1710 W MARINE VIEW DR 2024-01-03

On large projects that phase the clearing of the site, areas retained with native vegetation may be used as a temporary vegetative filtration area. Design Criteria Find land adjacent to the project site that has a vegetated field, preferably a farm field, or wooded area. . If the site does not contain enough vegetated field area consider obtaining permission from adjacent landowners (especially for farm fields). . Install a pump and downstream distribution manifold depending on the project size. Generally, the main distribution line should reach 100 to 200-feet long (large projects, or projects on tight soil, will require systems that reach several thousand feet long with numerous branch lines off of the main distribution line). . The manifold should have several valves, allowing for control over the distribution area in the field. . Install several branches of 4-inch diameter schedule 20 polyvinyl chloride (PVC), swaged -fit common septic tight -lined sewer line, or 6-inch diameter fire hose, which can convey the tur- bid water out to various sections of the field. See Figure 11-3.25: Manifold and Branches in a Wooded, Vegetated Spray Field. Determine the branch length based on the field area geography and number of branches. Typ- ically, branches stretch from 200-feet to several thousand feet. Lay the branches on contour with the slope. On uneven ground, sprinklers perform well. Space sprinkler heads so that spray patterns do not overlap. On relatively even surfaces, a level spreader using 4-inch perforated pipe may be used as an alternative option to the sprinkler head setup. Install drain pipe at the highest point on the field and at various lower elevations to ensure full coverage of the filtration area. Place the pipe with the holes up to allow for gentle weeping evenly out all holes. Leveling the pipe by staking and using sandbags may be required. To prevent over saturating of the vegetative filtration area, rotate the use of branches or spray heads. Repeat as needed based on monitoring the spray field. Table II-3.13: Flowpath Guidelines for Vegetative Filtration Average Slope Average Area % Slope Estimated Flowpath Length (ft) 1.5H :1 V 67% 250 2H :1 V 50% 200 4H :1 V 25% 150 6H:1 V 16.7% 115 10H:1V 10% 100 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 381