10200 19TH AVE SE COSTCO FUEL STATION 2022-05-23

2.1.10 Element 10: Control Dewatering • Discharge clean, non-turbid de-watering water, such as well-point groundwater, to systems tributary to, or directly into surface waters of the state, as specified in Element# 8, provided the de-watering flow does not cause erosion or flooding of receiving waters or interfere with the operation of the system. Do not route clean dewatering water through stormwater sediment ponds. Note that"surface waters of the state" may exist on a construction site as well as off site; for example, a creek running through a site. • Highly turbid or contaminated dewatering water shall be handled separately from stormwater. • Clean, non-turbid dewatering water, such as well-point ground water, can be discharged to systems tributary to, or directly into surface waters of the state, provided the dewatering flow does not cause erosion or flooding of receiving waters. Clean dewatering water should not be routed through stormwater sediment ponds. • Other dewatering disposal options may include: o Transport off site in a vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state waters. o Infiltration. o Ecology-approved on-site chemical treatment or other suitable treatment technologies. o Sanitary sewer discharge with local sewer district approval, if there is no other option. o Use of a sedimentation bag with outfall to a ditch or swale for small volumes of localized dewatering. The project site has a low groundwater elevation, and encountering groundwater is unlikely. However, dewatering activities may occur during the installation of on-site stormwater conveyance systems and/or excavation activities. Installation Schedules: Dewatering controls will be installed prior to any significant excavation activities. Inspection and Maintenance plan: TBD Responsible Staff: TBD Page 116