Part 1 - Common Comments on Erosion and Sediment Control Plans (Walter Hamilton, SDID)

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1 COMMON ERRORS Typical Site Review issues Part 1 - Common Comments on Erosion and Sediment Control Plans (Walter Hamilton, SDID) E&S Phase I Constructability (PFM ) Safety during construction and isolation/protection of public if a portion of site is used by public (VESCH 3.01) Sediment basins and traps should not be placed within proposed building footprint if at all possible. If not, geotechnical notes should be provided to address adequate foundation support. Initial clearing is shown for installation of phase I measures as deemed appropriate by the Director. (PFM ) Existing tree line and tree save areas are shown and is accurate (PFM and ) All erosion and sediment controls and tree protection devices shall be placed within the area to be disturbed and may not be located in areas shown to remain undisturbed. Construction entrance and tree protection should not be shown outside of the limits of construction. (PFM B) E&S Phase II Silt fence between curb and sidewalk (VESCH 3.05, , PFM B) All proposed work shall be within the limits of construction, including toe of fills. Limits of construction shall allow for E&S perimeter control installation - perimeter controls shall be outside of the graded area to accommodate grading operation. (PFM ) E&S Notes and Details We recommend using E&S Legend per VESCH. Use standard symbols. (VESCH Uniform Coding, VESCH Chapter 6 page VI-14) Narrative matches plan, site specific, not boiler plate. (VESCH Chap. 6, Page VI-2) Temporary and permanent seeding tabulations are shown according the correct Physiographic region. A good map of the provinces is attached to Technical Bulletin (VESCH 3.31 and 3.32, PFM I) Correct inlet protection detail is shown. Any storm drain inlet protection measure which completely blocks the drain throat or entrance shall not be used. Plates , and are not allowed in Fairfax County. (PFM C, (3)) An SW-10 certification is included in the plan that indicates if a water impoundment is or is not located within the potential influence area of the proposed land-disturbing activity. A bathymetric survey shall be done, if required per Technical Bulletin END PART 1 PART 2 NEXT PAGE 1

2 Part 2 - Typical site review issues (Kati Bárczay, SDID) Comment Response Letter Respond to every part of each comment. Provide reference to sheets where the changes are shown. Note: It is not necessary to say agreed in the comment response - just explain in detail how the comment is satisfied. Also list in the response letter all changes to design that are not related to the comments. Legibility/reviewability Very important to present a readable plan to o ensure timely review and approval, o avoid excessive number of comments and o avoid new comments on subsequent submissions o a clear plan also helps the inspector and the contractor. Clearly distinguish proposed improvements from existing (industry most often shows existing as dashed and/or thin and/or screened and proposed items black and bold.) No overlaps, readable letter size, scale properly chosen for readability. ( (c)) Freeze or screen unnecessary information on E&S2 and Landscape plans. Existing condition/demo plan separate from site/grading plan, if applicable Cover Sheet Plan Approval Information table shall be accurate and all information filled in: o All waivers listed (including waivers approved w/zoning application in BOS letter) o County tracking numbers shown in the County ID column, sheet numbers and approval dates listed in the Notes column o Soils report requirement checked. If limited report is required, it is identified in the notes column and page reference number is provided. Zoning Requirements tabulation: If the plan is associated with a zoning application (RZ, SE, etc.), requirements match the provided items per the approved zoning application. Stormwater information table complete. Make sure all applicable checkboxes are checked. (Technical Bulletin 07-05) Watersheds can be found with the watershed viewer: Certificate of no change filled in for submissions other than first in order to avoid unnecessary distributions. Table of contents is up-to date w/revisions and matches sheet titles Solid waste show and label location and type of containers on the site plan sheet as stated on the cover sheet. ( ) General Notes and Details Horizontal datum with required references and vertical datum is specified. Vertical datum must be NGVD (SP: , SD: (c)(5)) Notes shall be project specific and shall not refer to incorrect jurisdiction or plan. Parking tabulation shall show the Zoning Ordinance requirement for each use. ( ) 2

3 Existing Conditions/Demolition Plan Departing adjoining lot lines/right of way lines SP: Adjoining property owners, zoning and present use ( ). SD: Adjoining property owners or subdivision names and lot numbers. ( (c)(6)) Label type and height of fencing and retaining walls (existing and proposed) ( , ) Demolition of structures clearly labeled. Extent of pavement demolition clearly identifiable (hatching helps). Beginning and end of linear demolition clearly identified Tree protection (TP or SSF if used for tree protection) and clearing limits shown on the demolition plan, besides the E&S and landscape plans. (PFM A) (Note: showing E&S controls on the demolition plan is not a requirement.) Site/Grading Plan Clearly show property lines and right of way for the proposed development and departing lot lines and right of way for adjoining properties Flow arrows and labels for drainage pipes (ESI Checklist) Offsite topo and information about existing structures (e.g. houses, sheds, and swimming pools) on downstream contiguous lots so offsite drainage and impacts can be reviewed. (Note: field run or aerial topography is required; however, alternative sources may be accepted as determined by the Director if it is shown that access to adjoining properties has been denied.) (PFM , , LTI 05-19, ) No loading space in front yard. ( ) All proposed work shall be within the limits of construction, including toe of fills. (PFM D, ) Geotechnical Report A limited geotechnical investigation is required on the first submission plans for class IVB soils. (PFM A) For non-bonded INF plans, a signed and sealed eight-point certification by a professional authorized by the State can be provided instead of the limited report. (PFM B) Geotechnical report approval shall be shown on plan and approval conditions shall be addressed on plan. Recommendations of the Geotechnical Report are converted to requirements (enforceable language). Title of the sheet shall be Geotechnical Requirements and not Recommendations. (PFM ) The Geotechnical Engineer of the Record (GER) must acknowledge that the latest civil plan has been reviewed and the recommendations of the geotechnical report still apply and there is no deviation. The acknowledgement can be in the form of a signed and sealed statement on the plan and must be current. (PFM ) Waivers Approved waivers included in plan. Waiver condition narrative on how the conditions are satisfied shall be provided on the plan. 3

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5 Part 3 - Stormwater related issues (Daun Klarevas, SDID) Adequate Outfall Analysis Analysis needs to focus on immediate impact to downstream adjacent properties (PFM B.1). Narrative: includes all elements required by PFM ; addresses all outfalls, including ditches, sheet flow and also outfall during construction (PFM A); includes statement on which limit of analysis is used, with section of 124 referenced ( A&B); includes written opinion (PFM B(5)) on: o Either the downstream drainage system(s) is adequate or there is no adverse impact condition and proportional improvement of pre-development conditions have been achieved. o The cross-sections of the natural watercourse are representative of stream reaches for the entire extent of review. o There will be no flooding of existing downstream dwellings, or buildings by the 100- year storm event, or that any existing flooding condition will not be aggravated by drainage from the development site. Supporting information (cross sections, cross section location, maps with drainage divides, computations) are provided. Drainage divides are shown, and drainage areas are clearly labeled. Any referenced sheets that are included from other submissions, there purpose must be clearly conveyed in the narrative. Offsite topography and planimetrics are shown so offsite drainage and impacts can be reviewed. Sheet Flow Notice to Industry dated June 16, 2017 o Even though the notice is for Infill Lot Grading Plans, it is applicable to any type of plan. o Increased volume of sheet flow that might have an impact on downstream properties need to be addressed through detention or runoff reduction practices. ( E) Stormwater Management and BMP Stormwater Ordinance Determination (SWOD) included, if applicable (DEQ Memo. No ) When utilizing an existing pond, a note on plan that a maintenance agreement and private agreement between owners will be executed prior to plan approval (PFM ). BMP maintenance schedules for each facility type are provided (PFM B). Site specific SWM/BMP details are shown on first submission plan (PFM ). BMP Narrative (separate from SWM) is provided. (PFM A) SWM Narrative (separate from BMP) is provided. Hydrologic computations are provided, which include: o Time of concentration path and calculations, o CN calculations, and o Flow calculations. 5

6 Geometric input data from the model are provided. Input matches site details (outlet structure and its openings, such as weir, outflow culvert, etc.) PFM C Pond/SWM facility elevation vs. storage volume tabulation demonstrating water surface elevations at all openings (orifice, weir, etc.) and an appropriate increment (1 or 2 feet) are provided (PFM B). Routings tabular or graphical (pre-, post- inflow to storage, post outflow from storage) are provided. (PFM & PFM E) Discharge/storage information are shown (PFM B). Summary of pre-development and post-development flows with corresponding elevations and volume for each separate outfall, including comps req d for B.3.a or c are provided (PFM ). Summary of peak outflows to show that detention is met; there should be a cross reference to the detention facility diagram which should show the water surface elevations. If it is a complex system, we recommend a model diagram to be shown. For infiltration type BMP-s, seasonal high water elevation and infiltration test results are provided. (PFM & PFM L) Correct rainfall data is utilized. (PFM & A) Stormtech Chamber with Isolator row commonly used to meet SWM requirements: o Inlet pipe invert elevation needs to be set above 10-year water surface elevation to avoid pipe under submerged condition for long time Maintenance problem related to sediment build up in inlet pipe (PFM B & PFM J); o No detailed sizing computation for the Isolator row Treatment Volume needs to be converted to flow rate data shared with manufacturer to ensure adequate capacity (PFM D). PFM waiver (WPFM) is provided for any underground system that is smaller than 72 box or diameter pipe. (PFM H) Water Supply Protection Overlay District ( & DEQ Memo No. 15-1) No purchase of nutrient credits in order to meet WSPOD criteria. However, if the state requirements a more conservative, on site controls shall be provided on site to meet WSPOD, but anything above the WSPOD requirement nutrient credit can be purchased as long as it qualifies under Stormwater Management Ordinance B. Simple Subdivision or Subdivision with less than Seven Lots: BMP on individual lots has to treat runoff from each lot separately. (PFM ) Site Plans and Subdivision Plans Subject to Rezoning/Special Exception The SWM design has to be in substantial conformance with the approved RZ/SE Plats. It is common to see potential SWM facility as part of the FDPA or SE plat to meet Water Quality Control and during site plan submission applicant propose the purchase of offsite nutrient credit. This causes delay as most of the time we seek proffer interpretation. Resource Protection Areas (RPA) 6

7 RPA Delineation studies shall address all the core component specifically the presence of wetland that is connected with water body of perennial flow. (PFM D & (b)(4)) Storm Sewer Pipes HGL should not be below storm sewer pipes (PFM ). Profile, plan view and computations shall be consistent. END PART 3 Engineers are reminded to QC plans prior to submission. This will ensure timely review and approval, and avoid excessive number of comments. 7