PLN 2014-0080 06214011 Sumner Southwest – SW Infiltration Rate

December 5, 2014
KA Project No. 062-14011
J. K. Monarch, LLC
P.O. Box 188
Puyallup, WA 98371
Attn: Mr. Fred Herber
Email: [email protected]
Tel: (253) 840-5660
Sumner Southwest
Stormwater Infiltration Rate
7420 148th Avenue Court East & 14712 72nd Street East
Sumner, WA
Dear Mr. Herber,
As per your request, we have prepared this letter to provide stormwater infiltration rate recommendation
for the Sumner Southwest project located at 7240 148th Avenue Court East/14712 72nd Street East in
Sumner, WA.
Stormwater Infiltration Rate
We had previously prepared a geotechnical report titled “Limited Geotechnical Engineering Investigation
– Sumner Southwest, 7240 148th Avenue Court East/14712 72nd Street East, Sumner, Washington”,
dated October 21, 2014.
At the time our limited geotechnical engineering investigation was prepared a stormwater management
system consisting of infiltration pond in the southern portion of the site was being considered. We had
provided infiltration rate of 2.0 inches per hour for a well-maintained infiltration system using the native
sand with gravel and sand with silt in the southern portion of the site. We understand that the design team
is currently considering permeable pavement to manage the stormwater. We have been requested to
provide an infiltration rate for the design of the stormwater infiltration system consisting of permeable
Our explorations indicated that the site is underlain by native alluvium soils. Our previous recommended
infiltration rate was 2.0 inches per hour for a well-maintained infiltration system using the native sand
with gravel and sand with silt in the southern portion of the site. Due to the variability of the site soils
encountered in our test pits we have applied a safety factor of approximately 4 to the infiltration rate. We
recommend using an infiltration rate of 0.5 inches per hour for the design of the permeable pavement
stormwater infiltration system. The stormwater infiltration system should be designed by a Washington
State Licensed Civil Engineer.
922Valley Avenue NW, Suite #C-101, Puyallup, WA 98371 (253) 939-2500  FAX (253) 939-8556
With Offices Serving the Western United States
KA No. 062-14011
December 5, 2014
Page No. 2
Testing and Inspection
We should evaluate the soil conditions during construction of the stormwater management system to
confirm that the soil conditions are consistent with those encountered in our explorations. This activity is
an integral part of our services as acceptance of earthwork construction is dependent upon observation of
the consistency of the soil and groundwater conditions, and making appropriate adjustments if conditions
vary from those indicated by our explorations.
Geotechnical engineering is one of the newest divisions of Civil Engineering. This branch of Civil
Engineering is constantly improving as new technologies and understanding of earth sciences improves.
Although your site was analyzed using the most appropriate current techniques and methods, undoubtedly
there will be substantial future improvements in this branch of engineering.
In addition to improvements in the field of geotechnical engineering, physical changes in the site either
due to excavation or fill placement, new agency regulations or possible changes in the proposed structure
after the time of completion of the geotechnical letter may require the geotechnical letter to be
professionally reviewed. In light of this, the Owner should be aware that there is a practical limit to the
usefulness of this letter without critical review. Although the time limit for this review is strictly
arbitrary, it is suggested that two years be considered a reasonable time for the usefulness of this letter.
The recommendations made in this letter are based on the assumption that soil and groundwater
conditions do not vary significantly from those disclosed during our field investigation. If any variations
or undesirable conditions are encountered during construction, the geotechnical engineer should be
notified so that supplemental recommendations can be made.
The conclusions of this letter are based on the information provided regarding any proposed construction.
If the proposed construction is relocated or redesigned, the conclusions in this letter may not be valid.
The geotechnical engineer should be notified of any changes so that the recommendations can be
reviewed and re-evaluated.
This letter is a limited investigation with the purpose of evaluating the soil and groundwater conditions
and providing laboratory testing. The scope of our services did not include any environmental site
assessment for the presence or absence of hazardous and/or toxic materials in the soil, groundwater or
atmosphere, or the presence of wetlands. Any statements, or absence of statements, in this letter or on
any exploration log, regarding odors, unusual or suspicious items, or conditions observed are strictly for
descriptive purposes and are not intended to convey engineering judgment regarding potential hazardous
and/or toxic assessments.
Krazan & Associates, Inc.
Offices Serving The Western United States
KA No. 062-14011
December 5, 2014
Page No. 3
The information presented herein is based upon professional interpretation utilizing standard engineering
practices and a degree of conservatism deemed proper for this project. It is not warranted that such
information and interpretation cannot be superseded by future developments. We emphasize that this
letter is valid for this project as outlined above, and should not be used for any other site.
If you have any questions, or if we may be of further assistance, please do not hesitate to contact our
office at (253) 939-2500.
Respectfully submitted,
Michael D. Rundquist, PE
Senior Project Manager
Vijay Chaudhary, P.E.
Staff Engineer
Krazan & Associates, Inc.
Offices Serving The Western United States