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HomeMy WebLinkAbout2009-06-03-LYMAN CREEK WATER SYSTEM INFRASTRUCTURE IMPROVEMENTS PROJECT OMOMN ENGINEERS SURVEYORS PLANNERS MMERLE INC. SCIENTISTS 9 2880 TECHNOL06Y BOULEVARD WEST•PO BOX 1113•BOZEMAN,MT 59771 An Employee-Owned Company OFFICE:406-587-0721•FAX:406-922-6702•mmm-anet June 3, 2009 Denver Fraser, P.E.- " Public Water Supply— Plan Review Section Community Service Bureau Montana Department of Environmental Quality P.O. Box 200901 Helena, MT 59620-0901 RE: City of Bozeman Lyman Creek Water System Infrastructure Improvements Project MMI#: 0417.055 EQ# 09-2418 Dear Mr. Fraser: In response to your letter dated May 12, 2009, the following comments are provided: 1. To provide for testing of the new spring lateral, isolation valves and a blow off pipe are now provided on the revised plan sheet. See Sheet W-1. The valves will be abandoned in place once the source is approved as accidently shutting both valves at once will force the spring water to find a different flow path which may damage the clay cap on the spring. 2. The existing water line that is a concern for a possible cross connection will be disconnected and capped. See Sheet C-1. 3. A full size version of Sheet 12 (W-1) is enclosed that more clearly shows the topography at the spring site and has the existing spring collectors highlighted. Also included is a copy of the original spring construction plans for informational purposes. The Lyman Creek Spring was developed in 1991 in the two collectors shown on the original plans. The upper collector was installed where the water surfaced to form the creek that the City historically has used for water supply. The lower collector was installed to collect water that was seeping from the east side of the canyon bank. While these collectors are performing quite well they do not capture all of the spring water. As part of the construction of the upper collector, the stream channel downstream of the spring source was filled. At the toe of this fill, and at the Providing resources in partnership with clients to achieve their goals. Iy MORMSON `'��`. MMERLE,INC. beginning of the flowing creek, is a pipe that was likely part of the construction dewatering system installed when the original spring work was completed. Water flows from this pipe and from the bank surrounding the pipe. This water is un- captured water from the original upper collector construction. The intent of the further spring development is to capture this water. The drainage basin above the spring likely,produces some intermittent flow during significant snow melt and significant rain events; however, the City Operators have not seen water flowing above the location where the new spring development is proposed. The clay cap over the spring will prevent surface water from entering the spring collector line. During the significant events that produce runoff the surface water will flow over the surface, above the clay cap, and enter the surface flow of the perennial stream downstream of the spring collection system. 4. The peristaltic pumps proposed for sodium hypochlorite and fluoride injection are non-siphoning pumps based on their operation principles. At all times, there is a roller in contact with the tubing which maintains priming, breaks a siphon, blocks backflow, and provides the pumping action required. A manufacturer provided document is included to illustrate the operation of the peristaltic pump with confirmation of positive contact of a roller with the tubing at all times. In addition to the peristaltic non-siphoning pump type, the chemical injection will occur on pipes with positive pressure. 5. Hydrofluosilicic acid was proposed to be injected into the centerline of the pipeline using a chemical injector assembly shown on Sheet M-5. The project plans have been updated to include a 7" long solution tube inserted into the 12" process pipe to reach into the lower half of the pipe when inserted from the top. A cut sheet for the chemical injection assembly is included and provides the breakdown of the part number including the insertion length. The City of Bozeman operators prefer the injection assembly to be mounted on the top of the process piping for operation and maintenance considerations. 6. Venting of the chemical storage tanks to the exterior of the building is provided for both the sodium hypochlorite and hydrofluosilicic acid. A 1" vent pipe will be connected to each tank and installed to the building exterior. The project plans show the venting on Sheet M-2 and on Sheet M-5 in Details 1 and 2. 7. The spring box has been modified to comply with the finished water storage provisions. In accordance with DEQ-1, 7.0.8.2, the Halliday access hatches have been revised to a water-tight model. Finished grade was lowered to expose the top of the vault, and riser rings were added to bring the top of the hatches to 24 inches above the top of the vault. The overflow pipe has been modified to include a flexible check valve ("pinch Al MORRISON J MAIERLE,INC. valve") with an internal 2.5 mesh (3/8") screen to meet the intent of DEQ-1, 7.0.7. A 24 mesh screen is not suitable for this application due to the continuous and varying flow rate from the spring. Attached,is a cut sheet showing the proposed check valve which will provide for a more positive closure than a typical flapper valve. The flexible, curved-end check valve is designed to pinch closed around the discharge flow at all flow rates. The overflow pipe diameter was increased to allow discharge in excess of inflow rate from the spring, and the outlet end was raised to between 12 and 24 inches above the top of the riprap. In accordance with DEQ-1, 7.0.9, a 4-inch diameter vent was added to the vault. We appreciate your review of this project. Please do not hesitate to contact me at 587- 0721 or at jnickelson@m-m.net if you have any questions or concerns. Sincerely, A MORRISON-MAIERLE,nvc. James R. Nickelson, P.E. Bozeman Office Enclosures cc: Bob Murray, City Engineering Rick Moroney, Water Treatment Plant Superintendent N:\0417\055\DOCS\Correspondence\DEQ Plans Response Letter.docx