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4 Sanitary Sewer Overfiows (SSOs)

The City of Nashua is authorized to discharge from the Nashua Wastewater Treatment Facility and nine
combined sewer overflows (CSOs) to the receiving waters of Merrimack River (Wastewater Treatment
Facility (Outfall 001) and CSOs (Outfalls 002-005 and 014)) and Nashua River (CSOs (Outfalls 006-009)
under the Nashua Wastewater Treatment Facility NPDES Permit No. NH0100170. Under Section E.6
(g) of NPDES Permit No. NH0100170, SSOs are tracked and reported, pursuant to NH MS4 General
Permit Section 2.3.4.4(d). A summary of the SSOs and their causes, and a report of any corrective
actions taken as a result, are reported in the annual report related to the implementation of the
Collection System O&M Plan, submitted to EPA and New Hampshire Department of Environmental
Services (NHDES) under NPDES Permit No. NH0100170.

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5 Assessmentand Priority Ranking of Outfalls

The MS4 Permit requires an assessment and priority ranking of outfalls in terms of their potential to
have ilicit discharges related public health significance. The ranking helps determine the priority order
for performing IDDE investigations and meeting permit milestones.

5.1 Outfall Catchment Delineations

The catchments for each of the MS4 outfalls will be delineated to define contributing areas for
investigation of potential sources of illicit discharges. Refined catchment delineations will be completed
as part of the Phase II mapping to reflect information collected during catchment investigations

5.2 Outfall nventory and Initial
Ranking

Nashua has completed an initial outfall and interconnection inventory and priority ranking to assess
illicit discharge potential based on existing information. The inventory will be updated annually to
include data collected in connection with dry weather screening and other relevant inspections and
included in each annual report.

Outfalls were classified into one of the following categories:

1. Excluded outfalls:
¢ Outfalls with no potential for illicit discharges including roadway drainage in undeveloped
areas with no dwellings and no sanitary sewers; drainage for athletic fields, parks or
undeveloped green space and associated parking without services; cross-country drainage
alignments (that neither cross nor are in proximity to sanitary sewer alignments) through
undeveloped land.

2. Problem Outfalls: Outfalls with known or suspected contributions of illicit discharges based
on existing information shall be designated as Problem Outtfalls. This shall include any outfalls
where previous screening indicates likely sewer input. Problem Outfalls need not be screened
pursuant to Dry Weather Outfall and Interconnection Screening and Sampling. Likely sewer
input indicators are any of the following:

e Olfactory or visual evidence of sewage,

e Ammonia 2 0.5 mg/L, surfactants 2 0.25 mg/L, and bacteria levels greater than the
water quality criteria applicable to the receiving water, or

e Ammonia 2 0.5 mg/L, surfactants 2 0.25 mg/L, and detectable levels of chlorine.

3. High Priority Outfalls: Outfalls that have not been classified as Problem Outfalls and that are:

e Discharging to an area of concern to public health due to proximity of public beaches,
recreational areas, drinking water supplies or shellfish beds

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e Determined by the permittee as high priority based on the characteristics listed in
Appendix C.

4. Low Priority Outfalls: Outfalls determined by the permittee as low priority based on the
characteristics listed below or other available information.

Outfalls were ranked into the above priority categories (except for excluded outfalls, which may be
excluded from the JDDE program) based on the following characteristics of the defined initial
catchment areas, where information was available. Where no data was available, a level value of 0 was
assigned to the outfall. To prioritize initial mapping and outfall assessment work Nashua is using
location-specific characteristics of water body impairments to focus initial work as included in
Appendix B. The level values assigned for each outfall for each of the following characteristics were
summed to reach a final score for each outfall. For the initial outfall ranking and catchment
investigations this approach will target the worst areas first.

e Previous screening results — previous screening/sampling results indicate likely sewer input
(per the criteria above for Problem Outfalls). Outfalls were given a level value of 10 if previous
screening/sampling results indicate a problem outfall and a level value of 0 if not a problem
outfall.

e Past discharge complaints and reports — Outfalls were given a level value of 3 if greater than
5 complaints /reports were filed per year, a level value of 2 for 3-4 reports filed per year, a level
value of 1 for 1-2 reports per year, and a level value of 0 for no reports per year.

e Poor receiving water quality — Catchments draining to any waterbody impaired for the

following was designated either Problem Catchments or High Priority.

© Bacteria or Pathogens

o Nitrogen

o Phosphorus

o Legacy Impairments
Outfalls were given a level value of 10 if the receiving water body was impaired, 5 if threatened,
and 0 if not impaired/not assessed.

e Density of generating sites — Generating sites are those places, including institutional,
municipal, commercial, or industrial sites, with a potential to generate pollutants that could
contribute to illicit discharges. Examples of these sites include, but are not limited to, car
dealers; car washes; gas stations; garden centers; and industrial manufacturing areas. Outfalls in
industrial sites were assigned a level value of 3, institutional/commercial sites were assigned a
level value of 2, suburban sites were assigned a level value of 1, and rural sites assigned 0.

e Age of development and infrastructure — Industrial areas greater than 40 years old and areas
where the sanitary sewer system is more than 40 years old will probably have a high illicit
discharge potential. Developments 20 years or younger will probably have a low illicit discharge
potential. Outfalls in developments greater than 40 years old were assigned a level value of 3,
developments between 20 and 40 years old were assigned a level value of 2, and developments
less than 20 years old were assigned a level value of 1.

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e Historic combined sewer systems or sewer conversion — Contributing areas that were once
serviced by a combined sewer system but have been separated and contributing areas that were
once serviced by septic systems but have been converted to sewer connections may have a high
illicit discharge potential. Separated systems were assigned a level value of 3, converted systems
were assigned a level value of 2, and areas still on septic were assigned a 1.

e Surrounding density of aging septic systems — Septic systems 30 years or older in residential
land use areas are prone to have failures and may have a high illicit discharge potential. Outfalls
with surrounding septic systems over 30 years old were assigned a level value of 3, outfalls with
surrounding septic systems between 20 and 29 years old were assigned a level value of 2, outfalls
with surrounding septic systems between 10 and 19 years old were assigned a level value of 1,

and outfalls with surrounding septic systems less than 10 years old were assigned a level value of
0.

e Discharging to an area of concern to public health — Outfalls that discharge to or in the

vicinity of any the following areas:

© Public beaches

© Recreational areas

o Drinking water supplies

o Shellfish beds
Outfalls discharging to areas of body contact or drinking water inlets were assigned a level value
of 10, outfalls discharging to areas of high recreation or boat ramp access were assigned a level
value of 5, and outfalls discharging to areas with limited or no recreation were assigned a level
value of 0.

e CCTV storm drain data — Outfalls with hard pipe connections were assigned a level value of
10, outfalls with significant structural defects were assigned a level value of 5, and outfalls with
neither were assigned a level value of 0.

The following is an initial outfall prioritization flowchart, see Appendix C for an outfall
inventory and priority ranking matrix:

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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.

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6.1.2

Field Equipment

Table 6-1. Field Equipment —- Dry Weather Outfall Screening and Sampling

Equipment

Use/Notes

Clipboard

For organization of field sheets and writing surface

Field Sheets

Field sheets for both dry weather inspection and Dry weather sampling
should be available with extras

Chain of Custody Forms

To ensure proper handling of all samples

Pens/Pencils/Permanent Markers

For proper labeling

Nitrile Gloves

To protect the sampler as well as the sample from contamination

Flashlight/headlamp w/batteries

For looking in outfalls or manholes, helpful in early mornings as well

Cooler with Ice

For transporting samples to the laboratory

Digital Camera

For documenting field conditions at time of inspection

Personal Protective Equipment
(PPE)

Reflective vest, Safety glasses and boots at a minimum

GPS Receiver

For taking spatial location data

Water Quality Sonde

If needed, for sampling conductivity, temperature, pH

Water Quality Meter

Hand held meter, if available, for testing for various water quality
parameters such as ammonia, surfactants and chlorine

Test Kits Have extra kits on hand to sample more outfalls than are anticipated to be
screened in a single day
Label Tape For labeling sample containers

Sample Containers

Make sure all sample containers are clean.

Keep extra sample containers on hand at all times.

Make sure there are proper sample containers for what is being sampled
for (i.e., bacteria requires sterile containers).

Pry Bar or Pick

For opening catch basins and manholes when necessary

Sandbags For damming low flows in order to take samples
Small Mallet or Hammer Helping to free stuck manhole and catch basin covers
Utility Knife Multiple uses

Measuring Tape

Measuring distances and depth of flow

Safety Cones

Safety

Hand Sanitizer

Disinfectant/decontaminant

Zip Ties/Duct Tape

For making field repairs

Rubber Boots/Waders

For accessing shallow streams/areas

Sampling Pole/Dipper/Sampling
Cage

For accessing hard to reach outfalls and manholes

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6.1.3 Sample Collection and Analysis

If flow is present during a dry weather outfall inspection, a sample will be collected and analyzed for the
required permit parameters’. The general procedure for collection of outfall samples is as follows:

1. Fill out all sample information on sample bottles and field sheets
Put on protective gloves (nitrile /latex/other) before sampling

3. Collect sample with dipper or directly in sample containers. If possible, collect water from the
flow directly in the sample bottle. Be careful not to disturb sediments.

4. Ifusing a dipper or other device, triple rinse the device with distilled water and then in water to
be sampled (not for bacteria sampling)

5. Use test strips, test kits, and field meters (rinse similar to dipper) for most parameters (see
Table 6-1)

6. Place laboratory samples on ice for analysis of bacteria and pollutants of concern

7. Fill out chain-of-custody form for laboratory samples

8. Deliver samples to City of Nashua Wastewater Treatment Facility Laboratory or contracted
laboratory.

9. Dispose of used test strips and test kit ampules properly

10. Decontaminate all testing personnel and equipment

In the event that an outfall is submerged, either partially or completely, or inaccessible, field staff will
proceed to the first accessible upstream manhole or structure for the observation and sampling and
report the location with the screening results. Field staff will continue to the next upstream structure
until there is no longer an influence from the receiving water on the visual inspection or sampling.

Field test kits or field instrumentation are permitted for all parameters except indicator bacteria and any
pollutants of concern. Field kits need to have appropriate detection limits and ranges.

In the past, the City has contracted with the Nashua River Watershed Association for sample collection
and analysis and associated standard operating procedures.

6.2 Follow-up Ranking of Outfalls

Nashua will update and re-prioritize the initial outfall rankings based on information gathered during dry
weather screening. The rankings will be updated periodically as dry weather screening information
becomes available.

Outfalls where relevant information was found indicating sewer input to the MS4 or sampling results
indicating sewer input are highly likely to contain illicit discharges from sanitary sources.

Such outfalls will be ranked at the top of the High Priority Outfalls category for investigation. Other
outfalls may be re-ranked based on any new information from the dry weather screening.

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7 Catchment Investigations

Once stormwater outfalls with evidence of illicit discharges have been identified, various methods can be
used to trace the source of the potential discharge within the outfall catchment area. Catchment
investigation techniques include but are not limited to review of maps, historic plans, and records;
manhole observation; dry and wet weather sampling; video inspection; smoke testing; and dye testing.

Catchment Investigations shall be completed in accordance with Part 2.3.4.8 of the MS4 Permit and the
City of Nashua Written Catchment Investigation Procedures document.

7.1 MIllicit Discharge Removal

When the specific source of an illicit discharge 1s identified, Nashua will first contact the owner of the
suspect property and will exercise its authority as necessary to require tts removal. The annual report will
include the status of IDDE investigation and removal activities including the following information for
each confirmed soutce:

e The location of the discharge and its source(s)

e Adescription of the discharge

e The method of discovery

e Date of discovery

e Date of elimination, mitigation or enforcement action OR planned corrective measures and a
schedule for completing the illicit discharge removal

e Estimate of the volume of flow removed.

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8 Training

Annual IDDE training will be made available to employees involved in the IDDE program. This
training will at a minimum include information on how to identify dlicit discharges and may also include
additional training specific to the functions of particular personnel and their function within the
framework of the IDDE program. The frequency and type of training will be mcluded in the annual
report. The City of Nashua will take advantage of training opportunities offered by NHDES, the Lower
Merrimack Valley Stormwater Coalition, and the University of New Hampshire Technology Transfer
Center, including specifically the JODE Training Videos developed by the Lower Merrimack Valley
Stormwater Coalition for identifying and sampling illicit discharges. The City of Nashua will hire
consultants or contractors as needed to provide necessary trainings.

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