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Carver Engineering to Hansz/Request for Waiverrmm Carver Engineering, Inc-. June 9, 2009 Jim Hansz, P.E. City of Kalispell PWD PO Box 1997 Kalispell, MT 59903-1997 Consulting Engineers Civil Structural Environmental Re: Request for Waiver - Proposed Sewer System for Cottonwood Estates Dear Jim: In a letter from Paul Burnham dated June 8, 2009, Paul reiterates the City's position first pointed out in a May 11, 2009 letter to Roberta Struck, Manager of Flathead County Water & Sewer District #1 (Evergreen), and then again at a recent meeting with the City, District and representatives of Cottonwood Estates, that Cottonwood Estates is apparently not an appropriate application for a low pressure grinder pump system. Paul indicates in his June 8, 2009 letter that, "The grinder pump sewer system does not meet City standards in this application, for various reasons outlined in our previous letter dated May 11, 2009." In his June 8, 2009 letter, Paul recommends that we formally request a waiver of City standards and that the Public Works staff will present this request to the City Council and then follow their direction. On behalf of the owners/developers of Cottonwood Estates, this letter is intended to serve as a formal request for waiver. In Paul's letter, he asks that we address the following items in our request for waiver: 1) document specifically what you are requesting, 2) explain why Flathead County Water and Sewer District #1 restricts the use of a gravity main and lift station system in this case, and 3) describe your justification for building a non -City standard sewer system 1) The owners/developers of Cottonwood Estates are requesting that a low pressure grinder pump system, using individual Environment One (E/One) grinder pump systems and 1-1 /4" HDPE service lines on each lot, with 2", 3" and 4" HDPE force mains, cleanout/flushing manholes and a metering manhole in public rights -of -way, be permitted by the City of Kalispell for Cottonwood Estates, Phase 1 and subsequent phases of Cottonwood Estates. This type of sewer system is being proposed because Flathead County Water & Sewer District #1 (Evergreen) rejected an earlier design consisting of gravity sewer mains and a single duplex lift station, with 17 lots to be served by individual grinder pumps and small diameter force mains. Page 2 Cottonwood Estates June 9, 2009 2) The District rejected the initially proposed sewer system design because a significant portion of the gravity mains, manholes and lift station wet well would be in groundwater all, or part of, the year. They have experienced significant I & I problems in their existing gravity collection system in this general area and they do not want to add to those problems. As suggested by Paul in his May 11, 2009 letter, we looked at a more centrally located lift station and ran 8" gravity mains to that location trying to keep the gravity mains as shallow as possible (not less than 4 ft. to invert) and running them at a minimum grade of 0.40%. Although we ended up with a more shallow installation than the initial sewer system design, some parts of the system would still be partially in or completely submerged in groundwater during part of the year. We also ended up with the 17 lots that would have to be served by grinder pump systems and small diameter force mains. The District still did not like the fact that a portion of the system would be in groundwater and thought the subdivision would be better served by the proposed low pressure grinder pump system. 3) We are proposing a low pressure grinder pump system because we feel it is the best type of wastewater collection and conveyance system for this specific area of Evergreen. Our primary intentions were to address the concerns of the District and to overcome some of the physical limitations of the project site. The system is virtually water -tight, meaning no I & I. The system can also be installed at a relatively shallow depth (6 ft. to top of pipe) throughout the subdivision which reduces deeper excavations into caving gravel soils and groundwater, and the costs to the District for operation and maintenance of the force mains within the roadways will be significantly less than with minimum grade gravity sewer mains, manholes and a duplex lift station. We do not believe that the low pressure grinder pump system being proposed for Cottonwood Estates is a "non -City standard sewer system". Our only reference to established standards for sewer system design in the City of Kalispell is the City's Standards for Design and Construction. We have read the current July 2005 version of the Standards and we have read the version of the Standards presently under consideration by the City. In neither version is there anything that would indicate that a low pressure grinder pump system is not acceptable in the City, nor is there anything that indicates that such a system is acceptable. There is simply no mention of low pressure grinder pump systems. This matter was discussed with Paul when he delivered a copy of his June 8, 2009 letter, and he indicated that the Standards for Design and Construction were guidelines and were not intended to address every detail. Paul Page 3 Cottonwood Estates June 9, 2009 mentioned that the City "Standards" relating to this situation were essentially as outlined in his May 11, 2009 to Roberta Struck. Although not specifically mentioned, the letter clearly infers that gravity sewer mains and, when necessary, sewage lift stations are the preferred method of wastewater collection and conveyance in Kalispell, and that grinder pump systems are only appropriate in limited applications where an existing gravity sewer main is available for direct connection. Other comments or standards in his May 11, 2009 letter involved the lack of backup power with grinder pump systems; the requirement to have individual homeowners purchase and install the grinder pump units in which lack of oversight could result in "varying quality of workmanship by multiple contractors and homeowners"; the capacity limitations of low pressure grinder pump systems for expansion and future service to other areas; and operation and maintenance of the individual grinder pumping units. It was also pointed out that a grinder pumping system with 16 EIOne pumping units and a common force main was approved by the City for Granary Ridge along the east side of Whitefish Stage Road. These comments, along with additional comments somewhat critical of grinder pump systems, were discussed with Paul in a May 15, 2009 meeting with Roberta Struck, Andy Hyde and myself. Information or argument was provided that addressed all of Paul's comments, including grinder pump system capacity to withstand power outages up to seven (7) hours; system capacity to provide limited expansion of service to other areas; District oversight of individual grinder pump installations; and the operation and maintenance responsibilities of the District, homeowner's association, contract maintenance providers and individual homeowners. The owners/developers of Cottonwood Estates would greatly appreciate the City's consideration of this Request for Waiver of City Standards. Referenced letters are included with this Request for Waiver. Sincerely, CARVER EN7.' ING, INC. Tom Cowan, P.E.