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HomeMy WebLinkAboutWPO201900053 Correspondence WPO VSMP 2020-02-21SHIMP ENGINEERING, P.C. Design Focused Engineering February 21, 2020 John Anderson County of Albemarle Department of Community Development 401 McIntire Road, North Wing Charlottesville, Virginia 22902 RE: WPO 2019-00053 Eco Village — Comment Response 2 Dear John, Thank you for your review of the VSMP plan for Eco Village. We have revised the plans per your comments dated December 4, 2019 revised Dec. 13, 2019. Our responses are as follows: A. Stormwater Pollution Prevention Plan (SWPPP) 1. Notice of general permit coverage (Rev. 1) Pending. Pending — no action until precon meeting 2. Nature of the activity (use/development of the site, not the E&S controls). It should refer to redevelopment of the site, number of units, parking, private roads, support structures and stormwater controls. The narrative provided properly belongs in Section 4. (Rev. 1) Partially ,sed. As follow-up: Minor edit —Please revise description to reference 38 units. Noted, this has been corrected. 3. _._:i. 4. Addressed. 5. Addressed. 6. Addressed. 7. Addressed. 8. Addressed. 9. Sec. 1, Registration Statement, p.2, Sec. III (A., B.), Offsite Support Activity Location Information: Revise. If data unknown, please enter: Project requires offsite support; location information TBD (or sin -filar). Reg. Statement updated with requested note. 10. Sec. 1, Registration Statement, p.2, Sec. IV, E — MS4: Enter: Albemarle County, since project within MS4. Reg. Statement updated with requested note. 11. Sec. 1, Registration Statement, p.3, Sec. IV, F: Check yes, since project is a common plan of development. "Yes" now selected. B. Stormwater Management Plan (SWMP) 1. Show permanent drainage easement recording information on all parcels crossed by the Al-A-4 stormwater conveyance piping and structures. 17-304.E. (Rev. 1) Persists. Noted, this is still being obtained. 2. Addressed. 3. Addressed. 4. Addressed. 5. Provide calculations that demonstrate compliance with SP201800016, including hydrographs, routing calculations and other necessary documentation that the proposed stormwater system is adequate to manage the 25-year storm without downstream flooding. (Rev. 1) Partially addressed. 912 E. High St. Charlottesville, VA 22902 1 434.227.5140 I shimp-engineering.com As follow-up: See item 28.1., below. (Ref. pg. 97 of .PDF document of 10/25/19 SWM Calculation Packet — Link 12L.) (Same response will be used for 281., below) Noted, however the velocity data is shown on the LD-204, not in HydroCAD Link 12L. We use a different software to determine velocity. The pipes have velocities <20 fps, except for section A3-A2. We have made this section of pipe less steep. However, for the flow through this pipe, we would have to reduce the slope to 11% to achieve a 2-yr velocity of <20%. This represents a rather significant change in the design. 9VAC25-870-66.B.1.a. specifies that peak flow through manmade systems not cause erosion. We do not believe that abrasion is of concern for this system, due to the onsite nutrient and sediment treatment provided. Furthermore, we have specified a more durable pipe material (ADS HP - Storm is polypropylene). This material is designed for high performance applications, including abrasion resistance. See attached report. Thus, we request that county engineering approve this layout. 6. C4, General: Provide, show, label VDOT GR-2 (guardrail) on south side of lower parking, consistent with pending FSP comments, and recent Oak Hill Convenience Store review comments /discussion (unrelated project). Noted, GR-2 shown and labelled on lower side of parking lot. 7. C5: Building Lot/Str. 7A is partially within drainage easement. Revise structure /easement location. Building has been slightly shifted. It is now out of the easement. 8. C5: BMP D label (blue -circled text, image, below) is ambiguous. Please revise for clarity. That note has been revised for clarity. What we want to convey is that BMP E (formerly labelled D) treats 0.78 acres of untreated site runoff which flow into inlets B2, C2, & D2. It also treats 2.61 acres of runoff which had already been treated by BMP's A, B, & C which enters BMP E via storm drain B1-B2. 9. C7, Stormwater Note 6. mentions BMP C, C1, C2 —there are just two biofilters; please revise for clarity. This confusing notation has been revised — C1 is now C, C2 is now D, and D is now E. 10. C7, Stormwater Note `D'. Please renumber this, as Note 7. Revised as requested. 11. C7, Offsite Areas: Identify offsite areas as pre -requisite to Grading Permit. A note directing this has been added. 12. C8/C9: Label existing culverts under Rio Road E (X4, X3, X2, X1). Use light grayscale to indicate existing. Plans revised to show this. 13. C 13: Provide VDOT Anchoring detail. See VDOT Drainage Manual, 9.4.8.7 —image, below. Note caution against corrugated pipe (if excessive abrasive bed Load); slopes in excess of 16%; and flow velocities in excess of 10 fps. Revise design as needed. (Note: Storm profile Al-A5 is excessively steep). Noted, anchoring detail added to C12. We are not concerned about abrasive bed loads as full onsite treatment is provided, thus runoff flowing through the steep portion of the pipes will be clean. As such, we consider high -velocity flow through these sections of pipes to be acceptable as low abrasive loads should not significantly contribute to pipe wear. 14. C 13: Add SL-1 labels to Str. A4 and B5 (x 2) in profile views. Note alone is more likely to be overlooked. SL-1 note added in profile view for A4 and B5(x2). 15. C 13: Str. A5A INV OUT is shown as 387.50 and 386.50 in separate profiles. Please reconcile. Str. A5A invert out is now 387.00 in all profiles. 16. C 13: Str. C 1 — INV IN < INV OUT. Check /revise. This has been revised, there is a second SWM routing/overflow outlet in Manhole Cl. This has been better clarified with notes in the profile. 17. Withdrawn. 18. Withdrawn. 19. Withdrawn. 20. C13: Provide a E2 - E1 profile — Ref. Cale. report, pg. 57. (LD-229 Table) This has been provided — it 21. C13: Revise E2 - El slope to 16% Max., else provide VDOT anchors. E2-El slope reduced to --10%. 22. Withdrawn. 23. C14: Provide biofilter floor dimensions. Label biofilter contours in detail plan views. Dimensions added. The contours have also been shown. 24. C 15: Add flow lines to detail 1 internal to Isolator Row, StormTech chambers, Bayfilter, weir, bypass, etc. Additional follow-up comments relating to this are possible. Flow lines have been added (to what is now C16). This item functions similarly to a detention system, water will also flow through the stone layer below the arches. 25. C 15: Consider /revise ADS Sheet 4 red text; examples: "The outlet invert needs to be lowered...," "The Design Engineer must check..." This note was added earlier in the design phase when our system invert out was higher than current, we set the vault invert out to 402.83 per ADS design recommendation. 26. Provide standalone SWM Plan (1+ sheets). At present, there are only SWM details, no dedicated plan, or comprehensive SWM plan (view). SWM Plan should include: Noted, this is added to plans as (new) Sheet C11. a. Withdrawn. b. Show and label 1.26 Ac. Forest /Open Space Easement. Now shown on C11. Area is now 1.06 acres. c. Confirm Forest /Open Space Easement lies on hydrologic soil group type `A' soil. Also, ensure 1.26 Ac. Forest /Open Space Easement meets DEQ land cover guidance, April 2016, table, pgl2 See updated SWM Note 9 on C7. Soils linework added to New Sheet C11. d. Provide and label public drainage easements for all storm pipes downstream of SWM Facilities, including individual rain gardens, to the development property line. Ref. 14- 431.A.1 Noted, easements are shown. e. Show and label BMP D. Noted. f. Show and label (1. - 38.) raingardens that will be built with individual lots, that will be bonded with this WPO, and that are necessary (collectively and individually) for SWM quality compliance These are now shown. g. Provide plan sheet Note to identify raingarden area (SF) for facilities installed at Lots 18A- 23A. See table dimensions added to C11. Note has also been shown. h. Revise design. Revise LD-229 tables. (Rev. 12/13) As follow-up: On this site given site constraints and design objectives, Min. 8" DIA HDPE is allowed (Typically, with rare exception [other than Nyoplast® yard grate systems], a Min. 12" DIA is required for storm lines in easement/s. See Drainage Plan checklist). 8" x 12" reducers will be allowed since we anticipate no debris in HDPE raingarden collector lines. Most bends without MH Str. are allowed, in this instance. Proposed T-connection should be reviewed, carefully. T- connections are rarely (if ever) seen in gravity storm systems other than at a MH Str. Engineering will evaluate revised T-connection, and encourages alternative design. Last: provide cleanouts at terminal ends of raingarden collector lines, and intervals spaced not more than 150' apart. Noted. Following Engineering's request, we added adequate number of cleanouts at terminal ends and — 100' intervals. All bends more than 25' from anther cleanout/drain basin now have cleanouts. Str. G1 T-connection revised to be a 24" drain basin. i. Show and label two (2) Level 2 bioretention basins. (Rev. 12/13) As follow-up: Also, see item 26.k., below, for comparable level of VA DEQ Stormwater Design Specification No. 9 bioretention installation, inspection, and maintenance detail to include with VSMP /WPO plan. Noted, revised installation/inspection/maintenance details included on C1, and C7. j. Since retaining walls ar,_ south s. , - of the lower parking lot, _sayfilter Treatment System and ADS StormTech systems (incl Isolator Row) north and slightly west, to avoid conflict with segmental block retaining wall anchoring geogrid, and to help preserve parking during (eventual) future system replacement /maintenance, to maximum extent practical. (Rev. 12/13) As follow-up: Engineering continues to hold it is the long-term interest of development residents if the stormwater management system shifts, as outlined, north and slightly west. Also, County Engineer requests plan /profile detail of splitter /weir. Provide a manway or observation ports for both chambers of the StormTech system, if possible. At a minimum, provide manway access to flow splitter /weir structure, and ensure access is located outside of parking spaces. Stormwater system cannot be easily shifted due to the multiple alignments of pipes entering the system. Also, since this is a 1-way, single aisle, angled parking lot, replacement of the system would obstruct the drive aisle regardless of BMP location. (Hopefully, by the time the system is replaced, that parking area will be greenspace instead of vehicle storage -which would be in alignment with the future goals of the development.) Plan/profile detail of splitter has now been provided. Profile of system now provided. Manway access to the flow/splitter structure has been provided, outside of parking spaces. k. C7: Provide installation, inspection, and periodic maintenance Notes for raingardens; inspection and periodic maintenance Notes for bioretention basins similar to Notes provided for Bayfilter BMP. Ref. VA DEQ Stormwater Design Specification No. 9 (and Attached). (Rev. 12/13) As follow-up: Please ensure Spec. 9, Sections 8.2, 8.3, 9.2 thru 9.4 for raingardens, transfer to plans, and inform design. Note design specifications for raingardens, Table 9.2. Plans should identify Level 1 or Level 2 design. Captions for details on C5, C6 should identify whether typ. detail is Level 1 or Level 2. Include specification for media mix test. Above are specific Albemarle County Engineer requests. Thirty-eight raingardens to be built with residences, likely by builders not developer, on separately -owned private lots require initial care in design and installation, while inspection and maintenance will be essential. Easements must provide private or public access to inspect, repair, maintain or replace raingardens. These have been provided. See added Sheet C17. 27. Withdrawn. 28. SWM Calculation Packet a. Pg. 7: DA `A' and DA `B' raingarden CF is slightly inconsistent with C5 - C6 raingarden details. Revise for consistency. Check SF v. CF descriptions. Pg. 7 lists Treatment Volume (TV in cubic feet). These are consistent across plans. Pg. 7 does not specify media area/footprint (square feet). This is not a discrepancy, just shows different info. In the Plans, TV is only referenced in Sheet C7, to avoid confusion for the contractor/homeowners. Plans have been updated for clarity. b. Pg. 21: Compare 6" PVC Inv.=441.5' with C14 /Biofilter C1 6" PVC Inv. =441'. Revise. This elevation discrepancy has been fixed. c. Pg. 21: Revise Pipe Out Inv. Elev. (table value), consistent with C14. P. 21 table revised for consistency with plans. d. Pg. 21: Compare 15" HDPE OUT vs. 12" HDPE OUT with C 14 /Biofilter C2. Revise. Noted, revised for consistency with plans e. Pg. 21: Check /revise table DA C-2 Pre-treatment Vol. Noted, this has been fixed. f. Pg. 21: Biofilter bottom area (sf), 660 and 155, inconsistent with C14 profiles. Revise. Noted, revised for consistency with plans g. Pg. 22 thru 50: Relocate select material to plans. SWM Calc. Packet will not guide construction installation, inspection, or periodic maintenance (an obscure location for this data). Transfer relevant data to plans. (Rev.12/13) As follow-up: Not all 28-pg of material needs to transfer to the plans. Consider range of material already included on C15, refer to very useful descriptions on C7 for Bayfilter BMP (Installation, Inspection, Maintenance), and please ensure comparable data is included for the ADS StormTech detention system. It is possible minimal additional BMP installation, inspection or maintenance material now included in the Calc. packet should transfer. noted, installation & maintenance material transferred to New Sheet C 17. h. Pg. 53-54: Transfer to plans. (Rev. 12/13) Withdrawn. i. Pg. 55: Revise C2 and D2 throat length: C2, so no carryover across lower parking lot; D2 since any carryover at this inlet is untreated, yet inlet is included in `treated' DA. Noted, throat length revised, no carryover. j. Pg. 55: Revise A5Z throat length so no carryover; project may not release carryover into Rio Road. Noted, throat length revised, no carryover. k. Pg. 57: Revise LD-229 table, as needed, to reflect revised Min. storm pipe DIA. Noted. LD-229 is current. 1. Pg. 97: Provide Additional Link 12L data (velocity for comparison with channel protection requirements at 9VAC25-870-66.B.1.a. 2-yr. vel. (in pipe) Max. =20 fps. Also, size riprap at outfall near Meadow Creek. If riprap design is overlooked, please notify reviewer. All pipe slopes are now <16%. We request engineering accept this design, ref. response above (copied here) "The pipes have velocities <20 fps, except for section A3-A2. We have made this section of pipe less steep. However, for the flow through this pipe, we would have to reduce the slope to I I% to achieve a 2-yr velocity of <20%. This represents a rather significant change in the design. 9VAC25-870-66.B.1.a. specifies that peak flow through manmade systems not cause erosion. We do not believe that abrasion is of concern for this system, due to the onsite nutrient and sediment treatment provided. Furthermore, we have specified a more durable pipe material (ADS HP -Storm is polypropylene). This material is designed for high performance applications, and should provide satisfactory abrasion resistance. See attached report. Thus, we request that county engineering approve this layout." Rip -rap design had been left out of the calc packet, it is now included (page 79 of packet). 29. Storm lines need not be centered within drainage easements. Noted. 30. Min. easement width for raingarden collector lines =10'. Noted, this is achieved. 31. Locate easements such that there is 2'-3' minimum clearance to any portion of a structure (footing, deck support, etc.) In the future, current design participants /developer may be unavailable to mediate disputes concerning right of access to repair or replace structures located within public drainage easements. Noted, 2' clearance from storm pipes, and rain gardens, to all home structures has been provided. Easements as shown next to the homes are due to tight configuration. Please note that we have been working with the architect for this project, home layout is not conceptual, but represents each lots' building. Thus we are confident in the tight spacing shown herein, as the developer will not offer other house footprints. 32. With revised design or storm line placement, please ensure minimum water line v. storm line horizontal /vertical offset. Similarly, ensure minimum sanitary line v. storm line horizontal /vertical offset -clearance. Noted, this has been achieved. 33. Curb for private street is required. Noted, curb added. 34. Revisit super -elevation in 70' R curve. Superelevation provided. Details will be shown on road plans. 35. sure no drainage release to Rio Road L, Noted, this has been achieved. 36. Curb cuts are an option; release of uncontained runoff across lower parking lot is not an option. Noted, this is no longer an issue. 37. All easements downstream of raingardens are public drainage easements. All these easements shown as "public" 38. Consider effectiveness of pretreatment vis-a-vis proposed grade for private street, Road A (blue circle area; image, below). We believe this will be an effective pretreatment, the 2% cross slope is unlikely to cause erosion at the edge of pavement/sidewalk from sheetflow. Native grasses will function as a preatreatment for debris, and gentle slopes to the grass, and then right before the biofilter C, will protect against channelization and/or erosion. 39. Recommend continuous SWM Facility Easement fronting units 9A thru 16A, to provide easement access to raingardens sandwiched between drives. Image, below (blue -circled area, left). Noted, this is provided. 40. Propose `delineators' for geogrid /grass -pave fire -rescue access (Roads B, C, D) to limit vehicles operating beyond stabilized geogrid. Image, above (blue -circled area, right /Typ.). Noted, luminaire bollards have been provided at 20' intervals. 41. Albemarle recommends propose raingarden collector lines at (minimal) depth that still meets material design specifications for minimum cover, and minimum slope. Noted, design revised. 42. Ensure all individual lot lines are shown, that lot lines continue to exterior property boundary, and provide a complete boundary for each lot —this is not a request for platting, but to help ensure raingardens do not cross lot lines. (Lots 213, 313, 413, for example.) Lot lines are now shown. 43. Raingarden for Lot 7A appears to be located on Lot 8A. This cannot be approved. SWM Facility for Lot 7A may be located in common, or open. HOA space, but not another private residential lot. Noted. All rain gardens are now located in each respective lot. 44. Raingarden collector line for Lots 1 A, 2A (storm J2 — J 1) appears to dead-end. Ensure these raingardens on these lots connect with downstream treatment. The collector line for these rain gardens runs under a flume in the sidewalk and outlets into the pavement. This area does not run into BMP E, however, BMP E would provide minimal extra treatment for 3000 sf. We have designed a 0.14 lb treatment buffer into this development. for these 2 lots, there is a phosphorous load of 0.121bs. Treatment via rain gardens removes 0.071bs. The remaining 0.05 lbs of load would be routed to BMP E, which would provide a 70% removal. (0.7 * 0.05 = .035 removed, if routed to E). Thus, not routing these lots to BMP E, means that 0.0351bs are not treated. This is covered by the treatment buffer already built in. 45. Include Construction Record Drawing (As -built) for VSMP (.PDF) on the plans; link: http://www. albemarle. org/upload/images/forms—center/departments/Community—Developme nt/forms/Engineering_and_WPO_Forms/WPO_V SMP_Construction_Record_Drawings_Poli cy_23May2014.pdf This is shown on C15. C. Erosion and Sediment Control Plan (ESCP) 1. Addressed. 2. Sheet C2 does not show all of the disturbed area (omits the sanitary sewer and stormwater piping offsite). Please revise. Offsite disturbed area now shown on C2. 3. Sheet C7 Offsite Areas narrative appears to have a typo. Please clarify. Understood, offsite soil stockpile narrative note updated. 4. Addressed. 5. Addressed. 6. Addressed. 7. Addressed. 8. C8: DD is shown outside Limits of Disturbance (LOD). Show inside LOD, or expand LOD. It is inside LOD, that line is the basin drainage area. Revised for clarity. 9. C8: Phase 1 ESC shows proposed grading and utility (storm) system A that is to occur in Phase 2. Revise Phase 1 to remove Phase 2 grading and utilities (storm pipe). Phase 1 is shown correctly, the pipes shown are part of phase 1, and specifically mentioned in the sequence of construction. 10. C9: Legend shows LOD. Show LOD on plan view using legend line -type. LOD now shown. 11. C9: SB primary riser and portion of principal spillway pipe are not visible; please show, consistent with C8. These are now shown. 12. CIO: Show Phase 3 LOD on plan sheet. This is now shown. 13. C10: Provide soil stabilization blanket (VESCH Std. & Spec. 3.36) between Rio Road E and retaining walls at lower parking, ESC, Phase 3. Stabilization blanket, with detail (Detail 2, C13) added. D. Pollution Prevention Plan (PPP) 1. Addressed. 2. Addressed. Table in section C: f. Show a contractor laydown/storage area on the plan. (Rev. 1) Partially addressed. As follow-up: PPP exhibit may show relic Phase 2 stockpile labels; please check /remove unintentional labels. These stockpile labels are intentional, to show reference to areas where stockpiling may occur. This guides grading of other lots, first. E. Additional comments provided by Frank Pohl 1. I don't recall seeing the proposed property lines on the drawings. Please show those as it will help confirm if additional easements are needed, if they need to be adjusted, etc. Property lines are now shown. I forgot to verify, please include construction (sections 8.2 and 8.3 of DEQ Spec 9) and maintenance (sections 9.2, 9.3, 9.4 and table 9.7). This project has a large number of rain gardens, which is not typical, so additional notes is warranted. These notes are now included (see last sheets) Do the raingardens pass the 10-yr event without flooding into the streets? If not, additional inlets to prevent flooding are required. Rain gardens do pass the 10-yr event, updated HydroCAD analysis has been provided (SWM calc packet pages 120-130). DOCUMENTS INCLUDED: DIGITAL COPY OF WPO APPLICATION DIGITAL COPY OF VSMP PLANS DIGITAL COPY OF SWPPP DIGITAL COPY OF SWM CALC PACKET If you have any questions or concerns about these revisions, please feel free to contact me at keane@shimp-engineering.com or by phone at 434-299-9843. Regards, Keane Rucker, EI T Project Manager/Site Design Engineer Shimp Engineering, P.C. Drain- Area A Land Cover lacresl Eco Villiers VRRM RaDs, Spreadsheet D A. A (excluded) AMNSMAMIM A Soils BSolis CSolls DSolls Totals Land Cover Rv Forest/Open Space (acres) 0.00 0.00 Managed Turf (acres) 0.03 0.03 0.15 Impervious Covet (acres) 0.05 0.05 0.95 Total 0.08 Stormwater Best Manaeement Practices (RR = Runoff Reduction) Total Phosphorus Available for Removal in D.A. E (lb/yr) 0.12 Post Development Treatment Volume in D.A. E (ka) 189 .'colon from drnodnwn Runoff Managed Turt Impervious Volumefrom Runoff Remaining Total B Phosphorus Phosphorus UntreatedMP Phosphorus Remaining Practice Reduction Credit Area Cover Credit Upstream Reduction Runoff Treatment Removal Load from Phosphorus Removed By Phosphorus Downstream Practice to be Credit % ( ) acres (acres) Area (acres) ( Practice (fta) (ka) Volume k (a) Volume k (a) Efficiency % W ( ) Upstream Load to Practice (lb) ( ) Load (lb) ( Employed Practices (lb) Practice (lb) 1. Vegetated Roof (RR) l.a. Vegetated Roof #1 (Spec #S) 45 0 0 0 o 0.00 0.00 0.00 1.b. Vegetated Roof #2 (Spec #5) 60 - 0 0 0 0 0.no 0.00 0.00 2. Rooftop Disconnection (RR) 2.b. Simple Disconnection to C/D Solis 2, To Soil Amended lilta'P.;,( 11 per sp,rifiwati,ms (existing CID soils Spe,#4) 2.e. To Dry Well or French Drain #2, 2, To lain Garden #1, Urban Boretention (Spec #9, Appendix A, 3. Permeable Pavement (RR) 14. Grass Channel (RR) 4.b.GrassChann CID Soils (Spec #3) S. Dry Swale (RR) 16. Bioretentian (RR) (Spec Z 7. Infiltration (RR) 8. Extended Detention Pond (RR) 9. Sheetflow to Filter/Open Space (RR) TOTAL IMPERVIOUS COVER TREATED (ac) 0.05 AREA CHECK: OK. TOTAL MANAGED TURF AREA TREATED AREA CHECK: OK. TOTAL RUNOFF REDUCTION IN D.A. E (fits) 76 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. E (Ib/yr) 0.12 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. E (Ib/yr) 0.07 TOTAL PHOSPHORUS REMAINING AFTER APPLYING RUNOFF REDUCTION PRACTICES IN D.A. E (lb/yr) 0.05 SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS 10. Wet Swale (no RR) 11, Filtering Practices (no RR) 12. Constructed Wetland (no RR) 13, Wet Ponds (no RR) 13b, Wet Pond #1 (Coeval Plain) (Spec #14) 14. Manufactured Treatment Devices RR) (no TOTAL IMPERVIOUS COVER TREATED (ac) 0.05 AREA CHECK: OK. TOTAL MANAGED TURF AREA TREATED (ac) 0.03 AREA CHECK: OK. TOTAL PHOSPHORUS REMOVAL REQUIRED ON SITE (lb/yr) 3.52 TOTAL PHOSPHORUS AVAILABLE FOR REMOVAL IN D.A. E (Ib/yr) 0.12 TOTAL PHOSPHORUS REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. E (Ib/yr) 0.00 TOTAL PHOSPHORUS REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. E Qb/yr) 0.07 TOTAL PHOSPHORUS LOAD REDUCTION ACHIEVED IN D.A. E (Ib/yr) 0.07 TOTAL PHOSPHORUS REMAINING AFTER APPLYING BMP LOAD REDUCTIONS IN D.A. E (lb/yr) 0.05 SEE WATER QUALITY COMPLIANCE TAB FOR SITE COMPLIANCE CALCULATIONS NITROGEN REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. E (Ib/yr) 0.54 NITROGEN REMOVED WITHOUT RUNOFF REDUCTION PRACTICES IN D.A. E (Ib/yr) 0.00 TOTAL NITROGEN REMOVED IN D.A. E (lb/yr) 0.54 Nitrogen Nitrogen Load Untreated Nitrogen Remaining Removal from Upstream Nitrogen Load to Removed By Nitrogen Load Efficiency (%) Practices (Ibs) Practice (Ibs) Practice (Ibs) (Ibs) 1. Vegetated Roof o (RR) o.00 o.00 o.00 0 0.00 0.00 0.00 2. Rooftop Disconnection (RR) 3. Permeable Pavement (RR) 4. Grass Channel IRA) 5. Dry Swale (RR) 6. Bioretention (RR) 7. Infiltration (RR) 8. Extended Detention 8. Extended Detention Pond (RR) 9. Sheetflow to Filter/Open Space (RR) TOTAL RUNOFF REDUCTION IN D.A. E (fts) NITROGEN REMOVED WITH RUNOFF REDUCTION PRACTICES IN D.A. E (lb/yr) SEE WATER QUALITY COMPLIANCE TAB FOR SITE CALCULATIONS (Info, 10. Wet Swale (Coastal Plain) (no RR) 11, Filtering Practices (no RR) ®®®® 12. Constructed Wetland (no RR) 13. Wet Ponds (no RR) 14. Manufactured 14. Manufactured BMP (no RR) W2112o20 1 at1 2:41 PM LLL�L�Yr�F �a.a' E _ .rua�a.r„�7CA}..al.:ti�l • �li.�,i�lilllll. ��! F if a 1111 ; �'�. TECHNICAL NOTE Abrasion Resistance of Polypropylene l203 ri2012 April Ap Introduction With the introduction of ADS High Performance (HP) polypropylene (PP) pipe for the storm drainage and sanitary sewer markets, it is necessary for designers to have confidence in polypropylene's expected performance in conditions where the effluent may carry debris or abrasive materials. To address designer's concerns, a comparative evaluation of whether polypropylene had similar abrasion resistance to high density polyethylene (HDPE) was undertaken. While it was initially hypothesized that polypropylene would have comparable, if not better, abrasion resistance, testing verification is essential. If it could be established that polypropylene and HDPE have similar resistance to abrasion, the more extensive history and test data for HDPE could be applied to polypropylene insofar that polypropylene would behave similarly to HDPE in abrasive environments. To test this hypothesis, two types of tests were conducted. The first test used Taber° abrading wheels directly on a sample of thermoplastic material. The second test, in order to more closely mimic drainage and sewer conditions, involved placing thermoplastic samples in water flow carrying abrasive sand. Both tests measured the mass loss over time and provide a direct comparison between the two materials. Taber Abrasion Test In April 2009, Polymer Diagnostics, Inc. conducted Taber abrasion testing on polypropylene, HDPE and PVC material samples in accordance with ASTM D3389 in order to determine the material's mass loss under direct abrasion. Although this test does not simulate pipe carrying effluent, the test still provides a standardized method for comparing the abrasion resistance, or hardness, of different materials. Test Setup Each material sample was mounted on a Taber Abrader Model 5130 where the sample is subjected to rub -wear action of an abrading wheel. An abrasion pattern of crossed arcs simulates abrasion of the material from all angles. Directly abrading material in this manner allows for quick results through accelerated testing in order to simulate long-term use, which may otherwise take years to compile. The initial mass of each sample was recorded to determine the total mass loss of the respective material over the duration of the test. All samples were tested using a CS-10 abrasion wheel with 250 grams of force. The total test time was 40 hrs, allowing for 500 revolutions of the abrading wheel. Results Results in Table 1 indicate a greater mass loss of the PVC samples compared to both the polypropylene and HDPE samples. The mass loss of the HDPE sample was slightly higher than the polypropylene sample, but the proximity of values allows for the conclusion that both samples performed similarly. These results indicate a similarity between polypropylene and HDPE materials as it relates to material hardness. The final mass loss of PVC was 5 to 8 times that of polypropylene. 4640 TRUEMAN BLVD. HILLIARD, OH 43026 (800) 821-6710 www.ads-pipe.com 1 TN403 ©ADS 2012 Table 1 Taber Abrasion Test Results for Material Mass Loss Material Start Mass End Mass Total Mass g g Loss (mg) PP #1 30.6036 30.6034 0.2 PP #2 30.6868 30.6866 0.2 HDPE, 5% Carbon Black 31.6658 31.6655 0.3 PVC — white 50.8776 50.8759 1.7 PVC — gray 50.4187 50.4176 1.1 Abrasion Resistance in Water Flow While a direct correlation between polypropylene and HDPE materials' abrasion resistance is supported by the Taber abrasion test results, a second test was conducted to confirm those results and simulate the abrasion resistance of a pipe's invert when carrying effluent with suspended abrasives. ADS Facility Testing First, material plaques of both polypropylene and HDPE were cut and weighed to determine the initial mass of the sample. The samples were then scanned into AutoCAD in order to precisely measure the surface area that will be abraded. Additionally, each sample was inspected for any signs of abnormality including splitting, cracking, material thinning, etc. No abnormalities were noted and product was considered to be in good condition. Next, a closed -loop test system was constructed in order to achieve a controlled flow rate over the samples. A constant hydraulic loading was established in the system, which consisted of a 2" grinder pump, 18" trough and a collection basin as shown in Figure 1. OK-110 sand was added to the water flow so a relatively heavy sand loading was obtained. The grinder pump, in conjunction with a mixing tee, was used to ensure the sand stayed in a suspended state in the mixture. The flow rate of sand/water mixture over the plaques was 3 ft/sec. In the trough, four sample plaques, two of polypropylene and two of HDPE, were placed at the bottom of the trough in the flow path, shown in Figure 2. With the exception of removing the samples for weighing, the test unit allowed for continuous subjection of the samples to the slurry mixture. Figure 1 Close -Loop Test System Figure 2 2 4640 TRUEMAN BLVD. HILLIARD, OH 43026 (800) 821-6710 www.ads-pipe.com ATN403 ©ADS 2012 ..wxrµtass �xu�..a 1� _ il�( i�lllliJl:u 5i1I ''. Results It was noted during visual inspections of the samples throughout the test that minor scouring of the samples was occurring. These observations affirmed that the test was successful in creating the desired abrasive conditions for sample analysis. Comparing results in Table 2 of the mass and thickness loss, polypropylene performed slightly better than HDPE. The second sample of HDPE was removed from testing as it was damaged during detachment operations for periodic examinations; subsequently resulting in a large loss of material not related to the abrasion testing. Even so, results for both HDPE samples indicate a higher material loss value compared to the polypropylene sample results. Ultimately, these results favor polypropylene over HDPE for constant flow applications where the effluent carries a high bed load. Table 2 Material Loss Results Initial Weight (g) Final Weight (g) Time (hrs) Loss (g/hr) Surface Area (in A2) Loss (mills/yr) PP large sample 221.5 221.5 4029 0.00000 110.34 0.00 PP small sample 27.101 27.099 3483 0.00001 15.43 0.02 HDPE large sample 141 140.75 1 4029 0.00006 89.47 0.39 HDPE small sample Damaged during examination Conclusions Both tests indicate high abrasion resistance of polypropylene material. The Taber test indicated that polypropylene and HDPE behaved almost identical to direct rub -wear abrasion, and significantly better compared to PVC material. The test simulating abrasive water flow reaffirmed the Taber test results and indicated that polypropylene performs similarly or slightly better than HDPE. From these results it is reasonable to conclude that other abrasion resistance tests using HDPE samples are also representative of polypropylene material. With this relationship in mind, the tests outlined in the Drainage Handbook Durability section that are specific to HDPE and establish the material's superior resistance to abrasion compared to other pipe materials also support the argument for polypropylene's superior abrasion resistance. 4640 TRUEMAN BLVD. HILLIARD, OH 43026 (800) 821-6710 www.ads-pipe.com 1 3 ATN403 © ADS 2012