3301 SEAWAY BLVD WHOLE SITE 2025-10-30

2. Pond berm embankments shall be constructed by excavating a"key"equal to 50 percent of the berm embankment cross-sectional height and width(except on till soils where the"key" minimum depth can be reduced to 1 foot of excavation into the till). 3. Pond berm etnbankinent cores shall be constructed of compacted soil(a minimum of 95..percent of the nraxhnutn thy density,standard perictor_method per American Society for Testing and Materials[AS7 M]Dl 557)placed in 6-inch lifts,with the following soil characteristics per the USDA's textural triangle: a minimum of 30 percent clay,a maximum of 60 percent sand, a maximum of 60 percent silt,with nominal gravel and cobble content or as recommended by a geotechnical engineer. The core shall be adequate to make the embankment impervious. 4. Exposed earth on the pond side slopes and berms shall be sodded or seeded with appropriate seed mixture(see Volume II,Erosion and Sedimentation Control BMPs). Establishment ofprotective vegetative cover shall be ensured with appropriate surface protection BMPs and reseeded as necessary. 5. Where maintenance access is provided along the top of the berm,the minimum width of the top of the berm shall be 15 feet. 6. Pond berm embankments greater than 6 feet in height shall require a design by a qualified professional engineer licensed in the State of Washington. Berm embankment width shall vary as recommended by the professional engineer. 7. Embankments less than 6 feet in height shall have a minimum 6-foot top width unless otherwise recommended by a qualified professional engineer licensed in the State of Washington. 8. Embankments adjacent to a stream or other body of water shall be sufficiently protected with riprap or bioengineering methods to prevent erosion of the pond embankment Othercontrol measures may be necessary to protect the embankment. 9. Anti-seepage filter-drain diaphragms must be placed on outflow pipes in bean embankments impounding water with depths greater than 8 feet at the design water surface. See Dam Safety Guidelines,Part 1V,Section 3.3.B on pages 3-27 to 3-30. An electronic version of the Dam Safety Guidelines is available in PDF format at: <www.ecy.wa.govlprograms/wrldams/dss.html>. 2.3.2 Side Slopes I. Interior earthen side slopes up to the emergency overflow water surface shall not be steeper than 3H:1 V. 2. Exterior side slopes for grassed embankments shall be at least 3:1 to facilitate mowing. 3. Exterior side slopes shall not be steeper than 2H:1 V unless analyzed for stability by a geotechnical engineer. 4. Pond walls may be vertical retaining walls provided the following: a. the walls are designed by a geotechnical engineer or licensed civil engineer with structural expertise; b. a fence is provided along the top of the wall; c. an access ramp to the bottom of the pond is provided. Volume ill—Row Control and Treatment 2-4 1