HomeMy WebLinkAbout17532 Infiltration Memo - Avon DevelopmentG OT CH
CONSULTANTS, INC.
Memo
To: Hamid Korasani
Sazei Design Group, LLC
Address: 6608 —110th Avenue Northeast
Kirkland, Washington 98033
2401 -10th Avenue East
Seattle, Washington 98102
(425) 747-5618
JN: 17532
Frons Matt McGinnis
Marc R. McGinnis, P.E.
Date: October 5, 2017
Email: hamidkorasani@yahoo.com
RE: Assessment of Subsurface Infiltration Potential
Proposed Short Plat
1909 Northeast 14th Street
Renton, WA
This memo summarizes our observations of the subsurface conditions found in explorations
performed at the site, and our assessment for infiltration feasibility. We visited the subject site on
October 3, 2017 and explored the subsurface conditions by conducting two test. The test holes were
located on the eastern portion of the front yard and the western half of the back yard.
The explorations generally encountered approximately 18 inches to 2.5 feet of loose topsoil and fill
below the existing grade. Native, fine-grained silty sand that was initially loose to medium -dense was
encountered below the fill. As the explorations progressed with depth, the silty sand became dense,
and become cemented and till -like. These soils are glacially compressed and are consistent with the
Glacial Drift that has been mapped in the area. The dense silty sand is essentially impervious and
was encountered to the maximum depths of 3 to 3.5 feet that could be explored.
Due to the fine-grained, silty nature of the native soils, the impervious nature of the dense silty
sands, and the potential for adversely impacting the stability of the existing retaining walls and
neighboring lots, it is our opinion that subsurface infiltration is not feasible at this site. Infiltration tests
that have been conducted in similar soil conditions have yielded infiltration rates of less than 0.1
inches/hour. Water infiltrated or dispersed on this site would migrate laterally to adjacent developed
properties.
We trust that this memo meets your needs at this time. Please feel free to call us if you have any
questions.
Marc R. McGinnis, P.E.
Principal