for Highway Construction Page 517 of 71 5 SECTION 621 – SEEDING
621.01 Description.
Apply seed, including seed bed preparation, fertilizing, seeding, mulch mixtures, mulching, mulch anchoring (mechanical or tackifiers), HECPs, erosion blankets , and watering in the areas specified. Seed all disturbed areas on the project site, including foreslope, backslope, and embankment areas , specified. The Department may require seeding operations in conjunction with 212.
621.02 Materials.
Provide materials as specified in: Topsoil ..................................................................................................................................... 213.02 Seed ........................................................................................................................................ 711.05 Com mercial Fertilizer .............................................................................................................. 711.07 Mulch ....................................................................................................................................... 711.10 Rolled Erosion Control Product (RECP) ................................................................................. 711.11 Turf Reinforced Mat (TRM) ..................................................................................................... 711.12 Water ....................................................................................................................................... 711.13 Mulch Tackifier ........................................................................................................................ 711.16 Mulch plus Tackifier ................................................................................................................. 711.17 Mulch Mixture .......................................................................................................................... 711.19 Hydraulically Applied Erosion Control Product (HECP) ........................................................... 711.22 Seeding and Vegetation Special Guaranty .............................................................................. 107.21
621.03 Construction Requirements.
A.Gene ral. Perform seeding operations as specified. Perform seeding during the season(s) specified, except for seeding used as a temporary erosion and sediment control measure. Inspect areas within the project site and identify noxious weeds present or which weeds are most lik ely to be found on the project site and include treatment recommendations. Treat material used as specified throughout the growing season, and up to 2 weeks before transporting to the project site and seeding applications. Obtain approval for all products before use. Use mechanical (drill) seeding on areas with 3H:1V slopes or flatter and areas without excessive rock, gravel, or hardpan soil. Apply fertilizer, seed, and mulch in separate operations, one following the other in this order, with the exception that fertilizer may be applied with a fertilizer attachment at seeding time or with water when watering is specified, or as otherwise approved. Perform cultivating, tilling, and dr ill seeding operations in a cross- slope direction (horizontal) and ensure furrows remain open. for Highway Construction Page 518 of 71 5 Use broadcast seeding or hydroseeding applications on areas with slopes steeper than 3H:1V or areas where a mechanical seeder cannot reach. Perform hydro -applications with approved combinations of seed, fertilizer, soil amendments, mulch mixtures, mulching, mulch anchoring (tackifier), and hydraulically applied mulch with hydro- application equipment and equipped with appropriate centrifugal pump and engine size, paddle- type mechanical agitation, and independent liquid bypass circulation capable of handling and applying a thick homogenous slurry. Perform seeding and placement of soil conditioner, mulch, fertilizers, tackifiers, or other soil amendments between March 15 and April 30, October 15 and November 15, or as approved. When seed application during autumn does not establish well, reseed the area after April 1 and when the soil is not frozen. Perform seeding before mulch, tackifiers, or erosion control blanket product installation. Seeding may occur after conduit work progresses and the topsoil is in final placement within the seeding time period, provided the soil is not frozen. All mulch and soil conditioners are required to be certified noxious weed- free by the Idaho State Department of Agriculture (ISDA) or other state accredited laboratory.
B.Seedbed Preparation. Maintain areas to be seeded visibly free of weeds throughout the growing season using mechanical or hand-pulling methods, or by applying appropriate chemicals, or combinations unt il seeding time. Keep weeds from going to seed. Apply chemicals for treating weeds by a current licensed applicator and as specified in 107.20. Minimize ground disturbance using the least intrusive co nstruction techniques practical . Cultivate areas to be drill-seeded at least 3 inches deep. Work the soil to obtain a surface that allows proper operation of drill seeding equipment. Leave slopes in a rough condition after final grading and before seeding, or mulch or soil amendment applications. Seedbed preparation (e.g., raking, mechanical roughening) is required as specified or as approved. Do not apply the mulch, mulch mixture, or soil amendment to smooth sl opes. In all areas to be broadcast or hydroseeded, rake or mechanically roughen the soil at least 2 inches deep and leave in a rough condition immediately before applying seed, mulch , or soil amendments, similar to that obtained by walking a cleated- crawler tractor up and down the slopes. Where slopes are benched or serrated, the Department will not require additional preparation. In areas subject to severe erosion, ensure the seedbed preparation limits do not exceed the area on which the entire seeding and mulching can be applied within 1 day. If conditions occur that prevent seeding at specified furrow depths, or if the roughened condition is destroyed, prepare the seedbed again at no additional cost.
C.Fertiliz ing (Commercial). Provide the fertilizer type and application rate as specified. Apply fertilizer by the most appropriate of the following methods :
1.Fertilizer drill.
2.Broadcast.
3.Water applied. Collect random samples from at least 3 different locations and thoroughly mix and homogenize the samples into a single composite sample. Sample all changes in the soil (e.g., color, texture). for Highway Construction Page 519 of 71 5 Obtain a representative composite sample and submit for testing 2 months before final placement and seeding application to determine soil pH, nutrients, and organic materials present. Provide a soil analysis by an NAPT -PAP-accredited laboratory to determine fertilizer and organic materials (e.g., mulch , compost) required to amend the soil. Obtain a soil analysis report with recommended soil amendments to be added to the soil before beginning subsequent revegetation activities. Apply approved fertilizers, soil amendment products, and organic material as listed on the QPL, at se eding time and applied in accordance with seeding plans or at the manufacturer’s written rate. The application rate and timing of fertilizer application will be as specified or as recommended and approved. Add and lightly incorporate the specified fertilizer ingredients, soil amendments, and organic material as recommended into the top 6 inches of the topsoil and uniformly distribute to the areas to be seeded before subsequent revegetation activities as specified in this sec tion and 621.03.B. For slopes steeper than 3H:1V or where hydroseeding is specified, uniformly distribute the specified ingredients and organic material onto the soil surface by hydroseeding method. Fertilizer components and/or organic materials may be added to the mulch mixture and applied during the hydroseeding application. For slopes 3H:1V or flatter, dry fertilizers may be applied directly to the soil and lightly incorporated into the soil surface, followed by the seed appli cation. Apply fertilizer when average noontime temperatures are 60°F or lower on established stands. Wherever physically possible, place fertilizer with the seed when mechanical (drill) seeding using a fertilizer attachment. Fertilizer may be broadcast (wet or dry) or with a fertilizer drill attachment. Fertilizer may be applied with irrigation water as approved.
D.Seeding. The Contractor will pr ovide seed unless otherwise specified. Apply seed using hydroseeding or a mechanical seeding method on all disturbed areas. Before seeding begins, take steps to mechanically break up materials previously placed for the purpose of temporary soil stabilization and erosion control to the Engineer’s satisfaction. If seed is applied using broadcast seeding or hydroseeding methods, rake the soil before applying seed, fertilizers, mulch, and soil amendments. Use the specified seeding mix and application rate. Apply native shrub and forb species separately from grass species. In separate applications, apply seed, fertilizer, and mulch . Do not mix ferti lizer with the seed in the hydro- seeder unless otherwise approved. Apply seed to the seeding area first, followed by the fertilizer and mulch application second. Apply seed uniformly by the most appropriate method (as determined by slope, soil, or site conditions) using one of the following methods:
1.Mechanical seeding (no-till drill, double disc with agitator or spinning disc) for 3H:1V slopes or flatter.
a.Set drill rows according to the seed species size and dimension. Ensure drill spacing does not exceed 9 inches. Set drill depth according to the seed size and dimension, not to exceed 1- inch depth, and place seed on the furrow bottom. for Highway Construction Page 520 of 71 5 b. Regulate t he seed drill speed and spring pressure so ½ inch of soil covers the seed and the furrows are left open. Do not use drag chains.
c.When mulch is applied or used after mechanically seeding, place seed just below the soil surface and cover well.
d.Do not perform seeding when soil is too wet or too dry, frozen or otherwise untillable, or when wind or rain interferes with mulch or seed placement .
e.Broadcast native seeds immediately ahead of the drill or seed separately. Seed legume seed through a separate box from the grass seed, with seed spouts out, or broadcast ahead of the drill. Thoroughly mix seed before placing in the drill or seeder box.
f.If area is impractical for mechanical seeding , broadcast the seed using a hydroseeder or dry broadcast equipment.
g.Do not allow trucks or equipment to drive on the area after seed is in place.
2.Broadcast se eding.
a.Dry (whirlwind or hand broadcast) for embankment slopes or cut slopes steeper than 3H:1V or as approved.
b.Hydroseeder. Perform hydroseeding in 2 steps:
1.The Contractor may incorporate up to 5 percent of the total hydroseeding mixture with the seed to allow for easy application. Add all seed including grass and forb species to the hydroseeding mixture within 10 to 12 minutes of completing the hydroseeding application.
2.Apply the remaining mulch mixture, fertilizer, and soil amendments to the entire area. Uniform ly apply the mulch mixture in a thick, homogenous slurry by hydro application equipment. Apply the mulch mixture at a rate of 1,000 gallons of water per acre or as approved. Apply the hydroseeding mixture from opposite directions to achieve complete covera ge. When seeding areas greater than 1 acre, use appropriate equipment including a tank size with a minimum working capacity of 800 gallons. Use pump capable of pumping the specified mulch mixture at the full mix rate recommended by the manufacturer. The pump should provide a minimum discharge capacity of 105 pounds per square inch and 275 gallons per minute. The engine should be capable of handling, mixing , and discharging a thick slurry up to 100 feet. Equip the mixing tank with a paddle- type agitation system designed for maximum mixing extending the full length of the tank and supported at each end with an independent liquid bypass circulation. Ensure seed agitation time in the hydroseeder does not exceed 12 minutes. Do not apply hydroseeding mixture if rainy conditions are anticipated or outside the manufacturer’s written application instructions. If unanticipated rainy conditions occur, re- apply the hydroseeding mixture to uncured areas as direct ed and at no additional cost. Hydraulically apply seed to the soil surface. Spray each application from 2 opposing directions to achieve complete coverage. Do not perform seeding or mulching applications when wind interferes with seed placement . for Highway Construction Page 521 of 71 5 The Engineer and the Contractor will inspect the finished seeded and mulched slopes to ensure complete coverage has been met. If adequate coverage has not been achieved, re- seed and re- apply soil amendments, tackifiers, and mulch on the inadequately covered areas.
E.Mulch , Mulch Anchoring, and Hydraulically Applied Erosion Control Products . Apply weed- free organic mulch, soil amendment, and soil binder (tackifier) to disturbed areas on slopes 3H:1V and steeper after seed has been applied to the soil surface within 14 calendar days as specified. Supply support ing documents including proof of equivalent revegetation abilities in the form of test results obtained by independent peer -reviewed research efforts for similar landforms, soil types, aspect, climate, and elevation. Do not perform mulching when wind interferes with mulch placement . Apply straw, grass hay, wood fiber, soil amendments, mulch mixture, or any combination of these materials as directed. E nsure material applied to the ground allows for the absorption and percolation of moisture. Apply mulch so the underlying soil is not visible.
1.Mulch . Do not use hydro- mulch applications on slopes flatter than 3H:1V or in conjunction with drill seeding applications. Do not perform mulching when wind interferes with mulch placement . Apply straw, grass hay, wood fiber, soil amendments, mulch mixture, or combination of these materials as directed. Ensure material applied to the ground allows for moisture absorption and percolation. Apply at the following rates:
a.Straw or grass hay (air dry). 2 Ton/Acre
b.Wood fiber. 1 Ton/Acre
c.Soil amendments. As specified
2.Mulch Anchoring.
a.Mechanical. Use mechanical mulch anchoring on 3H:1V slopes or flatter as directed. Use a heavy disc with flat scalloped discs approximately ¼ inch thick, having dull edges, and spaced at least 9 inches apart to anchor mulch into the soil. Ensure anchoring to a depth of at least 2 inches with no more than 1 equipment pass on the same surface. Install mechanical anchoring in a horizontal direction to the slope.
b.Tackifier. Supply an organic, biodegradable, non- polluting, non- volatile, and non- toxic tackifier that is transparent, flexible, water soluble, retains flexibility after curing, and makes a porous lattice -like membrane structure within the upper soil layer. Obtain tackifier products listed on the QPL. Apply tackifier to stabilize slopes 3H:1V and steeper. Anchor mulch using a tackifier applied in accordance with the manufacturer’s written instructions and at a rate appropriate for the materi al, soil types, conditions, and degree of slope. Apply tackifier and mulch with seed as specified or as directed. Ensure tackifier product does not inhibit water, oxygen or seed growth, or leave undesirable residues in the soil. E nsure tackifier does not re- emulsify once cured (by drying) and is effective with acidic or alkaline soils. If applied separately, incorporate a method to differentiate between the tackifier and mulch material, by color or tracer material, during tacking operations. Do not apply tacking when wind interferes with tackifier placement . for Highway Construction Page 522 of 71 5 3. Hydraulically Applied Erosion Control Product (HECP). Hydraulically apply mulch and t ackifier that contains a qualified protein- rich nutrient source, weed- free organic mulch, biological soil stimulant, and humic substance on slopes steeper than 3H:1V during the seeding time period. Apply seed as specified in 621.03.D or as otherwise directed. Provide a mixture that is nontoxic to animals, soil microorganisms, and aquatic and plant life, and that does not interfere with or impede seed germination or vegetative growth and establishment. Apply mulch so the underlying soil is not visible. The application rate for the mulch, tackifier, or mulch and tackifier mix will be as specified by the manufacturer for the slope gradient and soil conditions.
a.Hydraulic Mulch . Mix and apply the mixture in accordance with the manufacturer’s written instructions and at a rate for the soil type, surface roughness, conditions, and slope steepness.
b.Stabilized Mulch Matrix. Mix and apply the mixture in accordance with the manufacturer’s written instructions and at a rate for the soil type, surface roughness, conditions, and slope steepness.
c.Fiber Reinforced Matrix. Mix and apply the mixture in accordance with the manufacturer’s written instructions and at a rate for the soil type, surface roughness, conditions, and slope steepness.
d.Bonded Fiber Matrix. Apply a hydraulic mixture of a qualified protein- rich nutrient source, weed- free organic mulch, biological soil stimulant, and humic substance soil amendment, and soil binders to 3H:1V and steeper slopes after seed has been applied. Mix and apply the mixture in accordance with the manufacturer’s written instructions at a rate for the soil type, surface roughness, conditions, and slope steepness. Furnish a QPL- qualified hydraulic mixture, with a cover factor meeting large scale testing of less than 0.01 coverage (not to exceed 0.05 percent coverage), meeting ASTM D7322 (600% -800%) and having a functional longevity of 6 to 12 months (minimum of 12 months for 2H:1V slopes or steeper). Submit testing documentation, including proof of equivalent revegetation abilit ies, in the form of test results by independent peer -reviewed research efforts for similar landforms, soi l types, aspect, climate, and elevation. Thermally process wood fiber products (within a pressurized vessel) within 3 percent of 80 percent. Provide a QPL -listed tackifier or an approved tackifier that is transparent, flexible, retains flexibility after curing , water soluble, and makes a porous lattice- like membrane structure within the upper soil layer. The tackifier product cannot inhibit water, oxygen, or seed growth and must be able to stabilize 2H:1V slopes or steeper. The tackifier will be organic, biodegradable, non- polluting, non- volatile, non- toxic, and leave no undesirable residues in the soil. The tackifier is not allowed to re- emulsify once cured (by drying) and will be effective in acidic or alkal ine soils. Apply tackifier and mulch with seed as specified or as directed.
F.Erosion Blankets.
1.Rolled Ero sion Control Products (RECP). Install RECPs on slopes in vertical direction and in accordance with the manufacturer's written instructions or as approved.
2.Turf Reinforced Mat (TRM). Install TRMs in accordance with the manufacturer's written instructions or as approved. for Highway Construction Page 523 of 71 5 G. Watering . Provide a temporary water delivery system by using sprinklers or trucks. Apply water by the acre unit (AU). Keep pipe connections tight to avoid leakage and washing. Maintain sprinklers in proper working order. If runoff begins, stop watering and apply the balance after earlier water has penetrated the soil. The standard application rate is 16,000 gallons per acre that constitutes the estimated water quantity that will saturate the soil to a 4- inch depth under average conditions. The Engineer will inspect for the 4- inch saturation depth by excavating to a depth of 4 inches and observing wetness. The wetness inspection locations will not be in “slick spots” or in unrepresentative areas. Apply water on seeded and stabilized areas until vigorous growth is established as determined by the Engineer. Ensure there is no damage to plantings or seeded areas. Obtain method and equipment approval before applying water to any plantings, seeded areas, or mulching applications. Apply water using tanker or water tank with pump, hose, and approved nozzle apparatus (water dispersion). The spray head must deliver a fine mist that will not damage plants or the mulch and tackifier. Seeding performed between May 1 and October 14, whether for permanent or temporary erosion control, will require irrigation until growth has been established . If the project has a mitigation area, install irrigation systems before seed and mulch are applied. Obtain approval before use of irrigation water by tanker, pump, hose, and spray head. The spray head must provide a fine mist th at does not damage plants or the erosion control blanket.
H.Performance Standard and Acceptance. Revegetated areas will be inspected at installation completion. If adequate coverage was not achieved, the Contractor will be required to re- seed and re-apply soil amendments and/or tackifier on seeded areas. The Engineer will make a final inspection and acceptance 1 year following seeding completion. The Contr actor will request the inspection at least 10 calendar days in advance.
621.04 Method of Measurement.
The Engineer will measure acceptably completed work as follows:
1.For determining areas, measurements will be taken parallel to the slope.
2.Seedbed preparation will be by the acre.
3.Seeding, mulching, mulch anchoring , soil amendment, mulch mixture, and fertilizing will be by the acre for each time this work is performed. Provide weight measurements to verify appropriate rates were applied.
4.Mulch plus tackifier will be by the acre or by the square yard for each time this work is performed.
5.HECPs will be by the acre or by the square yard for each time this work is performed.
6.Rolled erosion control products and turf reinforced mats will be by the square yard.
7.Water delivery system will be by lump sum.
8.Watering will be by the acre unit. An acre unit (AU) is the water quantity require d to saturate a 1 acre area to at least 4 inches deep. for Highway Construction Page 524 of 715 621.05 Basis of Paym ent. The Department will pay for acceptable quantities as follows: Pay Item Pay Unit Seedbed Preparation .............................................................................. Acre Seed ....................................................................................................... Acre Seeding .................................................................................................. Acre Mulching ................................................................................................. Acre Mulch Anchoring (Mechanical) ............................................................... Acre Mulch Anchoring (Tackifier) .................................................................... Acre Soil Amendments ................................................................................... Acre Mulch Mixture ......................................................................................... Acre Mulch plus Tackifier ................................................................................ SY or Acre Hydraulica lly Applied Erosion Control Products ...................................... SY or Acre Rolled Erosion Control Products ............................................................. SY Turf Reinforced Mat ................................................................................ SY Fertilizing ................................................................................................ Acre Water Del ivery System ........................................................................... LS Watering ................................................................................................. AU Weed control is the Contractor’s responsibility and is incidental . If seeding is performed between May 1 and October 14, watering is incidental to seeding, and the cost included in the seeding contract unit price. for Highway Construction Page 525 of 715 SECTION 622 – PRECAST CONCRETE HEADGATES
622.01 Description.
Provide and install precast concrete headgates.
622.02 Materials.
Provide materi al as specified in 509.
622.03 Construction Requirements.
Shape the area to be occupied by the headgate to conform to the structure and to provide a firm and uniform bearing over its entire area. Backfill and compact the dike or ditch aro und the structure t o avoid undercutting or erosion.
622.04 Method of Measurement.
The Engineer will measure acceptably completed work per each, including 1 length of pipe in addition to the pipe cast in the headwall.
622.05 Basis of Payment .
The Department will pay for accepted quantities at the contract unit prices as follows: Pay Item Pay Unit _____ Precast Concrete Headgate ........................................................ Each Structure excavation, ba ckfill, and compacting backfill are incidental and the cost included in the precast concrete headgate contract unit price.
Source: Idaho Standard Specifications for Highway Construction, 2023 Edition. Pages 553–560 of 768.