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Rocky Hill_Response to DEP_Figs.pdf August 6, 2019 VIA EMAIL Mr. Mark Stinson, Wetlands Circuit Rider MassDEP – Western Regional Office Division of Wetlands and Waterways 436 Dwight Street Springfield, MA 01103 Re: Rocky Hill Greenway Multi-Use Trail (#WE 246-0728) – MassDEP comments dated April 1, 2019 Dear Mr. Stinson: Horsley Witten Group, Inc. (HW) offers the following responses to MassDEP’s April 1, 2019 letter on the Rocky Hill Greenway Multi-Use Trail in Northampton, Massachusetts. Additionally, HW has revised the 25% plans (Rocky Hill Greenway Multi Use Trail, August 6, 2019, Revision 1) to address MassDEP Stream Crossing Standards in preparation for the Conservation Commission hearing scheduled for August 22, 2019. Responses below are provided in the same order and number system as the letter from MassDEP. [1] HW has complied with the Stream Crossing Standards (310 CMR 10.53(8)) to the maximum extent practicable. MassDEP and the Northampton Conservation Commission questioned the culvert crossings proposed as part of the Rocky Hill Greenway Multi-Use Path. The plans propose four culvert crossings, three of which have existing culverts at pathway stations 5+84, 8+55, and 13+82 (triple 15” CMP, 24” CMP, and 18” CMP respectively). The fourth culvert is proposed to provide a hydrologic connection between an existing wetland area and the proposed wetland replication area. This culvert will be located at approximately station 18+79. All culverts were originally sized as 24” x 24” box culverts to provide a hydrologic connection to adjacent wetland areas. On June 13, 2019 HW field personnel completed stream crossing assessment work at the three existing culvert locations at stations 5+84, 8+55, and 13+82. The two culverts at stations 8+55 and 13+82 did not have flowing water nor evidence of intermittent flow. The crossing at station 8+55 did not have a defined channel with bed and bank upstream of the culvert. The crossing at station 13+82 had a significant leaf buildup in the culvert and no sign of recent flows in either the channel or the culvert. These two crossings were determined to be crossing of ephemeral drainage systems and therefore not subject to the stream crossing standards. Mr. Stinson August 1, 2019 2 The crossing at Station 5+84 did have flowing water and a defined stream channel with a bed and bank both upstream and downstream from the triple 15” CMP existing culvert crossing. HW confirmed that a significant wetland area is immediately upstream of this culvert, running parallel to the existing access driveway and acts to supply the stream/culvert with at least intermittent flow during the wetter months of the year. HW staff measured bankfull width and depth at two locations upstream and downstream as shown in Table 1: Distance downstream (DS) and upstream (US) from culvert end Bankfull Depth Bankfull Width DS – 9.7 feet 0.4 feet 2.8 feet DS – 22.7 feet 0.4 feet 2.4 feet US – 8.1 feet 0.4 feet 2.9 feet US – 34.0 feet 0.15 feet 1.8 feet The average bankfull width at culvert crossing at station 5+84 equals 2.48 feet. The Stream Crossing Standards specify a number of parameters to enhance wildlife passage including: • Embedment. A culvert should have an open bottom or an embedded depth of at least 2 feet or approximately 25% of a culvert’s height; • Crossing span (width). Culverts should be at least 1.2 times bankfull width. For this culvert design the width should equal or exceed approximately 3.0 feet. • Openness. A culvert should have a minimum openness of 0.82 (openness is defined as a culvert’s cross-sectional area divided by the length). For this culvert the length must be at least 24 feet long (to provide driveway access to the gas pumping station), requiring a cross-sectional area of 19.7 ft2. (e.g., 4’ x 5’ box culvert, or 66” round culvert) • Substrate. A culvert should have a substrate matching the conditions immediately upstream and downstream of the culvert. Substrate conditions upstream of the culvert consist of significant amounts of organic deposition, likely associated with the adjacent wetland. Downstream of the culvert the substrate contains more mineral/cobble with slopes in the range of 5-10%. • Water depth and velocity. Water depths upstream and downstream of the culvert are less than 2 inches during low flow conditions. Proposed Culvert Based on the measured stream characteristics and review of design constraints a 29” x 45” (36” diameter equivalent) reinforced concrete horizontal elliptical pipe (RCHEP) was selected as the best option to meet the stream crossing standards to the maximum extent practicable. This culvert provides the following stream crossing metrics: Embeddedness: 11 inches of embedment is proposed (~38% of culvert height). Two feet of embedment was deemed undesirable to limit excavation to less than five feet to minimize temporary and permanent disturbance to the adjacent upstream wetland. Mr. Stinson August 1, 2019 3 Crossing Span: the 45-inch span of the proposed RCHEP equals 3.75 feet and exceeds 120% of bankfull width by approximately 0.75 feet. Openness: a 29” x 45” RCHEP has a cross-sectional area of 7.4 sq. ft. The openness ratio for the 24-foot length is therefore 0.31 feet. This value, while still considerably less than the 0.82 ft. target for new crossings is a big improvement over the existing 15” culvert crossing (0.05 ft openness) as well as the 24” x 24” box culvert originally proposed (0.17 ft. openness). Meeting the openness criteria was deemed not feasible for the following reasons: 1) A larger pipe meeting the criteria would need to be at least 48” high (48” x 76” RCHEP), resulting in an excavation depth upstream of approximately 6.5 feet below the edge of the existing driveway, resulting in significantly more temporary and permanent wetland impact; 2) the crossing length cannot be reduced further and still maintain the required access width to the gas pumping station; and 3) the driveway grade cannot be raised appreciably without increasing wetland impacts to the upstream system, nor would a raised road-grade be desirable for vehicle access to the pumping station. Substrate: The proposed substrate embedment is targeted as MassDOT native common fill (M2.01.0). This will provide a stable substrate through the culvert and will allow for continued organic material into the culvert. The material also replicates the substrate material downstream. Water depth and velocity: The proposed culvert is being designed with a slope of approx. 0.8% which will allow base flows through the culvert to approximately match the upstream gradient of the adjacent wetland. See revised planset titled Rocky Hill Greenway Multi Use Trail, August 6, 2019. This revision includes the proposed culvert revision on Construction Plans 1 (sheet 10) and rain gardens on Grading Plan 1 (sheet 13). Updated Resource Area Disturbances Location Disturbance (SF) BVW (SF) 3,840 Buffer to BVW (SF) 96,586 Bank (LF) 31 Buffer to Bank (SF) 610 Riverfront Area 0-100 ft (SF) 0 Riverfront Area 100-200 ft (SF) 9,037 [2] Concerning the requirements under 310 CMR 10.53(6) for path width not to exceed 10 feet, the project proposes to utilize an existing degraded access way, from Rocky Hill Road, as opposed to constructing a new path. There is an existing paved access way to a gas pumping station owned by the Tennessee Gas Transmission Company. The proposed project will not Mr. Stinson August 1, 2019 4 replace or widen the existing road, and at the end of the road the multi-use path will continue on at a reduced width of 10 feet. To comply with the 10-foot criterium the existing paved road would have to be reduced in width. However, the existing road is currently used by the gas company and is necessary to maintain at its current 16-ft width for truck access and transportation safety. Another option would be to construct a new 10-foot path alongside of the existing access road. This would result in greater impacts to the wetlands. The project does not propose to create or expand the existing access way, it makes good sense and complies with best management practices to use an existing access way (even if it is wider than what is required or what is regulated) than to construct a new section of the path. [3] The proposed project will have less than one acre of disturbance and therefore a SWPPP is not required. [4] HW will work with the Conservation Commission to ensure the Replication Checklist is complete and meets their standards prior to the final design. A monitoring plan (details provided below) has been established and a monitoring report (details provided below) will be submitted to the Conservation Commission per the Massachusetts Inland Wetland Replication Guidelines. The proposed wetland replacement area is designed to comply with the regulations at 310 CMR 10.55(4)(b) (1 through 7) as follows: The proposed wetland replacement area is 4,127 SF, providing a greater than 1:1 ratio of impacted BVW to mitigation wetland. This ratio is below the local standard, but meets the state and mitigation requirements, and is designed in an area that was determined to be an appropriate location for the proposed mitigation area. The proposed replacement area is located directly adjacent to a wetland segment, approximately 1,000 feet southeast of the proposed wetland crossing, and within the same approximate distance to the nearby unnamed perennial stream (Figures 6 & 7). It is sited within the same general hillside seep area, designed to be at the same or similar elevations, and to mimic the adjacent hill-side seep wetlands. The wetland replication area is smaller than would be required by the local performance standard; however, because the project is a multi-use trail designed for nonmotorized use it is subject to an exception, per Chapter 337-10 E(2)(c), Additional mitigation would result in the removal of undisturbed forested buffer zone, areas that are also important for the protection of wetland resources. The wetland replacement area is designed to achieve a 75 percent or greater native wetland plant community after two growing seasons. Native plantings obtained from nursery stock are the same or similar in composition to species observed within the undisturbed wetland. Native seed mixes will ensure cover of native species as well as provide erosion control during the grow-in period. The proposed wetland replacement area is designed to be consistent with all other performance standards for freshwater wetlands and will provide greater than 1:1 mitigation for lost wetlands that are currently disturbed (e.g., the culvert replacements). Provisions have been incorporated Mr. Stinson August 1, 2019 5 to provide additional wildlife habitat features, invasive species will be managed as part of the wetland replacement activities, and a monitoring plan has been established to control the spread of invasive species. Further, a rare species protection plan has been drafted for review and approval by NHESP to ensure no adverse effects to the local rare species populations. The replacement area will be monitored twice annually (approximately early to mid-June and early to mid-September) for a minimum of two growing seasons to assess the relative success of the replacement wetlands. Semi-annual site inspections conducted during late spring and late summer will include an assessment of the relative health and vigor of the planted vegetation, percent vegetative cover, percent cover of wetland species, and general compliance with the performance standards. Written reports detailing the findings of each monitoring event will be submitted on an annual basis for two years, to the Northampton Conservation Commission. Photographic documentation will be incorporated within the monitoring reports and photographs will be taken from pre-established vantage points for consistency between monitoring events. Recommendations will be made for the replacement of dead or dying plants, and any additional remediation, as necessary. [5] Concerning the riverfront area, please note that revisions have been made to the plans since the original submittal. The Wetland Replication Area has been moved from its original location within the Riverfront Area to a location outside of the Riverfront Area, approximately 1,000 feet to the southeast (see Figures 6 & 7). This results in less disturbance in the Riverfront Area. Approximately 9,037 SF of disturbance will occur in the outer 100-200-ft RFA, most of which is previously disturbed (3,461 SF, 4%). There is an existing paved access road to the gas pumping facility. This existing access road within the RFA will be used as part of the proposed multi-use trail. The proposed project will not replace or enlarge the existing road. At the end of the road, the multi-use path will continue on at a reduced width of 10 feet. The only permanent disturbance that will occur is for the culvert replacement at Station 5+85 and grading along the access road: Total Riverfront Area = 82,082 SF Total RFA disturbance = 9,037 SF Current degraded RFA = 3,461 SF RFA redevelopment standards compliance These resource areas are regulated under the Massachusetts Wetlands Protection Act and the City of Northampton Wetlands Ordinance (Chapter 337 of the Northampton Administrative Code) and associated regulations. Resource area impacts will be avoided and minimized to the extent practicable by using an existing paved access drive and footpath, while still maintaining a trail that is safe and adheres to the local building code. Activities within Riverfront Area will occur outside of the 0-100-foot Riverfront Area and will occur within previously degraded areas including the existing access road. The following Mr. Stinson August 1, 2019 6 performance standards for redevelopment in Riverfront Area will be met for work within Riverfront Area. (a) At a minimum, proposed work shall result in an improvement over existing conditions of the capacity of the riverfront area to protect the interests identified in M.G.L. c. 131 § 40. Work within the outer Riverfront Area will involve re-use of an existing paved (degraded) roadway. As part of the proposed project, existing culverts will be replaced to accommodate existing flows and improved stream crossing across the access road and proposed path. (b) Stormwater management is provided according to standards established by the Department. Stormwater management measures will be provided to the extent practicable, although these measures will occur outside of Riverfront Area. (c) Within 200 foot riverfront areas, proposed work shall not be located closer to the river than existing conditions or 100 feet, whichever is less, or not closer than existing conditions within 25 foot riverfront areas, except in accordance with 310 CMR 10.58(5)(f) or (g). The portion of the proposed project that will occur within Riverfront Area are along existing paved or otherwise degraded Riverfront Area, but no closer to the river than under existing conditions. Additionally, no work will occur within the inner 0-100-foot Riverfront Area. (d) Proposed work, including expansion of existing structures, shall be located outside the riverfront area or toward the riverfront area boundary and away from the river, except in accordance with 310 CMR 10.58(5)(f) or (g). The portion of the proposed project that will occur within Riverfront Area is along existing paved or otherwise degraded Riverfront Area and no closer to the unnamed perennial stream than under existing conditions. (e) The area of proposed work shall not exceed the amount of degraded area, provided that the proposed work may alter up to 10% if the degraded area is less than 10% of the riverfront area, except in accordance with 310 CMR 10.58(5)(f) or (g). The degraded area is estimated to be 4%, less than 10%, of the riverfront area. The Project will result in redevelopment of an existing degraded paved access way. The proposed work will alter 11% (includes the 4% existing degraded area), slightly more than the allowed 10%. However, the proposed project is restorative in nature with improved intermittent and seasonal stream flow and improved habitat and wetland connectivity. Additionally, the proposed project is a multi-use trail designed for non-motorized use, which is an exception per Chapter 337-10 (E(2)(c). (f) When an applicant proposes restoration on-site of degraded riverfront area, alteration may be allowed notwithstanding the criteria of 310 CMR 10.58(5)(c), (d), and (e) at a ratio in square feet of at least 1:1 of restored area to area of alteration not conforming to the criteria. Areas immediately along the river shall be selected for restoration. Alteration not Mr. Stinson August 1, 2019 7 conforming to the criteria shall begin at the riverfront area boundary. Restoration shall include: 1. removal of all debris, but retaining any trees or other mature vegetation; 2. grading to a topography which reduces runoff and increases infiltration; 3. coverage by topsoil at a depth consistent with natural conditions at the site; and 4. seeding and planting with an erosion control seed mixture, followed by plantings of herbaceous and woody species appropriate to the site; (Not applicable) (g) When an applicant proposes mitigation either on-site or in the riverfront area within the same general area of the river basin, alteration may be allowed notwithstanding the criteria of 310 CMR 10.58(5)(c), (d), or (e) at a ratio in square feet of at least 2:1 of mitigation area to area of alteration not conforming to the criteria or an equivalent level of environmental protection where square footage is not a relevant measure. Alteration not conforming to the criteria shall begin at the riverfront area boundary. Mitigation may include off-site restoration of riverfront areas, conservation restrictions under M.G.L. c. 184, §§ 31 to 33 to preserve undisturbed riverfront areas that could be otherwise altered under 310 CMR 10.00, the purchase of development rights within the riverfront area, the restoration of bordering vegetated wetland, projects to remedy an existing adverse impact on the interests identified in M.G.L. c. 131, § 40 for which the applicant is not legally responsible, or similar activities undertaken voluntarily by the applicant which will support a determination by the issuing authority of no significant adverse impact. Preference shall be given to potential mitigation projects, if any, identified in a River Basin Plan approved by the Secretary of the Executive Office of Environmental Affairs. (Not applicable) [6] Justification for Stormwater Conveyances The proposed multi-use path is a mix of new-development and redevelopment and has been designed to meet the Stormwater Standards to the maximum extent practicable (refer to original NOI narrative and as updated herein). The project includes the widening of the existing sidewalk along Rocky Hill Road (from Ice Pond Drive to the entrance of the Rocky Hill Trail), addition of a small parking lot consisting of eight parking spaces, improvements to the existing driveway to the Tennessee Gas Transmission Company pumping station with a width of 16 feet, and extension of the multi-use path beyond the existing driveway for approximately 1,865 feet with a width of 10 feet to meet the existing Manhan Rail Trail. The area of the parking lot and most of the 16 foot wide driveway are surrounded by existing wetlands and by definition saturated soils within a foot of the ground surface that restricts the use of porous pavement/infiltration as a stormwater control practice (i.e., cannot maintain two foot separation distance to groundwater). Two small rain gardens are proposed for the corners of the parking lot to provide water quality treatment for this parking area. The 10-foot wide section of the path is designed with an upgradient swale with check dams from approximate station 10+35 to station 13+85 to collect and convey runoff before it crosses the trail. The trail Mr. Stinson August 1, 2019 8 surface itself has been designed to sheet-flow runoff to downgradient areas. From approximately station 13+80 to 23+00 sheet flow can be maintained to manage runoff from the trail. A downgradient swale with check dams is proposed from approximately station 23+00 to the terminus with the existing Manhan Rail Trail at station 26+00 since concentrated flow off the trail will occur in this section. HW does not anticipate additional requirements as we are complying with the following regulations: Stream Crossing Standards for replacement crossings to the maximum extent practicable – see response to [1]. 401 Water Quality Certification (314 CMR 9.00) – The project meets the conditions outlined in 314 CMR 9.03(1). Alteration of BVW is less than 5,000 SF (disturbance to BVW is approximately 3,840 SF. The project meets the conditions outlined in the MAGP 10 (Linear Transportation Projects Including Stream Crossings). Cumulative permanent impacts for GP 10 total less than 5,000 SF. The project meets the conditions outlined in the MAGP 7 (Bank and Shoreline Stabilization). The existing crossing was not modified by decreasing the diameter of the crossing or increasing the friction coefficient. The proposed 29” x45” RCHEP will have a lower friction coefficient than the existing culvert. Bank stabilization along the banks of stream will be done in accordance with MAGP 7 and is less than 100 ft in length on each side of the stream bank. Additionally, it is important to note that there will be no discharge of dredged or fill material into waters of the US. Sincerely, Horsley Witten Group, Inc. Richard A. Claytor, Jr., P.E. President cc: Filbert Yee, Project Manager – MassDOT Wayne Feiden, FAICP – City of Northampton Sarah LaValley – City of Northampton Conservation Wetland Replication Area Document Path: H:\Projects\2015\15004 Northampton Rocky Hill Greenway Trail\GIS\Maps\Aerial_replication_area.mxd Wetland Replication AreaRocky Hill Greenway Multi-UseTrail (Bike Path)Northampton, MA± Date: 7/30/2019 Figure 61" = 200 feet 0 200 Legend Rocky Hill GreenwayMulti-Use Trail (approximate) Parcels *Aerial Imagery - ESRI 2016 Wetland Replication Area (approximate) Document Path: H:\Projects\2015\15004 Northampton Rocky Hill Greenway Trail\GIS\Maps\USGS_Replication_area.mxd Wetland Replication AreaRocky Hill Greenway Multi-UseTrail (Bike Path)Northampton, MA± Date: 8/2/2019 Legend *USGS Northampton 24K Quadrangle 0 500 1" = 500 feet Figure 7 Rocky Hill GreenwayMulti-Use Trail (approximate) Wetland Replication Area Wetland Replication Area (approximate)