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GRADING AND EXCAVATION MANUAL 2010 Edition

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SECTION 5: EROSION & SEDIMENT CONTROL

The Summit County Engineering Department administers all water quality control regulations in unincorporated Summit County by and through the authority granted in the Code and in state statutes, as a means to control pollution of surface waters entering Green Mountain and Dillon reservoirs and their tributaries, as well as to avoid overwhelming roadway drainage systems, culverts, and other stormwater conveyances that may exist in the County. The water quality control regulations established in the Code, in the Water Quality Control Manual (per §7004 of the Code, titled “Erosion and Sediment Control During Construction”), and in this Manual are created in order to prevent such pollution, and to prevent sedimentation of wetlands, protect creeks and streams and their associated floodplains, and to limit as much as possible civil disputes arising from unlawful trespasses in the form of erosion and sedimentation. All of these effects can be affected by the proper implementation of the standards presented in this Manual, in the Code, in the Water Quality Control Manual, and in supplemental reference materials (i.e. the Urban Drainage and Flood Control District (UDFCD) publication “Urban Storm Drainage Criteria Manual, Volume III” (USDCM VIII)). The Water Quality Control Manual presents a relatively in-depth discussion of the merits of, and justification behind, the standards and policies presented here. For that reason, this Manual will focus on specifics regarding the County standards, procedures, and policies applied to specific development projects. Any questions regarding these standards or their specific application to a project may be directed to the Engineering Department.

The primary goal of all water quality control is to limit the amount of erosion and/or sediment carried offsite in storm runoff. To that end, before any earth disturbing activities are undertaken, the first step is to plan the scheduling and coordination of the project such that the majority of disturbance is completed during the season when the probability of a significant rainfall event is at a minimum. In Summit County, depending on your location within the County, the excavation season typically ranges from about eight months (in the lowest elevations) to five months (at the highest elevations). This can become a very significant and costly constraint if it is not taken into consideration when planning and scheduling a project. Ideally, all excavation in the County should begin between May 1 and June 15, depending on seasonal conditions and location, and all excavations would be “buttoned up” no later than September 30. Buttoned up, in this context, means all excavated areas are backfilled, all grading for landscaping is completed in this timeframe, and revegetation (at least temporary) is installed. Adhering to this timeframe will allow for corrections and modifications to be made in the month prior to the first permanent snow of a season, and for those years where a late spring snowmelt prevents an earlier start. While we recognize that this is not possible because of the myriad other constraints and factors that dictate when a project begins or ends, this should be a guideline used to begin planning a project.

In addition to scheduling a project, equally effective in the prevention of erosion and sediment discharge is limiting the amount of disturbance involved in a project. The State of Colorado Department of Public Health and Environment (CDPHE) Water Quality Control Division (WQCD) requires Stormwater Construction Permits for any project involving over five acres of disturbance, and most projects involving over one acre of disturbance. Although the CDPHE permits do not apply to most single family permits, they do apply to most multi-family, commercial, industrial, institutional, and highway projects in the state. As part of the application for these permits a Storm Water Management Plan (SWMP) must be submitted to the CDPHE WQCD. Where a SWMP is required by the state, a copy of that plan and permit should be submitted to the Engineering Department for our records. On single-family projects, and projects where a SWMP is not required, the applicant/owner/contractor must follow similar guidelines to those that would be included in a SWMP for a state permit. In those cases where a SWMP is not submitted, the applicant shall submit plans to the County showing how they will limit disturbance to the minimum amount required for the project, protect those disturbed areas from erosion, prevent any erosion or sediment from leaving the project site boundaries, and permanently stabilize all disturbed areas from future erosive impacts.

Commonly referred to as Best Management Practices (BMP’s), the steps taken to limit erosion can be very simple or very complicated, based on the required disturbance and duration of a project. The first and most effective BMP is limiting disturbance. Once a disturbance limit is established, there are many possible structural BMP’s that may be implemented on a project during construction. These include but need not be limited to silt fencing, straw wattles (aka straw logs), gravel check dams, sedimentation ponds, concrete washout areas, vehicle tracking control pads (VTC), terracing, slope drains, grass buffers or swales, and run-on diversion. A fairly thorough discussion of these and other BMP’s can be found in the USDCM Vol. III published by the UDFCD or the Water Quality Control Manual published by the Summit County Engineering Department. At a minimum, all projects in Summit County should incorporate a VTC, silt fence or straw wattles (depending on slope and size of project), orange construction fence (OCF) or some other means of delineating a disturbance area, and concrete washout areas. Where a project drains to a County roadside ditch, gravel check dams should also be included in the ditch line periodically to the lowest hydrologic point of the project. Attached in the appendices of this manual are some details of commonly used BMP’s in the County. In addition to the details provided here, the USDCM Vol. III provides a comprehensive bank of details and procedures.

Prior to issuance of any GE permit, an erosion control inspection is required for the inspection of the construction BMP’s and/or evaluation of the applicability of specific BMP’s. There may be cases where it is not logical to install certain BMP’s at the beginning of a project, for example it is not reasonable to expect that a VTC is installed before the access to the project is constructed. In these cases follow-up inspections at specified stages of the project are appropriate and will be required. Failure to schedule inspection at the appropriate stages of a project may be grounds for cancelled inspections, stop-work orders, fines, or other legal action depending on the severity of the impacts of the transgression. The final inspection of any project (as required and with procedures specified in §6302.08: Inspection of Project Grading Work of the Code) will include inspection of the final structural BMP’s as well, including drainage structures (swales, channels, check dams, etc…), detention ponds, revegetation, and slope netting. Slope netting will be required on all finished grades with slopes steeper than 3:1. All disturbed areas of a site shall be revegetated with a native, weed-free grass seed mix prior to final approval by the Engineering Department. In areas where the native soil or site fill does not appear to be capable of fostering seed growth, topsoil or compost augmentation may be required. Re-inspection of failed items will be charged a re-inspection fee in accordance with the fee schedule approved by the BOCC and published on the County website, or available at the Planning and Engineering Department offices.

GRADING AND EXCAVATION MANUAL 2010 Edition

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