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23-105227-CSWPPP-10.27.23.pdfSECTION C.3 CONSTRUCTION STORMWATER POLLUTION PREVENTION (CSWPP) MEASURES The above measures must be implemented as needed to prevent the discharge of sediment-laden water and other pollutants from the construction site. Proposed measures must be shown on the Simplified site CSWPP plan required to be submitted with the Simplified drainage plans. Site-specific conditions during construction may require additional measures as deemed necessary by DPER. As noted in Section C.3 above, other ESC and/or SWPPS measures found in Appendix D of the SWDM may be needed or may be more appropriate for the project site as determined by DPER. C.3.1 STABILIZED CONSTRUCTION ENTRANCE Purpose Construction entrances are stabilized to reduce the amount of sediment transported onto paved roads by motor vehicles or runoff by constructing a stabilized pad of quarry spalls at the entrances to construction sites. Application Construction entrances shall be stabilized wherever traffic will be leaving a construction site and traveling on paved roads or other paved areas within 1,000 feet of the site. Design and Installation Specifications 1. See Figure C.3.1.A for details. 2. A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up into the rock pad. The geotextile shall meet the following standards: Grab Tensile Strength (ASTM D4632) 200 lbs min. Grab Tensile Elongation (ASTM D4632) 30% max.(woven) Puncture Strength (ASTM D6241) 495 lbs min. AOS (ASTM D4751) 20-45 (U.S. standard sieve size) 3. Hog fuel (wood based mulch) may be substituted for or combined with quarry spalls in areas that will not be used for permanent roads. The effectiveness of hog fuel is highly variable, but it has been used successfully on many construction sites. It generally requires more maintenance than quarry spalls. Hog fuel is not recommended for entrance stabilization in urban areas. The inspector may at any time require the use of quarry spalls if the hog fuel is not preventing sediment from being tracked onto pavement or if the hog fuel is being carried onto pavement. Hog fuel is prohibited in permanent roadbeds because organics in the subgrade soils cause difficulties with compaction. 4. Whenever possible, the entrance shall be constructed on a firm, compacted subgrade. This can substantially increase the effectiveness of the pad and reduce the need for maintenance. Maintenance 1. Quarry spalls (or hog fuel) shall be added if the pad is no longer in accordance with the specifications. 2. If the entrance is not preventing sediment from being tracked onto pavement, then alternative measures to keep the streets free of sediment shall be used. This may include street sweeping, an increase in the dimensions of the entrance, or the installation of a wheel wash. If washing is used, it shall be done on an area covered with crushed rock, and wash water shall drain to a sediment trap or pond. 3. Any sediment that is tracked onto pavement shall be removed immediately by sweeping. The sediment collected by sweeping shall be removed or stabilized onsite. The pavement shall not be 4/24/2016 2016 Surface Water Design Manual – Appendix C C-108 C.3.1 STABILIZED CONSTRUCTION ENTRANCE cleaned by washing down the street, except when sweeping is ineffective and there is a threat to public safety. If it is necessary to wash the streets, a small sump must be constructed. The sediment would then be washed into the sump where it can be controlled. Wash water must be pumped back onto the site and cannot discharge to systems tributary to surface waters. 4. Any quarry spalls that are loosened from the pad and end up on the roadway shall be removed immediately. FIGURE C.3.1.A STABILIZED CONSTRUCTION ENTRANCE PER KING COUNTY ROAD DESIGN AND CONSTRUCTION STANDARDS (KCRDCS), DRIVEWAYS SHALL BE PAVED TO EDGE OF R-O-W PRIOR TO INSTALLATION OF THE CONSTRUCTION ENTRANCE TO AVOID DAMAGING OF THE ROADWAY. IT IS RECOMMENDED THAT THE ENTRANCE BE CROWNED SO THAT RUNOFF DRAINS OFF THE PAD. PROVIDE FULL WIDTH OF INGRESS/EGRESS AREA IF A ROADSIDE DITCH IS PRESENT, INSTALL DRIVEWAY CULVERT PER KCRDCS GEOTEXTILE 4"- 8" QUARRY SPALLS R=25' MIN. NOTES: 2016 Surface Water Design Manual – Appendix C 4/24/2016 C-109 SECTION C.3 CONSTRUCTION STORMWATER POLLUTION PREVENTION (CSWPP) MEASURES 7/23/2021 2021 Surface Water Design Manual Appendix C C-116 C.3.6 SILT FENCE Purpose Use of a silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use Silt fence may be used downslope of all disturbed areas. Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Design and Installation Specifications 1. See Figure C.3.6.A and Figure C.3.6.B for details. 2. The geotextile used must meet the standards listed below. A copy of the manufacturer's fabric specifications must be available onsite. AOS (ASTM D4751) 30-100 sieve size (0.60-0.15 mm) for slit film 50-100 sieve size (0.30-0.15 mm) for other fabrics Water Permittivity (ASTM D4491) 0.02 sec-1 minimum Grab Tensile Strength (ASTM D4632) (see Specification Note 3) 180 lbs. min. for extra strength fabric 100 lbs. min. for standard strength fabric Grab Tensile Elongation (ASTM D4632) 30% max. (woven) Ultraviolet Resistance (ASTM D4355) 70% min. 3. Standard strength fabric requires wire backing to increase the strength of the fence. Wire backing or closer post spacing may be required for extra strength fabric if field performance warrants a stronger fence. 4. Where the fence is installed, the slope shall be no steeper than 2H:1V. 5. If a typical silt fence (per Figure C.3.6.A) is used, the standard 4 x 4 trench may not be reduced as long as the bottom 8 inches of the silt fence is well buried and secured in a trench that stabilizes the fence and does not allow water to bypass or undermine the silt fence. 6. Silt fences shall be located so as to avoid interfering with the movement of juvenile salmonids attempting to enter off-channel areas or drainages. Maintenance Standards 1. Any damage shall be repaired immediately. 2. If concentrated flows are evident uphill of the fence, they must be intercepted and conveyed to a sediment trap or pond. 3. It is important to check the uphill side of the fence for signs of the fence clogging and acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence or remove the trapped sediment. 4. Sediment must be removed when the sediment is 6 inches high. 5. If the filter fabric (geotextile) has deteriorated due to ultraviolet breakdown, it shall be replaced. C.3.6 SILT FENCE 2021 Surface Water Design Manual Appendix C 7/23/2021 C-117 FIGURE C.3.6.A SILT FENCE FIGURE C.3.6.B SILT FENCE INSTALLATION AND MAINTENANCE 2"X2" BY 14 Ga. WIRE OR EQUIVALENT, IF STANDARD STRENGTH FABRIC USED NOTE: FILTER FABRIC FENCES SHALL BE INSTALLED ALONG CONTOURS WHENEVER POSSIBLE JOINTS IN FILTER FABRIC SHALL BE SPLICED AT POSTS. USE STAPLES, WIRE RINGS OR EQUIVALENT TO ATTACH FABRIC TO POSTS. FILTER FABRIC BACKFILL TRENCH WITH NATIVE SOIL OR 3/4" TO 1-1/2" WASHED GRAVEL MINIMUM 4"x4" TRENCH 2"x4" WOOD POSTS, STEEL FENCE POSTS, REBAR, OR EQUIVALENT POST SPACING MAY BE INCREASED TO 8' IF WIRE BACKING IS USED 6' MAX. SECTION C.3 CONSTRUCTION STORMWATER POLLUTION PREVENTION (CSWPP) MEASURES 7/23/2021 2021 Surface Water Design Manual Appendix C C-120 C.3.9 STORM DRAIN INLET PROTECTION Purpose Storm drain inlets are protected to prevent coarse sediment from entering storm drainage systems. Temporary devices around storm drains assist in improving the quality of water discharged to inlets or catch basins by ponding sediment-laden water. These devices are effective only for relatively small drainage areas. Conditions of Use 1. Protection shall be provided for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless the runoff that enters the catch basin will be conveyed to a sediment pond or trap. 2. Inlet protection may be used anywhere at the applicant's discretion to protect the drainage system. This will, however, require more maintenance, and it is highly likely that the drainage system will still require some cleaning. 3. The contributing drainage area must not be larger than one acre. Design and Installation Specifications 1. There are many options for protecting storm drain inlets. Two commonly used options are filter fabric protection and catch basin inserts. Filter fabric protection (see Figure C.3.9.A) is filter fabric (geotextile) placed over the grate. This method is generally very ineffective and requires intense maintenance efforts. Catch basin inserts (see Figure C.3.9.B) are manufactured devices that nest inside a catch basin. This method also requires a high frequency of maintenance to be effective. Both options provide adequate protection, but filter fabric is likely to result in ponding of water above the catch basin, while the insert will not. Thus, filter fabric is only allowed where ponding will not be a traffic concern and where slope erosion will not result if the curb is overtopped by ponded water. Trapping sediment in the catch basins is unlikely to improve the water quality of runoff if it is treated in a pond or trap because the coarse particles that are trapped at the catch basin settle out very quickly in the pond or trap. Catch basin protection normally only improves water quality where there is no treatment facility downstream . In these circumstances, catch basin protection is an important last line of defense. It is not, however, a substitute for preventing erosion. The placement of filter fabric under grates is generally prohibited and the use of filter fabric over grates is strictly limited and discouraged. 2. It is sometimes possible to construct a small sump around the catch basin before final surfacing of the road. This is allowed because it can be a very effective method of sediment control. 3. Block and gravel filters, gravel and wire mesh filter barriers, and bag barriers filled with various filtering media placed around catch basins can be effective when the drainage area is 1 acre or less and flows do not exceed 0.5 cfs. It is necessary to allow for overtopping to prevent flooding. Many manufacturers have various inlet protection filters that are very effective in keeping sediment-laden water from entering the storm drainage system. The following are examples of a few common methods. a) Block and gravel filters (Figure C.3.9.C) are a barrier formed around an inlet with standard concrete block and gravel, installed as follows: Height is 1 to 2 feet above the inlet. Recess the first row of blocks 2 inches into the ground for stability. Support subsequent rows by placing a 2x4 through the concrete block opening. C.3.9 STORM DRAIN INLET PROTECTION 2021 Surface Water Design Manual Appendix C 7/23/2021 C-121 Do not use mortar. Lay some blocks in the bottom row on their side for dewatering the pooled water. Place cloth or mesh with ½ inch openings over all block openings. Place gravel below the top of blocks on slopes of 2:1 or flatter. An alternate design is a gravel donut. b) Gravel and wire mesh filters consist of a gravel barrier placed over the top of an inlet. This structure generally does not provide overflow. Install as follows: Cloth or comparable wire mesh with ½ inch openings is placed over inlet. Coarse aggregate covers the cloth or mesh. Height/depth of gravel should be 1 foot or more, 18 inches wider than inlet on all sides. c) Curb inlet protection with a wooden weir is a barrier formed around an inlet with a wooden frame and gravel, installed as follows: Construct a frame and attach wire mesh (½ inch openings) and filter fabric to the frame. Pile coarse washed aggregate against the wire/fabric. Place weight on frame anchors. d) Curb and gutter sediment barriers (Figure C.3.9.D) consist of sandbags or rock berms (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape, installed as follows: Bags of either burlap or woven geotextile fabric, filled with a variety of media such as gravel, wood chips, compost or sand stacked tightly allows water to pond and allows sediment to separate from runoff. Leave a "one bag gap" in the top row of the barrier to provide a spillway for overflow. Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 x 3 and at least 2 feet from the inlet. Construct a horseshoe shaped sedimentation trap on the outside of the berm to sediment trap standards for protecting a culvert inlet. 4. Excavated drop inlet sediment traps are appropriate where relatively heavy flows are expected and overflow capability is needed. If emergency overflow is provided, additional end-of-pipe treatment may be required. Excavated drop inlets consist of an excavated impoundment area around a storm drain. Sediment settles out of the stormwater prior to enter the drain. Install according to the following specifications: a) The impoundment area should have a depth of 1 - 2 feet measured from the crest of the inlet structure. b) Side slopes of the excavated area must be no steeper than 2:1. c) Minimum volume of the excavated area should be 35 cubic yards. d) Install provisions for draining the area to prevent standing water problems. e) Keep the area clear of debris. f) Weep holes may be drilled into the side of the inlet. g) Protect weep holes with wire mesh and washed aggregate. h) Weep holes must be sealed when removing and stabilizing excavated area. i) A temporary dike may be necessary on the down slope side of the structure to prevent bypass flow. SECTION C.3 CONSTRUCTION STORMWATER POLLUTION PREVENTION (CSWPP) MEASURES 7/23/2021 2021 Surface Water Design Manual Appendix C C-122 Maintenance Standards 1. Any accumulated sediment on or around inlet protection shall be removed immediately. Sediment shall not be removed with water, and all sediment must be disposed of as fill on site or hauled off site. 2. Any sediment in the catch basin insert shall be removed when the sediment has filled one-third of the available storage. The filter media for the insert shall be cleaned or replaced at least monthly. 3. Regular maintenance is critical for all forms of catch basin/inlet protection. Unlike many forms of protection that fail gradually, catch basin protection will fail suddenly and completely if not maintained properly. FIGURE C.3.9.A FILTER FABRIC PROTECTION FIGURE C.3.9.B CATCH BASIN INSERT NOTE: THIS DETAIL IS ONLY SCHEMATIC. ANY INSERT IS ALLOWED THAT HAS: A MIN. 0.5 C.F. OF STORAGE, THE MEANS TO DEWATER THE STORED SEDIMENT, AN OVERFLOW, AND CAN BE EASILY MAINTAINED. OVERFLOW GRATECATCH BASIN POROUS BOTTOM SOLID WALLS FILTER MEDIA FOR DEWATERING CATCH BASIN NOTE: ONLY TO BE USED WHERE PONDING OF WATER ABOVE THE CATCH BASIN WILL NOT CAUSE TRAFFIC PROBLEMS AND WHERE OVERFLOW WILL NOT RESULT IN EROSION OF SLOPES. GRATE STANDARD STRENGTH FILTER FABRIC C.3.9 STORM DRAIN INLET PROTECTION 2021 Surface Water Design Manual Appendix C 7/23/2021 C-123 FIGURE C.3.9.C BLOCK AND GRAVEL CURB INLET PROTECTION 1. USE BLOCK AND GRAVEL TYPE SEDIMENT BARRIER WHEN CURB INLET IS LOCATED IN GENTLY SLOPING SEGMENT, WHERE WATER CAN POND AND ALLOW SEDIMENT TO SEPARATE FROM RUNOFF. 2. BARRIER SHALL ALLOW FOR OVERFLOW FROM SEVERE STORM EVENT. 3. INSPECT BARRIERS AND REMOVE SEDIMENT AFTER EACH STORM EVENT. SEDIMENT AND GRAVEL MUST BE REMOVED FROM THE TRAVELED WAY IMMEDIATELY. 2x4 WOOD STUD OVERFLOW WATER A A PLAN VIEW NTS SECTION A-A NTS BLOCK AND GRAVEL CURB INLET PROTECTION NTS CATCH BASIN COVER CURB INLET CONCRETE BLOCKS CATCH BASIN COVER CURB INLET CATCH BASIN BACK OF SIDEWALK CURB FACE 3/4" DRAIN GRAVEL (20 mm) WIRE SCREEN OR FILTER FABRIC POND HEIGHT WIRE SCREEN OR FILTER FABRIC 2x4 WOOD STUD (100x50 TIMBER STUD) 3/4" DRAIN GRAVEL (20 mm) NOTES: SECTION C.3 CONSTRUCTION STORMWATER POLLUTION PREVENTION (CSWPP) MEASURES 7/23/2021 2021 Surface Water Design Manual Appendix C C-124 FIGURE C.3.9.D CURB AND GUTTER BARRIER PROTECTION SECTION D.2.2 SWPPS MEASURES 7/23/2021 2021 Surface Water Design Manual Appendix D D-84 D.2.2.4 MATERIAL DELIVERY, STORAGE AND CONTAINMENT Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on-site, store materials in a designated area, and install secondary containment. Conditions of Use These procedures are suitable for use at all construction sites with delivery and storage of the following materials: Petroleum products such as fuel, oil and grease Soil stabilizers and binders (e.g. Polyacrylamide) Fertilizers, pesticides and herbicides Detergents Asphalt and concrete compounds Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds Any other material that may be detrimental if released to the environment Design and Installation Specifications The following steps should be taken to minimize risk: 1. Temporary storage area should be located away from vehicular traffic, near the construction entrance(s), and away from waterways or storm drains. 2. Material Safety Data Sheets (MSDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. 3. Hazardous material storage on-site should be minimized. 4. Hazardous materials should be handled as infrequently as possible. 5. During the wet weather season (Oct 1 April 30), consider storing materials in a covered area. 6. Materials should be stored in secondary containments, such as earthen dike, horse trough, or even a -reactive materials such as detergents, oil, grease, and paints. Small 7. Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, and within secondary containment. 8. If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. Material Storage Areas and Secondary Containment Practices: 1. Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities. 2. Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed container volume of all containers, or 110% of the capacity of the largest container within its boundary, whichever is greater. D.2.2.4 MATERIAL DELIVERY, STORAGE AND CONTAINMENT 2021 Surface Water Design Manual Appendix D 7/23/2021 D-85 3. Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours. 4. Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums. These liquids shall be handled as hazardous waste unless testing determines them to be non- hazardous. 5. Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. 6. During the wet weather season (Oct 1 April 30), each secondary containment facility shall be covered during non-working days, prior to and during rain events. 7. Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill clean-up material (spill kit). 8. The spill kit should include, at a minimum: 1-Water Resistant Nylon Bag 3-Oil Absorbent S 2- 12- 1-Pair Splash Resistant Goggles 3-Pair Nitrile Gloves 10-Disposable Bags with Ties Instructions D.2.2.3 SAWCUTTING AND SURFACING POLLUTION PREVENTION 2021 Surface Water Design Manual Appendix D 7/23/2021 D-83 D.2.2.3 SAWCUTTING AND SURFACING POLLUTION PREVENTION Purpose Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high pH (concrete cutting), both of which can violate the water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from entering waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Sawcutting and surfacing operations include, but are not limited to, sawing, coring, grinding, roughening, hydro- demolition, bridge and road surfacing Design and Installation Specifications 1. Vacuum slurry and cuttings during cutting and surfacing operations. 2. Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight. 3. Slurry and cuttings shall not drain to any natural or constructed drainage conveyance including stormwater systems. This may require temporarily blocking catch basins. 4. Dispose of collected slurry and cuttings in a manner that does not violate ground water or surface water quality standards. 5. Do not allow process water generated during hydro-demolition, surface roughening or similar operations to drain to any natural or constructed drainage conveyance including stormwater systems. Dispose process water in a manner that does not violate ground water or surface water quality standards. 6. Handle and dispose cleaning waste material and demolition debris in a manner that does not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter waters of the state. If inspections show that a violation of water quality standards could occur, stop operations and immediately implement preventive measures such as berms, barriers, secondary containment, and vacuum trucks. D.2.2.1 CONCRETE HANDLING 2021 Surface Water Design Manual Appendix D 7/23/2021 D-77 D.2.2.1 CONCRETE HANDLING Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete discharge to surface waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, concrete process water, and concrete slurry from entering waters of the state. Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction projects include, but are not limited to, curbs, sidewalks, roads, bridges, foundations, floors, stormwater vaults, retaining walls, driveways and runways. Design and Installation Specifications 1. Assure that washout of concrete trucks, chutes, pumps, and internals is performed at an approved off- site location or in designated concrete washout areas. Do not wash out concrete trucks, chutes, pumps, or internals onto the ground, or into storm drains, open ditches, streets, or streams. Refer to BMP D.2.2.2 (p. D-78) for information on concrete washout areas. 2. Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site, except in designated concrete washout areas. 3. Wash off hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels into formed areas awaiting future concrete pours only. 4. Do not wash out to formed areas awaiting infiltration BMPs. 5. Wash equipment difficult to move, such as concrete pavers in areas that do not directly drain to natural or constructed stormwater conveyances. 6. Do not allow washdown from areas, such as concrete aggregate driveways, to drain directly to natural or constructed stormwater conveyances. 7. Contain washwater and leftover product in a lined container when no formed areas are available,. Dispose of contained concrete in a manner that does not violate ground water or surface water quality standards. 8. Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface waters. 9. Refer to BMPs D.2.2.7 and D.2.2.8 for pH adjustment requirements. 10. Refer to the Construction Stormwater General Permit for pH monitoring requirements if the project involves one of the following activities: Significant concrete work (greater than 1,000 cubic yards poured concrete or recycled concrete used over the life of a project). The use of engineered soils amended with (but not limited to) Portland cement-treated base, cement kiln dust or fly ash. Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. SECTION D.2.1 ESC MEASURES 7/23/2021 2021 Surface Water Design Manual Appendix D D-70 D.2.1.8 DUST CONTROL Preventative measures to minimize the wind transport of soil shall be taken when a traffic hazard may be created or when sediment transported by wind is likely to be deposited in water resources or adjacent properties. Purpose: To prevent wind transport of dust from exposed soil surfaces onto roadways, drainage ways, and surface waters. When to Install: Dust control shall be implemented when exposed soils are dry to the point that wind transport is possible and roadways, drainage ways, or surface waters are likely to be impacted. Dust control measures may consist of chemical, structural, or mechanical methods. Measures to Install: Water is the most common dust control (or palliative) used in the area. When using water for dust control, the exposed soils shall be sprayed until wet, but runoff shall not be generated by spraying. Calcium chloride, Magnesium chloride, Lignin derivatives, Tree Resin Emulsions, and Synthetic Polymer Emulsions may also be used for dust control. Exposed areas shall be re-sprayed as needed. Oil shall not be used for dust control. The following table lists many common dust control measures. Some of the measures are not recommended for use in King County and must have prior approval prior to use from the DLS-Permitting inspector assigned to specific projects. D.2.1.8 DUST CONTROL 2021 Surface Water Design Manual Appendix D 7/23/2021 D-71 TABLE D.2.1.8.A DUST CONTROL MEASURES METHOD CONSIDERATIONS SITE PREPARATION RECOMMENDED APPLICATION RATE Water -Most commonly used practice -Evaporates quickly -Lasts less than 1 day For all liquid agents: -Blade a small surface -Crown or slope surface to avoid ponding -Compact soils if needed -Uniformly pre-wet at 0.03 0.3 gal/sq yd -Apply solution under pressure. Overlap solution 6 12 inches -Allow treated area to cure 0 4 hours -Compact area after curing -Apply second treatment before first treatment becomes ineffective 0.125 gal/sq yd every 20 to 30 minutes Salts Calcium Chloride (CaCl) -Restricts evaporation -Lasts 6-12 months -Can be corrosive -Less effective in low humidity -Can build up in soils and leach by rain Apply 38% solution at 1.21L/m2 (0.27 gal/yd2) or as loose dry granules per manufacturer Magnesium Chloride (MgCl) -Restricts evaporation -Works at higher temperatures and lower humidity than CaCl -May be more costly than CaCl Apply 26 32% solution at 2.3 L/m2 (0.5 gal/yd2) Sodium Chloride (NaCl) -Effective over smaller range of conditions -Less expensive -Can be corrosive -Less effective in low humidity Per Manufacturer Silicates -Generally expensive -Available in small quantities -Require Second application Surfactants -High evaporation rates -Effective for short time periods -Must apply frequently Copolymers -Forms semi-permeable transparent crust -Resists ultraviolet radiation and moisture induced breakdown -Last 1 to 2 years 750 940 L/ha (80 100 gal/ac) Petroleum Products -Used oil is prohibited as a dust control method -Bind soil particles -May hinder foliage growth -Environmental and aesthetic concerns -Higher cost Use 57 63% resins as base. Apply at 750 940 L/ha (80-100 gal/ac) Lignin Sulfonate -Paper industry waste product -Acts as dispersing agent -Best in dry climates -Can be slippery -Will decrease Dissolved Oxygen in waterways therefore cannot be used adjacent to surface water systems Loosen surface 25-50 mm (1 2 inches) Need 4-8% fines Vegetable Oils -Coat grains of soils, so limited binding ability -May become brittle -Limited availability Per Manufacturer Spray on Adhesives -Available as organic or synthetic -Effective on dry, hard soils -Forms a crust -Can last 3 to 4 years Per Manufacturer SECTION C.3 CONSTRUCTION STORMWATER POLLUTION PREVENTION (CSWPP) MEASURES 7/23/2021 2021 Surface Water Design Manual Appendix C C-114 C.3.4 PLASTIC COVERING Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of Use 1. Plastic covering may be used on disturbed areas that require cover measures for less than 30 days. 2. Plastic is particularly useful for protecting cut and fill slopes and stockpiles. Note: The relatively rapid breakdown of most polyethylene sheeting makes it unsuitable for long-term applications. 3. Clear plastic sheeting may be used over newly-seeded areas to create a greenhouse effect and encourage grass growth. Clear plastic should not be used for this purpose during the summer months because the resulting high temperatures can kill the grass. 4. Due to rapid runoff caused by plastic sheeting, this method shall not be used upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes. Note: There have been many problems with plastic, usually attributable to poor installation and maintenance. However, the material itself can cause problems, even when correctly installed and maintained, because it generates high-velocity runoff and breaks down quickly due to ultraviolet radiation. In addition, if the plastic is not completely removed, it can clog drainage system inlets and outlets. It is highly recommended that alternatives to plastic sheeting be used whenever possible and that its use be limited. Design and Installation Specifications 1. See Figure C.3.4.A for details. 2. Plastic sheeting shall have a minimum thickness of 0.06 millimeters. 3. If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall be installed at the toe of the slope in order to reduce the velocity of runoff. FIGURE C.3.4.A PLASTIC COVERING TIRES, SANDBAGS, OR EQUIVALENT MAY BE USED TO WEIGHT PLASTIC SEAMS BETWEEN SHEETS MUST OVERLAP A MINIMUM OF 12" AND BE WEIGHTED OR TAPED TOE IN SHEETING IN MINIMUM 4"X4" TRENCH PROVIDE ENERGY DISSIPATION AT TOE WHEN NEEDED 10' MAX. 10' MAX. C.3.5 MARK CLEARING LIMITS/MINIMIZE CLEARING 2021 Surface Water Design Manual Appendix C 7/23/2021 C-115 Maintenance Standards for Plastic Covering 1. Torn sheets must be replaced and open seams repaired. 2. If the plastic begins to deteriorate due to ultraviolet radiation, it must be completely removed and replaced. C.3.5 MARK CLEARING LIMITS/MINIMIZE CLEARING Purpose Minimizing clearing is the most effective method of erosion control. Undisturbed vegetation intercepts and slows rainwater. Plant roots hold soil in place, and dead vegetation on the ground acts as a mulch. Applications Clearing limits shall be marked and clearing minimized on any site where significant areas of undisturbed vegetation will be retained. Design Specifications 1. Minimizing clearing should be incorporated into the site design. Clearing limits must be marked on the Simplified site CSWPP plan. 2. On the ground, clearing limits must be clearly marked with brightly colored tape or plastic or metal safety fencing. If tape is used, it should be supported by vegetation or stakes, and should be about 3 to 6 feet high and highly visible. Equipment operators should be informed of areas of vegetation that are to be left undisturbed. 3. The duff layer, native top soil, and natural vegetation shall be retained in an undisturbed state to the maximum extent practicable. If it is not practicable to retain the duff layer in place, it should be stockpiled on-site, covered to prevent erosion, and replaced immediately upon completion of the ground disturbing activities. Maintenance Fencing shall be inspected regularly and repaired or replaced as needed. SECTION C.3 CONSTRUCTION STORMWATER POLLUTION PREVENTION (CSWPP) MEASURES 7/23/2021 2021 Surface Water Design Manual Appendix C C-110 C.3.2 MULCHING Purpose The purpose of mulching soils is to provide immediate temporary protection from erosion. Mulch also enhances plant establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating soil temperatures. There is an enormous variety of mulches that may be used. Only the most common types are discussed in this section. Conditions of Use As a temporary cover measure, mulch should be used: 1. On disturbed areas that require cover measures for less than 30 days 2. As a cover for seed during the wet season and during the hot summer months 3. During the wet season on slopes steeper than 3H:1V with more than 10 feet of vertical relief. Design and Installation Specifications For mulch materials, application rates, and specifications, see Table C.3.2.A. Note: Thicknesses may be increased for disturbed areas in or near critical areas or other areas highly susceptible to erosion. Maintenance Standards 1. The thickness of the mulch cover must be maintained. 2. Any areas that experience erosion shall be re-mulched and/or protected with a net or blanket. If the erosion problem is drainage related, then the drainage problem shall be assessed and alternate drainage such as interceptor swales may be needed to fix the problem and the eroded area re-mulched. C.3.2 MULCHING 2021 Surface Water Design Manual Appendix C 7/23/2021 C-111 TABLE C.3.2.A MULCH STANDARDS AND GUIDELINES Mulch Material Quality Standards Application Rates Remarks Straw Air-dried; free from undesirable seed and coarse material 2"-3" thick; 2-3 bales per 1000 sf or 2-3 tons per acre Cost-effective protection when applied with adequate thickness. Hand-application generally requires greater thickness than blown straw. Straw should be crimped to avoid wind blow. The thickness of straw may be reduced by half when used in conjunction with seeding. Wood Fiber Cellulose No growth inhibiting factors Approx. 25-30 lbs per 1000 sf or 1000-1500 lbs per acre Shall be applied with hydromulcher. Shall not be used without seed and tackifier unless the application rate is at least doubled. Some wood fiber with very long fibers can be effective at lower application rates and without seed or tackifier. Compost No visible water or dust during handling. Must be purchased from supplier with Solid Waste Handling Permit. 2" thick min.; approx. 100 tons per acre (approx. 800 lbs per cubic yard) More effective control can be obtained by increasing thickness to 3". Excellent mulch for protecting final grades until landscaping because it can be directly seeded or tilled into soil as an amendment. Hydraulic Matrices (Bonded Fiber Matrix) This mulch category includes hydraulic slurries composed of wood fiber, paper fiber or a combination of the two held together by a binding system. The BFM shall be a mixture of long wood fibers and various bonding agents. Apply at rates from 3,000 lbs per acre to 4,000 lbs per acre and based on manufacturers recommendations The BFM shall not be applied immediately before, during or immediately after rainfall so that the matrix will have an opportunity to dry for 24 hours after installation. Application rates beyond 2,500 pounds may interfere with germination and are not usually recommended for turf establishment. BFM is generally a matrix where all fiber and binders are in one bag, rather than having to mix components from various manufacturers to create a matrix. BFMs can be installed via helicopter in remote areas. They are approximately $1,000 per acre cheaper to install. Chipped Site Vegetation Average size shall be several inches. 2" minimum thickness This is a cost-effective way to dispose of debris from clearing and grubbing, and it eliminates the problems associated with burning. Generally, it should not be used on slopes above approx. 10% because of its tendency to be transported by runoff. It is not recommended within 200 feet of surface waters. If seeding is expected shortly after mulch, the decomposition of the chipped vegetation may tie up nutrients important to grass establishment.