10725 19TH AVE SE 2023-04-07 - Laserfiche WebLink

Geotechnical Engineering Evaluation Zerzura Townhome Development 10725 — 19th Avenue SE Everett, Washington INTRODUCTION This report presents the results of our geotechnical engineering investigation and evaluation of the planned residential development project located at 10725 — 19th Avenue SE in Everett, Washington, as shown on the Vicinity Map in Figure 1. The subject site is situated on relatively flat ground and is bounded to the north, east, and south by existing residential properties and to the west by 19th Avenue SE. The parcel is currently occupied by a single-family residence and detached outbuilding within the western and eastern portions of the property, respectively. Grass-covered yard and scattered landscaping plants surround the existing structures within the site. We understand the proposed site development will consist of removing the existing structures and constructing four, three-unit townhome structures with associated parking areas and utilities. The existing and proposed site conditions are shown on the Schematic Site Plan in Figure 2. We also understand that stormwater generated within this site is proposed to be directed to on-site infiltration systems, if feasible. We have been requested to evaluate the infiltration capacity of the site soils. We will collect samples and determine the infiltration rate based on the Washington State Department of Ecology 2012 Stormwater Management Manual for Western Washington, as amended in 2014, and conduct on-site testing. According to this manual, long-term design infiltration rates for this site are to be determined by performing on-site infiltration testing consisting of the Small-Scale Pilot Infiltration Test(PIT). For our use in preparing this report, we were provided with a plan set titled "The Zerzura Building," dated August 17,2017,prepared by 2812 Architecture, showing the proposed developments. SCOPE The purpose of this study was to explore and characterize the site surface and subsurface conditions, evaluate infiltration capacity of the on-site soils, and provide general recommendations for the planned development. Specifically,our scope of services included the following: 1. Review available soil and geologic maps of the area. 2. Perform grain-size analysis on representative soil samples,as needed. 3. Explored the subsurface conditions throughout the site with trackhoe excavated test pits. Trackhoe was subcontracted by NGA. NELSON GEOTECHNICAL ASSOCIATES, INC.