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20141020122717796.pdf�l I �5 lir M . `00 '61(10) 1,1.\( ' i-iti1 -15 til September 19, 2014 Mr. George Olson c/o Roger Olin PO Box 3216 Everett, Washington 98213 ( V" ") "'a r"..� ,i , 8III'..B)i')r0 d`i i Construction Monitoring Summary Letter Olson Residence Edmonds, Wasl ington NGA File No. 8342C13 Dear Mr. Olson, 5'h ln(luwuv I ;111c. a V '.� Cqw h65-169(' IAN +':N) Wo -'i:('92' We were requested by your builder Roger Olin to prepare this summary letter for your residence project located at 15500 — 75th Place West in Edmonds, Washington. Introduction We were retained to provide part-time monitoring and consultation services during the earthwork phase of construction per the Special Inspections and Testing Agreement required by the City of Edmonds (Permit No. BLD20120858). Our earthwork monitoring activities at the project took place on a part-time basis from October 17, 2013 through June 24, 2014 and included observing pier installation, footing drain installation, and erosion control measures. Our observations and conclusions were documented in Field Reports 1 through 23, all of which have been submitted to you. We previously prepared a geotechnical engineering report for the property titled "Revised Geotechnical Engineering Report — Olson Residence — 15500-75`" Place West. — Edmonds, Washington," dated July 15, 2011. We also prepared a plan review letter for the project dated April 3, 2013. Construction Monitoring Summary Letter Olson Residence Edmonds, Washington Site Observations NGA File No. 8342C13 September 19, 2014 Page 2 We monitored drilled pier installation activities on October 28, 2013 through October 30, 2013 as documented in Field Reports #3 through 6. We observed the drilling of 23, 22 -inch diameter holes advanced to depths of approximately 26 feet below the ground surface throughout the entire residence foundation area. The holes were drilled with a large drilling auger and the soil exposed in the cuttings mostly consisted of light brown, fine to medium sand grading to dark gray clay. Minor caving was encountered in some of the holes and some of the holes required casing to remain open. After rebar cages were lowered into the drilled holes, the holes were backfilled with structural concrete to planned elevations. We also observed the installation of 18, 2 -inch pin piles for the planned deck posts on the western side of the residence. The pin piles consisted of Schedule 80 galvanized steel piles and were driven between 13 to 19 feet below the ground surface. The pin piles were driven with a 140-1b hammer to a refusal criteria of less than one inch of movement during 60 seconds of continuous driving. We observed the stormwater overflow pipe that was installed down the steep slope on the northern side of the property. The pipe consisted of an 8 -inch diameter HDPE pipe and was anchored to the slope using a clamp and cable system. The clamps were secured to the slope using 5 -foot long, 3 -inch diameter galvanized bars. We observed some of the backfill for the on-site utilities including storm and water lines and detention pipes and manholes. Some of the material consisted of on-site soil and other areas were backfilled with crushed rock. The areas where on-site material was used was generally over -optimum moisture when it was placed and was pumping. We tested the backfill with a nuclear densometer and the test results did not meet 95% compaction of ASTM D1557. We recommended to the contractor that the unsuitable soils be removed and replaced with drier soil, or re-evaluated at a later time. We returned to the site roughly two months later and retested the failed areas. Some of the areas met compaction, but an area on the northern side of the house was still over optimum. We discussed the slight potential for future settlement of this material. We were informed by Roger Olin that no structures were planned for this area and that they were aware of the risks. Construction Monitoring Summary Letter NGA File No. 8342C13 Olson Residence September 19, 2014 Edmonds, Washington Page 3 We also observed that footing drains were installed along the western, uphill side of the residence. The drains consisted of 4 -inch perforated pipes. We recommended that the drains be surrounded with washed rock and covered with filter fabric. The contractor agreed. The contractor informed us that the roof downspouts would not be connected to the footing drains, as we recommended in our geotechnical report. We visited the site on September 10, 2014 to observe the final landscaping preparation. We observed that the site had been graded and that some vegetation planted throughout the backyard and side yard. We did observe areas of exposed soils. We recommend that all remaining exposed areas be covered with landscaping plants and/or hydroseed to reduce the potential for soil erosion during the wet season. These areas should be closely monitored and repaired as needed. It is our opinion that the erosion control methods incorporated into the landscape design appear to be adequate and should help prevent surface water from reaching the steep slope once these systems are fully established. We also observed the steep slope and did not observe significant signs of instability. We should note; however, that the slope below the residence did experience a small landslide two to three years ago. Although the area that was affected by the slide is relatively far away from the new residence and should not have an impact on the recent improvements, during extreme weather, this area may experience additional movement. We recommend that this area be monitored from time to time, especially during heavy rainfall. We should be contacted should signs of renewed earth movement be observed. Conclusion Based on our part-time observations, it is our opinion that the geotechnical earthwork activities at this site, including residential foundation subgrade, pier installation, subsurface drainage, and erosion control methods were completed in general accordance with our recommendations, contract plans, and specifications. The steep slope should be closely monitored for any signs of distress. If any distress is observed, we should be contacted immediately to evaluate the conditions and provide recommendations for slope repairs. Also, long-term maintenance of the drains and landscaped areas is important to prevent water from flowing over the slope and creating instability concerns. All other recommendations and precautions presented in our report and memo regarding maintaining slope stability should be strictly followed. We recommend that our report and memo along with this letter be passed on to future home owners if the house is sold. Construction Monitoring Summary Letter Olson Residence Edmonds, Washington NGA File No. 8342C13 September 19, 2014 Page 4 We appreciate the opportunity to be of service to you on this project. We consider our services for this project to be complete, unless you specifically contact us for additional work. If you have any questions regarding this letter or require further information, please call. Sincerely, •, , Bala Dodoye-Alali Project Geologist Exp. July 28, 2015 Khaled M. Shawish, PE Principal BD:KMS:cja ODIUMC- wwhw-