04-01-2019 Council Packet 2 - Laserfiche WebLink

Home Search

WS – Item #4 WORK SESSION STAFF REPORT Work Session Item No. 4 Date: March 27, 2019 To: City Council From: Diane Hankee, City Engineer Greg Johnson, WSB & Associates, Inc. Re: Screened Test Well No. 7 Background The City is proposing to construct Well No. 7 on property located at 509 Birch Street and to use the farm house as the well house. As part of the Feasibility Study the council approved a test well. The site is currently owned by Anoka County and Well No. 7 would be completed in coordination with the County. A test well is typically used to provide representative water quality samples and test pumping results to demonstrate that the site would be suitable for a future municipal well. A standard bedrock test well typically costs $30,000 to $40,000. Construction of a municipal well would cost between $275,000 to $315,000. When considering a municipal well, a test well is recommended step to obtain site- specific information regarding the depth of water-producing zones, hard layers (confining layers) that separate aquifers, well production capabilities, and most importantly groundwater quality. The depth of the test well is the same as the proposed future well itself of 300 feet. A test well is typically 6 inches in diameter and municipal well is 10 - 12 inches in diameter, thus a test well is not sized large enough to become the municipal well and would significantly reduce the amount of water supplied. During the construction of the bedrock test well the contractor, Traut Companies, drilled approximately 142-feet into the Prairie du Chien formation. The uncemented portion of the formation was not stable and continually collapsed as Traut attempted to reach the Jordan formation below. Traut then switched their drilling method and was able to make it approximately 187-feet, which was close to the top of the Jordan aquifer. However, the well continued to collapse within the uncemented zone and produced sediment filled water. In working with the well drillers Traut and Barott Drilling Services (local well driller) it was concluded that a bedrock test well would not be feasible in this unique formation. Due to the geological conditions in this area, it is recommended to seal the bedrock test well and consider other options. The City could consider constructing a new screened test well, with Anoka County approval, in a different location on the 509 Birch Street site. The screened well would be