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Element 10: Control Dewatering (2.1.10) <br /> There will be no dewatering as part of this construction project. All dewatering water from <br /> open cut excavation, tunneling, foundation work, trench, or underground vault shall be <br /> discharged into a controlled conveyance system prior to discharge to a sediment trap or <br /> sediment pond, or will be treated with dispursion across vegetated areas or by other modular <br /> methods before being discharged to or draining to an uncontrolled collection and <br /> conveyance system. Channels will be stabilized, per Element#8. Clean, non-turbid <br /> dewatering water will not be routed through a stormwater sediment pond, and will be <br /> discharged to systems tributary to the receiving waters of the State in a manner that does <br /> not cause erosion, flooding, or a violation of State water quality standards in the receiving <br /> water. Highly turbid dewatering water from soils known or suspected to be contaminated, or <br /> from use of construction equipment, will require additional monitoring and treatment as <br /> required for the specific pollutants based on the receiving waters into which the discharge is <br /> occurring. Such monitoring is the responsibility of the contractor. <br /> However, the dewatering of soils known to be free of contamination will trigger BMPs to trap <br /> sediment and reduce turbidity. At a minimum, geotextile fabric socks/bags/cells will be used to <br /> filter this material. Other BMPs to be used for sediment trapping and turbidity reduction include <br /> the following: <br /> ■ Concrete Handling (BMP C151) <br /> ■ Use of a sedimentation bag, with outfall to a ditch or swale for <br /> small volumes of localized dewatering. <br /> Alternative BMP not included in the above bulleted list are included in Appendix B as a <br /> quick reference tool for the onsite inspector in the event the BMP(s) listed above are <br /> deemed ineffective or inappropriate during construction to satisfy the requirements set forth <br /> in the General NPDES Permit (Appendix D). To avoid potential erosion and sediment <br /> control issues that may cause a violation(s) of the NPDES Construction Stormwater permit <br /> (as provided in Appendix D), the Certified Erosion and Sediment Control Lead will promptly <br /> initiate the implementation of one or more of the alternative BMPs listed in Appendix B <br /> after the first sign that existing BMPs are ineffective or failing. <br /> Table 4— Dewatering BMPs <br /> Infiltration <br /> Transport off-site in a vehicle (vacuum truck for legal disposal) <br /> Ecology-approved on-site chemical treatment or other suitable treatment technologies <br /> Sanitary or combined sewer discharge with local sewer district approval (last resort) <br /> x Use of sedimentation bag with discharge to ditch or swale (small volumes of localized <br /> dewatering) <br /> 17 <br />