5_WK_ECP.pdf

EROSION CONTROL PLAN

William Kent Campground Construction 2017

Project Description

William Kent Campground Construction 2017 includes the installation of concrete pathways, drip line trenches, and infiltration basins, as well as the improvement of several camping spurs to decrease erosive potential and increase the quality of user experience. The campground is located 2 miles south of the junction of California State Routes 89 and 28 at Tahoe City.

Temporary BMPs will be employed during all construction activities and current erosion problems will be mitigated with a series of permanent infiltration basins, swales, and berms. Runoff from the campground drains directly into Lake Tahoe, and therefore all necessary precautions shall be taken to insure that erosive materials generated during construction do not leave the site.

Source Identification

1. Potential sources which may be expected to add pollutants to storm water discharges, or which may result in non-storm water discharges from the construction site are the following:

a. Soil disturbance associated with the concrete pathway and camping spur construction.

b. Stockpiled materials.

c. Vehicle circulation.

2. Attached plans indicate all potential areas of disturbance.

Best Management Practices Narrative

The following measures will be taken during construction to prevent off-site discharge:

1. Straw wattles and/or silt fencing will be used down slope of disturbance.

2. Multiple rows of straw wattles will be used in natural swales in the case of precipitation events that are within the project area.

3. Project boundary fencing will prevent unintended vehicle and pedestrian access to areas under construction.

4. Staging areas will be identified for stockpiling and equipment storage.

5. Disturbed areas outside of the final travelway will be covered with 2-4 inches of either pine needle mulch or wood chips. Native materials will be used to naturalize the area.

6. The proposed erosion and sediment control measures will be placed prior to local ground disturbing activities.

Estimated Size of Construction Site

The area of disturbance for base bid items is about 9,000 ft2. The area of disturbance for all possible option items is about 10,000 ft2. The Area of Maximum Disturbance is therefore about half an acre.

This disturbance is almost entirely areas of existing development and will not alter the hydrologic character of the site.

Construction Activity Schedule

This project will take place during the typical dry season. Construction is anticipated to begin May 1st and be complete by June 30th. If the project extends beyond the anticipated schedule, construction will adhere to the following winterization plan.

Winterization Plan

The project work area will be stabilized to prevent soil movement either permanently if the project is complete, or in a manner which will remain effective until May 1 of the following year if the project is not complete by Oct 15. If the project has not been completed, all disturbed areas will be covered with a pine needle mulch or wood chips. No ground disturbing work will occur between October 15 and May 1 unless a grading variance has been issued by the Water Board and Tahoe Regional Planning Agency. If work occurs under a grading variance, it will be conducted in a manner where the project can be winterized within 24 hours.

Storm Preparedness Plan

If the National Weather Service predicts a 30% or greater chance of precipitation at the project work area, tarping materials will be present on site that can be used to cover stockpiled materials that have the potential to generate sediment in the event of rain. If rain is anticipated to occur overnight, stockpiled materials that have the potential to generate sediment will be covered before ending work for the previous day. The contractor is responsible for knowing if such conditions exist.

All disturbed soil areas present during construction will be protected with sediment control measures such as silt fence and/or straw wattles. Additional erosion control measures such as mulch or chips will be available for deployment (either stockpiled on-site or available prior to a storm) to stabilize disturbed areas.

Qualified BMP Inspection Personnel

The following individuals are responsible for prestorm/poststorm event inspections, daily inspections and to ensure compliance with all ECP elements:

Title Name Office Phone Cell Phone

Inspector Matt Kauffman 530-543-2745

832-971-2415

Contracting Officers

Representative (COR)

TBD

Assistant

Forest Engineer Michael Alexander 530-543-2864 530-545-0851

Forest Engineer Michael Gabor 530-543-2642

775-339-1214

Office:

Lake Tahoe Basin Management Unit 35 College Drive South Lake Tahoe, CA 96150 530-543-2600

Erosion and Sediment Control Checklist

The checklist below lists BMPs considered for this project. It is adapted from the California Stormwater Quality Association, Stormwater Best Management Practice Handbook for Construction, Attachment C, November 2009. Selection of these control practices took into consideration site specific and seasonal conditions.

EROSION CONTROL BMPs

BMP No. BMP Considered for Project Check if Used

EC-1 Scheduling X

EC-2 Preservation of Existing Vegetation X

EC-3 Hydraulic Mulch

EC-4 Hydroseeding

EC-5 Soil Binders

EC-6 Straw Mulch

EC-7 Geotextiles & Mats

EC-8 Wood Mulching X

EC-9 Earth Dikes & Drainage Swales X

EC-10 Velocity Dissipation Devices

EC-11 Slope Drains

SEDIMENT CONTROL BMPs

SE-1 Silt Fence X

SE-2 Sediment Basin X

SE-3 Sediment Trap

SE-4 Check Dam

SE-5 Fiber Rolls X

SE-6 Gravel bag Berm

SE-7 Street Sweeping & Vacuuming X

SE-8 Sand Bag Barrier

SE-9 Straw Bale Barrier

SE-10 Storm Drain Inlet Protection

WIND EROSION CONTROL BMPs

WE-1 Wind Erosion Control X

TRACKING CONTROL BMPs

TC-1 Stabilized Construction Entrance / Exit X

TC-2 Stabilized Construction Roadway

TC-3 Entrance / Outlet Tire Wash

NON-STORM WATER MANGEMENT BMPs

NS-1 Water Conservation Practices

NS-2 Dewatering Operations

NS-3 Paving and Grinding Operations X

NS-4 Temporary Stream Crossing

NS-5 Clear Water Diversion

NS-6 Illicit Connection / Discharge

NS-7 Potable water / Irrigation

NS-8 Vehicle and Equipment Cleaning X

NS-9 Vehicle and Equipment Fueling X

NS-10 Vehicle and Equipment Maintenance X

NS-11 Pile Driving Operations

NS-12 Concrete Curing X

NS-13 Concrete Finishing X

NS-14 Material and Equipment use Over Water

NS-15 Demolition Adjacent to Water

NS-16 Temporary Batch Plant

WASTE MANAGEMENT AND MATERIALS POLLUTION CONTROL BMPs

WM-1 Material Delivery & Storage X

WM-2 Material Use X

WM-3 Stockpile Management X

WM-4 Spill Prevention and Control X

WM-5 Solid Waste Management

WM-6 Hazardous Waste Management

WM-7 Contaminated Soil Management

WM-8 Concrete Waste Management X

WM-9 Sanitary / Septic Waste Management

WM-10 Liquid Waste Management

Waste Management and Disposal

All wastes (including equipment and maintenance waste) will be removed from the project work area and disposed of in a manner that is in compliance with federal, state, and local laws, regulations, and ordinances.

Post-Construction Storm Water Management

The finalized project will establish impervious surfaces designed to disperse storm water. All surfaces are designed to be sloped, which will sheet flow water for infiltration into the forest floor. Swales are designed to match natural drainage patterns and prevent surfaces from diverting storm flows. Native materials will be used to naturalize the area.

Maintenance, Inspection, and Repair

An inspection of the construction site shall be made at the end of each work day during active construction periods, and at least once a month during long periods of inactivity (e.g., winter) by the resident engineer, superintendent, general contractor or equivalent. In addition, qualified personnel shall conduct construction site inspections prior to anticipated storm events, during extended storm events, and after actual storm events. Inspections shall be performed from the commencement of construction activities until project termination. The purpose of the inspections is to discover potential water quality problems at the construction site so the contractor can implement corrective measures immediately. An inspection shall consist of checking for the following items, as applicable:

1. Damage to containment dikes or erosion control fencing;

2. Improperly installed or ineffective erosion control fencing;

3. Unauthorized vehicle access;

4. Boundary fence damage or removal;

5. Disturbed areas with inadequate erosion prevention and sediment control protection;

6. Evidence of any sediment leakage through erosion control fencing or containment dikes;

7. Soil piles and other earthen materials which are unprotected or located in drainage way;

8. Spilled and improperly stored chemicals, paint, fuel, oil, solvents, sealants, etc.;

9. Upstream runoff diversion structures (in-place and operational);

10. Any evidence of sediment tracking from construction equipment;

11. Any signs of soil erosion or deposition down-gradient from runoff discharges;

12. Sediment accumulation within on-site storm water drainage control facilities.

The contractor shall maintain a site inspection logbook noting the date of the inspection, the inspection, the inspector’s name and position title, and problem areas discovered for each inspection performed.

The inspection log shall be made available to Forest Service staff for review if so requested.

Temporary BMPs and contract designs will be inspected by the Designated Forest Service Inspector and

Contracting Officer’s Representative. Inspections will be conducted as appropriate and necessary to ensure contract compliance. If deficiencies are found the contractor will be informed and documented in daily diaries. If the contractor fails to comply, the Contracting Officer will be notified and a Notice of

Non-Compliance will be issued. If the Contracting Officer feels it is an appropriate action, all work may be halted until deficiencies are addressed.

Other Plans

This ECP may incorporate, by reference, the appropriate elements of other plans required by local, state or Federal agencies. A copy of any requirements incorporated by reference shall be kept at the construction site.

Preparer

Matthew Kauffman Civil Engineer Lake Tahoe Basin Management Unit

Sediment Basin SE-2

Description and Purpose

A sediment basin is a temporary basin formed by excavation or by constructing an embankment so that sediment-laden runoff is temporarily detained under quiescent conditions, allowing sediment to settle out before the runoff is discharged.

Sediment basin design guidance presented in this fact sheet is intended to provide options, methods, and techniques to optimize temporary sediment basin performance and basin sediment removal. Basin design guidance provided in this fact sheet is not intended to guarantee basin effluent compliance with numeric discharge limits (numeric action levels or numeric effluent limits for turbidity). Compliance with discharge limits requires a thoughtful approach to comprehensive BMP planning, implementation, and maintenance. Therefore, optimally designed and maintained sediment basins should be used in conjunction with a comprehensive system of BMPs that includes:

• Diverting runoff from undisturbed areas away from the basin

• Erosion control practices to minimize disturbed areas on-

Categories

EC Erosion Control SE Sediment Control El TC Tracking Control WE Wind Erosion Control

NS Non-Stormwater Management Control Waste Management and

WM Materials Pollution Control

Legend:

El Primary Category

[] Secondary Category

Targeted Constituents

Sediment El Nutrients Trash El Metals Bacteria Oil and Grease Organics

Potential Alternatives

SE-3 Sediment Trap (for smaller areas) site and to provide temporary stabilization and interim sediment controls (e.g., stockpile perimeter control, check dams, perimeter controls around individual lots) to reduce the basin’s influent sediment concentration.

At some sites, sediment basin design enhancements may be required to adequately remove sediment. Traditional

February 2010 California Stormwater BMP Handbook

Construction www.casqa.org

CASQA

CALWORNIA STOK.’. WATER

(aka “physical”) enhancements such as alternative outlet configurations or flow deflection baffles increase detention time and other techniques such as outlet skimmers preferentially drain flows with lower sediment concentrations. These “physical” enhancement techniques are described in this fact sheet. To further enhance sediment removal particularly at sites with fine soils or turbidity sensitive receiving waters, some projects may need to consider implementing Active Treatment Systems (ATS) whereby coagulants and flocculants are used to enhance settling and removal of suspended sediments. Guidance on implementing ATS is provided in SE-u.

Suitable Applications Sediment basins may be suitable for use on larger projects with sufficient space for constructing the basin. Sediment basins should be considered for use:

• Where sediment-laden water may enter the drainage system or watercourses

• On construction projects with disturbed areas during the rainy season

• At the outlet of disturbed watersheds between 5 acres and 75 acres and evaluated on a site by site basis

• Where post construction detention basins are required

• In association with dikes, temporary channels, and pipes used to convey runoff from disturbed areas

Limitations Sediment basins must be installed only within the property limits and where failure of the structure will not result in loss of life, damage to homes or buildings, or interruption of use or service of public roads or utilities. In addition, sediment basins are attractive to children and can be very dangerous. Local ordinances regarding health and safety must be adhered to. If fencing of the basin is required, the type of fence and its location should be shown in the SWPPP and in the construction specifications.

• As a general guideline, sediment basins are suitable for drainage areas of 5 acres or more, but not appropriate for drainage areas greater than 75 acres. However, the tributary area should be evaluated on a site by site basis.

• Sediment basins may become an “attractive nuisance” and care must be taken to adhere to all safety practices. If safety is a concern, basin may require protective fencing.

• Sediment basins designed according to this fact sheet are only effective in removing sediment down to about the silt size fraction. Sediment-laden runoff with smaller size fractions (fine silt and clay) may not be adequately treated unless chemical (or other appropriate method) treatment is used in addition to the sediment basin.

• Basins with a height of 25 ft or more or an impounding capacity of 50 ac-ft or more must obtain approval from California Department of Water Resources Division of Safety of Dams

(http: //www.water.ca.gov/damsafety/).

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Construction www.casqa.org

• Water that stands in sediment basins longer than 96 hours may become a source of mosquitoes (and midges), particularly along perimeter edges, in shallow zones, in scour or below-grade pools, around inlet pipes, along low-flow channels, and among protected habitats created by emergent or floating vegetation (e.g. cattails, water hyacinth), algal mats, riprap, etc.

• Basins require large surface areas to permit settling of sediment. Size may be limited by the available area.

Implementation General A sediment basin is a controlled stormwater release structure formed by excavation or by construction of an embankment of compacted soil across a drainage way, or other suitable location. It is intended to trap sediment before it leaves the construction site. The basin is a temporary measure expected to be used during active construction in most cases and is to be maintained until the site area is permanently protected against erosion or a permanent detention basin is constructed.

Sediment basins are suitable for nearly all types of construction projects. Whenever possible, construct the sediment basins before clearing and grading work begins. Basins should be located at the stormwater outlet from the site but not in any natural or undisturbed stream. A typical application would include temporary dikes, pipes, and/or channels to convey runoff to the basin inlet.

Many development projects in California are required by local ordinances to provide a stormwater detention basin for post-construction flood control, desilting, or stormwater pollution control. A temporary sediment basin may be constructed by rough grading the post-construction control basins early in the project.

Sediment basins if properly designed and maintained can trap a significant amount of the sediment that flows into them. However, traditional basins do not remove all inflowing sediment. Therefore, they should be used in conjunction with erosion control practices such as temporary seeding, mulching, diversion dikes, etc., to reduce the amount of sediment flowing into the basin.

Planning To improve the effectiveness of the basin, it should be located to intercept runoff from the largest possible amount of disturbed area. Locations best suited for a sediment basin are generally in lower elevation areas of the site (or basin tributary area) where site drainage would not require significant diversion or other means to direct water to the basin but outside jurisdictional waterways. However, as necessary, drainage into the basin can be improved by the use of earth dikes and drainage swales (see BMP EC-9). . The basin should not be located where its failure would result in the loss of life or interruption of the use or service of public utilities or roads.

Construct before clearing and grading work begins when feasible.

• Do not locate the basin in a jurisdictional stream.

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• Basin sites should be located where failure of the structure will not cause loss of life, damage to homes or buildings, or interruption of use or service of public roads or utilities.

• Basins with a height of 25 ft or more or an impounding capacity of 50 ac-ft must obtain approval from the Division of Dam Safety. Local dam safety requirements may be more stringent.

• Limit the contributing area to the sediment basin to only the runoff from the disturbed soil areas. Use temporary concentrated flow conveyance controls to divert runoff from undisturbed areas away from the sediment basin.

• The basin should be located: (i) by excavating a suitable area or where a low embankment can be constructed across a swale, (2) where post-construction (permanent) detention basins will be constructed, and () where the basins can be maintained on a year-round basis to provide access for maintenance, including sediment removal and sediment stockpiling in a protected area, and to maintain the basin to provide the required capacity.

Design When designing a sediment basin, designers should evaluate the site constraints that could affect the efficiency of the BMP. Some of these constraints include: the relationship between basin capacity, anticipated sediment load, and freeboard, available footprint for the basin, maintenance frequency and access, and hydraulic capacity and efficiency of the temporary outlet infrastructure. Sediment basins should be designed to maximize sediment removal and to consider sediment load retained by the basin as it affects basin performance.

Three Basin Design Options (Part A) are presented below along with a Typical

Sediment/Detention Basin Design Methodology (Part B). Regardless of the design option that is selected, designers also need to evaluate the sediment basin capacity with respect to sediment accumulation (See “Step 3. Evaluate the Capacity of the Sediment Basin”), and should incorporate approaches identified in “Step 4. Other Design Considerations” to enhance basin performance.

A) Basin Design Options:

Option 1:

Design sediment basin(s) using the standard equation:

(Eq.i)

Where:

= Minimum surface area for trapping soil particles of a certain size

V = Settling velocity of the design particle size chosen (V, = 0.00028 ft/s for a design particle size of 0.01 mm at 68°F)

1.2 = Factor of safety recommended by USEPA to account for the reduction in basin efficiency caused due to turbulence and other non ideal conditions.

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Q=CIA (Eq.2)

Where

Q = Discharge rate measured in cubic feet per second

C = Runoff coefficient (unitless)

I = Peak rainfall intensity for the 10-year, 6-hour rain event (in/hr)

A = Area draining into the sediment basin in acres

The design particle size should be the smallest soil grain size determined by wet sieve analysis, or the fine silt sized (o.oi mm [or 0.0004 in.J) particle, and the Vs used should be 100 percent of the calculated settling velocity.

This sizing basin method is dependent on the outlet structure design or the total basin length with an appropriate outlet. If the designer chooses to utilize the outlet structure to control the flow duration in the basin, the basin length (distance between the inlet and the outlet) should be a minimum of twice the basin width; the depth should not be less than 3 ft nor greater than 5 ft for safety reasons and for maximum efficiency (2 ft of sediment storage, 2 ft of capacity). If the designer chooses to utilize the basin length (with appropriate basin outlet) to control the flow duration in the basin, the basin length

(distance between the inlet and the outlet) should be a specifically designed to capture

100% of the design particle size; the depth should not be less than 3 ft nor greater than 5 ft for safety reasons and for maximum efficiency (2 ft of sediment storage, 2 ft of capacity).

The basin should be located on the site where it can be maintained on a year-round basis and should be maintained on a schedule to retain the 2 ft of capacity.

Option 2:

Design pursuant to local ordinance for sediment basin design and maintenance, provided that the design efficiency is as protective or more protective of water quality than Option 1.

Option :

The use of an equivalent surface area design or equation provided that the design efficiency is as protective or more protective of water quality than Option 1.

B) Typical Sediment/Detention Basin Design Methodology:

Design of a sediment basin requires the designer to have an understanding of the site constraints, knowledge of the local soil (e.g., particle size distribution of potentially contributing soils), drainage area of the basin, and local hydrology. Designers should not assume that a sediment basin for location A is applicable to location B. Therefore, designers can use this factsheet as guidance but will need to apply professional judgment and knowledge of the site to design an effective and efficient sediment basin. The following provides a general overview of typical design methodologies:

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Stepi. Hydrologic Design

• Evaluate the site constraints and assess the drainage area for the sediment basin. Designers should consider on- and off-site flows as well as changes in the drainage area associated with site construction/disturbance. To minimize additional construction during the course of the project, the designer should consider identifying the maximum drainage area when calculating the basin dimensions.

• If a local hydrology manual is not available it is recommended to follow standard rational method procedures to estimate discharge. The references section of this factsheet provides a reference to standard hydrology textbooks that can provide standard methodologies. If local rainfall depths are not available, values can be obtained from standard precipitation frequency maps from NOAA (downloaded from http://www.wrcc.dri.edu/pcpnfreq.html).

Step 2. Hydraulic Design

• Calculate the surface area required for the sediment basin using Equation 1. In which discharge is estimated for a b-yr 6-hr event using rational method procedure listed in local hydrology manual and Vs is estimated using Stokes Law presented in Equation 3.

=2.8ld2 (Eq.3)

Where

V = Settling velocity in feet per second at 68°F d = diameter of sediment particle in millimeters (smallest soil grain size determined by wet sieve analysis or fine silt (0.01 mm [or 0.0004 in.])

• In general the basin outlet design requires an iterative trial and error approach that considered the maximum water surface elevation, the elevation versus volume (stage-storage) relationship, the elevation verses discharge (stage-discharge) relationship, and the estimated inflow hydrograph. To adequately design the basins to settle sediment, the outlet configuration and associated outflow rates can be estimated by numerous methodologies.

The following provides some guidance for design the basin outlet:

• An outlet should have more than one orifice.

• An outlet design typically utilizes multiple horizontal rows of orifices (approximately 3 or more) with at least 2 orifices per row (see Figures 1 and 2 at the end of this fact sheet).

• Orifices can vary in shape.

• Select the appropriate orifice diameter and number of perforations per row with the objective of minimizing the number of rows while maximizing the detention time.

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• The diameter of each orifice is typically a maximum of 3-4 inches and a minimum of 0.25-0.5 inches.

• If a rectangular orifice is used, it is recommended to have minimum height of 0.5 inches and a maximum height of 6 inches.

• Rows are typically spaced at three times the diameter center to center vertically with a minimum distance of approximately 4 inches on center and a maximum distance of i foot on center.

• To estimate the outflow rate, each row is calculated separately based on the flow through a single orifice then multiplied by the number of orifices in the row. This step is repeated for each of the rows. Once all of the orifices are estimated, the total oufflow rate versus elevation (stage-discharge curve) is developed to evaluate the detention time within the basin.

• Flow through a single orifice can be estimated using an Equation :

Q = BC’A(2gH)°5 (Eq.4)

Where

Q = Discharge in ft3/s C’ = Orifice coefficient (unitless) A = Area of the orifice (ft2) g = acceleration due to gravity (ft3/s) H = Head above the orifice (ft) B = Anticipated Blockage or clogging factor (unitless), It is dependent on anticipated sediment and debris load, trash rack configuration etc, so the value is dependent on design engineers professional judgment and/or local requirements (B is never greater than

1 and a value of 0.5 is generally used)

• Care must be taken in the selection of orifice coefficient (“C”); o.6o is most often recommended and used. However, based on actual tests, Young and Graziano

(1989), “Outlet Hydraulics of Extended Detention Facilities for Northern Virginia

Planning District Commission”, recommends the following:

• C’ = 0.66 for thin materials; where the thickness is equal to or less than the orifice diameter, or

• C’ = o.8o when the material is thicker than the orifice diameter

• If different sizes of orifices are used along the riser then they have to be sized such that not more than 50 percent of the design storm event drains in one-third of the drawdown time (to provide adequate settling time for events smaller than the design storm event) and the entire volume drains within 96 hours or as regulated by the local vector control agency. If a basin fails to drain within 96 hours, the basin must be pumped dry.

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• Because basins are not maintained for infiltration, water loss by infiltration should be disregarded when designing the hydraulic capacity of the outlet struchire.

• Floating Outlet Skimmer: The floating skimmer (see Figure 3 at the end of this fact sheet is an alternative outlet configuration (patented) that drains water from upper portion of the water column. This configuration has been used for temporary and permanent basins and can improve basin performance by eliminating bottom orifices which have the potential of discharging solids. Some design considerations for this alternative outlet device includes the addition of a sand filter or perforated under drain at the low point in the basin and near the floating skimmer. These secondary drains allow the basin to fully drain. More detailed guidelines for sizing the skimmer can be downloaded from http://www.fairclothskimmer.com/.

• Hold and Release Valve: An ideal sediment/detention basin would hold all flows to the design storm level for sufficient time to settle solids, and then slowly release the storm water. Implementing a reliable valve system for releasing detention basins is critical to eliminate the potential for flooding in such a system. Some variations of hold and release valves include manual valves, bladder devices or electrically operated valves. When a precipitation event is forecast, the valve would be close for the duration of the storm and appropriate settling time. When the settling duration is met (approximately 24 or 48 hours), the valve would be opened and allow the stormwater to be discharged at a rate that does not resuspend settled solids and in a non-erosive manner. If this type of system is used the valve should be designed to empty the entire basin within 96 hours or as stipulated by local vector control regulations.

Step 3. Evaluate the Capacity of the Sediment Basin

• Typically, sediment basins do not perform as designed when they are not properly maintained or the sediment yield to the basin is larger than expected. As part of a good sediment basin design, designers should consider maintenance cycles, estimated soil loss and/or sediment yield, and basin sediment storage volume. The two equations below can be used to quantify the amount of soil entering the basin.

• The Revised Universal Soil Loss Equation (RUSLE, Eq.5) can be used to estimate annual soil loss and the Modified Universal Soil Equation (MUSLE, Eq.6) can be used to estimate sediment yield from a single storm event.

A=RxKxLSxCxP (Eq.5)

Y=95(Qxqp)056 xKxLSxCxP (Eq.6)

Where:

A= annual soil loss, tons/acre-year

R = rainfall erosion index, in 100 ft.tons/acre.in/hr

K = soil erodibility factor, tons/acre per unit of R

LS = slope length and steepness factor (unitless)

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C = vegetative cover factor (unitless)

P = erosion control practice factor (unitless)

Y = single storm sediment yield in tons

Q = runoff volume in acre-feet qp = peak flow in cfs

• Detailed descriptions and methodologies for estimating the soil loss can be obtained from standard hydrology text books (See References section).

• Determination of the appropriate equation should consider construction duration and local environmental factors (soils, hydrology, etc.). For example, if a basin is planned for a project duration of 1 year and the designer specifies one maintenance cycle, RUSLE could be used to estimate the soil loss and thereby the designer could indicate that the sediment storage volume would be half of the soil loss value estimated. As an example for use of MUSLE, a project may have a short construction duration thereby requiring fewer maintenance cycles and a reduced sediment storage volume. MUSLE would be used to estimate the anticipated soil loss based on a specific storm event to evaluate the sediment storage volume and appropriate maintenance frequency.

• The soil loss estimates are an essential step in the design and it is essential that the designer provide construction contractors with enough information to understand maintenance frequency and/or depths within the basin that would trigger maintenance. Providing maintenance methods, frequency and specification should be included in design bid documents such as the SWPPP Site Map.

• Once the designer has quantified the amount of soil entering the basin, the depth required for sediment storage can be determined by dividing the estimated sediment loss by the surface area of the basin.

Step 4. Other Design Considerations

• Consider designing the volume of the settling zone for the total storm volume associated with the 2-year event or other appropriate design storms specified by the local agency. This volume can be used as a guide for sizing the basin without iterative routing calculations. The depth of the settling zone can be estimated by dividing the estimated 2-yr storm volume by the surface area of the basin.

• The basin volume consists of two zones;

- A sediment storage zone at least 1 ft deep.

- A settling zone at least 2 ft deep.

- The basin depth must be no less than 3 ft (not including freeboard).

• Proper hydraulic design of the outlet is critical to achieving the desired performance of the basin. The outlet should be designed to drain the basin within 24 to 96 hours (also referred

February 2010 California Stormwater BMP Handbook 9 of 18 to as “drawdown time”). The 24-hour limit is specified to provide adequate settling time; the 96-hour limit is specified to mitigate vector control concerns.

• Confirmation of the basin performance can be evaluated by routing the design storm (b-yr 6-hr, or as directed by local regulations) through the basin based on the basin volume (stage storage curve) and the outlet design (stage-discharge curve based on the orifice configuration or equivalent outlet design).

• Sediment basins, regardless of size and storage volume, should include features to accommodate overflow or bypass flows that exceed the design storm event.

- Include an emergency spiliway to accommodate flows not carried by the principal spillway The spiliway should consist of an open channel (earthen or vegetated) over undisturbed material (not fill) or constructed of a non-erodible riprap (or equivalent protection) on fill slopes.

- The spiliway control section, which is a level portion of the spiliway channel at the highest elevation in the channel, should be a minimum of 20 ft in length.

• Rock, vegetation or appropriate erosion control should be used to protect the basin inlet, outlet, and slopes against erosion.

• The total depth of the sediment basin should include the depth required for sediment storage, depth required for settling zone and freeboard of at least 1 foot or as regulated by local flood control agency for a flood event specified by the local agency.

• The basin alignment should be designed such that the length of the basin is more than twice the width of the basin; the length should be determined by measuring the distance between the inlet and the outlet. If the site topography does not allow for this configuration baffles should be installed so that the ratio is satisfied. If a basin has more than one inflow point, any inflow point that conveys more than 30 percent of the total peak inflow rate has to meet the required length to width ratio.

• An alternative basin sizing method proposed by Fifield (2004) can be consulted to estimate an alternative length to width ratio and basin configuration. These methods can be considered as part of Option 3 which allows for alternative designs that are protective or more protective of water quality.

• Baffles (see Figure 4 at the end of this fact sheet) can be considered at project sites where the existing topography or site constraints limit the length to width ratio. Baffles should be constructed of earthen berms or other structural material within the basin to divert flow in the basin, thus increasing the effective flow length from the basin inlet to the outlet riser.

Baffles also reduce the change of short circuiting and allows for settling throughout the basin.

• Baffles are typically constructed from the invert of the basin to the crest of the emergency spiliway (i.e., design event flows are meant to flow around the baffles and flows greater than the design event would flow over the baffles to the emergency spiliway).

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• Use of other materials for construction of basin baffles (such as silt fence) may not be appropriate based on the material specifications and will require frequent maintenance (maintain after every storm event). Maintenance may not be feasible when required due to flooded conditions resulting from frequent (i.e., back to back) storm events. Use of alternative baffle materials should not deviate from the intended purpose of the material, as described by the manufacturer.

• Sediment basins are best used in conjunction with erosion controls.

• Basins with an impounding levee greater than 4.5 ft tall, measured from the lowest point to the impounding area to the highest point of the levee, and basins capable of impounding more than 35,000 ft3, should be designed by a Registered Civil Engineer. The design should include maintenance requirements, including sediment and vegetation removal, to ensure continuous function of the basin outlet and bypass structures.

• A forebay, constructed upstream of the basin may be provided to remove debris and larger particles.

• The outflow from the sediment basin should be provided with velocity dissipation devices

(see BMP EC-io) to prevent erosion and scouring of the embankment and channel.

• The principal outlet should consist of a corrugated metal, high density polyethylene (HDPE), or reinforced concrete riser pipe with dewatering holes and an anti-vortex device and trash rack attached to the top of the riser, to prevent floating debris from flowing out of the basin or obstructing the system. This principal structure should be designed to accommodate the inflow design storm.

• A rock pile or rock-filled gabions can serve as alternatives to the debris screen, although the designer should be aware of the potential for extra maintenance involved should the pore spaces in the rock pile clog.

a The outlet structure should be placed on a firm, smooth foundation with the base securely anchored with concrete or other means to prevent floatation.

• Attach riser pipe (watertight connection) to a horizontal pipe (barrel). Provide anti-seep collars on the barrel.

a Cleanout level should be clearly marked on the riser pipe.

Installation

• Securely anchor and install an anti-seep collar on the outlet pipe/riser and provide an emergency spillway for passing major floods (see local flood control agency).

a Areas under embankments must be cleared and stripped of vegetation.

• Chain link fencing should be provided around each sediment basin to prevent unauthorized entry to the basin or if safety is a concern.

February 2010 California Stormwater BMP Handbook 11 of 18

Costs The cost of a sediment basin is highly variable and is dependent of the site configuration. To decrease basin construction costs, designers should consider using existing site features such as berms or depressed area to site the sediment basin. Designers should also consider potential savings associated with designing the basin to minimize the number of maintenance cycles and siting the basin in a location where a permanent BMP (e.g., extended detention basin) is required for the project site.

Inspection and Maintenance a BMPs must be inspected in accordance with General Permit requirements for the associated project type and risk level and as required by local requirements. It is recommended that at a minimum, basins be inspected weekly, prior to forecasted rain events, daily during extended rain events, and after the conclusion of rain events.

• Examine basin banks for seepage and structural soundness.

• Check inlet and outlet structures and spiliway for any damage or obstructions. Repair damage and remove obstructions as needed.

• Check inlet and outlet area for erosion and stabilize if required.

• Check fencing for damage and repair as needed.

• Sediment that accumulates in the basin must be periodically removed in order to maintain

BMP effectiveness. Sediment should be removed when sediment accumulation reaches one-half the designated sediment storage volume. Sediment removed during maintenance should be managed properly. The sediment should be appropriately evaluated and used or disposed of accordingly. Options include: incorporating sediment into earthwork on the site

(only if there is no risk that sediment is contaminated); or off-site export/disposal at an appropriate location (e.g., sediment characterization and disposal to an appropriate landfill).

• Remove standing water from basin within 96 hours after accumulation.

• If the basin does not drain adequately (e.g., due to storms that are more frequent or larger than the design storm or other unforeseen site conditions), dewatering should be conducted in accordance with appropriate dewatering BMPs (see NS-2) and in accordance with local permits as applicable.

• To minimize vector production:

- Remove accumulation of live and dead floating vegetation in basins during every inspection.

- Remove excessive emergent and perimeter vegetation as needed or as advised by local or state vector control agencies.

References A Current Assessment of Urban Best Management Practices: Techniques for Reducing

Nonpoint Source Pollution in the Coastal Zones, Metropolitan Washington Council of

Governments, March 1992.

February 2010 California Stormwater BMP Handbook 12 of 18

Draft-Sedimentation and Erosion Control, an Inventory of Current Practices, USEPA. April 1990.

U.S. Environmental Protection Agency (USEPA). Erosion and Sediment Control, Surface Mining in the Eastern U.S., U.S. Environmental Protection Agency, Office of Water, Washington, DC,Washington, D.C., 1976.

Fifield, J.S. Designing for Effective Sediment and Erosion Control on Construction Sites.

Forester Press, Santa Barbara, CA. 2004.

Goldman S.J., Jackson K. and Bursztynsky T.A. Erosion and Sediment Control Handbook.

McGraw-Hill Book Company, 1986.

U.S. Environmental Protection Agency (USEPA). Guidance Specifying Management Measures for Nonpoint Pollution in Coastal Waters. EPA 84o-B-9-oo2. U.S. Environmental Protection

Agency, Office of Water, Washington, DC, 1993.

Guidelines for the Design and Construction of Small Embankment Dams, Division of Safety of

Dams, California Department of Water Resources, March 1986.

Haan C.T., Barfield B.J. and Hayes J.C. Design Hydrology and Sedimentology for Small

Catchments. Academic Press. 1994.

Inlet/Outlet Alternatives for Extended Detention Basins. State of California Department of

Transportation (Caltrans), 2001.

Manual of Standards of Erosion and Sediment Control Measures, Association of Bay Area

Governments, May 1995.

McLean, J., 2000. Mosquitoes in Constructed Wetlands: A Management Bugaboo? In T.R.

Schueler and H.K. Holland [eds.], The Practice of Watershed Protection. pp. 29-33. Center for

Watershed Protection, Ellicott City, MD, 2000.

Metzger, M.E., D. F. Messer, C. L. Beitia, C. M. Myers, and V. L. Kramer. The Dark Side of

Stormwater Runoff Management: Disease Vectors Associated with Structural BMPs, 2002.

National Management Measures to Control Nonpoint Source Pollution from Urban Areas, United States Environmental Protection Agency, 2002.

Proposed Guidance Specifying Management Measures for Sources of Nonpoint Pollution in

Coastal Water, Work Group-Working Paper, USEPA, April 1992.

Stormwater Management of the Puget Sound Basin, Technical Manual, Publication #91-75, Washington State Department of Ecology, February 1992.

Stormwater Quality Handbooks - Construction Site Best Management Practices (BMPs) Manual, State of California Department of Transportation (Caltrans), November 2000.

Water Quality Management Plan for the Lake Tahoe Region, Volume II Handbook of

Management Practices, Tahoe Regional Planning Agency, November 1988.

February 2010 California Stormwater BMP Handbook 13 of 18

Young, G.K. and Graziano, F., Outlet Hydraulics of Extended Detention Facilities for Northern Virginia Planning District Commission, 1989.

February 2010 California Stormwater BMP Handbook 14 of 18

Sediment Basin

FIGURE 1: TYPICAL TEMPORARY SEDIMENT BASIN

MULTIPLE ORIFICE DESIGN

NOT TO SCALE

SE-2

February 2010 California Stormwater BMP Handbook

Construction www.casqa.org

Embankment

N

Emergency spiliway

TOP VIEW

Riser w/ hood & trash rack

Inflow

Settling depth 24” Mm depth

Sediment storage depth — 12” Mm

Em erg en c y p ii way

Riser encased in gravel jacket. Upper two—thirds perforated.

Outlet

Anti—seep collars

Anti—floatation block

SIDE VIEW

Maintenance & emergency discharge outlet

Water quality discharge orifices

Maintendnce & emergency discharge-outlet

FIGURE 2: MULTIPLE ORIFICE OuTLET RISER

NOT TO SCALE

SE-2

February 2010 California Stormwater BMP Handbook

Construction www.casqa.org uttlow

Debris screen

Trash rac

Pon

ProfHeDebris screen-tflow

NOTES

ISOMETRIC VIEW

JLET END ORIFICE

INSIDE SCREEN AND

ACCESSIBLE

THROUGH DOOR

FIGURE : TYPICAL SKIMMER

NOT TO SCALE

February 2010 California Stormwater BMP Handbook 17 of 18

PROFILE

1. THE MOST IMPORTANT DESIGN PARAMETER IS

THE CONTROL OF ORlFICE SIZE, WHICH CAN CONTROL DESIRED DEWATERING liME. ThE LONGER ThE DEWATERING TIME, THE BElIER THE OUAIfTY OF WATER DISCHARGED FROM ThE SEDIMENt BASIN.

2 OESIGN BY w FAIRCLOTH (PATENT #5,820.751).

3. FiGURE IS MEANT TO CONVEY CONCEPT ONLY.

SIZES/MATERIALS SPECIFiED DURING DETAILED

DESIN.•

TO

OR

BARREL PIPE LONGER

THAN SHOWN

OUTLET PIPE

ELEVA1ION

, VARIES

SECT A A’

SE-2

r TOP OF RAFFLE

MAX. WATER /

_9LV!l2N

ELEVATION —

FIGURE 4: TYPICAL TEMPORARY SEDIMENT BASIN

WITH BAFFLES

NOT TO SCALE

February 2010 California Stormwater BMP Handbook

Construction www.casqa.org

SECT B—B’

RISER

EMDANKMENT

PLAN

NI

1 BAFFLES ARE TO BE CONSTRUCTED TO MEET

THE REQUIRED LENGTH TO WIDTH RATiOS.

2. CREST OF ThE WFFLES SHOULD BE LEVEL

WITH OR JUST BELOW THE CREST OF THE

EMERGENCY SflLLWAY.

• EMERGENcY

SP1LLWAY

Street Sweeping and Vacuuming Categories

SE-7

EC Erosion Control

SE Sediment Control I1 TC Tracking Control

WE Wind Erosion Control

NS

Non-Stormwater Management Control iNM Waste Management and Materials Polluon Control

Legend:

0 Primary Objective

0 Secondary Objective

Description and Purpose

Street sweeping and vacuuming includes use of self-propelled and walk-behind equipment to remove sediment from streets and roadways, and to clean paved surfaces in preparation for final paving. Sweeping and vacuuming prevents sediment from the project site from entering storm drains or receiving waters.

Suitable Applications Sweeping and vacuuming are suitable anywhere sediment is tracked from the project site onto public or private paved streets and roads, typically at points of egress. Sweeping and vacuuming are also applicable during preparation of paved surfaces for final paving.

Limitations 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).

Implementation

• Controlling the number of points where vehicles can leave the site will allow sweeping and vacuuming efforts to be focused, and perhaps save money.

Targeted Constituents

Sediment 0 Nutrients

Trash 0 Metals Bacteria

Oil and Grease I?1 Organics

Potential Alternatives

None

• Inspect potential sediment tracking locations daily.

• Visible sediment tracking should be swept or vacuumed on a daily basis.

• Do not use kick brooms or sweeper attachments. These tend to spread the dirt rather than remove it.

November 2009 California Stormwater BMP Handbook

Construction www.casqa.org

CLIFORNIA STORMWTER

QUALITY,

Street Sweeping and Vacuuming SE-7

• If not mixed with debris or trash, consider incorporating the removed sediment back into the project

Costs Rental rates for self-propelled sweepers vary depending on hopper size and duration of rental.

Expect rental rates from $58/hour ( yd3 hopper) to $88/hour (ç yd3 hopper), plus operator costs. Hourly production rates vary with the amount of area to be swept and amount of sediment. Match the hopper size to the area and expect sediment load to minimize time spent dumping.

Inspection and Maintenance

• Inspect BMPs prior to forecast rain, daily during extended rain events, after rain events, weekly during the rainy season, and at two-week intervals during the non-rainy season.

• When actively in use, points of ingress and egress must be inspected daily.

• When tracked or spilled sediment is observed outside the construction limits, it must be removed at least daily. More frequent removal, even continuous removal, may be required in some jurisdictions.

• Be careful not to sweep up any unknown substance or any object that maybe potentially hazardous.

• Adjust brooms frequently; maximize efficiency of sweeping operations.

• After sweeping is finished, properly dispose of sweeper wastes at an approved dumpsite.

References Stormwater Quality Handbooks - Construction Site Best Management Practices (BMPs) Manual, State of California Department of Transportation (Caltrans), November 2000.

Labor Surcharge and Equipment Rental Rates, State of California Department of Transportation

(Caltrans), April 1, 2002 — March 31, 2003.

November 2009 California Stormwater BMP Handbook 2 of 2

Stabilized Construction Entrance/Exit TC-1

Categories

EC Erosion Control

SE Sediment Control F1 TC Tracking Control 0 WE Wind Erosion Control

NS

Non-Stormwater Management Control Waste Management and Materials Polluon Control

Legend:

El Primary Objective

0 Secondary Objective

Description and Purpose A stabilized construction access is defined by a point of entrance/exit to a construction site that is stabilized to reduce the tracking of mud and dirt onto public roads by construction vehicles.

Suitable Applications Use at construction sites:

. Where dirt or mud can be tracked onto public roads.

• Adjacent to water bodies.

• Where poor soils are encountered.

• Where dust is a problem during dry weather conditions.

Limitations

• Entrances and exits require periodic top dressing with additional stones.

• This BMP should be used in conjunction with street sweeping on adjacent public right of way.

Targeted Constituents

Sediment El Nutrients

Trash Metals Bacteria

Oil and Grease

Organics

Potential Alternatives

None

• Entrances and exits should be constructed on level ground only.

• Stabilized construction entrances are rather expensive to construct and when a wash rack is included, a sediment trap of some kind must also be provided to…