10822 EVERGREEN WAY 2016-11-07 - Laserfiche WebLink

PART I The Offsite Drainage Analysis TASK i. Study Area Description This project will add approximately 1.9 acres of graveled temporary storage yards with no buildings and with less than 5000 sq ft of paving. Only the 2 20'x20' asphalt pads for driveway entrance are required and shown on the DHA construction plan. No water or sewer services are called for on this construction plan. The site was originally forested and some ponding in the winter although the soils letter(see page 3c below) states that the on-site soils are not of wetlands soil types. Subsequently the site has been cleared, surrounded with at least a double stack of ecology blocks on the south and westerly sides and filled with imparted soil to approximately 4' high, 4' being the maximum. Three important isssues as noted below are addressed with the following construction changes and the SEPA requirements have been met with the other changes noted below: 1 The issue of too high block walls: Stacks of ecology blocks have been reduced to 2 blocks high on the east side of the exiwting duplex - see DHA drawing #1 of 1 and general note #1. 2 The issue of rerouting the subsurface drain going along the west and north property line bordering the residential area from the County area. The outlet has been rerouted to empty into the existing drainage swale at the southwest comer of site as shown on DHA Plan #1 of 1. 3 The issue of no outlet for the duplex lot which is bordered on the south and east with eco-blocks. Three outlets of 4" PVC are shown on the DHA plan to outlet under the block wall to relieve any overflow to the property to the south of site. 4 The issue of controlling onsite storm water_ The DHA plan provides for a 51' x 30' dry R/D pond to detain the 2, 10 and the f100 year-24 hr storm. The maximum storm flojw of 0.95 cfs will be reduced to 0.44 cfs. 5 The issue of spreading out the onsite storm flows to approximate the existing condition: A 9 pipe manifold outlet of 4" PVC pipes is shown on the DHA Drawing, 6 The DHA plan has been designed to provide erosion control during constrcution with silt fences, the existing graveled driveways and dthe 2