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SynC · Historical revision

Stormwater Management and Detention Systems

Revision3
EditedOct 8, 2026
StatusSuperseded
Contents

View changes in this revision   Revision history

Historical revision. This is editorial revision 3, kept so citations to it stay resolvable. It is not the current text of this standard — see the current revision.

SynC Standards Team — Specifier (Platform Standards) ✓ OfficialDiscloses employment SynC (SynC Platform Team)
Remade from scratch to the authoring rules: covers the detention, retention or infiltration facility and its outlet control; storage volume and release rates come from the stormwater report and permit, never a default

1 Scope

NOTE This standard governs the materials, construction, testing, and acceptance of the post-construction stormwater management facility that detains, retains, infiltrates, or treats runoff from the site before it leaves the site. (1.1)
NOTE The facility begins at the pretreatment device or the inlet connection where the storm sewer enters it and ends at the outlet connection where the controlled discharge leaves the outlet control structure, and it includes the storage, the liner or the infiltration surface beneath it, the aggregate envelope, the outlet control, the emergency overflow, and the access provisions the Owner will maintain it through. (1.2)
NOTE The following are outside this standard and are governed elsewhere: (1.3)
  • The storage volumes, the allowable release rates, the design storms, and the water-quality volume, which are set by the stormwater permit and the governing design manual and recorded in the stormwater management report
  • The storm sewers, inlets, and outfalls that convey runoff to and from the facility, under Storm DrainageStorm DrainageResolves to the current adopted revision.sync/storm-drainage
  • Temporary sediment basins and the other construction-phase controls that may occupy the facility footprint before it is built, under Erosion And Sediment ControlErosion and Sediment ControlResolves to the current adopted revision.sync/erosion-and-sediment-control
  • The mass excavation that forms a surface basin and the backfill above the storage envelope of an underground facility, under EarthworkEarthworkResolves to the current adopted revision.sync/earthwork
  • Bioretention, rain gardens, constructed wetlands, and other vegetated practices whose performance depends on a planting medium
NOTE Whether a facility detains, infiltrates, or does both is the decision every other selection in this standard follows from: an open-bottom chamber bed and a lined chamber bed are the same product with a different base, and they are permitted, tested, and accepted on different terms. (1.4)
1.5 The Contractor shall construct the facility to the lines, grades, invert elevations, and storage geometry shown, and shall not alter them to suit field conditions without the written direction of the Engineer of Record.
1.6 The Contractor shall report to the Engineer of Record any condition that prevents the facility from being built as drawn, including groundwater or bedrock encountered above the elevation the geotechnical report anticipated, a subgrade that differs from the soil the infiltration design was based on, a utility conflict, and an invert that does not meet the connecting storm sewer.
1.7 Work under this standard shall be coordinated with Storm DrainageStorm DrainageResolves to the current adopted revision.sync/storm-drainage for the inlet and outlet connections and their inverts, with Erosion And Sediment ControlErosion and Sediment ControlResolves to the current adopted revision.sync/erosion-and-sediment-control for protection of the facility during construction, with EarthworkEarthworkResolves to the current adopted revision.sync/earthwork for excavation and backfill, and with SubdrainageSubdrainageResolves to the current adopted revision.sync/subdrainage where an underdrain is placed beneath a lined facility.

2 Referenced Standards

2.1 Materials, fabrication, installation, and testing shall comply with the latest adopted edition of each of the following unless a specific edition is cited in the Contract Documents.
2.2 Where the Contract Documents, the stormwater permit, the governing design manual, and the referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
Standard Title
ASTM F2418 Polypropylene (PP) Corrugated Wall Stormwater Collection Chambers
ASTM F2922 Polyethylene (PE) Stormwater Collection Chambers
ASTM F2787 Structural Design of Thermoplastic Corrugated Wall Stormwater Collection Chambers
ASTM C857 Minimum Structural Design Loading for Underground Precast Concrete Utility Structures
ASTM C858 Underground Precast Concrete Utility Structures
ASTM C913 Precast Concrete Water and Wastewater Structures
ASTM C1433 Precast Reinforced Concrete Monolithic Box Sections for Culverts, Storm Drains, and Sewers
ASTM C1504 Manufacture of Precast Reinforced Concrete Three-Sided Structures for Culverts, Storm Drains, and Sewers
ASTM C478 Circular Precast Reinforced Concrete Manhole Sections
ASTM C443 Joints for Concrete Pipe and Manholes, Using Rubber Gaskets
ASTM C990 Joints for Concrete Pipe, Manholes, and Precast Box Sections Using Preformed Flexible Joint Sealants
ASTM C877 External Sealing Bands for Concrete Pipe, Manholes, and Precast Box Sections
ASTM C1244 Concrete Sewer Manholes by the Negative Air Pressure (Vacuum) Test Prior to Backfill
ASTM C76 Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe
ASTM D2321 Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity-Flow Applications
ASTM D3385 Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer
ASTM D5084 Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter
ASTM D698 Laboratory Compaction Characteristics of Soil Using Standard Effort
ASTM D5820 Pressurized Air Channel Evaluation of Dual Seamed Geomembranes
ASTM D6392 Determining the Integrity of Nonreinforced Geomembrane Seams Produced Using Thermo-Fusion Methods
ASTM D7176 Non-Reinforced Polyvinyl Chloride (PVC) Geomembranes Used in Buried Applications
GRI GM13 Test Methods, Test Properties and Testing Frequency for High Density Polyethylene (HDPE) Smooth and Textured Geomembranes
GRI GM17 Test Methods, Test Properties and Testing Frequency for Linear Low Density Polyethylene (LLDPE) Smooth and Textured Geomembranes
AASHTO M43 Sizes of Aggregate for Road and Bridge Construction
AASHTO M288 Geosynthetic Specification for Highway Applications
AASHTO M294 Corrugated Polyethylene Pipe, 12 in. to 60 in. Diameter
AASHTO M330 Polypropylene Pipe, 12 in. to 60 in. Diameter
AASHTO M36 Corrugated Steel Pipe, Metallic-Coated, for Sewers and Drains
AASHTO M196 Corrugated Aluminum Pipe for Sewers and Drains
AASHTO LRFD LRFD Bridge Design Specifications (Section 3, Loads; Section 12, Buried Structures)
ACI 350 Code Requirements for Environmental Engineering Concrete Structures
ACI 318 Building Code Requirements for Structural Concrete
40 CFR 122 EPA National Pollutant Discharge Elimination System Permit Program
2.3 The stormwater permit, the governing state or municipal stormwater design manual, and any maintenance agreement the permit requires shall be confirmed with the Authority Having Jurisdiction before the facility is constructed, and the criteria in those instruments shall govern over this standard where they are more stringent.
NOTE The federal program sets the floor for post-construction stormwater control; the enforceable criteria on a given site, including the storms to be matched, the volume to be retained, and the pollutant removal to be shown, come from the state design manual and the local ordinance, which differ from one another more than any other site-civil requirement. (2.4)

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for the Engineer of Record's review and acceptance before any chamber, vault, pipe, liner, or outlet structure is procured or fabricated:
  • Product data for the storage product, identifying the governing product standard, the nominal dimensions and storage volume per unit, the published minimum and maximum cover for the design live load, and the manufacturer's installation instructions
  • Shop drawings showing the facility layout, row and header arrangement, invert and crown elevations, the aggregate envelope section, the liner or infiltration surface, the geotextile extents, inspection ports, access structures, and the connections to the storm sewer
  • Structural calculations for the storage product and for every access structure under the design live load, sealed by a professional engineer licensed in the jurisdiction
  • Flotation calculations for every underground structure and lined facility whose base lies below the seasonal high groundwater elevation
  • Outlet control structure shop drawings showing the structure, the orifice plates and weirs with their sizes and elevations, the trash racks, the drawdown provision, and the access cover
  • Product data and the manufacturer's seaming and quality control plan for the liner, where a liner is specified
  • Product data for the pretreatment and water-quality treatment devices, with the verification or certification document on which the removal performance is claimed
  • Gradation test results for each proposed storage aggregate source, with the fines content and the aggregate's measured or published void ratio
  • Geotextile product data and certification under GeosyntheticsGeosynthetics and GeotextilesResolves to the current adopted revision.sync/geosynthetics for each geotextile function in the facility
Action Submittals Requiredcheckbox
☐ Storage product data with cover limits and installation instructions
☐ Facility shop drawings with layout, inverts, envelope section, and access
☐ Sealed structural calculations for the design live load
☐ Flotation calculations for structures below seasonal high groundwater
☐ Outlet control structure shop drawings with orifice and weir schedule
☐ Liner product data and seaming quality control plan
☐ Treatment device product data with performance verification document
☐ Storage aggregate gradation, fines, and void ratio results
☐ Geotextile product data and certification
3.1.2 No storage product, liner, or outlet structure shall be delivered to the site before the action submittal covering it has been accepted.

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following for the record as each becomes available:
  • The field infiltration test report, where an infiltration facility is specified, identifying the test method, the test locations and depths relative to the facility bottom, the measured rates, and the design rate derived from them
  • The geotechnical confirmation that the seasonal high groundwater elevation and the bedrock elevation at the facility are as the design assumed
  • Precast plant certification and the certificate of compliance with the governing product standard for each precast structure
  • The liner installer's seam test records, where a liner is specified
  • Concrete mix designs and strength reports for cast-in-place structures, as required under Site Concrete StructuresCast-in-Place Site Concrete StructuresResolves to the current adopted revision.sync/site-concrete-structures
Informational Submittals Requiredcheckbox
☐ Field infiltration test report with the derived design rate
☐ Geotechnical confirmation of groundwater and bedrock elevations
☐ Precast certification and certificates of compliance
☐ Liner seam test records
☐ Cast-in-place concrete mix designs and strength reports

3.3 Closeout Submittals

3.3.1 Before substantial completion the Contractor shall submit the following:
  • Record drawings showing the as-built facility footprint, bottom and crown elevations, every control elevation of the outlet structure, the as-built orifice and weir dimensions, the inspection port and access structure locations, and every deviation from the Contract Documents
  • The as-built storage verification, comparing the surveyed storage at each control elevation with the design storage at that elevation
  • Signed reports for every acceptance test required by this standard, each identified to the facility and showing a pass or fail determination
  • Video inspection recordings and logs of the underground rows and headers, where video inspection is required
  • The operation and maintenance manual for the facility, identifying each component, its inspection interval, the sediment depth at which cleaning is triggered, the cleaning method and access point for each component, and the replacement parts for the outlet and treatment devices
  • The maintenance agreement, easement, or covenant the stormwater permit requires, executed and recorded where recording is required
  • The as-built certification the Authority Having Jurisdiction requires, sealed by the professional engineer the permit names
  • Manufacturer warranties for the storage product, the liner, the treatment devices, and the precast structures, assigned to the Owner
Closeout Submittals Requiredcheckbox
☐ Record drawings with as-built elevations and control dimensions
☐ As-built storage verification against the design storage
☐ Signed acceptance test reports with pass or fail by facility
☐ Video inspection recordings and logs
☐ Operation and maintenance manual with cleaning triggers
☐ Recorded maintenance agreement or easement
☐ Sealed as-built certification to the Authority Having Jurisdiction
☐ Assigned manufacturer warranties
NOTE The recorded maintenance agreement and the sealed as-built certification are conditions of the stormwater permit on most sites, and a certificate of occupancy has been withheld over each of them; neither can be produced after the fact without the survey and the test records this standard requires along the way. (3.3.2)

4 Quality Assurance

4.1 Design and Installer Qualifications

4.1.1 The hydrologic routing, the storage sizing, and the outlet control design shall be the work of a professional engineer licensed in the jurisdiction, and this standard does not revise them.
4.1.2 Structural calculations for the storage product and for cast-in-place structures shall be sealed by a professional engineer licensed in the jurisdiction, and the calculations for a thermoplastic chamber system shall follow ASTM F2787.
4.1.3 The Contractor installing an underground storage system shall have completed not fewer than three installations of the same product family within the preceding five years, and shall submit those project references on request.
4.1.4 The liner installer shall be approved by the liner manufacturer and shall have installed not less than 100,000 ft² of the liner material proposed, with seaming performed by technicians the manufacturer has trained on the equipment to be used.
4.1.5 Field infiltration testing shall be performed by or under the supervision of the geotechnical engineer of record.

4.2 Product Qualification and Marking

4.2.1 Precast concrete structures shall be produced at a plant certified under a plant certification program accepted by the Authority Having Jurisdiction, and each unit shall bear the plant identification, the product standard designation, and the production date.
4.2.2 Thermoplastic chambers shall bear the manufacturer's identification, the product standard designation, and the production date or lot number on each chamber.
4.2.3 A storage product, liner, or precast structure that cannot be traced to its certification records shall be rejected and removed from the site, and the cost of removal and replacement shall be borne by the Contractor.

4.3 Preinstallation Conference

4.3.1 Before excavation of the facility begins the Contractor shall convene a preinstallation conference attended by the Contractor's site superintendent, the civil engineer of record, the geotechnical engineer of record, the storage product manufacturer's representative where the manufacturer offers one, the liner installer where a liner is specified, and the Authority Having Jurisdiction's inspector where the permit requires attendance.
4.3.2 The conference shall review the construction sequence relative to stabilization of the contributing area, the protection of the infiltration surface, the embedment and compaction requirements, the construction load limits over the storage, the liner seaming and testing plan, the acceptance tests and the as-built survey, and the inspection hold points.

4.4 Inspection Hold Points

4.4.1 The Contractor shall give the Engineer of Record and the Authority Having Jurisdiction's inspector not less than 24 hours' notice before each hold point listed below, and shall not proceed past a hold point until the inspection has been performed and released in writing:
  • The excavated facility subgrade, before any geotextile, liner, or aggregate is placed
  • The liner, after seam testing and before the protection layer or aggregate is placed over it
  • The bedding stone and the geotextile, before chambers, pipe, or vaults are set
  • The storage product as set, with the headers and inspection ports in place, before the stone envelope is completed
  • The completed stone envelope and the top geotextile, before backfill
  • The outlet control structure, with the orifice plates and weirs installed and their elevations surveyed, before the structure is backfilled
  • The embankment cutoff trench and each embankment lift, for a surface basin
  • Each acceptance test and the as-built storage survey
4.4.2 Where an inspection is not performed within 24 hours of the scheduled time through no fault of the Contractor, the Contractor may proceed past the hold point after notifying the Engineer of Record in writing, and the Owner shall bear the cost of any later uncovering required to inspect that work.

5 Design Basis and Service Conditions

5.1 Facility Function

5.1.1 The hydraulic function of the facility shall be as indicated in the datasheet.
Facility Hydraulic Functionradio
○ Detention with a controlled release to a positive outlet
○ Infiltration to the native soil without a positive outlet for the design volume
○ Combined infiltration of the retained volume with controlled release of the remainder
NOTE Detention gives back the runoff volume at a slower rate, which is what a peak-rate criterion asks for and which works on any soil; infiltration removes the volume from the surface system altogether, which is what a retention or recharge criterion asks for and which is available only where the soil drains, the groundwater is deep enough, and the contributing area carries no pollutant the aquifer cannot receive. A combined facility infiltrates the frequent small storms through an open bottom and routes the large storms through an outlet, which meets both criteria on a site that can infiltrate but not the whole design volume. (5.1.2)
5.1.3 The storage volume provided at each control elevation shall be as indicated in the datasheet.
Design Storage Volume at the Overflow Elevationtext
Enter value...
ft³
Per drawings — the stormwater management report and the facility stage-storage table (deferred by default)
5.1.4 The allowable release rate for each recurrence interval the permit requires to be matched shall be as indicated in the datasheet.
Allowable Peak Release Rates by Recurrence Intervaltext
Enter value...
cfs
Per drawings — the stormwater management report and the stormwater permit conditions (deferred by default)
5.1.5 The water-quality volume to be captured and treated shall be as indicated in the datasheet.
Water-Quality Treatment Volumetext
Enter value...
ft³
Per drawings — the stormwater management report and the stormwater permit conditions (deferred by default)
NOTE The storage, the release rates, and the water-quality volume are outputs of the routing in the stormwater management report and are never set by this standard; the storm sewers that bring runoff to the facility are sized separately, for Design Storm FrequencyDesign Storm FrequencyParameterEach project supplies its own value.design-storm-frequency, under Storm DrainageStorm DrainageResolves to the current adopted revision.sync/storm-drainage, and the facility's own criteria usually span a set of recurrence intervals rather than that single event. (5.1.6)
5.1.7 Where the stormwater permit requires more than one recurrence interval to be matched, the facility and its outlet shall satisfy every required interval, and the Contractor shall not alter an orifice or weir to improve the performance at one interval without the Engineer of Record's written direction.

5.2 Groundwater, Bedrock, and Infiltration Rate

5.2.1 The bottom of the storage, or of the stone envelope beneath it, shall be separated from Seasonal High Groundwater ElevationSeasonal High Groundwater ElevationParameterEach project supplies its own value.seasonal-high-groundwater-elevation by not less than the vertical distance indicated in the datasheet.
Minimum Vertical Separation from Seasonal High Groundwater to the Facility Bottomrange
ft
123456810
Derived — the facility hydraulic function and the separation the governing stormwater design manual requires for that function (by default)
NOTE Separation is what the design manual trades against infiltration credit: an infiltration facility needs unsaturated soil beneath it to drain into and to treat through, and a lined detention facility needs none, which is why the required distance follows from the function rather than from a preference. Groundwater that rises into the stone envelope also takes the storage it occupies, and the elevation that governs is the seasonal high, not the level on the day of the boring. (5.2.2)
5.2.3 The bottom of an infiltration facility shall be separated from bedrock by not less than the distance the governing stormwater design manual requires, and the geotechnical report shall confirm the bedrock elevation at the facility.
5.2.4 Where an infiltration facility is specified, the infiltration rate of the soil at the facility bottom shall be measured in the field by the method indicated in the datasheet, at the number, depth, and locations the governing design manual requires, and in not fewer than one test at the elevation of the facility bottom in each facility.
Field Infiltration Test Methodselect
Double-ring infiltrometer per ASTM D3385
Test pit falling-head or constant-head test per the governing design manual
Borehole percolation test per the governing design manual
Laboratory hydraulic conductivity of undisturbed samples per ASTM D5084
NOTE A double-ring infiltrometer measures the surface rate on a prepared horizontal face and is the method most design manuals name; a test pit test wets the full depth of the excavation and is favored where the facility bottom is deep and layered; a borehole test is quick and reaches depth but overstates the rate where the hole crosses a permeable seam; and a laboratory test on an undisturbed sample gives a controlled value for a cohesive soil but misses the fissures and root channels that carry most of the flow in the field. Many design manuals accept only one or two of these for infiltration credit, and that acceptance decides the method more often than the soil does. (5.2.5)
5.2.6 The design infiltration rate shall be the measured rate divided by the factor of safety indicated in the datasheet.
Infiltration Rate Factor of Safetyrange
11.522.534
Derived — the factor of safety the governing stormwater design manual applies to the test method used (by default)
5.2.7 An infiltration facility shall not be constructed where the measured rate, divided by the factor of safety, falls below the minimum design rate the governing design manual accepts for infiltration credit, and the Contractor shall report that result to the Engineer of Record before proceeding.
NOTE Specifying an open-bottom facility on a soil whose rate was taken from a soil survey texture class rather than measured is the single most common cause of a facility that holds water for days and of a permit certification the Authority Having Jurisdiction refuses to accept. (5.2.8)

5.3 Structural Loading

5.3.1 The design live load on an underground facility and on every access structure shall be as indicated in the datasheet.
Design Live Load on the Underground Facilityselect
Pedestrian and landscape loading with no vehicular access
AASHTO H-10 light vehicular loading
AASHTO HS-20 or HL-93 highway loading
AASHTO HS-25 loading
Aircraft, crane, or container-handling loading
Derived — the surface use above the facility shown on the civil site plan, including fire lanes and maintenance vehicle routes (by default)
NOTE A facility under a lawn still receives the vacuum truck that services it, and a facility under a plaza receives the fire apparatus the plaza was designed to look as if it never would; the load case that governs is the heaviest vehicle that can reach the surface over the storage, not the one the surface is drawn for. (5.3.2)
5.3.3 Finished cover over an underground facility shall be not less than the minimum cover indicated in the datasheet.
Minimum Finished Cover over the Storage Producttext
Enter value...
in
Derived — the storage product and the minimum cover the manufacturer publishes for the design live load (by default)
5.3.4 Finished cover over an underground facility shall not exceed the maximum cover indicated in the datasheet.
Maximum Finished Cover over the Storage Producttext
Enter value...
ft
Derived — the storage product and the maximum cover the manufacturer publishes for the design live load and the backfill material (by default)
NOTE Cover below the published minimum lets the wheel load reach the arch before the soil has spread it, and cover above the published maximum loads the arch with more dead weight than its design wall carries; the two limits are structural ratings of the product, and finished grade over the facility is set between them before the grading plan is finalized. (5.3.5)
5.3.6 Where the design cover at any point over the facility falls outside the published limits for the product indicated, the Contractor shall report the condition to the Engineer of Record before the product is ordered.

5.4 Flotation

5.4.1 Every underground structure, every lined facility, and every empty vault whose base lies below Seasonal High Groundwater ElevationSeasonal High Groundwater ElevationParameterEach project supplies its own value.seasonal-high-groundwater-elevation shall be designed to resist flotation in the empty condition, with a factor of safety not less than the value indicated in the datasheet, counting only the dead weight of the structure, the soil directly over it, and any ballast or anchorage provided.
Flotation Factor of Safety for the Empty Facilityrange
1.11.21.251.31.5
5.4.2 The flotation resistance provision shall be as indicated in the datasheet.
Flotation Resistance Provisionselect
Extended base slab engaging the weight of the soil over it
Mass concrete ballast on or within the base
Tie-down anchors or helical anchors into the subgrade
Deadman anchors with straps over the structure
Not required, facility base above seasonal high groundwater
NOTE An extended base slab is the usual answer for a precast vault because it comes from the plant with the structure and relies on backfill that must be placed anyway; mass ballast costs volume the facility was built to provide; anchors into the subgrade cost less storage but depend on a soil the geotechnical report must confirm; and a lined stone bed, which weighs almost nothing when empty, is the case most often left out of the calculation and most often found floating. The factor of safety a jurisdiction requires reflects how well it trusts the groundwater elevation, and a higher value is applied where that elevation was estimated rather than measured through a wet season. (5.4.3)
5.4.4 A lined facility shall not be left empty below the seasonal high groundwater elevation before its flotation resistance is complete, and the Contractor shall maintain dewatering under Excavation Support And DewateringExcavation Support and DewateringResolves to the current adopted revision.sync/excavation-support-and-dewatering until it is.

5.5 Frost and Cold Weather

5.5.1 The outlet control structure base and the footing of any cast-in-place structure in frost-susceptible soil shall bear below Frost DepthFrost DepthParameterEach project supplies its own value.frost-depth.
NOTE A low-flow orifice in a surface basin ices over in a winter thaw cycle and holds the basin at the orifice elevation until the ice clears, which is the condition under which the facility most often overtops its emergency spillway; where the site sees sustained freezing, the orifice protection article of this standard offers the hooded and submerged arrangements that keep the opening below the ice. (5.5.2)

6 Storage Facility Type

6.1 The storage facility type shall be as indicated in the datasheet.
Storage Facility Typeselect
Surface dry detention basin
Surface extended dry detention basin with a micropool at the outlet
Surface wet retention pond with a permanent pool
Underground thermoplastic arch chamber bed in a stone envelope
Underground corrugated pipe storage with headers
Underground precast concrete vault or box sections
Underground cast-in-place reinforced concrete vault
Underground modular plastic crate storage
NOTE A surface basin is the least expensive storage per cubic foot where land is available, and it is also the only form the Owner can see fill, drain, and silt in; a wet pond adds the permanent pool that settles and biologically treats runoff, at the cost of a dam, a drawdown provision, and a maintenance dredge. Underground storage returns the surface to parking or building use: arch chambers in a stone envelope store the most per excavated cubic foot at a shallow depth and infiltrate readily; corrugated pipe storage suits a long narrow footprint and a shallow cover; precast vaults carry the heaviest loads, fit a tight or deep footprint, and give an open interior that can be inspected on foot; a cast-in-place vault fits any geometry, including beneath a building, at the longest construction duration; and plastic crate storage stores the highest void ratio in a modular block but depends on the manufacturer's long-term creep testing for its structural basis, which the Authority Having Jurisdiction may not accept under a trafficked surface. (6.2)
6.3 Where more than one facility is shown, the facility type, function, and storage geometry of each shall be as indicated on the stormwater facility plan and sections.
6.4 The facility shall be located to satisfy the setbacks from building foundations, property lines, septic systems, water supply wells, and steep slopes that the governing design manual and the health authority require, at the location indicated on the stormwater facility plan.
NOTE Infiltration beside a foundation saturates the bearing soil and the backfill against the wall, and infiltration up-gradient of a well delivers the runoff's dissolved load to the aquifer the well draws from; the required setbacks are set by the design manual and the health authority and are confirmed before the footprint is fixed. (6.5)

7 Surface Basins and Ponds

7.1 Requirements in this article apply where a surface dry detention basin, an extended dry detention basin, or a wet retention pond is selected as the storage facility type.

7.2 Embankment and Cutoff

7.2.1 The embankment of a surface basin shall be constructed of the structural fill class designated under EarthworkEarthworkResolves to the current adopted revision.sync/earthwork, placed in lifts and compacted to not less than the density indicated in the datasheet, with a cutoff trench beneath the embankment centerline keyed into the native soil below the stripped surface.
Embankment Compaction, Percent of Maximum Dry Density per ASTM D698range
%
90929598100
7.2.2 The embankment shall provide freeboard above the design high water of the largest storm the permit requires the facility to pass of not less than the value indicated in the datasheet.
Minimum Embankment Freeboard above the Design High Waterrange
ft
0.511.523
NOTE An embankment that impounds water above the surrounding grade is a dam, however small, and the two failures that take one out are seepage along the outlet barrel and overtopping through a low spot in the crest; the cutoff trench, the barrel seepage control, and the freeboard are the answers to those two, and an embankment above the height or storage threshold of the state dam safety program is outside this standard and designed under that program. (7.2.3)
7.2.4 Topsoil, organic material, and the fill of any temporary sediment basin that occupied the footprint shall be removed from beneath the embankment before fill is placed.

7.3 Basin Grading and Side Slopes

7.3.1 Interior and exterior side slopes of the basin shall be not steeper than the ratio indicated in the datasheet.
Minimum Side Slope Ratio, Horizontal Units per 1 Verticalrange
H per 1 V
23456
NOTE A 3 to 1 slope is the steepest a tractor mower works across and the steepest most design manuals allow without a fence; a 4 to 1 or flatter slope is required where the basin is in a public space, where children can reach the water, or where the soil will not hold a steeper cut, and it costs footprint for every foot of depth. (7.3.2)
7.3.3 The floor of a dry basin shall slope toward the low-flow channel or the outlet at not less than the gradient indicated in the datasheet, so that the basin drains completely between storms.
Minimum Dry Basin Floor Slope toward the Outletrange
%
05
7.3.4 The low-flow conveyance across a dry basin floor shall be as indicated in the datasheet.
Dry Basin Low-Flow Conveyanceselect
Concrete-lined low-flow channel
Riprap-lined low-flow channel
Turf-reinforced vegetated low-flow channel
Micropool at the outlet without a channel
NOTE A dry basin that does not drain in the time the design manual allows breeds mosquitoes, kills the turf on its floor, and is the basin the Owner's neighbors complain about; the floor slope, the low-flow channel, and the orifice protection together are what make it dry. A concrete channel stays open and carries the base flow with no maintenance, a riprap channel costs less and traps the sediment that reaches it, a vegetated channel treats the base flow but needs mowing and re-establishment after every large storm, and a micropool concentrates the standing water in one spot the design manual accepts at the price of a permanently wet corner. (7.3.5)

7.4 Wet Pond Provisions

7.4.1 A wet retention pond shall maintain a permanent pool at the elevation and depth indicated on the pond sections and the outlet control structure detail.
7.4.2 The provision of a safety bench and an aquatic bench at the permanent pool edge shall be as indicated in the datasheet.
Wet Pond Perimeter Benchesselect
Safety bench above the pool and aquatic bench below it
Safety bench above the pool only
Aquatic bench below the pool only
No benches
NOTE A safety bench is a flat shelf above the permanent pool that stops a person who slips down the slope before the water, and an aquatic bench is a shallow shelf below the pool that grows the emergent vegetation that takes up nutrients and discourages entry; most design manuals require the first wherever the public can reach the pond and the second wherever the pond is credited with water-quality treatment. (7.4.3)
7.4.4 The permanent pool shall be provided with the drawdown provision specified in the outlet control structure article of this standard, so that the pool can be lowered for sediment removal.

7.5 Emergency Spillway

7.5.1 The emergency spillway of a surface basin shall be as indicated in the datasheet, and shall pass the storm the stormwater permit requires the facility to pass with the primary outlet blocked, at the location and elevation indicated on the basin grading plan.
Emergency Spillway Constructionselect
Vegetated earthen spillway cut in natural ground with a turf reinforcement mat
Riprap-lined spillway
Concrete-lined spillway or broad-crested weir
Articulated concrete block armoring over the embankment crest
Overflow through the outlet structure riser without a separate spillway
NOTE A spillway cut in natural ground beside the embankment is the arrangement every design manual prefers, because it does not cross the fill, and it is the one that needs the width a tight site may not have; riprap and concrete linings let the spillway sit on the embankment at the cost of a hard surface that must be inspected after every event it carries; armoring the crest lets the whole embankment overtop; and relying on the riser alone is accepted only where the facility cannot be overtopped onto anything that matters. (7.5.2)
7.5.3 The spillway shall not be constructed on fill unless the Contract Documents show it there and the lining is designed for the velocity the spillway carries.
7.5.4 The turf reinforcement mat, riprap, and permanent seeding of the spillway and the basin slopes shall be as specified under Erosion And Sediment ControlErosion and Sediment ControlResolves to the current adopted revision.sync/erosion-and-sediment-control.

8 Underground Thermoplastic Arch Chambers

8.1 Requirements in this article apply where an underground thermoplastic arch chamber bed is selected as the storage facility type.
8.2 Chambers shall be of the material indicated in the datasheet and shall conform to the product standard for that material.
Arch Chamber Materialradio
○ Polypropylene per ASTM F2418
○ Polyethylene per ASTM F2922
8.3 Chambers shall be structurally designed in accordance with ASTM F2787 for the design live load and the cover range of the facility, and the design shall be furnished by the chamber manufacturer and sealed as required in the Quality Assurance section of this standard.
8.4 The nominal chamber height shall be as indicated in the datasheet.
Nominal Arch Chamber Heightrange
in
872
Per drawings — the stormwater facility sections and the storage product schedule (deferred by default)
NOTE Chamber height sets the storage per unit of footprint and the excavation depth together: a taller chamber stores more under the same parking stall, needs more cover above and more stone around it, and raises the invert of the inlet the storm sewer must reach. (8.5)
8.6 End caps shall be furnished by the chamber manufacturer for every row end, and rows shall be joined to the headers through the manufacturer's manifold fittings rather than field-cut openings.
8.7 Rows receiving an inlet pipe shall have a woven scour-protection geotextile laid on the bedding stone beneath the inlet chamber for the length the chamber manufacturer publishes for the inlet pipe size.
NOTE The inlet jet on an unprotected stone floor scours a channel through the bedding under the first chambers and carries the fines it lifts into the rest of the row; the woven strip under the inlet chambers is the manufacturer's stated condition for the storage and structural rating of the row. (8.8)
8.9 Chambers shall be set, the stone envelope placed, and the stone compacted in the lifts and with the equipment the chamber manufacturer's installation instructions publish for the product, and the Contractor shall keep those instructions on the site during installation.
NOTE The structural basis of an arch chamber is the stone around it, which carries the load the arch sheds into it, so a lift placed too thick, a corner left unfilled, or a roller used where the manufacturer calls for a plate compactor removes support that the ASTM F2787 design counted on and that no later inspection can see. (8.10)

9 Underground Corrugated Pipe Storage

9.1 Requirements in this article apply where underground corrugated pipe storage is selected as the storage facility type.
9.2 Storage pipe shall be of the material indicated in the datasheet.
Storage Pipe Materialselect
Corrugated polyethylene pipe per AASHTO M294
Corrugated polypropylene pipe per AASHTO M330
Corrugated steel pipe per AASHTO M36, aluminized Type 2 or polymer coated
Corrugated aluminum pipe per AASHTO M196
Reinforced concrete pipe per ASTM C76
NOTE Thermoplastic pipe stores the most per dollar at diameters up to 60 in. and is joined with gaskets that make a closed system watertight; corrugated metal reaches larger diameters and arch shapes for a shallow cover, with a service life set by the coating and the soil chemistry rather than the load; and concrete pipe carries the heaviest cover and the longest life at the highest material and handling cost, and is the material most often used where the storage doubles as a culvert. (9.3)
9.4 Storage pipe shall be joined with the gasketed joint the pipe standard provides, and where the facility function is detention the joints shall be qualified as watertight under Storm DrainageStorm DrainageResolves to the current adopted revision.sync/storm-drainage for that pipe material.
9.5 Where the facility function includes infiltration, the storage pipe shall be perforated to the pattern the pipe manufacturer publishes for storage service and shall be set on and surrounded by the stone envelope specified in the storage aggregate article of this standard.
9.6 Headers, manifolds, tees, and end plugs shall be fabricated by the pipe manufacturer in the same material and joint as the storage pipe, and field-cut openings shall be made only with the pipe manufacturer's published procedure.
9.7 Storage pipe shall be installed in accordance with ASTM D2321 for thermoplastic pipe and with the pipe manufacturer's installation instructions for the other materials, and the cover limits of the Structural Loading article of this standard apply.

10 Underground Precast and Cast-in-Place Concrete Vaults

10.1 Requirements in this article apply where an underground precast concrete vault, box sections, or a cast-in-place reinforced concrete vault is selected as the storage facility type.

10.2 Precast Vault Products

10.2.1 The precast product form shall be as indicated in the datasheet.
Precast Vault Product Formselect
Modular precast vault sections per ASTM C858 with loading per ASTM C857
Precast box sections per ASTM C1433 set in parallel runs
Precast three-sided structures per ASTM C1504 on cast-in-place footings
Precast circular sections per ASTM C478 as storage galleries
NOTE Modular vault sections give a single open chamber with the fewest joints and a floor that can be inspected on foot; box sections are a culvert product that stacks into long parallel cells with a joint every section, which suits a narrow footprint and a short lead time; three-sided units leave the native soil or a stone floor open for infiltration beneath a structural roof; and circular manhole sections store the least per unit of footprint but are stocked by every precaster and fit between utilities a vault cannot. (10.2.2)
10.2.3 Precast vault sections shall be designed for the design live load of this standard, for the lateral earth and groundwater pressure at the installed depth, and for the flotation condition, and the design shall be sealed as required in the Quality Assurance section of this standard.
10.2.4 The joint between precast sections shall be sealed as indicated in the datasheet.
Precast Section Joint Sealselect
Preformed flexible butyl joint sealant per ASTM C990
Confined rubber gasket per ASTM C443
Butyl sealant per ASTM C990 with an external sealing band per ASTM C877
Open joint for infiltration, with geotextile over the joint on the exterior
NOTE Butyl sealant seals a box or vault joint against soil and against the water a detention vault holds for a day, and it is the seal every precaster furnishes as standard; a rubber gasket is used where the vault will hold water continuously or where the joint is tested; an external band is added where the joint lies below groundwater and must keep fines out under a head; and an open joint is the deliberate choice on an infiltration vault, where the geotextile over it keeps the stone out and lets the water through. (10.2.5)
10.2.6 Pipe openings in precast vaults shall be cast or cored at the plant to the pipe outside diameter and connector, and the connection shall be as specified for pipe-to-structure connections under Storm DrainageStorm DrainageResolves to the current adopted revision.sync/storm-drainage.
10.2.7 Precast sections shall be set on a prepared bedding of the thickness and material the precaster publishes, leveled so that the joint faces meet uniformly, and shall not be shimmed on one side to correct a bedding that was not level.

10.3 Cast-in-Place Vaults

10.3.1 A cast-in-place vault shall be designed under the code basis indicated in the datasheet, by a professional engineer licensed in the jurisdiction.
Cast-in-Place Vault Design Code Basisradio
○ ACI 350 environmental engineering concrete structures
○ ACI 318 with the exposure class and crack control the Engineer of Record designates
10.3.2 The concrete, reinforcement, waterstops, joints, curing, and field testing of a cast-in-place vault shall be as specified under Site Concrete StructuresCast-in-Place Site Concrete StructuresResolves to the current adopted revision.sync/site-concrete-structures and Concrete Joints And WaterstopsConcrete Construction Joints and WaterstopsResolves to the current adopted revision.sync/concrete-joints-and-waterstops, and this standard does not restate those requirements.
10.3.3 A cast-in-place vault that is to hold water as a detention facility shall have waterstops at every construction joint below the design high water elevation.

11 Storage Aggregate and Geotextile Envelope

11.1 Requirements in this article apply where the storage product sits in a stone envelope, which includes every arch chamber bed, perforated pipe storage, open-bottom vault, and plastic crate installation, and the aggregate beneath and around a precast vault where the precaster calls for crushed stone bedding.
11.2 Storage aggregate shall be washed, clean, crushed, angular stone of the gradation indicated in the datasheet, with not more than 2 percent by mass passing the No. 200 sieve unless the storage product manufacturer's installation instructions require less.
Storage Aggregate Gradation per AASHTO M43select
No. 2
No. 3
No. 357
No. 4
No. 467
No. 57
No. 67
NOTE The larger open gradations store more water per cubic foot and let it move to the chambers faster, and they are also the hardest to place to a level bed and the ones a thin chamber foot can punch into; the smaller gradations bed more easily and support a precast vault better, with a lower void ratio and a bed that silts faster. Chamber manufacturers publish the gradations their structural rating was tested with, and the gradation is selected from that list before it is selected for its storage. (11.3)
11.4 The storage volume credited to the aggregate shall be computed with the void ratio indicated in the datasheet, and the Contractor shall furnish a measured void ratio for the source where the Authority Having Jurisdiction requires one.
Design Void Ratio of the Storage Aggregaterange
%
2545
Default: 40 %
NOTE Forty percent is the void ratio the industry attributes to clean crushed angular stone and the value most design manuals cap the credit at; a rounded gravel or a dense gradation falls short of it, and a facility credited at 40 percent and built with stone that yields 30 stores a quarter less than its permit assumes. (11.5)
11.6 Recycled concrete aggregate, slag, rounded gravel, and any aggregate with a fines content above the limit shall not be used as storage aggregate unless the datasheet or the Engineer of Record in writing permits it for the facility.
NOTE Recycled concrete releases lime into the water that passes through it, which raises the pH of the discharge and cements the fines at the bottom of the bed, and rounded gravel neither interlocks to support the chamber nor holds the void ratio the credit assumes. (11.7)

11.8 Geotextile Envelope

11.8.1 The extent of the nonwoven geotextile around the stone envelope shall be as indicated in the datasheet.
Geotextile Wrap Extent around the Stone Envelopeselect
Top and sides of the stone envelope, with the bottom left open to the subgrade
Top, sides, and bottom of the stone envelope
Top of the stone envelope only
NOTE The top geotextile keeps the backfill fines out of the stone, which is where the storage is lost first, and every manufacturer requires it; the sides do the same against the trench walls. The bottom is the decision: a geotextile on the floor of an infiltration bed is the layer that blinds with the sediment the bed receives and ends its infiltration, and most chamber manufacturers prohibit it, while a few design manuals require it as a separation layer on a soil that would pump into the stone, and a lined facility has a liner there instead. (11.8.2)
11.8.3 The nonwoven geotextile shall be a filtration geotextile with the apparent opening size, permittivity, and AASHTO M288 survivability class specified under GeosyntheticsGeosynthetics and GeotextilesResolves to the current adopted revision.sync/geosynthetics, matched to the adjacent soil by the geotechnical engineer of record.
11.8.4 Geotextile panels shall overlap not less than 24 in. at every seam, and the overlap shall be placed so that the upstream or upper panel laps over the downstream or lower panel.
11.8.5 The geotextile shall be placed without wrinkles that would fold into the stone, shall be covered within the exposure period the geotextile manufacturer publishes, and a panel torn or punctured during stone placement shall be patched with a panel of the same material extending not less than 24 in. beyond the damage in every direction.

12 Liners

12.1 The liner beneath and around the storage shall be as indicated in the datasheet.
Facility Linerselect
None, infiltration surface open to the native soil
Compacted clay liner
Geosynthetic clay liner
High-density polyethylene geomembrane per GRI GM13
Linear low-density polyethylene geomembrane per GRI GM17
Reinforced polypropylene geomembrane
Polyvinyl chloride geomembrane per ASTM D7176
Ethylene propylene diene monomer geomembrane
NOTE A liner is what turns a stone bed into a detention cell, and it is required wherever the water must not reach the soil: over a contaminated site, in karst, within a well setback, where the groundwater is too close, where the contributing area is a fueling or loading area that the permit classifies as a hotspot, or where the design simply claims no infiltration. A compacted clay liner is built from the site's own soil where that soil will reach the permeability required, and it cracks if it dries before it is covered; a geosynthetic clay liner seals by swelling and tolerates subgrade irregularity, at the cost of strict protection from hydration before confinement; HDPE is the stiffest, most chemically resistant, and least forgiving of a rough subgrade, so it is seamed by fusion and cannot follow a tight corner; LLDPE and reinforced polypropylene conform to the geometry of a chamber bed and are seamed in the field with the same equipment; PVC conforms best and is the easiest to seam, with a lower resistance to hydrocarbons; and EPDM is used where the liner will be exposed on a pond slope. (12.2)
12.3 Requirements in the remainder of this article apply where a liner other than none is selected.
12.4 The geomembrane thickness shall be as indicated in the datasheet.
Geomembrane Thicknessrange
mil
20303640456080
NOTE A thicker geomembrane resists the puncture of the stone placed on it and holds a seam better, and it is also stiffer, heavier, and slower to deploy around a chamber bed; the thickness that a given material needs under a given stone is published by the geomembrane manufacturer for the protection layer used, and 40 mil is the lightest HDPE that fusion-welds reliably in the field. (12.5)
12.6 A geosynthetic clay liner shall be the product, and shall have the bentonite mass and hydraulic conductivity, specified under GeosyntheticsGeosynthetics and GeotextilesResolves to the current adopted revision.sync/geosynthetics, and shall be protected from hydration before it is confined as that standard requires.
12.7 A compacted clay liner shall be constructed to the thickness, the maximum hydraulic conductivity, and the compaction the Engineer of Record indicates on the facility liner detail, and shall be kept moist until the stone over it is placed.
12.8 The liner shall extend up the sides of the excavation to the elevation indicated on the facility sections, and shall be continuous beneath the storage, across the subgrade to the outlet structure, and sealed to every pipe and structure that penetrates it with the manufacturer's pipe boot or a mechanical batten with a gasket.
12.9 The subgrade beneath a geomembrane shall be free of stones larger than 3/8 in., roots, and sharp projections, and a cushion geotextile of the class the geomembrane manufacturer requires shall be placed on each face of the geomembrane where the stone envelope bears on it.
12.10 Field seams in a geomembrane shall be made by thermal fusion or extrusion welding with the equipment and the trial seam procedure the geomembrane manufacturer publishes, and solvent or adhesive seams shall be used only on PVC and EPDM where the manufacturer publishes that method.
12.11 Every field seam shall be tested nondestructively over its full length by air pressure per ASTM D5820 for dual-track fusion seams or by vacuum box for extrusion seams, and destructive samples shall be cut and tested per ASTM D6392 at the frequency the liner manufacturer's quality control plan states, which shall be not less than one sample per 500 ft of seam.
12.12 A seam that fails shall be repaired by a cap strip extrusion-welded over the failed length, and the repair shall be retested nondestructively and, where the destructive test failed, bracketed by additional destructive samples until a passing sample bounds the failure on each side.
NOTE A liner that is sound everywhere but at one seam defeats the facility: the water it was built to keep off the soil leaves through the seam, carries the fines around it, and empties the cell into the subgrade from which the groundwater was supposed to be protected. (12.13)
12.14 Where a lined facility is to drain through an underdrain, the underdrain beneath or within the liner shall be as specified under SubdrainageSubdrainageResolves to the current adopted revision.sync/subdrainage, and its outlet shall be sealed through the liner as a penetration.

13 Pretreatment and Water-Quality Treatment

13.1 Pretreatment Devices

13.1.1 Runoff shall pass through the pretreatment devices indicated in the datasheet before it enters the storage.
Pretreatment Devices Providedcheckbox
☐ Sediment forebay at each inlet to a surface basin
☐ Isolator row of chambers with a woven geotextile floor and an inspection port
☐ Hydrodynamic separator upstream of the facility inlet
☐ Sumped catch basin with a hood at each inlet structure
☐ Catch basin filter inserts at the contributing inlets
☐ Pretreatment provided upstream by others
NOTE Sediment that reaches the storage is the maintenance problem of the facility: in a stone bed it fills the voids that cannot be cleaned, in a vault it is a confined-space entry to remove, and in a pond it is a dredge. A forebay settles the coarse load where a loader can reach it, and it is the device every surface basin carries; an isolator row routes the first flush along one row of chambers over a woven floor that a jet-vac can clean from the inspection port, and it is the device the chamber manufacturers built their maintenance case around; a separator removes the coarse load in a structure the Owner vacuums from the surface, at a cost and a head loss; and a sumped catch basin or an insert catches what it can at the inlet and depends on being emptied before the next storm. (13.1.2)
13.1.3 A sediment forebay shall have a hardened bottom or a fixed sediment depth marker so that the sediment depth can be measured, and a volume not less than the share of the water-quality volume indicated in the datasheet.
Forebay Volume as a Share of the Water-Quality Volumerange
%
525
Default: 10 %
13.1.4 An isolator row shall be furnished with the manufacturer's woven geotextile on the bedding stone beneath the full length of the row, an inlet manhole with a weir that directs the first flush into the row, and an inspection port at the downstream end.

13.2 Water-Quality Treatment

13.2.1 The water-quality treatment of the facility shall be as indicated in the datasheet, and shall provide the pollutant removal the stormwater permit requires.
Water-Quality Treatment Provisionselect
Permanent pool of the wet retention pond
Extended detention of the water-quality volume in the storage facility
Infiltration of the water-quality volume through the facility bottom
Hydrodynamic separator sized for the water-quality flow
Media filter vault with replaceable cartridges
Sand filter bed with an underdrain
No water-quality treatment required by the permit
NOTE A permanent pool settles the fine sediment and takes up dissolved nutrients biologically, and it earns the highest removal credit in most design manuals for the longest maintenance interval; extended detention holds the water-quality volume for the drawdown time the manual sets and settles what settles in that time; infiltration removes the volume and its load from the surface altogether, where the soil permits it; a separator removes coarse solids and floatables and little that is dissolved, at a small footprint; a cartridge filter removes fine sediment, metals, and some nutrients in the smallest footprint of all, and its cartridges are replaced on a schedule the Owner pays for; and a sand filter does the same with a bed the Owner rakes instead. The permit names the pollutants and the removal, and the design manual assigns each device its credit. (13.2.2)
13.2.3 The total suspended solids removal the treatment provision is required to demonstrate shall be as indicated in the datasheet.
Required Total Suspended Solids Removalrange
%
5095
Per drawings — the stormwater permit conditions and the stormwater management report (deferred by default)
13.2.4 A proprietary treatment device shall be furnished with the performance verification indicated in the datasheet, and the removal credited to it shall be the removal that verification assigns for the treatment flow and the particle size distribution the Authority Having Jurisdiction specifies.
Proprietary Treatment Device Performance Verificationselect
New Jersey Department of Environmental Protection certification
Washington State Department of Ecology TAPE general use level designation
Listing under the state or regional verification program the Authority Having Jurisdiction accepts
Project-specific performance testing accepted by the Authority Having Jurisdiction in writing
Derived — the verification program the Authority Having Jurisdiction accepts for the device furnished (by default)
NOTE Manufacturers' removal claims for proprietary devices are made against different test sediments and flow rates, so the same device carries a different credit under each program; the New Jersey and Washington programs are the two most jurisdictions accept by reference, and a jurisdiction that runs its own list accepts nothing not on it. The verification document, not the product brochure, is what the Contractor submits. (13.2.5)
13.2.6 A proprietary treatment device shall be sized by the manufacturer for the water-quality flow or volume in the stormwater management report, and the manufacturer's sizing shall be included in the action submittal.

14 Outlet Control Structure

14.1 Outlet Configuration

14.1.1 The outlet control configuration shall be as indicated in the datasheet.
Outlet Control Configurationselect
Single orifice through the structure wall or an orifice plate on the outlet pipe
Multi-stage riser with a low-flow orifice and an overflow weir
Multi-stage riser with a low-flow orifice, an intermediate weir, and an overflow grate
Proprietary vortex flow control in the outlet structure
Actively controlled valve with level sensing and remote operation
NOTE A single orifice controls one storm and is enough where the permit matches one; a riser with an orifice and a weir controls two, with the weir taking over as the stage rises; a third stage is added where the permit matches three recurrence intervals and the orifice sized for the small storm would hold the large one back too long; a vortex control passes a nearly constant flow across the full stage range through an opening several times the size of the equivalent orifice, which is why it is selected where the small orifice would clog; and an actively controlled outlet lowers the facility ahead of a forecast storm and holds water for treatment afterward, on sites where the permit gives credit for it and the Owner will maintain a powered device on a pond bank. (14.1.2)
14.1.3 Orifice diameters, weir lengths and crest elevations, the overflow elevation, and the invert of the outlet pipe shall be as indicated on the outlet control structure detail, and the Contractor shall not alter any of them.
14.1.4 The outlet control structure shall be constructed as indicated in the datasheet.
Outlet Control Structure Constructionselect
Precast circular reinforced concrete sections per ASTM C478
Precast rectangular reinforced concrete structure per ASTM C913
Cast-in-place reinforced concrete
Thermoplastic structure fabricated by the storage product manufacturer
NOTE A circular precast structure is stocked by every precaster and carries the orifice on a plate bolted over a cored opening; a rectangular precast structure carries a weir wall across its width and a longer weir than a circular section can, which is what a wet pond riser usually needs; a cast-in-place structure fits a weir geometry no precaster carries and is the one on which the elevations are most often surveyed wrong, because they are set by the form rather than the plant; and a thermoplastic structure is light, resists the water chemistry of a chamber bed, and is limited to the shallow depth and small opening the manufacturer rates it for. (14.1.5)
14.1.6 Orifice plates shall be of the material indicated in the datasheet, with the orifice cut to the diameter shown within a tolerance of 1/16 in., with a square sharp edge, and fastened over the opening with stainless steel anchors so that the plate can be removed and replaced from inside the structure.
Orifice Plate Materialselect
Stainless steel Type 304
Stainless steel Type 316
Aluminum
High-density polyethylene
Hot-dip galvanized steel
NOTE The orifice is the one dimension in the facility that the permit certification measures directly, and a plate the Owner can unbolt is the difference between correcting a release rate and rebuilding a structure; stainless steel holds the edge and the dimension through decades of wetting, Type 316 is chosen where the water is brackish or de-icing salt is heavy, aluminum and HDPE are lighter and are cut on site, and galvanized steel is the lowest cost and rusts at the cut edge first. (14.1.7)
14.1.8 Weir plates and weir walls shall be set level, with the crest elevation surveyed and recorded before the structure is backfilled.

14.2 Orifice Protection and Trash Racks

14.2.1 The low-flow orifice shall be protected as indicated in the datasheet.
Low-Flow Orifice Protectionselect
Trash rack over the orifice on the structure face
Reverse-slope pipe drawing from below the permanent pool or micropool surface with a hood
Perforated riser or sleeve over the orifice within a stone jacket
Skimmer hood over the orifice to exclude floatables
No protection, orifice larger than the design manual's unprotected minimum
NOTE A trash rack keeps the leaves and bottles out of a small orifice and is the arrangement the Owner can see and clear; a reverse-slope pipe draws from a foot below the surface, where neither floatables nor ice reach, and it is the arrangement that keeps a wet pond outlet open in winter; a perforated sleeve in stone filters the flow to the orifice until the stone silts; a skimmer hood excludes oil and floatables on a hotspot site; and an orifice larger than the design manual's unprotected minimum, usually 3 in. to 4 in., needs none of them. (14.2.2)
14.2.3 The clear spacing of trash rack bars shall be not greater than the value indicated in the datasheet, and the net open area of the rack shall be not less than the multiple of the protected opening area that the governing design manual requires.
Trash Rack Maximum Clear Bar Spacingrange
in
0.56
14.2.4 Trash racks and overflow grates shall be of the material indicated in the datasheet, shall be hinged or removable for cleaning without tools other than a hand wrench, and shall be fastened with stainless steel hardware.
Trash Rack and Overflow Grate Materialselect
Hot-dip galvanized steel
Aluminum
Stainless steel Type 304
Fiber-reinforced polymer
NOTE Galvanized steel is the lowest cost and heaviest, which matters to the person lifting it, and it rusts at the welds within the warranty where de-icing salt reaches the structure; aluminum is light and does not rust, and it is the rack most often stolen; stainless steel outlasts the structure; and a polymer rack is light, does not corrode, and carries less impact resistance than the metals where debris strikes it at velocity. (14.2.5)
14.2.6 The overflow grate on a riser shall be set so that it cannot be lifted off by the flow or by a person without removing its fastening, and where the riser is in a surface basin an anti-vortex plate or hood shall be provided on the overflow.

14.3 Barrel Seepage Control

14.3.1 Where the outlet barrel passes through the embankment of a surface basin, seepage along the barrel shall be controlled as indicated in the datasheet.
Outlet Barrel Seepage Control through the Embankmentselect
Anti-seep collars on the barrel within the embankment
Filter diaphragm of sand around the barrel at the downstream third
Concrete cradle and cutoff wall with the barrel encased
Not required, no embankment
NOTE Water follows the outside of the barrel through an embankment because the fill cannot be compacted against a pipe as well as against itself; a collar lengthens the seepage path and is the detail every older design manual shows, a filter diaphragm intercepts the seepage and lets it out without carrying fines, which is the detail the federal conservation practice standards have moved to, and a concrete cradle both supports the barrel and cuts the path where the embankment is high enough to justify the concrete. (14.3.2)
14.3.3 The outlet barrel shall be a watertight gasketed pipe of a material permitted under Storm DrainageStorm DrainageResolves to the current adopted revision.sync/storm-drainage, bedded on compacted fill the full length through the embankment, and the embankment fill around it shall be placed and compacted by hand-operated equipment to the same density as the embankment.

14.4 Drawdown and Spill Control

14.4.1 The drawdown provision for lowering the facility for maintenance shall be as indicated in the datasheet.
Facility Drawdown Provisionselect
Pond drain pipe through the riser with a valve operable from the structure top
Removable low-level orifice plate or drain plug in the structure
Pump-out from an access structure, no permanent drain
NOTE A wet pond is dredged only after its pool is lowered, and a valved drain through the riser is the provision that makes that a half day instead of a pumping contract; a removable plate gives a dry basin or an underground facility the same ability at lower cost; and pump-out is accepted where the facility is small enough, or its outlet low enough, that a drain adds nothing. (14.4.2)
14.4.3 Where the contributing area includes a fuel dispensing or storage area, a loading dock, a vehicle maintenance area, or another area the stormwater permit classifies as a hotspot, the outlet shall be provided with spill control as indicated in the datasheet.
Spill Control at the Outletradio
○ Manually operated shutoff valve or gate on the outlet pipe within the structure
○ Not provided
Derived — whether the contributing area shown on the civil site plan includes a fuel storage, fuel dispensing, loading, or vehicle maintenance area (by default)
NOTE A shutoff on the outlet turns the facility into the containment the fuel tank standard assumes exists downstream of a release; the grading that keeps the release itself out of the storm inlets is the work of Site Rough GradingSite Grading and Subgrade PreparationResolves to the current adopted revision.sync/site-rough-grading, and the facility that receives whatever reaches the inlet is the last place the release can be held. (14.4.4)

14.5 Active Outlet Control

14.5.1 Requirements in this article apply where an actively controlled valve with level sensing and remote operation is selected as the outlet control configuration.
14.5.2 The actively controlled outlet shall fail to the passive release the stormwater management report assigns it on loss of power, loss of communication, or controller fault, and the passive orifice or weir shall be provided in the structure as if no active control existed.
14.5.3 The controller enclosure shall be rated as indicated in the datasheet.
Active Outlet Controller Enclosure Ratingselect
NEMA Type 3R
NEMA Type 4
NEMA Type 4X
NOTE The controller sits on the bank or at the structure top in the weather; Type 3R sheds rain and is the rating the controller ships with, Type 4 is required where it is hosed down or stands in spray, and Type 4X is required where de-icing salt, a coastal exposure, or a corrosive site atmosphere reaches it. (14.5.4)
14.5.5 The controller and the level sensor shall be rated for operation at Site Ambient Temperature MinimumSite Ambient Temperature MinimumParameterEach project supplies its own value.site-ambient-temperature-minimum without a heater, or shall be furnished with a thermostatically controlled enclosure heater.
14.5.6 Power and communication to the controller shall be furnished under the electrical standards, and the controller manufacturer shall state the voltage, the load, and the communication path in the action submittal.

15 Inspection Ports and Maintenance Access

15.1 Every storage row, header, isolator row, pretreatment device, and the outlet control structure shall be accessible for inspection and cleaning from the surface with the jet-vac equipment the operation and maintenance manual names, without entering the storage.
15.2 The provision of inspection ports on underground storage rows shall be as indicated in the datasheet.
Inspection Ports on Underground Storage Rowsselect
Inspection port to grade at every row
Inspection port at the isolator row and at every fourth row
Inspection port at the isolator row only
NOTE An inspection port is a small riser through the chamber crown to a cover at grade, through which the sediment depth on the row floor is measured with a stadia rod and a camera is lowered; a port on every row shows the Owner where the sediment is, a port every fourth row is the manufacturer's usual minimum, and a port on the isolator row alone measures the one row designed to catch the sediment and assumes the rest stays clean. (15.3)
15.4 Access manholes shall be provided on the inlet header, the outlet header, and the isolator row manifold of an underground facility, with a clear opening not less than 24 in., and the spacing of access structures along the storage shall not exceed the value indicated in the datasheet.
Maximum Spacing of Access Structures along Underground Storagerange
ft
50100150200300400
NOTE A jet-vac hose cleans a straight run of 200 ft to 300 ft from a manhole before its pull and its vacuum fall off, so an access spacing beyond that leaves a middle the Owner cannot reach; closer spacing costs a structure and a casting in the pavement for each one, and spacing is set against the reach of the equipment the Owner actually has rather than the longest the manufacturer allows. (15.5)
15.6 Frames, grates, covers, and the casting load rating at every access structure and inspection port shall be as specified under Storm DrainageStorm DrainageResolves to the current adopted revision.sync/storm-drainage, rated for the design live load of this standard at that location.
15.7 Access covers on the outlet control structure and on any vault with a clear interior depth greater than 4 ft shall be lockable or bolted, and a vault access opening shall be furnished with a fall-protection grate beneath the cover unless the Owner's confined-space entry program directs otherwise in writing.
15.8 A maintenance vehicle route to each access structure, the forebay, and the outlet structure shall be provided as indicated on the stormwater facility plan, and no access point shall be located where a vacuum truck cannot park within hose reach of it.

16 Installation

16.1 Sequencing and Protection during Construction

16.1.1 An infiltration facility shall not be excavated to its final subgrade, and no storage product shall be placed, until the contributing drainage area has been stabilized under Erosion And Sediment ControlErosion and Sediment ControlResolves to the current adopted revision.sync/erosion-and-sediment-control, unless the facility is isolated from construction runoff by a diversion the erosion and sediment control plan shows.
16.1.2 Where the facility footprint serves as a temporary sediment basin during construction, the sediment basin shall be as specified under Erosion And Sediment ControlErosion and Sediment ControlResolves to the current adopted revision.sync/erosion-and-sediment-control, and the accumulated sediment and the disturbed subgrade shall be removed to below the final subgrade elevation before the permanent facility is built.
16.1.3 The infiltration surface of an open-bottom facility shall be excavated with equipment working from outside the footprint or with low-ground-pressure tracked equipment, shall not be driven on by wheeled equipment, and shall be scarified to a depth of 6 in. immediately before the geotextile or stone is placed.
NOTE A compacted infiltration surface does not infiltrate, and the compaction happens before anyone measures it: the loader that cleaned out the sediment basin, the truck that delivered the stone, and the roller that proof-rolled the floor out of habit each take a decade off the facility in an afternoon. (16.1.4)
16.1.5 The infiltration surface shall not be proof-rolled, and a Proctor-referenced compaction requirement shall not be applied to it.
16.1.6 Sediment-laden runoff that reaches a completed stone bed or vault before the facility is placed in service shall be removed, and where the stone has been contaminated the Contractor shall remove and replace the contaminated stone at the Contractor's expense.

16.2 Stone Envelope Placement

16.2.1 Bedding stone shall be placed on the geotextile or the liner protection layer, struck level to the design elevation within 1 in., and compacted or consolidated only as the storage product manufacturer's installation instructions direct.
16.2.2 Stone around and over chambers and pipe shall be placed in lifts not exceeding the thickness the manufacturer publishes, from the outside of the rows toward the center, so that the stone fills the space between rows before it covers the crown.
16.2.3 Equipment shall not travel on the storage product, and no equipment shall cross the facility until the cover in place meets the minimum the manufacturer publishes for that equipment's weight.
NOTE The construction case governs the chamber, not the parking lot it will sit under: the loaded dump truck that backs over the bed with 6 in. of stone on it is heavier than anything that will drive there once the pavement is down. (16.2.4)
16.2.5 The top geotextile shall be placed over the completed stone envelope before any backfill, and backfill above the stone envelope shall be the material and compaction specified under EarthworkEarthworkResolves to the current adopted revision.sync/earthwork for the surface above it.

16.3 Precast and Cast-in-Place Structure Setting

16.3.1 Precast vaults and the outlet control structure shall be set on a bedding of the thickness and material the precaster publishes, on a subgrade released at the hold point, leveled so that the joint faces meet uniformly, and backfilled on all sides in balanced lifts so that the structure is not loaded laterally from one side.
16.3.2 The elevations of every orifice, weir crest, and overflow in the outlet control structure shall be surveyed after the structure is set and the plates installed, and before backfill, and the survey shall be recorded on the record drawings.
16.3.3 A cast-in-place vault or outlet structure shall be constructed as specified under Site Concrete StructuresCast-in-Place Site Concrete StructuresResolves to the current adopted revision.sync/site-concrete-structures, and its formwork shall be checked for the weir and orifice elevations before the concrete is placed.

16.4 Surface Basin Construction

16.4.1 The basin shall be excavated and the embankment constructed to the lines and grades shown, with the outlet barrel and its seepage control installed before the embankment fill is placed over it.
16.4.2 The basin floor and slopes shall receive the topsoil depth, the permanent seeding or planting, and the slope protection specified under Erosion And Sediment ControlErosion and Sediment ControlResolves to the current adopted revision.sync/erosion-and-sediment-control and Planting And Soil PreparationPlanting and Soil PreparationResolves to the current adopted revision.sync/planting-and-soil-preparation before the basin is placed in service, and the basin shall not receive runoff from an unstabilized area until its own slopes are stabilized.
16.4.3 A pond liner on the slopes of a surface basin shall be anchored in a trench at the top of the slope, covered with the soil depth the liner manufacturer requires for the slope, and protected from the equipment that places the cover.

17 Testing and Acceptance

17.1 Acceptance Tests Required

17.1.1 The acceptance tests indicated in the datasheet shall be performed, witnessed by the Engineer of Record, and reported before the facility is placed in service.
Acceptance Tests Requiredcheckbox
☐ Infiltration test on the finished subgrade of the infiltration facility before stone placement
☐ Flood or drawdown test of the completed infiltration facility
☐ Liner seam testing and a leak survey of the completed liner
☐ Vacuum test of precast structures per ASTM C1244 before backfill
☐ Surveyed verification of every outlet control elevation and orifice dimension
☐ Video inspection of underground rows and headers
☐ As-built storage volume survey

17.2 Infiltration Verification

17.2.1 Where an infiltration facility is specified, the infiltration rate of the finished subgrade shall be measured by the field infiltration test method of this standard after the final excavation and scarification and before any geotextile or stone is placed, and the measured rate divided by the factor of safety shall be not less than the design infiltration rate.
17.2.2 Where the finished subgrade fails the infiltration test, the Contractor shall report the result to the Engineer of Record, and the Engineer of Record shall direct remediation of the subgrade, revision of the facility, or conversion to a lined facility, with the cost borne by the Contractor where the failure results from compaction or contamination of the subgrade during construction.
17.2.3 Where a flood test is required, the completed facility shall be filled with clean water to the elevation the Engineer of Record directs, the drop in water level shall be recorded at intervals not exceeding one hour until the facility is empty, and the drawdown time shall not exceed the time the stormwater management report assigns.
NOTE The drawdown time is what the permit certification asks for and what the Owner's neighbors measure: a facility that takes longer than the report's drawdown is holding the next storm's volume, and the infiltration test on the subgrade is the measurement that explains why before the stone has covered it. (17.2.4)

17.3 Liner Verification

17.3.1 Where a geomembrane is specified, the seam test records of this standard shall be complete and passing before the protection layer is placed, and the completed liner shall be surveyed for leaks by the method the liner manufacturer's quality control plan names where the Contract Documents require a leak survey.
17.3.2 A geomembrane holding water during a flood test shall show no drop in level beyond evaporation over 24 hours, and a lined facility that loses water shall have the liner uncovered at the Contractor's expense to the extent needed to locate and repair the leak.

17.4 Outlet Verification

17.4.1 Every orifice diameter, weir length, weir crest elevation, overflow elevation, and outlet invert shall be measured in the completed structure and compared with the outlet control structure detail, and a dimension or elevation outside the tolerance the detail states, or outside 1/16 in. on an orifice diameter and 0.05 ft on an elevation where the detail states none, shall be corrected before acceptance.
NOTE The outlet is where the facility is certified: the permit reviewer who checks the as-built compares each control dimension against the stage-discharge table in the report, and an orifice cut a quarter inch large on a small storm releases a measurable fraction more than the report shows. (17.4.2)

17.5 Storage Verification and Video Inspection

17.5.1 The completed facility shall be surveyed, and the as-built storage at each control elevation shall be computed and compared with the design storage at that elevation, with a deficit not greater than the value indicated in the datasheet.
Allowable As-Built Storage Deficit at Any Control Elevationrange
%
2510
17.5.2 A facility whose as-built storage falls short of the allowance shall be corrected by the Contractor, by regrading, by additional storage, or by a revised outlet the Engineer of Record designs and the Authority Having Jurisdiction accepts, at the Contractor's expense where the shortfall results from the Contractor's work.
NOTE The storage of an underground facility is computed from the surveyed footprint, the surveyed bottom and crown elevations, the product's published volume per unit, and the design void ratio; a stone envelope built 6 in. shallow over a large footprint removes a volume no one can see until the survey is reduced. (17.5.3)
17.5.4 Where video inspection is required, every underground row and header shall be inspected by camera after the facility is cleaned and before it is placed in service, with the recording referenced to distance from the access structure and every defect, deposit, displaced end cap, and standing-water location identified.
17.5.5 Defects identified in the video record shall be corrected and the affected row re-inspected, at the Contractor's expense where the defect results from the Contractor's work.

17.6 Test Records and Final Acceptance

17.6.1 Every test, whether passing or failing, shall be recorded on a report identifying the facility, the test, the method, the readings, the date, and the names of the Contractor's test supervisor and the witnessing inspector, and shall be submitted within five working days of the test.
17.6.2 The Contractor shall not remove or replace a failing test report with the report of a subsequent passing test.
17.6.3 Final acceptance of the facility shall require passing results on every required test, the as-built storage verification within the allowance, the record drawings, the operation and maintenance manual, the recorded maintenance agreement where the permit requires one, the sealed as-built certification where the permit requires one, and removal of every temporary control within the facility.
17.6.4 Acceptance shall not waive the Contractor's warranty obligations or the Contractor's liability for latent defects.

18 Operation and Maintenance Turnover

18.1 The party responsible for maintaining the facility after acceptance shall be as indicated in the datasheet.
Facility Maintenance Responsibility after Acceptanceradio
○ The Owner under a recorded maintenance agreement with the Authority Having Jurisdiction
○ A property owners' association under a recorded covenant
○ The municipality after dedication and acceptance
Per drawings — the stormwater permit conditions and the recorded maintenance agreement (deferred by default)
NOTE Most permits bind the Owner and every successor to maintain the facility under a recorded agreement that gives the jurisdiction the right to inspect and, on default, to do the work and lien the property; a facility dedicated to the municipality is maintained by it only after it has been accepted to that municipality's own standards, which may differ from this one. (18.2)
18.3 The operation and maintenance manual shall state, for each component, the inspection interval, the sediment depth or the condition that triggers cleaning, the access point and the equipment for cleaning it, and the replacement part and its manufacturer part number where a part is consumable.
18.4 The Contractor shall record the baseline sediment depth at every inspection port, forebay marker, and sump at turnover, and that record shall be the reference from which the Owner's first cleaning interval is measured.
18.5 The Contractor shall clean every storage row, header, forebay, pretreatment device, and the outlet control structure of construction sediment and debris at turnover, and sediment removed shall be disposed of off site or at a location the Owner approves in writing.
NOTE A facility turned over with construction sediment in it begins its service life partly full, and the Owner's first scheduled cleaning, years out, is when the shortfall against the permit is discovered. (18.6)

19 Delivery, Storage, and Handling

19.1 Thermoplastic chambers, storage pipe, and liner rolls shall be stored out of direct sunlight or covered with an opaque, ventilated covering where they will be on site longer than the exposure period the manufacturer publishes, and chambers shall be stacked no higher than the manufacturer's published limit.
19.2 Precast vaults, box sections, and outlet structures shall be lifted only at the designated lifting points, with spreader bars where the precaster requires them, shall not be rolled or dropped, and shall be stored on dunnage on level ground.
19.3 Geosynthetic clay liner rolls shall be stored off the ground, under cover, and protected from every source of moisture until they are deployed.
19.4 Orifice plates, weir plates, trash racks, and valves shall be stored indoors or in a closed container, with their dimensions verified against the outlet control structure detail on receipt and any plate that does not match rejected before it is installed.
19.5 Materials shall be inspected for damage on delivery and again before installation, and a chamber with a cracked foot, a crushed corrugation, or a deformed end, a precast unit with a cracked joint face, and a liner roll with a cut through more than one wrap shall be removed from the site.

20 Warranty

20.1 The warranty period for the stormwater management facility shall be as indicated in the datasheet.
Stormwater Facility Warranty Periodrange
years
1235
NOTE One year from substantial completion is the period most site civil work carries and the one in which a facility that was built wrong shows it, through its first wet season; a longer period is bought where the facility is dedicated to a municipality that requires it, or where the Owner wants the installer answerable through the settlement and the second wet season that a lined or an infiltration facility takes to prove itself. (20.2)
20.3 The Contractor shall warrant the facility, including the storage product, the stone envelope, the liner, the geotextile, the outlet control structure, the pretreatment devices, the embankment, and the connections, against defects in materials and workmanship for the warranty period beginning at substantial completion.
20.4 Warranty obligations shall include correction of a facility that fails to drain within the drawdown time of the stormwater management report where the cause is construction, a liner that leaks, settlement of the pavement or the surface over an underground facility, settlement or seepage of the embankment, displacement of chambers or end caps, and an outlet control component that fails or corrodes.
20.5 Where the Contractor repairs or replaces work under the warranty, the repaired work shall carry a warranty running from the date of the repair for the full warranty period or for the remainder of the original period, whichever ends later.
20.6 The Contractor shall bear the cost of the warranty repair and of restoring the pavement, landscape, and surface finishes disturbed by that repair to the condition documented in the preconstruction condition record for that area.
20.7 The Contractor's warranty shall not cover loss of infiltration capacity attributable to sediment delivered from the contributing area after acceptance, and where the parties disagree whether a loss of capacity is attributable to construction or to post-acceptance sediment, the Engineer of Record shall make the initial determination.
20.8 The manufacturer's structural warranty on the storage product and the liner manufacturer's material warranty shall be assigned to the Owner at closeout, and where the storage product manufacturer publishes a structural warranty longer than the facility warranty, the longer term shall be furnished.
20.9 The warranty period shall not limit the Contractor's liability for non-conforming work discovered after it expires.
NOTE An orifice cut to the wrong diameter, a stone envelope built below its design elevation, a liner that was never seam-tested, and a bottom geotextile placed where the design showed none are non-conforming work whenever they are discovered, not defects that expire with the warranty. (20.10)

21 Spare Parts

21.1 The Contractor shall furnish the spare parts indicated in the datasheet, delivered with the closeout submittals and identified by manufacturer part number.
Spare Parts Furnishedcheckbox
☑ One spare orifice plate of each size installed
☐ One spare trash rack of each type installed
☐ One replacement cartridge set or media charge for each filter device
☐ One spare inspection port cover of each type installed
☐ One spare level sensor for the active outlet controller
NOTE The orifice plate is the part the permit certification depends on and the one a maintenance crew damages while clearing the rack in front of it; a matching spare on the shelf restores the certified release rate the same day rather than after a fabrication lead time. (21.2)
21.3 The storage product manufacturer and the treatment device manufacturer shall each commit in writing that replacement components for the products furnished will remain available for not less than ten years from the date of manufacture.

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