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17415 76 AVE- Geotech Report.pdfJ. KEITH CROSS, P.E. Geotechnical Engineering Consultant (425) 747-2150 STRE P.O. Box 1986, Bellevue, Washington 98009-1986 May 31, 2015 Brian Boggess Roberta Stady Carole Altomari swc 19317 142nd Avenue SE Renton, Washington 98058 0104 Geotechnical Engineering Prior -to -Salle Site Reconnaissance, Vacant Lot, 17415 76th Avenue W (aka Lot B), Edmonds, Washington Project No. 9526-001 This letter is prepared to provide a summary of a brief geotechnical engineering site reconnaissance and data review related to geotechnical engineering issues associated with the subject property. On the morning of May 18, 2015, 1 made a visit to the above referenced site to observe the general geotechnical related site conditions. After having done some prior research of readily available geotechnical data and mapping, I walked around the lot and observed the general conditions. At the site visit, the neighbor to the east followed me around and related some of his experiences related to permitting for his carport. The subject property is located in the northern portion of the Perrinville area of Edmonds Washington. At the specific property location and nearby toward the west, the ground is relatively gently sloping. Steeper slopes are located east of the site and a short distance to the west. This terrain was created by a combination of tectonics, glacial sculpting and erosive processes along the shorelines of Puget Sound. I have reviewed the agricultural soil mapping and geologic mapping for the site, and site vicinity. The agricultural soil mapping obtained from the Web Soil Survey site of the USDA Natural Resources Conservation Service indicates that the site is underlain by Alderwood group soils. These agricultural soils are indicated to be developed on a glacial till substrate. Geologic mappings of the Edmonds East and part of the Edmonds Quadrangels by Makey Smith, 1975, and James P. Minard, 1983, somewhat agree with the agricultural soil mapping, indicating either a glacial till or the underlying advance outwash sands as the substrate. Detailed soil boring information was not available in the accessible State of Washington database for sites in the immediate vicinity. , Glacial till is usually described as a mixture of silt, sand and gravel with scattered cobbles and boulders that has been clensified by overriding glacial ice to a very dense condition, similar to weak concrete. The advance outwash sands are typically a fine to coarse sand with varying Letter to Brian Boggess Project No. 9526-001 May 31, 2015 Page 2 amounts of gravel and silt. These sands were deposited in advance of the most recent glacier as it expanded southward into the Puget Sound trough. They have also been densified by overriding glacial ice to a very dense condition. At the site, I observed piles of sand and gravel mixtures that had been dug up by burrowing animals. These piles could be the product of either the glacial till or a gravelly outwash phase. With the indications of previous development on the lot, likely including plowing for farm and nursery products, near surface soils are likely to be mixed and disturbed. Soils exposed as fill along the access drive along the south side of the property appeared to be derived from a glacial till source. The near surface soils also appeared to have a high organic content in areas which is likely to be associated with the reported previous agricultural usage of the property. The western portion of the property contains a series of low concrete walls that are reported to be associated with previous greenhouse structures. There is also a pile of metal debris in the northwestern corner of the property. Vegetative cover on the property consists of a few trees and overgrown laurel, in addition to invasive blackberry and other scrub growth. Grasses and other "ground cover" type vegetation were scattered around the property. One of the concerns that was expressed that instigated my site reconnaissance was the reported presence of water on the site. While there are suggestions of periodic standing water in areas around the old greenhouse structure, the predominance of the water that I observed was associated with channelized water directed onto the site from properties upslope to the east. The most significant amount of this water was along the access roadway that runs across the southern margin of the property. Water is running in a well defined ditch on the south side of the access drive on the property to the east and the eastern 1/3 to 1/2 of the subject property. At that point the water enters a culvert which runs northward beneath the roadway to a ditch on the north side of the roadway, parallel to the roadway. This water appears to enter a buried storm water drain system near the western property line, just north of the roadway. The property owner to the east told me that there are several sources of channelized water from the east, some of which are being used by other neighbors to the south to provide the water source for ponds on their properties. There is a similar less well defined ditch, along the south side of the access roadway for properties to the north, which is also directing offsite water onto the subject site. This water flows along the north margin of the site toward the northwest property corner, where a portion of the water flows over the pavement to the north side of that roadway. It was unclear how the developers of these properties to the north expected to provide control of their channelized water, without impacting the subject property. However, I understand that you would J. KEITH CROSS, P.E. P.O. Box 1986, Bellevue, Washington 98009-1986 Letter to Brian Boggess Project No. 9526-001 May 31, 2015 Page 3 have a legal right to keep adverse behavior from effecting your property by continuing to control this water. A sketch of these drainage features is attach to this letter. This sketch is not to scale and is intended to only provide a conceptual representation of the channelized water flow that passes through the subject lot. Indications of ground water seepage not associated with these controlled drainages was not observed at my site visit. Other than keeping the water that is being directed toward the lot under control, there do not appear to be significant technical geotechnical issues that should adversely impact the potential conventional residential construction on the subject lot. The lot does not appear to be in an area that would be expected to be impacted by the typical landsliding that occurs in the Puget Sound lowland. The geologically mapped soils are expected to provide a level of residential foundation support that provides for a quality level of performance. As with any lot that has previously been subject to human activity, there may be site disturbances and/or buried conditions that will not be readily apparent until new site development activities are undertaken. Removal of previous usage features should be expected to be part of the site development process. Within the limitations of scope, schedule and budget for my work, I warrant that my work has been done in accordance with generally accepted practices followed in this area at the time this report was prepared. No other warranty, expressed or implied, is made. If there are any questions concerning this report, or if I can provide additional services, please call. Yours very truly, J. Keith Cross, P.E.84 4 At y :. ,rr CONAL J. KEITH CROSS, P.E. P.O. Box 1986, Bellevue, Washington 98009-1986 M anuana y,9L i U N L. co ,i1 0) cu cl L -1--+ cu U cu `t U cis U CO) O 0 c . p W o CL N 0) U r Z y U O Y o cc a' BCL2