HomeMy WebLinkAboutGrant DFR 3-3-21.pdfCobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
Date: March 3, 2021 Project: 1600 Grant Avenue S. Job No.:
Contractor: Gary Location: Renton Weather: Clouds 45
Observations:
At your request and authorization, Cobalt Geosciences, LLC was on site to observe pothole
excavations at four locations along the water line alignment. Specifically, we observed excavation
of the thrust blocks and soil behind them at two water valve locations, a hydrant, and a pipe bend.
Three of the locations were in the northern portion of the site near the detention vault and the
fourth was in the site entrance (south side).
The City of Renton inspector (Patrick) was on site during the excavation work. All areas were
probed and found to be medium dense to dense and suitable to provide lateral support of the thrust
blocks. The soils in these areas included mixtures of sand, gravel, crushed rock, quarry rock, silty-
sand, and recycled concrete. Nuclear densometer testing would not be useful for these highly varied
materials.
We observed backfill and compaction of the locations using a jumping jack up to subgrade. A fifth
location further east of the vault was not excavated as the area was located in native glacial till.
Sincerely,
Cobalt Geosciences, LLC
3/3/2021
Phil Haberman, PE, LG, LEG
Principal
PH/sc
2063311097; phil@cobaltgeo.com