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CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br />3.2.5 BMP C106: Wheel Wash <br />' Purpose <br />Wheel washes reduce the amount of sediment transported onto paved roads by motor vehicles. <br />Conditions of Use <br />When a stabilized construction entrance (see BMP C105) is not preventing sediment from being tracked <br />onto pavement. <br />Wheel washing is generally an effective BMP when installed with careful attention to topography. For <br />example, a wheel wash can be detrimental if installed at the top of a slope abutting a right-of-way where <br />the water from the dripping truck can run unimpeded into the street. <br />Pressure washing combined with an adequately sized and surfaced pad with direct drainage to a large 10 x <br />10-foot sump can be very effective. <br />Design and Installation Specifications <br />1. Applicable details are shown in Figure 3.1. A minimum of 6 inches of asphalt treated base over <br />crushed base material or 8 inches over a good subgrade is recommended to pave the wheel wash. <br />2. Use a low clearance truck to test the wheel wash before paving. Either a belly dump or lowboy <br />will work well to test clearance. <br />3. Keep the water level from 12 to 14 inches deep to avoid damage to truck hubs and filling the <br />truck tongues with water. <br />4. Midpoint spray nozzles are only needed in extremely muddy conditions. <br />5. Wheel wash systems should be designed with a small grade change, 6 to 12 inches for a 10-foot- <br />wide pond, to allow sediment to flow to the low side of pond to help prevent re -suspension of <br />sediment. A drainpipe with a 2- to 3-foot riser should be installed on the low side of the pond to <br />allow for easy cleaning and refilling. Polymers may be used to promote coagulation and <br />flocculation in a closed -loop system. <br />Maintenance Standards <br />1. The wheel wash should start out the day with fresh water. <br />2. The washwater should be changed a minimum of once per day. On large earthwork jobs where <br />more than 10 to 20 trucks per hour are expected, the washwater will need to be changed more <br />often. <br />3. Wheel wash or tire bath wastewater shall be controlled by pumping back on site to an approved <br />infiltration facility, or otherwise must be prevented from discharging into systems tributary to <br />state surface waters. Options include discharge to the sanitary sewer, or discharge to an approved <br />offsite treatment system. For discharges to the sanitary sewer, permits must be obtained from the <br />City's Industrial Pretreatment Program at (425), 257-8874. <br />Volume 11 — Construction Stormwater Pollution Prevention <br />3-6 <br />