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HomeMy WebLinkAboutCONSERVATIONminutes09102007-20071023132814 Conservation Meeting September 10, 2007 Present: Colin Cauldwell, Chair; Paul Boyden, Vice Chair; Carole Matthew; Joe Mulkern; Cindy Ostrowki; Ben Monachino; Michele Grenier, Conservation an Environmental Planner. ;ri~*;i!t~~~Jilg,; .... ~~~i~~.if:~P:~iJj. !:"i~ff~gm~~l;i~ijijWfi.;:'. Hearing started at 7:00 pm. John Sullivan, Town Engineer and Mark Mitsch, Weston & Sampson project manager were present. Kingman Pond Dam is an earth embankment with a fixed weir concrete primary spillway and a low-level outlet structure. The dam has been classified as a significant hazard potential structure and is considered to be in poor condition. Mark told the Commission the embankment has become overgrown with large trees and brush and seepage has been observed along a good portion of the downside of the dam. The vertical alignment of the embankment is inconsistent and several depressions were observed, possibly caused by uprooted trees. Several animal burrows were also observed. The primary spillway is in poor condition with the concrete training walls cracked, displaced, deteriorated and undermined. Mark said the spillway is significantly undersized for current dam safety standards. The low-level outlet is no longer operating. The intake structure for the low-level outlet is a circular concrete manhole riser with a concrete slab roof. Water continually leaks into the riser and out through the discharge pipe, which discharges uncontrolled below the normal water level at the downstream right side of the existing primary spillway. The dam rehabilitation design process consists primarily of identifying options for spillway replacement to improve hydraulic capacity and identifying options for improving the condition of the embankment while limiting the costs of the project. Based on the April 2006 dam safety inspection, the Town of Mansfield, Engineering Department proposes the following actions to be taken to address the deficiencies found at the dam during inspection and evaluation. · Design and construct a new, properly sized spillway system for the dam. · Design and reconstruct the embankments to an appropriate crest elevation that is coordinated with the spillway design. To improve hydraulic capacity. · Develop and implement appropriate operations and maintenance procedures consistent with the new design features of the dam. Mark told the Commission Weston & Sampson has flagged the wetlands and have done a survey base plan and hydraulic and hydrology studies. Michele asked why the dam is being reconstructed instead of removing it. She said in most states the dams are being removed and the Army Corps is giving the states money for this purpose. Mark told her he first recommended the dam be removed but there are issues with the removal. Mark told the Commission the removal of the dam would be very simple; the concrete structure would be removed, the water level in the pond would be reversed to a stream and a wetland meadow. The problem is that when this has happened in the past the odors (an organic issue) from the area are tremendous. By draining the water, the industrial contamination in the sediment is exposed, creating more of a hazard to the public. If the dam were to be removed, an evaluation of the environmental conditions of the sediment would need to be done. If contamination were found, the town would become locked into the Mass Contingency Plan, a 4 phase process for investigation and clean up. It could even involve another level of bureaucracy; he said the town does not want to go this route if it can be avoided. It is manageable now through the reconstruction of the dam. A clean up of the hazardous waste would involve the EP A and potentially be very costly to the town. Mark gave as an example a dam removed in Dalton, MA. It was thought the removal of the dam would cost approximately $50,000. The final cost to remove the dam was well in excess of 5 million dollars because of industrial contamination. Mark reviewed some of the design alternatives for the improvement of the dam; a combination fixed crest weir with a stop log channel, deep sluice or low-level outlet, similar to Fulton Pond Dam; small fixed crest weir and protected embankment and a fixed crest weir system. Mark told the Commission the combination fixed crest weir with a stop log channel, deep sluice or low-level outlet is not suitable for this site. Because Kingman Pond is shallow, a substantial amount of dredging in the pond would be required to create a suitably deep upstream channel for a stop log channel or other low-level outlet to function effectively. Regular maintenance of the channel, including occasional dredging, would be required to prevent silt buildup in the channel. Sediment dredging in Kingman Pond is not recommended since the pond is located on the Rumford River downstream from the Hathaway Patterson Company site, which is on the EP A National Priorities List due to environmental contamination. No action within Kingman Pond is required at this time relative to potential contamination in the sediment. If this method for the reconstruction is used, it is possible the dredged sediment may need to be disposed of as contaminated material at a cost that could exceed the cost of the dam rehabilitation. The fixed weir option involves replacing the existing spillway and low-level outlet structure with a spillway system. However, if this method is used there is the potential for flooding if the embankment is overtopped. Since private residences surround the pond, an option that allows overtopping and flooding is not recommended. A stepped fixed weir configuration is recommended for this site. The lowest step would be set at E1.139.0, 0.2 ft above the lowest level of the existing weir and matches the normal water level in the pond. A second step would be set at a higher elevation and would act as an auxiliary spillway to discharge moderate to large storms. The auxiliary spillway weir would have a crest elevation of El. 141.0 and would be 220 ft. long. The width of the primary spillway weir would expand from 38 ft. be 90 ft. long. Mark said this is a nice solution; it will keep the impact to the wetlands due to construction at a minimum, dredging and disturbing the sediment in the pond would not be necessary and operational/maintenance needs of the dam would be minimized. The disturbance to the wetland resources would be less than 5,000 sq. ft. This solution also keeps the project out ofDEP jurisdiction but more importantly, away from the Army Corps of Engineers. The reconstruction will require a Programmatic General Permit. The project is considered to be a Category 1, a "non-reporting" project, and does not require a filing with the Corps. Mark said if the town is required to file with the Army Corps, it could hold the project up for 6 months. A low-level outlet is not considered necessary for this solution. Temporary pumping or siphoning could be used in the unlikely event a drawdown is necessary. The low-level outlet will remain in place to maintain the pond level at normal summer levels during construction to reduce the cost of the project, additional costs incurred by the need for construction dewatering. The existing low-level outlet will be sealed and abandoned as soon as the project is completed. Silt fence/hay bales will be installed along the limits of work and along the full length of both sides of the site access way from Spring Street. Embankment improvements would include removal of trees including their root systems, regrading the embankment to a consistent crest level to limit the potential for erosion and seepage through the embankment and protecting the upstream slope from erosion by installing a turf-reinforcing mat. A drainage/stabilization system on the downstream slope will be constructed if necessary. There are several large sycamore trees on the dam and are shown on the plan as being protected during construction with the intention that the Town would maintain these trees even though it is generally not recommended that trees be allowed to grow on a dam. Mark said Weston & Sampson would talk to the Office of Dam Safety about keeping the trees but he feels they might require that the trees be removed. He explained that tree roots loosen the soil on the dam. Mark said the removal of the trees and the root system will be one of the most costly parts of the project. He told the Commission the neighbors, when asked about the trees, said they would like the trees removed. Mark told the Commission that tree roots are growing around the old stonewall on the property and undermining it. Paul wanted to know the longevity of the reconstructed dam. He asked what would be the area most in need of assessment, the area most likely to deteriorate. Mark said the life span of the reconstructed dam would be around 50 years. Mark said the area most susceptible to deteriorate is the primary spillway, where you have significant water flow and freeze/thaw conditions. Cindy wanted to know if the sediment gets stirred up during a storm event. Mark told her there is not much disturbance because the sediment is buried under water. Sediments are not churned up during storm events or during normal operation of the dam. Mark said the construction access way would follow the existing footpath from the gravel parking area to the dam. On the plan submitted, Mark included a provision for a truck wash area to clean the trucks of mud and dust before they re-enter onto Spring Street. It should be set up in the existing parking area. Cindy asked what the cost would be for this project. John said the cost would be between $550,000 and $650,000. Paul asked ifthere were any grants to help reduce the cost. Mark said there really isn't a lot of funding available anymore. Michele asked when John thought the project would begin. He said the bids would go out the end of October; all bids to be returned by November. It would then go to Town Meeting in April 2008. Ifpassed at Town Meeting, John hopes the work can start in July 2008. Paul made the motion to accept the plans for the reconstruction of the Kingman Pond Dam as drawn, titled "For Permit Approval Only"and dated 8-14-2007, and any amendment there of. Cindy seconded. Passed 6-0. Mark told the Commission the plan still needs to go through a technical review within Weston & Sampson. Michele asked that when the review is completed, if Mark would make sure Conservation receives a plan of record, stamped and dated. Hearing ended at 7:45 pm. jj~'~m~~~~ti~~!9i~i.R~i~lm: ..',~t9~1~lt~;~~~" :'~~;'~~m'~~Ji~~ri John Sullivan wanted to make the Commission aware of the work on the underpass, even though Mass Highway has indicated that no filing is necessary for this project. John said maintenance repair or replacement of existing roadways and associated drainage is exempt from the Mansfield by-law, provided the Conservation Commission is notified. John told the Commission there has been a groundwater problem at the railroad underpass for a number of years, more so in the winter months. John said federal and state funding was secured a number of years ago. The improvements include upgrading the existing drainage pump station and the existing underground drainage discharge line adjacent to the railroad tracks. This drains into the Rumford River. Existing pumps are not adequate. The existing18" gravity fed line will be replaced with an 18"force main (pump will create pressure to force water out). Spare pumps will also be installed and also a new generator. The design process is almost done and construction will start in 2008, Paul, Ben, Carole and Cindy conducted a site walk at 4:30 pm today, September 10,2007 at 900 Maple Street and Map 40, Parcel 92. Michele, Joe and Colin will walk the site tomorrow, September 11th. Motion to approve the minutes of August 27, 2007. Motion was made to adjourn at 8:15 pm. Paul/Joe Next meeting will be October 15,2007. @2~ (f4~ Colin Cauldwell, Chairman /tJ/tr/o7 t Date