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Hands Mill Dam Removal Study and Preliminary Engineering Design


Location
Vermont
Publication Date
06/01/2020 01:26 PM EDT
Closing Date
06/30/2020 11:59 PM EDT
Issuing Organization
Winooski Natural Resources Conservation District
Solicitation Number
Description

Specifications include, but are not limited to: 1)Participate in a project initiation stakeholder meeting to guide scope and design considerations.2)Field Investigations: a)Review any existingrecords including inspection reports, engineering designs and drawings for the dam, property plans and monumentation.b)Identify and take note of upstream, downstream, and adjacentinfrastructure that could potentially be impacted by the loss of the impoundment (e.g., roads, building,private wellsetc.), and any utility infrastructure (e.g., water lines) that couldpotentially run through the impoundment and therefore would need to be taken care of during construction.c)Identify and take note of trees upstream, downstream and adjacentthat may need to be removed and their species type and count. d)Perform the surveying and probing necessary to determine if removing the dam structure will likely improve aquatic organism passage (i.e. presence of natural bedrock barrier). e)Develop a hydraulic model to predict changes in floodplain inundation, channel patterns and stream velocities that could take place following dam removal. Confirm Aquatic Organism Passage flowobjectives will be met with removal. f)Perform the necessary survey to develop a longitudinal channel profile and cross sections for the affected upstream and downstream reaches. Ideally the longitudinal profile would extend upstream past the end of the impoundment and downstream 20-30x the bankfull width. Determine the channel’s natural bankfull width at the site of the dam. Assess the upstream and downstream reaches and develop a description of the channel and adjacent floodplain/wetland areas and a prediction of the future channel profile and pattern following dam removal.g)Document the extent and approximate dimensions of the wedge of deposited sediment upstream of the dam. Include an estimate of sediment volume and the amount of sediment that may mobilize during dam removal andduring an uncontrolled failure. Identify a sediment management alternative for the dam removal.h)Collect 4-6 sediment grab samples and analyze for grain size and phosphorus concentration. Based on the results, provide an opinion on the need for additional sediment testingin the next Phase II Final Design.Review the past and present land use upstream of the dam to evaluate the need forothersediment sampling for laboratory analysis for potential contaminants in the impounded sedimentssuch as metals, PAHs and organic contaminants as per the VT DEC 2016 Recommended Guidelines for Evaluating Contaminant Concentrations in Freshwater Sediments and the Potential for those Contaminants to Adversely Affect Aquatic Biota(Attachment F). 3)Prepare a memorandum summarizing results and conclusions from field investigations and modeling. Memorandum should also include:a)A concept design for discussion and clear area of impact to inform historical assessment. b)A feasibility and alternatives to removal analysis that includes life cycle costsfor all alternatives(for more guidance see: Attachment B and https://dec.vermont.gov/water-investment/water-financing/srf/srfstep1/PER)

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