PEAK RUNOFF RATES (CUBIC FEET PER SECOND)

Transcription

1 Water Quality Swales would be provided in the median where space is available. The existing inside lanes of the northbound and southbound roadway from south of Route 110 in Amesbury to the northern project limit currently drain into the median via sheet flow. The runoff drains to drop inlets that outlet into a collector pipe. Where sufficient space would be available under the post-development condition, water quality swales would be constructed to convey sheet flow runoff from the edge of the pavement into a swale located between the median. Gutter inlets would also be located in the median, which would divert stormwater runoff to the adjacent wetlands on the outside of the highway in the same locations as the existing outlets. Except where feasible and hydraulically possible, the collector pipe would be diverted through a basin for additional treatment. A pea-gravel diaphragm or equivalent surface treatment for the unpaved portion of the roadway shoulder would be necessary for pretreatment in order to receive credit for TSS removal from a water quality swale. Deep Sump Catch Basins would be located along the project corridor. They would be incorporated in areas where the highway layout is relocated, and in areas where the layout would be expanded. The existing inlets would be maintained for the unchanged areas of the highway layout. Water Quantity Peak Rate Attenuation There would be a 15.1-acre increase in impervious area (a 28 percent increase over existing). To maintain pre-development runoff rates, a detention component would be incorporated into each proposed stormwater BMP. As required by Standard 2 of the stormwater performance standards, each of the proposed basins would include a detention level that would maintain the pre-development peak rate of runoff for the 2-, 10-, 25- and 100-year, 24-hour storm events. A hydrologic analysis was performed (using the computer program HydroCAD ) to determine the peak discharge rate for existing and proposed conditions. Runoff hydrographs were generated for the 2-, 10-, 25- and 100-year, 24-hour storm events using the SCS TR-20 Method and Type III rainfall distribution. Under the Preferred Alternative, the postdevelopment runoff hydrographs were flood routed through the proposed stormwater management facilities. The project spans three major watershed basins: the Parker River, Merrimack River, and North Coastal Basin. The portion of the project that is located in the Parker River Basin includes the extension of the shareduse path, which will extend south to the Newburyport Park-and-Ride at Exit 57. The portion of the project included in the North Coastal Basin includes stormwater runoff tributary to Meader Brook, and stormwater runoff tributary to an unnamed brook that flows north into Cains Brook. Within each of these watersheds, 11 design points were used to evaluate the post-development runoff rates. Each design point relates to a specific portion of highway or tributary area that contributes stormwater runoff to an appropriate discharge point for an evaluation of peak rates of runoff. The tributary areas were further broken down into subcatchment areas corresponding to distinct drainage patterns within the tributary area. Peak runoff rates under the Preferred Alternative would be less than existing conditions (Table 5-28). TABLE 5-28: DP 1 PEAK RUNOFF RATES (CUBIC FEET PER SECOND) 2-Year Storm 10-Year Storm 25-Year Storm 100-Year Storm Pre Post Pre Post Pre Post Pre Post Peak Rate Attenuation will be provided for 2 and 10 Year Storms* DP DP DP DP DP DP DP DP DP DP * Peak rate attenuation at DP-1 will be provided for the 2 and 10 Year Storms only. This area discharges directly to the Merrimack River in a location that currently experiences an approximate 8 foot tide. Flood control for larger storm events is unnecessary for DP-1 given the site s location on the Merrimack River in proximity to the Atlantic Ocean. The project site is located partially within Hydrologic Soil Groups (HSG) A, B, C, and D classified soils. Additionally, there are portions of the highway corridor that are unmapped or classified as udorthents (see Figures 4-48 through 4-51 in Chapter 4). Infiltration basins would be provided to avoid or minimize the loss of annual recharge to groundwater. The quantity, size, and proposed location of the each infiltration basin is based on available soil mapping information and has been confirmed through limited subsurface testing (refer to Appendix G for subsurface testing logs). The infiltration basins have been specifically located in areas with suitable soils and will maintain a minimum separation distance of 2 feet above the estimated seasonal high groundwater table. The basins were sized using the static method described in the MassDEP Whittier Bridge/I-95 Improvement Project EA/DEIR Chapter 5.0: Environmental Consequences (5.15 Utilities and Stormwater Drainage Systems) Massachusetts Stormwater Handbook. Using the appropriate infiltration rates, drawdown analyses were performed on the infiltration basins to verify that they will be empty within 72 hours of the beginning of the storm (Table 5-29). TABLE 5-29: Basin DRAWDOWN ANALYSIS Rv (cubic feet) K2 (in/hr) Bottom Area3 (sf) Drawdown Time (hr) Infiltration Basin 1 20, , Infiltration Basin 2 2, , Infiltration Basin 1B 4, , Infiltration Basin 3 4, , Infiltration Basin 4 3, , Infiltration Basin 5 3, , Infiltration Basin 6 2, , Wet Basin 7A No Credit Taken For Recharge Wet Basin 7B No Credit Taken For Recharge Extended Detention Basin 9A No Credit Taken For Recharge Infiltration Basin 9B 10, , The Preferred Alternative would achieve a level of recharge consistent with the stormwater management standards for new development, and to the maximum extent practical for redevelopment. Table 5-30 summarizes the volumes of recharge provided per watershed. TABLE 5-30: RECHARGE VOLUME SUMMARY New Development (required recharge volume) (cf) Redevelopment (recharge required to the maximum extent practical ) (cf) Recharge Provided by Infiltration Basins (based on preliminary basin sizing) (cf) Drainage Zone Parker River 1,100 2,000 Merrimack River 11,800 37,700 35,200 Meader Brook 2,500 13,200 10,500 Water Quality Total Suspended Solid Removal Standard 4 of the Stormwater Performance Standards requires a minimum of 80 percent TSS removal for new development. The redevelopment portion of the project is required to comply with this standard to the maximum extent practical and improve existing conditions. The infiltration basins and two wet basins have been located throughout the project to specifically facilitate compliance with this standard. 5-59

2 Whittier Bridge/I-95 Improvement Project EA/DEIR Chapter 5.0: Environmental Consequences (5.15 Utilities and Stormwater Drainage Systems) Consistent with the MassDEP Massachusetts Stormwater Handbook, the infiltration basins would be designed to provide a minimum 0.5 inch of water quality treatment for the contributing impervious area, and the wet basins would be designed to provide a minimum of 1-inch of water quality treatment for the contributing impervious area. A sediment forebay would be sized to treat an equivalent of 0.1 inch of runoff for the contributing impervious area and located upstream of each proposed basin. Deep sump catch basins would be installed throughout the project as previously described. Water quality swales may be incorporated in isolated portions of the project where sufficient median space is available. Table 5-31 summarizes the various treatment trains proposed throughout the project and the respective TSS removal rates that would be achieved based on the MassDEP Massachusetts Stormwater Handbook. TABLE 5-31: PROPOSED TREATMENT TRAINS Treatment Train TSS Removal Rate Deep Sump Catch Basins 25% Sediment Forebay 25% Deep Sump CB/Sediment Forebay 44% Water Quality Swales (where adequate median is available) 70% Extended Detention Basin & Sediment Forebay 50% Infiltration Basin & Sediment Forebay 80% Wet Basin & Sediment Forebay 80% Deep Sump Catch Basins/Sediment Forebay/Infiltration Basin 85% Deep Sump Catch Basins/Sediment Forebay/Wet Basin 85% Tables 5-32 through 5-35 summarize each regulated resource area within the project and the TSS removal rate that would be achieved. In summary, 80 percent TSS removal or greater would be achieved at each regulated wetland resource area for the new development portion of the project. Water quality treatment would be provided to the maximum extent practical for the redevelopment portion of the project. It is important to note that for some areas currently classified as redevelopment, the actual scope of roadway improvements may be limited to pavement striping or minor road resurfacing. The proposed BMPs would also provide water quality treatment for removal of pollutants such as nitrogen, phosphorous, pathogens, and metals. TABLE 5-32: TOTAL SUSPENDED SOLID REMOVAL RATES (PARKER RIVER WATERSHED) Existing Pavement Proposed Pavement Redev. New Devel. Redev. New Devel. Design Point Discharge Location (AC) (AC) (AC) (AC) TSS Removal Rate TSS Removal Rate DP 11 I-95 Drainage/Wetland A % TABLE 5-33: TOTAL SUSPENDED SOLID REMOVAL RATES (MERRIMACK RIVER WATERSHED) Design Point Discharge Location Existing Pavement (acres) Proposed Pavement (acres) Redev. (acres) New Devel. (acres) Redev. TSS Removal Rate New Devel. TSS Removal Rate DP 1 Merrimack River % 85% Wetland E % 85% DP 2 Wetland F N/A 25% N/A Wetland I N/A 25% N/A Wetland % 85% DP 3 Wetland G N/A 25% N/A Wetland H % 85% DP 4 Rt 110 Collector Pipe % 85% DP 5 Wetland N N/A 0% N/A Wetland J/ % 85% DP 6 Wetland O N/A 0% N/A Wetland K % 85% TABLE 5-34: Design Point Multiple DP 7 DP 9 TABLE 5-35: Design Point DP 10 TOTAL SUSPENDED SOLID REMOVAL RATES (MEADER BROOK WATERSHED) Discharge Location Existing Pavement (acres) Proposed Pavement (acres) Redev. (acres) New Devel. (acres) Redev. TSS Removal Rate New Devel. TSS Removal Rate Wetland R % 80% 8.0 Wetland X N/A 0% N/A Wetland Q N/A 0% N/A Wetland M N/A 0% N/A Wetland Q N/A 0% N/A Wetland W N/A 0% 85% Wetland U N/A 0% N/A Wetland T % 85% TOTAL SUSPENDED SOLID REMOVAL RATES (CAINS BROOK WATERSHED) Discharge Location Existing Pavement (ac) Proposed Pavement (ac) Redev. (ac) New Devel. (ac) Redev. TSS Removal Rate New Devel. TSS Removal Rate Wetland N/A 61% N/A Wetland 4/ N/A 0% N/A Table 5-36 summarizes the expected range of removal efficiency for the various types of BMPs. 5-60

3 TABLE 5-36: POLLUTANT REMOVAL EFFICIENCIES BMP Total Total Nitrogen Phosphorous Metals Pathogens Infiltration Basin 50 60% 60 70% 85 90% 90% Wet Basin 10 50% 30 70% 30 75% 40 90% Extended Detention Basin 15 50% 10 30% 30 50% 0 10% Water Quality Swale 10 90% 20 90% 0% 0% Infiltration Trench 40 70% 40 70% 85 90% 90% Discussion on Redevelopment Total Suspended Solid Removal Rates The following briefly discusses the limitations along the project corridor with respect to the TSS removal rates proposed for the redevelopment portions of the project. Merrimack River: Subcatchment 1B would include the runoff generated from the bridge that would be discharged directly to the Merrimack River via scuppers. Subcatchment 1A would include pavement that may not be hydraulically connected to Infiltration Basin 1. Deep sump catch basins would be incorporated into Subcatchment 1A. Wetland E: Subcatchment 2-B would include pavement that could not be hydraulically connected to Infiltration Basin 2 because of topographical limitations Deep sump catch basins would be incorporated into this subcatchment. Wetland F: Subcatchment 2-A would include significant topographical changes between the existing edge of pavement and Wetland F. Deep sump catch basins would be incorporated into this subcatchment. Wetland I: Subcatchment 2-C would include significant topographical changes between the proposed edge of pavement and Wetland I. Deep sump catch basins would be incorporated into this subcatchment. Wetland G: Subcatchment 3-B would include significant topographical changes between the edge of pavement and Wetland G, since there is bedrock present in the upland area located south of Wetland G. Deep sump catch basins would be incorporated into this subcatchment. Wetland H: Subcatchment 3-C would include significant topographical changes between the edge of pavement and Wetland G. Stormwater measures implemented in this subcatchment would include deep sump catch basins for the outside lanes and water quality swales in the median for the inside lanes. Wetland N: Subcatchment 5-A would include significant topographical changes between the existing edge of pavement and Wetland N. The scope of work for this subcatchment would be limited to pavement restriping or minor resurfacing without drainage improvements. Wetland O: Subcatchment 6-A would include significant topographical changes between the existing edge of pavement and Wetland O. The scope of work for this subcatchment would be limited to pavement restriping or minor resurfacing without drainage improvements. Wetland K: Subcatchment 6-B would be diverted to Wet Basin 6. Subcatchment 6-C would include significant topographical changes between the edge of pavement and Wetland N, and it would not be possible to hydraulically connect this area to Wet Basin 6. Wetland R would directly receive stormwater discharges for a total of approximately 10.7 acres of pavement under the post development condition. Most of the undeveloped ROW in this portion of the project is encumbered by BVW, which results in very few locations that will support a stormwater basin. Approximately 3.1 acres of pavement would be diverted to treatment BMPs that will achieve the desired TSS Removal. The remaining 7.6 acres cannot be hydraulically connected to a stormwater basin. The inside lanes would be diverted via sheet flow into a proposed water quality swale located in the median. Wetland Q: Subcatchment 7-D would include significant topographical changes between the existing edge of pavement and Wetland Q. The scope of work for this subcatchment would be limited to pavement restriping or minor resurfacing without drainage improvements. Wetland M: Subcatchment 7-A currently discharges stormwater runoff via sheet flow to a drainage swale located outside the existing edge of pavement; the swale has been classified as Wetland M. The scope of work for this subcatchment would be limited to pavement restriping or minor resurfacing without drainage improvements. Wetland OQ: Subcatchment 7-B currently discharges stormwater runoff via sheet flow to a drainage swale located outside the edge of pavement. This swale, which is approximately 1 2 feet wide, has been classified as Wetland OQ and would be affected as result of Extended Detention Basin 7A. Wetland X: Subcatchment 7-V, 8-D, and 9-E discharge stormwater runoff directly into Wetland X through both sheet flow and pipe discharges. Because of space restrictions between the existing edge of pavement and the adjacent wetland, there would be limited opportunity to incorporate treatment BMPs. These subcatchments would not be altered under the post-development condition; the scope of work for this area would be limited to pavement restriping or minor resurfacing without drainage improvements. Whittier Bridge/I-95 Improvement Project EA/DEIR Chapter 5.0: Environmental Consequences (5.15 Utilities and Stormwater Drainage Systems) Wetland W: Subcatchment 9-D currently discharges stormwater runoff directly into Wetland W via sheet flow. Because of space restrictions between the existing edge of pavement and the adjacent wetland, there would be limited opportunity to incorporate treatment BMPs. This subcatchment would not be altered under the post-development condition; the scope of work for this area would be limited to pavement restriping or minor resurfacing without drainage improvements. Wetland U: Subcatchment 9-A currently discharges stormwater runoff via sheet flow to a drainage swale located outside the edge of pavement; the swale has been classified as Wetland U. The scope of work for this subcatchment would be limited to pavement restriping or minor resurfacing without drainage improvements. Wetland 2: This portion of the project would include Subcatchment 10-C, which could not be hydraulically connected to a location with sufficient space to locate a treatment BMP. Wetland 4/5: Subcatchment 10-A currently discharges stormwater runoff directly into Wetland 4/5 via sheet flow. Because of space restrictions between the existing edge of pavement and the adjacent wetland, there would be limited opportunity to incorporate treatment BMPs into Subcatchment 9-D. This subcatchment would not be altered under the post-development condition; the scope of work for this area would be limited to pavement restriping or minor resurfacing without drainage improvements Conformance with Massachusetts Stormwater Performance Standards Standard 1 No new stormwater conveyances (e.g., outfalls) may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth. All proposed outfalls as a result of this project will be designed in a manner to include the necessary scour protection in order to prevent erosion. Several existing stormwater discharges (outfalls) would be relocated under the post-development condition. Where necessary to relocate an existing discharge, the relocated discharge would not be considered a new outfall, and the relocated discharge would thereby qualify for the same level of relief from the stormwater regulations as an existing discharge that would, whereas it would need to comply with Standard 1 only to the maximum extent practicable. The relocated outfalls are associated with the same closed drainage system and therefore are not new discharges. All relocated outfalls are expected to be provided with some level of treatment, except that it is not possible for every relocated outfall to be provided with a level of treatment that would otherwise be required 5-61

4 Whittier Bridge/I-95 Improvement Project EA/DEIR Chapter 5.0: Environmental Consequences (5.15 Utilities and Stormwater Drainage Systems) in order to satisfy the water quality requirements as further defined under Standard 4 TSS Removal. Consequently, compliance with this standard would be achieved. Standard 2 Stormwater management systems shall be designed so that post-development peak discharge rates do not exceed pre-development peak discharge rates. Compliance would be achieved at all of the previously described design points. Standard 3 Loss of annual recharge to ground water shall be eliminated or minimized through the use of infiltration measures including environmentally sensitive site design, low impact development techniques, stormwater best management practices and good operation and maintenance. At a minimum, the annual recharge from the post development site shall approximate the annual recharge from the pre-development conditions based on soil type. Full compliance with this standard will be met for the new development portion of the project on a sub-watershed basis. Compliance to the maximum extent practicable with an improvement over existing conditions will be achieved for the redevelopment portion of the project. Standard 4 Stormwater management systems shall be designed to remove 80% of the average annual post-construction load of Total Suspended Solids (TSS). This Standard is met when: a. Suitable practices for source control and pollution prevention are identified in a long-term pollution prevention plan and thereafter are implemented and maintained; b. Structural stormwater best management practices are sized to capture the required water quality volume determined in accordance with the Massachusetts Stormwater Handbook; and c. Pretreatment is provided in accordance with the Massachusetts Stormwater Handbook. Full compliance would be achieved for an equivalent portion of the project that is new development at each down gradient regulated resource area (Merrimack River, Wetland X, Wetland S, etc.). Compliance to the maximum extent practical would be achieved for the redevelopment portion of the project; consequently, compliance with this standard would be achieved. Standard 5 For land uses with higher potential pollutant loads, source control and pollution prevention shall be implemented in accordance with the Massachusetts Stormwater Handbook to eliminate or reduce the discharge of stormwater runoff from such land uses to the maximum extent practicable. If through source control and/or pollution prevention, all land uses with higher potential pollutant loads cannot be completely protected from exposure to rain, snow, snow melt and stormwater runoff, the proponent shall use the specific structural stormwater BMPs determined by the Department to be suitable for such use as provided in the Massachusetts Stormwater Handbook. Stormwater discharges from land uses with higher potential pollutant loads shall also comply with the requirements of the Massachusetts Clean Waters Act, M.G.L. c. 21, 26 through 53, and the regulations promulgated thereunder at 314 CMR 3.00, 314 CMR 4.00 and 314 CMR Roadway surfaces do not constitute areas of higher potential pollutant loads in accordance with the MassDEP Massachusetts Stormwater Handbook; consequently, this standard is not applicable. Standard 6 Stormwater discharges within the Zone II or Interim Wellhead Protection Area of a public water supply and stormwater discharges near or to any other critical area require the use of the specific source control and pollution prevention measures and the specific structural stormwater best management practices determined by the Department to be suitable for managing discharges to such area as provided in the Massachusetts Stormwater Handbook. A discharge is near a critical area, if there is a strong likelihood of a significant impact occurring to said area, taking into account site-specific factors. Stormwater discharges to Outstanding Resource Waters and Special Resource Waters shall be removed and set back from the receiving water or wetland and receive the highest and best practical method of treatment. A storm water discharge as defined in 314 CMR 3.04(2) (a)1. or (b) to an Outstanding Resource Water or Special Resource Water shall comply with 314 CMR 3.00 and 314 CMR Stormwater discharges to a Zone I or Zone A are prohibited, unless essential to the operation of the public water supply. There are no existing or proposed stormwater discharges to a Zone A or Zone I. A portion of the highway corridor south of Whittier Bridge is located within the water resource protection Zone II associated with the Newburyport water supply wells, and is located within the water resource Zone B associated with Bartlett Spring Pond, an active drinking water reservoir. The existing drainage system for the highway in this area consists of a closed piping collection system, such that all existing stormwater runoff generated from the highway is discharged directly into the Merrimack River. Under the post-development condition, the stormwater would be collected through a similar closed piping system; however, it would be diverted to Infiltration Basin 1 prior to discharging into the Merrimack River. Infiltration Basin 1 would be located specifically outside of the Zone II limits. Consequently, full compliance with this standard would be achieved. Standard 7 A redevelopment project is required to meet the following Stormwater Management Standards only to the maximum extent practicable: Standard 2, Standard 3, and the pretreatment and structural stormwater best management practice requirements of Standards 4, 5 and 6. Existing stormwater discharges shall comply with Standard 1 only to the maximum extent practicable. A redevelopment project shall also comply with all other requirements of the Stormwater Management Standards and improve existing conditions. As previously stated, the redevelopment component of the project would comply with the maximum extent practicable to the applicable standards and improve overall existing conditions. The MassDOT Stormwater Handbook for Highways and Bridges (May 2004 or latest version) would be used as guidance for applicable and practical mitigation measures; consequently, compliance with this standard would be achieved. Standard 8 A plan to control construction related impacts including erosion, sedimentation and other pollutant sources during construction and land disturbance activities (construction period erosion, sedimentation and pollution prevention plan) shall be developed and implemented. A detailed stormwater pollution prevention plan would be developed and implemented for this project; consequently, compliance with this standard would be achieved. Standard 9 A long-term operation and maintenance plan shall be developed and implemented to ensure that the stormwater management system functions as designed. An operation and maintenance plan would be developed based on the specific BMPs implemented throughout the corridor; consequently, compliance with this standard would be achieved. Standard 10 All illicit discharges to the stormwater management system are prohibited. There are no known or proposed illicit discharges within the project limits. Should any illicit discharges be identified during the course of construction they shall be reported to the Resident Engineer or MassDOT District 4 Environmental Engineer to determine the source and potential for resolution through MassDOT s IDDE program. Additionally, in areas of the project where there are off-site or existing municipal local drainage connections to the existing highway system, investigations shall be conducted to determine if potential illicit discharges exist. These investigations shall include, but are not limited to the observation of outfalls for dry weather flows or evidence of surface water contamination by non-stormwater discharges. Consequently, compliance with this standard will be achieved. 5-62

5 5.16 ECONOMICS Methodology The social and economic impact assessment was based on a review of planning and economic development reports, U.S. Census population records, and interviews with local and regional planners Consequences of the No Build and Preferred Alternatives The project is not expected to have a major effect in inducing population or employment growth in the Merrimack Valley Region since there would be only modest increases in traffic at the interchanges within the project area. The increased traffic volumes are projected to occur even in the absence of the proposed highway capacity increases (i.e., three to four lanes in each direction) and would largely serve through traffic, especially on summer weekends, at a better traffic LOS than now. Population data projections prepared for the MVPC s 2007 Regional Transportation Plan indicate a modest rate of growth in the recent past in Newburyport and Amesbury (Table 5-37). From 2000 to 2005, Newburyport population increased by 1.31 percent from 17,189 to 17,414, and Amesbury population increased by 1.17 percent from 16,450 to 16,643; however, Salisbury s population increased 5.84 percent from 7,827 to 8,284. The MVPC regional population grew at a modest rate of 2.04 percent. These past growth trends, which MVPC is now updating for the 2011 Regional Transportation Plan, are considered too high to be a realistic indicator of future conditions given current economic conditions. Updated projections are expected to be lower. TABLE 5-37: POPULATION GROWTH (NEWBURYPORT AND AMESBURY) Community 1990 Population 2000 Population Estimated 2005 Population Percent Change Newburyport 16,317 17,189 17, Amesbury 14,997 16,450 16, Salisbury 6,882 7,827 8, MVPC Total 288, , , The No Build and Preferred Alternatives are similar in that they are expected to have little or no impact on community changes, environmental justice populations, public facilities and services, or tax impacts, as described below. The No Build and Preferred Alternatives differ in their economic impacts. The potential direct negative effects on existing businesses would be minor. There would be potential benefits to existing local businesses associated with the improved accessibility resulting from the study alternatives. The Preferred Alternative would generate approximately 120 temporary construction jobs. Community Changes. The Preferred Alternative would improve an existing transportation corridor and the surrounding area, which is already developed. The proposed project improvements would not divide neighborhoods or subdivisions or separate them from their public services. No community changes will be associated with the No Build Alternative. With the Preferred Alternative, the communities would gain an improved roadway with an additional lane of traffic and the construction of a shareduse path for alternative modes of transportation, which would improve regional mobility, improve access to and from the study area to regional jobs, improve safety by reducing the potential for crashes and fatalities, and shift through traffic from minor arterials and collector roads. Environmental Justice. As documented in Section , there are no concentrations of minority or low-income populations within the project study area; therefore, neither of the alternatives would disproportionately affect concentrations of minority or low-income populations. Public Facilities/Services. There would be no direct impacts to public services or facilities in the study area for neither of the alternatives. Tax Impacts. Since project improvements would be located within the existing ROW, the Preferred Alternative would not result in a tax loss for local jurisdictions of total taxes collected. No Build The No Build Alternative will not affect the social/economic characteristics of the project corridor and will not change employment characteristics in the project area. This alternative will not increase roadway capacity and, therefore, will result in longer future travel times for commuters in this corridor. Preferred Alternative The Preferred Alternative would not change long-term employment in the project area but would increase temporary employment during construction. This alternative would increase roadway capacity and, therefore, would result in improved future travel times for commuters in this corridor Impacts on Residences within the Project Area (Relocations, Partial Takings) No takings are expected under the No Build or Preferred Alternatives. There may be a need for some temporary construction period easements, which would be identified as the design is developed. Whittier Bridge/I-95 Improvement Project EA/DEIR Chapter 5.0: Environmental Consequences (5.17 Navigation) As noted in Section , there are few residences near the project ROW; however, there are two condominium developments to the north of the Merrimack River at Whittier Point in Amesbury that are within 150 feet of the project ROW. Under the Preferred Alternative, the alignment would be shifted closer to the condominium residences located to the east of I-95. Temporary construction access may be required to construct a new retaining wall and snow barrier along the edge of the ROW adjacent to the condominium complex Impacts on Businesses within the Project Area The proposed project would have no adverse economic impacts on businesses because the entire project would be constructed within the existing ROW owned by MassDOT. There would be no takings with the No Build Alternative or the Preferred Alternative. Temporary construction easements may be needed in some locations, which would be identified during the design process. As a result, there may be some minor temporary adverse impacts to businesses Conclusions The No Build and Preferred Alternatives are expected to have little or no impact on community changes, environmental justice populations, public facilities and services, or tax impacts. Under the Preferred Alternative, the potential direct negative effects on existing businesses would be minor. There would be potential benefits to existing local businesses associated with the improved accessibility resulting from the Preferred Alternative NAVIGATION Existing Conditions The existing Whittier Bridge includes four piers within the waterway and five spans or openings beneath the bridge. There are two navigation channels under the bridge, namely the north (primary) and south (secondary) channels, which maintain vertical clearances of 56 feet and 32 feet, respectively. The north channel is mapped and maintained by the USACE as a 150-foot-wide federal channel (herein referred to as Federal Channel) with a 7-foot channel depth. The south channel is referred to as Steamboat Channel according to the US Coast Guard Light List, Volume 1, Atlantic Coast, dated The Federal Channel is between existing Piers 3 and 4, and the Steamboat Channel is between existing Piers 1 and 2. According to the hydrographic survey performed beneath the bridge, the span in the middle of the bridge between Piers 2 and 3 is not used for navigation because of shallow depths. The remaining openings located between existing Piers 1 and 4, 5-63

6 Whittier Bridge/I-95 Improvement Project EA/DEIR Chapter 5.0: Environmental Consequences (5.17 Navigation) adjacent to the north and south banks, respectively, do not provide safe passage for navigation also because of shallow depths. Potential impacts were considered for both the construction (temporary) and operational (permanent) phases for both the No Build Alternative and Preferred Alternative. The Preferred Alternative would both construct a new bridge crossing and demolish the existing Whittier Bridge. Operational impacts would include the location and number of bridge piers within the Merrimack River and the potential impact to the existing navigation channels and existing river boat traffic. The following discusses the potential impacts associated with constructing the permanent bridge piers and temporary work within the waterway for the No Build and Preferred Alternatives Consequences of the No Build and Preferred Alternatives No Build Alternative (Temporary and Permanent Impacts) Under the No Build Alternative there will no temporary or permanent impacts to navigation. Maritime traffic will not be affected, and boaters will continue to navigate beneath the existing bridge. Preferred Alternative (Temporary Impacts) The Preferred Alternative design includes three sets of piers for each bridge structure, totaling six piers in the waterway for the northbound and southbound structures. There would be four spans or openings beneath both bridges, with the two existing navigable Federal and Steamboat Channels maintained for marine traffic. The bridge piers for both structures would be constructed in the same east-west alignment. The distance between the existing piers within the Federal Channel is approximately 280 feet, while distance between the proposed piers would provide a wider 360-foot opening beneath the bridge. Similarly for the Steamboat Channel, the opening would increase from approximately 200 feet between the piers to a width of 360 feet. The staging scheme would include a new, wider bridge constructed on the east side of the existing bridge so that upon completion, all six lanes of traffic on I-95 could be immediately relocated over to the new bridge, thus permitting the existing truss spans to be demolished free of traffic and in one phase. The new I-95 southbound carrying four lanes of traffic could be built in the new space provided. Once opened to traffic, the I-95 northbound bridge could be reconfigured for the four lanes and necessary shoulders on each side of the travel lanes. Preferred Alternative (Permanent Impacts) The overall construction duration for this option is expected to be 48 months. In-water work period for demolition and construction would occur throughout most of this period, the final duration is dependent on the final design of the new bridges. For the new structures, the in-water work would include installing piles, piers, and footings; in-water demolition activities would require removing the existing bridge piers. The Preferred Alternative permanent bridges structures would not reduce existing vertical or horizontal clearance and there would be no adverse impacts to navigation. The northbound and southbound bridges structures would include placing new piers within the waterway while maintaining the existing horizontal and vertical clearances provided beneath the existing Whittier Bridge. Appropriate fendering systems and navigational lighting would provide permanent navigation safety features. Preferred Alternative (Construction and Demolition Temporary Impacts) The duration of in-water work associated with construction and demolition is a key factor in determining the overall temporary impacts to navigation. In addition, the bridge type and associated method of construction and demolition will directly influence the potential impact to navigation for the Preferred Alternative. Construction Phased construction of the northbound and southbound bridge structures would minimize adverse effects to river navigation. In-water work would likely occupy only part of the river at one time, maintaining a channel for navigation. Closures or restrictions on river traffic would be communicated in advance, enabling river users to accommodate their schedules without undue interruption. Additional tugs may be needed to assist vessels through areas of reduced clearances, especially during times of high volume of marine traffic (e.g., summer months). The major components are substructure support, including driven piles or drilled shafts; the footing or pile cap; pier construction; and the superstructure. Six piers would be constructed to support the northbound and southbound structures. Substructure. In-water construction in the navigation channels where depth is sufficient would take place from barges. Cofferdams would be constructed at each proposed pier location to provide work access and allow work to be performed in the dry. In addition to the cofferdams, turbidity curtains would be located in select areas to minimize potential sediment transport and adverse water quality impacts. Substructure activities would consist primarily of constructing cofferdams (vibrating in steel sheet piles), dewatering, pile driving or installing drilled shafts into stable river-bottom soils or rock, followed by constructing footings or pile caps, and, finally, erecting the bridge pier. Constructing the piles or drilled shafts would require large-scale construction equipment (pile drivers or cranes) to drive large-diameter piles or place steel casings. Equipment would operate from deep-draft barges. Footings or pile caps would be constructed by precast units, floated in by barge, and set into place by spudded anchors or cofferdam construction to allow for placement of concrete and reinforcing steel in the dry. Finally, the pier construction would take place above the footings and provide vertical support to the superstructure. The piers would also be constructed from barges and consist of concrete or steel. Construction of the northbound bridge would require the construction of temporary piers to support the bridge deck during installation. Only one such temporary structure would be anticipated within the river, and the structure would be located outside the limits of the navigation channels. No temporary supports would be required for the construction of the southbound bridge as the existing Whittier Bridge piers would provide support during assembly of the bridge deck. Superstructure. Floating cranes and tower cranes would be required to construct the main tower and lift the superstructure. Bridge superstructures would consist of either steel-box girder, cast-in-place or precast concrete or steel-tied arch. Precast segmental concrete sections would be constructed off-site, barged or trucked in, and then lifted with a crane or overhead gantry system. Barge-mounted cranes may be used if segments arrive by barge. Steel-box girder and steel-tied arch sections would be prefabricated off-site and similar to the concrete segments, which would be transported by truck or barge. Demolition Following the construction of the initial six-lane northbound structure, the simultaneous placement of temporary and permanent structures in the waterway for demolishing the existing bridge and constructing the new four-lane southbound structure would occur. During this time, the waterway would experience the greatest amount of construction-related equipment in the waterway. Demolishing the existing bridge may require placing temporary piles in the river or jack up barges to provide support while portions are removed. At a minimum, in-water demolition activities would require placing and operating equipment similar to bridge construction, including work platforms, barges, and work zones within the waterway. Superstructure. Removal of deck structures could be performed by separating them into pieces or by removing them panel by panel. Steeltruss spans over the water could be removed in several different ways. One method would be to construct temporary supports under the span and disassemble the truss segment by segment. Other methods could 5-64

7 include constructing access embankments, or using special shallow-draft barges or rigging devices for sliding sections onto barges from the bridge deck. Protective measures would be taken to prevent materials or debris from falling into the Merrimack River. Substructure. Large structural elements could be lifted from their bases in one piece or piece-by-piece. Demolishing the concrete foundations at the piers would require reducing the reinforced concrete to pieces that are small enough to be hauled away. Removal of the piers to below the mud line could be accomplished by constructing cofferdams around each pier, dewatering the cofferdams and demolishing the piers to the existing mud line CONSTRUCTION IMPACTS Conceptual Construction Staging for the Preferred Alternative Proposed improvements for the Whittier Bridge/I-95 Improvement Project would be constructed in several separate construction stages. The scope of work included in each stage would be developed based on maintaining three available lanes in each direction on I-95 at all times to accommodate peak traffic flow. Selective phases of the work may require limited shoulder or lane closures during off-peak hours. The construction duration is estimated to be 42 months. A suggested sequence of construction staging is outlined as follows and illustrated on Figure 5-17A through Figure 5-17G. As the design of the project advances, this concept staging plan will be refined and reviewed with appropriate agencies. Stage 1A Stage 1A would begin the construction of the new I-95 northbound Whittier Bridge and a portion of the new I-95 northbound roadway and shared-use path located east of the existing highway. This stage would also include work preparing required traffic lane alignment shifts during subsequent stages. Erosion and sedimentation control elements and temporary stormwater treatment areas would be constructed during this stage. Traffic. All traffic on existing roadways would be maintained on existing alignment. Southbound and northbound traffic near the Route 110 interchange would have reduced lane and shoulder widths to allow for construction in the median. South of Whittier Bridge. Construction would begin on the new I-95 northbound alignment and would include constructing the roadway embankment and retaining walls southeast of the new I-95 northbound Whittier Bridge. A portion of this road construction would be prepared to shift the northbound traffic in Stage 1A-1. Whittier Bridge/Evan s Place Bridge. Construction would begin on the new I-95 northbound Whittier Bridge and the new I-95 northbound Evan s Place Bridge. The new I-95 northbound alignment would be constructed as far north as possible without affecting the existing I-95 northbound alignment. Route 110 Interchange. Work during this stage would include installing temporary north- and southbound concrete median barriers, widening the existing I-95 southbound barrel within the median, constructing temporary widening and crossover within the median to support the I-95 northbound shift to the median in Stage 1C, and constructing railroad bridges within the median at Route 110 and the railroad ROW to the north. Construction would also include portions of temporary I-95 northbound ramps to Route 110. North of Route 110 Interchange. No construction would occur in this area in this stage. Stage 1A-1 Stage 1A-1 would focus on the area south of the Whittier Bridge to shift the northbound traffic, allowing the construction of the new Pine Hill/Ferry Road Bridge pier in the median. There would be no change to the staging from the Whittier Bridge to the north as shown in Stage 1A. Traffic. The I-95 northbound traffic near the Pine Hill/Ferry Road Bridge would be shifted east onto a portion of the new I-95 northbound alignment constructed in Stage 1A. Traffic on Pine Hill Road at the bridge would be reduced to one-way east/west alternating traffic, using temporary traffic signals. All other traffic would remain in the configuration set up in Stage 1A. South of Whittier Bridge. Demolition of the southern portion of the existing Pine Hill/Ferry Road Bridge and construction of the new bridge would begin. Constructing the I-95 northbound alignment, including the installation of the roadway embankment and retaining walls southeast of the new I-95 northbound Whittier Bridge, would be completed in Stage 1A. Whittier Bridge/Evan s Place Bridge. Construction would continue as in Stage 1A Route 110 Interchange. Construction would continue as in Stage 1A Whittier Bridge/I-95 Improvement Project EA/DEIR Chapter 5.0: Environmental Consequences (5.18 Construction Impacts) North of Route 110 Interchange. No construction would occur in this area in this stage. Stage 1B Stage 1B would shift the I-95 northbound traffic to continue constructing the Route 110 and railroad ROW bridges while southbound traffic would remain on the existing alignment. Traffic. Northbound traffic near the Route 110 interchange would be shifted onto pavement and bridges constructed in the median in Stage 1A to allow existing I-95 northbound deck replacement at the Route 110 and railroad ROW bridges. Access to Route 110 east and west from I-95 northbound would be maintained via temporary ramps that would cross over the existing I-95 northbound lanes. All other traffic would remain in the configuration used in Stage 1A-1. South of Whittier Bridge. The new Pine Hill /Ferry Road Bridge would be completed and opened to two-way traffic. Demolition of the northern portion of the existing structure would be completed. Whittier Bridge/Evan s Place Bridge. Construction would continue as in Stage 1A with both bridges being completed in this stage. Route 110 Interchange. Work during this stage would include relocating the temporary northbound concrete median barrier, constructing the existing I-95 northbound Route 110 and railroad ROW bridge deck replacements, and constructing the new I-95 northbound alignment north of the new I-95 northbound bridge over Evans Place, including the modifications to the I-95 northbound ramps to Route 110 east and west and the modifications to the Route 110 on ramp to I-95 northbound. North of Route 110 Interchange. Construction would begin on widening I-95 north- and southbound alignments within the median. Stage 2A Stage 2A would begin once the new northbound I-95 Whittier Bridge is completed. This stage would be a substage to allow for the work necessary to make the crossover connections from the existing I-95 southbound alignment to the new north/south interim condition of new I-95 northbound and shared-use path alignment and bridges. Traffic. Northbound traffic would be shifted from the configuration set up in Stage 1A-1 to north/south interim condition of the new I-95 northbound and shared-use path alignment and bridges. Southbound traffic would remain on the existing I-95 southbound alignment. 5-65

8 Figure 5-17A

9 Figure 5-17A

10 Figure 5-17A

11 Figure 5-17B

12 Figure 5-17C

13 Figure 5-17C

14 Figure 5-17C

15 Figure 5-17D

16 Figure 5-17D

17 Figure 5-17D

18 Figure 5-17E

19 Figure 5-17E