requirements. The desire to have a larger footprint for the increased watershed is understandable, but please note that the county accepts 4% of the impervious area as the biofilter bed, as opposed to 5%shown in the calculation (the VSMH specifies both). Additionally, there seems to be room to stretch the biofilter to the north and minimize the wall height on the west side. Response: Guardrail has been added along Stonefield Boulevard (District Avenue). Please refer to Dwg. C-8 of the plans for details. 2. Comment: Please update all drainage area maps and calculations to include the proposed changes to the Regal Cinema plan. The calculations for the system downstream of 46.4 seem to account for the parking lot water, but the map does not match the calculations. The biofilter calculations and map do no include this area; only a note references the reason for the increased size of the facility. 3040 Avemore Square Place•Charlottesville,Virginia 22911 Telephone(434)984-2700•Fax(434)978-1444 Lynchburg•Charlottesville Response: The drainage area map has been revised to show the additional areas. Please refer to Dwg. C-21 of the plans for details. 3. Comment: Biorention facilities, as well as most BMPs in the Virginia Stormwater Management Handbook, are volume-based facilities and achieve their specific removal rates by capturing the first flush (1/2"or 1", depending on RR) of storm events. The full first flush volumes cannot be caught with current configurations of structures 39.1 and 46.1. For the Sperry facility, if you wish to provide a bypass pipe for larger storms,please size all pipes to the biofilter(no restrictor plates)for the full discharge, add a structure just south of the biofilter wall, move the bypass pipe to the newly added structure, and set the elevation of the bypass pipe at Ift above the bed elevation. A similar arrangement will need to be made for the northern biofilter. Response: The orifice plate has been removed from the 15" low flow pipe to allow more flow to the biofilter and the pipe has been upsized to 18". The calculated flow rate for the 1" first flush is 3.8 cfs. The calculated 2yr flow rate for the drainage area is 11.3cfs. The capacity of the 18" low flow pipe as designed is 11.2 cfs. The capacity of the pipe is more than adequate to guarantee that that the first flush will be captured and directed to the biofilter. In addition the 18" pipe has already been installed by the contractor. 4. Comment: Sediment forebays are required on all SWM quality facilities. Biofilter forebays should be between 10%and 20%of the biofilter floor area. Response: A sediment forebay has been added to the biofilter as requested. Please refer to Dwg. C-22 of the plans for details. 5. Comment: Please sped the rim elevation of Structure 42.1 in the biofilter details. Response: The top elevation of Structure 42.1 has been specified on the biofilter details as requested. Please refer to Dwg. C-22 of the plans for details. 6. Comment: Please provide details of the retaining wall in this set. The set of details should include a typical cross-section and specific details for the pipes through the wall. The pipe from the facility is likely designed through the wall's footer or base. Response: Typical retaining wall details have been added to the plans as requested. Specific details for the pipes penetrating the walls will be provided by the wall manufacturer. Please refer to Dwg. C-22 of the plans for details. 7. Comment: What material are the walls made out of? Will the walls be permeable? Is it possible for the drain behind the wall to be a point that ponded water from the biofilter can bypass the treatment media? The wall will need to be watertight up to the rim of the grate. Response: The details specify a segmental retaining wall. Notes have added to the plans to specify that the contractor shall place a watertight coating on the 3040 Avemore Square Place•Charlottesville,Virginia 22911 Telephone(434)984-2700•Fax(434)978-1444 Lynchburg•Charlottesville Page 2 of 4 walls from the base of the footing to an elevation 2' above the biofilter surface. The watertight coating will prevent any ponded water from bypassing the treatment media. Please refer to Dwg. C-22 of the plans for details. 8. Comment: The invert out of the drop inlet is only 2.5ft below the bed elevation. A typical biofilter design sets this elevation at 3.5ft to 4ft below the bed elevation because of the underdrain. Please address this oversight. The underdrain cannot be placed in the biofilter media mix. The bed must be raised at least Ift, the outlet pipe and structure must be dropped at least Ift, the underdrain must be eliminated with soil tests supporting an acceptable infiltration rate, or the applicant must design elbow fittings on the underdrain so that a permanent pool of water exists inside the facility as long as the water elevation is at least 18"below the top of the bed elevation (Internal Water Storage). Response: Elbows have been added to the underdrains to create a permanent pool. The permanent pool water surface elevation will be 2.5' below biofilter surface. Please refer to Dwg. C-22 of the plans for details. 9. Comment: This application will require that a new Stormwater Management Facility Maintenance Agreement be recorded. Please complete this form and submit it to Ana Kilmer with a$17 recordation fee after reading the instructions online. The applicant should wait until they are sure they are going forward with this application to record this agreement. Response: Noted. 10. Comment: The SWM bond will increase with this revision. Before any road plan amendment is authorized for construction, a SWM bond will need to be posted under this application, WPO-2012-00001. The SWM bond with WPO-2011-00036 can then be released. Please provide a completed Bond Estimate Request Form to the county engineer to receive a new SWM bond. Response: Noted. B. Road Plan Review Comments (SUB-2012-00002) 1. Comment: A fee of$400 is required for this private street review. X14-2031 Response: The additional fee was submitted to the County on Jan. 25, 2012. 2. Comment: Please see comments A.1, A.2, and A.3. Response: These comments have been addressed with this submittal. Please refer to the responses above. 3. Comment: Major deviations from the public street plans such as the reduction of clear zones, restriction of entrance widths, removal of gutter pans, and addition of the 4-way stop have been reviewed by the county engineer in conjunction with ZMA-2011-00007. The plan 3040 Avemore Square Place•Charlottesville,Virginia 22911 Telephone(434)984-2700 •Fax(434)978-1444 Lynchburg•Charlottesville Page 3 of 4 **we Nive cannot be approved until it is consistent with the plan/proffers approved by the Board of Supervisors. Response: Noted. 4. Comment: One of the items not identified in the staff report is the southern median at the intersection of District Avenue and Bond Street. County engineering staff does not approve of the extension of the median to the curb line tangent of Bond Street. The plan does not have to meet the median design approved by VDOT, but County engineering staff will require the median to be moved at least loft from the tangent line. [14-412B] Response: The median has been revised as discussed. Please refer to Dwg. C-9 and Dwg. C-14 for details. 5. Comment: Street furniture must be shown on District Avenue as designated by Appendix B of the Code of Development. Response: The locations of the street furniture on District Avenue will be supplied as part of the Albemarle Place Towncenter Final Site Plan Amendment to be submitted under separate cover. I trust that the above responses and plan changes properly address the outstanding issues. If you have any questions, please contact me. Sincerely, WW Associates, Inc. ff7L/---4111(: 1111111Mlw;a'w----- John D. Beirne, Jr., P.E. Senior Project Engineer cc: Thomas R. Gallagher, Edens 3040 Avemore Square Place•Charlottesville,Virginia 22911 Telephone(434)984-2700•Fax(434)978-1444 Lynchburg•Charlottesville Page 4 of 4 Philip Custer From: Philip Custer Sent: Friday, January 20, 2012 5:17 PM To: 'Tom Gallagher'; 'Herbert F. White Ill, P.E.' Cc: Glenn Brooks Subject: Engineering review of Stonefield Blvd. Amendments Attachments: El_swm rp_PBC_wpo-2012-00001 sub-2012-00002 Stonefield Blvd. Plan Amendment.doc Good evening, Attached is the comment letter from the review of the amendments to the Stonefield Blvd. Road and SWM plans(WPO- 2012-00001 and SUB-2012-00002), received 28 December 2011. Please let me know if you have any questions. Thanks, Phil 296-5832 x3072 1 4sAIA,111t7 RGI MOM COUNTY OF ALBEMARLE Department of Community Development 401 McIntire Road Charlottesville,Virginia 22902-4596 Phone(434)296-5832 Fax(434)972-4126 Project: Stonefield Blvd. Plan Amendment; WPO-2012-00001 & SUB-2012-00002 Plan preparer: Mr. Herb White,PE; W& W Associates Owner or rep.: Albemarle Place EAAP LLC Date received: 28 December 2011 Date of Comment: 20 January 2012 Engineer: Phil Custer The SWM and road plan amendments for Stonefield Blvd. (WPO-2012-00001 and SUB-2012-00002), received on 28 December 2011,have been reviewed. The plans can be approved after the following comments have been addressed: A. Stormwater Management Review Comments(WPO-2012-00001) 1. The 7.5ft retaining wall so close to the roadway presents a considerable safety issue. If the wall cannot be eliminated or reduced significantly,this design change may not be approved by county staff or guardrails around half of the facility will be needed. It seems that there are two design changes that led to the addition of the wall: the lowering of the invert of structure 46 and a dramatic increase to the size of the BMP. In the original design of structure 46,the pipe seemed to be at a sufficient depth below the pavement at the Sperry entrance. There also appears to be plenty of fall in the system to allow the outlet to be raised and still meet minimum slope requirements. The desire to have a larger footprint for the increased watershed is understandable,but please note that the county accepts 4% of the impervious area as the biofilter bed, as opposed to 5% shown in the calculation(the VSMH specifies both). Additionally,there seems to be room to stretch the biofilter to the north and minimize the wall height on the west side. 2. Please update all drainage area maps and calculations to include the proposed changes to the Regal Cinema plan. The calculations for the system downstream of 46.4 seem to account for the parking lot water, but the map does not match the calculations. The biofilter calculations and map do no include this area; only a note references the reason for the increased size of the facility. 3. Biorention facilities, as well as most BMPs in the Virginia Stormwater Management Handbook, are volume-based facilities and achieve their specific removal rates by capturing the first flush (1/2"or 1", depending on RR)of storm events. The full first flush volumes cannot be caught with current configurations of structures 39.1 and 46.1. For the Sperry facility, if you wish to provide a bypass pipe for larger storms,please size all pipes to the biofilter(no restrictor plates)for the full discharge, add a structure just south of the biofilter wall, move the bypass pipe to the newly added structure, and set the elevation of the bypass pipe at 1 ft above the bed elevation. A similar arrangement will need to be made for the northern biofilter. 4. Sediment forebays are required on all SWM quality facilities. Biofilter forebays should be between 10%and 20%of the biofilter floor area. 5. Please specify the rim elevation of Structure 42.1 in the biofilter details. 6. Please provide details of the retaining wall in this set. The set of details should include a typical cross-section and specific details for the pipes through the wall. The pipe from the facility is likely designed through thew/411's footer or base. 7. What material are the walls made out of? Will the walls be permeable? Is it possible for the drain behind the wall to be a point that ponded water from the biofilter can bypass the treatment media? The wall will need to be watertight up to the rim of the grate. 8. The invert out of the drop inlet is only 2.5ft below the bed elevation. A typical biofilter design sets this elevation at 3.5ft to 4ft below the bed elevation because of the underdrain. Please address this oversight. The underdrain cannot be placed in the biofilter media mix. The bed must be raised at least 1 ft,the outlet pipe and structure must be dropped at least 1 ft,the underdrain must be eliminated with soil tests supporting an acceptable infiltration rate, or the applicant must design elbow fittings on the underdrain so that a permanent pool of water exists inside the facility as long as the water elevation is at least 18"below the top of the bed elevation(Internal Water Storage). 9. This application will require that a new Stormwater Management Facility Maintenance Agreement be recorded. Please complete this form and submit it to Ana Kilmer with a$17 recordation fee after reading the instructions online. The applicant should wait until they are sure they are going forward with this application to record this agreement. 10. The SWM bond will increase with this revision. Before any road plan amendment is authorized for construction, a SWM bond will need to be posted under this application, WPO-2012-00001. The SWM bond with WPO-2011-00036 can then be released. Please provide a completed Bond Estimate Request Form to the county engineer to receive a new SWM bond. B. Road Plan Review Comments (SUB-2012-00002) 1. A fee of$400 is required for this private street review. [14-203] 2. Please see comments A.1,A.2, and A.3. 3. Major deviations from the public street plans such as the reduction of clear zones, restriction of entrance widths, removal of gutter pans, and addition of the 4-way stop have been reviewed by the county engineer in conjunction with ZMA-2011-00007. The plan cannot be approved until it is consistent with the plan/proffers approved by the Board of Supervisors. 4. One of the items not identified in the staff report is the southern median at the intersection of District Avenue and Bond Street. County engineering staff does not approve of the extension of the median to the curb line tangent of Bond Street. The plan does not have to meet the median design approved by VDOT, but County engineering staff will require the median to be moved at least l Oft from the tangent line. [14-412B] 5. Street furniture must be shown on District Avenue as designated by Appendix B of the Code of Development.