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PATTERSON STREET UNDERPASS - ESTIMATE OF PROBABLE CONSTRUCTION COSTS <br />5000 gpm. The hydrogeologic conditions assumed for this analysis include a Transmissivity <br />=100,000 gpd/ft and a pumping rate of 500 gpm per well. <br />The cost estimate assumes 10 wells, l6-inch diameter, installed to a depth of 100 feet. <br />Analysis is based on the assumption that the ground water presence determined during the <br />Eugene U.S. Courthouse geotechnical investigation (October 2003) might be closer to the <br />surface by 3 to 4 ft. in the winter/spring. In the absence of specific information, <br />characteristic transmissivity of gravel aquifer material was used for this estimate. <br />Geotechnical borings at this location did not fully penetrate the water bearing units <br />encountered at 10 to 13 feet. This material is described as loose gravel. The assumed aquifer <br />thickness of 45 ft. was used in the prediction of dewatering. <br />!III, ~ Additional drilling and aquifer testing at this location would significantly improve the <br />accuracy of this dewatering prediction and cost estimate. <br />~, <br />Permanent Dewatering <br />i <br />Permanent dewatering is to be accomplished by leaving two of the construction dewatering <br />I wells in place. These well pumps would be interconnected with the stormwater pumping <br />_! station standby generator for enhanced reliability. Operational cost for the permanent <br />dewatering is not included in the estimate. <br />Utility Relocation <br />Sanitary and water mains in 8th Ave. were the only utilities included in the utility relocation <br />! cost. It was assumed all the franchised utilities (e.g. gas, power, phone, etc) would be <br />- relocated by those companies, without cost to this project. <br />Existing data was not available for the size of the water main in 8th Ave. The two parallel <br />pipes were assumed to be 8" or 10" pipe for the estimate. The relocation cost includes the <br />relaying of the existing pipes that would be depressed below Patterson Street and reconnect <br />- , on the other side. <br />The sanitary system in 8th Ave. is to be terminated at Patterson Street. The cost estimate <br />assumed that the pipe west of Patterson Street would be re-layed at a flatter slope and is <br />extended approximately 170' east of the 8th Street/Ferry Street intersection. This should <br />provide adequate sewer coverage since the property north of 8th Ave. is not developed and <br />construction of Patterson Street will eliminate the building located south of 8th Avenue and <br />west of Patterson Street. <br />The sanitary system in 8th Avenue east of Patterson Street will be relayed to flow from west <br />to east, then south in the realigned Hilyard Street and connect to the existing system in <br />Broadway. Invert elevations for the system were not available for the project and should be <br />confirmed during final design. If the invert elevation for the pipe in Broadway is found to be <br />too high, an alternative approach of installing a single service for the business between <br />Hilyard Street and Patterson Street could be considered. Currently, these are the only <br />buildings in the area that contribute flow to the 8th Avenue (east of Patterson Street) sanitary <br />system. <br />PDX/PATTERSON STREET UNDERPASS TECH MEMO 062504 PAGE 3 OF 6 <br />