20170160 Preliminary Drianage Report 03312017ENGINEER'S CERTIFICATE
hereby certify that this Preliminary Drainage Report has been prepared by myself or under my
supervision and meets the current City of Yelm standards, and normal standards of engineering practice.
hereby acknowledge and agree that the jurisdiction does not assume liability for the sufficiency,
suitability, or performance of drainage facilities designed by me.
Prepared By:
u- Cf
Debbie Maroon, P.E.
SKILLINGS CONNOLLY
.v INC
3j;?w-zj 17
Date
Existing nd i io n
The project site, which is approximately 0.6 acres in size, contains an existing building, two existing
driveway approaches, fencing, and graveled parking and access areas. The existing vegetation consists
mainly of grasses. The site previously contained a meat market, but the building has not been used in
several years.
The project site sits lower than the road, and slopes from south to the north. Runoff on the site is
currently being handled by two drywells.
Proposed Conditions
The Owners intend to remodel the building for use as an automotive repair shop. Future plans call for a
30 foot extension on the north side of the existing building.
Per the city of Yelm Standards, the Owners will provide paved access and parking areas. The driveway on
the west side of the site will be for employees only while the driveway on the east side will be for
customer use.
Preliminary Storm Drainage Design
The storm drainage system will be designed in accordance with the latest Washington Department of
Ecology (DOE) Stormwater Management Manual for Western Washington per the City standards.
According to the USDA Soils Survey., the soils on the site are Spanaway Gravelly Sandy Loam, which is a
Hydrologic Soil Group A /B. Type A/B soils have moderate to high infiltration rates and can be used to
meet the SID performance standard and the flow control requirement provided that the infiltrated
stormwater does not cause a violation of groundwater.
Because roofs are not normally considered pollution generating, we are proposing that the runoff from
the front of the building be infiltrated in drywellsf
Runoff from the remainder of the building and from the paved parking and access areas will be collected
in a drainage system and conveyed to a bioretention facility (rain garden) where it will be treated prior
to infiltrating into the ground.
Conclusion
The design presented is preliminary in nature, and is intended to show a possible solution for the storm
drainage. If the soils testing shows a different soil than that anticipated, or if the Owner desires to do a
different type of drainage facility, which still must meet the Ecology Manual, the final design may vary
from the design that is currently shown.
Skillrngs Connolly 1
Consulting Engineers
Standley Commercial Development
Preliminary Drainage Report
March 2017