05-09-07 Email Response to MDNS Comments 001GEOENGINEERS~
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G EOE NGIN EE RS~ i~~°°-
May 9, 2007
Pacific Frontier, LLC
1 I 1 5th Street Northeast
Auburn, Washington 98002
Attention: Jack Long
Subject: Letter
Response to Mitigated Determination of Non Significance Comments
Crystal Springs Project
Yelm, Washington
File No. 15854-001-01
INTRODUCTION
This letter presents our response to a City of Yelm comment in the Mitigated Determination ofNon Significance
fMDNS) dated Maroh 27, 2007 regarding the hydrogeologic assessment conducted by Geo Engineers. Inc.
(GeoEngineers) related to the subject project in Yelm, Washington. In the hydrogeologic assessment,
dated February 19, 2007, we evaluated the hydrogeologic characteristics oC the site, Our evaluation was
in response to a January 18, 2007 letter from the City of Yelm to Pctra Engineering, LLC requesting a
hydrogeologic report pertaining [o potential high groundwater flood hazard areas (City of Yelm Code
Chapter 14.08.120.G) on or near the site.
Crystal Springs is a Planned Residential Development (PRD) of 4.15 acres located within a portion of
Section 19, Township 17 North, Range 2 East, W. M. in Thurston County. The proposed development
will include approximately 29 new single-family residential lots. The development will also include
paved roadways, water and sanitary sewer mains, miscellaneous utilities, stormwater conveyance and
detention systems. No inf Itration facilities are proposed for the site. stormwater will be collected and
routed to a detention pond located in the eastern portion of the site. Septic effluent will be piped to the
City of Yelm's sewer system. A signifcant amount of fill will be placed to level the site and raise the
overall elevation of the ground surface.
SCOPE OF SERVICES
The intent of our letter is to provide a response to a Cily of Yelm comment Specifically, we are responding
to the MDNS Mitigation Measures comment p3:
3. The applicant shall provide ilGcntrnlion in (he form of a wriilen report demonstrating rha! the requested
mndrficgtions proposed in the Hydrogeological Assessment addressing the high ground warerJlood hazard
areas will nat direc(!he high ground water !n a way which could potentially have an adverse ojjeet (sic) to
neighboring praper[iec
E[IM SF[M[iite[oelpp 1580 Woeeri0[t Yr 5[ uiepme 380]69.M00
Yorl 8rc4ar0. W[ 98186 mr w 3BOi89.8T00
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Pacific Frontier, LLC
May 9, 2007
Page 2
RESPONSE
The stormwater captured within the Crystal Springs project will be routed to a detention pond on the
eastern portion of the site with a discharge at Elevation 330 feet Q00.year floodplain elevation). The
groundwater (low gradient beneath the pond is from southwest to northeast toward Yelm Creek. If
inf ltration occurs, our evaluation indicates the groundwater gradient will direct the flow toward Yelm
Creek. The stormwater infiltration, should any occur, could result in a localized mounding of
groundwater beneath the pond which is within the 100-year floodplain. Because our evaluation indicates
[hat the existing structures on [he adjaeen[ properties to the southeast, south and west are upgradient from
the detention pond, t si tt our opinion the mounding will not be adversely affected by potemial groundwater
mounding from stormwater infiltration Discharge from the detention pond and groundwater infi llratiou,
if it occurs, would be to Yelm Creek and not toward adjacent properties.
CONCLUSION
It is our opinion that the stormwater facilities a[ [he site will not direct groundwater in a way that will
have an adverse effect to neighboring properties because oftwo main reasons: 1) our evaluation indicates
[he stormwater pond is located downgradient of the neighboring properties, and 2) the natural
groundwater flow gradient will therefore direct any infiltrated stormwater toward Yelm Creek.
LIMITATIONS
We have prepared this letter for [he exclusive use of the Pacific Frontier, LLC and their authorized agents
Cor the Hydrogeologic Assessment for [he Crystal Springs project in Yelm, Washington.
Within [he limitations of scope, schedule and budget, our services have been executed in accordance with
generally accepted practices in the field of geotechnical engineering in [his area at the time this report was
prepared. No warranty or otlter wndilions, express or implied, should be understood.
File No_ liffi4-OOI-01 GEOENGINEERS~
Pacific Frontier, LLC
May 9, 2007
Page 3
Thank you for providing this opportunity for GeoEngineers m be of service. If you have any questions
regarding this letter, please contact our office at (360) 769-8400.
Sincerely,
GeoEngineers, Inc.
W ~a.~'-
el W. Purdy, LQ L~
Senior Hydrogeologist
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Tw'o copies submitted
cc: Jeff Mclnnis, P.E
Petra Engineering, LLC
535 Dock Street, Suite 213
Tacoma, Washingron
Disclaimer Any eleevanie form. facsimile or Fard wpy of the original dowmEnl (emetL mxl, table, end/or figure), if pmvidcrl and gay
vltachments arc only a copy of tM1e anginal document the original ancumem is sorcfi by GeoLngineers, In¢ antl will serve es the oRicial
tlonimcm of ruaod
File Na_ ISN54"OOI-01 GFOENGINEERS~