The chapter lays out the criteria and methods to be employed
during construction to limit erosion and the discharge of sediment
and other pollutants from construction sites.
Requirements for temporary controls during construction are
applicable to the following projects:
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Land disturbing activity of one acre or more or
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Land disturbing activity of less than one acre, where the activity
is part of a common plan of development that is one acre or larger.
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A common plan of development refers to a construction activity
that is completed in separate stages, separate phases, or in combination
with other construction activities.
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Local Provisions: City of Azle
has established minimum guidelines for controlling construction runoff
for all land disturbance activities, even where there is less than
1 acre of disturbed surface (See Figure 1.2).
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Construction activities shall comply with the SWPPP requirements
in the effective TPDES General permit relating to Stormwater Discharges
from Construction Activities, of the Stormwater Pollution Control
Ordinance and the appropriate federal (Environmental Protection Agency)
and state (Texas Commission on Environmental Quality) regulations.
When the ordinance and applicable regulations are in conflict, the
most stringent requirements shall apply.
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See Appendix D (Sediment and Erosion Control Guidelines for
Small Sites).
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(Ordinance 2012-10 adopted 8/21/12)
iSWM requires the use of temporary controls during construction
to prevent or reduce the discharge of sediment and other pollutants
from the construction site. The temporary controls are known as Best
Management Practices (BMPs). BMPs may be activities, prohibitions,
maintenance procedures, structural controls, operating procedures
and other measures to prevent erosion and control the discharge of
sediment and other pollutants.
Construction BMPs shall be considered when developing the Preliminary
iSWM Plan and shall be coordinated with the Final iSWM Plans. Construction
BMPs fall into three general categories: Erosion Control, Sediment
Control, and Material and Waste Control. The first category prevents
erosion, and the second catches soil from erosion that does occur.
It is generally more effective and less expensive to prevent erosion
than to treat turbid runoff. Material and waste controls are for other
sources of stormwater pollutants on a construction site.
The following priorities shall be applied to the selection of
construction BMPs:
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Retain native topsoil and natural vegetation in an undisturbed
state by incorporating natural drainage features and buffer areas
into the site design.
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Limit the area of disturbance and vehicle access to the site.
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Limit the extent of clearing operations, and phase construction
operations to minimize the area disturbed at any one time.
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Stabilize disturbed areas as soon as possible (not at the end
of construction), particularly in channels and on cut/fill slopes.
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Minimize the disturbance of steep slopes during construction,
and minimize slope length and steepness.
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Coordinate stream crossings, and minimize the construction of
temporary stream crossings.
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Provide sediment controls, including but not limited to perimeter
controls, where stormwater discharges will occur from disturbed areas.
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Prevent tracking of sediment off-site through the establishment
of stabilized construction entrances and exits.
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Control sediment and other contaminants from dewatering activities.
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Control discharges of construction materials and wastes.
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State Requirements
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In addition to the municipality requirements outlined in this
chapter, land disturbing activities must comply with the Texas Commission
on Environmental Quality (TCEQ) requirements under General Permit
Number TXR150000, commonly referred to as the “Construction
General Permit.” This permit contains requirements for a Stormwater
Pollution Prevention Plan (SWP3), state and local notifications, and
installation, maintenance, and inspection of best management practices
on construction sites. The Water Quality Technical Manual contains
guidance for preparing a SWP3. However, compliance with the Construction
General Permit is beyond the scope of this iSWM Criteria Manual and
is the sole responsibility of the construction site operator(s).
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Local Provisions: NONE
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(Ordinance 2012-10 adopted 8/21/12)
The iSWM Construction Plan shall include, but shall not be limited
to, the following:
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Topography;
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Limits of all areas to be disturbed by construction activity,
including off-site staging areas, utility lines, batch plants, and
spoil/borrow areas;
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Location and types of erosion control, sediment control, and
material and waste control BMPs;
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Construction details and notes for erosion control, sediment
control, and material and waste control BMPs; and
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Inspections and maintenance notes.
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BMPs and notes shall be provided for all the elements listed
in this section, unless site conditions render an element not applicable.
BMPs shall be selected and designed according to the technical criteria
in the Construction Controls Technical Manual. Site data gathered
and analyzed in Step 2 of the integrated Development Process shall
be the basis for selecting BMPs.
The minimum design storm for temporary BMPs is the 2-year, 24-hour
duration storm event. Plans for temporary BMPs shall be prepared by
a Certified Professional in Erosion and Sediment Control (CPESC) or
a licensed engineer or registered landscape architect in the State
of Texas who has documented experience in hydrology and hydraulics
and erosion and sediment control.
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Local Provisions: City of Azle
allows flexibility to use BMPs not listed in the Construction Controls
Technical Manual with approval of the Storm Water Manager.
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Capacity calculations shall be included in the iSWM Construction
Plan.
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It is the responsibility of the engineer to design appropriate
BMPs for each site. If the most appropriate BMP is not in the NCTCOG
BMP Manual, the engineer shall submit calculations and references
for design of the BMP to City of Azle.
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14.4.3.1
Erosion Controls
Erosion control is first line of defense and the primary means
of preventing stormwater pollution. The shall be designed to retain
soil in place and to minimize the amount of sediment that has to be
remove from stormwater runoff by other types of BMPs. Fact Sheets
for different types of Erosion Control BMP are in the iSWM Technical
Manual.
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Limits of Disturbance
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On the iSWM Construction Plans, clearly show the limits of the
area to be disturbed.
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Design Criteria
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Minimize the disturbance of steep slopes.
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Constrain the disturbed area to the minimum necessary to construct
the project.
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Include the contractor’s staging area, borrow/spoil area,
utilities and any other areas on- or off-site that will be disturbed
in support of the construction activity.
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Specify construction fencing or similar protective measures
to prevent disturbance of natural drainage features, trees, vegetative
buffers and other existing features to be preserved.
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Slope Protection
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Slope protection shall be provided for disturbed or cut/fill
slopes that are one vertical on three horizontal (3H:1V) or steeper,
50 feet in length or longer, or on highly erodible soils. Show the
location and type BMPs to on the plans.
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Design Criteria
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Where feasible, add notes that prohibit disturbing the slope
until final site grading.
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Where a stabilized discharge point is available, provide temporary
berms or swales to direct stormwater away from the slope until the
slope is stabilized.
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Check dams shall be used within swales that are cut down a slope.
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Temporary terraces, vegetated strips or equivalent linear controls
shall be specified at regular intervals to break up slopes longer
than 50 feet until the slope is stabilized.
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Specify final stabilization measures to be initiated within
14 days of completing work on the slope.
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Hydromulch is prohibited for slope stabilization unless the
slope is one vertical on five horizon (5H:1V) or less.
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Channel Protection
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Show the location and type of BMPs used to prevent the erosion
of channels, drainageway streambanks, and outfalls until permanent
structures and final stabilization measures are installed.
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Design Criteria
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Provide temporary energy dissipaters at discharge points.
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If final channel stabilization consists of vegetation, anchored
erosion control blankets, turf reinforcement mats, or an equivalent
BMP that is resistant to channel flow shall be installed until the
vegetation is established.
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If the BMPs include check dams, velocity dissipaters or other
structures that extend into the channel, the BMPs shall be designed
by a licensed engineer to function under the flow conditions produced
by the design storm. The engineer shall verify that the BMPs will
not divert flow or cause flooding of adjacent properties and structures.
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Specify final stabilization measures to be initiated within
14 days of completing work on the channel.
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Temporary Stabilization
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Temporary stabilization practices shall be specified for disturbed
areas where work stops for 14 days or more.
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Design Criteria
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Stabilization measures shall be appropriate for the time of
year, site conditions, and estimated duration of use.
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Stabilization BMPs shall be provided for soil stockpiles.
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Final Stabilization
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Final stabilization practices shall be specified for disturbed
areas that are not covered by buildings, pavement or other permanent
structures upon completion of construction. Final stabilization measures
shall be coordinated with the site’s landscaping plan.
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Design Criteria
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Final stabilization shall be specified to start within fourteen
days of completing soil disturbing activities.
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If space is available, topsoil shall be stockpiled during construction
and distributed onto the surface of disturbed areas prior to final
stabilization.
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If topsoil has not been stockpiled, soil amendments (compost,
fertilizer, etc.) shall be specified with the final stabilization
measures.
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Final stabilization measures must provide a perennial vegetative
cover with a uniform density of 70% of the native background vegetative
cover or equivalent permanent measures (riprap, gabion, or geotextiles).
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Include notes requiring temporary BMPs be removed within 30
days of establishing final stabilization.
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Local Provisions:
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Temporary Stabilization
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Portions of a site that have been disturbed but where no work
will occur for more than 21 days shall be temporarily stabilized as
soon as possible, and no later than 14 days, except when precluded
by seasonal arid conditions or prolonged drought.
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Temporary stabilization shall consist of providing a protective
cover, without large bare areas, that is designed to reduce erosion
on disturbed areas. Temporary stabilization may be achieved using
the following BMPs: temporary seeding, soil retention blankets, fibrous
mulches, hydro-mulches and other techniques that cover 100 percent
of the disturbed areas until final stabilization can be achieved or
until further construction activities take place.
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Final Stabilization
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Hydro-mulch will not be allowed in vegetated swales, channels
or other drainageways. BMPs may remain in place during stabilization;
however, BMPs shall be removed after stabilization is achieved. The
plan for final stabilization shall be coordinated with the permanent
BMPs in the SWPPP and with the landscaping plan, if applicable.
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Notice of Termination (NOT)
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A NOT must be filed in accordance with the TCEQ TPDES General
Permit TXR15000, usually within 30 days after final stabilization
of operational control. All parties that submitted a NOI shall submit
a NOT within 30 days after final stabilization is established. When
the owner of a residential subdivision transfers ownership of individual
lots to builders before final stabilization is achieved, the SWPPP
shall include controls for each individual lot in lieu of final stabilization.
These controls shall consist of stabilization of the right-of-way
and placement of structural BMPs at the low point of each individual
lot or equivalent measures to retain soil on each lot during construction.
Additionally, the builder must submit a valid NOI before an NOT can
be submitted by the owner.
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14.4.3.2
Sediment Controls
Sediment control BMPs shall be designed to capture sediment
on the site when preventing erosion is not feasible due to ongoing
construction activity. Sediment control BMPs and their locations shall
be designed to change with the different phases of construction as
site conditions and drainage patterns change. Sediment controls for
the initial phase of construction shall be installed before any site
disturbing activities begin. Fact Sheets for different types of Sediment
Control BMPs are in Section 3.0 of the Construction Controls Technical
Manual.
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Sediment Barriers
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Sediment barriers may be linear controls (silt fence, compost
socks, sediment logs, wattles, etc.), check dams, berms, sediment
basins, sediment traps, active treatment systems and other structural
BMPs designed to capture sediment suspended in stormwater.
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Design Criteria
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Sediment barriers shall be designed to treat the volume of runoff
from the design storm. Sediment barriers are not required for areas
of the site that are undisturbed.
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If linear controls are used as the only sediment barrier for
a project, the linear control shall be provided at a rate of 100 linear
feet per quarter-acre of disturbed area. A series of linear controls
may be needed throughout the site and are not limited to the perimeter.
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Linear controls shall not be used across areas of concentrated
flow, such as drainage ditches, swales and outfalls.
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A sediment basin shall be provided where stormwater runoff from
10 acres or more of disturbed area flows to a common drainage location,
unless a basin is infeasible due to site conditions or public safety.
The basin shall be designed for the volume of runoff from the total
area contributing (on-site and off-site) to the common drainage location,
not just the volume from the disturbed portion of the contributing
area. Stormwater diversion BMPs may be used to divert stormwater from
upslope areas away from and around the disturbed area to minimize
the design volume of the sediment basin.
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Both existing topography and graded topography shall be evaluated
when determining if 10 acres or more discharges to a common location.
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If a sediment basin is infeasible on a site of 10 acres or more,
a series of smaller sediment traps and/or linear controls shall be
provided throughout the site to provide an equivalent level of protection.
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Permanent detention and retention basins may be used as a sediment
basin during construction if all sediment is removed upon completion
of construction.
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Perimeter Controls
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A linear BMP shall be provided at all down slope boundaries
of the construction activity and side slope boundaries where stormwater
runoff may leave the site. Linear sediment barriers may be used to
satisfy the requirement for perimeter controls.
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Storm Drain Inlet Protection
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Storm drain inlet protection shall not be used as a primary
sediment control BMP unless all other primary controls are infeasible
due to site configuration or the type of construction activity. Inlet
protection is intended to be a last line of defense in the event of
a temporary failure of other sediment controls.
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Design Criteria
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Municipality approval is required before installing inlet protection
on public streets.
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Inlet protection shall only be specified for low point inlets
where positive overflow is provided.
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Drainage patterns shall be evaluated to ensure inlet protection
will not divert flow or flood the roadway or adjacent properties and
structures.
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Construction Access Controls
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BMPs shall be provided to prevent off-site vehicle tracking
of soil and pollutants.
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Design Criteria
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Limit site access to one route during construction, if possible;
two routes for linear projects.
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Design the access point(s) to be at the upslope side of the
construction site. Do not place the construction access at the lowest
point on the construction site.
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Specify rock stabilization or an equivalent BMP for all access
points.
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Include notes requiring soil tracked onto public roads be removed
at a frequency that minimizes site impacts and prior to the next rain
event, if feasible.
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Using water to wash sediment from streets is prohibited.
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Dewatering Controls
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Water pumped from foundations, vaults, trenches and other low
areas shall be discharged through a BMP or treated to remove suspended
soil and other pollutants before the water leaves the site. The plans
shall include notes that prohibit discharging the water directly into
flumes, storm drains, creeks or other drainageways. Where state or
local discharge permit requirements exist for the pollutant(s) suspected
of being in the water, the plan shall include the discharge permit
conditions.
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Local Provisions: Special approval
is required by City of Azle regarding location and design of any inlet
controls. Where permitted, the operator will be expected to diligently
monitor storm conditions and to remove them when there is a risk of
flooding.
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14.4.3.3
Material and Waste Controls
Notes shall be placed on the iSWM Construction Plan for the
proper handling and storage of materials and wastes that can be transported
by stormwater. At a minimum, notes shall be provided for the materials
and wastes in Table 14.4.1. Additional notes and BMPs shall be provided
if other potential pollutants are expected to be on-site. Construction
details shall be provided when necessary to ensure proper installation
of a material or waste BMP.
All material and waste sources shall be located a minimum of
50 feet away from inlets, swales, drainageways, channels and waters
of the U.S., if the site configuration provides sufficient space to
do so. In no case shall material and waste sources be closer than
20 feet from inlets, swales, drainageways, channels and waters of
the U.S.
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Table 14.4.1. Requirements for Materials and Wastes
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Material or Waste Source
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Requirements
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Sanitary Facilities
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Sanitary facilities shall be provided on the site, and their
location shall be shown on the iSWM Construction Plan. The facilities
shall be regularly serviced at the frequency recommended by the supplier
for the number of people using the facility.
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Trash and Debris
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Show the location of trash and debris storage on the iSWM Construction
Plan. Store all trash and debris in covered bins or other enclosures.
Trash and debris shall be removed from the site at regular intervals.
Containers shall not be allowed to overflow.
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Chemicals and Hazardous Materials
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The amount of chemicals and hazardous materials stored on-site
shall be minimized and limited to the materials necessary for the
current phase of construction. Chemicals and hazardous materials shall
be stored in their original, manufacturer’s containers inside
of a shelter that prevents contact with rainfall and runoff. Hazardous
material storage shall be in accordance with all Federal, state and
local laws and regulations. Storage locations shall have appropriate
placards and secondary containment equivalent to 110% of the largest
container in storage. If an earthen pit or berm is used for secondary
containment, it shall be lined with plastic. Containers shall be kept
closed except when materials are added or removed. Materials shall
be dispensed using drip pans or within a lined, bermed area or using
other spill/overflow protection measures.
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Fuel Tanks
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On-site fuel tanks shall be provided with a secondary enclosure
equivalent to 110% of the tank’s volume. If the enclosure is
an earthen pit or berm, the area shall be lined with plastic. Show
the location of fuel tanks and their secondary containment on the
iSWM Construction Plan.
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Concrete Washout Water
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An area shall be designated on the iSWM Construction Plan for
concrete washout. A pit or bermed area, lined with plastic, or an
equivalent containment measure shall be provided for concrete washout
water. The containment shall be a minimum of 6 CF for every 10 CY
of concrete placed plus a one-foot freeboard. The discharge of washout
water to drainageways or storm drain infrastructure shall be prohibited.
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Hyper-chlorinated Water from Water Line Disinfection
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Hyper-chlorinated water shall not be discharged to the environment
unless the chlorine concentration is reduced to 4 ppm or less by chemically
treating to dechlorinate or by on-site retention until natural attenuation
occurs. Natural attenuation may be aided by aeration. Water with measurable
chlorine concentration of less than 4 ppm is prohibited from being
discharged directly to surface water. It shall be discharged onto
vegetation or through a conveyance system for further attenuation
of the chlorine before it reaches surface water. Alternatively, permission
from the sanitary sewer operator may be obtained to discharge directly
to the sanitary sewer.
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Vehicle/Equipment Wash Water
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Vehicle and equipment washing is prohibited on the site unless
a lined basin is provided to capture 100% of the wash water. The wash
water may be allowed to evaporate or hauled off for disposal.
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Soil Stabilizers
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Lime or other chemical stabilizers shall be limited to the amount
that can be mixed and compacted by the end of each working day. Stabilizers
shall be applied at rates that result in no runoff. Stabilization
shall not occur immediately before and during rainfall events. Soil
stabilizers stored on-site shall be considered a hazardous material
and shall meet all the requirements for chemicals and hazardous materials.
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Concrete Saw-cutting Water
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Slurry from concrete cutting shall be vacuumed or otherwise
recovered and not be allowed to discharge from the site. If the pavement
to be cut is near a storm drain inlet, the inlet shall be protected
by sandbags or equivalent temporary measures to prevent the slurry
from entering the inlet.
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Local Provisions: NONE
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14.4.3.4
Installation, Inspection and Maintenance
The iSWM Construction Plan shall include details and notes that
specify the proper installation, inspection and maintenance procedures
for BMPs. The BMPs for the initial phase of construction must be implemented
before starting any activities that result in soil disturbance, including
land clearing. Notes shall indicate the sequence of BMP installation
for subsequent phases of construction.
Notes on the iSWM Construction Plan shall indicate the frequency
of inspections and the areas to be inspected. Inspections shall include:
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Inspecting erosion and sediment controls to ensure that they
are operating correctly;
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Inspecting locations where vehicles enter or exit the site for
evidence of off-site tracking;
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Inspecting material and waste controls to ensure they are effective;
and
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Inspecting the perimeter of disturbed areas and discharge points
for evidence of sediment or other pollutants that may have been discharged.
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Erosion, sediment, and material and waste controls shall
be repaired, replaced, modified and/or added if inspections reveal
the controls were not installed correctly, are damaged, or are inadequate
or ineffective in controlling their targeted pollutant.
Notes for maintenance of BMPs shall require the removal of sediment
from BMPs when the sediment reaches half of the BMP’s capacity
or more frequently. Sediment discharged from the site shall be removed
prior to the next rain event, where feasible, and in no case later
than seven days after it is discovered. Upon completion of construction,
sediment shall be removed from all storm drain infrastructure and
permanent BMPs before the temporary BMPs are removed from the site.
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Local Provisions: See Section 14.5.5.
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(Ordinance 2012-10 adopted 8/21/12)
