Stormwater Management

Outline

• Background• Colorado Regulatory Requirements• Stormwater Management Plans (SWMPs)• Best Management Practices (BMPs)• Questions

Background

• In 1992, the State of Colorado stormwater regulation went into effect to control municipal and industrial stormwater discharges, based on EPA regulations.

• The State regulation(5 CCR 1002-61) covers discharges from specific types of industries including construction sites, and storm sewer systems for certain municipalities. In Colorado, the program is under the Colorado Department of Public Health &Environment.

• The Colorado program is referred to as the Colorado Discharge Permit System (CDPS), and regulated stormwater discharges from construction activities are covered under the CDPS General Permit for Stormwater Discharges Associated with Construction Activities (the Stormwater Construction Permit)

Background

• June 30, 2005 – The Colorado Water Quality Control Division extends permitting for stormwater discharges from construction activities associated with small construction activity (those that disturb between one and five acres)– Stormwater permitting was previously required

for all sites with disturbance in excess of five acres

Colorado Regulatory Requirements

• Stormwater Discharges are Regulated by the CDPHE Water Quality Control Division– Stormwater permit coverage is required for all

construction activities that disturb one acre or greater• Coverage is also required for construction that is

part of a larger common plan of development• Oil & gas activities covered include construction of

well pads, road, pipelines, pumping stations, etc.

Colorado Regulatory Requirements (cont.)

• Permit coverage for construction activities is obtained under CDPHE’s Construction General Permit– Application for coverage must be submitted at

least 10 days prior to the start of construction– A Stormwater Management Plan (SWMP) has

to be prepared at the time the application is submitted

– Implementation of SWMP must occur immediately upon initiation of construction

Colorado Regulatory Requirements (cont.)

• CDPHE Permit Requires Routine Self-Inspections– Active Sites (Disturbed but Not Seeded)

• Must be inspected at least once every 14 days and after any precipitation or snowfall event that causes erosion

– Completed Sites (Seeded but not Stabilized)• Must be inspected at least once every month

– Stabilized Sites (at least 70% vegetation established)• Inspections no longer required

– Inspections are not required when snow cover exists over the entire site for an extended period and melting conditions do not exist

– Inspection records must be maintained for a period of 3 years and must be made available to CDPHE/EPA upon request

Colorado Regulatory Requirements (cont.)

• CDPHE Allows Some Flexibility in Defining the Area to be Covered by a Stormwater Permit– Single site with disturbance greater than 1

acre– Multiple sites within a common plan of

development• Interpreted to be sites up to ¼ mile apart

and/or having the area between the sites disturbed

Colorado Regulatory Requirements (cont.)

• Final Stabilization as Applied to Construction– Construction has been completed and disturbed

areas have been built on, paved, or at least 70% of pre-disturbance vegetation has been established or equivalent permanent, physical erosion reduction methods have been employed

– Stabilized unpaved surfaces – Dirt road surfaces and portions of pads that cannot be revegetated due to operational necessity are considered finally stabilized as long as they are prepared as to prevent ongoing erosion issues

Stormwater Management Plans (SWMPs)

• SWMP Goal– to describe appropriate controls and measures

to improve water quality by reducing pollutants in stormwater discharges and ensure compliance with the requirements of the stormwater permit. The SWMP must be completed and implemented at the time the project breaks ground, and revised if necessary as construction proceeds to accurately reflect the conditions and practices at the site.

Stormwater Management Plans (Cont.)

• SWMP Requirements– General Requirements• Prepared in accordance with good engineering,

hydrologic and pollution control practices• Identifies Best Management Practices (BMPs)• Identifies potential sources of pollution associated

with construction activity• Construction operations must implement the

provisions of the SWMP

Stormwater Management Plans (Cont.)

• SWMP Requirements (cont.)– Narrative Site Description

• Describe construction activity• Sequence for major activities• Estimates of total area of site and area that will be

disturbed• Estimate of runoff coefficient of the site before and after

construction• Location of other potential pollution sources• Location and description of non-stormwater components

of discharge (springs, landscape irrigation return, etc.)• Name and description of receiving water(s) or municipal

storm sewer

Stormwater Management Plans (Cont.)

• SWMP Requirements (cont.)– Site Map

• Construction site boundaries• Areas of soil disturbance• Areas of cut and fill• Areas used for storage of building materials, soils or

wastes• Location of any dedicated batch plants• Location of major erosion control facilities or structures• Surface waters• Boundaries of 100-year flood plains

Stormwater Management Plans (Cont.)

• SWMP Requirements (cont.)– BMPs and Other Controls

• Description of appropriate controls and measures that will be implemented– Structural Practices– Non-Structural Practices– Identify procedures to control spills, etc. (coordinate

with SPCC plans)– Identify other measures to control pollutants (waste

disposal, limiting off-site soil tracking, etc.)– Site stabilization methods

– Inspection and maintenance procedures

Stormwater Management Plans (Cont.)

• SWMP Requirements (cont.)– SWMP Revision• The SWMP must be modified to accurately reflect the

actual field conditions and BMPs used

– SWMP Administration• The SWMP must be on site during active construction

and site inspections and available to those directly responsible for installing an maintaining BMPs

Best Management Practices (BMPs)

• Reflect the measures taken to control stormwater as dictated by the SWMP.

• Proper selection and implementation of BMPs are the keys to an effective stormwater management program– Common sense approach– There is no one right answer– Often involves trial and error to find what works best

• Describe a wide range of structural treatment processes, pollution prevention practices, schedules of activities, prohibition on practices, and other management practices

Best Management Practices (cont.)

• BMPs fall into 2 general categories– Nonstructural – Operational/managerial techniques, such as

• Phasing of operations• Housekeeping practices• Spill prevention• Preventive maintenance• Preserving natural vegetation

– Structural – Physical processes• Erosion Control BMPs – Practices to prevent the erosion

of soil• Sediment Control BMPs – Practices to remove sediment

from runoff

BMP Examples

Silt Fence

The silt fence needs to be repaired and BMPs should not be placed in drainage waters of the US

The silt fence has been installed correctly

Straw Bales/Waddles

• This technique utilizes bound straw bales to filter sediment from runoff of small areas

• Limitations– Filters sheet flow from small drainage areas– Short term use– Decomposes and/or consumed by livestock– Removal of stakes will be necessary after stabilization is

complete• Installation

– Embed into trench– Anchor with 2 stakes (metal or wood)– Compact backfill on the upgradient side– Use at outfall points from sediment ponds, diversion ditches,

turnouts, etc.

Straw Bales/Waddles

Sediment Pond (Trap)

• This technique uses a pond to hold sediment-laden water so that sediment can settle and water is absorbed into the soil. Sediment traps are useful for construction sites where excessive runoff will need to be captured and filtered.

• Limitations– Size of surrounding area– Require regular maintenance due to sediment build-up

• Installation– Excavate trap or basin within area where runoff may be directed

toward– Sideslopes should be machine compacted– Sideslopes should be 2:1 or flatter– Volume of trap should handle runoff from 2-year storm event– Construct spillway or outfall structure with rock, straw bale, or

other appropriate BMP

Sediment Pond

Vertical and steep slopes should be avoided as these will result in erosion

Diversion Ditch

• This technique is useful to filter sediment from concentrated flows and/or runoff of moderate grades and larger drainage areas. Additionally, rock berms may be utilized to reduce velocity of flows within diversion ditches

• Limitations– Availability and/or cost of rock– Difficult to remove after construction– Require regular maintenance due to sediment build-u

• Installation– Use medium to large diameter rock– May secure rock within woven wire sheathing (not required)– Berm side slopes should be 3:1 or flatter– Top of berm should be a minimum of 2 feet wide

Diversion Ditch

Geotextiles/Erosion Blankets

• Geotextiles and erosion blankets are typically a porous fabric constructed of woven fibers. They are useful for stabilization and preventing erosion on slopes, especially adjacent to streams

• Limitations– Decompose– Effectiveness depends on proper installation– Expensive

• Installation– Select appropriate fabric type for necessary purpose– Remove any protruding rocks and smooth soil prior to installation– Fabric needs to be entrenched into the soil– Anchor fabric securely– Apply seed prior to fabric installation for final stabilization of sitesFollow manufacturer’s recommendations for installation

Erosion Control Blanket

Surface Roughening (Tracking)

• This technique utilizes the horizontal grooves created by tracks of construction equipment to reduce runoff flow velocities. Tracks are established on the slopes perpendicular to water flow.

• Limitations– Not for use on rocky slopes– May cause soil compaction which limits vegetation re-

growth– Roughening may have to be re-established if lost due to

heavy sheet flow runoff• Installation

– Tracking should be done up and down the slope, not across the slope

Surface Roughening

Road-Side Ditches

• This technique requires construction channels parallel to access roads. The ditches convey concentrated runoff of surface water from roads and surround areas to a stabilized area

• Limitations– Erosion occurring within channel– Channel does not necessarily filter sediment from runoff

• Installation– Excavate channel along roadside to a width and depth that can handle

expected flows– Slope channels so that water velocities do not cause excessive erosion– Install BMPs into the ditches to slow water velocities and collect

sediment

Road-Side Ditches

Berm/Water Bar

• This technique may be used to collect runoff from undisturbed areas and divert around construction activity. Additionally, berms can be used to limit the accumulation of water volume by diverting runoff from construction area into a stabilized outlet (i.e. rundown, sediment pond) or a well-vegetated area

• Limitations– Not for use on concentrated flows– May cause concentrated flows from sheet flow– Requires vegetative cover or other filter at discharge point

• Installation– Pile and compact soil (berms need to be compacted to hold water,

prevent blow-outs and minimize vandalism/intention breaches)– The side slopes should be 2:1 or flatter– Increase the frequency of water bars with an increased slope– Discharge should enter a well-vegetated cover (water bars) or a

stabilized out (a constructed sediment pond)

Water Bar

Questions ?