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HomeMy WebLinkAboutWPO202200017 Correspondence 2023-02-13SHIMP ENGINEERING, P.C. Design Focused Engineering February 9, 2023 John Anderson County of Albemarle Department of Community Development 401 McIntire Road, North Wing Charlottesville, Virginia 22902 RE: Response Letter #1 for WPO202200017 664 West Rio Dear John, Thank you for your review of the VSMP plan for 664 West Rio. This letter contains responses to County comments dated May 22, 2022. Our responses are as follows: SWPPP 1. SWPPP /calculation cover pages to reference WP0202200017, The SWPPP cover page has been revised to reference WP0202200017. 2. Revise WPO plan, SWPPP and calculations as needed to reflect change to initial site plan, since it is our understanding that the ISP is deferred to revise layout consistent with public street requirements. The WPO plan, SWPPP and calculations have been revised with this submission. 3. Sec. 1, Registration Statement: a. Sec. II.F.: List Albemarle MS4 since project is in Albemarle MS4. Sec.II.F. has been revised to Albemarle MS4. b. Sec. II.G.: Recommend revise project start date since ISP deferred. Project start date has been revised. c. Sec. III: Identify Vol. /type of export material, approved off -site ESC plan /Grading permit #, and destination for (off -site) excavated material disposal prior to preconstruction and as pre -condition of state VAR10 permit issuance. Please indicate off - site estimated area to be disturbed. The site requires approximately 12,000 cubic yards of soil import with this revision. A note was added to Sheet C10 under project narrative in this regard. 4. Sec. 3, Nature of Activity: a. Lists total area of disturbance 3.13 Ac., while registration statement indicates 3.12 Ac. Please reconcile. Limits of disturbance were revised with this submission. With the additional parcel, the limits of disturbance are is 4.02ac. b. Revise Phase L-4. Sequence, once WPO plan sequence is revised. The sequence has been revised. 5. Sec. 4 /Sec. 5 (ESC/SWM plan sheets): Update once WPO plan is revised. Section 4/5 were updated with this submission. SHIMP ENGINEERING, P.C. Design Focused Engineering 6. Sec. 6.A, PPP Exhibits: Please relocate sanitary waste (porta-john) to avoid area upslope of sediment trap. The porta-john has been relocated. 7. Sec. 61 : Please list an individual responsible for pollution prevention practices prior to state permit issuance /prior to preconstruction. Comment noted. Contractor is to be determined at this time. 8. Sec. 8: Please list an individual responsible for VESCH compliance inspections prior to state permit issuance /prior to preconstruction. Comment noted. Contractor is to be determined at this time. B. Pollution Prevention Plan (PPP) —see SWPPP items 6, 7 above The PPP content requirements can be found in County Code section 17-404. C. Stormwater Management Plan (SWMP) VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP. This plan is disapproved for reasons listed below. The stormwater management plan content requirements can be found in County Code section 17-403. 1. C1: Revise C1 to Incl. ref. to WPO2022-00017. C1 is revised to include WPO2022-00017. 2. C3/C3-A a. Revise New V.W. Private SWM facility esmt labels to read public, rather than private. All SWM easement labels are revised with this submission. 3. C4 b. Provide bumper blocks as safety measure at nine perpendicular parking spaces near boundary with TM. 45-105. Engineering recommends VDOT GR-2 /guardrail at this location, but bumper blocks as a minimum measure. See proposed grading at this location, C5-A. Bumper Blocks were added to the parking spaces near boundary with TMP 45-105. a. Relocate proposed UG detention away from parking deck entrance. In the future, should maintenance repair /replacement require excavation, site parking (for block 1 residents) would be impossible, design is untenable. A possible alternative location for this portion of the proposed UG detention system is at the opposite end of the parking deck. Engineering cannot approve current proposed location at entrance to parking deck. Note: all site parking other than the proposed 2-level parking deck as well as area beneath existing 30' joint access easement (where it branches to development property) and access aisle fronting storage facility are proposed to include underground SWM detention systems. Permeable pavers may provide a design alternative less intrusive and with a less -total effect, since permeable pavers may be repaired or replaced in sections that avoid wholesale or deep excavation of entire parking areas or drive aisles. The site design has been revised with this submission. There is no parking deck proposed. Detention system 1 is located minimum of 25ft from the concrete retaining wall. SHIMP ENGINEERING, P.C. Design Focused Engineering b. Similarly, future access to proposed UG system at edge of dumpster concrete pad is untenable since: i. Block 1 residential units may not be deprived of waste disposal service during any period of future UG system repair or replacement. No alternative to a continuously -available solid waste dumpsters serving block 1 apartments is practical, or possible (for example: curbside receptables or temporarily relocated dumpsters that invites damage to pavement in areas without concrete pad. Revise to provide continuously -available waste disposal /dumpster location, or alternatively, show -label a second concrete dumpster pad that may be striped as available parking until required as a temporary dumpster pad. This second dumpster pad should be designed to present no conflict with future UG SWM detention system repair or replacement. Design has been revised with this submission. The underground detention system is away from the dumpster concrete pad. c. Delineate /discriminate via linework and labels: i. Private drainage easement for SWM conveyance /pipe networks upstream of proposed SWM facility. On -site SWM facilities are designated public, as stated above. Labels and linework for the easements have been revised accordingly with this submission. ii. VAR Width Public SWM facility easement Labels and linework for the easements have been revised accordingly with this submission. iii. Public drainage easement for SWM facility outfall/s downstream of any proposed SWM facility. Labels and linework for the easements have been revised accordingly with this submission. d. Revisit proposed SWM-related easements to allow offset to proposed self -storage building footers. Conflict appears imminent. Engineering judgment advises against easement so close to building foundation which may prevent future access to proposed UG detention system between storage units and 2-leval parking. While we understand the concern for the stormwater detention system and easement being relatively close to the self -storage building, we are proposing an 8-ft compacted clay core wall to be designed per the earthen embankment detail to act as a separator between the building underground stories/foundation and the underground detention system. Please see detail 14 on sheet C8. The entire detention system can be excavated & removed without impacts to the building foundation for the storage building. SHIMP ENGINEERING, P.C. Design Focused Engineering e. Ensure all VAR Width public SWM facility easement widths are consistent with ACDSM easement diagram, p. 15 .:'• SIHPI. le OWMDLi We have ensured that all the easement calculations are per the equation above. Below are the required and provided width of easements. o A4B-D1: 1.25+2+2*(10.96-5)+10=25.17' Required; 26.00' Provided. o D2-D1: 1.25+2+2*(9.68-5)+10=22.61' Required; 23.00' Provided. o D3-D2: Located in the ROW, No Easement Needed. o A8-A8A: 1.25+2+2*(10.5-5)+10=24.25' Required; 24.50' Provided. o A8A-A8B: 1.25+2+2*(8.61-5)+10=20.47' Required; 21.00' Provided. o A8B-A8C: Located in the ROW, No Easement Needed. o C1-C2: 1.25+2+2*(4.99-5)+10=13.23; Lies within Detention System 2 Easement o B1-B2: 1.25+2+2*(5.26-5)+10=13.77; Lies within Detention System 2 Easement o A7-A7A: 1.5+2+2*(8.41-5)+10=20.32; Lies within Detention System 1 Easement o A7A-A7B: 1.5+2+2*(7.33-5)+10=18.16' Required; 20.00' Provided o Al-A2: 2+2+2*(6.08-5)+10=16.16' Required; 20.00' Provided. o A2-A3: 2+2+2*(9.66-5)+10=23.32' Required; 23.50' Provided. o A3-A4: 2+2+2*(12-5)+10=28.00' Required; 28.00' Provided o A4-A5: 2+2+2*(9.47-5)+10=22.94' Required; 23.00' Provided. o A5-A6: 1.5+2+2*(6.44-5)+10=16.38' Required; 20.00' Provided o A6-El: 1.5+2+2*(13.51-5)+10=30.52' Required; 31.00' Provided o Det. Sys. 1: 49.25+2+2*(12.122-5)+10=75.49' Required; 79.50' Provided. o Det. Sys. 2: 6.25+2+2*(11.33-5)+10=30.91' Required; 33.00' Provided. SHIMP ENGINEERING, P.C. Design Focused Engineering f Dimension riprap outfall protection at public drainage outfall to existing stream (L xW x D). Dimensions of riprap outfall are now provided. Please see sheet C5 and Sheet C6. g. Revise public drainage outfall to existing stream with MH that redirects SWM discharge to be >90-deg. Relative to existing stream downstream reach. Proposed public drainage outfall directs system discharge upstream. SWM discharge must align (or be > 90-deg.) with downstream reach to avoid erosion of existing stream, or proposed outfall protection. Revise proposed acute angle of intersection to > 90-deg. Note: Any revision in range 90-135' relative to downstream reach may require existing stream far -bank structural armoring to prevent erosion of existing stream bank. >135-deg, erosion poses less concern. The riprap design has been revised to avoid < 90 degrees discharge. h. Provide lintel detail for public drainage easement if storm pipe passes beneath retaining wall in vicinity of dumpsters. Retaining wall footers/pipe crossing details are provided with this submission. Please see details 8 & 9 on Sheet C6. i. Label length of each section of proposed UG detention system. The lengths of the detention system sections are provided on Sheet C7. Provide /label CG-6 wherever proposed final grade concentrates surface runoff against curbing, for example: curb lines above Str. E2A, C4, C5, etc. CG-6 and its labels are provided where deemed appropriate. Please see Sheet C3. k. Provide storm runoff capture /conveyance immediately prior to lower -level parking deck entrance, else lower deck may receive runoff that poses nuisance, or risk, especially in winter. (See C5-A) Comment no longer applicable. There is no deck on site anymore. Two leader lines appear to point to the same pipe leading to Str. A4 and identify this pipe as 18" HDPE pipe / 6" HDPE pipe. C8 profile clarifies (2 pipes occupy same vertical space). Please revise labels to indicate 6" HDPE /PVC is below 18" HDPE. Note: C8 identifies 6" pipe material is PVC while C4 indicates 6" pipe is HDPE; please clarify 6" pipe material. Comment no longer applicable. The design has been revised where the pipes are running in parallel. All labels are depicted on sheet C5 (Utility Sheet), Sheet C6, C7, & C8 for profiles and sections of the storm pipes. m. Provide 84" CMP detention system (System 1) label and 96" CMP detention system (System 2), consistent with C8 system labels /profile captions. Comment no longer applicable. The detention system has been revised to Stormtech MC-3500 instead of the initial proposed 84" CMP's. n. Show parking deck (leader line) connection with either system 1 (84" CMP) or system 2 (96" CMP). Comment no longer applicable. SHIMP ENGINEERING, P.C. Design Focused Engineering 4. C8: 5. C9: a. Structure A4 detail appears to propose a 0.75" DIA (`0.75" Hole drilled at bottom of cap') low -flow orifice. This exceeds bounds of acceptable engineering practice for SWM facility design. 2.5"-3" is a reasonable lower limit for low -flow orifice DIA. While'/4" may satisfy SW water quantity detention requirements in theory, orifice of this slight dimension may obstruct almost immediately, even by innocuous items (debris, cloth), no matter frequency of maintenance, or inspections. Obstruction of/4" orifice short-circuits the entire detention system design, with water quantity requirement/s then not met. Please revise design, Str. A4, and underground system components upstream of A4 to provide a more resilient /reliable /practical low -flow orifice DIA. '/4" DIA low -flow orifice cannot be approved. Acknowledged. The design was revised to have a 1.5" orifice modeled to meet the 1- yr storm EBE. We have designed the orifice to be supplied solely from the underdrain pipe which is not subject to receiving any impediments larger than fine particles which might seep through the stone and filter fabric wrapped around the underdrain pipe. The 6" underdrain pipe with threaded cap installed on the downstream face of the weir wall where the cap has a 1.5" nipple at the invert elevation. b. Str. D3: comments at item a., above, apply to this structure, as well (0.75" orifice) Acknowledged. Response to item a applies to this comment as well. c. Show VDOT safety slab (manway pass-thru) in 72" and 60" MH-I, and MH-1 steps in plan view to ensure no conflict with proposed pipes in/out, at ea. str. (Str. A4/133). VDOT S1-1 and steps are provided on the section views/profiles where applicable. Sheet C6/C7/C8. a. Label detention pipe floor slope (0.0%, 0.1%, etc.) All pipes and detention systems are labeled with slopes on the profiles/sections. C6/C7/C8. b. Provide contractor note to avoid negative detention slope if proposed detention system pipe slope =0.0%. A note is provided on sheet C7 regarding detention slopes. 6. C10: a. Provide orifice trash rack details for revised low flow orifice DIA. Detail is for 5" orifice. Orifice trash rack detail is provided on Sheet C7. The 5" was a typo and has been fixed. 7. Revise calculations to accommodate any design change. Acknowledged. Calculations have been updated as the design has changed. 8. Revise calc. packet cover to ref. WP02022-00017. The stormwater packet now includes WPO2022-00017 on the cover sheet. SHIMP ENGINEERING, P.C. Design Focused Engineering 9. General: a. ZMA201800013 staff report makes reference to lack of commitment to construct block 1 building on Rio Road, while the WPO plan indicates block 1 building will be constructed. Provide WPO plan design consistent with block 2, block 1 sequence of development approved with ZMA201800013. Consistency may require additional design detail, notes, labels, calculations, etc. should Applicant wish to construct only the storage building in block 2, for a period of years, or even indefinitely. A WPO plan showing entirety of site developed affects review, approval, inspections, bond amount, routings, calculations, permit close-out, and bond release. A less than full build -out (especially indefinitely) could disadvantage Applicant from SWM water quality /quantity perspective. Engineering recommends WPO plan present alternative that shows partial build -out; that is: SWM design meeting requirements should only the storage facility be built. Without alternative block 2/storage-only design, Applicant runs risk that SWM system design may over -control, or that system components may be located in such manner that prevents adjustment or may increase system expense beyond that required for block 2-only development. As example: Proposed Phase 3, 4 sequence of construction, C 11, requires construction of detention system 1 that serves the block 1 residential structure, and then requires construction of system 2 to serve the storage facility. A system equivalent to detention system 1 might be sufficient to serve the storage facility only, if shown as an approvable alternative SWM facility design. This project is being developed in accordance with the FBC for the Rio/29 area. Prior project developers imagined phased construction, however, current owners intend upon completing development of the storage and residential at the same time. b. SWM facility and public drainage deed of easement is required. This is a separate application, and review. Easement recordation is required prior to WPO plan approval. Comment noted. We will submit the SWM facility and public drainage deed of easement once the VSMP is close approval. C. A discrete SWM plan is not included in the VSMP /WPO plan, only detention system profiles. Please provide a SWM plan with the VSMP /WPO plan. Include: i. General Narrative Stormwater narrative is included on sheet C10. ii. Ref. to calculation packet (correlate VSMP /WPO SWM plan with calculations) The stormwater calculation packet is now referenced on sheet C16. iii. Summary of storm water quality /quantity compliance (text /tables /narrative) Summary of storm water quality/quantity compliance is included on Sheet C10 and C16. iv. Pre- /post development land cover values Pre -/Post Development land cover maps and values are included on the VSMP Plan with this submission. Please see Sheet C16. v. Site and summary tabs from VaRRM.xls re -development spreadsheet VRRM maps and calculations are now included on the VSMP Plan. Please see Sheet C18. SHIMP ENGINEERING, P.C. Design Focused Engineering vi. Letter of nutrient credit availability if nutrient credit purchase proposed Letter of nutrient credit availability will be provided with the next submission. vii. Pre- /post drainage divides Pre -/Post development drainage divide are depicted on the drainage area maps. Please see Sheet C16. viii. Ref. to 25% on -site ZMA201800013 SWM control requirement. Requirements of ZMA201800013 are not applicable to this project. D. Erosion and Sediment Control Plan (ESCP) Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan is disapproved for reasons listed, below. The erosion control plan content requirements can be found in County Code section 17-402. 1. CIL a. Please revise Sequence of Construction notes to explain how SWM facilities installed prior to site stabilization are protected, how sediment deposits within UG detention systems will be removed, and how stream adjacent to site is to be protected from sediment that may bypass SWM facilities should low -flow orifice/s become blocked, or detention short-circuited. The sequence of construction notes has been revised with submission. All storm inlets/manholes are to be blocked during all erosion and sediment control phases. A note was added to phase 2, 3, and 4 to instruct the contractor accordingly. b. Revise Sequence to clarify storm conveyance elements between /including Str. A4 and Al do not occur as depicted in Phase 1 of ESC plan. The sequence has been revised so that the installation of structures A4-Al are installed during phase 2. 2. C 12: a. Storm conveyance system elements between /including A4 and Al may not be installed at this early stage of clearing. These are final storm conveyance elements, and proposed phase 1 ESC plan showing these elements with discharge to an existing stream is nearly certain to invite stream impact during land disturbance in initial constructive phase. Installation of stone conveyance system elements is disapproved at this point in ESC /land clearing sequence. Revise ESC plan to remove these elements. The E&S plan has been revised so that structures A4-Al installation occurs during phase 2 instead of phase 1. Please note that building construction cannot start without these structures/pipes in place as they are the outlet for sediment trap 1. The pipes can easily be cleaned and we have specified the cleaning of all storm pipes/structures/detention systems once site is stabilized and the site work is near complete. b. Label ST weir 15' (wide /long?) weir length, or width. Clarify weir dimensions. The weir dimensions are now provided on all applicable sheets. SHIMP ENGINEERING, P.C. Design Focused Engineering c. Show change /modification to existing curb to roll-top along Rio Road West at PCE, such that curb is mountable to construction vehicles. During phase 1 of E & S the construction entrance is located where the existing site entrance is, the existing curb at that location is a roll-top curb. The sidewalk/CG-6 are to be removed where the construction entrance during phase 2, 3, and 4 is located. A note was added to phase 1 to show the demolition of CG-6/Sidewalk d. Revise CE to P(paved)CE. PCE detail has been added to sheet C15. e. Obtain VDOT land use permit for Rio Road W, prior to working within public RW. We understand that VDOT land use permit for Rio Road W is necessary prior to working within public ROW. Contractor shall obtain this once VSMP is approved. 3. C13: a. As permanent storm conveyance /pipe elements downslope of sediment trap may be unavoidable once block 2 storage facility footers are built, consider /explain how these storm elements and stream are to be protected during phase when earth is disturbed, and sediment trap sediment -laden discharge to pipes /stream is possible, or likely. We understand that possible discharge to the system might be unavoidable. We have specified that all stormwater elements to be cleaned once site is stabilized. b. Please revise ESC legend to identify RWD as right-of-way diversion, rather than temporary diversion dike. The legend has been revised. 4. C16: a. Include paved construction entrance detail, ACDSM, p. 8. PCE detail has been added to sheet C15. b. Provide Mfr. underground detention system: i. Installation notes Stormtech installation guide is provided on Sheet C20. ii. System details Complete ADS design packet with be provided with the next submission. iii. Maintenance schedule Inspection and Maintenance for the detention systems is provided on sheet C20. iv. Periodic inspection checklist Inspection and Maintenance for the detention systems is provided on sheet C20. c. Include Construction Record Drawing (As -built) for VSMP (.PDF) on plans. The notes are provided with this submission on sheet C3. If you have any questions or concerns about these revisions, please feel free to contact me at Stephanie@shimp-engineering.com or by phone at 434-227-5140. Regards, Stephanie Paul Shimp Engineering, P.C.