TITLE 35: ENVIRONMENTAL PROTECTION
SUBTITLE C: WATER POLLUTION
CHAPTER II: ENVIRONMENTAL PROTECTION AGENCY
PART 375
COMBINED SEWER OVERFLOW EXCEPTION CRITERIA
AND FIRST FLUSH DETERMINATION
SUBPART A: INTRODUCTION
Section
375.101 Policy
375.102 Definitions
375.103 Prohibitions
SUBPART B: WATER QUALITY INVESTIGATION
375.201 Policy
375.202 Phase I - Background Information
375.203 Phase II - Preliminary Stream Inspection
375.204 Phase III - Detailed Water Quality Evaluation
375.205 Special Analysis for Congested Areas
375.206 Time Schedule
SUBPART C: ASSESSMENT OF CONTROL OPTIONS
Section
375.301 Water Quality Evaluation
375.302 Control Alternatives
375.303 Benefits Assessment
SUBPART D: FIRST FLUSH DETERMINATION
375.401 Variables in First Flush Determination
375.402 Conditions for Determination
375.403 Field Studies
375.404 Modeling
APPENDIX A First Flush Graph
AUTHORITY: Implementing Section 12(a) and authorized by Section 4 of the
Environmental Protection Act (Ill. Rev. Stat. 1981, ch. 111 1/2, pars.
1012(a) and 1004) and by 35 Ill. Adm. Code 306.352.
SOURCE: Adopted and Codified at 7 Ill. Reg. 10808, effective August 23,
1983; amended at 8 Ill. Reg. 19436, effective September 26, 1984.
SUBPART A: INTRODUCTION
<BSection 375.101 Policy>>
This policy provides guidelines for:
a) Determination of water quality impacts attributable to combined
sewer overflows and treatment plant bypasses;
b) Estimation of potential water quality improvements;
c) Selection of a combined sewer overflow (CSO) control program that
can be justified on the basis of local environmental conditions
and fiscal responsibility;
d) Evaluation and review of discharger's submittals pursuant to 35
Ill. Adm. Code 306.351; and
e) Determination of first flush as referenced in 35 Ill. Adm. Code
306.305(a).
(Source: Amended at 8 Ill. Reg. 19436, effective September 26, 1984.
<BSection 375.102 Definitions>>
All definitions in 35 Ill. Adm. Code 301 shall apply here. No
incorporation by reference in this Part contains any later amendment or
addition.
"Combined Sewer" means a sewer designed and constructed to
receive both wastewater and land runoff.
"Dry Weather Flow" means the flowrate consisting of wastewater
and non excessive sewer infiltration in the absence of inflow
sources attributable to direct precipitation or snowmelt and is
not restricted to meteorologic drought conditions. Nonexcessive
sewer infiltration is defined at 40 CFR 35.2005(1984).
"First Flush" is defined as that volume of water and associated
flow rate needed to carry solids or BOD concentrations is excess
of the dry weather flow. This volume is shown on the "cross
hatched" area in Appendix A.
35 Ill. Adm. Code 306.305(a) uses the term "first flush to
describe those flows requiring complete treatment. When
sewage is flowing through a sewer system at fairly uniform
lower velocities, which occur during dry weather conditions,
some of the solids present in the waste are deposited in the
pipes. In addition, solids and some organic material that
may be washed into the combined sewer systems tend to build
up on streets, parking lots, etc.
When a storm event occurs, the volume of wastewater carried
by the sewer increases and the velocities in the sewer also
increase. The high volume of storm water causes material to
be washed from the streets into the sewer and the sludge
deposited in the sewers to be scoured from the pipes. This
material is carried to the sewage treatment plant where it
exerts an additional organic load on the biological system
and an additional solids load on the physical systems. The
maximum impact of this phenonmenon tends to occur at the
beginning of a storm event and taper off as the storm
continues and there are no additional solids to remove.
"Human Contact Activities" means wading, swimming or any other
activity involving partial or total immersion of the human body
in the subject waterway whether for recreational or other
purpose.
"Wet Weather Flow" means a flowrate condition, elevated above dry
weather flow, attributable to land runoff as the result of
snowmelt or a precipitation event.
(Source: Amended at 8 Ill. Reg. 19436, effective September 26, 1984)
<BSection 375.103 Prohibitions>>
a) Dry weather overflows are expressly prohibited under existing
regulations and are not eligible for consideration under the
provisions of this rule. Combined sewer overflow programs that
will result in continued or future dry weather overflows or
treatment plant bypasses will not be approved by the Agency.
b) This policy applies to overflow from combined sewer systems and
treatment plant bypasses resulting from wet weather flow
conditions. Overflows from separate sanitary sewers and from
portions of combined sewer communities served by separate
sanitary sewers are not subject to this rule.
SUBPART B: WATER QUALITY INVESTIGATION
<BSection 375.201 Policy>>
It is the intent of this policy that water quality investigations be no
more extensive than is necessary:
a) to identify the degree of CSO control appropriate for a specific
community as mutually agreed to by discharger and Agency, and
b) to substantiate the appropriateness of the proposed control
program under the scrutiny of the Board in a proceeding pursuant
to 35 Ill. Adm. Code 306: Subpart D.
<BSection 375.202 Phase I - Background Information>>
a) A community seeking to pursue alternate CSO control requirements
under provisions of 35 Ill. Adm. Code 306: Subpart D and this
Part shall review existing documents including facility planning
reports, sewer maintenance records, and Discharge Monitoring
Reports to assemble pertinent background information. To the
extent available in existing resources, pertinent background
information shall include the following:
1) a map of the sewer system depicting:
A) portions of the community served by combined sewers and
separate sanitary sewers; and
B) location of each overflow and receiving water body;
2) size of watershed of receiving water body at point of each
overflow;
3) drainage area and population tributary to each overflow;
4) land use, zoning classification and projected growth
patterns in the vicinity of each overflow using the
following classifications: residential, commercial,
industrial, recreational, agricultural;
5) actual or potential use of the affected waterway for human
contact activities;
6) history of complaints regarding the stream and surrounding
environment and downstream of overflows;
7) history of other complaints concerning the sewer system;
8) description of structural and physical condition of sewer
system including age of system, incidence of sewer
collapses, bottlenecks in the system; and
9) list of industrial and other sewer users tributary to
overflows which contains substances in wastewater or storm
drainage in concentrations likely to create hazardous or
toxic conditions at the point of combined sewer overflow.
b) Submittals:
1) A written report of review conducted in subsection (a) above
shall be submitted to the Agency along with a request for
Agency participation on an advisory and review basis in a
CSO impact/evaluation project.
2) Submittals shall be addressed to:
Illinois Environmental Protection Agency
Construction Grant Section
Division of Water Pollution Control
2200 Churchill Road
Springfield, Illinois 62706
c) Upon receipt and review of discharger's report, an Agency
representative will be designated as project coordinator and
contact person for the Agency's participation in the project.
The Agency Project Coordinator will contact the Applicant's
representative to schedule a conference regarding second phase
activities.
d) After Phase I, conferences shall be held between the Agency and
discharger's representatives to discuss and agree upon the nature
and extent of each subsequent phase of investigation prior to
commencing that phase.
<BSection 375.203 Phase II - Preliminary Stream Inspection>>
This phase requires a physical inspection of the receiving water body and
near stream property. Additionally, any necessary elements missing from
the Phase I background report shall be addressed in this step. Factors to
be considered include:
a) Inspection of stream in and around vicinity of each overflow for
sludge deposits, sewage related odors, floating debris of
sanitary sewage origin, and any other visible signs of pollution
impact. Inspection techniques shall be selected so as to assure
maximum reliability of the results including:
1) probing, disturbance and extraction of bottom sediments in
pools and other quiescent portions of stream to note color,
texture, odor and other aspects of sediments that are
indicative of sewage sludge:
2) estimates of extent and severity of sludge deposition in
terms of depth of deposition, area of stream affected and
percentage of stream bed within affected area that contains
sludge deposits; and
3) inspection of shoreline vegetation, logjams and other
obstructions likely to retain floating sewage debris.
b) Stream Hydraulics:
1) Stream hydraulic factors shall be identified including:
average width of stream channel from bank to bank, height of
stream banks above thalweg, stream bed gradient.
2) For receiving streams with a 7Q10 (average seven day low
flow which occurs once in 10 years) flow greater than 10
cubic feet per second this information can be omitted,
substituting the 7Q10 value.
c) Stream morphological factors including:
1) substrate type;
2) variation of structure via natural meandering, pool and
riffle sequence;
3) degree of dredging, channelization or other alteration of
natural stream character; and
4) accumulation of logjams and other naturally occurring
vegetative debris.
d) Description of stream side property including:
1) topography;
2) land cover including forrested, agricultural row crop,
marsh, grass buffer strip, residential lawn, and
3) land use if not already identified in Section 375.202(a)(4)
including a specific determination if affected area is
utilized by or accessible to children for recreational
activities.
<BSection 375.204 Phase III - Detailed Water Quality Evaluation>>
Areas to be addressed in a detailed water quality survey shall include,
consistent with 35 Ill. Adm. Code 306.361 (d):
a) water column chemistry -
1) upstream/downstream and overflow sampling;
2) wet weather/dry weather sampling;
3) diurnal sampling for dissolved oxygen (D.O.);
4) parameters generally will include BOD5, suspended solids,
volatile suspended solids, ammonia. Other parameters may
become important depending on the nature of the overflow;
and
5) other parameters as deemed appropriate relative to 35 Ill.
Adm. Code 375.302(a)(8).
b) sediment analysis -
1) sediment oxygen demand;
2) percent volatile matter;
3) particle size distribution; and
4) other parameters as deemed appropriate relative to 35 Ill.
Adm. Code 375.302(a)(8).
c) biological survey -
1) benthic macroinvertebrates;
2) fishes; and
3) plant productivity assessment (algal blooms).
d) hydraulic and hydrologic factors including storm hydrographs for
receiving stream and overflow.
<BSection 375.205 Special Analysis for Congested Areas>>
In small drainage basins receiving combined sewer overflows from
collection systems belonging to several separate governing bodies the
significance of the aggregate CSO load may well dictate a basin wide
evaluation of alternate control levels in lieu of community by community
evaluation. Resolution of CSO issues in such basins may require
evaluation of all CSO sources concurrently with cooperative data
collection efforts involving several communities. This is especially
applicable in major metropolitan areas.
<BSection 375.206 Time Schedule>>
a) Once a water quality investigation is initiated, every effort
shall be made to expedite each step of the activity, completing
the investigation in the shortest possible time without
compromising the validity of the findings. Effective field
activities are dependent upon proper seasonal, hydrologic and
meteorologic conditions which will require flexibility in
scheduling. Nevertheless the following time table is suggested
as a general guideline.
b) Phase I - 30 to 60 days for completion plus 30 to 60 days for
Agency review and planning of Phase II.
c) Phase II - 30 to 60 days for completion plus 30 to 60 days for
Agency review and planning of Phase III.
d) Phase III - 6 months to 1 year and generally containing the
summer months of June, July and August.
SUBPART C: ASSESSMENT OF CONTROL OPTIONS
<BSection 375.301 Water Quality Evaluation>>
It is intended that water quality evaluation performed under Subpart C of
this Part will be undertaken in conjunction with or subsequent to first
flush analysis and CSO studies consistent with Subpart D. Control options
being evaluated shall not be limited to alternatives resulting in full
compliance with 35 Ill. Adm. Code 306.305; lesser control options of
varying degrees shall be evaluated also.
(Source: Amended at 8 Ill. Reg. 19436, effective September 26, 1984)
<BSection 375.302 Control Alternatives>>
Alternatives resulting in noncompliance with existing water quality
standards and requiring regulatory relaxation of water quality standards
may also be considered by the discharger. Water quality revisions being
considered shall be consistent with the purpose and objectives of the Act
and the CWA.
<BSection 375.303 Benefits Assessment>>
Benefits shall not be assessed solely on a pound pollutant removed basis
but also on instream improvement of a documented pollutional impact or
reduction in a public health risk. Acceptable techniques for estimating
water quality improvements will vary depending on individual circumstances
but may include:
a) consideration of receiving water body assimilative capabilities
and strategic relocation of overflows;
b) selection of size of storm to design controls for based on stream
hydrograph, available dilution, turbulance and velocity under
storm conditions and their affect on assimilation (since CSO's
are dominated by suspended rather than soluble pollutants, major
emphasis will be placed on prevention of instream deposition);
and
c) mathematic modeling.
SUBPART D: FIRST FLUSH DETERMINATION
<BSection 375.401 Variables in First Flush Determination>>
The intensity and duration of first flush are a function of certain
variables including:
a) Physical and hydraulic features of the sewer system and tributary
watershed.
b) Amount of sediment accumulated in the sewer system and on
impervious surfaces of the watershed.
c) Intensity and duration of the storm event causing the flushing.
(Source: Added at 8 Ill. Reg. 19436, effective September 26, 1984)
<BSection 375.402 Conditions for Determination>>
For any given sewer system, or portion of a sewer system, first flush
volume subject to full treatment requirements of 35 Ill. Adm. Code
306.305(a) and associated flow rate shall be determined for the following
condition(s):
a) A storm of 1.2 inch per hour intensity with a duration of 60
minutes, which approximates a one year-one-hour storm for most
sections of the state.
b) There shall be sufficient time between the storm event chosen to
determine first flush and any previous event to allow for adequate
solids deposition in the sewers and on the streets to demonstrate
first flush under this Part. In general a ten day period should
be sufficient.
(Source: Added at 8 Ill. Reg. 19436, effective September 26, 1984)
<BSection 375.403 Field Studies>>
a) First flush volumes may be determined through direct field
measurement at a point of overflow, modeling of the collection
system or equally accurate techniques. Either approach is
dependent on a field monitoring program as described in (c) below.
Commonly, first flush for the design storm is determined by direct
measurement of flush rate and volume for several storms of varying
intensity and extrapolating to the design storm (1.2 in/hr.).
b) Detailed monitoring may be limited to less than the total number
of overflow locations in the system when monitoring all locations
would be impossible or would not be helpful in demonstrating the
capabilities of the system. Sampling sites should be selected in
order to monitor the largest discharges in terms of loading.
Consideration shall also be given to the different land use
patterns, population densities, and sewer system characteristics
tributary to a given overflow site within the study area.
c) General guidance for field measurement includes:
1) A minimum of 3 storms should be monitored for each sampling
site.
2) There shall be a least one rain gauge located within the
study area. For systems serving an area of over 2 squares
miles, multiple gauges shall be used and located to achieve
gauge spacing of 2 miles or less throughout the study area.
Rain gauges should be on the continuous recording type,
otherwise manual readings should be recorded on intervals of
10 minutes or less. If only one gauge is used it should be
located near the center of the study area; multiple gauges
shall be located so as to identify variations in storm
intensity across the study area.
3) Flow monitoring shall be initiated at the onset of a storm
and continue through and beyond the sewer flushing period.
Flow meters may be located in interceptor manholes, diversion
structures, outfall sewers or other locations where dependale
opertion is assured. Caution should be taken to protect
instrumentation from flooding, corrosion, excess humidity,
vandalism or other factors which jeopardize either the
equipment or reliability of the data.
4) Water samples should be collected at the onset of the storm
and at 10 or 15 minute intervals thereafter. In most
instances a moderate to heavy storm will fully flush the
system within two hours. Most automatic discrete samplers
have adequate capacity to contain the entire flush period
with 10 minutes sampling frequency. Again, caution should be
taken to protect against flooding, corrosion, or excess
humidity that may cause malfunctioning or failure of the
mechanical or electronic components of the sampler. Samples
should be analyzed for BOD as defined in 35 Ill. Adm. Code
304.120(a), total and volatile suspended solids with sample
preservation, and analysis consistent with Standard Methods
15th Edition (1980).
5) Overflow points that are not subject to direct flow and
quality monitoring should be inspected during the storm
period to determine if the overflows are functioning and to
estimate the rate and duration of overflow.
(Source: Added at 8 Ill. Reg. 19436, effective September 26, 1984)
<BSection 375.404 Modeling>>
a) If all of the overflow locations to be studied cannot be sampled
and monitored, or field conditions were not available through
direct field measurement as described in Section 375.403, then
other methods, including modeling of section (s) of the study
area, shall be required to determine first flush. These methods
should be used to:
1) Predict the quality and quantity of loads and concentrations.
2) Identify significant sources.
3) Analyze hydraulics of the tributary system.
b) Data supplied for the modeling must be based on factors particular
to a given system or study area and should include:
1) Rainfall data
2) Size of drainage area
3) Land use
4) Population density
5) Hydraulics of area
6) Percentage of combined and/or separate sewers
c) The type of modeling to be used for a given collection system or
study area shall be addressed in the Plan of Study for the CSO
Analysis. References, such as texbooks, technical papers, etc.,
for the modeling methods to be used shall be listed.
d) Verification that the model(s) is valid shall be provided by
comparing the output obtained from the model(s) with actual
sampling and monitoring data from overflow points specified in
accordance with Section 375. 403 for two or more storms.
(Source: Added at 8 Ill. Reg. 19436, effective September 26, 1984)
<BSection 375.APPENDIX A First Flush Graph>>
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