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HomeMy WebLinkAboutSDP202000011 Review Comments Critical Slope Waiver 2020-02-27 (2) Christopher Perez From: Craig Kotarski <Craig.Kotarski@timmons.com> Sent: Thursday, February 27, 2020 4:05 PM To: John Anderson Cc: Christopher Perez; Frank Pohl; U Lopez; Kim Mellon Subject: RE: Critical Slope Waiver Request [ SDP2020-00011] ; RE:WP0202000005 - Boys and Girls Club, Northside, VSMP/WPO Attachments: Fill Slope Benching Examples - B&G Club Northside.pdf;44523 CRITICAL SLOPES WAIVER EXHIBIT 3.pdf;44523 CRITICAL SLOPES WAIVER EXHIBIT 4.pdf CAUTION:This message originated outside the County of Albemarle email system. DO NOT CLICK on links or open attachments unless you are sure the content is safe. John, thanks for the feedback below. I've put together some responses,as we have looked at and evaluated other options. Let me know if this changes anything from your perspective or if these items should be woven into the request for the waiver. Is it worth us getting together to discuss to better unpack the safety concerns, as well as clearly ensure the safe guards we are putting in place for slope stability are communicated and clear? Thanks for your thoughtful review of all of this. Best, Craig From:John Anderson <janderson2@albemarle.org> Sent:Thursday, February 27, 2020 11:06 AM To: Craig Kotarski<Craig.Kotarski@timmons.com> Cc:Christopher Perez<cperez@albemarle.org>; Frank Pohl <fpohl@albemarle.org> Subject:Critical Slope Waiver Request [SDP2020-00011] ; RE: WP0202000005- Boys and Girls Club, Northside,VSMP /WPO Craig, Engineering cannot support the critical slopes waiver request for this project in its current form, under current proposed design. • While acknowledging relief from strict application of critical slopes preservation requirements should be granted to a degree to help ensure safety of boys and girls attending the Club,no alternatives are presented. We have studied other alternatives. I've attached two. One shows a 3:I slope,however we impact 3x as many critical slopes(1.54 acres), while also infringing into the WPO buffer and the stream itself. The other option,which considered the wall,featured a pond that creates constructability and maintenance issues due to its location. (below,2/11, county staff wrote, `public safety is always the highest public purpose, in my view'—Engineering supports a site design that is inherently safe for those who routinely visit or use the facility.) • Please consider alternatives. Present several at least. Nominate preferred alternative to current design. Engineering cannot support current design with recommendation of waiver approval,absent alternative consideration. Alternatives attached. Note:Alternative analysis is a technical and not economic or cost-benefit analysis. Agreed,however the issue of safety can be subjective,as there are several technical ways for us to reduce the impacts to the slopes,but not without sacrificing the safety concerns that the club has to a large extent(30' wall)or even smaller extents(6' walls). Overall, the average wall height is around 20'...even if it is tiered it creates safety issues and concerns. • Waiver request gives no indication cost influenced design to this point. In fact, letter from James R. Pierce, CEO, Boys and Girls Clubs of Central Virginia,d. 2/21/20,makes persuasive arguments that are not economic in the least. There was a cost trade off,although exact dollars were not measured,as the elimination of the wall(and pond)was traded for 1 the underground stormwater detention system underneath the play field. This rest like an appropriate trade of costs, as this was determined to be a safer layout. • Yet it appears proposed design eliminates all retaining walls,not just very high walls(20'-30' single,standalone retaining walls). The average retaining wall that was required along the back of the site was around 20',making the wall, in its entirety, substantial. • Please consider range of design approaches available. A hybrid approach the relies on walls of modest height placed farther from main activity areas/main building with less steep grading across critical slopes would position design favorably relative to critical slopes requirements,and position Engineering to support an alternative design. The best hybrid approach would include some amount of tiered walls and setting those walls off from the edge of the Club, however this is cost-prohibitive as an excessive amount of fill material would need to be imported in to shift walls out. While these costs have not been completely vetted,if we assume 60' of gently sloped area from the curb's edge (approximately 300')at an average of 20' of fill,then we are looking at bringing in approximately 20,000 cy of dirt, which would equate to approximately$800,000,not to mention the additional cost of the wall,which is nearly $500,000. Those costs would represent a significant amount of the Club's budget and require them to significantly reduce the program and the number of students that could be served at this facility. • Engineering,reviewing VSMP plan and waiver request,notes nearly all impacts to critical slopes are in fill sections, that virtually all fill on critical slopes is 2:1 (image,below). 2:1 slopes would uniformly steepen existing critical slopes. 2:1 fill slopes are problematic in multiple if not most settings. We have worked with the geotechnical engineer to develop a detail for keying in the fill along these critical slopes,as we too recognize the importance of installation here. I've attached a detail that shows benching in every 9' along this area. • Once constructed, if erosion establishes patterns across 2:1 fill slopes,it is hard to reverse or stabilize 2:1 slopes. The situation is made worse in this instance:fill placed on slopes rated susceptible to erosion,are then made steeper. We understand the concern and have made commitments to ensure that these slopes are blanket matted,as well as that the areas are reforested. While the reforestation will take time to extend roots and assist in the stabilization of the slopes, blanket matting and seeding will also be used to assist with the early maintenance of the slopes. • Albemarle is engaged with minor to severe 2:1 (even 3:1)fill slope erosion at several commercial and residential projects where slopes include significant vertical intervals. While I am not sure of the other project specifics, in this example there will be no upstream flow discharged to these slopes,meaning the only stormwater that will engage these slopes is what will fall on it. All other stormwater associated with the upstream disturbance of the Club,its parking area,and outdoor amenities will be internally captured and discharged down at the stream. This strategy will actually reduce the stormwater flow that the critical slopes currently see. • Most remedies have not worked to halt erosion on 2:1 fill slopes,not even after multiple attempts. Experience guides response to proposed design/critical slopes waiver request. • Fill slopes are more susceptible to erosion,since fill is less stable than cut underlain by consolidated,undisturbed ground;this is why VESCH prohibits emergency spillways for SWM facilities in fill sections. Agreed,however as described in one of the previous bullets,the stormwater that will run through these areas is minimized,as it takes on no upstream flow. • Engineering is not positioned to recommend approval of critical slopes waiver than proposes no walls of any height in any location(even modest 5-6' walls,or series of 3 or 4,5' high walls). • Tiered walls of modest height could,in less than 20',eliminate elevation gain of 20'. • If tiered walls are spaced,located not immediately adjacent to main activity centers/main building,and are protected (access to tops of walls restricted)with landscape fencing,risk to girls and boys attending the facility,if not eliminated, is minimized. We weighed these options and considered fencing,but that to presented potential problems. One of those problems was that the area for fencing and/or potential landscape increases wall height,while the fence provides something to climb,creating additional safety risks for the Club. • There is no eliminating malicious intent of any human being. Walls are attractive to children. Children are curious. Alternatives should consider wall placement,shielding walls,restricting points of access along walls, especially tops,and at wall ends. • Thought and care in design can significantly limit risk posed by tiered walls of modest height. • Engineering recommends consider and present concepts that rely on slopes no steeper than 3:1,and tiered walls of modest height. Engineering intends to recommend waiver approval of less-steep proposed fill slopes if a portion of design objective is met through retaining walls of modest height. • Engineering will not recommend strict application of critical slopes requirements to this project,or insist that a hybrid 3:1 slope-retaining wall design be limited to 0.45 Ac.critical slope impact. • If revised impact exceeds current estimate of 0.45 Ac.,yet proposed(3:1)grade has a better chance of long-term stability,if wall heights do not pose same risk as risk posed by 20'-30' walls,then Engineering will recommend the preferred design alternative for critical slopes waiver approval. 2 Note:For the moment,Site and WPO plans received 1/31 and 1/22,respectii take an all-or-nothing approach to retaining walls. There is surely a middle-ground alternative design approach that address myriad facility use,safety, resource protection,and technical county code objectives. While tiered walls and 3:1 slopes all would help, in this specific situation the feasibility is difficult due to two factors, 1)tiering walls and increasing the slope will result in more impact not only to the critical slope,but the entire down hill side. This will result in a larger area of disturbance, which will not allow stormwater requirements to be met,as a larger area of undetained flow will be generated from those limits. Additionally,the larger grading impact will remove more mature vegetation from the hillside. 2)The cost of adding the walls and necessary imported fill would typically make this a cost prohibitive procedure. When considering alternatives,please: • Apply 18-30.7.5 steep slopes standards,which are wholly appropriate for waiver request proposal that must reflect best engineering practice to limit potential for erosion,and increase likelihood of post-developed slope stabilization. All items at 18-30.7.5 are relevant(a./b./c./d.). • Estimate total area of critical slopes that exist on TMP#06000-00-00-078A0;this value is reported in table format in Engineering recommendation to Planning,along with proposed impact to critical slopes(0.45 Ac./current design). (An estimate of total area of critical slopes that exist on this 216.69 Ac.parcel provides context(-0.45 Ac. impact) relative to overall presence of critical slopes on the parcel under development.) While I understand the request of this exercise,the Club does not have access to any locations on the parcel,as this is the location that ACPS has been willing to lease to the Club. • Parcel acreage=216.69 Ac. A guess without real basis is 3-5%of this parcel is comprised of slopes steeper than 4:1 (critical). • Could Timmons use county GIS topographic data layer to analyze extent of critical slopes on this parcel,as a percentage? Note:A close approximation is helpful,provides context,and is far better than a guess. Also,image caption,below. Left:GIS critical resource map turned on;Right:GIS critical resource map with floodplain/stream buffer layers off. Image right emphasizes presence of critical slopes. It's possible more than 5%of the total area of this county-owned parcel is steeper than 4:1 (25%),or more than 10 Ac.of the parcel is in critical slopes. It would be helpful to know. It would be helpful to report that proposed design impact of 0.45 Ac.is<5%of critical slopes that exist on-site, for example. Engineering would also like to frame impact to critical slopes in context of site development LOD,6.49 Ac. 7%of area of disturbance is on critical slopes. 93%of proposed development avoids critical slopes. Less steep alternative design with modest walls and limited impact to critical slopes is a favorable design that Engineering can support. • fr • .. 14• • #ret, I:I AP' t. :c e ks. - 1•;17 F' 111 -44...4,. 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'CP .....''' ,..1 i 11, , 1.> Illirl N*N44 41..' 4 t. -, ii,... ,, , ,.. p . 4- ) .11\- .. .."'‘. • ot \ _ _,_17 \ ,__ .e...__.444%: N , „,/,..**.y. , •:!, _,, k 4 ,v..•,\, .Illft. ..4"..„.._--, _dmilillh, t--- ,-, \,';', 1 ';•' _,--,4 lik• 4111;1',,f'pi:iv --0 /, WP02020-00005,C4,ESC Plan,Phase III—proposed 2:1 slopes across critical slopes. Please note:Elev.490' to Elev. 530 is a 40-ft. unbroken vertical interval. Engineering requests design conform with standards at 18-30.7.5.c./d. Per the detail attached this is what we are specifying...additionally,the drainage strategy does not allow any concentrated flow to outfall on these slopes. That detail is not yet on our plans, but will be as we move forward. 5 / / / / i // 1s$ 4 _ � _ i L ` fP(S \ti IL ✓Ilk ii4t- 'W -t5s, t - / /* s . #i",P sem .` i ALIL ,d$ss" . .�; T� -- ��,__ • sr, .� 411111. ir--"_ >>eCID �/ �� PS illillik 4..!..-.-- - - ✓�r� B/M �� I ' I SF - - Sea sin - 40 14 1,;,\;-,,, _ —480' ^ Thanks,Craig best,J.Anderson 434.296-5832-x3069 John Anderson,PE,Civil Engineer II • (434)296-5832-x3o69 Community Development Dept. I Engineering Division County of Albemarle 14oi McIntire Road Charlottesville,Virginia 22902-4596 From: Craig Kotarski <Craig.Kotarski@timmons.com> Sent:Tuesday, February 11, 2020 12:45 PM To:John Anderson <janderson2@albemarle.org> Cc: Bill Fritz<BFRITZ@albemarle.org>; Frank Pohl<fpohl@albemarle.org>; Christopher Perez<cperez@albemarle.org>; U Lopez<Ilopez@milestonepartners.co> Subject: RE: WPO202000005- Boys and Girls Club, Northside,VSMP/WPO One question we have, as we prepare our special exception, is the reference to section 32.3.10(d), within 4.2.5.a.1 below. In looking for that,that section does not exist...is that actually pointing to a different section? Any help or info would be great. 6 Thanks! Craig From:John Anderson <ianderson2@albemarle.org> Sent:Tuesday, February 11, 2020 10:32 AM To: Craig Kotarski<Craig.Kotarski@timmons.com> Cc: Bill Fritz<BFRITZ@albemarle.org>; Frank Pohl<fpohl@albemarle.org>; Christopher Perez<cperez@albemarle.org>; U Lopez<Ilopez@milestonepartners.co> Subject: RE:WPO202000005-Boys and Girls Club, Northside,VSMP/WPO Craig, Thanks for your note. Since it may be difficult to establish or argue 18-4.2.5.a.3. - b./c. as rationale for granting a modification, or waiver,your email may indicate likely best path(rationale)for granting a modification,or waiver; a./d.: public safety is always the highest public purpose, in my view. Thanks again for your note. best,J. Anderson 434.296-5832-x3069 Sec. 4.2.5- Modification or waiver. Any requirement of section 4.2.1,4.2.2.4.2.3 or 4. .a may be modified or waived as provided herein: a. Modification or waiver by the commission.The commission may modify or waive any requirement that is not sut t. Request.A developer or subdivider requesting a modification or waiver shall file a written request in accorc pertains to a modification or waiver of the prohibition of disturbing slopes of 25 percent or greater(hereina large-scale movement of soil and rock,excessive stormwater run-off,siltation of natural and man-made boc and welfare factors-)that might otherwise result from the disturbance of critical slopes. 2. Consideration of recommendation;determination by county engineer.In reviewing a request for a modificz commission. If the request pertains to a modification or waiver of the prohibition of disturbing critical slope factors so that the disturbance of the critical slopes will not pose a threat to the public drinking water suppli engineer shall evaluate the potential for soil erosion,sedimentation and water pollution that might result fry of Virginia Erosion and Sediment Control Handbook and Virginia State Water Control Board best manageme 3. Findings.The commission may grant a modification or waiver if it finds that the modification or waiver wou practices;and at least one of the following: a. Strict application of the requirements of section 4,a would not forward the purposes of this chapter or b. Alternatives proposed by the developer or subdivider would satisfy the intent and purposes of section c. Due to the property's unusual size,topography,shape,location or other unusual conditions,excluding would result in significant degradation of the property or adjacent properties:or d. Granting the modification or waiver would serve a public purpose of greater import than would be sen From:Craig Kotarski<Craig.Kotarski@timmons.com> Sent:Tuesday, February 11, 2020 8:42 AM To:John Anderson<'anderson2 albemarle.or-> Cc: Bill Fritz<BFRITZ@albemarle.org>; Frank Pohl<fpohl@albemarle.org>; Christopher Perez<cperez@albemarle.org>; U Lopez<llopez@milestonepartners.co> Subject: RE: WPO202000005- Boys and Girls Club, Northside,VSMP/WPO 7 CAUTION: This message originated outside the County of Albemarle email system. DO NOT CLICK on links or open attachments unless you are sure the content is safe. John, thanks for your email. We are in the middle of preparing a Special Exception request for the impact to the critical slopes. We have looked at retaining walls, however those walls ended up begin over 30'tall. This poses a major safety issue for the Boys&Girls Club, since they will have hundreds of students on campus during the day. Due to the nature of the overall site and the ability to tie in the grades,they were ecstatic that the retaining walls could be removed. Regarding the erosion control,the site does have its challenges. We have taken extra precaution to sit down with the contractor, prior to finalizing this design to get their input. We worked hard to place erosion control measures in locations that they can stay during construction, limiting additional earth movement. On this site,while certain slopes are "critical", all of the slopes are steep and will require care and attention to detail during the construction process. We are hoping to submit the Special Exception application next week. While there will be no action on it, prior to the SRC meeting, hopefully it gives everyone a sense and some comfort of where we are going with this overall application. Best, Craig From:John Anderson<ianderson2@albemarle.org> Sent: Monday, February 10, 2020 6:12 PM To: Craig Kotarski<Craig.Kotarski@timmons.com> Cc: Bill Fritz<BFRITZ@albemarle.org>; Frank Pohl<fpohl@albemarle.org>; Christopher Perez<cperez@albemarle.org> Subject:WP0202000005- Boys and Girls Club, Northside,VSMP/WPO Craig, Since proposed design requires Planning Commission modification or waiver of critical slopes requirements,which depend on Findings(18-4.2.5.a.3.; Also, 18-4.2.5.a.1.,2. County Engineer waiver role), has Timmons considered retaining walls rather than grading so steeply into critical slopes below contour elevation 515? We routinely see private development propose tiered(or high)walls to avoid critical/steep slopes, and it is an option when designing to avoid critical slopes. Glad to see that the proposed layout of building, paved areas, and site access nearly entirely avoids critical slopes. The majority impact to critical slopes appears to be grading(with proposed grade quite steep),which may be avoidable if design were to use retaining walls. I will review site and WPO plans,and hope to send comments by late next week, if not a bit earlier—but critical slopes are a concern. C3.2, ESC plan, phase 1,proposes substantial grading to install sediment traps on critical slopes(in preparation for upslope development). What design alternatives exist that might lessen direct yet long-lasting impact of temporary ESC measures on critical slopes? Would retaining walls allow a more measured ESC approach that causes less impact to critical slopes? Thanks for your time and patience—please feel free to share any thoughts. ( I will review site and WPO plans as soon as possible.) best, J. Anderson 434.296-5832 -x3069 C4.0 8 SHEETS C4.1, C5.0 & C5.3 • ors • 4 0 • /N. _ 111�111 i T - l � l1,� • „, T : illllllllll� lll '. `tea f \' : 1 . . • • • C3.2 9 l TOP OF DAMELEVATION 314 50 • \ i ( 44.44., N. \\:,,,:c ,,, IWINIMINS N MI CD IMININIMIRIN• MIMI NN N. \ 0\ \.. N \ �%* ` ���11 ° ' '11 N Q a \ \STONE 9VEIR ,` a N \ \ a a \ © a \i• — — N \ 0S S of . �, \ _ 1 6.49 S. \ \ \ SOLTYPE \ \ \ \ o :t1 \ j a \ N .ri, N \ \ \ SEOaENT TRAPPS. �:• a ~ DRAINAGE AREA.2 74 AC a TT! CY ' a CYi ..., - 3 S \ N '-\ ` a a / ( a i i t ./..... -- 111115 I ft -, 0 sN,._ to, 4 4441,... A --- ...__ _ Ili% \ -— N , ..f :..'1, .k Cl . _ %.% ♦ ' Ô!W N �� �. ` STONE WM `�''�_ 1 ► ♦ \ ♦ ♦ o ` " 1 \ • ♦ ♦ , ' , r : ,�1 ' '1 \ % ` ail am?me me on John Anderson,PE,Civil Engineer II • (434)296-5832-x3o69 Community Development Dept. I Engineering Division 10 • County of Albemarle 14oi McIntire Road Charlottesville,Virginia 22902-4596 11