HomeMy WebLinkAbout502155010 Stormwater Mgmt
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NTI
NORTHWESTERN TERRITORIES, INC.
A JLS GROUP COMPANY .
.fLa GROUP,
INC.
717 SOUTH PEABODY STREET, PORT ANGELES, WA 98362
o Engineers 0 Land Surveyors 0 Geologists
o Construction Inspection 0 Materials Testing
(360) 452-8491 FAX 452-8498 wwwnli4u.com E-MaH: inro@nli4u,com
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August 3. 2005
Lorin E. Mustoe
785 SW 67th PI
Portland, OR 97225-6156
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Subject: Review of Proposed Infiltration System. Tax Parcel 502155010.304 Black Point Road
Dear Mr. Mustoe:
As requested by Jefferson County and Bill Payton. I have reviewed the enclosed roof drain "drywell"
detail which you have proposed for use in lieu of a tightline to the beach, I have enclosed a copy of
the two pages of drawings which you submitted,
· 25 year, 24 hour design event
· 6,2 inches of rain in 24 hours
· Infitration rate of 6 inches per hour
· 24 inches wide by 24 inches deep by 50 feet long
· 1.700 square feet catchment area
· Rainfall hydrograph as input to infiltration facility
· Zero time of concentration
APPROVED
STORMW A TER PLAN
I analysed the operation of the drywell underthe following assumption
SEP 2 6 2005
JEFFERSON COUNTY
DEPT. OF ( :VF.UJI>MF.NT
SIGNATURE:
Based on these operational parameters, the infiltration facility may be moderately overloaded based
on the 25 year design storm. I recommend increasing the length of the infiltration trench to 60 feet.
This will handle the 25 year storm with just over 2 inches of remaining unused capacity,
I trust I have adequately addressed your concerns,
Yours Sincerely.
NTI ENGINEERING & SURVEYING
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David Hanna, PE
Civil Engineer
Enclosure
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_._~T~~MWATER PLAN
SEP 2 6 ID05
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JEFFERSON COUNTY
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APPROVED
STORMWATER PLAN
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NTI
NORTHWESTERN TERRITORIES, INC.
A JLS GROUP COMPANY
717 SOUTH PEABODY STREET, PORT ANGELES, WA 98362
o Engineers 0 Land Surveyors 0 Geologists
o Construction Inspection 0 Materials Testing
(360) 462-8491 FAX 452-8498 _.nti4u.com E-Mail: info@nti4u,com
RECEIVED
"LS GROUP,
INC.
June 1 0, 2005
}\.PPROVED
STCRMWATER PLAN
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JEffERSON COUNlY OeD
Lorin Mustoe
14566 SW 161 Ave
Tigard, OR 97224
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Subject:
Addendum t 9,2004 for Tax # 502155010
located in Section 15, Township 25.North, Range 2 West; W.M., Jefferson
County, WA .'
E . FERSONC'OUNTY
I>EI'T 01- (" IN ",.tOl'MENT
Sl(i~;A": 'R!'
Dear Mr. Mustoe:
NTI Engineering and Surveying (NTI) completed a geotechnical report for the above referenced
property on May 19, 2004. In that report, we recommended a tightline drain to the base of the
bluff as the preferred method (from a geotechnical perspective) of controlling surface runoff from
hard surfaces such as roofs, driveways, walkways and patios.
You have requested that we amend our report to allow for onsite infiltration of this water as
opposed to tightliniilg due to the regulatory difficulties of permitting a tightline drain.
We hereby amend our report to allow for onsite infiltration of this water. We recommend that the
water be infiltrated at least 50 feet back from the edge of the bluff and farther if possible. We
further recommend that the water be dispersed rather than being released as a point discharge.
Please refer to Volume 5 of the Washington State Department of Ecology.2001 Stormwater
Management Manual for Western Washington for technical guidelines.
If you need further assistance or have questions regarding this matter, please don't hesitate to
contact us.
Sincerely,
NORTHWESTERN TERRITORIES, iNC.
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Robert A. Lea ,'~.E., MBA
Principal Engineer
I EXPIRES
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1213lli2OO6 'l
Bill Payton, L.E.G.
Engineering Geologist
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G:\Gen\Bill\Reports\MUST0401, 15(25-2).addendum Ieller.doc
Expires 11/06105