RES 88069 - Laserfiche WebLink

BISSELL & KARN. INC. Job ~8704139.20 January 4, 1988 Page 2 The recommended criteria which requires 25 psi at the first floor of all houses under maximum day conditions with a 10 gpm demand was developed to provide adequate supply pressure for average irrigation systems. We reviewed manufacturer's literature for various domestic sprinkler heads and found that most sprinkler heads operate properly with a minimum pressure of 20 psi at their bases. Allowing 5 psi for pressure losses in the irrigation system piping, and assuming that the irrigation system connects to the service at the house, the 25 psi requirement would leave enough pressure at the heads of most irrigation systems for themto operate properly. Finally, most broad-coverage heads distribute between two and four gallons per minute. At 10 gpm, three to five such heads could operate simultaneously. PROJECTED IMPACTS Of the homes which are currently slated for transfer to the lower zone (along Foothill Road), we have estimated that water service to about 8 homes currently does not meet the pressure criteria. That includes three which have booster pumps. After the transfer, we estimate that, at most, 22 homes will not meet the pressure criteria. All other homes in the area will experience pressure drops ranging from about 15 to 20 psi, depending on demands, and their water service will meet the requirements of the pressure criteria. If the City adopts the recommended criteria, based on the stated assumptions, it will need to mitigate the low pressure problems at these approximately 22 homes. Additionally, temporary complaints can be expected from residents in the area whose service connections or irrigation systems are currently being throttled to compensate for high pressure until adjusted. It should be noted that this estimate assumes average irrigation systems with the total flow in the largest branch plus interior usage not more than 10 gpm. If, under the stated conditions, flow exceeds 10 gpm, pressure losses may increase significantly. For example, a 25% greater flow, or 12.5 gpm, may cause about 50% greater pressure losses. In such a case, sprinkler performance could become unsatisfactory unless mitigated. Testing, as discussed in the section on Implementation, is the only way to determine the residences, if any, where this could be a problem. MITIGATION MEASURES For the 22 or so residences in the area where service pressure will be less than the recommended criteria, improvements will need to be made. These improvements may consist of upgrading service lines, upsizing meters, modifying irrigation systems, or installation of booster pumps. Homes with throttled service lines will need adjustments to, or removal of pressure reducing valves. Included in the 22 homes are two of the three homes which currently have booster pumps and whose systems will need improvements. JND.2.42