5A - Conditional Use Permit for the RV Resort Village at the Preserve (continued)

Home Browse Search

MEMO wlMiT S Date: April 12,2006 NOLTING To: Dan Helbling From: Mark Hallan Cc: Dave Reese,Tun-M,6 Brian Ross Project Name: RV Resort Village at the Preserve Project No.: 0158B0001 Subject: Water Supply System Water supply wells for the RV Resort Village are proposed to be located along the north side of the property at the general location shown on the attached plan. This location will provide the minimum 300 foot separation to existing drain fields at the Jeff Oelke and Jerry Grossoeh residences. The well locations would be approximately 300 feet south of the north property line which would provide separation from a future incompatible land use(drain field) on the property to the north. Water demand and related pumping for the wells will be based on guidelines in AWWA Design and Construction of Small Water Systems. Table 1-4 in this publication(attached)provides water demand for water use fixtures or appliances. The number of units to be served by the well system will be greater than 30 so the 120 gallons per hour(2 gpm) or each unit design recommendation for peak flows will be used. Utilizing this guideline the 157 units would require a 314-gpm peak flow capacity from the well system. Ten States Standards, Section 7.2.2, states the well and pump capacity should be at least ten times `... the average daily consumption rate. Daily water consumption is estimated at 23,850 gallons for the wastewater system design. How this water is used over a typical day determines an average rate (gpm) for the water supply wells. Figure 3-3, Daily Water Use Pattern for Single-family Residence from EPA 625/R-00/008 Manual, shows water use broken down by fixtures for a 24-hour period. This manual advises that eighty to ninety-percent of water use occurs over a 12-hour period during the day. Ninety-percent of 23,850 gpd is 21,465 gpd. Usage over a 12-hour period provides a rate of 30 gpm(21,4650 gpd_ 12 hrs/day_ 60 min/hr). Ten times this figure would be 300 gpm for the well system peak pumping capacity. This compares to the 314 gpm value per AWWA guidelines. The water supply system will be handled by two wells each designed and constructed to supply a 150 gpm pumping rate at each well. Controls will be cycled between wells for each fill event of the pressure tanks. The well pumping rate of 150 gpm will be based on 60 psi(138') of pressure head for the proposed 40 to 60 psi system operating range. The affect the pressure range has,when viewing pump curves, is the well pump capacity will be 20 to 25%higher at 40 psi than at 60 psi. For example,when pressure in the system falls to 40 psi the control panel will start a well pump. The pumping rate will be in the 180 to 185 gpm range at the start and decrease to around 150 gpm at the pressure in the system increases from 40 to 60 psi. The control panel will have a second low pressure setting around 35 psi. During peak water demand events that are greater than a single well pump capacity the second pump will be started when the pressure drops to the second low point pressure around 35 psi. Both well pumps operating at this pressure will have a pumping rate in the 320 to 350 gpm range(depending on final pump curve selections) which will meet the peak flow demand of 300 gpm. J:\15 8-Helbling\001-HelblingRVsik\Corresp\Letters\dh041206-MEMO.doc 7804 Industrial Park Road•PO Box 2720■ Baxter,MN 56425-2720■TEL:218.829.51 17 ■FAX:218.829.2517•WEB:www.wsn-mn.com ENGINEERING ARCHITECTURE LAND SURVEYING ENVIRONMENTAL SFRVI (- FC .,«