12 19 07 Wiltsie Comment re NOA 001Edward A. Wiltsie
PO Box 6 ] 02
Olympia, Washington 98507
19 December 2007
CiTy of Yelm
PO Box
Yelm, Washington 98597
ATTENTION: Ms. Tammy Merriman, Community Development Department
SUBJECT: Purvis Residential Development-50 Acres/160 Residential Lots
Dear Ms. Merriman:
Pursuant to the City's Public Notice for the above referenced project, I submit the
following comments:
OVERVIEW
The Public Notice indicates that the application is fora 50 acre parcel to be developed to
inclede 160 residential lots. The design information provided with the application
addresses only 24 residemia] lots. The application and public record should be amended
to reflect that the application is for Phase 1 of the Purvis Development and only for 24
lots on 5.36 acres.
TRAFFIC
Recent Public Hearings and Hearings Examiner's finding for the Tahoma Terra
Subdivision -Divisions 5 & 6, Berry Valley Development and Wyndstone developments
were required to provide a combined regional traffic analysis for Yelm Avenuc,Tahoma
Boulevard, Berry Valley Road, Longmire Street and Cullen Road. The combined
analyses showed a number of these public rights of way to be operating in excess of their
design capacity. The addition of this development will add traffic to this condition
increasing [he overload condition. Hence, new regional traffic mitigation will be required
along numerous of the routes. Please provide me with copies of the traffic studies that
address these issues on a regional basis.
WATER SUPPLY
W SDOE records indicate that the City of Yelm does not own [he required Water Rights
to justify entertaining additional residential development at this time. Application for this
development should be placed on hold until the Water Rights required by Washington
State Law have been procured and perfected in the name of the City of Yelm.
STORMWATER
There are numerous disconnects behveen the Stormwater Report and its incorporated Soil
Investigation Report, and ongoing Thurston County Stormwater/Thompson Studies.
The report and analyses performed do not mention or coordinate with [he
ongoing Thurston County/City of Yelm Flood /Study being performed along
Thompson Creek from its headwaters south of the 1'ahoma Terra Subdivision and
93rd Avenue and on to SR-510 to the north.
The site drainage report by KPFF lists three different site acreages for the Phase
] development, 5.56 acres, 6.0 acres, 6.43 acres, and 8.49 acres in the same
drainage report without explanations for the differences. At one point reference
is made to 1.07 acres of wetland area, which fits the difference between the 5.56
and 6.43 acres. The Public Notice does not reference any of these Phase 1
acreages, only the 50 acre total parcel size. The Application, Notice of
Application and Storm Reports should be revised and reissued to facilitate Public
Review of documents that are internally consistent and facilitate the review of
accurate and representative design documents.
Section 3 of the Stormwater report states that `Groundwater was not discovered
in any test pits on the Phase 1 site." The incorporated Soil Investigation Report
states on page 2 that groundwater and evidence of seasonal groundwater was
encountered in test holes A, B, C, F & 7. It is difficult to determine precisely
from the mapping provided, but test hole F is detinicely within the Phase 1 area
and test holes A, B and C may be within the Phase 1 area. The report and
designs represented need to be corrected to reflect these conditions and site
conditions consistently and accurately. The revised documents should be
reissued for public review of accurate and representative design documents.
Stormwater analyses presented in the Drainage Report use the smallest of the site
acreages listed for the site 5.36 acres. This value may not represent all of the
land area impacted by the development The report should be modified to clarify
this issue and provide a clear technical audit trail for all land areas involved.
The Drainage Report discusses both storm pond release by sidewall infiltration
and controlled release to surface flow.
0 1992 WSDOE Stormwater Manual requirements for infiltration in areas
restricted by shallow groundwater or impervious surfaces (Darey's
Equation Analysis) are no[ presented to support this approach and
infiltration values are not presented either in the Soil Report or Drainage
Report.
o The controlled release analyses use an 8.49 acre tributary are to calculate
the undismrbed release rates, while the post-development tributary area
flow contributions are calculated using a 5.36 acre area. If a portion of the
predevelopment site is to remain undisturbed, it can not be used in
calculating the post-development release rates. In short, if 5.36 acres arc
being developed, facilities release rates mast be calculated using 5.36
acres. Hence, the release rates listed in the Drainage Report are overly
optimistic and are not in accordance with the procedures established in
the 1992 WSDOE Manual.
Finally, the 1992 WSDOE Manual requires that the downstream flow path and
environment be analyzed for facilities that release flow to the surface. This
project area is tributary to Thompson Creek, which has experienced severe
flooding during the 2005/06 and 2006/07 wet season during storms that were far
below the City of Yelm design events rainfall levels (see Figure below). As a
result of this recent flooding Thurston County in conjunction with the City of
Yelm is in the process of monitoring and studying Thompson Creek from its
headwaters (south of Tahoma Terra) to SR-510. This study and the potential
downstream impacts of this development in a proven sensitive watershed and
creek reach has not been addressed in this report. The proposed design will alter
the transit time for surface and shallow groundwater to Thompson Creek,
changing the local hydrology in a basin wherejurisdictional efforts are being
expended to define and preserve the existing and natural hydrology.
It is further noted that there is a potential for the storm pond to release to the west into an
existing wetland. If this is the case, the 1992 WSDOE Manual requires that the
hydroperiod of the wetland be studied and defined prior to stormwater release into the
wetland and designs, calculations and additional mitigation be provided to insure that the
natural hydroperiod of the wetland is not disturbed or modified.
Based on the foregoing, the documents submitted do not appear to be accurate, complete,
internally consistent or inaccordance with the 1992 WSDOE stormwater Manual. As
such, the subject documents should be returned to [he developer for revision so that a
review of accurate, consistent, representative and compliant (with City of Yelm Code and
the 1992 WSDOE Manual) can be reviewed as part of the Public Comment process. To
this end I request that revised application and Public Notice documents be prepared along
with the support document revisions be developed and reissued.
Should you have any questions of required additional information, please contact me at
ed,~n eawiltsie.com.
Yours truly,
E A Wiltsie