Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Erosion & Sediment Control Measures

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1 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Erosion & Sediment Control Measures 4.0 EROSION & SEDIMENT CONTROL MEASURES After performing the analysis summarized above, Burns & McDonnell civil engineers, construction personnel, and environmental personnel walked both Newgate/Phelps Road and Hatchett Hill Road areas on July 21 and 22, Another site walk of both areas was conducted on March 30, Prior to both visits to these areas it had rained steadily for 24 to 36 hours. Some surface runoff, primarily channel flow, was observed. Although not analytically confirmed, observations in the field lead Burns & McDonnell to believe the drainage problems in some areas may be partially due to ground water seepage rather than overland flow, particularly in the Newgate/Phelps Road area. 4.1 VEGETATION REMOVAL A dense tree canopy currently exists in both areas, however it would be necessary to remove 80 to 100 feet of this forested area along the east side of the existing transmission lines to construct the Project. Although no impervious surfaces will be created, and only a small percentage of each sub-basin would be impacted, the vegetation removal would result in a small, short-term increase in surface water flow coming from both areas. This increase would be mitigated somewhat because the majority of the stumps from the cut vegetation would be left in place, as would the leaf and duff layer that has accumulated over time. The recommended control measures will ensure that the remainder of the small increase in runoff will be effectively controlled until site stabilization is achieved. The existing root systems, leaf layer, and duff layer would also help minimize the potential for erosion. Additionally, many of the hardwood tree and shrub stumps can be expected to start re-sprouting soon after the cutting, sometimes during the same growing season. Many of the stored seeds of a variety of tree, shrub, and herbaceous species in the leaf and duff layers would also respond vigorously to the increased light and water and quickly germinate. Therefore, these areas would very likely re-vegetate themselves quickly. The areas where hemlock is more prevalent (Hatchett Hill Road Area) would likely take longer to re-vegetate, therefore these areas would be more prone to increased erosion potential. In all areas, the stability of the sites would be closely monitored by environmental inspectors, including the third party inspector that the CSC has ordered CL&P to hire. This third party inspector will perform weekly inspections of all disturbed sites, and on a bi-weekly basis will report directly to the CSC. If conditions warrant additional controls (beyond current recommendations), any of the following measures, at a minimum, could be used to temporarily stabilize the site until natural vegetation, which will be maintained in an early successional state according to NU s vegetation maintenance standards, has successfully re-established itself: installing staked hay bales, silt fences, filter socks/logs, mulch, and erosion control blankets; as well as Northeast Utilities 4-1 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 17 of 36

2 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Erosion & Sediment Control Measures seeding disturbed ground with fast growing herbaceous species. It is not anticipated, nor is it recommended, that planting of native trees and shrubs will be necessary within the cleared areas. As stated above, it is expected that the natural vegetation will quickly reestablish itself within these areas. Supplemental plantings of native trees and shrubs would require regular maintenance (most importantly watering), would likely be impacted by deer and other wildlife browsing, and very likely would quickly be overtopped by the resprouting natural vegetation. As a result mortality of these supplemental plantings would likely be high. 4.2 NEWGATE/PHELPS ROAD AREA EROSION & SEDIMENT CONTROL The long-term quantity of runoff is not expected to increase because pre- and post- runoff coefficients are the same. However control measures are proposed to mitigate the small, short-term increase in runoff and protect against the movement of sediment from disturbed portions of the Project. Due to the linear conditions of the Project Route, the most effective method of erosion and sediment control in the Newgate/Phelps Road area is a combination of rock check dams and silt fence, and quick stabilization of disturbed ground, to re-establish ground cover. Due to the difference between concentrated flow and sheet flow, different erosion control measures are recommended. As shown on the Site Drawings in Appendix A, the majority of the sediment control consists of silt fence on the down slope side of the construction and clearing areas to control and filter sheet flow leaving the site. Because the largest threat of erosive volume and velocity results from the installation of on-site improvements, silt fence or wire-reinforced silt fence should be installed up slope from some of the crane pads. This installation provides two benefits: 1. Protecting the crane pads (required to safely construct the Project) from water gaining enough velocity to cause erosive damage to them and 2. Slowing the water velocity as it moves across the site, providing an additional measure of protection for the residents down slope. Stone check dams will be installed within three areas of concentrated flow identified near Line List 1092 and 1093, and up slope of Line List 1130 and 1144 to control and filter runoff leaving these areas. An area of concentrated flow identified by the owner of Line List 1083 originates from the forested area uphill and to the east of the ROW. In this area several very small, ephemeral streams in moderately-defined channels converge within the ROW to form one, main channel which carries water to Newgate Road in this area. There also appears to have been some grading done within the ROW in the past. A berm was created to intercept water Northeast Utilities 4-2 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 18 of 36

3 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Erosion & Sediment Control Measures flowing down the hill, and direct it to the south. The water flowing south along this berm has created the channelized flow that is now present. A combination of wire reinforced silt fence and stone check dams (not shown on the plans at this time because location of the channels has not been definitively identified with GPS) will likely be used down slope of the disturbed area to control and filter concentrated and sheet flow leaving the site in this location. Another area of concentrated flow was identified up slope of Line List 1151 and In this area there are several well-defined ephemeral stream channels generally flowing from east to west. A man-made feature (origin unknown) does play a part in intercepting some of this flow, but ultimately the confluence of these channels results in one main channel that directs flow to the side of Line List A combination of wire reinforced silt fence and stone check dams (not shown on the plans at this time because location of the channels has not been definitively identified with GPS) will likely be used down slope of the disturbed area to control and filter concentrated and sheet flow leaving the site in this location. The Typical details for both types of control measures are shown in Appendix B Silt Fence During construction, a typical geotextile silt fence (GSF) would be installed on the downhill side of the disturbed areas. The GSF would provide erosion protection along embankment slopes where sheet flow occurs. (Embankments are all areas not defined as concentrated flow path.) It is expected that runoff entering the site is anticipated to be minimal, so erosion and sedimentation control does not appear necessary up slope of the ground disturbing activities associated with the Project. However, silt fence, or in some cases wire-reinforced silt fence is recommended up slope of some of the crane pads to provide an additional layer of protection for these disturbed areas Stone Check Dam In areas where concentrated flows may cause erosion, the use of a typical energy-dissipating stone check dam (SCD) system would be used. A typical, temporary stone check dam would be designed and constructed per section of the 2002 Connecticut Guidelines for Soil Erosion and Sediment Control to safely pass the peak flow expected from a ten-year frequency storm without structural failure and adverse tail water effects. These stone check dams would be particularly effective in protecting water quality at culverts and allowing the culverts to remain operational throughout construction. Northeast Utilities 4-3 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 19 of 36

4 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Erosion & Sediment Control Measures Summary As designed, the control measures would provide sufficient temporary control of sheet flow during a fifty-year storm event and concentrated flow during a ten-year storm event in this area. After a larger storm event the control measures will likely require maintenance. The recommended control measures would only provide temporary control of surface water flow (sheet and concentrated) within this area during construction and until the areas have been stabilized. These measures will not provide ground water control within or outside this area, nor will they permanently reduce the amount of runoff that ultimately leaves the area. As part of the D&M Plan development, the location of additional controls required to protect wetlands and watercourses, prevent sedimentation and erosion issues, and maintain the stability of all improved surfaces (access roads and crane pads) will be determined. The final D&M Plan, which will be submitted to the CSC, would also include all controls identified in this report. 4.3 HATCHETT HILL ROAD AREA EROSION & SEDIMENT CONTROL Long-term the quantity of runoff is not expected to increase because pre- and post- runoff coefficients are the same. However, control measures are proposed to mitigate for the small short-term increase in runoff and protect against the movement of sediment from disturbed portions of the Project. Because there were no point sources (concentrated flow) identified in the Hatchett Hill Road area, the most effective method of erosion and sediment control would be the installation of silt fence in conjunction with quick stabilization of any disturbed ground to reestablish ground cover as quickly as possible. As shown on the Site Drawings in Appendix A, the sediment control consists of silt fence on the down slope side of the construction and clearing areas to control and filter sheet flow leaving the site. Because the largest threat of erosive volume and velocity results from the installation of on-site improvements, silt fence or wire-reinforced silt fence should be installed up slope from some of the crane pads. This installation provides two benefits: 1. Protecting the crane pads (required to safely construct the Project) from water gaining enough velocity to cause erosive damage to them; and 2. Slowing the water velocity as it moves across the site, providing an additional measure of protection for the residents down slope. The typical detail for this type of control measure is shown in Appendix B. Northeast Utilities 4-4 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 20 of 36

5 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Erosion & Sediment Control Measures The resident s concern is that Marsh Pond often exceeds the capacity of its basin and water begins to backup towards his property. This seems unlikely since the pond is approximately 12 feet lower in elevation than the southern edge of his property. Based on GIS analysis and on site observations it is more likely that water moves from north to south, towards Marsh Pond. His property is also clearly lower in elevation than the adjacent scrub/shrub wetland in the ROW to the east, so as water moves from north to south along the ROW and through this wetland it ultimately does reach his property because water naturally flows to the lowest point. The recommended control measures will ensure that the small increase in runoff will be effectively controlled until site stabilization is achieved Silt Fence During construction, a typical geotextile silt fence (GSF) would be installed on the downhill side of the disturbed areas. The GSF would provide erosion protection along embankment slopes where sheet flow occurs. (Embankments are all areas not defined as concentrated flow path.) It is expected that runoff entering the site is anticipated to be minimal, so erosion and sedimentation control does not appear necessary up slope of the ground disturbing activities associated with the Project. However, silt fence, or in some cases wire-reinforced silt fence is recommended up slope of some of the crane pads to provide an additional layer of protection for these disturbed areas Summary As designed, the control measures would provide sufficient temporary control of sheet flow during a fifty-year storm event in this area. After a storm event greater than a fifty-year, the control measures are likely to require maintenance by the contractor. The recommended control measures will provide temporary control of surface water (sheet flow) within this area during construction through stabilization. These measures will not provide control of ground water within or outside this area, nor will they permanently reduce the amount of runoff leaving the area. As part of the development of the D&M Plan, the location of additional controls needed to protect wetlands and watercourses, prevent sedimentation and erosion issues, and maintain the stability of all improved surfaces (access roads and crane pads) will be determined. The final D&M Plan, which will be submitted to the CSC, would also include all controls identified in this report. Northeast Utilities 4-5 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 21 of 36

6 GSRP 345-kV Line D&M Plan Appendix E: Page 22 of 36

7 APPENDIX A S ITE DRAWINGS GSRP 345-kV Line D&M Plan Appendix E: Page 23 of 36

8 GSRP 345-kV Line D&M Plan Appendix E: Page 24 of 36

9 Concord Dr \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_CT_Erosion_Control_200_Scale_FIXED.mxd Date: 07/29/10 COPYRIGHT 2010 BURNS & McDONNELL ENGINEERING COMPANY, INC. W Hatchett Hill Ln 280 Hampden Hartford Litchfield Tolland Legend Hatchett Hill Rd 290 Proposed Structure Existing Structure - Remain Existing Structure - Remove Existing Structure - Reuse Proposed 345kV Route Centerline Vegetation Removal Limit Proposed Pad Location Existing LiDar Access Roads 1001 Line List Number Existing Preferred Route Existing Alternate Route New Preferred Route New Alternate Route NU Owned Property Existing Culvert Proposed Temporary Culvert Proposed Permanent Culvert Replaced Permanent Culvert Watercourse Erosion Control Standard Vernal Pool GSF-3 - Silt Fence Wetlands GSF-3 - Wire Reinforced Silt Fence Wall Town Boundary SCD-2 - Stone Check Dam Contours (2 ft) Metacomet Trail W Feet Source: AECOM, Coler and Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics W Greater Springfield Reliability Project Erosion Control Maps July 29, 2010 Sheet 01 of 07 GSRP 345-kV Line D&M Plan Appendix E: Page 25 of 36

10 Lexington Dr \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_CT_Erosion_Control_200_Scale_FIXED.mxd Date: 07/29/10 COPYRIGHT 2010 BURNS & McDONNELL ENGINEERING COMPANY, INC W Hampden Hartford Litchfield 250 Tolland Legend Proposed Structure Existing Structure - Remain Existing Structure - Remove Existing Structure - Reuse Proposed 345kV Route Centerline Vegetation Removal Limit Proposed Pad Location Existing LiDar Access Roads 1001 Line List Number Concord Dr 1035 Existing Preferred Route Existing Alternate Route New Preferred Route New Alternate Route NU Owned Property Existing Culvert Proposed Temporary Culvert Proposed Permanent Culvert Replaced Permanent Culvert Watercourse Vernal Pool Wetlands Wall Town Boundary Contours (2 ft) Metacomet Trail 280 Adams Dr Erosion Control Standard GSF-3 - Silt Fence GSF-3 - Wire Reinforced Silt Fence SCD-2 - Stone Check Dam W9-227 Culvert 3163 # Holcomb St W Feet Culvert #104 Culvert #103 W W Culvert #1 W Source: AECOM, Coler and Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics W W9-232A 3166 W Greater Springfield Reliability Project Erosion Control Maps July 29, 2010 Sheet 02 of 07 GSRP 345-kV Line D&M Plan Appendix E: Page 26 of 36

11 \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_CT_Erosion_Control_200_Scale_FIXED.mxd Date: 07/29/10 COPYRIGHT 2010 BURNS & McDONNELL ENGINEERING COMPANY, INC Litchfield Hampden Hartford W Tolland Legend W W9-254 Proposed Structure Existing Structure - Remain Existing Structure - Remove Existing Structure - Reuse Proposed 345kV Route Centerline Vegetation Removal Limit Proposed Pad Location Existing LiDar Access Roads 1001 Line List Number Existing Preferred Route Existing Alternate Route New Preferred Route New Alternate Route NU Owned Property Existing Culvert Proposed Temporary Culvert Proposed Permanent Culvert Replaced Permanent Culvert Watercourse Vernal Pool Wetlands Wall Town Boundary Contours (2 ft) Metacomet Trail Erosion Control Standard GSF-3 - Silt Fence GSF-3 - Wire Reinforced Silt Fence SCD-2 - Stone Check Dam Copper Hill Ter Country Club Ln Feet Newgate Rd Woodledge Dr 1076 Source: AECOM, Coler and Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics 2007 Copper Hill Rd Greater Springfield Reliability Project Erosion Control Maps July 29, 2010 Sheet 03 of 07 GSRP 345-kV Line D&M Plan Appendix E: Page 27 of 36

12 W \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_CT_Erosion_Control_200_Scale_FIXED.mxd Date: 07/29/10 COPYRIGHT 2010 BURNS & McDONNELL ENGINEERING COMPANY, INC Litchfield 1085 Hampden Hartford Tolland Legend Proposed Structure Existing Structure - Remain Existing Structure - Remove Existing Structure - Reuse Proposed 345kV Route Centerline Vegetation Removal Limit Proposed Pad Location Existing LiDar Access Roads 1001 Line List Number Existing Preferred Route Existing Alternate Route New Preferred Route New Alternate Route NU Owned Property Existing Culvert Proposed Temporary Culvert Proposed Permanent Culvert Replaced Permanent Culvert Newgate Rd Watercourse Vernal Pool Wetlands Wall Town Boundary Contours (2 ft) Metacomet Trail Erosion Control Standard GSF-3 - Silt Fence GSF-3 - Wire Reinforced Silt Fence SCD-2 - Stone Check Dam Culvert #5 W Feet Source: AECOM, Coler and Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics Wyncairn W Culvert #65 W9-257 W9-257 Greater Springfield Reliability Project Erosion Control Maps July 29, 2010 Sheet 04 of 07 GSRP 345-kV Line D&M Plan Appendix E: Page 28 of 36

13 \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_CT_Erosion_Control_200_Scale_FIXED.mxd Date: 07/29/10 COPYRIGHT 2010 BURNS & McDONNELL ENGINEERING COMPANY, INC. W W Culvert # W Hampden Hartford Litchfield Culvert #66 Tolland Legend Proposed Structure Existing Structure - Remain Existing Structure - Remove Existing Structure - Reuse Proposed 345kV Route Centerline Vegetation Removal Limit Proposed Pad Location Existing LiDar Access Roads 1001 Line List Number Existing Preferred Route Existing Alternate Route New Preferred Route New Alternate Route NU Owned Property Existing Culvert Proposed Temporary Culvert Proposed Permanent Culvert Replaced Permanent Culvert Watercourse Vernal Pool Wetlands Wall Town Boundary Contours (2 ft) Metacomet Trail Erosion Control Standard GSF-3 - Silt Fence GSF-3 - Wire Reinforced Silt Fence SCD-2 - Stone Check Dam Feet Source: AECOM, Coler and Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics W Newgate Rd Greater Springfield Reliability Project Erosion Control Maps July 29, 2010 Sheet 05 of 07 GSRP 345-kV Line D&M Plan Appendix E: Page 29 of 36

14 \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_CT_Erosion_Control_200_Scale_FIXED.mxd Date: 07/29/10 COPYRIGHT 2010 BURNS & McDONNELL ENGINEERING COMPANY, INC Hampden Hartford Litchfield 3208 W W Tolland 380 W9-259 Legend Culvert # Proposed Structure Existing Structure - Remain Existing Structure - Remove Existing Structure - Reuse Proposed 345kV Route Centerline Vegetation Removal Limit Proposed Pad Location Existing LiDar Access Roads 1001 Line List Number 1132 Existing Preferred Route Existing Alternate Route New Preferred Route New Alternate Route NU Owned Property Existing Culvert Proposed Temporary Culvert Proposed Permanent Culvert Replaced Permanent Culvert Watercourse Erosion Control Standard Vernal Pool GSF-3 - Silt Fence Wetlands GSF-3 - Wire Reinforced Silt Fence Wall Town Boundary SCD-2 - Stone Check Dam Contours (2 ft) Metacomet Trail W Feet Source: AECOM, Coler and Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics Newgate Rd Greater Springfield Reliability Project Erosion Control Maps July 29, 2010 Sheet 06 of 07 GSRP 345-kV Line D&M Plan Appendix E: Page 30 of 36

15 1143 \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_CT_Erosion_Control_200_Scale_FIXED.mxd Date: 07/29/10 COPYRIGHT 2010 BURNS & McDONNELL ENGINEERING COMPANY, INC Litchfield Hampden Hartford Culvert # Tolland Legend Proposed Structure Existing Structure - Remain Existing Structure - Remove Existing Structure - Reuse Proposed 345kV Route Centerline Vegetation Removal Limit Proposed Pad Location Existing LiDar Access Roads 1001 Line List Number Existing Preferred Route Existing Alternate Route New Preferred Route New Alternate Route NU Owned Property Existing Culvert Proposed Temporary Culvert Proposed Permanent Culvert Replaced Permanent Culvert 550 Watercourse Vernal Pool Wetlands Wall Town Boundary Contours (2 ft) Metacomet Trail 1148 Erosion Control Standard GSF-3 - Silt Fence GSF-3 - Wire Reinforced Silt Fence SCD-2 - Stone Check Dam Feet Source: AECOM, Coler and Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics METACOMET TRAIL 480 Phelps Rd Greater Springfield Reliability Project Erosion Control Maps July 29, 2010 Sheet 07 of 07 GSRP 345-kV Line D&M Plan Appendix E: Page 31 of 36

16 GSRP 345-kV Line D&M Plan Appendix E: Page 32 of 36

17 APPENDIX B TYPICAL EROSION CONTROL MEASURE DETAILS GSRP 345-kV Line D&M Plan Appendix E: Page 33 of 36

18 GSRP 345-kV Line D&M Plan Appendix E: Page 34 of 36

19 Figure SCD-2 Stone Check Dam Installation in Drainageways Stone Check Dam (SCD) Source: USDA-NRCS Connecticut Guidelines for Soil Erosion and Sediment Control GSRP 345-kV Line D&M Plan Appendix E: Page 35 of 36

20 Figure GSF-3 Toe of Slope Installations with Wings 5' 10' from toe of slope Geotextile Silt Fence (GSF) Detail of Fence Joint (Top View) Section A Section B 6" by 6" backfilled trench Existing subgrade Wing Detail 12" min. Max. fence height 30" Supporting post at least 42" long, 1.5" square hardwood stake or steel post 6" by 6" backfilled trench Wing oriented to intercept flow Posts Position posts to overlap as shown above, making certain that fabric folds around each post one full turn Drive posts tightly together and secure tops of posts by tying off with cord or wire to prevent flow-through of built-up sediment at joint. Direction of flow collecting behind fence Direction of flow from adjacent slope 6" by 6" backfilled trench Connecticut Guidelines for Soil Erosion and Sediment Control GSRP 345-kV Line D&M Plan Appendix E: Page 36 of 36