Los Alamos National Laboratory Storm Water BMP Manual (TPD1103039)

Blank pages in document are for duplex printing purposes.

TABLE OF CONTENTS                                                            

Table of Contents……………………………………………………………………………………………………………. i

Acronyms………………………………………………………………………………………………………………………. ii

1. 1.                   General Guidance

1.1.                                     Introduction (how to use this guidance document)……………………………………….. 1

1.2.                                     Best Management Practice Use Matrix……………………………………………………… 3

1.3.                                     LANL Considerations……………………………………………………………………………. 5

1.4.                                     References………………………………………………………………………………………… 7

1. 2.                   Good Housekeeping and Scheduling Practices

2.1.                                     Good Housekeeping…………………………………………………………………………….. 9

2.2.                                     Scheduling Practices…………………………………………………………………………… 13

1. 3.                   Sediment Control

3.1.                                     Silt Fence and S-Fence……………………………………………………………………….. 17

3.2.                                     Fiber Rolls…………………………………………………………………………………………. 23

3.3.                                     Triangular Silt Dike……………………………………………………………………………… 27

3.4.                                     Construction Entrance/Exit……………………………………………………………………. 35

3.5.                                     Brush Barrier……………………………………………………………………………………… 39

3.6.                                     Storm Drain Inlet Protection………………………………………………………………….. 43

1. 4.                   Runon/Runoff Control

4.1.                                     Berms and Channels…………………………………………………………………………… 49

4.2.                                     Check Dams……………………………………………………………………………………… 57

4.3.                                     Waterbars and Runouts……………………………………………………………………….. 61

4.4.                                     Terracing………………………………………………………………………………………….. 65

4.5.                                     Surface Roughening…………………………………………………………………………… 71

4.6.                                     Sediment Traps………………………………………………………………………………… 77

4.7.                                     Storm Water Detention Basins………………………………………………………………. 81

1. 5.                   Erosion Controls

5.1.                                     Revegetation…………………………………………………………………………………….. 87

5.2.                                     Temporary Stabilization……………………………………………………………………….. 91

5.3.                                     Rolled Erosion Control Products (RECP)…………………………………………………. 95

5.4.                                     Dust Suppression……………………………………………………………………………….. 99

5.5.                                     Gabions………………………………………………………………………………………….. 101

5.6.                                     Riprap……………………………………………………………………………………………. 105

5.7.                                     Permanent Capping………………………………………………………………………….. 109

ACRONYMS                                      

AOC                 Area of Concern

BFM                 Bonded Fiber Matrix

BMP                 Best Management Practice

CGRP               Cerro Grande Rehabilitation Project DOE                 Department of Energy

ECB                 Erosion Control Blanket

EM&R               Emergency Management & Response ENV-RCRA       LANL Water Quality Group

EPA                 Environmental Protection Agency

FGM                 Flexterra or other Flexible Growth Medium HDPE               High Density Polyethylene

IECA                 International Erosion Control Association LANL                Los Alamos National Laboratory

MgCl                Magnesium chloride

MSGP              Multi-Sector General Permit

MSS                 Maintenance and Site Services

NM                   New Mexico

NMED              New Mexico Environment Department NOI                   Notice of Intent

NPDES             National Pollutant Discharge Elimination System PAM                 Polyacrylamide

RECP               Rolled Erosion Control Product

SPCC               Spill Prevention Control and Countermeasure SWMUs            Solid Waste Management Units

TRM                 Turf Reinforcement Mat

TSD                  Triangular Silt Dike

UV                    Ultraviolet

WMC                Waste Management Coordinator

ii

This guidance document was developed to provide information on the selection, function, installation, inspection, and maintenance of Best Management Practices (BMPs) for storm water management, sediment and erosion control and the management of other potential surface water pollutants at Los Alamos National Laboratory (LANL). Its intent is to provide a consistent approach in the selection and use of BMPs at LANL. The information provided in this document is not intended to replace an engineering design where such designs may be applicable, but should be used in support of and in conjunction with the LANL Engineering Standards and specifications. This document is also not inclusive of all the BMPs that may be applicable at LANL.

WHAT IS A BMP?

HOW TO USE THIS GUIDANCE DOCUMENT

BMPstands for Best Management Practice.

BMPscan be procedures, practices, or physical structures or controls.

BMPsminimize the potential for pollutant transport.

BMPscan be either temporary or permanent.

The BMPs identified in this manual are common industry practices, are types or categories that can be utilized with a variety of “off the shelf” products, and are those that have proven effective for LANL conditions and climates.

However, the BMP industry is dynamic. New products and innovations are continually being introduced. If new or modified BMPs not identified in this guidance document are identified or desired for use, the LANL Water Quality & RCRA Group (ENV-RCRA) should be consulted for guidance and approval. Installation of manufactured BMPs should follow installation guidance and recommendations as provided by the manufacturer.

This manual is organized in the following sections:

1. Start by looking at the BMP Use Matrix in Section 1.2, to help you select appropriate BMPs.
2. Go to the detailed BMP information to see information on proper usage, useful combinations and alternatives.
3. Use the detailed BMP information to learn more about installation and maintenance requirements.

Construction Sites/Activities

• Use this manual to help choose BMPs when a design is not available.
• Use this manual to supplement information provided in the LANL Engineering Standards and construction specifications.
• Use this manual to ensure BMPs are properly installed and maintained.

MSGP

Facilities

• Use this manual to help select additional BMPs if current controls are not adequate.

Individual Storm Water Permit / Solid Waste Management Units

(SWMUs)

• Use this manual to select new BMPs based on site conditions and needs.
• Use this manual to provide guidance on how to install new BMPs, and inspect and maintain existing BMPs.

Best Management Practice Use Matrix

LANL CONSIDERATIONS

LANL ENGINEERING STANDARDS

The Los Alamos National Laboratory Engineering Standards are comprised of several mandatory Functional Series documents including the Engineering Standards Manual (ESM), master guide specifications, standard details, example drawings, and a drafting manual. The purpose of the Engineering Standards is to define the minimum technical requirements for the design and construction of new and existing structures at LANL.

This Manual should supplement and support use of the Engineering Standards. As specified in their respective sections, storm water detention basins, riprap, and permanent capping must be designed using the Engineering Standards to ensure proper function of these BMPs. The Engineering Standards are also to be used in the design and construction of berms and check dams in excess of two feet in height.

Additionally, if the failure of a BMP has the potential to cause injury, loss of life, or property damage, the Engineering Standards would supersede the use of this document and the Standards should then be applied in the design and specification of the BMP. The Engineering Standards would provide design procedures and criteria associated with but not limited to:

• The sizing of controls for management or conveyance of storm water.
• Sizing or specifying material suitable for the applicable forces and stresses exerted on a BMP.
• Proper construction requirements to ensure a safe and functioning BMP.

When utilizing the LANL Engineering Standards for BMP design, the ESM and the master guide specifications should both be used. The ESM can be found at http://engstandards.lanl.gov/ESM_Chapters.shtml#esm3, and the master guide specifications are found at http://engstandards.lanl.gov/specs.shtml. For additional guidance on the applicability of the Engineering Standards for BMP design, contact the LANL Water Quality Group (ENV-RCRA).

SWMUs and AOCs

• Do not direct storm water to a Solid Waste Management Units (SWMU), Area of Concern (AOC).
• Water should not be encouraged to pond on a SWMU or AOC.
• Based on the site constituents, environmental media (e.g. soil, sediment, surface and ground water) may constitute solid waste and/or hazardous waste. If there is any potential for accumulated sediment or other media to be considered waste, a waste determination must be made and documented. For guidance, see the Laboratory’s procedures on Waste Management.
• BMPs used on SWMUs or AOCs may be considered waste based on site constituents and BMP use. Consider the use of biodegradable or permanent BMPs that can be left on site.

SPCC Plans

As per the LANL procedures and EPA Regulations, any facility or Project with a total aboveground storage capacity greater than 1,320 gallons with a minimum container size of 55 gallons must have a Spill Prevention Control and Countermeasures (SPCC) Plan. This includes not only diesel storage tanks, but also equipment such as compressors and drill rigs.

Contact the LANL Water Quality Group (ENV-RCRA) for guidance and support.

STATE REQUIREMENTS

Velocity Dissipation For soil disturbing activities subject to NPDES Construction General Permit coverage, State requirements mandate that runoff velocity from a construction project cannot increase from pre-development rates.  Pre-development is defined as prior to any original disturbance. Install velocity dissipation devices such as check dams and detention ponds. Sites over 10 acres must install storm water detention ponds.

Sediment Yield           For soil disturbing activities subject to NPDES Construction General Permit coverage, State requirements mandate that sediment yield from a construction project cannot increase from pre-development rates. Stabilize disturbed areas and utilize appropriate erosion controls.

Liquid Discharges onto the Ground

Request assistance from the LANL Water Quality Group (ENV-RCRA) to gather and submit information for preparation of a NMED Notice of Intent to Discharge (NOI) or LANL Un-permitted Liquid Discharge Log Report.

Examples: planned potable water, storm water drainage from secondary containment units, fire suppression test/flush, steam condensate, fire hydrant flush, pothole water, waterline disinfect/flush, land application of groundwater.

REFERENCES

LANL ENGINEERING STANDARDS AND CONSTRUCTION SPECIFICATIONS

http://engstandards.lanl.gov/

LANL CONSTRUCTION ACTIVITIES COMPLIANCE

http://int.lanl.gov/environment/h2o/cw_npdes.shtml

EPA CONSTRUCTION BMP MENU

http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=min_m easure&min_measure_id=4

EPA NPDES CONSTRUCTION GENERAL PERMIT (2008)

http://www.epa.gov/npdes/pubs/cgp2008_finalpermit.pdf

EPA NPDES MULTI-SECTOR GENERAL PERMIT (MSGP) (2008)

http://www.epa.gov/npdes/pubs/msgp2008_finalpermit.pdf

EPA NPDES INDIVIDUAL PERMIT – NM0030759 (2010)

ftp://ftp.nmenv.state.nm.us/www/swqb/NPDES/Permits/NM0030759- LANLStormwater.pdf

INDUSTRY ORGANIZATIONS

Land and Water Magazine http://www.landandwater.com/

Stormwater Magazine http://www.stormh2o.com/

IECA     http://www.ieca.org/

The International Erosion Control Association (IECA) is devoted to helping solve the problems caused by erosion and its byproduct—sediment.

Good Housekeeping

Description                  Good housekeeping includes controls that are practices (as opposed to structural controls) that are used to reduce or prevent pollutants.

Applications                Low cost alternative to structural BMPs.

Limitations                  Only prevents the initial migration of pollutants from the source.

Performance and Longevity

Design and Construction Guidance

In general, use of practices to prevent pollutants from contact with storm water is extremely effective.

Good housekeeping practices are implemented before project activities begin and throughout project activities. These practices are temporary in nature and are only meant to last through the construction activity process.

Material storage

• Designate material storage areas away from the nearest watercourse and in locations that do not receive a substantial amount of upslope run- on.
• Store soils uphill of BMPs or the excavation.

• Hazardous materials, fluids, and chemicals should be placed within covered storage, or a lined berm or other appropriate secondary containment.
• Drums containing liquids or hazardous materials should be stored on secondary containment pallets that minimize storm water accumulation.

Wastes

• Designate a waste collection site that does not drain to a watercourse and that does not receive a substantial amount of upslope run-on.
• Refuse containers should have lids that will remain closed to prevent rain exposure. Bins should be leak proof.
• Waste collection should be scheduled to prevent overflow of refuse.
• Trash, material cuttings, and any other waste should be managed or disposed of at the end of each workday and prior to an anticipated storm event.
• Portable lavatories should be used and maintained in accordance with manufacturer’s recommendations; staked to the ground to prevent being knocked over by wind; and lavatory waste must be treated off-site.

Material Transport or Movement

• Material should be transported in appropriate containers or vehicles so that facility locations outside the project boundaries and public roadways will not be adversely impacted through sediment tracking or waste spillage.
• Spill control equipment should be present during any transfer operations.
• Movement of liquid filled containers or transfers of oil or chemicals will not occur during precipitation events
• Containers must be upright and secured to the vehicle/hand truck it is being transported on
• Drums are not to be rolled or tipped, even while empty, to prevent damage to containers
• Containers will be inspected before and after they are transported for leaks or damage.
• Storm drain covers will be used at adjacent storm drains if necessary to prevent a potential spill from entering the storm drain before it would be controlled.
• Transfers from portable containers to equipment occur away from storm drains. Spigots or pumps should be used, do not pour directly from drums. Consider placing absorbent mats before a transfer occurs.

Vehicle and Equipment Refueling & Maintenance

Vehicle and equipment control techniques include:

• Properly covering and providing secondary containment for fuel drums and other similar materials.
• Refueling of equipment shall be conducted at least 100 feet from any storm drain, drainage, or wetland, including dry arroyos.
• Refueling operations will be completed such that head space is provided within fuel tanks to allow for fuel expansion.
• Develop and implement spill prevention and cleanup plan.

• Maintain a spill kit on site.
• Use a covered, paved area dedicated to vehicle maintenance.
• Wash vehicles and equipment only at facilities approved for washing activity.
• All vehicles and equipment will be observed for leaks and if found drip pans will be used until fixed.
• Leaks will be fixed as soon as practicable and leaking vehicles and equipment will be removed from service and repaired.
• Spills of all products will be cleaned up and managed per applicable state and federal regulations.

Potholing

• Spoils must be properly disposed of.
• Discharge spoils only in approved designated areas.
• Do not discharge to the environment any glycol treated water.

Concrete Washouts

Concrete washouts should be used to contain concrete and liquids when rinsing equipment used for mixing or delivering concrete, or for excess concrete. They consolidate solids for easier disposal and prevent contaminated water from mixing with runoff.

• Washouts should be located a minimum of 100’ from a watercourse or storm drain and in a location that allows convenient access for concrete trucks and equipment.
• Containment areas will not be constructed in areas designated as Solid Waste Management Units (SWMUs), Areas of Concern (AOCs), or Treatment Storage and Disposal Facilities (TSDFs).
• Washouts are typically built below grade to prevent breaches and reduce runoff.
• Washouts should be sized to manage both concrete washout and storm water accumulation from precipitation events.
• Use appropriate control measures that act as a continuous line barrier to prevent the runoff of discharges and the co-mingling of discharges with storm water.
• Prefabricated washout containers must protect against spills and leaks, be watertight, and should be used in accordance with manufacturer specifications.
• Inspect washout area for damage and repair as necessary to ensure structure integrity.
• Once a washout facility has reached 75% capacity the materials should be removed and properly disposed of.

Street Sweeping

Street sweeping and vacuuming includes use of self-propelled and walk-behind equipment to remove sediment from streets and roadways.

• Vacuuming is essential because sweeping alone may cause dust pollution and off-site sediment transport.
• Points of site egress are especially vulnerable to off-site sediment tracking.

• A proper construction entrance/exit may be needed if street sweeping efforts are not sufficient to prevent sediment from leaving the site.
• Sweeping and vacuuming may not be effective when sediment is wet or when tracked soil is caked (caked soil may need to be scraped loose).
• Sweeping should be performed at a frequency necessary to minimize visible sediment tracking from the site.

Inspection and Maintenance

• Check that materials are properly stored.
• Check that washout areas are being used.
• Check for vehicle leaks and proper maintenance.
• Check for tracking of sediment from site.

What not to do…

Sweeping without vacuuming causes severe dust migration leading to sediment transport offsite.

Improper waste disposal and storage of waste products.

Containerize and separate waste items for proper disposal.

Scheduling Practices

Description                  Scheduling practices are controls that are practices (as opposed to structural controls) that are used to reduce or prevent pollutants.

Applications                Low cost alternative to structural BMPs.

Limitations                  Only prevents the initial migration of pollutants from the source.

Performance and Longevity

In general, use of practices to prevent pollutants from contact with storm water is extremely effective.

Scheduling practices are implemented before project activities begin. These practices are temporary in nature and are only meant to last through the construction activity process.

Design and Construction Guidance

Downstream Impacts

Consider ways to ensure that runoff from your project does not affect sensitive locations downstream of your project such as wetlands, archaeological sites, Threatened and Endangered Species habitat, or SWMUs.

Timing Considerations

The timing and sequencing of soil disturbing activities can also be utilized as a BMP.

Construction site phasing involves disturbing only part of a site at a time to minimize erosion and runoff from inactive parts.

• Some projects may have timing restrictions for biological restrictions.
• Complete grading activities and stabilize disturbed areas on one part of the site before grading and construction commence at another part.
• Begin stabilizing the site or portions of the site as early as possible in the construction project.
• Consider installing permanent storm water management BMPs as early as possible in the construction project.
• Utilize permanent BMPs in place of temporary BMPs where possible.
• Plan to do construction outside of the rainy season (July-Sept) when possible.
  • When working during monsoon season (July-Sept) recognize that sudden intense storms may occur and arrange your project so that pollutants are not left exposed to storm water and so that water does not run into excavations.
  • In late February the ground starts to thaw and freeze.
  • Do not drive heavy equipment on saturated soil.
  • Plan revegetation efforts to coincide with the monsoon season.
  • Re-seed prior to or at the beginning of the monsoon season to take advantage of seasonal rains.
  • Schedule stabilization of disturbed areas as soon as possible.

Preservation of Existing Vegetation

• Existing vegetation includes low-growing vegetation classified as grasses and shrubs; and piñon-juniper, ponderosa pine and mixed conifer vegetation is classified as forested.
• Existing vegetation provides erosion control and storm water infiltration.
• Plan the project to disturb as small amount of existing vegetation as possible.
• Use paved areas for staging of equipment and waste bins.
• Preserve trees when possible.
• Stockpile topsoil from clearing and grubbing operations for reuse as soil conditioning to improve outcome of vegetative stabilization.
• Reuse brush from clear and grub operations as brush barriers or chop it into mulch.

Reusable BMPs

Reduce waste at the Lab by utilizing reusable BMP products such as S-Fence,

Eco-Blok, Gravel Bags, Triangular Silt Dike, and construction entrance tracking devices. These products can be re-used over and over again and moved between jobs.

Spill Prevention, Response and Reporting

Spill Prevention includes inspecting equipment regularly for safety, cleanliness and leaks; and implementation of appropriate controls. Equipment found to be leaking should be removed from service and repaired. When possible, park equipment on asphalt or concrete to minimize generation of waste materials caused by spills on soil.

If a spill occurs, the following procedures shall be followed:

Disposal occurs by the Waste Management Coordinator (WMC) per LANL Procedure P409 Waste Management http://policy.lanl.gov/pods/policies.nsf/MainFrameset?ReadForm&DocNum=P40 9&FileName=P409.pdf.

Inspection and Maintenance

ENV-RCRA will complete required state, federal, and DOE Order 231.1A ORPS reporting requirements, in accordance with Laboratory and DOE policies and federal and state regulatory reporting requirements per P 322-3 Manual for Communication, Investigation, and Reporting Abnormal Events https://policy.lanl.gov/pods/policies.nsf/MainFrameset?ReadForm&DocNum=P3 22-3&FileName=P322-3.pdf.

• Check for spills.

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Silt Fence and S-Fence™

Description                Silt fences are typically used as temporary perimeter controls around sites where construction activities will disturb the soil. They can also be used within the interior of a site. A silt fence consists of a length of woven, permeable geotextile, stretched

between anchoring posts spaced at regular intervals along the site at low/downslope areas. The filter fabric should be entrenched in the ground between the support posts. When installed correctly, silt fences create ponding of runoff from the site, allowing transported sediment to settle out. Silt fences can be an effective barrier to sediment leaving the site.

The S-Fence is made from HDPE material and is much stiffer than the silt fence material. It is buried 3 inches in the ground and can be secured to an existing chain link fence or can be installed by itself and fastened to wood stakes. Each section is 7 feet long and comes in two heights: 10 inch and 14 inch. S-Fence is designed to allow water to flow through it and significantly reduces erosive energy and provides particle filtering.

Applications              Silt fences apply to construction sites with relatively small drainage areas. They are appropriate in areas where runoff will occur as sheet flow. The drainage area for silt

fences should not exceed 0.25 acre per 100-foot fence length. Silt fence should not be used for runoff velocity control or placed in areas of concentrated runoff such as drainage channels and storm drain inlets and outlets. Silt fence should be installed along the contour to minimize channeling of runoff. They may also be placed perpendicular to prevailing winds at staggered intervals to address wind erosion. The same applications apply to S-Fence.

Limitations                 · Do not install silt fences along areas where rocks or other hard surfaces will prevent uniformly anchoring the fence posts and entrenching the filter fabric. Improper installation prevents proper function.

• Silt fences are not suitable for areas where large amounts of concentrated runoff are likely. Do not install silt fences across streams, ditches, or waterways.
• High winds can make the filter fabric deteriorate faster, so installing fences in open, windy areas should be avoided.
• When the pores of the fence fabric become clogged with sediment, pools of water are likely to form on the uphill side of the fence. Siting and design of the silt fence should account for this. Take care to avoid unnecessarily diverting storm water from these pools, causing further erosion damage.
• UV exposure degrades silt fence filter fabric, causing separation of the fabric strands which leads to greater potential for holes and wind damage.

Performance and Longevity

Studies have approximated the following effectiveness ranges for silt fences constructed of filter fabric that are properly installed and well maintained:

• Average total suspended solids removal of 70 percent
• Sand removal of 80 to 90 percent
• Silt-loam removal of 50 to 80 percent
• Silt-clay-loam removal of 0 to 20 percent.

Removal rates are highly dependent on local conditions and installation.

Silt fence in the LANL area will typically experience the onset of degradation due to UV exposure over a period of 6 to 12 months and will need to be maintained or repaired due to damage from wind and runoff.

S-Fence can also be used as a perimeter control but is made from an HDPE material and has a functional life greater than 4 years. It can also be reused. The product will stand up to winds and UV exposure and can be recycled at the end of its life.

Design and Construction Guidance

Materials Silt Fence

• The material for silt fences should be a pervious sheet of synthetic fabric such as polypropylene, nylon, polyester, or polyethylene yarn.
• Choose the material based on the minimum synthetic fabric requirements shown in Table 1.

Table 1. Minimum requirements for silt fence fabric

S- Fence Product Characteristics

• Unit weight, 10” / 14” (Lbs/ft) (max) 0.35 / 0.48
• Reusable YES
• Functional life (minimum)(years) 4+
• Filter capability – AOS (ASTM D4751) (microns) 250
• Dimension – length per module (ft) 7
• Percentage Open Area (COE 22125-86) (min %) 20%
• Dimension (freeboard height in inches) 10.0 / 14.0
• Tensile Yield ASTM D-638 (lb/in2) 1800 – 2800
• Installed freeboard height (inches) 7.0 / 11.0
• Ultimate Tensile Strength: ASTM D-638 (lb/in2) 2000 – 2800
• Recyclable Post consumer #2 YES Service temperature (deg F) -30 to 160

Installation

• Standard-strength fabric can be reinforced with wire mesh behind the filter fabric to increase the effective life of the fence.
• Attach the filter fabric to wood or metal stakes at least 4 feet long. Stakes should have a minimum diameter of 2 inches if a hardwood like oak is used or at least 4 inches in diameter if soft woods such as pine are used. When using metal posts in place of wooden stakes, they should weigh at least 1.00 to 1.33 lb/linear foot. If metal posts are used, attachment points are needed for fastening the filter fabric with wire ties.
• Erect silt fence in a continuous fashion from a single roll of fabric to eliminate gaps in the fence. If a continuous roll of fabric is not available, overlap the fabric from both directions only at stakes or posts. Overlap at least 6 inches in a shingle pattern in the direction of runoff flow.

• Excavate a trench to anchor the bottom of the fabric fence at least 6 inches below the ground surface. The trench should be backfilled and the soil compacted over the toe of the filter fabric. Alternatively use a slicing machine to install the filter fabric.
• Install posts along the length of the fence at a height of 18 to 36 inches above the original ground surface. Posts should be driven into the ground a minimum of 12 inches. If standard-strength fabric is used with wire mesh, space the posts no more than 10 feet apart. If extra-strength fabric is used without wire mesh reinforcement, space the posts no more than 6 feet apart. Attach the filter fabric to the posts.
• The ends of the silt fence should be turned uphill to prevent flow from running around the ends of the fence.
• Install silt fence at least 6 feet from the toe of a slope.
• Once installed, silt fence should remain in place until all areas upslope have been permanently stabilized by vegetation or other means.

Inspection and Maintenance

• Inspect fences to make sure that they are intact and that there are no gaps where the fence meets the ground or tears along the length of the fence.
• If gaps or tears are found, repair or replace the fabric immediately.
• Remove accumulated sediments from the fence base when the sediment reaches one-third to one-half the fence height.
• Remove sediment more frequently if accumulated sediment is creating noticeable strain on the fabric and the fence might fail from a sudden storm event.
• When removing the fence, remove the accumulated sediment as well.

What not to do…

Silt fence should be properly entrenched for proper operation.

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22

Fiber Rolls

Description                Fiber rolls are tube-shaped erosion-control devices filled with straw, flax, rice, coconut fiber material, gravel, or composted material. Common types of this BMP include: straw wattles, coir logs, compost socks, gravel bags, and Terra-Tubes®. Straw wattles are wrapped with UV-degradable polypropylene netting for longevity or with 100% biodegradable materials like burlap, jute, or coir.  Coir logs are very similar to straw fiber rolls but are comprised of long lasting coconut fiber. They are also resistant to being consumed by wildlife. Compost socks and gravel bags are three dimensional tubular devices comprised of woven mesh fabric or other similar material and filled with gravel, rock or compost material. Terra-Tubes® are similar to fiber rolls except they are treated with special polymers that react (flocculate) with suspended soil particles, increasing the ability of the suspended solids to settle.

These devices can be used to break up a slope length, reducing the effects of runoff on long or steep slopes. They also help reduce sediment loads to receiving waters by filtering runoff or capturing sediments. Fiber roll BMPs can be used as check structures to reduce runoff velocity and can be placed around storm drain inlets for velocity and sediment control.

Applications              ·      Along the toe, top, face, and at-grade breaks of exposed and erodible slopes to shorten slope length and spread runoff as sheet flow.

• Along the perimeter of exposed soil areas.
• Gravel bags only can be used as check dams in unlined ditches.
• Around temporary stockpiles (on dirt).
• Around storm drain inlets (see Section 3.5).

Limitations                 ·      They have a limited sediment capture zone.

• Some may have problems with ice buildup.
• Must be trenched in to function properly.
• Straw and rice fiber rolls are susceptible to damage and consumption by wildlife.

Performance and Longevity

Design Criteria and Construction Specifications

Materials

• Most will come prefabricated. Some may require filling onsite, such as gravel bags and compost socks.
• Straw fiber rolls must be at least 8” diameter. To be effective, fiber rolls at the toe of slopes must be at least 20 inches in diameter. An equivalent installation, such as stacked smaller-diameter fiber rolls, can be used to achieve a similar level of protection.
• Compost socks: the compost shall be free of any refuse, contaminants or other materials toxic to plant growth. Non-composted products will not be accepted. Filter socks used for erosion control are usually 12 inches in diameter.
• Gravel bags: filled with clean 3/4” crushed or 1/4” pea gravel. If subject to impact from equipment or vehicles, fill bags only ½ to ¾ full with non-angular rock.
• Terra-Tubes® can be used where additional reductions in turbidity are required.
• Stakes installed per manufacturer recommendations.

Installation.

• On projects with slopes, install fiber rolls along the contour with a slight downward angle at the end of each row to prevent ponding at the midsection. Turn the ends of each fiber roll upslope to prevent runoff from flowing around the roll.
• Install fiber rolls in shallow trenches dug 3 to 5 inches deep for soft, loamy soils and 2 to 3 inches deep for hard, rocky soils.
• Determine the vertical spacing for slope installations on the basis of the slope gradient and soil type. General Guidance is as follows:
  • 1:1 slopes = 10 feet apart
  • 2:1 slopes = 20 feet apart
  • 3:1 slopes = 30 feet apart
  • 4:1 slopes = 40 feet apart

• Fiber rolls can be anchored in the following ways:

1. Drive the stakes through the middle of the fiber roll and deep enough into the ground to anchor the roll in place. About 3 inches of the stake should stick out above the roll, and the stakes should be spaced 3 to 4 feet apart.
   1. Stakes may be placed on each side of the roll tying across with a natural fiber twine or staking in a crossing manner ensuring direct soil contact at all times.

• Gravel bags do not require staking.
• Terminal ends of fiber rolls may be dog legged up slope to ensure containment and prevent channeling of sedimentation.
  • Backfill the length of the fiber roll with the excavated soil and compact.

Inspection and Maintenance

• Ensure that the rolls remain firmly anchored in place and are not crushed or damaged by equipment traffic.
• Check that fiber rolls are trenched in and no gaps exist under the rolls.
• Check that fiber rolls are adequately aligned with the next roll. Either overlapped uphill of the next or doglegged.
• Check that fiber rolls are securely anchored.
• Repair or replace split, torn, unraveled, or slumping fiber rolls.
• Rills or gullies upslope of the rolls and any undercutting is to be repaired.
• Sediment deposits shall be removed when the sediment reaches one-third of the fiber rolls functional freeboard height. Removed sediment shall be deposit within the project in such a way that the sediment is not subject to erosion by wind or water.
• Additional fiber rolls can be placed on top of existing ones to increase sediment capacity.

What not to do…

A rill is forming under the fiber roll. The rill should be filled in. The fiber roll should be properly entrenched into the soil so that water velocity is decreased and water is forced to pool behind to promote sedimentation and flow over the fiber roll.

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Triangular Silt Dike

Description                A Triangular Silt Dike (TSD) is a prefabricated triangular shaped piece of foam encased in filter fabric with built in aprons on both sides of the foam body. It is typically used as a temporary control to help reduce the velocity of storm water in a channel or swale or as a perimeter sediment control. A TSD can also be used as a diversion berm to divert storm water around a site or direct the storm water within a site. TSDs can withstand light vehicle traffic.

Applications              ·      Use in channels and swales as a temporary check dam.

• Use as a diversion berm to divert water within or around the site, or as a temporary lined channel.
• Use as inlet protection.
• Use as a sediment control around disturbed areas and soil stockpiles.

Limitations                 ·      Ends of TSD sections must be tightly joined to prevent storm water from bypassing the control.

Performance and Longevity

Design Criteria and Construction Specifications

Locate TSD as you would other similarly used BMPs.

• Tuck the ends of adjacent flaps on the dike together to ensure there are no gaps between TSD sections and secure with U-shaped staples, pressing the staples through the fabric and foam material.
• Trench in and staple the leading edge (apron) on the uphill sides to prevent undercutting.
• Staple the apron to the ground at the base of the dike on the downhill side.
  • Ensure that the dikes are placed appropriately for the specific use (see check dam and silt fence sections)
  • When used as a check structure, ensure that the center of the TSD is lower than the outside edges. This can be done at any point by driving one or more U-shaped staples into the TSD and compressing the foam.

Inspection and Maintenance

• Evidence of erosion, undercutting, bypassing, or other damage in the surrounding area.
• Removed sediment accumulations shall not be placed within any drainage, either above or below the BMP. Removed sediment shall be stabilized to prevent future migration from storm water runoff.

What not to do…

Note that the Triangular Silt Dike sections are not properly joined together and that cinder blocks have been utilized to fill the gap. Sediment accumulations need to be removed from the Triangular Silt Dike.

Construction Entrance/Exit

Description                A temporary construction entrance/exit is an area with a singular or series of controls established to manage and reduce off-site tracking of sediment from equipment and vehicles. It reduces the sediment that collects on vehicle tires and minimizes off-site tracking of sediment.

Applications              ·      Locations where mud tracking is a problem during wet weather or where dust is a problem during dry weather.

• Locations where construction activities are adjacent to roadways.

Limitations                 ·      May require replacement of rock during project.

• Requires a large entrance space.
• Can be high maintenance when rock is the only material used.
• Must be used in conjunction with sweeping for optimal performance.

Performance and Longevity

Design Criteria and Construction Specifications

• Ensure that entrance cannot be bypassed by vehicles and equipment.

Rock entrance

• The rock used for pad construction shall be 4-6 inch maximum size aggregate. Do not use base course.
• Geo-textile fabrics must be used to improve the stability of the pad foundation.
• Rock shall be spread to a minimum thickness of 6 inches.
• Rock placement shall conform to the grade and dimensions shown on the design drawings.
• The pad shall extend the full width of the entrance/exit. Minimum pad width shall be 10 feet.
• Minimum pad length shall be 50 feet.

Grizzly Tracker® or similar

• Install per manufacturers recommendations, typically a minimum of 16’.

Wheel Wash Stations

• Use per manufacturers recommendations.

Inspection and Maintenance

• Inspect for sediment accumulations and the need to remove the accumulations or replace gravel.
• Inspect for compaction of the rock into the surrounding ground, creating a surface that does not adequately shake vehicles as they pass over the entrance. As required, add additional layers of rock to the pad to prevent off-site tracking of sediment.
• Inspect for signs of vehicles bypassing the entrance and block off alternate egress routes.

What not to do…

Failure to install a construction entrance has lead to sediment transport offsite.

TEMPORARY  GRAVEL  CONSTRUCCTTIIOON

Brush Barrier

Description                Branches, limbs, and brush are piled at the downhill edge of the site to provide minor runoff pooling to reduce offsite sediment transport.

Applications              ·      Place below the toe of exposed and erodible slopes and at low points of site perimeter.

• Downslope of exposed soil areas.
• Linear construction projects.

Limitations                 ·      Adequate brush may not be readily available.

• Cannot be used on steep slopes (>3:1).
• Only applicable for sheet flow runoff and minor concentrated flow.

Performance and Longevity

Design Criteria and Construction Specifications

• Barriers can be constructed of cleared and grubbed materials such as brush and logs.
• Brush barriers can be covered with a filter cloth to stabilize the structure and improve barrier efficiency if fabric can be entrenched and anchored on the upslope side.
• Ensure that brush and tree limbs are not removed from an area of contamination.
• Juniper Bales are premade in bound form.
• When placed at the toe of a slope, the barrier should be installed a minimum of 5-6 feet away from the toe of the slope.
• Pile barrier material uniformly in a row, minimizing voids. Minimize the amount of top soil included with the barrier material. Fill gaps with appropriate loose material. To anchor the barrier, place wooden stakes along the downhill edge.
• Logs shall be entrenched into the ground in order to capture sediment. Soil berms may used to help entrench logs where extreme rock areas are encountered.
• Juniper bales should be embedded in a trench that has been excavated to a minimum depth of 4 inches. Backfill material shall be firmly compacted. Bales should tightly abut one another. Anchor the bales in place with 2 x 2 inch stakes or rebar through each bale.
• Ensure barriers are only located in areas with sheet flow runoff or minor concentrated flow.

Inspection and Maintenance

• Ensure logs and bales are entrenched into ground or have adequate berming to capture sediment.
• Look for gaps in brush barriers
• Barriers can be left in place throughout final stabilization as final site conditions allow or barriers can be shredded and used as mulch on the site.
• Closely inspect juniper bales for deterioration.
• Remove accumulated sediment when it reaches 1/3 to 1/2 the height of the barrier. Removed sediment accumulations shall not be placed within any drainage, either above or below the BMP. Removed sediment shall be stabilized to prevent future migration
  • If channels form through or around the barrier, the barrier should be reconstructed to eliminate the channels.
  • If barriers are subject to concentrated runoff, or are undermined or overtopped, replace with a more appropriate BMP or add additional controls to the site.

What not to do…

Notice how the down slope perimeter is unprotected with minimal brush, insufficient for adequate sediment control.

Storm Drain Inlet Protection

Description                The purpose of inlet protection is to filter sediment while still allowing storm water to drain to the inlet or to create ponding around an inlet to allow transported sediment to settle out. These measures are temporary and are implemented before a site is disturbed.

Applications              Where sediment laden surface runoff may enter an inlet.

Limitations                 ·      Typically requires additional upstream controls for optimal performance.

• Most effective only when placed in a sump condition.

Performance and Longevity

Design Criteria and Construction Specifications

• Choose the BMP appropriate for the location and type of inlet. Some hold up to traffic or are low profile, and some are suitable for use in sites still under construction that require higher ponding levels.
• Block and Gravel: Block and gravel inlet barriers should be at least 1 foot high (2 feet maximum). Lay the bottom row of blocks at least 2 inches below the soil surface, flush against the drain for stability. Place one block in the bottom row on each side of the inlet on its side to allow drainage. Place 1/2-inch wire mesh over all block openings to prevent gravel from entering the inlet. Place gravel (3/4 to 1/2 inch in diameter) outside the block structure at a slope no greater than 2:1.
• Install in a sump condition
• Ensure BMP does not divert flow and create downstream flooding.
• Ensure BMP placed in locations subject to traffic have overflow capabilities to minimize potential for upstream flooding and traffic hazards.
• Pre-manufactured devices: Install per manufacturer’s instructions.

Inspection and Maintenance

• Ensure there is a spillway
  • Accumulated sediment shall be removed when it reaches 1/3 to 1/2 the height of the inlet protection.
  • Storm drain inlet protections shall be removed when the area has been finally stabilized.
  • Removed sediment accumulations shall not be placed within any drainage, either above or below the BMP. Removed sediment shall be stabilized to prevent future migration from storm water runoff.
  • Ensure there are no gaps under or between elements of the inlet protection.
  • Check materials for tears.

What not to do…

Remove sediment and debris in a timely manner from storm drains.

NOTES:

1. DROP INLET SEDIMENT BARRIERS ARE TO BE USED FOR SMALL, NEARLY LEVEL (LESS THAN 5%) DRAINAGE AREAS.
2. BLOCKS SHALL BE EMBEDDED IN A TRENCH AROUND THE INLET TO A MINIMUM DEPTH OF 3″, WITH THE ENDS TIGHTLY ABUTTING.
   1. BACKFILL THE BLOCKS WITH GRAVEL TO ASSIST IN SEDIMENT RETENTION.
   2. THE TOP OF THE STRUCTURE (PONDING HEIGHT) MUST  BE  WELL  BELOW THE GROUND ELEVATION DOWNSLOPE TO PREVENT RUNOFF FROM BYPASSING THE INLET.

Berms and Channels

Description                Berms and channels are most often used to prevent run-on from eroding an exposed or disturbed area, and to divert sediment-laden runoff to a sediment trap, sediment basin or other suitable, stabilized discharge outlet. When used as a temporary control, berms are most often constructed from compacted soil or loose gravel, stone, or crushed rock. Berms may serve as a permanent structural control

when constructed from asphalt, concrete, or other similar material. Channels can be incorporated into a berm design or function as a stand-alone BMP, and are typically constructed from compacted soil or lined with a suitable material.

Applications              Effective in diverting run-on away from unprotected areas and reducing flow velocities; effective to retain small amounts of runoff and sediment onsite.

Limitations                 ·      A berm with a height of over 2 feet or located in an area where failure of the berm would result in damage to facilities, the environment or other safety issues requires an engineered design.

• Increased potential for failure if the upslope gradient is too great, resulting in high velocity flows.
• Earth berms may require vegetative stabilization to prevent erosion of the berm itself.
• Excessive sediment accumulation on upslope side of berm needs frequent clean-out.
• Channels may require engineering calculations to ensure the channel material is adequate to withstand flow velocity and shear stress.

Performance and Longevity

Design and Construction Guidance

• Berms should be constructed during initial land-disturbing activities and must be operational prior to upslope land disturbance.
• A shallow trench or swale to contain the diverted run-on/runoff can be incorporated into the berm design.
• Where applicable, on-site material should be used for berm construction.
• Berm material needs to meet requirements for gravelly clay or sandy clay. Do not use gravelly sand or gravelly loam to construct berms.
• When used as a perimeter or down slope control, berms should divert runoff to a sediment trapping control such as a sediment trap or basin.
• Berms should be located so as to minimize damage by construction operations and traffic.
• Triangular Silt Dike® berms can be used in locations subject to minor traffic flow.
• Earth berms must be adequately compacted to prevent failure.
  • Logs must be delimbed, trenched in and backfilled. If necessary, secure with wooden stakes on either side of the log.
  • Rock berms must be constructed of large angular rock. Height and depth of the berm is dependent on the expected storm water flow. Ends of berm should be brought forward to help contain the flow.
  • Channel material must be adequate to withstand flow velocity and shear stress.
  • Ensure channels are designed and constructed with a defined flow line adequate to convey flows.
  • Spillways on berms should be at least 6 inches in depth and should be protected against scour. Use rock or TRM for stabilization of the spillway.

Inspection and Maintenance

• Seeded areas which fail to establish a vegetative cover shall be reseeded as necessary.
• Damage from vehicle or construction traffic shall be repaired prior to the end of each working day or prior to the next storm event, whichever is sooner.
• Conduct required repairs immediately.
• Temporary berms may be removed when the site has been finally stabilized or when drainage patterns changed so that the berms are no longer functional.
• Berms that are designed to trap sediment should be cleaned out as necessary or after each storm event.
• Inspect for erosion or other damage, and repair.

What not to do…

Berm was not well stabilized and could not stand up to run-on flows. Berms and swales should be designed and constructed to handle site specific run-on or run- off flows.

EARTH   BERM

Check Dams

Description                   A check dam is a small dam constructed across a channel, drainage ditch or other area of concentrated flow. Check dams reduce erosion and promote sedimentation by reducing runoff flow velocity and encouraging sediment to settle

out. Check dams are usually constructed of rock, gravel bags, sandbags or other proprietary products and may either be a temporary or permanent structural control.

Applications              ·      Use to minimize down cutting in channels, retain sediment, and reduce velocity.

• Useful in temporary ditches that will be removed after construction.

Limitations                 ·      A check dam with a height of over 2 feet or located in an area where failure of the check dam would result in damage to facilities, the environment or other safety issues requires an engineered design.

• Significant sediment accumulations behind the check structure may destroy vegetation lining the channel.
• Requires regular maintenance and sediment removal.
• May not be used in a drainage that is a perennial stream.
• May cause increased erosion if not installed correctly.

Performance and Longevity

Design and Construction Guidance

• Check dam must be located in a defined channel to reduce runoff velocity or retain sediment.
• If high flows are expected, ensure scour protection has been installed on the downstream of the check dam.
• Check dams should be spaced at a distance to allow the elevation of the ponded water from the downstream check dam to match the elevation of the toe of the upstream dam.
• Flows must be directed over the check dam.
  • When using rock, ensure the material diameter is appropriate to create ponding.
  • Straw bales and wattles should not be used as check dams.
    • The center of a check dam must always be lower than its outside edges and the channel bank height to allow proper flow over the check structure.

Installation:

• Should be installed as soon as possible while construction activities are occurring.
• The center of the dam should be at least six-inches lower than its edges.
• Check dam material should be entrenched into the sides and bottom of the channel to ensure flow does not go around or under the check dam.
• Rock should be placed individually by hand or by mechanical methods (no dumping of rock).

Inspection and Maintenance

• Check for damage and erosion caused by flows around or under the dam structure. Repair erosion around a check dam and lower the center if required.
• Remove any debris that would impede flow over the check dam.
• When the sediment has reached a height of approximately one-half the original height of the dam (measured at the center), remove accumulated sediment from the upstream side of the dam.
• Remove check dams made from temporary materials when the adjacent site is stabilized.
• Before removing a check dam, remove all accumulated sediment from the channel. If sediment is placed on adjacent slopes, stabilize it with native vegetation.

What not to do…

Silt fence cannot be used as a check structure and is not designed for concentrated flow.

Notice how runoff bypassed the check structures. Channel banks

must be sufficient to withstand flows and the dam center must be lower to allow flow over the check dam.

Waterbars and Runouts

Description                Features that are used on sloping roads or other linear projects to reduce flow length and to direct runoff from a disturbed area into stabilized areas.

Waterbars are constructed at an angle across the road or disturbed area to prevent water from running a long distance and causing erosion, and to direct runoff into stabilized areas.

Runouts or Turnouts are breaks in a roadside ditch to allow water to exit the ditch and discharge into a stabilized area. This reduces erosion potential and sediment accumulation in the ditch.

Applications              Use on dirt or gravel roads, or other longer disturbed areas with a slope, to prevent rills from forming.

Limitations                 May require rebuilding after large storms or if driven over while soil is saturated.

Performance and Longevity

• Good results for spreading out runoff flows and thereby reducing erosion.
• Longevity is good, dependent on traffic and storm events.

Design and Construction Guidance

Spacing between waterbars and runouts should be based upon site conditions and surface material. General spacing guideline is as follows:

• Waterbars should have a small dip on the uphill side to convey runoff along the base of the waterbar. They should cross the road at a 30 degree angle to the road. This angle prevents excess sediment buildup and reduces the chances of the water jumping the bar.
• Runouts – construct at a frequency to allow water to leave the roadway at regular intervals (see above). Cut an exit in the roadside channel and stabilize the exit as below if needed. When possible, flatten out the outflow area rather than channelizing it.
• If needed install rock or TRM stabilized outlet or other method per design.

Inspection and Maintenance

• Check that runouts and waterbars are graded properly to drain towards a stabilized outlet, and are the proper size and distance apart.
• Inspect for erosion blowouts after rainfall. Backfill and compact any rills that may form.

What not to do…

Notice how waterbars are ineffective in diverting and reducing erosive velocity of water.  Loose uncompacted soil was used and waterbars were not installed at an approximate 30 degree angle to the road. Water jumped the bars and was not diverted.

Terracing

Description                Gradient Terracing is a term used to describe a ridge and channel arrangement constructed across the face of a slope at regular intervals. This break in grade

shortens slope lengths. Each “step” catches material which sloughs from above, and provides a level site where vegetation can become established. Storm water runoff is captured and redirected to a stable outlet. Terracing slopes reduces erosion by decreasing runoff velocities, trapping sediment, increasing water infiltration and promoting vegetative cover.

Applications              ·      Gradient terracing is useful on longer, steeper slopes that have been cleared and are prone to erosion problems.

• Stair-step grading is useful in areas containing rock.
• Should be used when there is a need for reduction in water flow velocity.

Limitations                 ·      Terracing is not suitable for use on sandy or thin cover soils, or on

excessively steep slopes, and may cause sloughing if too much water

infiltrates the soil.

• Terracing requires stable runoff outlets.
• Soils should be stabilized with vegetation post construction
• Terracing for long slopes may require an engineered slope stabilization design.

Performance and Longevity

Terraces are generally meant to be permanent, though they can be used in soil staging piles as well.

Design and Construction Guidance

• Terraces can be simple breaks in the slope or an engineered design with rundowns.
• Stair steps should be wide enough to work with standard earth moving equipment. Though in some cases narrow terraces and the use of hand tools may be sufficient.
• Make the vertical cut distance less than the horizontal distance.
• Slightly slope the horizontal step slightly inclined back towards the hill.

Terrace spacing

• Terraces should not be constructed completely along the contour, they should slope slightly downhill to direct water towards the stabilized rundown.
• Place fill slopes with a gradient steeper than 3:1 in lifts not to exceed 8 in. and make sure each lift is properly compacted.
• Install slope drain piping or rock or TRM stabilized rundown per design.
• If desired to further slow runoff, roughen the face of the slopes using tracking or create shallow grooves using normal tilling, disking, or harrowing to create a series of ridges and depressions that run across the slope and on the contour. Make grooves formed by such implements close together, less than 10 in. and not less than 1 in. deep.
• Apply seed, fertilizer, and mulch according to LANL Construction Specifications.

Inspection and Maintenance

• Check that terraces are graded properly to drain backwards into the hill and to run towards a stabilized outlet.
• Inspect that stabilization measures such as vegetation are installed and functioning.
• Inspect slopes for erosion blowouts after rainfall.
• Take action as necessary to ensure proper drainage and slope stability. Backfill and compact any rills that may form.

What not to do…

Water must run along the contour and not jump the terraces.

Surface Roughening

Description                The use of mechanized equipment to provide a rough texture to soil surfaces.

Applications              Used on bare soil surfaces on a slope. Surface roughening or scarification is a technique used for creating unevenness on bare soil to help prevent slope erosion and formation of rills.

Limitations                 Does not permanently stabilize area.

Performance and Longevity

Design and Construction Guidance

• Roughening methods with agricultural equipment include tilling, disking, and harrowing.
• Tracking with equipment MUST BE DONE UP AND DOWN THE SLOPE.
  • Factors to be considered in choosing roughening or tracking include slope steepness, long term slope maintenance and mowing requirements, type of soil, and whether the slope is formed by cutting or filling.
  • Roughening can be performed during any stage of grading activity.

• Grooves should be less than 10 inches apart and not less than one inch deep.
• Apply fertilizer, mulch, top soil, or other soil amendments as necessary after surface roughening.

Inspection and Maintenance

• Check that roughening was performed in the correct direction.
• Check for erosion and rilling to be repaired.

What not to do…

Note that the exposed slope was graded with no tracking. This allowed storm water runoff to concentrate and form rills in the soil.

Note that the slope was track-walked in the wrong direction. This will cause rills to

form as water will be allowed to follow the grooves in the soil and gain velocity causing erosion. Track walking with machinery up and down the slope creates grooves that will catch seed and fertilizer and will promote mulch cover to stay on the slope. It will also slow water velocity and reduce runoff and erosion.

Sediment Traps

Description               Sediment traps are typically excavated depressions or naturally low areas with earthen embankments, or other similar structures, surrounding all or a portion of the trap footprint. They are used to detain storm water runoff to facilitate the settling of suspended sediment prior to release of the runoff. Sediment is

deposited and retained in an area of specified size identified as a settling zone. The amount of sediment retained, as well as the particle size of the retained sediment, is dependent upon soil characteristics and runoff detention time. Traps also help to reduce runoff velocity through detention, and runoff is generally released from a sediment trap via a spillway that functions similar to a weir and through infiltration into the soil. Sediment traps are most commonly used as temporary BMPs.

Sediment traps are used to detain storm water runoff to facilitate the settling of suspended sediment and to release it at a reduced rate through a controlled outlet structure. The ponding of storm water allows sediment to drop out.

Sediment accumulations must be removed periodically. Sediment traps are typically smaller in size than basins and do not have pipe outlets.

Applications             ·      At locations where runoff velocity or sediment deposition is a concern.

• At locations of concentrated flow.
• At locations where site runoff, either during or after construction, must be released at a specified rate.

Limitations                ·      A single sediment trap should only be used for small drainage areas.

• Use of sediment traps for large drainage areas will require the construction of a series of coordinated traps.
• Sediment traps are typically temporary BMPs. Use of traps as permanent structures will require regular and frequent inspection and maintenance.
• Water cannot be ponded on SWMUs at LANL and must be released within 96 hours.

Performance and Longevity

Design and Construction Criteria

• Sediment trap cut and fill slopes should have a maximum slope of 3:1.
• Sediment traps shall not be located within a natural watercourse.
• Traps shall not be used as permanent structures.
• Sediment trap outflow must discharge through a stabilized low point.
• Spillways should be designed to provide the trap with a minimum 1.5 foot settling zone and 1 foot sediment storage zone.
• Embankment fill material should be placed in 6 inch lifts and compact each lift with a compactor or the appropriate earth moving equipment.
• Stabilize the trap embankment, with seed and erosion control blankets, seed and hydromulch, or other appropriate stabilization.
• The basin entrance should be as far as practicable from the outlet to maximize time for runoff detention and sediment settling.
• Ensure drainage basins fully discharge within 96 hours by releasing runoff through a control structure or through infiltration into the soil.

Inspection and Maintenance

• Ensure that outlet and spillway are lower than pond edges and are adequately stabilized
• Inspect for effectiveness in controlling storm water runoff and sediment settling.
• Inspect inlet, outlet and embankment slopes for damage such as vegetation loss, bank stability, debris build-up, erosion, and rock displacement.
• Remove accumulated sediment when it exceeds 25% of the design sediment storage volume.
• Removed sediment accumulations shall not be placed within any drainage, either above or below the trap to prevent future migration from storm water runoff.
• Removed sediment shall be stabilized to prevent future migration from storm water runoff.
• Potentially contaminated sediment may require disposal.

What not to do…

There is no defined/armored pathway for water to flow in and out of the pond.

Storm Water Detention Basins

Description               Storm water detention basins are typically excavated depressions or naturally low areas with earthen embankments, or other similar structures, surrounding all or a portion of the basin footprint. They may also be underground systems located

beneath asphalt or concrete surfaces. Underground systems can be comprised of concrete, corrugated metal pipe, or high density polyethylene material in various geometric configurations.

Detention basins are used to detain storm water runoff to facilitate the settling of suspended sediment and to release runoff at a reduced rate through a controlled outlet structure. The ponding of storm water allows sediment to drop out.

Sediment accumulations must be removed periodically.

Applications             ·      At locations where runoff velocity or sediment deposition is a concern.

• At locations of concentrated flow.
• At locations where site runoff, either during or after construction, must be released at a specified rate.

Limitations                ·      Required basin size is highly dependent upon the ground cover and associated runoff characteristics of the surrounding drainage area. If areas surrounding the basin are developed after the basin is constructed the basin may not be adequate in size to handle increased flows.

• Basins can require a significant area to accommodate the runoff storage area, maintenance access, and the control structure.
• Basins will require an engineered design.
• If areas surrounding the basin are developed after the basin is constructed the basin may not be adequate in size to handle increased flows.
• Water cannot be ponded on SWMUs at LANL and must be released within 96 hours.

Performance and Longevity

Design and Construction Criteria

• Detention basins should be designed by a qualified engineer.
  • Basins should be located where loss of containment would not cause loss of life or property damage, and shall not be located in a natural watercourse.
  • Consider, based on site conditions, the installation of a trash rack on the top of control structure standpipes to minimize the potential for entry of debris into the pipe.
  • Provide an emergency spillway with the crest elevation being a minimum of six inches lower than the top of the basin berm. Ensure that the emergency spillway is stabilized with concrete, filter fabric and rock, turf reinforcement mat, or other appropriate material.
  • Embankment fill material should be placed compacted prior to stabilization.
    • Ensure that fill material for embankments is free of roots, woody vegetation, and large stones.
    • Stabilize the basin and basin embankment, with seed and erosion control blankets, seed and hydromulch, or other appropriate stabilization.
    • Design the basin configuration to facilitate future maintenance.
      • Ponding depth should be based on settling zone size and projected fall velocity of the minimum sediment size.
      • The basin entrance should be as far as practicable from the outlet to maximize time for runoff detention and sediment settling.
      • Ensure drainage basins fully discharge within 96 hours by releasing runoff through a control structure or through infiltration into the soil.
      • The lowest drain hole on the riser pipe should be a minimum of 6” above the ground surface to facilitate settling of suspended sediment.
      • Provide appropriate BMPs at the outlet of basin control structure.
        • Basins shall be constructed prior to the start of any major land disturbing activities.

Inspection and Maintenance

• Closely inspect embankments for undermining, erosion, or other damage.
  • Ensure that outlet and spillway are lower than pond edges and are adequately stabilized
  • Inspect for effectiveness in controlling storm water runoff and sediment settling.
  • Inspect inlet, outlet and embankment slopes for damage such as vegetation loss, bank stability, debris build-up, erosion, and rock displacement.

• Ensure standpipe drain holes are clear of debris or other matter that would restrict flow.
• Remove accumulated sediment when it exceeds 25% the design sediment storage volume.
• Removed sediment accumulations shall not be placed within any drainage, either above or below the basin to prevent future migration from storm water runoff.
• Removed sediment shall be stabilized to prevent future migration from storm water runoff.
• Potentially contaminated sediment may require disposal.

What not to do…

Embankments of pond should be stabilized following initial grading of pond.

Standpipe overflow height is higher in elevation than the basin spillway.

Revegetation                                                                                      

Description          Revegetation is the establishment of short-term or long-term vegetative cover, through seeding, on disturbed surfaces or other areas that pose a high risk of erosion. Seeding can provide temporary or permanent stabilization with reduced

erosion, runoff, and sediment transport. Temporary seeding can be used on any temporary earthen structure, construction sites, topsoil stockpiles, etc. Typical areas appropriate for permanent seeding include denuded areas where long-term vegetative cover is desired, buffer areas, steep slopes, stream banks, and areas where soils are unstable.

Applications        · Temporary or permanent stabilization at construction sites, topsoil stockpiles, etc.

• Denuded areas where long-term vegetative cover is desired, buffer areas, steep slopes, stream banks, and areas where soils are unstable.

Limitations           · Establishment of vegetation can take one or more growing seasons and is dependent upon growing conditions (temperature, rainfall, soils, etc.).

• May require ongoing irrigation and maintenance to establish vegetation.
  • Incorrect revegetation methods may inhibit growth and may not be fully evident until after the growing season.
  • Effectiveness can be greatly reduced if rills or gullies are allowed to form underneath blankets, or if hydromulch is subject to concentrated flows.
  • Soil may require agronomic evaluation and/or amendment before revegetation can be successfully implemented or established.

Performance and Longevity

Design Criteria and Construction Specifications

Design Criteria: Use LANL Master Specification 32 9219 for detailed guidance on seedbed preparation, applicable seed mixes, seeding operations, application rates, and mulch cover products. (http://engstandards.lanl.gov/specs/32_9219R3.doc)

• Seeding should be initiated as soon as practicable following completion of soil disturbing activities.
• Permanent seeding should be applied prior to seasonal rains or freezing weather.
• If soil is compacted, loosen soil with disking, raking or harrowing. Remove large clods and stones, or other foreign material that would interfere with seeding equipment and installation of erosion control blankets (ECB).
• If seeding requires harrowing, tracking, or furrowing, these activities shall be conducted horizontally across the face of the slope.
• Native species appropriate to site conditions should be used wherever possible.
  • Seed shall be applied uniformly using calibrated broadcast spreaders, mechanical drills, or hydroseeders.
  • Do not seed during windy weather, or when topsoil is dry, saturated or frozen.
    • Apply slow-release organic fertilizers in accordance with manufacturer recommended rates.
    • The application of mulch shall immediately follow seeding.
      • Apply hydromulch and soil amendments in accordance with manufacturer’s specifications.
      • Select appropriate mulch material or erosion control blanket based on slope, required longevity, irrigation or non-irrigation, and site and soil conditions.
      • If hydraulically applying mulch as part of the broadcast seeding process, use a 2-step process. Apply seed with a tracer. Once seed is applied, apply full complement of mulch. This will allow seed to be in good contact with soil surface and not suspended in the mulch matrix.
      • Mix hydromulch slurry in a tank with an agitation system and spray, under pressure, uniformly over soil surface.
      • Lay ECBs loosely and maintain direct contact with the soil. Do not place over protruding objects; rocks, bushes, etc.
      • Install storm water diversion and conveyance controls as needed to divert concentrated flows away from seeded areas.

Inspection and Maintenance

ECB and Hydromulch Usage Table

• Ensure seed and mulch is applied at the specified rate.
• Inspect seeded area for uniform application of seed and mulch.
  • For hydromulch applications on slopes, inspect the mulch application from multiple directions (i.e., looking both up and down the slope) to ensure uniform application and no “shadowing” (absence of mulch on the back side of a furrow caused by spraying hydromulch from only one direction).
  • Ensure ECBs are properly trenched, overlapped, and anchored. Check that rocks, sticks, or vegetation are not interfering with the blanket’s contact with the ground.
  • Ensure that ECBs have been placed such that they maintain contact with the ground surface.
  • Inspect seeded area for evidence of erosion (rills, gullies).
    • Check for erosion and undermining. Backfill and compact any rills. Install storm water diversion and conveyance controls as needed to divert concentrated flows away from seeded areas.
    • Repair torn or windblown blankets.
      • Inspect reseeded areas for uniform growth of vegetation. Check for areas for damage by vehicles or other equipment.
      • Install storm water diversion and conveyance controls as needed to divert concentrated flows away from seeded areas.

Visual Key for Proper Application (Flexterra-FGM shown)

Proper Application: 3,000 lb/acre – 4.1 mm thick

Improper Application (thin)

What not to do…

Properly prepare seed bed and ensure mulch or blanketing is installed correctly in order to promote vegetation growth and control erosion.

Temporary Stabilization

Description                 Temporary stabilization is used for short-term stabilization; when it is known that the area will be disturbed again or when stabilization methods such as seeding are out

of season. The use of rock or recycled wood chip mulch can break up raindrop impact. Hydromulch can be used without seed to provide short-term erosion protection. Dust control additives such as gorilla snot bind the clay particles to provide short-term erosion protection.

Applications              ·      Efficient method of providing immediate, temporary erosion control.

• Use to stabilize a site during winter until seeding can begin.
• Stabilize a portion of a site or soil piles until final grading occurs.

Limitations                 ·      Not a permanent control; re-application may be required throughout the season to achieve effective erosion control.

• Not appropriate during all seasons.

Performance and Longevity

Performance is not as good as permanent stabilization for erosion control; temporary stabilization generally only lasts for a season. Rock and wood mulch last longer but should not be used alone as permanent stabilization.

Design Criteria and Construction Specifications

• Rock mulch should be applied in a thin layer if it is meant to be used in conjunction with seeding in the future.
• Install hydromulch per manufacturer’s recommendations. Select a type of mulch based on longevity needs.
• Temporary seeding can be done with cover crops (e.g., annual barley, oats, winter rye, etc.) or sterile, non-invasive annual species such as Quickguard sterile triticale hybrid or Regreen. See Revegetation Section 5.1 for seeding guidelines.
• Recycled wood mulch (MSS has equipment) can be applied as temporary stabilization in areas that do not receive concentrated flows.

Inspection and Maintenance

• Check for erosion and undermining.
• Backfill and compact any rills.
  • Storm water diversion and conveyance controls may be installed to divert concentrated flows away.
  • Reapply hydromulch or dust suppression substances as necessary if temporary stabilization period is extended.

What not to do…

Base course should not be used for stabilization in areas of high flow.

Hydromulch should not be applied too lightly or in areas of high flow.

Rolled Erosion Control Products

Combinations and Alternatives

Turf reinforcement mats (TRMs) may be used in conjunction with temporary or permanent sediment and erosion control BMPs to promote vegetation growth. Areas where TRMs are applied should be seeded prior to installation.

Erosion Control Blankets (ECBs) may be used in conjunction with temporary or permanent sediment and erosion control BMPs to promote vegetation growth. Areas where ECBs are applied should be seeded prior to installation.

Description                Turf reinforcement mats are a long term non-degradable rolled erosion control product (RECP) comprised of UV stabilized, non-degradable, synthetic fibers or nettings. TRMs are especially useful in areas such as channels that receive higher velocity flows and on slopes requiring immediate permanent soft stabilization.

TRMs can enhance the natural ability of vegetation to protect soil from erosion.

Erosion control blankets are generally a machine produced mat of organic, biodegradable mulch such as straw, curled wood fiber (excelsior), coconut fiber or a combination thereof, evenly distributed on or between photodegradable polypropylene or biodegradable natural fiber netting. ECBs are used to temporarily stabilize and protect disturbed soil from raindrop impact and surface erosion, to increase infiltration, decrease compaction and soil crusting, and to conserve soil moisture. Mulching with erosion control blankets will increase the germination rates for grasses and legumes and promote vegetation establishment. Erosion control blankets also protect seeds from predators; reduce desiccation and evaporation by insulating the soil and seed environment.

Applications              TRMs:

• TRMs may be used in areas where hard armoring or impervious lining would be required.
• Excellent for stabilizing soil in high shear stress/velocity channels or any area exposed to high volume or high velocity storm water runoff such as drainage ditches and runoff conveyance systems. TRMs may be used in channels where shears are up to 11 lbs/ft² and velocities range up to 20 ft/sec.

• May be used on slopes requiring immediate permanent soft stabilization.
• Remain in place as permanent stabilization.
• Helps establish and maintain vegetative cover.

Limitations                 ·      The slopes must be uniform and relatively smooth before installation to ensure complete contact with the soil.

• Should not be used when anticipated hydraulic conditions are beyond the limits of TRMs.
• ECBs will often mask slope failures from all but the most intense scrutiny until erosion is too far along to effectively treat the slope with spot methods.
  • Erosion control blankets are generally more expensive than hydroseeding.

Performance and Longevity

Design Criteria and Construction Specifications

Site preparation is essential to ensure that RECPs perform as intended and remain in close contact with the soil. Ensure soil amendments are applied as necessary and seed according to LANL Master Specifications Section 32 9219 Seeding. Choose the appropriate turf reinforcement mat for a channel based on the calculated shear stress and water velocities.

Anchoring:

• U-shaped wire staples, metal geotextile stake pins, or triangular wooden stakes can be used to anchor mats to the ground surface. Wire staples should be a minimum of 11 gauge. Metal stake pins should be 3/16 inch diameter steel with a 1 1/2 inch steel washer at the head of the pin. Wire staples and metal stakes should be driven flush to the soil surface. All anchors should be 6-8 inches long and have sufficient ground penetration to resist pullout. Longer anchors may be required for loose soils.

Installation of TRM or ECB on Slopes:

• Begin at the top of the slope and anchor the RECP in a 6 inch deep x 6 inch wide trench. Backfill trench and tamp earth firmly.
• Unroll RECP downslope in the direction of the water flow.
• The edges of adjacent parallel rolls should be overlapped 2-3 inches and be stapled every 3 feet.
• When RECP must be spliced, place mats end over end (shingle style) with 6 inch overlap. Staple through overlapped area, approximately 12 inches apart.
• Lay RECP loosely and maintain direct contact with the soil – do not stretch or allow “tenting” of the material.

• RECP should be stapled sufficiently to anchor mat and maintain contact with the soil.
• Staples should be placed down the center and staggered with the staples placed along the edges.

Installation of TRM in channels:

• Dig initial anchor trench 12 inches deep and 6 inches wide across the channel at the lower end of the project area.
• Excavate intermittent check slots, 6 inches deep and 6 inches wide across the channel at 25-30 foot intervals along the channel.
• Cut longitudinal channel anchor slots 4 inches deep and 4 inches wide along each side of the installation to bury edges of matting. Whenever possible extend matting 2-3 inches above the crest of channel side slopes.
• Beginning at the downstream end and in the center of the channel, place the initial end of the first roll in the anchor trench and secure with fastening devices at 1 foot intervals.
• In the same manner, position adjacent rolls in anchor trench, overlapping the preceding roll a minimum of 3 inches.
• Secure these initial ends of mats with anchors at 1 foot intervals, backfill and compact soil.
• Unroll center strip of matting upstream.
• Unroll adjacent mats upstream in similar fashion, maintaining a 3 inch overlap.
• Shingle-lap spliced ends by a minimum of 1 foot with upstream mat on top to prevent uplifting by water
• Anchor overlapped area by placing two rows of anchors, 1 foot apart on 1 foot intervals.
• Place edges of outside mats in previously excavated longitudinal slots, anchor and backfill and compact soil.
• Anchor, fill and compact upstream end of mat in a 12 inch x 6 inch terminal trench.
• Secure mat to ground surface using U-shaped wire staples, geotextile pins, or wooden stakes.

Inspection and Maintenance

• All mats should be inspected periodically following installation.
  • Inspect mats after significant rain events to check for erosion and undermining. Any failure should be repaired immediately.
  • If washout or breakage occurs, re-install the material after repairing the soil damage

What not to do…

TRM installation was not continued along swale where water flow is concentrated, causing erosion.

Properly anchor blanketing on a properly prepared surface.

Dust Suppression

Description                Dust control measures are implemented to prevent the soil from leaving the site. Dust control practices include minimization of soil disturbance, water application, mulching, establishing vegetation, and using soil stabilizers or tackifiers.

Applications              Apply dust suppression techniques on any site subject to wind erosion and off- site tracking, especially at construction sites and on roads.

Limitations                 Some temporary dust controls must be reapplied and/or maintained frequently.

Performance and Longevity

Design Criteria and Construction Specifications

• Mulch- Can reduce wind erosion by up to 80 percent.
  • Tillage – Roughening the soil can reduce soil losses by approximately 80 percent in some situations.
  • Soil Stabilizers – Effectiveness of polymer stabilization methods range from 70 percent to 90 percent.

• Water Application: Sprinkling the ground surface with water is an effective dust control method for roads. If this method is to be employed at a construction site, it is recommended that a proper construction entrance/exit be created to prevent tracking sediment off-site.

Inspection and Maintenance

What not to do…

• Apply water in a manner that does not result in runoff from the site.
  • Soil Stabilizers: select product and application based on site conditions and required longevity. Apply in accordance with manufacturer’s recommendations.
  • MgClshould not be used at LANL.
    • Tillage: This practice roughens the soil and brings clods to the surface. Plowing should begin on the windward side of the site using chisel-type plows spaced about 12 inches apart, spring-tooth harrows, or similar plows.

• If dust is blowing, reapply.
• Temporary dust control measures, such as water, require frequent renewal.

Dust control was not applied sufficiently.

Gabions

Description                A gabion is wire enclosed riprap that forms a pervious structure designed to stabilize and protect channels and slopes subject to erosion. By trapping sediment between the stones, gabions also facilitate vegetative growth. The

traditional gabion is a rectangular basket used as a building block for retaining walls and grade control structures. Gabion mattresses, which are not as thick as traditional gabions, are used to line storm drain outlets and channel side slopes and bottoms. The wire used in gabion construction is typically double-twist, hexagonal mesh or welded wire.

Applications              In channels for permanent stabilization.

Limitations                 ·      Proper design is essential.

• Expensive and difficult to install.

Performance and Longevity

Design Criteria and Construction Specifications

Gabion installation should be designed and specified by qualified personnel in accordance with engineering specifications. Installation shall be completed in accordance with the design requirements and manufacturers’ standards and specifications. Additional general information on gabion installation follows:

• Stones are usually rounded river rock and are well graded to promote interlocking.
• Gabions should be filled with minimum of 3-5 inch stone.
• Gabion mattresses should be filled with 4-8 inch stone.
• Baskets shall be constructed of wire mesh specified for this purpose and baskets are attached to each other with proper fasteners.
• Filter fabric must be used underneath the gabions.
  • Connect joints of the filter fabric with a minimum overlap of 1 foot and space anchor pins approximately every 3 feet along the overlap.
  • The ends of the filter fabric shall be buried to a minimum depth of 12 inches.
  • Use steel railroad rails, standard weight galvanized steel pipe or steel angles minimum 4” × 4” × 3/8 in. for stakes to anchor to the ground.
  • Gabion installation should be done in accordance with the design.
  • For channel stabilization place in a trench excavated to 24 in below the toe of the slope of the Embankment or side of channel. Brush, trees, stumps, and other objects that would interfere with placement should be removed. Excavate loose material as necessary to establish a stable foundation for each structure.
  • Gabions and gabion mattresses shall be secured to the stream bank or stream bed.
  • Place riprap stones in lifts a maximum of 12 inches thick forming a continuous blanket. Some hand placement is necessary to fill in gaps and voids and avoid bulging.
  • When gabions are assembled, corners should be first joined together. Untied edges shall be assembled by tying with lacing wire or approved fasteners. Gabion baskets should be joined to each other along adjacent edges, both horizontally and vertically.

Inspection and Maintenance

• Check that filter fabric was used under the gabion.
• Check that gabion is anchored to the ground.
• Check that gabions are fastened to each other.
• Check that baskets are adequately filled with no voids or bulges.
• Check that adjacent slopes have been filled adequately to prevent erosion and scour around the edges of the structure.
• Inspect for erosion and scour around and beneath the gabions.
• Check for excessive slumping, gabions are flexible and minor settling can be accommodated.
• Check for corroding wire mesh.
• Check for excessive growth of bushes, trees and other vegetation that may damage gabions.

What not to do…

Obstructions not removed from channel before gabion was installed. No filter fabric under the gabions. Scour under the gabions.

Riprap

Description                Riprap is a permanent, erosion-resistant layer made of stones. It is intended to protect soil from erosion in areas of concentrated runoff. Riprap generally consists of crushed rock and for added effectiveness may be placed on filter

fabric on a prepared surface. The individual stones are typically angular in shape and well graded to promote interlocking.

Applications              · Riprap is effective in protecting culvert inlets and outlets and preventing scouring and undercutting.

• Useful in the stabilization of stream or channel banks and drainage channels.
• Can be used to stabilize cut and fill slopes, storm drains and slope drains.
• Should be considered where perennial flows or frequent ponding would drown a vegetated lining.

Limitations                 ·      Proper design and stone selection for expected flow velocity is essential.

• Should not be placed on slopes greater than 1.5:1.
• Cost may be a prohibitive factor in large scale applications.
• Difficult to remove sediment accumulations.

Performance and Longevity

Design Criteria and Construction Specifications

• Riprap installations should be designed and specified by qualified personnel in accordance with the LANL ESM Section G10 6.0.E.7.a.
• Use stones angular in shape and well graded to promote interlocking.
• Filter fabric must be used underneath.
  • Connect filter fabric joints with a minimum overlap of 1 foot and space anchor pins approximately every 3 feet along the overlap.
  • The ends of the filter fabric shall be buried to a minimum depth of 12 inches.
  • Brush, trees, stumps, and other objects that would interfere with riprap placement should be removed.
    • Place riprap stones forming a continuous blanket to minimum thickness of 12 inches.
    • Place the riprap in a trench excavated to 24 inches below the toe of the slope of the embankment or side of channel.

Inspection and Maintenance

• Check that filter fabric was used under the riprap.
• Check that riprap installed in a channel has a low point in the center to prevent flows from going around the rock.
• For riprap aprons, inspect for erosion around the riprap and dislodgment of stones.
• Check for slumping on hillsides.
• Check for scour or undermining – replace or reposition riprap as necessary.

What not to do…

Properly installed riprap at culvert outlet will control erosion.

Permanent Capping

Description                Permanent capping can be achieved using asphalt, concrete, geotextile, clay or soil with vegetative cover. Permanent caps are used when no other alternative

is available to prevent pollutants at a site from leaving. Permanent capping is used to isolate areas of potential soil contamination from storm water. Used when no infiltration or erosion is allowed.

Applications              Permanent capping is used when no other alternative is available to prevent pollutants at a site from leaving.

Limitations                 Expensive engineered control.

Performance and Longevity

Design Criteria and Construction Specifications

Permanent Caps will be designed and inspected by an engineer at the time of installation.

Materials:

• Material used for capping must be obtained from an uncontaminated source.

Installation:

• Earthen caps must be at least 24 inches thick and should be vegetated or covered with rock or gravel to protect the cap from erosion.
• Asphalt caps should be a minimum of 4 inches thick.