3505 UPLAND AVE 2020-09-08 - Laserfiche WebLink

2. EXISTING CONDITIONS SUMMARY The site covers approximately 0.62 acres. The proposed disturbance area of the existing, pre 1997 site consists of a SFR, landscaping and a gravel driveway which takes access from both roadways to the east and south. (Upland Ave. & Sound Ave.) The existing SFR and gravel driveway will be removed from the site. Therefore, not all of the proposed roof and driveway surfaces will be considered new impervious surfaces. Some proposed impervious surfaces will be placed on what is currently roof or driveway. Those surfaces will be considered replaced. The surface area of the pre 1997 PGIS totaled approximately 1,712 sf(0.04 acres).and the NPGIS totaled approximately 1,760 sf(0.04 acres). The total existing impervious surfaces within the property lines is approximately 3,472 sf(0.08 acres). The proposed improvements for this project include the removal of all existing impervious surfaces. A portion of the existing impervious surfaces will be replaced and the remainder of the existing impervious surfaces will be restored with amended soils to landscaped conditions. The overall impervious surfaces on-site between the three lots will increase by approximately 9,073 sf(0.21 acres). Approximately all of lots 1, 2 and 3 will be disturbed as needed for the clearing/grubbing and restoration of the existing site. The overall slope of the short plat runs from east to west at approximately 5 percent. The on-site slopes vary between flat and steep. The only steep slopes on-site are located near the northern property line. The existing roadways(Sound Ave. and Upland Ave.) are able to sheet flow runoff onto the project site. There is also a 12 inch diameter private concrete culvert, which drains directly into a drainage ditch located along the eastern property line. Said drainage ditch does not properly convey the runoff downstream from this location. Through field observations and conversations with neighbors it was determined that the ditch fills with water and spills onto the existing landscaping west of the ditch. The runoff then sheet flows over the landscaping and around the existing house towards the western property line and to an open ditch/stream located on the adjacent parcel to the west. This project will improve the storm drainage conveyance system currently in use by installing a series of catch basins and manhole structures. These structures will be tied directly into the existing storm drainage pipe located on-site near the southwest property corner of Lot 1 after passing through the proposed detention facility. Improvements to the conveyance system and paving along the frontage is intended to prevent upstream runoff from entering the project site as it does in the current conditions, as well as collect excess runoff generated on-site. All runoff from the proposed developed portion of this site will be collected and conveyed to the proposed detention system except for the landscaping north of the proposed SFRs which is already considered landscaping and no conversion of those surfaces are proposed. Since this project site has been cleared and graded previously the USDA Web-Soil Survey was used to determine the existing soil conditions for the three lots on the project parcel. Refer to Figure 4. The soils are mapped as Alderwood Gravelly Sandy Loam. The general site slopes, on the three lots is flat to moderate and averages approximately 5 percent. Based on the existing soil information and the setbacks of the proposed improvements from any of the property lines or critical areas there is little potential for erosion or sedimentation during construction, assuming the basic BMPs included in the SWPPP are installed and maintained properly. Refer to Figure 2 for an existing basin map. Uplands Short Plat 14-0108 June,2016 Page 4