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Home My WebLink AboutWPO202100063 Correspondence 2022-05-20 ROUDABUSII, GALE & ASSOC. , Inc. IV A PROFESSIONAL CORPORATION Serving Virginia Since 1956 To: Albemarle County Community Development Department Date: 05/19/2022 401 McIntire Road Charlottesville, VA 22902 Project: Dunlora FafFil Village—WPO Plan WPO 2021-00063 Please find below the items associated with revisions for Dunlora Village WPO Plan. _X_ Included (via digital submission) Under separate cover via the following items: Quantity Description Revised WPO Plan Revised Stormwater Pollution Prevention Plan (SWPPP) WPO Application Comment Response Letter-Albemarle County HydroCAD Reports Sediment Basin Design Forms r CGP Registration Statement VRRM Spreadsheet (.xls) Comments: *(1) hard copy of the WPO plan and SWPPP will be hand delivered Friday, 5/20 to the CDD for John Anderson. **Check in the amount of $2,652.00 to be hand delivered Friday, 5/20 to the CDD. These are transmitted as checked below: For Approval/Signature For your use Please return _As requested x Resubmitted w/revisions _Review/Comment For Bids due Other Signed: Chris Mulligan (cmulligan@roudabush.com) cc: Zach Dahl (zdahl@roudabush.com) If enclosures are not as noted, kindly notify us at once. RECEIVEC Received By: yll a i c N O e Date: OO�� MAY 2 0 2022 COMMUNI F� 999 Second Street SE.Charlottesville VA 22902 -DEVELOPMEN T 434.977.0205 ROUDABUSH,GALE&ASSOCIATES,INC. ENGINEERS,SURVEYORS AND LAND PLANNERS May 12th, 2022 Mr.John Anderson Albemarle County Engineering Department 401 McIntire Road Charlottesville,VA 22902 Project Title: Dunlora Farms-Village—VSMP Plan Dear John, Please consider this the cover letter for the resubmittal of the Dunlora Farm WPO Plan. In particular,the current WPO plan was revised so as to avoid the impacts of the preserved steep slopes associated with installation of Temporary Erosion Control & Permanent Stormwater Management Facilities. In addition,the concentrated stormwater outfalls have been directed to the existing concentrated outfall locations,where runoff reduction is provided to each outfall, as well as decreases to the 2 & 10 year pre-developed runoff quantities, ensuring channel adequacy at each point of release. The unfortunate result of having limited concentrated outfall locations is that the drainage areas to each facility are in excess of 5 acres. To circumvent your concerns of the larger CDA's,we have introduced plunge pools and demising walls to 'clean'the runoff prior to entering into each facility independently; this should allow for maintenance and also reduce the influx of sediment into the sand filter sections. Also, since plunge pools are now included in the design-to remove sedimentation concerns-, there was no need for the addition of sump inlets Since hardship conditions for terrain and steep slopes were recognized on this challenging site,offsite nutrient credits (16.33 lbs/yr.)from the same HUC watershed shall provide the remaining pollutant removal for this development. There will also be 14.5 acres of preserved and dedicated Open Space- primarily utilized to preserve the Steep Slopes located within and outside of the lots. Additionally, there are some storm sewer linear impacts to the steep slopes in Ph. 2 &3 essential to effectively draining the site into the permanent stormwater facilities;alternatively,to avoid,the storm sewer depth was becoming much too deep. The Stormwater Narrative explains the water quality and quantity compliance strategy in depth, and the Outfall Compliance Sheet provides the outfall summaries for the pre and post developed runoff conditions to each outfall location. The supporting documentation does include a few files due to software limitations, however the files are named/organized in a manner that can hopefully be followed rather easily. Lots of hydrographs and routing data,for sure. The basins have been routed utilizing Modified Rational Method with a Runoff factor of 0.60. With this,the bulk graded site should be properly controlled during construction so as to avoid transport of sediment offsite or into environmentally sensitive areas. It is also note-worthy to point out that since SWM 'D' outfalls into SWM 'E', dewatering holes were implemented into SWM'D' riser to ensure that the distilling area remains dry without manual intervention between rainfall events. I wanted to point this out should you feel that this reduces the Dunlora Village—VSMP Plan Page 2 of 4 treatment volume,via allowance of the slow release. By combining SWM 'D'&SWM 'E'outfalls,we have avoided offsite improvements necessitating drainage easements;Ph. 3&Ph.4 are combined into a single concentrated outfall location exiting SWM'E'. Below is the most recent email from you in review of the WPO Plan. I have also included 'blue' responses below, where I felt helpful. Should you have any difficulties finding any pertinent information during your review, please do not hesitate reaching out. Sincerely, Chris Mulligan, P.E. To the concept presented: 1. 9VAC25-870-69:As design is refined with more detailed spatial elements, including size of facilities, Engineering expects design to hold to phosphorus reduction values approximated by VaRRM.xls. a. Engineering accepts that statements concerning site constraints(email below)are reasonable factual and accurate in context of practical limits to on-site SWM water quality control. Thank you for this consideration. b. Compared with initial design,current concept presents an alternative concept that avoids steep slopes,and aims to achieve maximum on-site phosphorous reduction. There are no steep slopes to be impacted with the current WPO Plan. c. Engineering views 16.33 lb.remaining TP load reduction required as a reasonable and practically-attainable target: i. Though not representing 75%on-site phosphorus reduction,proposed concept represents 63.55%on-site reduction. ii. With subsequent submittal,provide narrative text(SWM Notes)that specifically address items listed at 9AVC25-8700-69.B.3.(i)-(iv). iii. Engineering review will reference/link narrative text SWM Notes as supportive of accepting lesser on-site reduction as sufficient. iv. Remaining approximate 16.33 lb.to be met via combination of off-site compliance options available and outlined via state code. This is the maximum offsite nutrient offset/load needed to support the current design. In all likelihood,the final dedicated Open Space area will be greater than 14.5 acres. 2. Engineering will evaluate filtering practices in strict comparison with VA DEQ Stormwater Design Specification No. 12(strict evaluation against): a. Maximum contributing CDA of 5 Ac.for surface sand filters,and a maximum CDA of 2 Ac. (recommended for perimeter or underground filters). Plunge pools and demising walls have been introduced to reduce the maximum drainage area to under 5 acres to each filtration bed. b. Please note that"filters have been used on larger drainage areas in the past,but greater clogging problems have typically resulted." VA DEQ Tech Spec No. 12, c. Soil testing requirements: Ref.6.2, Soil testing requirements,p. 7,BMP specification No. 12. Soil testing will be provided as available. Dunlora Village—VSMP Plan Page 3 of 4 d. Overall sizing requirements, Ref.6.1., including storage volume of at least 75%of Design Treatment Volume(p.6). Sand Filter Area and Volume sizing provided in plan-set. e. Depth to water table and bedrock, Ref.p.4. Preliminary borings indicate this is a minimal concern,but will verify with soils borings. f. 7.3,Steep Terrain,several key design criteria, including(p. 11): i. Gradient of slopes contributing runoff to sand filters Utilized plunge pools and gravel diaphragms to alleviate concerns of sediment transport ii. 2-cell,terraced design for steep terrain;energy dissipation Multi-cell with riser&barrel to minimize energy transfer; only largest storm events utilize above ground/weir flow to progress downstream to outfall locations. In particular, SWM 'A' has a concrete spillway with rip-rap toe to enter into the lowest extended detention facility. iii. Drop in elevation between cells limited to 1 foot Not really applicable here, since drainage is being conveyed via storm pipes between facilities. iv. Slope armored with river stone or equivalent Cl. 1 Rip-rap w/Underlying F.F. 18"min depth is my typical section 7.4,Cold climate and winter performance(p. 11). Plunge Pools and optional by-pass can be utilized to alter,protect and/or maintain the facilities while operational. g. 6.5,Filter media and surface cover,Impervious drainage area:The contributing drainage area should be as close to 100%impervious as possible in order to reduce the risk that eroded sediments will clog the filter. These facilities are maintained by the HOA and should have regular inspections. In addition, plunge pools and/or gravel diaphragms have been introduced prior to most of the facilities to maximize the longevity of the filters. h. 6.4,Conveyance and overflow(p.8): Engineering notes BMP practice states that'Most filtering practices are designed as off-line systems so that all flows enter the filter storage chamber until it reaches capacity,at which point larger flows are then diverted or bypassed around the filter to an outlet chamber and are not treated. Runoff from larger storm events should be bypassed using an overflow structure or a flow splitter. Claytor and Schueler (1996)and RAC(2001)provide design guidance for flow splitters for filtering practices. Some underground filters will be designed and constructed as on-line BMPS. In these cases,designers must indicate how the device will safely pass the local design storm (e.g., 10 year event)without resuspending or flushing previously trapped material.' The larger filters have been located offline,and also have plunge pools to minimize filter sedimentation. There are adjacent risers located within each to pass the larger storm events. 3. It is unclear if filtering practices with associated upslope forebays and distilling ponds are capable of meeting energy balance at release points to natural conveyances: a. Each discharge to a natural channel or terrain feature is required to meet 9VAC25-870- 66.B.3, Energy balance. Shown for each concentrated outfall proposed. In addition,all capturable sheet-flow is to be directed to the SWM devices. Perimeter terrain offers some limitations to achieving this goal, and is depicted on the Outfall Summary Sheet b. Can RGA provide detail or at a conceptual outline of how proposed SWM concept meets energy balance at each discharge point? Runoff Reduction Calculations including pre/post mapping provided with this submittal. c. Is it via forebays,distilling ponds,and sand filters alone? d. Do preliminary routings indicate this to be the case? 4. Given BMP design criteria,Engineering evaluates concept plan(as presented): a. Likely requires adjustment/concept revision to ensure compliance with: i. Max.CDA • Dunlora Village—VSMP Plan Page 4 of 4 ii. Impervious CDA iii. Steep terrain design criteria iv. SWM quality/quantity requirements(likely not met with limited number of filtering devices proposed) v. Note:Numerous,smaller,strategically placed filtering practices may be required. vi. Engineering cannot approve,per ordinance(17-408.C.2.), BMP design that does not attain BMP Clearinghouse Website design criteria. Design that deviates from BMP Clearinghouse design criteria is an unapproved BMP (design). vii. It is not possible to provide a more detailed review of the concept,without more detail. Thank you for the insight provided within your comments to-date,and hope that this submittal has addressed the majority of your concerns. 5. From email,below:"Open space area of 14.77 acres shall be dedicated for restriction across the entire 80.77 acre parcel,to include future recreation fields,and access from Dunlora to a parking lot a boat ramp,alongside." I may be misreading this,but recreation fields or access from Dunlora to a parking lot and boat ramp are not eligible for consideration as forest/open space from a SWM perspective. Recreation fields are mowed. Access to parking/boat ramp,same. Eligible areas may not be developed,or include impervious surface,or be bush-hogged more than 4 times per year. Got it,thanks. Final Open Space needed is 14.5 ac.to meet WPO requirements. 6. Rooftop runoff not captured/conveyed to SWM facilities: SWM/WPO plan design(and later, independent homebuilders)may not propose release of concentrated downspout runoff to fill or cut slopes(Ref. 18-4.3.3.C.4). Noted in plans. Physically capturable rear yard drainage is being directed via rear yard swales toward stormwater inlets of facilities. 7. Please exercise caution when representing uncollected runoff as sheet flow, in post-developed condition;for example:rooftop runoff requires transition to sheet flow,if not conveyed to a dedicated SWM facility. Since the uncollected runoff areas were not included/treated as a portion of the necessary stormwater compliance strategy,areas of concentration are being directed to Level Spreaders,so as to achieve sheet- flow. Smaller,more remote and uncapturable areas-due to terrain constraints-shall have graded yards to initiate the sheet-flow conditions. 8. Items above relate to compliant filtering practice design(Engineering evaluates against BM P specifications),compliance with 9VAC25-870-66.B.3,and 9VAC205-870-69. 9. Additional comment may be possible with additional detail. Hope you find approach this approach to be more favorable than the last. Look forward to hearing from you, Best THE COUNTY OF ALBEMARLE Community Development Department 401 McIntire Road,North Wing }}�� 4Y Charlottesville, VA 22902 K,�� J RE: APPLICATION RECEIPT- Must accompany' in-person or mail-in payments Applicant Name: Zach Dahl Owner Name: E L &Ann Phillips: Phillips Living Trust etal c/o Caroline Molina-Ray Submission Number: WPO 2022 73 Submission Type: New Application Tax Map Parcel Number: 062000000016A0 Project Address: 1315 DUNLORA FARM RD Payments can be made in-person or by mail at: THE COUNTY OF ALBEMARLE Community Development Department 401 McIntire Road,North Wing Charlottesville, VA 22902 ATTN:Application Processing (434)296-5832 To pay for your application either in person or by mail,please follow these steps: 1. Print out both this Application Receipt and the receipt from the Payments tab. (See additional help below.) 2. Include both forms together(the Application Receipt and the printed Payments tab)when sending payment. 3. When paying either in person or by mail,PAY THE SUBTOTAL AMOUNT NOTED ON THE PRINTED PAYMENTS TAB PAGE. (NOTE: No extra processing charge is required when paying in person or by mail. The processing fee only applies to payments made online.) 4. Submit the payment with the Application Receipt and the printed Payments tab. 5. NOTE: To print the receipt from the Payments tab,click the Payments tab to find the fees as shown on the following screenshot. 1 -MimeQ'WV wew welcome Content Terra stymy •New Single Family Dwelling Ampiiuda° Detail% Documents Map Payments St tvity 5rim Click Payments to find Fees for Application the l fees° nt pie and include wnh the tanvary 19 10?? Payment Form,along with your payment of cash or check Unpaid DTP 5.4E FR OESCaMrrnw Wrr.M Grcundwne.Tar 1 aeenemenr GN .00 55900 553TDTn1 sss Cod COMIC=PAY THIS AMOUNT(subtotal). e NwalEFtamac A+a[ssretar s2.07 The non-refundable processing fee does not apply to you.Please do not Total Amount Due S61 07 inc./nude tha fee in your payment Questions? Please call the Applications Processing team at(434)296-5832 for assistance or send an email to Camino@Albemarle.org. We look forward to serving you and appreciate your business! 2 Firefox https://app.oncamino.com/albemarlecounty-va/dashboard/116336/guide/... Fees for Application NUMBER WPO-2022-73 ADDRESS 1315 DUNLORA FARM RD APPLICANT Zach Dahl May 17,2022 Unpaid STEP NAME FEE DESCRIPTION AMOUNT Equal to or Greater than 10 and less than 50 acres VSMP_LGLESSTHN50 $2550.00 (VSMP) 4°%0 Surcharge-Technology_SURCHAR-TECH $102.00 SUBTOTAL: $2652.00 0 NON-REFUNDABLE PROCESSING FEE: $79.51 Total Amount Due: $2731.51 1 of 1 5/20/2022, 11:29 AM