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c. If the 100-year peak discharge is greater than 0.5 cfs for either existing or developed conditions, or if a significant adverse impact to downgradient properties or drainage systems is likely, then a conveyance system must be provided to con- vey the concentrated runoff across the downstream properties to an acceptable dis- charge point(i.e., an enclosed drainage system or open drainage feature where concentrated runoff can be discharged without significant adverse impact). Stormwater control or treatment structures should not be located within the expected 25- yearwater level elevations for salmonid-bearing waters. Such areas may provide off- channel habitat for juvenile salmonids and salmonid fry. Designs for outfall systems to protect against adverse impacts from concentrated runoff are included in Chapter V-4 - General Requirements for Stormwater Facilities (p.795). 1-2.5.5 Minimum Requirement #5: On-site Stormwater Management Projects shall employ On-site Stormwater Management BMPs in accordance with the following projects thresholds,standards, and lists to infiltrate, disperse,and retain stormwater runoff on-site to the extent feasible without causing flooding or erosion impacts. Projects qualifying as flow control exempt in accordance with 1-2.5.7 Minimum Requirement#7: Flow Control (p.64) do not have to achieve the LID performance standard, nor consider bioretention, rain gardens, permeable pavement,and full dispersion if using List#1 or List#2. However,those projects must implement BMP T5.13: Post-Construction Soil Quality and Depth (p.911); BMP T5.10A: Down- spout Full Infiltration (p.905) or BMP T5.10B: Downspout Dispersion Systems (p.905) or BMP T5.10C: Perforated Stub-out Connections (p.905); and BMP T5.11: Concentrated Flow Dispersion (p.905) or BMP T5.12: Sheet Flow Dispersion (p.908), if feasible. Project Thresholds Projects triggering only Minimum Requirements #1 through #5 shall either: a. Use On-site Stormwater Management BMPs from List#1 for all surfaces within each type of surface in List#1; or b. Demonstrate compliance with the LID Performance Standard. Projects select- ing this option cannot use Rai ardens.They may choose to use Biore- tention BMPs as described in Chapter V-7 -Infiltration and Bioretention Cannot evaluate the feasibility of LID BMP's as Soils information has ndard. not been provided to this consultant. P lJJct,LA LI I JJGJ II IU lviii IIIIlUIII IWGLIUIICIIICIILJ rr I LI II Vl1yII rr,a, IIILI I.WC t the require- ments in Table 1-2.5.1 On-Site Stormwater Management Requirements for Projects Triggering Minimum Requirements#1 -#9 (p.56). 2014 Stormwater Management Manual for Western Washington Volume I- Chapter 2 -Page 55