2207 GIBSON PL 2022-10-28 - Laserfiche WebLink

5. SOURCE CONTROL This project proposes to construct a new garage on this parcel with driveway additions/improvements to serve the new building. Per Volume 1 of the 2019 SWMMWW (DOE), residential development does not require source control. 6. PRESERVATION OF NATURAL DRAINAGE SYSTEM The runoff from the impervious improvements will be collected and tight lined directly to the toe of the bluff to the north within the BNSF railroad R/W. This is based on the City of Everett Staff decision to prohibit infiltration of impervious surfaces on this site due to erosion concerns regarding the proximity to the bluff. This will slightly change the existing conditions of the site but the outfall from the proposed system will be within 100-feet of Puget Sound. . �� -'oi-PAQ,»e� RepccTi'' cio..t-�C, rtS 20t(, �4----P perkiv 7. ON-SITE STORMWATER MANAGEMENT ® ' ' �' The on-site soils were found to be Esperance sands, with the water table not encountered at a depth of 31.5 feet below grade and an infiltration rate of 4.5 in/hr. It has been determined that infiltration is not feasible due to the presence of the existing steep slopes/bluff along the north side of this site. Therefore, a collection/conveyance system 1 has been installed under the short plat to the west which was sized to accommodate up to 710.97 cres of impervious. As of the date of this report, there is a total of 0.28 ac impervious on the parcel to the west, 0.06 ac of driveway southwest of this parcel connecting to Gibson PI and 0.14 ac of impervious on this parcel. This totals 0.48 acres of existing impervious surfaces collected and tributary to the drainage system piping the flows north over the bluff. This project is proposing to add an impervious area of 0.06 acres. This increases the total impervious surface area collected by the conveyance system to 0.54 ac, leaving -of impervious runoff capacity in the system for any future development on the existing two lots to the south and west of this parcel. Finally, any area of the site not proposed to be covered with impervious surfaces but graded or compacted will be treated to meet the criteria for DOE BMP T.5.13. Please refer to the engineering plans for the locations of the soil amendments and additional details. rce-� -I-0 4kt e,6� (02 I ! G ; I.oso ,�Qa M' S4ort i r s c `port`� _ 12, /27 4: lc_ C * (i/0)07? Cx1s4;,t 0 .4-- 3,2 97 ctctd ) 7�•-7 c_ � ' Sup 1-1- UJ )1oorLk_ + : r-\v outly 21930sFpO.G4A c,, 1-3C n,t s r cP P C 22,D , G t S�vt 1 ��Qx-- 5c-0 r wow -- —. z3 SS`' s f. 9 1- n 12s .,>i tAll.'Pt'cofutv/-)5-1- ‘,‘,t-(,---\ In_u-t iptsrL cuCL' -(,. (,;.-1 ), . Langus Garage 15-0403-L March,2022 Page 9