 King County Road Services - Stormwater Best Management Practices (BMP) sites
Project overview: We are trying to find effective, cost-efficient ways to treat stormwater in roadside ditches. This study is being conducted to test an in-line ditch BMP that, if effective, could potentially be widely used by jurisidictions trying to minimize the impacts of stormwater runoff on surface water bodies and groundwater aquifers. This study is made possible, in part, through funding from the Washington State Department of Ecology and will continue through 2011. Project location: North shoulder of S.E. 136th St. between 169th Ave. S.E. and 170th Ave. S.E. Drainage basin: Dominated by residential properties with a density of four houses per acre; the ditch drains to a catch basin across from 169th Ave. N.E. that discharges to a small tributary stream. Traffic: Moderate [average daily traffic (ADT) volume of approximately 1,521 vehicles); busy with morning and early afternoon school traffic]. BMP type: Water quality. BMP description: Compost treatment media mixed with washed gravel and wrapped in filter fabric and secured inside a rock check dam treatment cell. Compost meets Washington State Department of Transportation (WSDOT) specification for use in stormwater treatment projects. Filter fabric is Geotex 801. Three BMPs are to be evenly spaced over approximately 100 foot section of ditch. Monitoring: Stormflow and water quality samples are collected upstream and downstream from BMP. Flow composite samples are collected for total suspended solids, total kjeldahl nitrogen, nitrate-nitrite, orthophosphate phosphorus, dissolved metals, and PAH. Grab samples are collected for total petroleum hydrocarbons and fecal coliform. Equipment: - Flow measurement: Primary devise-12 inch Thel-Mar weirs placed in the ditch at the upstream and downstream monitoring locations; water level measurement and data logger: Isco bubble meters measure water level in the weirs, log data and convert water level to flow in gallons per minute.
- Water quality samples: Flow composited samples are collected using Isco 6712 autosampler receiving flow signals from the bubble meter. Grab samples are collected by hand.
- Rainfall:
Rainfall data is obtained from a permanent gage operated by the King County Hydrologic Information Center located at the King County Roads Maintenance Facility in Renton, Washington (approximately 2.5 miles west of the Southeast 136th Street BMP site). A raingage is also staged at the downstream monitoring site for real-time rainfall records.
- Housing: large electrical utility boxes staged at the up and downstream sites secure equipment.
- Power: Group 24-12 volt deep cycle glass-mat batteries with solar panel assist.
Project photos
Upstream stretch of study area, looking downstream. Upstream flow monitoring equipment is installed in catch basin. Sampling equipment is housed in metal utility box.
(Enlarged view, 193KB .jpg)
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Downstream stretch of study area prior to BMP installation, looking downstream. Downstream flow monitoring equipment is installed in cement culvert beneath driveway. Sampling equipment is housed in metal utility box.
(Enlarged view, 175KB .pdf)
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Have questions?For more information about this project, please contact: Environmental Unit
King County Roads Maintenance Section
155 Monroe Ave. N.E.
Renton, WA 98056
206-205-7107
Information from the Road Services Division's website is available to people with disabilities in alternate formats upon request by calling 206-263-6482 or 711 for the TTY relay service.  = External link
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