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• <br /> • <br /> • <br /> daz . ' • <br /> INTEROFFICE MEMORANDUM <br /> • . <br /> TO: County Commission <br /> John Link, County Manager <br /> Marvin Collins, Planning Director <br /> • <br /> FROM; Paul Thames, County Engine --- <br /> • 'DATE: May 22, 1989 <br /> SUBJECT: McLennan's -Farm Subdivision -Low Pressure System 'Design- <br /> I have reviewed the document entitled "Wastewater Facilities <br /> -- Planning Report"-by Morgan & Associates for McLennan's Farm -. <br /> Subdivision and a document entitled "Report on Soil Absorption . <br /> Wastewater Treatment Technology" by North State Utilities for <br /> • OWASA. The latter document , has a section which specifically • <br /> reviews the low pressure system design for McLennan's Farms. A <br /> copy of this portion of the North State document attached herein. <br /> Generally I have no problem with the basic design premise <br /> presented in the Morgan report. The use of individual septic <br /> tanks and pump stations for each household in the subdivision is <br /> an excellent method of primary treatment. I do have doubts, some <br /> of which where triggered by the North State report, about the <br /> 1 apparent design for the low pressure field, the <br /> pump station <br /> design and the system management, ownership .and responsibility for <br /> the overall system. <br /> The available area for the low pressure field is apparently <br /> almost the exact required size for a primary and repair field. <br /> There appears to no provision for buffers, or for field layout <br /> adjustment mandated by the physical charaCteristics of the field. <br /> The overall field appears to be subdivided into four subfields, <br /> • two of which will be dosed simultaneously by -two:pumps.operating <br /> simultaneously with one -pump for each field.. Each f.ield <br /> apparently will contain approximately 3000 linear .feet bf • <br /> distribution lateral . It is my opinion that dosing more than 1000 <br /> to 1200 linear feet at one time will result in flow equalization <br /> problems which will cause hydraulic overload on the upstream side <br /> of field. The report also includes a document' which recommends <br /> that the pumps be set to run for a minimum 3 minute time period. <br /> It generally takes 3 minutes to purge the air from even a smaller <br /> • <br /> • <br /> • <br /> • <br /> • <br /> • <br />