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Home My WebLink AboutWPO201600065 Correspondence 2022-11-10John Anderson From: John Anderson Sent: Thursday, November 10, 2022 12:05 PM To: Dan Ratzlaff Cc: Frank Pohl; Emily Cox Subject: RE: Planning Application Review for WPO201600065 Pantops Public Safety Facility - VSMP. [ As -built review; Approved ] Attachments: RE: Pantops - road profile (sketch 18); FW: Pantops PSF - 100 year storm volume; Pantops Public Safety Facility - WPO201600065; FW: Pantops - road profile (sketch 18); Pantops Public Safety Facility, Sta. 16 - road profile (sketch 18); RE: Pantops Public Safety Facility, Sta. 16 - road profile (sketch 18); FW: Pantops PSF - Road profile comparison Dan, As follow-up to discussion earlier this morning. First, you have the right impulse: to ask questions; second, to ensure we have what we need prior to closing a project. I admire and appreciate this. Flooding of Pantops Public Safety Sta. 16 site access is a non -issue operationally, practically, and from compliance /project close-out perspective. We rely upon DJG design consultant evaluation. ( see attached) • Jun-2016 thru Mar-2018, I was with FES (now FPC). I corresponded with the County Engineer during this period, specifically, on topic of revised road (site access) alignment. • This is a county project. Neither site access (road) nor VSMP WPO plans were required to be bonded. During this period, FES/FPC working closely with Engineering and DJG. • Items coordinated with county engineer: landing, grade, etc /site access. Please note approved plan included 3-24" RCP beneath site access, MV ELEV.=420.75' which is 0.25' higher than principal spillway riser rim ELEV. • DJG calculation packet dated 1/5/17, p. 8 ( available at CV, )APO201600065), states: `The secondary spillway for the detention pond is a set of three 24" RCP that pass beneath the new entrance road which will permit vehicles to leave the site under flooding conditions.' Again, INV IN for triple -line 24-RCP =420.75'. • Triple line 24" RCPs, bid Additive #2 were not installed. Please see attached emails for additional revised roadway alignment information, including landing /grade, with exhibits indicating removal of 3-24" RCP beneath Pantops Sta. 16 site access. • DJG was specifically consulted. DIG advised on removal of emergency spillway pipes (3-24" RCPs). No effect /no flooding of site access during 25-yr storm event. This is the design standard that applies to subdivisions with single point of access. • Ref. attached, email, Darren R. Curtis, LA, DJG, to J. Anderson, 10/24/2017 1:52 PM. • Ref attached, email, Darren R. Curtis, LA, DJG, to S. Hoffmann, August 31, 2017 8:27 AM. • Partial text, 8/31/17 DJG email: `I cannot determine precisely the storm frequency that will top the roadway, as I do not have the data or time available to model the upstream system. However, the new pond total volume is 103,890 CF (if the pond was filled up until water started pouring over the roadway). The 100 year storm volumes flowing into the new detention pond is 97,600 CF. This means that if you assumed that no stormwater left the pond during a 100 year event, the road would still be accessible throughout the duration of the 100 year storm. So it will take a storm larger than the 100 year storm to flood the roadway.' • FES /FPC, S. Hoffmann, coordinated with Engineering. Ref attached email, 8/31/2017 11:17 AM. • Also, attached (same) email chain, J. Anderson to Darren Curtis, 10/24/2017 12:33 PM; partial text: `As -built low -point elevation of Access road is shown as 423.91'. Design Low Pt. Elev.=424.50'. Will SWM basin primary spillway (riser) pass the 25-yr storm event without overtopping the Access Road at its lowest point, which is 0.59' lower than designT • DJG 10/24/17 response to 10/24/17 J. Anderson (FPC) email: Partial text, addressing effect of removing 3-24" RCPs beneath site access: `The maximum elevation of the pond during the 25 year storm will be 420.90. To further ease your concern, note that the pond volume (with an emergency spillway of 423.91), is about 90,000 CF. The 100 year storm will contribute approximately 96,000 CF to the pond. The _ storm will contribute approximately —. So even if the outfall control structure were to clog completely, the 25 year storm would be held within the pond.' • Revised site access low point ( 24" pipes removed), reviewed by Engineering at FES /FPC request, is 423.91'. This, in effect, became the new emergency spillway elevation. It is important to note that with basin storage of 90,000 CF, and 100-yr total volume—96,000 CF, that if the principal spillway ( riser +48" outfall pipe) passed only =6,000 CF, the 100-yr event would not be projected to crest Pantops Sta. 16 site access /road. • Albemarle consulted with DIG at time of construction re. revised site access /road; revised design indicated removal of 3-24" RCPs beneath site access. • DIG evaluated condition of principal spillway outfall control structure in a completely obstructed condition, and advised detention basin volume of about 90,000 provides adequate storage for 25-yr event, which contributes, in total, approximately 63,000 CF of storm runoff to the detention basin. • In my judgement, FES/FPC (S. Hoffmann) coordinated conscientiously with staff (FES Mgmt. /Engineering) and design consultant at time of design revision (2017) to properly address questions relating to removal of 3-24" RCP beneath Pantops Public Station 16 site access —exemplary coordination, to my mind. I appreciate your asking questions that help ensure Engineering obtains information required to close out projects. Thanks especially for keeping me on track. I had no recollection of project details /correspondence dating to my time with FES /FPC, vis-a-vis this project over 5 years ago. I am glad we have what we need. Approved As -built for Pantops Public Safety Sta. 16 (CV) indicates 3-24" RCP were not installed; this as -built condition is acceptable and compliant with state stormwater management requirements. Please let me know if you have any other questions. best, J. Anderson John E. Anderson, PE I Civil Engineer 11 Department of Community Development I County of Albemarle, Virginia 401 McIntire Road I Charlottesville, VA 22902 434.296.5832 ext. 3069 From: John Anderson Sent: Thursday, November 10, 2022 8:41 AM To: Dan Ratzlaff <dratzlaff@albemarle.org> Subject: RE: Planning Application Review for WP0201600065 Pantops Public Safety Facility - VSMP. [ As -built review; Approved] Dan, It is not. Without the triple line emergency spillway that would provide relief via 3 pipes located beneath site access, volume /elevation of detained runoff (from Pantops Sta. 16) in the basin increases during infrequent events, were detained storm runoff volume (from Sta. 16) to reach rim of principal riser. Emergency relief, once detained elevation reaches principal spillway rim is the site access itself, which is, in effect, a higher -elevation paved embankment. Site access provides ultimate relief should detained volume of an infrequent event exceed principal spillway capacity. A very infrequent event may result in up /downslope erosion of Sta. 16 access embankments before flow returns to existing channel downslope of site access, if detained volume ever crested site access. Possible erosion may require repair, as it would in any location during an event with peak flow surpassing design. Albemarle opted to eliminate triple -line 24" RCP prior to bid, in effect increasing stored volume. Emergency relief exists in form of relatively flat paved site access. Relatively few emergency spillways are paved: some are turf, others armored (riprap), others, as in this instance (bid Alt. #2), are culverts that provide non -erodible emergency relief /outlet at lower elevation. Key: higher emergency relief=larger detained volume, which intuitively and actually reduces QP�k release from the detention basin at Pantops Public Safety Sta. 16. I appreciate your checking. Thanks, best, J. Anderson John E. Anderson, PE I Civil Engineer 11 Department of Community Development I County of Albemarle, Virginia 401 McIntire Road I Charlottesville, VA 22902 434.296.5832 ext. 3069 From: Dan Ratzlaff <dratzlaff@albemarle.org> Sent: Thursday, November 10, 2022 8:08 AM To: John Anderson <0anderson2@albemarle.org> Subject: RE: Planning Application Review for WP0201600065 Pantops Public Safety Facility - VSMP. [ As -built review; Approved] So just to confirm, the 3-24" pipe assembly is NOT required? Dan Ratzlaff Manager of Engineering Compliance Albemarle County d ratzlaff(o)al bema rle.org 434-296-5832 x3438 401 McIntire Road, North Wing, Charlottesville, VA 22902 From: John Anderson <janderson2@albemarle.org> Sent: Wednesday, November 9, 2022 4:40 PM To: Dan Ratzlaff <dratzlaff@albemarle.org> Cc: Steven Hoffmann <shoffmann@albemarle.org>; Geoff Elsie <gelsie@albemarle.org> Subject: Planning Application Review for WP0201600065 Pantops Public Safety Facility - VSMP. [ As -built review; Approved] The Review for the following application has been completed: Application Number = WP0201600065 — As -built review Reviewer = John Anderson Review Status = Approved Completed Date = 11/09/2022 This email was sent from County View Production. Dan, based upon review of As -built v. design, familiarity with project (site visits, months apart), 7/27/22 photos, aerial /satellite image, and 5/25/21 biofilter plant counts, the As -built drawing (which relies on Albemarle furnished data; see Note below) is approved. Several years after construction: biofilter /SWM plantings thrive; detention basin contours approximate design; and all areas in vicinity of bioretention (1,2), pretreatment cells (1,2,3), and detention basin are stabilized. As -built biofilter surface areas exceed design (sheet CG-101 . No issues present. Triple line of 24" RCP (detention emergency spillway) beneath Public Safety Sta. 16 site access are not installed; As -built drawing clearly indicates this (triple line was Additive bid item #2). CV is updated. Approved As -built is uploaded to CV. Link to approved As -built, which should display by 6pm. Thanks for your help and patience. best, J. Anderson Additional AB drawing Note THESE RECORD DRAWINGS HAVE BEEN PREPARED BASED ON INFORMATION PROVIDED BY ALBEMARLE COUNTY. THE A/E IS NOT RESPONSIBLE FOR EITHER ERRORS IN INFORMATION PROVIDED BY THE COUNTY OR OTHERS, OR FOR INFORMATION OMITTED BY THE COUNTY FOR ITS AS —BUILT DRAWINGS. Reuresentative photos. 7/27/22 �S 1.�H V P� H �r C -_ �1 '� �UN ��. �, �,:. ,sal!! _.. i!_.. �3.