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HomeMy WebLinkAboutWPO201400024 Checklist 2014-03-05 Albemarle County Engineering Stormwater Management Plan checklist for plan reviewers 5 Mar 2014 (Use the latest checklist from the Team Services engineering forms site) A stormwater management plan is a plan detailing all measures and facilities to handle and treat stormwater runoff and protect downstream waters and channels. [17-303,304, and the Virginia Stormwater Management Handbook, and the BMP Clearing House] A note to plan reviewers; This list is an aid to review. No plan is perfect. Not all items will be applicable,and some will be compromised. Reference key; [Square Brackets] are County Code references, {Curved Brackets; are policy references, and(regular parenthesis)are explanatory. Links to reference documents are provided where possible. Title information: (applicable to any type of plan) )C Project title. Titles should be appropriate. It should be a stormwater management plan, not an erosion control plan, or site plan etc. Professional seal, with original signature and date. [18-32.6.1] )� Content: The stormwater management plan is a permanent document with should be part of a package for the WPO application and the VSMP. It should not be part of a site plan or road plan. These must be separate documents,to be reviewed and bonded separately. If these are included,they must be removed. X VSMP general consruction permit application made with DEQ. A completed copy of the standard stormwater maintenance agreement and fee for recordation for any stormwater management facilities [17-304E] copies of manufacturer's approval of the plan for any manufactured stormwater management facilities (filterra, stormfilter, sandfilter, etc.) {Policy; pro-rated share payment for any sites which drain to County regional stormwater management facilities. (This should have been identified with the preliminary plan or plat) [17-316] Existing conditions plan view information: (applicable to any type of plan) ✓ accurate current existing topography at the time of submittal, including all existing site features, and any recent disturbances, all at a legible scale [18-32.6.2] ✓ date and source of the topographic information: [18-32.6.21 All topography should be at least visually field verified by the designer within the last year {Policy, WPO buffer limits; 100' from stream or wetland bank, 200' from reservoirs, or floodplain limit if greater [17-317] 'V floodplain limits, including 100yr flood limits for any channel with a drainage area of 50+ acres [18-32.6.2d, 18-30.3] all existing easements (access, drainage, sight, sanitary easements, etc.)with deed book / references, locations and dimensions [18-32.6.2] V all critical slopes (typically shaded) [18-32.5.21 Proposed plan view information: (applicable to final site plans, road and drainage plans) Grading: [18-32.6.2. 14-303] Albemarle County Engineering Stormwater Management Plan Checklist • Page 2 of 6 `• proposed topography at minimum 2' contour intervals—tied into existing contours, as well as all proposed site features. (Sites with less than 6' of grade change should consider using smaller contour intervals.) proposed slopes are all 2:1 (horizontal:vertical) or flatter {Design Manual, section 8} proposed slopes steeper than 3:1 have low maintenance (not grass) ground cover specified on the plan {Design Manual, Section 8} existing critical slopes are not disturbed, unless a waiver or exemption has been granted for the disturbance. [18-4.2. 14-304] Retaining Wall Plans. Any walls supporting necessary infrastructure require engineered plans (not generic manufacturer's details) and computations. -{Design Manual, section 8} This will also be required where walls are close to property lines and there is the danger of affecting neighboring property, either during construction, with later failures, or with pedestrian or vehicle safety. ' Easements: [Zoning Ordinance 18-32.7.4, Subdivision Ordinance, Article IV, Division 4] all proposed permanent easements, dimensioned and labeled stormwater management easements over all facilities and associated structures and access permanent stormwater management easement encompasses 100yr high water mark, all structures (embankments if present, and culvert release channels) and access all drainage easements are a minimum 20' wide. Required width: 10'+(pipe dia. or channel width) +2'+2(depth-5'). The pipe, channel or structure must be within the center third of the easement. {Design Manual, section 6} no structures or trees within drainage easements {Design Manual, section 6} Faci ies: stormwater facility and site layout as shown on the site or subdivision plan sheets, preferably at a scale of 1"=30' or 1"=20'. ✓ 90% or more of site development captured in facilities for water quality (o dinapce _L , ,/ fa- requires as much as practical, 90/o is a target) f Go �¢pt / g � Albemarle County general stormwater notes ✓ facilities are not in the floodplain facilities are not in buffer areas with Program Authority authorization mitigation plan. facilities are off-line of major streams (retention ponds might be an exception) '"? facilities are not built over any other utilities (sanitary sewer, water, gas, fiber optic, etc.) flow is not short-circuited. A good target for flow path length is 2:1 in all water quality facilities, without the excessive use of baffles or extended dikes (VSMH 3.06-12). Cross-sections and details of each facility: Cross-sections and details should be drawn to scale. (NTS drawings can be deceptive and not identify slopes and relationships accurately) The existing ground should be shown in a dashed line on cross-sections. n (�, embankments (between 3 and 25 in height) top width 8ft min., 10' for eights 15' to 20', 12' for dams over 20', heights measured from the utsi toe upstream face slope :lf or flatter, labeled downstream slope 3:1 r flatter, labeled l 0yr and 100yr high watc elevations labeled with 1 ft freeboard for 100yr storm with emergency spillway (31\:2‘. ft freeboard without emergency spillway Albemarle County Engineering Stormwater Management Plan Checklist Page 3 of 6 an impervious core a cut.ff trench of minimum 4' wide, 4' deep and 1:1 sloped sides principle spil ay riser cre 1' below emergency .pillway if present trash racks ,ver all inlets ant controls to prevent clogging trash rack ov- riser crest not flat(no DI-7's). A pre-cast anti-vortex top is acceptable, as . ; stan•,' g cages. Debris should fall off. riser size and mate '. `s labeled barrel size, strew .terial, inverts and slope labeled all orifices, wei or othe ontrol devices labeled with dimensions and inverts control orifle not more th. 25% of riser perimeter at any point(does not affect riser struc AA al integrity, 25% is target) riser ba size and dimensions lab-led access'to riser is provided (riser should be in dam, not free-standing without structural support and analysis) emergen spillway dimensioned and labeled inv. labeled dime 'ons in control sec 'on dimensi. .s in channel -ction provided if different than control section linings labe z• and own where applicable spillway over n. ,e soils, and/or sufficient armoring provided. The spillway should never • '`ov- ill material. appropriate aterials fo ontrols (for example, a computation which relies on a flow dep in inches for flo control should not be specifying rip-rap, where this is imps sible) se.' ent forebays provided for all retention b.: ns, constructed wetlands, and basin biofi .-rs at all inlets zed to 0.25"of runoff per impe ous acre (can be included in WQV) di -ct vehicle access provided f► cleanout stru , al walls and weirs, like •abion baskets, need foundations and slope tie-ins. These .-nd to be weak poi that are washed around/out. biofilters with imum floor di, ensions labeled does not re.-ive any st -am base flows, and; areas of shee' ow in • facilities are protected from erosion by appropriate scour protection stone •r : ergy dissipation measure plants are shown ., • labeled with height or caliper 3 plant species e sp.cified (3 trees if present, 3 shrubs) with sizes for survivability / biofilter floos 2.5% of i 'pervious cover for type I, or 4% of impervious cover for type II his must be us-• with judgement. This assumes almost all of the area drai ge to a facility is i ..ervious. If there are large areas draining to a facility herwise,this will not ark. Also, if the water quality volume is not subst tially captured, which is the'- tent, the water quality volume should gove .) 2.5' depth of sand/soil media 1', 1.5' stone drain in geotech fabric under edia, with 6"perforated PVC pipe to daylight Albemarle County Engineering Stormwater Management Plan Checklist Page 4 of 6 . ' ponding depth prow'l ed in facility at 5%imp., 1.0' at 2.5% (see volume co ents above) ove •w provided biofilte ea is fl cleanouts : e p e vided at the end of the underdrain pipe, and every 50' in subdivisions, face ies are in open space where present. In subdivision with no open space, facilities ar; ou •f yards and away from residences. Facilities must not be a nuisance in desi: or loc. ion. [17-304F] overland relie is provided •r any facility in case of clogging. The failure of any system will not cau:e structures or y. i s to flood [17-304F] `,Retentio .asins .00d base flow, or 10 acres or more drain to the pond normal pool elevation is labe •d on plans 5%of surface area is a d-.+th of 1.5' or less 1 °o of surface area is a •epth of 1.5' to 2' 70°, of surface area is depth of 2' to 6' (greater depths are counted in WQV) a 10'4 ' vegetated ip/safety bench is provided around the perimeter for Type II, a 10- wide and 1-1.5' deep aquatic bench is provided typ. al 10 x10' planting area specified for aquatic bench at leAt species of aquatic plant used extended detention b. In II (enhanced) has marsh zones normal poo elution is labeled on plans 20%pool eas 1.5,'-4' deep 40% sh. ow marsh .5'-1.5' deep, contains 1WQV 40% .gh marsh 0.5' ep or less as-built dat. is provided for exi 'rig ponds and drainage structures and facilities existing p'nds and drainage structures and facilities are brought up to current standards (the rest o f this list) \ vehicl, access roads provided to all fa' ities access graded to 10' width and le than 20% grade minimum 10' wide permanent easei' ent over access gravel surface or better for grades ove' 10% underground facilities have adequate manhole a ess at upstream and downstream points. manufactured pre-fabricated water quality facilitie .Dave a written approval of the plan from the manufacturer. minimum pipe sizes into and out of the facility are 15" diameter for maintenance Stormwater management computations: Maps: Existing drainage area map: lI existing conditions for site and off-site areas draining to proposed stormwater facilities (The stormwater management analysis should not include off-site areas r which do not drain to proposed facilities) drainage divides for all drainage areas to proposed facilities as used in computations acreage of each drainage area, labeled on the map area and matching comps \/ coefficient used for each drainage area as used in comps Albemarle County Engineering Stormwater Management Plan Checklist Page 5 of 6 time of concentration for each drainage area where applicable as used in comps �'✓ as closely as possible,the drainage areas represent the site development, and not off-site areas Proposed drainage area map: lI/proposed conditions for the site and any off-site areas draining to proposed stormwater facilities. The analysis should not include off-site areas which do not drain to proposed facilities, and should not include large off-site areas in relation to the site. \ drainage divides for total drainage areas (not sub-areas)to proposed facilities, matching the computations. Sub-areas may be shown on added exhibits or sheets. '/ acreage of each drainage area, labeled on the map matching comps �, coefficient for each drainage area, labeled on the map matching comps V time of concentration for each area labeled on the map where applicable, matching comps v for future development to be considered in the analysis, include assumed land uses, impervious areas, and hydrologic coefficients on the proposed drainage map Existing drainage divides should be honored as much as possible. Compensation schemes and unnatural divides which may not hold up in extreme weather are discouraged. Target Values: Water quality; ¶1 ,a,1 P removal rate computation summary for each facility S "- ° `" 7c, X agreement on target removal rates, required water quality Water quantity; existing flow release summary for each facility or release point from the site ✓r agreement on existing target flow rate for each release point from the site Compliance: ,C facilities meet or exceed requirement removal rates riser floatation computations for risers which are not concrete, or are taller than 10' hydrology for each facility used to generate inflow hydrographs including; 24hr storm hydrographas are used (the modified rational method is not accepted) hydrologic land use coefficients (CN), areas and flow times are reasonable computations are provided for composite coefficients times of concentration are representative of watersheds. If the omission of small sheet flow areas yields a higher peak flow,the small sheet flow areas are not used. Sheet flow should not exceed 200'. With steep slopes it should not exceed 50'. times of concentration generally decrease with development areas over 50 acres make use of more than one hydrologic method to verify computation of peak flows contour areas and elevations used for storage, matching the plans a stage-storage (elevation vs. storage volume ) table with water quality volume requirements computed for facilities with volume requirements the hydraulic dimensions and coefficients for each weir, orifice, culvert or other control structure used in the routing model, matching plans Water quality; Albemarle County Engineering Stormwater Management Plan Checklist Page 6 of 6 drawdown computations for any extended detention facilities basins and biofilters have required water quality volume; 3WQV for type I, 4WQV for type II. Water quantity; routing model and results for each detention facility flow control is maintained by the riser when present, not the outlet barrel pipe the emergency spillway is not active during the 10yr storm event unless it is designed as a primary outlet struture (concrete). riser crest stays within weir flow control during the 10yr storm detention computation summary for each facility channel computations for erosion and capacity for emergency spillway channels detention storage and routings are over and above water quality volumes 1 (X.C11_, -2. A.,A,tev Albemarle County Engineering Erosion and Sediment Control Plan checklist for plan reviewers 5 Mar 2014 (Use the latest checklist from the Team Services engineering forms site) An erosion and sediment control plan is a document which illustrates the measures used to control erosion and sedimentation during construction. All measures follow the Virginia Erosions and Sediment Control Handbook. Reference key; [Square Brackets] are County Code references, {Curved Brackets} are policy references, and(regular parenthesis)are explanatory. Links to reference documents are provided where possible. Application information: / Completed WPO application and fees,with owners signature [County Code 18-32.4.3.2, 18-32.3.9, 17-203, 17-303] Erosion Control plans require a Water Protection Ordinance (WPO) application and original owner's signature. No review is provided without application, owner signature and fees. This is true even for revisions. It is important that the owner be aware of comments and resubmittals, and this is the county assurance. ilia Copies of federal and state permits for any wetland or stream disturbance. (Army Corps, VDEQ, etc) [17-312A,B. 17-319B,D. 17-320C.D. 18-32.1.2, 14-311] Title information: X Project title. Titles should be appropriate. It should be an erosion control plan, not a stormwater plan, or site plan, etc. In some cases a WPO package will contain a stormwater plan and a mitigation plan, but they should be on separate sheets with keys and page titles. Professional seal, with original signature and date for professionally prepared plans. Content: The erosion control plan must not contain information regarding permanent improvements that do not also appear on other plans. Erosion control plans are temporary documents that are discarded after projects are complete. Existing conditions plan view information: accurate current existing topography at the time of submittal, including all existing site 7. features, and any recent disturbances, all at a legible scale date and source of the topographic information: All topography should be at least visually ! field verified by the designer within the last year O!a WPO buffer limits; 100' from stream or wetland bank, 200' from reservoirs, or floodplain limit if greater. 11,(a No buffter disturbances without WPO Program Authority approval and a mitigation plan. yl,la floodplain limits, including 100yr flood limits for any channel with a drainage area of 50+ acres. 11)Cv Floodplain undisturbed. Disturbances require a Special Use Permit or Floodplain 7) Development Permit. '�c F all existing easements (access, drainage, sight, sanitary easements, etc.) with deed book `�� references, locations and dimensions all critical slopes (typically shaded) 7\rA Zoning Ordinance buffers shown and protected undisturbed. Disturbances require Planning approval of a waiver. Albemarle County Engineering E&SC Plan Checklist Page 2 of 4 Proposed plan view information: Grading: [18-32.6.2, 14-303] proposed topography at minimum 2' contour intervals—tied into existing contours, as well as all proposed site features. (Sites with less than 6' of grade change should consider using smaller contour intervals.) These should agree with other final plans. proposed slopes are all 2:1 (horizontal:vertical) or flatter {Design Manual, section 8} proposed slopes steeper than 3:1 have low maintenance (not grass) ground cover specified on the plan {Design Manual, Section 8} existing critical slopes are not disturbed, unless a waiver or exemption has been granted for the disturbance. 118-4.2. 14-3041 Retaining Wall Plans approved. Any walls supporting roads or necessary infrastructure require engineered plans (not generic manufacturer's details) and computations. {Design Manual. section 81 This will also be required where walls are close to property lines and there is the danger of affecting neighboring property, either during construction, with later failures, or with pedestrian or vehicle safety. final contour shapes and slopes ensure no undrained pockets or stagnant pools Narrative: narrative and project title (Narratives are now optional, and not reviewed by the County, other than noting whether they are not seriouly in error, like a boilerplate with another County's name on it.) acs, t t Erosion and sediment control measures: limits of clearing and grading encompassing all disturbances, entrances, staging and parking areas, areas where sediment laden runoff will cross, or any construction related activities. This must match any landscaping and conservation plans submitted with site pl a construction entrance (CE) draining to a sediment trap or basin Vj dust control symbols (DC) temporary and permanent seeding symbols (TS, PS) ✓ existing drainage divides existing vegetation. with trees to be saved located by drip lines. This must match any landscaping and conservation plans. protection provided for all stages/phase of construction.from initial land clearing to final grades and hardscapes. This is our most important item. Plans which show only Albemarle County Engineering E&SC Plan Checklist Page 3 of 4 inlet protection on proposed drainage systems, which are only possible to install upon completion of grading, should be denied without further review. no erosion control measures in the way of construction access or grading. Diversion dikes or silt fence are not placed in the middle of the site, or through access or grading. Sediment traps are not under or on top of fill material or held up by retaining walls. Construction entrances are not on fill, etc. If the concept for site protection is not adequate in this regard,further review of the plan may not be possible. existing soil boundaries are shown with labels. Areas already disturbed are indicated, with constructed fill depth or cut noted. critical erosion areas are identified; areas of constructed slopes, areas near property lines vv-adjacent off-site disturbances are shown with erosion control facilities a stockpile location. where cut or fill balances have a 10,000 cubic yard deficit or more, plans should not be approved without a waste area identified. This must a on-site, or on another approved and permitted site. (Don't make the inspectors chase trucks to find the violation.) a staging and parking area, or other construction related areas ,-,,-diversion dikes are used to direct drainage to traps and basins silt fence is not used across contours in place of diversion dikes. s.," silt fence is limited to areas of sheet flow with 1/4 acre per 100ft of level on-grade silt fence. Plans showing only silt fence, without sediment trapping measures, should not be approved unless they meet this criteria and fill dirt is minimal. all swales and low points at the perimeter of the site have a sediment trap or basin. Silt fence in swales is typically not adequate. Check dams do not substitute for traps. If the concept for site protection is not adequate in this regard,further review of the plan may not be possible. ` temporary slope drains (TSD) or diversions are provided to prevent discharge over icdisturbed or fill slopes inlet protection(IP) on all inlets culvert inlet protection(CIP) on all culvert inlets ✓� outlet protection(OP) on all outlets "4-A- all watercourses are protected and encroachments minimized stream crossing(USC,SC) and diversions are provided at all stream crossings. adequate channels (MS-19) provided for each outfall (see Design Manual for minimum content) 1 all traps and basins are shown with proposed contours. Simple boxes or symbols are not sufficient, in most cases, to determine layout or bond amounts. For each trap; drainage area is 3 acres or less sized for total drainage area, including those for in-line upstream facilities wet storage is 67cy or more dry storage is 67cy or more wet storage is 4' deep or less wet storage side slope is 1:1 or flatter dry storage side slope is 2:1 or flatter stone weir is 6ft per acre of drainage area embankment and stone weir height is 5' maximum from outside toe embankment top width is adequate (see table 16 reference) 2:1 length:width ratio for flow path Albemarle County Engineering E&SC Plan Checklist Page 4 of 4 For each basin; (GB 3.14) sized for total drainage area, including those for in-line upstream facilities wet storage is 67cy or more dry storage is 67yr or more wet storage side slope is 1:1 or flatter dry storage side slope is 2:1 or flatter embankment 15' high or less from downstream toe principle and emergency spillways sized per handbook requirements embankment has 1' freeboard during 25yr storm with emergency spillway j embankment has 2' freeboard during 25yr storm without emergency spillway ✓ trash rack/anti-vortex device specified per handbook requirements riser anchor size specified per floatation computation dewatering device sized for 6+hr drawdown of dry storage: 3"dia. minimum safety fence and signs stating"danger, quick sand, do not enter"provided if near any residential properties, or public access structures and embankment match permanent design for facilities to be converted to permanent stormwater management facilities embankment top width is adequate (see Design Manual reference details) 2:1 length:width ratio for flow path. If necessary, baffles specified only on temporary structures (p.III-79) Details: a paved construction entrance detail (see Design Manual reference details) for projects in the development areas over 10 acres a typical section for each temporary channel or diversion, referenced from the plan sheets. Existing ground should be shown at the maximum cross-slope on the plan. details and copies of Program Authority permissions for any variances. Mass or Early Grading: mass grading Planning approval. (This is also called rough or early grading plans which contain only approximate finished grades and culverts necessary to grade) Mass grading can only be permitted within planned developments where a concept grading plan was approved with the rezoning. The agent(Director of Planning) needs to formally determine that the grading plan is in general conformity with the approved rezoning plan. Otherwise, an initial site plan needs to be approved prior to issuance of a grading permit. Issuance of a grading permit at the initial site plan stage, as apposed to after final plan approval, requires specific approval from the County Engineer.