Wood El-Infil Vault Monitoring-AES.pdf[d ED 10]
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11980 NE 24"' Strect, Suitc, 200
Helk,witc, Washijigtort 98005
Allentiou: Vfs, Tiflitay Brown
snl'rjecL fiffilh-21ti0ki VaUllt Verificatimi Monfloriog Plan
Plat a�l Woodway He mierit,,iry Scbool,
Edmorids, Washinglori
Dear Ms. ffiomiw
AS INJUMed, tris letter provides, our with respect u) inhitradon vault,
verificatim) rnordtoring at die Wo6dway Elenrentary School plat redevelopinent projt-xi. We
raliriliar with the project, through (or oajoWg des gn sqVort for hifiltrationfeasibility and
gaitmAnkol analysis, III IcUci- should be used f(,)gc[hcr with oul pFtVq(,1S VVOI,J( 01-r (]-I(,
project. This letter` has b(-,TTi prepared in accordance with local staridards of pracdco at the
time it was wrilteri. No other warranty, express of iinplk',d, is
Tris letter Us based on a current civil plart set, dated February 14, 2013, provided to us by
the 11lueline Groul,), die project civil engineer. Specinnify, we reviewed plan sheet VT-Ol (12
of 13) to cornrime Us Own One should refer to our previous letters/reports for interpretive
subsolface logs of' tl-.Ie explorations and infiltr-ation testing performed at the site -
PURPOSE AND SCOPE
We anticipate that construction monitoring and operatiorial verifi(--°afiol) 1r,or the vault will be
provided by Associated Eartb Scienc.es, Inc, (AESI), with review arid approval by the Ci(y of
Edmonds, and roil[ include: 1) as -kilt documentation t 2 vault construction incets approved
design plans; 2) infiltration pefformancc Mointorilig of the vault in the form of pit drain
infiltration testing. The monitoring protocol described below provides a methodology to verify
that the infUtration vaWt is operating in accordance Mitt the intent of the approved design,
BACKGROUP41)
Al -,Sl pn,.Mously colDlActed stlmntm expkwakmm hick0ing expkm5n frits and one
moniW.ring, well, KJOratkni lestinj gumnd mwr mounding analysis, aml geoccchuical
I( If i :'� d F v c r m N Jhcuma
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engineering plan reviews for the project. The current design proposal is based on our earlier
work and is consistent with our recommendations. In general, the area proposed for
infiltration is underlain by a thick unsaturated sequence of Vashou advance outwash (Qva).
Ground water was not present in any of our explorations completed to a maximum depth of 50
feet as measured from existing ground surface. The advance outwash consists primarily of
stratified fine to medium sand with variable coarse sand and gravel content, and minor
quantities of silt.
Surface water drainage from the project will be collected and routed to the planned storm water
vault. The vault will be a below -grade, cast -in-place structure with a concrete lid and an open
bottom. AESI will be on-site during pit drain construction to verify that pit drain construction
conforms to our recommendations. Based on review of plan sheet VT -01, one 15 -foot -deep pit
drain is currently proposed within the vault footprint. Water will infiltrate from the bottom of
the vault through the pit drain into the thick unsaturated Qva receptor horizon,
Construction monitoring and operational verification for the vault will include: 1) as -built
documentation that vault construction meets approved design plans; and 2) performance
monitoring of the vault consisting of pit drain infiltration rate testing. Performance monitoring
will be in accordance with "Performance Testing" outlined on Page 5-60 of the 2009 King
County Surface Water Design Manual which allows small-scale infiltration testing in the
bottom of the facility because a ground water mounding analysis was used during design of the
facility. Monitoring will be performed by a representative of AESI.
The design infiltration rate for the vault was calculated by the Blueline Group based on AESI
recommended design infiltration rate of 7.0 inches per hour (iph) for the proposed infiltration
vault. This value would be used as the benchmark for performance verification testing.
Pit Drain Infiltration hate Testing During Construction
At the time of construction, AESI will complete infiltration rate testing in the planned pit drain
installed within the vault. Pit drain testing will incorporate equipment and procedures in a
similar manner as previously used during design -phase testing, as described in detail in our
letter dated October 5, 2012. In summary, the infiltration testing will utilize a continuous
water supply source to obtain steady state flow conditions during the test period. Water levels
in the pit drain will be monitored via a 2 -inch polyvinyl chloride (PVC) sounding tube, and
flow rates from the water supply will be metered to obtain both instantaneous rates and total
volume. The inflow portion of the test will be continued until steady state conditions are
maintained for at least one hour at the design infiltration rate.
2
Corrective Action.
If vault infiltration performance is below the design infiltration rate, AESI will provide
recommendations for corrective action, if needed. Corrective action would likely include
installation of additional pit drains or other measures.
Monitoring equipment will be calibrated according to the manufacturer's instructions during
use. Water level measurements during pit drain testing will be measured by a technician with
experience in flow rate and water level measurement.
A letter -report will be prepared following drain .construction documenting methods,
observations of subsurface conditions, test results, and other relevant information. This report
will be submitted to the City of Edmonds for final acceptance of the vault. No additional
monitoring will be required at the conclusion of the performance monitoring period, assuming
the design infiltration discharge rate has been documented during the performance test.
M_L�'fII t'l
It has been our pleasure to be of continued service on this project. Please do not hesitate to
call if we can answer questions regarding this letter or other aspects of the project within our
areas of expertise.
Sincerely,
ASSOCIATED EARTH SCIENCES, INC.
Kirkland, Washington
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