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; <br /> CE <br /> T <br /> CONDOR EARTH TECHNOLOGIES INC. <br /> 188 Frank West Circle <br /> Suite <br /> SStockton, CA 952015 <br /> September 19, 2002 <br /> (209) 234-0518 <br /> FAX (209) 234-0538 <br /> Debra Keeland <br /> Plant Engineer <br /> Granite Construction Company <br /> 30909 S. Tracy Boulevard <br /> Tracy, CA 95376 <br /> Subject: Rose Excavation—Off-Site Drainage Study <br /> E Condor Project No. 0104L <br /> r <br /> Dear Ms. Keeland: <br /> As per your request, Condor Earth Technologies, Inc. (Condor) has delineated the off-site watershed <br /> contributing runoff to the proposed Tracy Expansion - Rose Excavation (Excavation) and estimated its <br /> corresponding runoff. For additional information relating to the Excavation,please refer to the drawings <br /> sheets 1 through 6 prepared by Condor, which were issued for permitting July 7, 2002. It is our <br /> understanding that this watershed discharges to the Excavation through three culverts under Interstate <br /> 0 I-580 . We have estimated flow rates from the off-site watershed at the upstream end of these 1-580 <br /> culverts. <br /> The sub-basins comprising the off-site watershed, shown on accompanying.Figure 1, were delineated <br /> based upon the topography shown on the Tracy USGS quadrangles, dated 1954 and photo revised in <br /> 1981. The Army Corp of Engineer's computer model HEC-1 was utilized to estimate peak flows from a <br /> 100-year, 24-hour storm event discharging runoff from the sub-basins depicted on Figure 1. Hydrologic <br /> data utilized by this model includes regional precipitation depth-duration data, Soil Conservation Service <br /> (SCS) runoff curve numbers (CN), watershed areas, time of concentrations, and watershed storage <br /> coefficients. Precipitation depth-duration data and CN values were taken from the County of San Joaquin <br /> properties used for CN determination <br /> hydrologic soil ro <br /> Hydrology Manual dated September 1997. Thep <br /> were based on the SCS's Soil Survey of San Joaquin County, California, 1992. The contributing <br /> watershed consists of primarily grass/range land (fair condition assumed) and lies in the hills southwest <br /> of 1-580 and of the Excavation. Table 1, enclosed, depicts the calculations and results of the .CN <br /> weighting for the sub-basins Table 2, also enclosed, depicts the calculations and results for the sub- <br /> basins' time of concentration. <br /> I t <br /> I k <br /> t <br /> ENVIRONMENTAL GEOLOGICAL ENGINEERING GEOTECHNICAL <br /> http://www.coridorearth.com <br />