SOW Att 5 - Pittsburgh ES Plan Final 2014.docx

EROSION AND SEDIMENTATION POLLUTION CONTROL PLAN

911th AIRLIFT WING

PITTSBURGH INTERNATIONAL AIRPORT

AIR RESERVE STATION,

MOON TOWNSHIP, PENNSYLVANIA

Prepared for:

HEADQUARTERS, AIR FORCE RESERVE COMMAND

HQ AFRC/CEVQ

255 Richard Ray Boulevard Robins Air Force Base, Georgia 31098-6137

Prepared by:

EA Engineering, Science, and Technology, Inc.

405 S. Highway 121 Building C, Suite 100 Lewisville, Texas 75067

Contract No. F41624-03-D-8596, Delivery Order 0015 EA Project No. 2970015

December 2004

Updated July 2014

Erosion and Sedimentation Pollution Control Plan PIA ARS

SOW Attachment 5

EROSION AND SEDIMENTATION POLLUTION CONTROL PLAN

PITTSBURGH INTERNATIONAL AIRPORT

AIR RESERVE STATION,

MOON TOWNSHIP, PENNSYLVANIA

[Insert Project Location Here]

Prepared for:

1113 Herman Avenue Coraopolis, PA 15108-4421

Prepared by:

[Insert Company Name Here]

[Current Date]

Erosion and Sedimentation Pollution Control Plan PIA ARS iv

QUALIFICATION OF THE PLAN PREPARER

[Insert preparer information]

TABLE OF CONTENTS

LIST OF APPENDICIES

Appendix

LIST OF FIGURES

Figure

LIST OF TABLES

Table

2-1 Rainfall Depth in Allegheny County, Pennsylvania for 24-Hour Duration Storms with Various Return Frequencies 2-2 Average Monthly Temperatures and Precipitation in Allegheny County, Pennsylvania 3-1 Soil Limitations for Town and Country Planning 3-2 Soil Limitations for Recreational Facilities

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Erosion and Sedimentation Pollution Control Plan PIA ARS v This document is to serve as a template for the A/E to create an Erosion and Sedimentation Pollution Control Plan for construction activities occurring on PIA ARS. This template should be modified by the A/E to provide information and Best Management Practices associated with the project type, size, and location.

INTRODUCTION

This Erosion and Sedimentation Pollution Control Plan (ESPCP) is intended to satisfy the requirements of the Pennsylvania Department of Environmental Protection (PADEP) Chapter 102 Rules and Regulation, and General Permit (PAG-2) for Stormwater Associated with Construction Activities (Appendix C). The PAG-2 applies to earth disturbance activities, other than agricultural plowing and tilling, timber harvesting activities, and road maintenance activities, that disturb one (1) acre or more occurring at Pittsburgh International Airport Air Reserve Station (PIA ARS). The permit also requires that a Notice of Intent (NOI) be submitted to PADEP or Allegheny County Conservation District (ACCD) at least 60 days prior to commencing the construction activity for general permits, and 120 days for individual permits. Act 67, 68, and 127 of Pennsylvania Code requires permit applicants to notify local governments of planned land development activities and to provide local governments the opportunity to identify any land use planning or zoning ordinance conflicts associated with the proposed project before the Department or authorized county conservation district completes its review of the NOI/permit application. The municipality and county government must receive the written notice at least thirty (30) days before the Department may issue or deny a permit. The written notice (letter) must also include either a completed DEP General Information Form (GIF) or answers to the 5 Land Use Information questions found in Appendix A of the general permit.

Under the terms of agreements with the PADEP, ACCD administers Chapters 92a and 102 of the Clean Streams Law, which were established to prevent pollution of the waters of the Commonwealth by sediment runoff from construction sites. ACCD requires that ESPCPs must be prepared for earthmoving projects disturbing more than 5,000 square feet in the County, and must be available at the project site at all times. Projects that disturb less than 5,000 square feet are not required to develop an ESPCP; however these sites are still required to implement BMPs to minimize erosion and sedimentation. When the total area of a project exceeds one (1) acre, a PAG-2 permit is required. These sites are also required to develop a Post Construction Stormwater Management Plan (PCSMP). ACCD reviews ESPCPs and conducts regular site inspections to assure measures provided for in the plan are in place and are functioning properly. Figure 1-1 illustrates a decision chart to aid in developing an ESPCP.

Specifically, this plan covers the [insert the name of the specific construction project here] project at PIA ARS located in Moon Township, Allegheny County, Pennsylvania. Figure 1-1 is the PIA ARS site map and Figure 2-2 presents the location of PIA ARS. Figure 4-1 in Appendix F presents construction project site map at PIA ARS.

Figure 1-1 ESPCP Flow Chart Are you disturbing more than 5,000 ft2?

Yes No

Are you disturbing more than 1 acre?

No ESPCP necessary, however BMPs are still required

No Yes

Develop an ESPCP Develop an ESPCP along with a PCSMP.

Apply for a PAG-2 permit and submit permit and Plans to ACCD.

Figure 1-2 Map of Pittsburgh International Airport Air Reserve Station

Project Scope [Project scope should be inserted here.]

The ESPCP Application and Owner / Operator Information The ACCD Application for ESPCP Adequacy Review is in Appendix B. The owner (PIA ARS) and operator (construction contractor) of record for this project is as follows: [insert the applicable information in the table below] Table 1-1 Owner /Operator Information Facility Name:

Pittsburgh International Airport Air Reserve Station

Project Name:

Owner:

Pittsburgh International Airport Air Reserve Station

Address 1:

Address 2:

City, State, and Zip Code:

Point of Contact:

Position/Title:

Phone:

Email:

Operator:

Address 1:

Address 2:

City, State, and Zip Code:

Point of Contact:

Position/Title:

Phone:

1-3

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1-4

TOPOGRAPHIC FEATURES OF THE PROJECT AREA

Topography PIA ARS and the surrounding area are characterized by a hilly topography (Figure 2-1). The north part of the PIA ARS lies in the graded plateau section of the airport and contains the aircraft aprons and hanger. The facility is characterized by nearly level plateau to moderately steep sloping topography, with elevations ranging from 1,147 feet (ft) mean sea level (MSL) in the north to 1040 ft MSL at the southeast border. The land occupied by PIA ARS is largely improved acreage that has been previously disturbed.

80o 12’ 33” W 40o 29’ 42” N 4483 N N N

Source: USGS Oakdale Quadrangle (1993) Figure 2-1 Topographical Map of PIA ARS and Surrounding Region

Location Map PIA ARS is located in Moon Township, Allegheny County, Pennsylvania in the southwest corner of the State. The 115-acre facility is located in Moon Township approximately 15 miles west of downtown Pittsburgh. The west and south boundary of PIA ARS abuts the Pittsburgh International Airport, while the eastern boundary is defined partially by Airport Parkway (Business 60). Figure 2-2 shows the location of the PIA ARS in relation to Western Pennsylvania and the surrounding region. PIA ARS is home to the 911th Airlift Wing (AW), which is comprised of three groups and one medical unit.

Figure 2-2 Location Map of Pittsburgh International Airport Air Reserve Station, Pennsylvania

Land Use and Development

Current Land Use PIA ARS has a total of 50 buildings, two of which are transient housing facilities. The largest concentration of buildings is classified as an industrial land use category and includes facilities for civil engineering, supply, petroleum, oil, and lubricant (POL), and vehicle maintenance. Aircraft operations and maintenance facilities make up the second largest land use category, while the remaining buildings are used for administrative office space, dining, training, security, and other miscellaneous activities. Existing land uses include aircraft operation and maintenance, industrial, administrative, medical and housing, airfield, outdoors recreation and open space.

Future Development Opportunities for future development exist at PIA ARS. Capital improvements involving future development will include construction of additional multi-story buildings and building expansions and upgrades for aircraft operation and maintenance, industrial, and administrative use.

Land development activities are the main cause of accelerated soil erosion at PIA ARS. Heavy equipment is used to remove vegetation, grade, and relocate soil during construction. This process leaves large tracts of land and soil piles barren and exposed to precipitation. These conditions are extremely conducive to soil erosion. Although most land disturbing activities at the PIA ARS are less than one acre, a few will be over one acre. Erosion and sedimentation controls will always be required to control land-disturbing activities that may cause significant impact to the downstream watercourses. Most construction activities are and will continue to be low-density residential and utility projects. There is an overall PIA ARS Installation Development Plan (IDP) that governs general base development, but construction projects are done individually, not as part of a large plan.

Wetland Section V of the Mapping Report for United State Air Force Greater Pittsburgh Air Reserve Station dated October 17, 1994 indicates that there is no wetland area within the PIA ARS at that time. The report is in Appendix I.

PIA ARS Drainage Patterns and Receiving Waters PIA ARS is situated within the Ohio River Basin. The unnamed tributary to McLaren’s Run is the major surface drainage stream for the PIA ARS. This stream flows in a southwesterly/south direction south of the PIA ARS, until its confluence with the McLaren’s Run. McLaren’s Run flows in a southeasterly direction and confluence with Montour Run which eventually discharges into the Ohio River several miles downstream. The unnamed tributaries of McLaren’s Run and McLaren’s Run have no classification pursuant to Chapter 93.

Climate Allegheny County averages 36 inches of rain per year that is distributed equally throughout the year. Summers average 82.5 degrees and are humid. The average temperature in the winter is 33.7 degrees and snow does accumulate during the winter months with March often being the snowiest month. Table 2-1, 2-2, and 2-3 shows the rainfall depth for 24-hour duration storms with various return frequencies, average monthly precipitation and temperatures respectively.

Table 2-1. Rainfall Depth in Allegheny County, Pennsylvania for 24-Hour Duration Storms with Various Return Frequencies

Table 2-2 Average Monthly Temperatures and Precipitation in Allegheny County, Pennsylvania

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3-1 3-3

TYPE DEPTH, SLOPE AND EXTENT OF THE SOILS

Soil Map Three soil series were mapped at the PIA-ARS (Appendix K) and include soils from the Atkins silt loams, Gilpin, Weikert, and Culleoka shaly silt loams, Urban land-Culleoka complex, gentle sloping and the Urban land-Culleoka complex, moderately steep Series mapping units. Table 3-1 summarizes the soil limitations for town and country planning, and Table 3-2 for recreational facilities.

Table 3-1. Soil limitations for town and country planning

Source: Modified from Soil Survey of Allegheny County, Pennsylvania.

Table 3-2. Soil limitations for recreational facilities

Source: Modified from Soil Survey of Allegheny County, Pennsylvania.

Physical Characteristics of the Soils

Gilpin, Weikert, and Culleoka shaly silt barns (GSF) GSF - Gilpin, Weikert, and Culleoka shaly silt barns, very steep - This mapping unit is in long, narrow, contour areas on valley sides that parallel the unnamed tributary of McLaren’s Run stream on the east and southeast areas of PIA ARS. Slopes are convex and are 25 to 80 percent. The composition of this mapping unit is more variable and areas are generally much larger than those of most other mapping units in the county. But mapping is adequate for the anticipated uses of the soils. In the northern part of Allegheny County, areas of this mapping unit are about 50 percent Gilpin soils, 25 percent Weikert soils, and 25 percent other soils. In the southern part of the county, the areas are about 40 percent Culleoka soils, 35 percent Weikert soils, and 25 percent other soils. The Weikert soils in this mapping unit have the profile described as representative of the Weikert series. Included in mapping are small areas of soils that have some characteristics of the Gilpin, Weikert, and Culleoka soils and a few areas of Hazleton, Wharton, and Dormont soils. Also included are small areas of soils that have slopes of less than 25 percent, a few areas where the soils are eroded and the subsoil is exposed, and scattered bedrock ledges. Surface runoff is rapid to very rapid. The soils in this mapping unit have limitations for community development and recreation use (Table 3-1 and 3-2) because of their depth to bedrock and slope. They are not suited to cultivated crops because of their slope and for construction sites as it is located within the stream bed and construction will not be done on the stream bed. These soils are suited to woodland and wildlife habitat.

Urban land-Culleoka complex (UCB) UCB - Urban land-Culleoka complex, gently sloping - This mapping unit is on the top of ridges or in long, narrow areas on hillsides and is located at the western and central part of the PIA ARS. Slopes are 0 to 8 percent. The composition of this mapping unit is more variable and areas are generally much larger than those of most other mapping units in the county. Mapping is adequate, however, for the anticipated uses of the soils. The complex is about 75 percent Urban land, 15 percent Culleoka soils, and 10 percent other soils. In the Urban land part, the natural soils and underlying bedrock have been cut from some places and used as fill in other places. Buildings and other structures cover many of these areas. Much of the exposed cut and fill material is strongly acid to extremely acid. Included in mapping are small areas of Gilpin, Dormont, Guernsey, and Wharton soils and small areas where slopes are more than 8 percent. Also included, mostly in the suburbs, are areas that are mainly Culleoka soils. In other areas, such as much of Pittsburgh, the Culleoka soils are minor in extent. In some areas, very steep cut and fill escarpments are also included. Areas of this complex are variable, and onsite investigation is required to determine the kind and degree of limitations for land use (Table 3-1 and 3-2). The intense urban development generally precludes most other uses.PIA ARS

Urban land-Culleoka complex (UCD) UCD - Urban land-Culleoka complex, moderately steep - This mapping unit is on hillsides and is located in the north, central and south part of PIA ARS. Slopes are 8 to 25 percent. The composition of this mapping unit is more variable and areas are generally much larger than those of most other mapping units in the county. Mapping is adequate, however, for the anticipated uses of the soils. The complex is about 65 percent Urban land, 20 percent Culleoka soils, and 15 percent other soils. In the Urban land part, the natural soils and under- lying bedrock have been cut from some places and use as fill in other places. Buildings and other structures cover many of these areas. Much of the exposed cut and fill material is strongly acid to extremely acid. Included in mapping are small areas of Gilpin, Dormont, Guernsey, Weikert, and Wharton soils and small areas of soils that have slopes of less than 8 percent or more than 25 percent. Also included, mostly in the suburbs, are areas that are mainly Culleoka soils. In other areas, such as much of Pittsburgh, the Culleoka soils are very minor in extent. In many areas, very steep cut and fill escarpments are also included. Areas of this complex are variable, and onsite investigation is required to determine the kind and degree of limitations for land use (Table 3-1 and 3-2). Slope is generally a limitation. The intense urban development precludes most other uses.

Description of the Soils for the Project Area [Insert description of the soils for the construction project site]

PROPOSED ALTERATION TO THE PROJECT AREA

Impacted Area The impacted area of the construction project site is the total area to be disturbed by excavation, grading staging area, or other earthmoving activities. The total area of the site that is expected to be disturbed includes areas of grubbing, clearing, excavating, filling, or grading including off-site borrow areas. The disturbed/impacted area for specific construction project is described below.

Construction Project Site Description [Insert description of the construction project site and reference the site plan drawing in Appendix F.]

Site Plan Drawing Site plan drawing for the [Insert construction project site] (Figure 4-1 in Appendix F) shows the:

· Existing topographical features that adequately describes the site at a scale interval of 1 inch equals 50 feet or less, with 2-foot contour interval;

· Location of earth-disturbing activity of the site including associated off-site borrow or spoil areas with respect to roadways, municipalities, streams, water courses;

· Existing and proposed contours. A delineation of drainage watersheds expected during and after major grading activities as well as the size of each drainage watershed, in acres;

· Soils types for all areas of the site, including locations, depth and slope;

· Existing and planned locations of buildings, roads, parking facilities and utilities and other identifiable landmarks;

· Location of all erosion and sediment control practices, including the location of areas likely to require temporary stabilization during the course of site development;

· Sediment and storm water management basins if required, noting their sediment settling volume and contributing drainage area;

· Permanent storm water management practices to be used to control pollutants in storm water after construction operations have been completed;

· Areas designated for the storage or disposal of solid, sanitary and toxic wastes, including dumpster areas, areas designated for cement truck washout, and vehicle fueling;

· Location of designated construction entrances where the vehicles will access the construction site; and

· Location of any in-stream activities including stream crossings if project is adjacent to a stream.

8-4

AMOUNT OF RUNOFF FROM THE PROJECT AREA AND UPSTREAM WATERSHED

Calculating the Amount of Runoff from the Construction Project and Upstream Watershed Area The area draining to a particular Best Management Practice (BMP) must be determined. In some instances the drainage area will increase or decrease as the site grading proceeds. In such cases, the maximum drainage area to the BMP selected (Section 7.0 and 8.0) must be used to determine the design capacity. Design capacity requirements for BMPs are included below.

The procedures for calculating the storm water runoff volume and peak runoff for storm water ponds are shown below:

Weighted Coefficient Select the appropriate runoff coefficient from Table 2 of Erosion and Sediment Pollution Control Manual by PADEP (Appendix G). For drainage areas with mixed land uses, compute a weighted average (Cw) of the “C” values for the individual subareas according to the following formula:

Cw = (C1 x A1) + (C2 x A2) + Cn x An) A(total)

Discharge Design Capacity Calculate time of concentration (travel time for the hydraulically longest watershed flow path) by adding the calculated travel time for Sheet flow, shallow concentrated flow and channel flow as outlined on Page 9 of Erosion and Sediment Pollution Control Manual by PADEP (Appendix G). Due to the irregular topography, the maximum sheet flow length to be used for unpaved areas in Pennsylvania is 150 feet with a most likely maximum length of 50-100 feet. The theoretical maximum length of 300 feet is achieved only in unique situations such as uniformly sloped paved parking lots. The maximum flow path length (L) for any disturbed area is 50 feet. The sheet flow equation is not used for newly graded fills or cut slopes. Runoff from these areas is considered shallow concentrated flow.

Peak Flow Runoff Estimation of peak flow rates (Appendix G) in small watershed of 200 acres or less for construction projects will use the following rational equation:

Q = C I A Where: Q = Peak runoff rate in cubic feet per second (cfs) C = Cw = Runoff coefficient (dimensionless) (See following steps for explanation of Cw) I = Rainfall intensity (inches/hour)** A = Drainage area (acres) **Use worksheets 19 and 20 or Figure 2 on Page 11 in Erosion and Sediment Pollution Control Manual to determine the rainfall intensity.

Calculations for Anticipated Peak Flows for Designed Storms [An analysis of the impact that runoff from the project site will have on existing downstream watercourses' resistance to erosion and design computations for appropriate protective measures for downstream watercourses if required should be inserted in this section. Calculations for anticipated peak flows for the storm should be included in this section.]

STAGING AND SCHEDULE OF EARTHMOVING ACTIVITES

The following section includes a description of appropriate controls and measures that will be implemented at the construction site including: (1) initial perimeter control BMPs, (2) intermediate grading and drainage BMPs, and (3) final BMPs. This section identifies the appropriate staging and access requirements for construction. Additionally, the appropriate control measures and the timing during the construction process are described for each major activity. Implementation and maintenance of all controls described in this section are the responsibility of the construction contractor.

PIA ARS and its contractors must make use of practices which preserve existing natural conditions as much as possible. Such practices may include: preserving riparian areas adjacent to surface waters of the state, preserving existing vegetation and vegetative buffer strips, phasing of construction operations in order to minimize the amount of disturbed land at any one time and designation of tree preservation areas or other protective clearing or grubbing practices. This ESPCP includes measures to perform the following:

· Minimize the amount of disturbed soil

· Prevent runoff that originates in offsite areas from flowing across disturbed areas

· Slow down the runoff flowing across the site

· Remove sediment from onsite runoff before it leaves the site, and

· Meet or exceed local or State requirements for sediment and erosion control plans

The construction contractor must strictly comply with placement and maintenance of erosion control devices during all stages of construction, including the post-construction period until vegetation or other means of soil stabilization have been established.

Sequence of Major Earthmoving Activities [Insert and modify the this section to describe detailed step by step construction sequence] Soil disturbing activities will include: clearing and grubbing; installing a stabilized construction entrance, perimeter, and other erosion and sediment controls; grading; excavation for the sedimentation pond, storm sewer, utilities, and building foundations; construction of curb and gutter, roads, and parking areas; and preparation for final planting and seeding of disturbed areas.

Summary of intended sequence of major activities that will disturb soils are:

(a) Initial Perimeter BMPs/Stabilization Measures

(b) Clearing and Grubbing Activities

(c) Excavation Activities

(d) Infrastructure Activities

(e) Immediate Stabilization

(f) Final Stabilization/ Landscaping

Nature of construction activity:

Soil disturbing activities, which will take place in phases (a) through (d), will accomplish the following tasks:

Site preparation:

· Install and employ erosion and sediment controls including sediment barriers and storm drain protectors,

· Establish screening fence separating the construction area from the adjacent areas,

· Site clearing,

· Remove surface debris encountered during excavation and relocate to designated on-site locations

· Provide and employ dust suppression equipment and techniques to control fugitive dust emissions during excavation activity

· Miscellaneous site work, including site cleanup, restoration, and temporary or permanent re-vegetation of areas disturbed during construction activities. Cover stockpiles when not in use.

Implementation Schedule The construction contractor will submit a project implementation schedule, similar to the implementation schedule outlined in Table 6-1 and in Appendix H, which describes the sequence of major construction operations (i.e. grubbing, excavating, grading) and the implementation of erosion, sediment and storm water practices to be employed during each operation of the sequence, and become a part of the ESPCP.

Table 6-1. Implementation Schedule* Implementation Schedule

Initial Perimeter BMPs/Stabilization Measures

Clearing and Grubbing Activities

Excavation Activities

Infrastructure Activities

Immediate Stabilization

Final Stabilization/ Landscaping

* The Implementation Schedule needs to be updated with project specifics

The project implementation schedule will include: initial erosion control and stabilization measures, initial mobilization, initial clearing and grubbing, excavation of borrow material, debris relocation and related earthwork; secondary erosion and sediment controls installation, and permanent landscaping stabilization.

TEMPORARY CONTROL MEASURES

This section outlines the erosion and sediment control BMPs to be implemented by the construction contractor at the construction site, with oversight from 911th Civil Engineering personnel. The erosion and sediment control BMPs will be used for a site being disturbed and will be implemented as per PADEP Erosion and Sediment Pollution Control Manual. Examples of selection conditions include the aerial extent of the site, presence of critical slopes, proximity to storm sewer inlets or surface waters, and volume of run-on to a site. The selection of improper or inadequate erosion and sediment control BMPs can cause serious erosion and allow large quantities of sediment to enter waters of Commonwealth of Pennsylvania.

[It is the responsibility of the A/E to select the appropriate BMPs described below for construction project site. See the PADEP Erosion and Sediment Pollution Control Manual for more information. The A/E shall provide construction details and supporting calculations as well as make reference to location of the BMPs on the construction project site drawing in Appendix F.]

Sediment Barriers Sediment barriers are physical barriers that are designed to capture and stop sediment from flowing further downstream. Periodic inspections of sediment barriers are necessary to check for any sediment piles or undercutting of barriers that may occur. Prompt removal of sediment and maintenance of undercutting allows sediment barriers to function properly. Sediment barriers will be installed before initiation of earthmoving activities:

· Downstream from a construction site at the toe of a slope,

· Where no other practice is feasible, and where there is no concentrations of water in a channel or drainage way above the barrier, and

· Only where sheet flow would take place.

Filter Socks

Filter socks (Figure 7-1) are a specific type of sediment barrier that are designed to intercept and stop sediment from sheet flow runoff. Filter socks are flexible temporary barriers of geotextile fabric (filter cloth) used to intercept sediment-laden runoff from small drainage areas. Filter socks can be used to promote sheet flow, to reduce runoff velocity, and to help retain transported sediment on the site, thus reducing erosion and enhancing water quality. Filter socks are especially useful on steep slopes. Heavy vegetation should be removed prior to install the sock. Filter socks can be used on rocky slopes if sufficient preparation is made to ensure good contact of the sock with the underlying soil along its entire length. They may also be used on pavement as a perimeter control. The anticipated functional life of a biodegradable filter sock should be 6 months; for photodegradable socks it is 1 year. Some other types may last longer. Projects with disturbances anticipated to last longer than the functional life of a sock should plan to replace the socks periodically or use another type of BMP.

As with other sediment barriers, filter socks should be placed parallel to contour with both ends of the sock extended upslope at a 45 degree angle to the rest of the sock to prevent end-arounds. Socks placed on earthen slopes should be anchored with stakes driven through the center of the sock or immediately downslope of the sock at intervals recommended by the manufacturer. Where socks are placed on paved surfaces, concrete blocks should be used immediately downslope of the socks (at the same intervals recommended for the stakes) to help hold the sock in place. Socks should be placed at maximum slope lengths recommended by the manufacturer.

Upon stabilization of the tributary area, the filter sock may be left in place and vegetated or removed. In the latter case, the mesh is typically cut open and the mulch spread as a soil supplement. In either case, the stakes should be removed.

Adapted from PennDOT

Figure 7-1 Filter Sock

Rock Filter Outlets

Rock filter outlets (Figure 7-2) are structures designed to control erosion at the outlet of a channel or conduit by reducing the velocity of flow and dissipating the energy. These structures are installed where straw bale barriers or sediment barriers have been undermined or topped, but may also be added at any time, as necessary. Sediments must be removed when accumulations reach 1/3 the height of the outlet.

Figure 7-2 Rock Filter Outlet

Rock Construction Entrance

Rock construction entrances will be constructed to minimize soil removal form the construction site. However, rock construction entrances with wash racks will be considered wherever soil and/or traffic conditions on site require washing the construction vehicle wheels prior to exiting the site to avoid excessive tracking of mud onto a highway. Approaches to the wash rack will be lined with AASHTO #1 or R-3 rock a minimum of 25’ on both sides. The wash rack will discharge to a sediment removal facility, such as a vegetated filter strip or into a channel leading to a sediment removal device. Rock construction entrances will be constructed to the minimum length, width, and thickness dimensions shown on Figure 7-3. Rock construction entrances will be maintained to the specified dimensions by adding rock when necessary at the end of each work day. A stockpile of rock material will be maintained on site for this purpose. Sediment deposited on paved roadways will be removed and returned to the construction site.

Modified from Maryland DOE

Figure 7-3 Rock Construction Entrance

Sediment Basins

A sediment basin is formed by constructing an embankment with a stone outlet across a drainage swale, to detain sediment-laden runoff from disturbed areas and allow enough time for the sediment to settle out. A sediment storage zone of 1,000 cubic feet per disturbed acre within the watershed of the basin is required. A dewatering zone of 5,000 cubic feet for each acre tributary to the basin is to be provided. Reductions in the dewatering zone are allowed unless the basins is in a HQ or EV watershed, however the minimum required dewatering zone is at least 3,600 cubic feet per acre.

Sediment basins must have a flow length to width ratio of at least 2:1. Sediment basins must dewater in a period ranging from 2 to 7 days. Skimmers are the preferred dewatering device, however perforated risers are also acceptable. Every sediment basin should be provided with an emergency spillway with a minimum bottom width of 8'. The elevation of the emergency spillway crest must be at least 6” above that of the principal spillway (top of dewatering zone). Sediment basin spillways must be able to discharge 2 cfs/acre from the entire contributing watershed. A minimum of 24 inches of freeboard is required above the elevation of the 2 cfs/acre. A sediment storage zone of 1,000 cubic feet per disturbed acre within the watershed of the basin is required. The elevation at which the required capacity is provided should be marked on a clean-out stake located near the center of the basin. Accumulated sediment shall be removed from the basin whenever it reaches that elevation on the clean-out stake. A dewatering zone of 5,000 cubic feet for each acre tributary to the basin is to be provided. Reductions in the dewatering zone are allowed unless the basins is in a HQ or EV watershed, however the minimum required dewatering zone is at least 3,600 cubic feet per acre.

If the emergency spillway is being used to provide part of the 2 cfs/acre discharge, the freeboard must be provided above the design flow elevation in the emergency spillway. When a perforated riser is selected as the means to dewater the basin, the diameter of the riser should be at least 1.25 times that of the outlet barrel. The minimum riser diameter is 15”. The minimum barrel diameter is 12”. In some instances a sediment basin may be later used for a stormwater management pond. In those cases it may be necessary to use a temporary riser while the basin is performing as a sediment basin (Figure 7-4).

Adapted from VA SWCC

TYPICAL SECTION

Figure 7-4 Diagram of a Sediment Basin

NOTE: This figure is for illustration purposes only and should not be used as a construction detail.

Rock Filters Rock filters may be used to control runoff within constructed channels until the protective lining is installed. They may also be used below construction work within an existing stream channel while flow is being diverted past the work area. In such cases, the filter should be located between the work area and the discharge from the bypass system. Rock filters may not be used in lieu of sediment basins. Rock filters may be used to control sediment originating within a channel, either during construction of the channel (before the channel is stabilized) or during a temporary disturbance within the channel. Rock filters may not be used in collector channels in lieu of sediment basins. Rock filters should not be used in lieu of appropriate channel linings. This practice often results in overtopping of the channel during storm events, scouring of the channel bottom below the filter, or erosion of the channel side slopes as sediment deposits build up behind the filter.

Rock filters should not be used in lieu of an adequate protective lining in sediment basin emergency spillways. This can reduce the effective discharge capacity of the spillway and, in doing so, increase the possibility of embankment failure.

Rock filters should be constructed according to the specifications shown in Figure 7-5. Rock filters should be constructed with Riprap sized as follows:

· For channels with Total Depth > 3 feet, use R-4.

· For channels with Total Depth between 2 and 3 feet, use R-3.

· For channels with Total Depth between 1 and 2 feet, use R-2.

Rock filters should not be used in channels of less than 1-foot total depth. The filter should be equal in height to ½ the total depth of the channel with a 6” depression in the center. A 1- foot thick layer of AASHTO #57 stone should be placed on the upstream side of the filter. Rock filters should be inspected weekly and after each runoff event. Clogged filter stone (AASHTO # 57) should be replaced. Needed repairs should be initiated immediately after the inspection. Sediment must be removed when accumulations reach 1/ 2 the height of the filters. Immediately upon stabilization of each channel, accumulated sediment and Rock Filter will be removed and disturbed areas stabilized.

Figure 7-5 Rock Filter

Dust Control Dust controls for earth disturbance activities reduce the potential for particles being carried through air or water. Types of dust control are:

· Irrigation as a temporary measure involving a light application of water to moisten the soil surface. The process should be repeated as necessary.

· Minimizing soil exposure to reduce the amount of soil available for transport and erosion.

· Wind breaks that reduce airborne particles by slowing wind. Leaving existing trees and large shrubs in place creates effective windbreaks. Other temporary types of windbreaks are solid board fences, snow fences, tarp curtains, bales of hay, crate walls, and sediment walls.

Dust controls can be used on any site where dust may be generated and where the dust may cause onsite and offsite damage. When possible, work that causes soil disturbance should be done in phases and should be accompanied by temporary stabilization measures. This control should be used in conjunction with other sedimentation controls such as sediment traps.

Temporary Stabilization Temporary stabilization measures can be taken, such as temporary seeding, mulching, and dust control. Temporary vegetative stabilization is encouraged whenever a site is undisturbed for more than three weeks. Annual plants, which sprout rapidly and survive only one growing season, are suitable for temporary vegetative stabilization. Annual plant species include: Kentucky bluegrass, tall fescue, meadow fescue, colonial bent grass, and brome.

Off-Site Soil Disposal and Storage Cut and fill practices at construction sites require the movement and stockpiling of large quantities of soil. Excess soil may be stored at the construction site, moved to other parts of the base, or taken to an off-site construction waste disposal facility. All soil stockpiles should be covered by rainproof material or temporarily stabilized (i.e., temporarily seeded, graded with slopes of 2:1 or less) until they are reused or spread at the site. Soil that is stockpiled is subject to the same control measures as other disturbed areas.

PERMANENT CONTROL MEASURES/STABILIZATION METHODS

Upon completion of construction activities, the project site must be permanently stabilized to prevent accelerated erosion. Permanent stabilization, such as permanent seeding and planting, buffer zones, preservation of natural vegetation, and stream bank stabilization, needs to be implemented for long-term benefits to reduce erosion and fluctuating drainage patterns. All slopes, channels, ditches, or any disturbed area should be stabilized as soon as possible after final grade has been completed. Final stabilization is achieved when:

· All soil disturbing activities at the sites are complete;

· A uniform perennial vegetative cover (e.g., evenly distributed, without large bare areas), with a density of at least 70 percent cover for the area, has been established on all unpaved areas and areas not covered by permanent structures or equivalent stabilization measures (such as the use of mulches, rip-rap, gabions or geotextiles) have been employed; and

· All temporary erosion and sediment control practices are removed and disposed of and all trapped sediment are permanently stabilized to prevent further erosion.

[Select the appropriate BMPs described below for construction project site. Provide construction details and supporting calculations. Make reference to location of the BMPs on the construction project site drawing in Appendix F]

Site Stabilization Stabilization on slopes that are 3:1 or steeper, and more than 40” high, benches at 30” vertical intervals are recommended. Surface roughening and erosion control blankets should be applied to all slopes steeper than 3:1 unless a stable rock face is provided. Surface roughening is the practice of providing a rough soil surface with horizontal depressions for the purpose of reducing runoff velocity, increasing infiltration, aiding the establishment of vegetation, and reducing erosion. Details for Stair Stepping, Grooving, and Tracking are provided below.

STAIR STEP (Figure8-1) grading may be conducted on slopes having bedrock soft enough to be ripped by a bulldozer. Wherever stair step grading is used the size of the horizontal cut should exceed that of the vertical cut by at least 10”. Individual vertical cuts should not exceed 30” in soft materials or 40” in harder rock. The horizontal cut should be graded toward the vertical cut (i.e. into the cut).

Figure 8.1 Stair Step Grading of Cut Slopes

GROOVING (Figure 8-2) slopes consists of using machinery to create depressions parallel to contour along the slope. In softer materials and on slopes gentler than 3:1, this may be done with discs, tillers, or harrows; the teeth of a front end loader may be used for harder materials. Grooves should be at least 3” deep and no more than 15” apart.

Figure 8-2 Grooved Slope Details

TRACKING SLOPES (Figure 8-3) is done by running tracked machinery up and down the slope, leaving tread marks parallel to the contour. If a bulldozer is used, the blade should be up. Care should be exercised on soils having a high clay content to avoid over-compaction.

Figure 8-3 Tracking a Fill Slope

Non-Structural Preservation Methods Contractors must make use of practices which preserve the existing natural condition as much as feasible. Such practices may include: preserving riparian areas adjacent to surface waters of the state, preserving existing vegetation and vegetative buffer strips, and phasing of construction operations in order to minimize the amount of disturbed land at any one time and designation of tree preservation areas or other protective clearing or grubbing practices.

Stream Protection If construction activities disturb areas adjacent to streams, structural practices outlined above will be designed and implemented on site to protect all adjacent streams from the impacts of sediment runoff. No structural sediment controls (e.g., the installation of a sediment barrier or a sediment settling pond in-stream) will be used in a stream. For all construction activities immediately adjacent to surface waters of the state, it is recommended that a setback of at least 25-feet, as measured from the ordinary high water mark of the surface water, be maintained in its natural state as a permanent buffer. Where impacts within this setback area are unavoidable due to the nature of the construction activity (e.g., stream crossings for roads or utilities), the project will be designed such that the number of stream crossings and the width of the disturbance within the construction area are minimized. Any work and construction activity conducted within 50 feet of the tributary boundary requires a PADEP General Permit 3 (PG-3).

Seeding and Mulching The PADEP recommends the use of the Penn DOT’s Publication # 408, Section 804 (Appendix J) as a reference to use for selection of species, seed specifications, mixtures, liming and fertilizing, time of seeding, and seeding methods. Specification for seeding may also be obtained by contacting Allegheny County.

The PADEP also recommends that soil testing be done prior to seeding and mulching to determine the proper soil amendments and application rates for the proposed seed mixture(s). Site conditions such as soil limitations, steepness of slope, and proposed land use should be considered in selecting seed mixtures. Wherever seeding is to be done on steep slopes (> 3:1), seed mixtures should be selected that are appropriate for steep slopes. Fill slopes should be seeded and mulched at regular vertical increments (15’ max.) as the fill is being constructed. In critical areas (e.g. adjacent to or within 50' of streams, ponds, or wetlands), consideration should be given to providing a protective blanket for seeded areas. Mulch with netting or protective blankets should be provided for seeded areas on slopes steeper than 3:1. All seeded areas should be mulched to minimize the potential for failure to establish an adequate vegetative cover. Mulching may also be used as a temporary stabilization of disturbed areas in non-germinating seasons.

General Seeding Requirements Seeding rates are stated as pounds per acre (lb/A) of pure live seed (PLS). PLS is the product of the percentage of pure seed times the percentage of germination divided by 100 (e.g. [85% pure seed × 72% germination] ÷ 100 = 61% PLS). Actual seeding rates may be determined by dividing the PLS seeding rate by the %PLS shown on the seed tag, or calculated as shown above (e.g. for a PLS seeding rate of 12 lb/A from a seedlot with a PLS of 35%, the actual seeding rate is equal to 12 ÷ 0.35 = 34.3 lb/A). If more than one species is used, indicate the application rate for each species. General requirements for seeding are in Appendix J.

Vegetative Strips A vegetative filter strip consists of a well-vegetated, grassy area below a disturbed area that can be used to remove sediment from runoff prior to its reaching water body. To be effective, the vegetative cover must be established prior to the disturbance and runoff must be in the form of sheet flow.