HomeMy WebLinkAboutSWG Letters / Memos - 2/6/1989 ENGINEERING REPORT
LARGER ON-SITE SEWAGE SYSTEM
BELFAIR ELEMENTARY SCHOOL
BELFAIR, WASHINGTON
Owner: North Mason School District
P.O. Box 167 9SPOH""
Belfair, WA 98528
Attn: Chuck Jeu
(206) 275-2883F _ :,Engineer: Art Anderson Associates '�i198 First Street oFFlCrLBremerton, WA 98310 - `_aEZ__.J
Attn: James R. Levey, P.E.
(206) 979-5600
Project Description: Modernization and additions to Belfair
Elementary School
Project Location: State Hwy 3, Belfair, Washington
Tax Parcel No. 12332-90-60000
Existing System: The school presently consists of two buildings,
each with its own septic tank and gravity fed drainfield. One is
located southeast of the school and has a 3758 gallon septic tank
with 556 L.F. of drainfield trench. The other is located northwest
of the school and contains a 3600 gallon septic tank and 556 feet of
drainfield trench. The existing system serves an occupant load of
460 students and staff. There are no showers in the building and
the kitchen is only a serving kitchen so the design flow would be 10
gal/day/person or 4600 gallons per day. The required septic tank
capacity is 6900 gallons compared to the combined capacities of the
existing tanks of 7358 gallons. The combined length of drainfield
trench for the two systems is 1206 feet. The loading rate per foot
of trench length is 3. 8 gal/lin ft.
Domestic Water Source: Belfair Water District provides water to the
school and surrounding properties.
Land use: Present land use is residential on the north and south,
public use on the west, and undeveloped on the east.
Area Wells: The 1" = 2000' area map shows the site and drainfield
locations. There are no wells within the area. Plan sheets Cl and
C2 show the existing and proposed drainfield areas, 'sttuc'E'ufesj
roads, parking, storm drainage system, site contours and water and
sewer lines and drainage patterns. There is a small creek east and
south of the new drainfield site.
Geology and Soils: Detailed descriptions of the area geology and soils
were prepared in reports by Grover Way dated 16 Sep 88 and 27 Nov '
88. The soils are principally sandy, glacial tills. There is some
evidence that periodic ground water seepage will occur during wet
conditions.
Location: The proposed drainfield area is located southwest of the
school building. The drainfield is 150 feet from the school in an
area with average slope of 1.5%.
Design Criteria: The design flow for the new additions is 10 gals.
per person per day. The addition has no showers or kitchen. The
occupancy of the new addition is 84 . The total daily design flow
will be 840 gallons.
The effluent loading rate for the drainfield is 0.8 gal/day/sq. ft.
for the silty fine sand. The trenches will be 3 feet wide, and the
total length will be 354 feet.
The septic tank is sized for 1500 gallons with a scum storage area
of 300 gallons. The baffles would permit buildup of sludge in the
bottom before failure.
Operation and Maintenance: This system will be operated and
maintained by North Mason School District and district personnel
will respond to emergencies, when warranted. Routine maintenance as
outlined in O/M manual will be integrated into the district' s
planned maintenance program.
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