Laserfiche WebLink
TASK 0 PRELIMINARY WELL <br />INTERFERENCE EVALUATION <br />SEH will also evaluate interference with the existing City <br />wellfield, because the 2021 model showed that drawdown <br />from the wellfield extends well beyond 500 feet. SEH will: <br />o Identify all municipal and private wells within 500 feet <br />of each site from the Minnesota Well Index and County <br />parcel data, and confirm which are finished in the <br />Tunnel City-Wonewoc aquifer <br />o Estimate drawdown at each nearby well with analytical <br />solutions (Theis and Hantush-Jacob) using the aquifer <br />parameters from Task 1, at the planned pumping rate <br />and duration for Wells #9 and #10 (SEH used this <br />method for the Rosemount Well 17 siting evaluation) <br />o Run the regional Metropolitan created Metro Model 3 <br />with presumed locations of Wells #9 and #10 added at <br />each candidate site to estimate drawdown across the <br />wellfield under present-day and 2040 demand <br />o Compare predicted drawdown at private wells to <br />available water column and pump setting depths where <br />records allow <br />Deliverables: Interference table for each site <br />and drawdown contour maps from the analytical and <br />model results. <br />TASK'S SITE RISK EVALUATION <br />SEH will rate each recommended site for the three risk <br />categories in the RFP. SEH will evaluate: <br />o Aquifer vulnerability: evaluate confining conditions, <br />depth to bedrock, and the MDH geologic sensitivity <br />rating for each site, and note where the Tunnel City is <br />the first bedrock and the enhanced -permeability zone <br />is in contact with glacial sediments <br />o Regulatory safe -yield thresholds: compare predicted <br />drawdown to the MnDNR thresholds of 50% and 25% <br />of available head above the top of the aquifer, using <br />the modeled results from Task 3 — Single -well pumping <br />already approaches the 50% threshold in some City <br />wells, so this is a key screening factor <br />o Private well impacts: summarize the number of <br />private wells within 500 feet and the predicted <br />drawdown at each from Task 3, and identify wells that <br />may need mitigation based on typical MnDNR feedback <br />to make sure domestic users will not be impacted by a <br />new appropriation permit <br />o Other risks: summarize other risks for each site, <br />including access, discharge routing for test pumping, <br />and future watermain connection <br />Deliverables: Risk summary table and narrative for <br />each recommended site. <br />TASK. TECHNICAL MEMORANDUM <br />SEH will prepare a technical memorandum that presents <br />the Task 1 through 4 findings and the recommended test <br />hole and test well locations. For this task, we will: <br />o Summarize work completed in previous tasks including <br />the hydrogeologic setting, aquifer parameters, and <br />water quality by area <br />o Present the site screening, interference, and risk results <br />with figures and tables <br />o Recommend two to four sites and the test hole and test <br />well locations, target depths, and construction for each <br />o Review the draft memorandum with City staff and <br />incorporate comments before we finalize it <br />*/ Deliverables: Draft and final technical memorandum <br />with figures, tables, and well records as attachments. <br />TASK 0 TREATMENT COST ESTIMATES <br />For this task SEH will update that comparison for each <br />recommended site. SEH will: <br />o Estimate the raw watermain route, length, and cost <br />to connect each site to the WTP, including crossings, <br />easements, and restoration <br />o Estimate the capital cost of an on -site pressure <br />filtration facility for iron and manganese removal sized <br />for the expected well capacity, including building, <br />filters, chemical feed, backwash handling, controls, and <br />electrical service <br />o Estimate annual operating costs for each option, <br />including energy, chemicals, media replacement, labor, <br />and maintenance <br />o Compare the options on a life -cycle basis for each site <br />and identify which option is more cost effective <br />s' Deliverables: Cost comparison table and short <br />narrative for each recommended site. <br />TASK ® MNDNR PRELIMINARY WELL <br />CONSTRUCTION ASSESSMENT <br />SEH suggests a permit scoping call with the DNR and the <br />City before proceeding on any location, so we can: <br />o Learn if there are any site selection or target aquifer <br />issues before completing the site assessments <br />o See if there are any total appropriation issues <br />SHORT ELLIOTT HENDRICKSON INC. <br />WELL SITING ASSESSMENT FOR MUNICIPAL WELLS #9 AND #10 <br />