04-0180 High Groundwater meeting 021506
City of Yelm
Community Development Department
105 Yelm Avenue West
P.O. Box 479
Yelm, WA 98597
February 16, 2006
Erling Birkland, Director of Facilities
Yelm Community Schools
PO Box 476
Yelm, WA 98597
RE: Ridgeline Junior High School – Stormwater System
Rocky:
This is a follow-up to our meeting of February 15, 2006, regarding the high groundwater flooding conditions at Ridgeline Junior High School. I want to take this opportunity to clarify
the direction you received from the City at the meeting.
As noted by Grant Beck during the meeting, the City’s concern and the reason for my letter of February 3, 2006 is not to have any potential impacts to property owners south of the School
site, but rather in the vicinity of the new storm facility near the Hawks Landing subdivision. The information presented at the meeting by Ed Wiltsie, P.E. confirms the City’s initial
conclusion that the flooding in the area of Fox Hill Road was high groundwater which was not significantly altered by any construction activities by the School District, including the
placement of fill material to raise the elevation of the proposed track.
Based on the above, I want to be clear that the City is not requiring that the ‘flood storage’ lost to the fill placed for the construction of the football field be replaced within the
high groundwater area.
The purpose for my letter previously was to ensure that the placement of the storm pond within a high groundwater area would not significantly increase the base flood elevation and impact
the ‘downstream’ properties in Hawks Landing. This concern stems from the fact the system will be collecting stormwater from the entire Mill Pond School/Ridgeline Junior High School
site and discharge it to the high groundwater area. According to the preliminary analysis by Ed Wiltsie, the collection and transportation of stormwater from the entire site to the
storm system does not impact the flood elevation as this water is part of the pre-existing condition and the only change is the amount of time it takes for the water to enter the high
groundwater area.
If the School District provides a report stamped and signed by an engineer licensed in the State of Washington which verifies Mr. Wiltsie’s preliminary conclusion that the collection
of stormwater from the site and subsequent discharge into the high groundwater area does not significantly impact the elevation of the high groundwater, the City will consider the existing
approved design of the stormwater system to be adequate. If the analysis shows that the groundwater elevation would raise, additional stormwater storage will need to be created within
the high groundwater area.
Community Development Department
Respectfully,
Jim Gibson, P.E.
Development Review Engineer
c. Bob Tauscher, P.E. JWMAA
Ed Wiltsie, P.E. JWMAA