HomeMy WebLinkAboutGRD99-00025 Construct Pond Embankments - GRD Letters / Memos - 1/7/2000 MASON COUNTY
PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER
Shelton,Wuhington 98584
INTER-DEPARTMENTAL COMMUNICATIONS DATE: Jan. 7, 2000
TO: Randy Neff, DCD - Planner
FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. Work Order No. 99905
SUBJ: Grading Proposal Review NAME: Mason Co./North Bay Reclamation
Facility GRD99-0025
Additional material has been received and reviewed by Public Works pertaining to the construction of the
pond embankments as an element of the North Bay Water Reclamation Facility development.
A concern expressed in my November 181h, 1999 IDC was that the proposed pond embankments are to be
constructed without an impervious core, and the plans do not indicate that the embankments be "keyed"
into the supporting subgrade. Investigation of suitable core materials for earthen dams* indicate that
Unified Soil Classification soil designations of SM, SP, GM, & GP are considered acceptable core
construction materials, and that the composition of the dam's shell material is not critical. The same
reference supports the embankment geometries including sideslopes and minimum berm top width.
With the entire earthen dam constructed of what may be considered core/impermeable material,the
contact zone between the embankment and underlying subgrade exceeds minimum requirements for the
seal between the embankments and the underlying soils, and I feel the absence of a constructed key is not
a critical factor and within the engineer's discretion not to include in the construction of the embankment's
foundation.
Certification by the project engineer that the embankments have been constructed in accordance with the
approved design, and are satisfactory to the engineer should be required at project completion. Copies of
compaction tests and results collected during the embankment construction should be required to be made
available to the County.
A Stormwater Site Plan conforming to PSWQA minimum requirements is still awaited for review and
acceptance before grading activities are allowed to proceed.
Please feel free to contact me at County extension 461 if you have any questions regarding this review, or
these comments.
S/inncerely,
Al
Alan A. a
Cc: HES—GRAY& OSBORNE, Inc.
* DESIGN OF SMALL DAMS, U.S. Department of the Interior & Bureau of
Reclamation
File: H:\WP\GRADING\NBWRF-2.doc