07_NCS000427_General Operating Conditions for IDDE_20230502

GENERAL OPERATING GUIDELINES
FOR
ILLEGAL DISCHARGE
DETECTION AND ELIMINATION
Dry Weather Screening
Town of Cary
STORM WATER DIVISION

TABLE OF CONTENTS
• FIELD SCREENING OVERVIEW
• SITE SELECTION
• FIELD PROCEDURES
• LAB PROCEDURE
• OUTFALL CLASSIFICATION
• FOLLOW-UP RECOMMENDATIONS
• REPORTING PROCEDURES
• TRACKING DATA
APPENDICES
• EQUIPMENT CALIBRATION
• SAFETY ISSUES
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IDID FIELD SCREENING OVERVIEW
As part of the overall storm water quality management program or "SWQMP" the
illicit discharge and improper disposal field screen has been established to detect
and characterize all non-storm discharges throughout the Town. The IDID field
screening program will determine if the discharges are illicit connections
containing contamination or whether the discharge is a natural base flow.
Discharges which occur after a preiod of at least 72 hours without rain will be
referred to as "DRY WEATHER FLOW". During such dry weather there should
be no flow from the storm drainage system with the exception of flow from piped
streams. The field screen for this program will involve visiting each outfall in the
Town of Cary and running a series of screening tests if dry weather flow is found.
Each dry weather flow will be tested and observations recorded at the time of
inspection. The screening will address indicator pollutants that can be reliably
tested for in the field and/or lab. The following parameters will be tested for:
conductivity, dissolved oxygen, temperature, and pH.
The storm water section will be responsible for collection of data related to dry
weather flow. Additional parameter screening will be for odor, color, oil/grease, oil
sheen and any other indicators of past or present discharges. If screening
indicates a possible illegal discharge it will receive follow-up investigation in an
effort to remove sources of pollutants from the Town's water resources.
TEST SITE SELECTION
The NPDES permit requires that each of the Town's outfalls be screened for dry
weather flow.
Town-wide screening
i. basin-by-basin
ii. source driven monitoring
Town-wide screening of all outfalls can be accomplished by reviewing each basin
systematically or by monitoring around identified pollutant sources or a
combination of both methods. The permit recommends monitoring streams and
targeting dry weather sampling to problem areas.
IDID PROCEDURE
During dry weather (it should have been at least 72 hours without rain):
a. Select watershed
b. Mark each outfall on the map
c. Note the condition of the outfall and presence of flow
d. Test for screening to note if there is significant dry weather flow
0 in outfall, measure pH, DO, conductivity, and temperature

• in receiving stream (upstream of outfall) measure pH, DO, conductivity,
turbidity and temperature 0
• fill out field sheet
• all (flow & no flow) observed outfalls will be marked and assigned a
number
e. Classify outfalls
f. Track results
g. Proceed with follow-up as needed
FIELD METHODS
The following equipment should be retrieved from the vehicle and carried in the
field using the carrying trays. Note: equipment should be properly calibrated prior
to use; see Appendix and calibration manual/logs for more information.
1. Plastic squeeze bottles filled with de-ionized water
2. Clip board
3. Data sheets/ pens
4. Tablet or Phone to put in information on collector app in GIS. (IDDE Dry
Weather Map)
5. Map of basin
6. PH meter, conductivity meter, DO meter with temperature
7. Sample bottles
8. Phone (to maintain contact between teams and/or office)
The streams can be walked during any dry weather condition, however sampling
for dry weather flow should be done after at least 72 hours without rain. It will be
most efficient to walk the stream, sample field parameters.
Once a dry weather flow has been located mark the location on the map and
determine if the flow is natural or a potential IDID. Fill out the IDDE Field
Screening Form.
The sampling technician should note any visual or physical characteristic of the
outfall as noted on the form; Odor, color, clarity, floatables, deposits/stains,
vegetation condition, structural condition and biological characteristics. Some
physical characteristics to look for would be; Structural damage to outfalls or
pipes, staining and vegetation, large amounts of algae, and absence of
vegetation instream.
• fill a beaker and measure pH, conductivity, turbidity and temperature
• measure DO in the outfall (or just below the outfall)
• in receiving stream (upstream of outfall) measure pH, DO, conductivity and
temperature
• fill out field sheet

• Data Interpretation:
pH- Large pH variations can be indicative of a batch dump by industry or an
intermittent process release such as rinsing or cleaning of equipment. A spike in
either direction can be indicative of illegal dumping or chemical spills. pH values
greater than 8.5 or less than 6.0, or large variations within a 24 hour period, can
be used as an indicator of concern. If significantly different from upstream pH, an
IDID may be suspected.
METHOD- Oakton pH meter
CONDUCTIVITY- The ability of water to conduct an electrical charge. The total
number of dissolved minerals/solids v.s. the temperature of a sample is
expressed in micromhos per centimeter. Changes in conductivity from normal
may indicate changes in mineral composition of the water. Intrusion of pollutants
such as salts would be an indicator of an un-natural occurrence warranting further
investigation. A measure of more than 400 micromhos could indicate an IDID.
METHOD - Hanna Conductivity meter
DISSOLVED OXYGEN - a measure of oxygen content in the water, the meter
also measures oxygen saturation. A very low or very high DO level could indicate
an IDDE; a DO significantly different from upstream level may indicate an IDDE.
METHOD- Ecosense D200 handheld dissolved oxygen system
FLOW TEMPERATURE-A temperature measured in dry-weather flows that is
significantly different from upstream flow may be an indicator of an illicit
connection to the storm sewer system by either industrial, commercial, or
residential sources. For example, a consistently high temperature dry-weather
flow during a cold weather period could be an indicator of an IDID.
METHOD- Handheld thermometer or metered probe with temperature
measurement capabilities.(measured in degrees centigrade).
In temperate weather, the field walking and testing can be done all day

ANALYSIS OF DATA
To evaluate the dry weather flow, compare the results to the detection range,
values which are typical of Town water, and the stream standards. If the
results are outside of the detection range for a piece of equipment or test
method, check the equipment and test methods and note the results. If the
dry weather flow is similar to Town water, there is likely a non-storm water
discharge present. Check the list of permittable sources under our ordinance.
If stream standards are exceeded, a follow-up must be done.
TEST method detection range Town water stream standard concern if
H su H 0-14 7-8 6-9 outside 6-9
temp(C) M 0-32 variable seasonal different from
upstream
DO(mg/1) M 0-20 nla 5 <4-5 mgll or
very high
conductivity M 0- 96-145 200* >400
umhoslcm
Allowable discharges under Storm Water Ordinance
1. water line flushing
2. diverted stream flows
3. rising ground waters
4. uncontaminated ground water infiltration or pumped ground water from
potable sources
5. foundation drains
6. air conditioning condensation
7. irrigation water
8. springs
9. water from crawl space pumps
10.footing drains
11.lawn watering
12.car washing at one's residence (not for hire) and charity events
13.flows from riparian habitats & wetlands
14.dechlorinated swimming pool discharges
15.street wash waters
16.discharges from fire fighting
17.spray ground with no recirculation
*Any other discharges must be removed or permitted.

CLASSIFICATION OF OUTFALL
An indicator level is a measurable amount of a test constituent which is indicative
of a possible IDID. Indicator levels have been established for the following test
constituents.
Based on these levels, each outfall with dry weather flow will be classified as
• no action
• watch
FOLLOW-UP INVESTIGATIONS
Based on the classification of the outfall, follow-up actions should be taken. A
"watch" should trigger further investigation. These outfalls should be noted
follow-up initiated as soon as possible.
Follow-up investigations are not siginifcantly different from citizen complaint
investigations or spill response. All investigations require locating the source of
the problem and working with the proper parties to alleviate the discharge.
Having located and tested sources of dry weather flow via the field screening
process, monitoring technicians will create a list of outfalls requiring follow-up.
The list will include a rating of outfalls by URGENT or WATCH.
1. select outfall requiring follow up
2. gather available maps of storm water infrastructure
3. gather available information on facilities in area 1 land use
4. re-locate outfall requiring follow-up
5. trace flow to source
6. re-test parameters which triggered follow-up
7. notify source of problem (verbal & written)
8. discuss solutions
9. select a solution
10.schedule corrective action
11.document all findings
12.update database
13.inspect area at later date
The most difficult part of this process may be locating the source of the flow.
a. walk up gradient, lifting manhole covers and inspecting for flow
b. to confirm that a flow source is reaching a particular outfall, the flow source
can be dyed and additional sampling can be performed by Public Works
c. if there is no apparent flow source, smoke testing may be employed to locate a
source such as an illegal connection
d. if there is a significant pollutant source and no apparent source after the above
have been tried, you may schedule to have the lines TV-ed by Utilities.

APPENDIX:
I. EQUIPMENT CALIBRATION
Equipment calibration will be performed on all test equipment prior to IDID field
screening. A calibration manual and log has been established to keep track of the
different intervals of calibration required for each item of field testing equipment.
The following is a list of test equipment and recommended calibration schedule.
■ Hanna portable PH meter- Calibrate daily, refer to calibration manual for
step by step instructions.
■ DISSOLVED OXYGEN Meter- Calibrate each time unit has been turned
off; refer to calibration manual for step by step instructions.
■ Conductivity meter CALIBRATE PERIODICALLY as probe ages or is
changed. Calibration with a standard solution of known conductivity
value near the typical temperature of the sample solution will
improve accuracy.
II. SAMPLE COLLECTION AND HOLDING TIME
field parameters
1. DISSOLVED OXYGEN - measure in situ (in stream) Ecosense meter
2. pH- Oakton meter in situ
3. TEMPERATURE- measure with Ecosense meter
4. CONDUCTIVITY - measure in situ or in beaker (in field); Hanna meter