MPCA Design Guidance for Large Subsurface Wastewater ...

Example 3: Measured Flow Other Establishments
Establishment: Campground
Period Measured: Fourth of July Week.
Daily flow measurements (gals) and utilization rate (%):
Day Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
Measured Flow (gpd) 3,000 3,500 5,000 4,000 4,200 4,000 3,200
Percent Utilized (in
decimal form)
Extrapolated for max.
capacity (flow / %
capacity)
Calculation of measured average daily flow:
0.60 0.75 0.90 0.85 0.85 0.85 0.65
5,000 4,667 5,556 4,705 4,940 4,705 4,923
(5,000 + 4,667 + 5,556 + 4,705 + 4,940 + 4,705 + 4923) / 7 = 4,928 gallons + Inflow and Infiltration
Step C2 — (question repeated) Will a single SSTS or group of SSTSs under single ownership within
one-half mile of each other be designed to treat a design AWW flow greater than 10,000
gallons per day as determined below?
Yes — the system requires SDS permit from the MPCA. Please see
www.pca.state.mn.us/programs/ists/business.html#largeists.
No — Go to Step C3.
Step C3 — Will the SSTS or group of SSTSs cause adverse public health or environmental impacts if
not regulated under a state permit (such as systems in environmentally sensitive areas, those
with unsubstantiated or unexpected flow volumes, or systems requiring exceptional
operation, monitoring and management)?
Yes — The system may need a SDS permit issued by the MPCA. Please see
www.pca.state.mn.us/programs/ists/business.html#largeists.
No — The system is regulated under a LGU permit. Contact the local permitting authority
(either county environmental health or planning and zoning office, or township office
or city building inspector).
Step C4 — Does the system serve fewer than four dwellings or does it serve an Other Establishment with
a design AWW flow of 2,500 gallons per day or less? (See Attachment 2 to calculate flow.)
Yes —The system is an individual sewage treatment system (ISTS).
No — The system qualifies as a midsized sewage treatment system (MSTS) with an average
daily flow of sewage greater than 2,500 gallons and less than or equal to 10,000
gallons. The following attachments may be used to aid in the design and review of the
proposed system.
Design Guidance for Large Subsurface
Minnesota Pollution Control Agency
Wastewater Treatment Systems April 2010
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