The URL can be used to link to this page

REVIEWED RESUB1 BLD2023-0799+GEO REPORT+3.5.2024_9.05.33_AM+4103115March 1, 2024 NELSON GEOTECHNICAL ASSOCIATES. INC. RESUB Mar 05 2024 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT Ryan and Sydney Cochran Via Email: ryanrcochran@gmail.com ................................................ REVIEWED BY CITY OF EDMONDS BUILDING DEPARTMENT' Geotechnical Comment Response Letter Cochran Residence Development Supplemental Infiltration 8475 Frederick Place Edmonds, Washington NGA File No. 10218623 Dear Mr. and Mrs. Cochran: 17311-135' Ave. N.E. Suite A-500 Woodinville, WA 98072 (425)486-1669 www.nelsongeotech.com This letter presents our geotechnical engineering comment response regarding the proposed residence development project located at 8475 Frederick Place in Edmonds, Washington. INTRODUCTION We understand that the proposed development for the property will include the construction of a new single-family residence and pool. We previously prepared a stormwater infiltration evaluation for the property for the previous owner dated February 2, 2018 and have since provided an updated memo dated February 21, 2023. We understand that the City of Edmonds has requested additional information regarding the geotechnical aspects of this project in a letter dated August 11, 2023. For our use in preparing this plan review letter, we have been provided with the following documents: • Civil plan set titled "Cochran Residence," dated February 23, 2024, prepared by CG Engineering. In the following section, we summarize the City's comments and our responses. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington NGA File No. 10218623 March 1, 2024 Page 2 CITY OF EDMONDS STORMWATER REVIEW COMMENTS AND OUR RESPONSES Comment 11: Please provide a geotechnical memo addressing the retaining wall drainage and update the drainage plans accordingly. Our Response 11: Based on review of the plans it appears that all site retaining walls will have wall footing drains that will discharge into the proposed on -site infiltration system and on -site drywells. The residence retaining walls will be backed with a Miradrain mat tightlined to the footing drain and backfilled with free -draining backfill. The other site retaining walls will be backfilled within free -draining backfill surrounding the foundation footing drain. Comment 15: Edmonds GIS shows landslide and erosion hazards on site. Please provide a geotechnical memo supporting the placement of the proposed infiltration trench, building, pool, and other hardscapes in relation to the steep slopes on site. Additionally, please provide the Geotech with an updated proposed development footprint as the previous geotechnical memo shows that the Geotech did not have the updated proposed development footprint. Our Response 15: Please see the attached updated Site Plan in Figure 1 showing the most recent residence location footprint. Comment 24: The geotechnical report was completed using the 2014 DOE SWMMWW. Please submit a memo from Geotech that states that it is in compliance with the 2019 DOE SWMMWW. Our Response 24: In our opinion, our previous stormwater infiltration testing consisting of the small-scale PIT test was performed in compliance with the updated 2019 DOE SWMMWW. Comment 25: Please provide a memo from Geotech providing all of the information listed in Checklist 2, Lines 111 and Our Response 25: An itemized list of the items within Lines 111 and 112 of Checklist 2 have been included below. Our response to each item is followed in bold. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington LINE 111 List: Soils Report includes the following: • Topography within 500 feet of the proposed facility NGA File No. 10218623 March 1, 2024 Page 3 - Topography within 500 feet of the subject development generally slopes gently down toward the property from the east, south and west and gently away and down from the property to the north. Please see attached Figure 4 showing topographic contours within a 500 foot radius of the proposed development. • Depth to hydraulic restriction layer - A hydraulic restrictive layer was not encountered in our previous explorations. Please review attached exploration logs in Figures 2 and 3. • Detailed soil logs (see below) - Please review attached exploration logs in Figures 2 and 3. • Visual grain size analysis - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Grain -size distribution (required if using the grain size analysis method to estimate infiltration rates) - This is not applicable as infiltration rates were based on on -site infiltration testing. • Textural class - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Percent clay content (include type of clay, if known) - Clay soils were not encountered within our explorations so this is not applicable. • Cation exchange capacity - Cation exchange capacity testing was not performed on soil samples as the proposed infiltration facilities are not being utilized for groundwater quality treatment. • Color/ mottling - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Variations and nature of stratification - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington LINE 112 List: NGA File No. 10218623 March 1, 2024 Page 4 Detailed logs for each test pit or hole were prepared, along with a map showing the locations of the test pits or holes. Logs include: • Depth of log - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Soil description - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Depth to groundwater - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Evidence of seasonal high groundwater elevation - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Existing ground surface elevation - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Proposed basin bottom elevation - Based on review of the most recent civil plans, it appears that the base of the proposed infiltration trench is at elevation 38.30 feet. • Presence of stratification that may impact the infiltration design - We did not encounter any stratification that may impact the infiltration design within our soil explorations. CLOSURE We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork activities comply with contract plans and specifications. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington NGA File No. 10218623 March 1, 2024 Page 5 We appreciate the opportunity to provide service to you on this project. Please contact us if you have any questions regarding this letter or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Lee S. Bellah, LG Senior Geologist 3.01.2024 Khaled M. Shawish, PE Principal LSB:KMS:dy Four Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. Site Plan LEGEND — • — Property line INF-1 Number and approximate location I of previous infiltration test pit TP-1 0 30 60 Number and approximate location of previous test pit HA-1 HA-101 Scale: finch - 30 feet Number and approximate _�_ Number and approximate location of previous hand auger I location of recent hand auger Reference: Site Plan based the civil plan set titled "Cochran Residence," dated February 23, 2024, prepared by CG Engineering Project Number Cochran Residence nELson GEOTECHnICAL No. Date Revision By cK 102181323 Development Infiltration , ASSOCIATES, inn 1 2/29/24 Original LSB LSB Figure 1 Site Plan / W. di -ill. Moe Wenatchee."lce , 7311-, 95th Ave. NF, A-500 105 Palouse St. Woodinville, WA 98072 Wenatchee, WA 98801 songeotech-com (425) 486-1669 / Fax: 481-2510 (509) 665-7696 / Fax: 665-7692 LOG OF EXPLORATION DEPTH (FEET) TEST PIT ONE (ELEV:46 FEET) 0.0 - 0.1 0.1 - 1.5 1.5 - 2.3 2.3 - 7.1 7.1 - 8.0 8.0 - 9.5 TEST PIT TWO (ELEV:57 FEET) 0.0 - 0.4 0.4 - 1.7 1.7 - 3.8 3.8 - 9.0 HAND AUGER ONE (ELEV:53 FEET) 0.0 - 0.3 0.3 - 2.0 2.0 - 3.6 3.6 - 5.0 LSB:KMS USC SOIL DESCRIPTION TOPSOIL SM BROWN SILTY FINE TO MEDIUM SAND WITH ROOTS AND TRACE IRON OXIDATION STAINING (LOOSE, DRY) SP-SM LIGHT YELLOW -TAN FINE TO COARSE SAND WITH SILT (MEDIUM DENSE, DRY -MOIST) SP-SM LIGHT GRAY -TAN FINE TO MEDIUM SAND WITH SILT AND TRACE FINE GRAVEL AND IRON OXIDATION STAINING (DENSE, MOIST) SM BROWN SILTY FINE TO MEDIUM SAND WITH TRACE COARSE SAND AND IRON OXIDATION STAINING (MEDIUM DENSE, MOIST) SM GRAY SILTY FINE TO COARSE SAND WITH IRON OXIDATION STAINING (DENSE, WET) SAMPLES WERE COLLECTED AT 3.5, 4.5, 7.3, 7.5, AND 8.2 FEET MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 8.7 FEET TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 9.5 FEET ON 1/17/18 LIGHT GRAY SILT AND FINE TO MEDIUM SAND WITH ROOTS AND FINE GRAVEL (LOOSE, DRY -MOIST) (FILL) SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) SAMPLES WERE COLLECTED AT 1.5, 3.0, AND 9.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 9.0 FEET ON 1/17/18 LIGHT GRAY SILT AND FINE TO MEDIUM SAND WITH ROOTS AND ORGANIC AND ANTHROPOGENIC DEBRIS (LOOSE, DRY) (FILL) SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) NO SAMPLES WERE COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED HAND AUGER WAS TERMINATED AT 5.0 FEET ON 1/17/18 NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 102181323 FIGURE 2 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION INFILTRATION PIT ONE (ELEV:46 FEET) 0.0 - 0.9 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST) (TOPSOIL) 0.9-2.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE - MEDIUM DENSE, MOIST) 2.0 - 5.0 SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SAMPLES WERE COLLECTED AT 0.5 AND 2.5 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED INFILTRATION TEST PIT WAS TERMINATED AT 5.0 AT DEPTH ON 1/17/2018 HAND AUGER 101 (ELEV:48 FEET) 0.0 - 1.0 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST) (TOPSOIL) 1.0 - 2.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) 2.0 - 9.0 SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER WAS COMPLETED AT 9.0 FEET ON 2/8/23 HAND AUGER 102 (ELEV:48 FEET) 0.0 - 1.0 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST) (TOPSOIL) 1.0 - 3.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) 3.0 - 9.0 SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER WAS COMPLETED AT 9.0 FEET ON 2/8/23 LSB:KMS NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 102181323 FIGURE 3 0� �(D en Wm D iv o� m z= o � m C) a` N I/1 N Q m -1_ m CD =3 Z q� Z CD0 (n �� N 3 O CD N �$ Z (/1 -� -.m CD 1I C C (D Q4,� N � � 00 � W W O / W o rn Ate■ v N 0 / O O. V) )0 � � s S_ Q �■ o v m s l A Pf a m / 0 r: m n c 'o cn -6 w J ' '7 3. CD < • � $05 � 6058 � 8 I � O 0 CD ill, US m 3 m' 8£b8 o � a� S 8 I o a � Lb s z �s 9 � o v 0 0 `� ■ N n / Cn oX. �c 3 Zt 8 CD ^' n i fll N ■ 8 O _ O ZO£8 n 8 I I Z8 N N O _ m p o "1\ ~� 1 O z Project Number nELson GEOTEMICAL No. Date Revision By CK 1 Cochran Residence 10218B23 Development Infiltration ' ASSOCIATES, inn 1 2/29/24 Original use Ls6 Nearby Vicinity Topographic Woo „,.e We.i Figure 4 ,�31,-,35th Ave. NEB A-500 105 Pal 5t. Site Plan wnelson9eotech.com (425 Woodinville 8fi i1669IF z948125,0 (509 6657696;F z96657692