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areas drain to the ditch located next to Highway 10. There is a small depression in the east end of <br /> 0 the park which will detain some of the runoff prior to discharging into the ditch and the gas station <br /> has a small detention pond which drains to the ditch. <br /> Hydrologic Model <br /> Based on Figure 1,the existing hydrologic system was modeled. The method used was HydroCAD <br /> which reproduces results of the SCS TR-20 hydrologic model. A SCS Type II storm distribution <br /> with Antecedent Moisture Condition(AMC)2 was used for all storm events. A summary of the <br /> results for key areas is shown in Table 1. Detailed computer results are in Appendix A. <br /> Proposed Systems <br /> Options Studied. <br /> • <br /> A preliminary investigations of eight options were reviewed. Below is a detailed description of <br /> each options. Table 2 compares the cost of the eight options. After the city determines which <br /> option(s) are feasible or desirable, additional review of utility conflicts and soil borings may need to <br /> be undertaken. The purpose of this report is to outline the alternatives available to the city. <br /> Option 1 - Sump Manhole-No Surge Manhole. 410 ti ' WA'VWr 414 W ,114y 410 LI <br /> Create sump catch basins at each inlet to the pond which drain to the pond. IMArL4 1,0 1.114 1-0 <br /> Excavate the existing pond to native material. 144‘ (&Vv(,(, . <br /> • Fill the pond with granular material to elevation 904.6(elevation of the outlet in the highway <br /> ditch) <br /> Connect a 12-CMP standpipe to the highway storm sewer to discharge the pond into the <br /> existing system. <br /> a <br /> This eliminates standing water. However, it does not eliminate the detention function of the area; <br /> therefore,the existing"hole" would remain. A sump inlet would be provided at the current <br /> discharge point of the two storm sewer system to remove larger sediment particles. The detention <br /> pond would be modified to treat the runoff by use of a CMP standpipe which should compensate <br /> for lost water quality treatment of the site. The pond bottom would be set at elevation 904.6 which <br /> is the invert of the outlet pipe in the highway ditch. <br /> Project Cost. $20,000 - <br /> Benefits: <br /> Cheapest option <br /> Easiest to construct <br /> Non-Benefits <br /> Bottom of pond is lower than existing normal water elevation <br /> Higher maintenance since sump manholes would need to be cleaned annually. <br /> Does not get rid of the existing hole for the pond. <br /> Will have short term ponding during rainfall events. <br /> 0 Option 2. Sump Manhole- With Surge Manhole <br />