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MN Stormwater comment page

Erosion Prevention And Sediment Control: INSPECTOR’S COMPLIANCE GUIDE (under Minnesota’s General Storm Water Permit for Construction Activity)

When doing inspections:

1. Document time and date of the inspection, weather conditions and on-site contact persons.
2. Report any potential violations to the general contractor and representative of the owner.
3. Document all potential problems in field notes and photographs.

RECORDS

The project’s final plans and specifications, which include both temporary and permanent control plan requirements, must be available at the construction site in either a field office or an inspector’s or contractor’s vehicle.

Temporary Erosion and Sediment Control Plan, completed in accordance with the permit Appendix A must be available within 24 hours.

Permanent Erosion and Sediment Control Plan, completed in accordance with the permit Appendix B must be available within 24 hours.

Records of all inspections must be available within 24 hours, including:

• date of all rainfall events
• date and time of inspections,
• finding of inspections,
• corrective actions taken (including dates and times), and
• documentation of all changes to the Temporary Erosion and Sediment Control Plan made during construction.

If the records requirements are not being complied with, it may be a violation of permit provisions (see permit provisions parts I.C.1, I.C.2.a, I.C.2.b, I.C.2.c).

Permit Coverage Card

A notice of stormwater permit coverage card must be placed in a visible location at the construction site throughout the duration of the project. The card can be placed at any of the following locations:

• construction site entrance, visible from the nearest public roadway;
• where no construction site entrance exists, at a location visible from the nearest public roadway;
• at the field office (if applicable); or

• for linear utility and noncontiguous municipal projects (i.e., city street improvements), at the office responsible for the project’s administration.

If the records requirements are not being complied with, it is a violation of permit provisions (see permit provisions parts I.C.2.d, I.C.3).

EROSION AND SEDIMENT CONTROL DURING CONSTRUCTION

Erosion Control. Permittee must use horizontal slope grading, construction phasing, temporary diversions, and/or other practices that minimize erosion.

Exposed slopes within 100 lineal feet from a water of the state, or from a curb, gutter, storm sewer inlet, or temporary or permanent drainage ditch that is connected to a water of the state should have temporary protection or permanent cover within the following time frames:

• steeper than 3:1, within 7 days.
• less than 3:1, but steeper than 10:1, within 14 days.
• flatter than 10:1, within 21 days.

If erosion control is not being complied with, it is a violation of permit provisions (see permit provisions parts I.D.1.a, I.D.1.b).

Ditch and Outlet Stabilization. The bottom of any temporary or permanent drainage ditch constructed to drain water from a construction site must be stabilized within 100 lineal feet from a water of the state. Stabilization must be initiated within 24 hours of connecting the drainage ditch to a water of the state, existing gutter, storm sewer inlet, drainage ditch or other stormwater-conveyance system that discharges to waters of the state. Stabilization must be completed within five calendar days. (Note: Normally this should be completed before connection)

Before to connecting any pipe to a water of the state or drainage ditch, the pipe’s outlet must be provided with temporary or permanent energy dissipation to prevent erosion.

If the ditch and outlet stabilization is not being complied with, it is a violation of permit provisions (see permit provisions parts I.D.1.c, I.D.1.d).

PERIMETER CONTROLS.

All down gradient perimeter sediment-control bmps must be in place before any up gradient land-disturbing activity begins.

The permittee must minimize vehicle tracking of sediment off-site wherever vehicles exit the construction site onto paved surfaces. In areas where curb and gutter exist, inlet protection must be in place, along with a plan to keep impervious surfaces free of sediment.

Where 10 or more contiguous acres of exposed soil contribute to a discernible point of discharge, temporary sedimentation basins meeting the following criteria must be provided prior to runoff leaving the site of entering waters of the state:

• Basins must provide 1,800 cubic ft of storage per exposed acre drained.

• Basin outlets must be designed to prevent short circuiting and the discharge of floating debris.

If the perimeter controls are not being complied with, it is a violation of permit provisions (see permit provisions parts I.D.2.a, I.D.2.b, I.D.2.c.1, I.D.2.c.2).

If permanent ponds are required, they can often be used in place of temporary ponds, but construction sediment should be removed before final Notice of Termination has been submitted.

BMP INSPECTION

Inspect all erosion- and perimeter-sediment-control BMPs to ensure integrity and effectiveness. All nonfunctional perimeter-sediment-control BMPs should be repaired when the trapped sediment reaches one-third of the height, or replaced or supplemented with functional BMPs within 24 hours of discovery. All nonfunctional erosion-control BMPs should be repaired or replaced within 24 hours of discovery, or as soon as field conditions allow access.

Inspect all sedimentation basins to ensure their effectiveness. When the depth of the sediment collected in the basin reaches the heights of the riser, or the storage volume, the basin should be drained and the sediment removed within 72 hours of discovery, or as soon as field conditions allow access.

If inspection and maintenance is not being complied with, it is a violation of permit provisions (see permit provisions parts I.E.1.a, I.E.1.b).

SEDIMENT LEAVING THE SITE

Inspect all drainage ditches and other waters of the state for evidence of sediment leaving the site. Unless the project has received approval or certification for depositing fill into waters of the state, the permittee should remove all sediment in drainageways, catch basins or other waters of the state and restabilize the areas where sediment removal results in exposed soil. The removal and stabilization must take place within seven days of discovery unless precluded by legal, regulatory or physical access restraints. If precluded, removal and stabilization must take place within seven calendar days of obtaining access.

Inspect all construction site vehicle exit locations for evidence of sediment being tracked off-site. Sediment should be removed from paved surfaces which do not drain back into the construction site within 24 hours of discovery.

If sediment leaving the site is not being inspected and corrected, it is a violation of permit provisions (see permit provisions parts I.E.1.c, I.E.1.d).

VIOLATION FOLLOW-UP

Alleged violations must be brought to the attention of the on-site general contractor and representative of the owner (if that person is present) before leaving the site.

Inspectors should follow this procedure:

1. Thoroughly and accurately document all potential violations through the use of fieldinspection notes, photographs and audiovisual equipment, if possible.
2. Write up a detailed inspection report and transmit it to the responsible party as soon as possible after the inspection.
3. Request all potential violations be corrected in accordance with the time frames specified in the permit.
4. Report continued potential violations and inadequate response to inspections to the MPCA.

Violations not remediated in accordance with the time frames specified in the permit are subject to MPCA enforcement action, pursuant to Minn. Stat. §§ 115.071, 116.072, and 609.671, for violation of water-quality environmental laws.

Sample Check List:

CHECKLIST FOR RESOURCE MANAGEMENT PLAN REVIEW BY: SCOTT SOIL AND WATER CONSERVATION DISTRICT

General information to be included with or as part of the Resource Management Plan (RMP):

• Project Description – narrative describing the nature and extend of the land disturbing activity.
• Existing Site Conditions – describe existing topography, drainage patterns and wetlands.
• Soils – show soil boundaries, include: mapping unit, soil name, slopes and hydrologic group.
• Location Map – show the site with respect to the surrounding areas.
• Drawing Data – indicate north, show scale and include benchmark for horizontal and vertical datum.
• Plan Preparer – name and phone number of individual responsible for plan preparation.
• Existing Contours – show existing 2 foot contours (at least 200 ft beyond property boundaries).
• Final Contours – show proposed 2 ft contours for proposed grading.
• Existing Vegetation – show different cover conditions for the entire site with approximate areas.
• Property Boundaries – show property boundaries, lot lines, section lines and adjacent plats.
• Adjacent Areas – narrative describing which neighboring properties will be affected by proposed plat.
• Elevation and Grade – street and ditch grades, pond, wetland, lake NWL and HWL, pipe inverts.
• Location of BMP’s – location of erosion and sediment control features (BMP Criteria).
• Location of Utilities – location of existing and proposed utilities if known.

Stormwater Management information to be included on or with the Resource Management Plan

• Drainage Areas – show existing and proposed drainage areas used for stormwater analysis.
• Runoff Curve Numbers (RCN’s) – detailed breakdown of existing and proposed RCN’s used.
• Impervious Coverage – list assumptions for determining impervious area (house pad, driveway, etc.

List new impervious area for each subwatershed (if 1 acre or more drains to a discernible point, a wet detention pond is needed for treatment of runoff prior to discharge to water of the state according to W.W. Walker criteria. If development does not require a pond based on these standards and the development will be creating over an acre of impervious, a wet detention pond is still needed).

• Drainage Calculations – show calculations for 2, 10 and 100 year peak discharge rates comparing existing and proposed conditions with comparable subwatersheds (TR 55 method or similar methodologies).
• Precipitation Events – rainfall depths for the 2, 10 and 100 year 24-hour frequency storm events are 2.8, 4.2 and 6.0 inches respectively (reference US Weather Bureau Technical Paper 40). Stormwater ponding will be based on the 6.0 inch event. On site conveyance systems will be designed for the 4.2 inch event.
• Detention Pond – calculations for pond used to control peak discharge rates (BMP Criteria)
• Wet Detention Pond – NURP pond used for nutrient removal and peak discharge rate control. Show calculations for estimated inflow and outflow, permanent and temporary storage volumes, mean depth, outlet design, downstream stabilization, emergency spillway, pond profile and pond cross section. (W.W. Walker criteria.)
• Floatable Skimmers – included on outlet of wet detention ponds. Show construction details on plan.
• Volume Increase – increased RCN’s will increase the volume and duration of runoff leaving the site. These increases in volume and duration may have a negative effect on downstream conveyance.
• Ground Water Sensitivity – areas identified as being highly susceptible to ground water contamination need the following standards incorporated into the design of the wet detention pond: pond will be lined with 2 ft of impermeable soil.
• Flood Plain – show protected waters on the grading plan with associated predicted 100 year flood plain. Show calculations for 100 year flood plain predictions.
• Any land locked areas need to be accounted for in the design analysis for existing conditions. If no outlet is present, what is the predicted 100 year flood elevation and how will this be maintained?
• Show existing tile lines. Design should plan as though tiles will no longer function unless an easement is supplied for future maintenance.

Erosion Control information to be included on or with the Resource Management Plan

• Implementation Schedule – list the order of operations for construction activities. Include:

1. Phasing of construction – start and completion dates for each phase.
2. List order of operations – all erosion control measures shall be installed and must be functional prior to upslope grading activities taking place.
3. Contact Person – individual responsible maintaining the erosion and sediment control features.
4. Disposal or removal of erosion and sediment control features upon final stabilization of project.
5. Pond clean out – removal of sediment from pond upon final stabilization to design elevations.

• Critical Erosion Areas – describe areas with potential for serious erosion problems.
• Limits of Disturbed Area – if 5 acres or more drain to a discernible point, then a temporary sediment control basin is needed to treat runoff.
• Stabilization of exposed and soil stockpile areas.
• Stabilizing of waterways and outlets – on site conveyance systems capable of handling the 5 year 24-hour frequency storm (3.6”) without erosion.

1. Adjacent properties protected from erosion.
2. Storm Sewer Inlets – protection provided to prevent sediment laiden water from entering (if applicable).
3. Permanent Erosion Control – grass seed, fertilizer and mulching specifications and rates listed. Mulch anchoring methods and time requirements for permanent seeding listed. (15 days after substantial grading completed).

• Rip Rap – rip rap placed at all culvert outfalls to minimize scour.
• Rock Construction Entrances – entrances planned where applicable to minimize tracking onto roads.
• BMP Construction Details – include on the erosion control plan all construction details for BMP’s used.
• Incorporate horizontal slope grading where applicable.

Wetlands

• Has wetland delineation been submitted to the LGU and the Scott Soil and Water Conservation District for review.
• Have the wetlands been surveyed as part of the plat.
• Show normal water levels and 100 year flood elevations for all wetlands.
• Have wetland easements been identifed around all wetland areas delineated as wetland.
• Have wetland regulations been complied with prior to approval of preliminary plat.

Erosion Prevention and Sediment Control: PROVISIONS IN CONTRACTS

Once the planner has decided upon methods of pollution prevention and control, the plan must be implemented. Work that is being constructed under unit-priced contracts will require a clear and concise explanation of the requirements in contract documents.

The specifications for the job should include a detailed description of the pollution-preventionand- control work required, stating clearly what is required, when it is required and who is responsible for carrying it out. Do not rely upon a boilerplate statement of the contract that states that the contractor must comply with all local ordinances to cover all pollution-prevention-andcontrol work. Any work that will be required should be clearly described and included in appropriate bid items. Unit-priced bid items are suggested because they provide more flexibility for quantity variations than do lump-sum bid items. A sample contract specification for including details on this work is shown below.

The best construction-and-management practices possible will not help if they are not installed at the proper time. The contract should specify that sediment-control structures must be installed before the contributing drainage area is disturbed. There are times when this may not be possible, but those are the exception and not the rule. Also, sediment-control structures will not be effective unless they are maintained. Specifications should indicate how and when practices should be maintained. Another provision that may be important to include on some jobs is to require approval for the contractor to open new work areas. This provision is not intended to prevent the contractor from having an efficient operation; it is intended to prevent areas from being stripped several months before they are needed. It also provides an opportunity to discuss sediment-control measures for the area that is about to be opened.

The drawings for a job should show the location for planned pollution-prevention-and-control structures. Details of structures should also be shown so they are installed and maintained properly. During construction, change orders may be needed to address additional pollution-preventionand-control needs that are identified in the field. Also, the contractor’s operation may eliminate the need for certain measures or may alter the location where they will be most effective. All changes to the plan should be documented.

Sample Construction Specification for Pollution Control

1. Scope

The work should consist of installing measures or performing work to control erosion and minimize delivery of sediment and other pollutants to water and air during construction operations in accordance with these specifications.

2. Materials

All materials should meet the requirements of the Material Specifications listed in these specifications.

3. Erosion- and Sediment-control Measures

The measures should include, where appropriate, but not be limited to, the following (as shown on the drawings or as specified in the appropriate section of this specification).

• Staging of Earthwork Activities. The excavation and moving of soil materials should be scheduled so that the smallest possible area will be unprotected from erosion for the shortest time feasible.
• Seeding. Seeding to protect disturbed areas should be used as specified on the drawings or in the appropriate sections of this specification.
• Soil Stabilization. Soil stabilizers, mulching, sodding, erosion-control blankets or turf-reinforcement mats should be used as appropriate to temporarily protect soil surfaces from erosion.
• Diversions. Diversions should be used to divert water away from work areas or to collect runoff from work areas for treatment and safe disposition.
• Stream Crossings. Stream crossings should be used where fording of streams by equipment is necessary.
• Sediment Basins. Sediment basins should be used to settle and filter out sediment from eroding areas to protect water quality and properties below the construction site.
• Silt Fences. Silt fences should be used to trap sediment from areas of limited runoff. Silt fences are temporary and should be removed when the contributing area is permanently stabilized.
• Inlet Protection. Inlet protection is required in the permit and should be used as appropriate.
• Waterways. Waterways should be protected by the safe disposal of runoff from surface areas, diversions, and other structures or measures.

Sample Construction Specification for Pollution Control (cont.)

4. Chemical Pollution Gasoline, oil, sanitary facilities, such as toilets, and other chemicals or tanks should not be located next to streams, wells or springs. They should be located a sufficient distance to prevent water contamination, and should be installed in accordance with all state and local regulations.

The contractor should provide tanks, barrels, secondary containment, dikes, spill-collection materials or sumps (using approved materials) to collect pollutants produced as a byproduct of the project’s work (for example, drained lubricating or transmission oils, hydraulic fluid, antifreeze/ coolants, greases, soaps or asphalt). At the completion of work, the pollutants should be removed from the site and disposed of in accordance with state and local regulations.

5. Air Pollution

State and local regulations concerning the burning of brush, slash or other materials must be adhered to. In no case will tires be allowed to ignite or be burned with tree or brush piles. All public or haul roads used during construction of the project should be maintained as necessary to suppress dust.

6. Maintenance and Removal

All measures and works should be adequately maintained in a functional condition as long as needed during the construction operation. All temporary measures should be removed and the site restored as nearly to original condition as practicable as directed by the engineer.

7. Measurement and Payment

For all items of work for which specific unit prices are established in the contract, each item will be measured to the nearest unit applicable. Payment for each unit will be made at the contract unit price for that item. Such payment will constitute full compensation for all labor, materials, equipment, tools, labor, and other items necessary and incidental to the completion of the work.

8. Withholding

Payment will be subject to withholding of a portion of the contract amount to cover the reasonable value of any uncompleted operation that is designated as a part of the complete project. The amounts withheld for erosion control will be based upon the estimated surface area exposed to probable erosion without the required surface-finishing and turf establishment operations being completed.

9. Items of Work and Construction Details'

In this section, you should list specific practices that are required, material specifications, maintenance requirements, etc. Be certain to specify when they must be installed, and how long they must remain in place.