6 Dry Weather Outfall Screening and Sampling
Dry weather flow is a common indicator of potential dlicit connections. The MS4 Permit requires all
outfalls (excluding Problem and Excluded Outfalls) to be inspected for the presence of dry weather
flow. The Engineering Department is responsible for conducting dry weather outfall screening, starting
with High Priority outfalls, followed by Low Priority outfalls, based on the initial priority rankings
described in the previous section by the end of Year 3.
Dry weather outfall Screening and Sampling shall be completed in accordance with Part 2.3.4.7.b of the
MS4 Permit. Plans and procedures for such screening and sampling shall be incorporated into this plan.
6.1 Dry Weather Screening/ Sampling
Pro cedure
6.1.1 General Procedure
The dry weather outfall inspection and sampling procedure consists of the following general steps:
1. Identify outfall(s) to be screened/sampled based on initial outfall inventory and priority ranking
Acquire the necessary staff, mapping, and field equipment (see Table 6-1 for list of potential
field equipment)
3. Conduct the outfall inspection during dry weather:
a. Mark and photograph the outfall
b. Record the inspection information and outfall characteristics (using paper forms or
digital form using a tablet or similar device)
c. Look for and record visual /olfactory evidence of pollutants in flowing outfalls
including odor, color, turbidity, and floatable matter (suds, bubbles, excrement, toilet
paper or sanitary products). Also observe outfalls for deposits and stains, vegetation,
and damage to outfall structures.
4. If flow is observed, sample and test the flow following the procedures described in the
following sections.
5. Ifno flow 1s observed, but evidence of illicit flow exists (illicit discharges are often intermittent
or transitory), revisit the outfall during dry weather within one week of the initial observation, if
practicable, to perform a second dry weather screening and sample any observed flow. Other
techniques can be used to detect intermittent or transitory flows including conducting
inspections during evenings or weekends and using optical brighteners.
6. Input results from screening and sampling into spreadsheet/database. Include pertinent
information in the outfall /interconnection inventory and priority ranking.
7. Include all screening data in the annual report.
Hic it Discharge Detection and Himination Plan 13
