Agenda - 11-16-2004-9a - Laserfiche WebLink

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15 MEMORANDUM TO: David Stancil, ERCD Director FROM: Paul Thames, PE, County Engineer DATE: September 2.3, 2004 SUBJECT: Water and sewer utility extension costs to serve Twin Creeks property As per your request, I have re- estimated (original estimate by memo to you 11/1/2000) the costs of providing water and sewer utilities to serve the proposed (9/2/2004 draft /preliminary park master plan) reshoom/concession facility for the Twin Creeks Park. I have included two small color maps (scale V" =400') to show potential routings for those utilities for which I have estimated costs, In general, I estimate the cost of 8" gravity sewer lines at between $100 and $125 per lineal ° foot (as per recent information provided by OWASA) and 12" water line at $75 to $100 per linear foot. Per foot prices are inclusive of the costs of construction, design, project administration, some rock excavation, permitting fees, easement acquisition, etc. There are a number- of water and sewer utility issues that must be resolved through the master planning of the utilities that will ultimately serve the portions of the Twin Creeks properties that may house school facilities. Extension of utilities that will serve the as yet undeveloped Carrboro north -west area will also involve utility planning for the Twin Creeks property. Specifically, extension of gravity sewer outfall lines along the creeks through some portion of each of the Twin Creeks properties will be necessary to provide gravity sewer collection to the area around and north and east of the Old NC 86 /Eubanks Road intersection. While sewer lines that can address the maximum levels of park generated wastewater flow can be sized at the minimum required for public sewer extensions (8" mains), mains providing additional capacity will be necessary to serve the combined demands of schools and other development in the northwest area. Extension of water service to the park will require activating a 2000 foot section of OWASA's existing 16" transmission main along Old NC 86 to a point adjacent to the Twin Creeks property and then extension of a water service main from the 16" line to the internal areas of the property. I cannot imagine a scenario in which potable water demand (assuming that water for irrigation would come from wells or something other than OWASA's potable water system) for the park would exceed 50 gallons per minute and 5000 gpd (although the draft master, plan shows a "water playground for which water demand has not been defined). This demand can be easily met with a 3" water main. However, a 3" main would not be sufficient to provide for fire protection or an adequate water supply for one or more schools located internal to the Twin Creeks properties- If one or more schools are to be located on the Twin Creeks properties, the properties will ultimately need to be crossed by waterlines in the 10" to 12" range (as necessary to provide for fire flows and pressures). It would be a mistake to construct lines of this size for the park because the quantity of water stored in the lines themselves would be far in excess of even a weekly demand for the park in most cases and seasons. The water would go "stale" (lose its chlorine residual), necessitating line flushing, re- chlorination and similar problematic water system operational problems. These problems may arise with just the :3" line as well, in that — with the 2000 feet of existing 16" line — approximately 22,000 gallons of water (or more than 4 days' demand) can be stored in the system.