9826 7TH AVE SE 2025-03-25 - Laserfiche WebLink

SD&C PO Box 413,White Salmon,WA 98672 Phone(206)459-5775 6. If the closed retention storage volume is exceeded, stormwater will pond within the parking lot along the western site boundary. At elevation 505.5 the ponding stormwater will enter the site discharge catch basin and be released to the downstream drainage network. Straw waddles and storm drain inlet protection(per City of Everett standard detail 210)will be installed around the storm discharge structure for sediment control and an 8"PVC downturned elbow will be installed on the outlet pipe to prevent oils/fuel from entering the existing storm system(proposed). 7. Install a sump pump in the existing 4,500-gallon containment vault and temporary discharge to the sanitary sewer. Initial proposal is to use a 20-gpm pump to slowly drawdown the closed retention volume over several hours.The benefit of drawing down the water level slowly is the oil/fuel will remain suspended at the water surface and not discharged from the site. Another benefit of using the lower pump rate is contaminated water discharged to the existing sanitary sewer will be diluted by the larger sewer flows within the public system. The pump will incur a total dynamic head loss of 15.3' from the sump of the containment vault to the rim of the temporary catch basin at the 20 gpm flowrate.A Zoeller 50 Series Sump Pump(or equivalent,per the contractor's discretion)shall be used.Pump sizing calculations are included with the IDPP. Using the Western Washington 10-year, 24-hour isopluvial in the Snohomish County Drainage Manual, the site will receive approximately 2.12 gallons per minute of stormwater in the 10-year storm(0.225"of rainfall in the 10- year, 24-hour storm onto the 21,740 SF area tributary to the 4,500-gallon containment vault). The 20-gpm sump pump will be adequate for the project site but can be adjusted if more capacity is needed(proposed). 8. All branches of the existing storm flow though API Oil/Water separators. The existing parking lot drainage lines (red)flow through a 300-gallon API OWS vault. The Pacific Pride(magenta)and Nelson Fueling(blue) islands each flow through a 1,000-gallon API OWS. Therefore,all stormwater discharged under the interim plan received water quality treatment prior to discharge from the site(done). As interim practice,Nelson is monitoring the volume of water collecting in the underground vault and disposing the water off site. During the recent rain,approximately 2,500 gallons of water which collected in the vault was disposed off-site using a subcontractor Marine Vacuum Service. If you have any questions concerning the Interim Discharge Plan or the facility,please contact SD&C at (206) 459- 5775 or Kory DeMun,Facility Coordinator with Nelson Petroleum Inc.at(425)353-9701. Sincerely, SD&C PACE Engineering r' S. Slottcv Timothy S Slotta L.G.L.H.G.L.E.G Rosanna Brown,P.E. Hydrogeologist#2175 Professional Engineer