[Federal Register Volume 77, Number 1 (Tuesday, January 3, 2012)]
[Notices]
[Pages 112-123]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2011-33661]
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ENVIRONMENTAL PROTECTION AGENCY
[EPA-HQ-OW-2010-0884, FRL-9615-3]
Effluent Limitations Guidelines and Standards for the
Construction and Development Point Source Category
AGENCY: Environmental Protection Agency (EPA).
ACTION: Notice.
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SUMMARY: The Environmental Protection Agency is issuing a notice to
solicit data and information associated with revisions to the Effluent
Limitations Guidelines and New Source Performance Standards for the
Construction and Development Point Source Category issued under the
Clean Water Act. The regulation, as originally issued on December 1,
2009, established requirements that reduce pollutants discharged from
construction and development sites, including requirements for a subset
of sites to comply with a numeric effluent limitation for turbidity. On
November 5, 2010, EPA published a direct final rule and companion
proposal staying the numeric turbidity limitation established by the
December 2009 rule to correct a calculation error. The Agency received
no adverse comments regarding the stay, and therefore, effective on
January 4, 2011, the numeric turbidity limitation was stayed. In
today's notice, EPA is seeking data on the effectiveness of
technologies in controlling turbidity in discharges from construction
sites and information on other related issues. Today's notice also
seeks comment on passive treatment data already available to the
Agency.
DATES: Comments must be received on or before March 5, 2012, 60 days
after publication in the Federal Register.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OW-
2010-0884, by one of the following methods:
http://www.regulations.gov: Follow the on-line
instructions for submitting comments.
Mail: Water Docket, U.S. Environmental Protection Agency,
Mailcode: 28221T, 1200 Pennsylvania Ave. NW., Washington, DC 20460.
Hand Delivery: Water Docket, USEPA Docket Center, Public
Reading Room, 1301 Constitution Avenue NW., Room 3334, EPA West
Building, Washington DC 20004. Such deliveries are only accepted during
the Docket's normal hours of operation, and special arrangements should
be made for deliveries of boxed information.
Instructions: Direct your comments to Docket ID No. EPA-HQ-OW-2010-
0884. EPA's policy is that all comments received will be included in
the public docket without change and may be made available online at
http://www.regulations.gov, including any personal information
provided, unless the comment includes information claimed to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Do not submit information that you
consider to be CBI or otherwise protected through www.regulations.gov
or email. The http://www.regulations.gov Web site is an ``anonymous
access'' system, which means EPA will not know your identity or contact
information unless you provide it in the body of your comment. If you
send an email comment directly to EPA without going through
www.regulations.gov your email address will be automatically captured
and included as part of the comment that is placed in the public docket
and made available on the Internet. If you submit an electronic
comment, EPA recommends that you include your name and other contact
information in the body of your comment and with any disk or CD-ROM you
submit. If EPA cannot read your comment due to technical difficulties
and cannot contact you for clarification, EPA may not be able to
consider your comment. Electronic files should avoid the use of special
characters, any form of encryption, and be free of any defects or
viruses.
Docket: All documents in the docket are listed in the http://www.regulations.gov index. Although listed in the index, some
information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, will be publicly available only in hard copy.
Publicly available docket materials are available either electronically
in http://www.regulations.gov or in hard copy at the Water Docket, EPA/
DC, EPA West, Room 3334, 1301 Constitution Ave. NW., Washington, DC.
The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday
through Friday, excluding legal holidays. The telephone number for the
Public Reading Room is (202) 566-1744, and the telephone number for the
Water Docket is (202) 566-2426.
FOR FURTHER INFORMATION CONTACT: Mr. Jesse W, Pritts, Engineering and
Analysis Division, Office of Water (4303T), Environmental Protection
Agency, 1200 Pennsylvania Ave. NW., Washington, DC 20460; telephone
number: (202) 566-1038; fax number: (202) 566-1053; email address:
[email protected].
SUPPLEMENTARY INFORMATION:
A. Does this action apply to me?
Entities potentially affected by this action include:
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North American
Industry
Category Examples of affected Classification
entities System (NAICS)
Code
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Industry....................... Construction activities required to
obtain NPDES permit coverage and
performing the following activities:
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Construction of 236
buildings,
including building,
developing and
general contracting.
Heavy and civil 237
engineering
construction,
including land
subdivision.
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[[Page 113]]
EPA does not intend the preceding table to be exhaustive, but
provides it as a guide for readers regarding entities likely to be
affected by this action. Other types of entities not listed on the
table could also be affected. To determine whether your may be affected
by this action, you should carefully examine the applicability criteria
in Section 450.10 of the December 1, 2009 final rule (74 FR 62995) and
the definition of ``storm water discharges associated with industrial
activity'' and ``storm water discharges associated with small
construction activity'' in existing EPA regulations at 40 CFR
122.26(b)(14)(x) and 122.26(B)(15), respectively. If you have questions
regarding the applicability of this action to a particular activity,
consult one of the persons listed in the preceding FOR FURTHER
INFORMATION CONTACT section.
Table of Contents
I. Overview
II. Background
A. NPDES Regulations, Construction General Permits and
Applicability of 40 CFR Part 450 Requirements
B. Petitions for Administrative Reconsideration and Petitions
for Review of the Final Construction and Development Regulation in
the U.S. Circuit Court of Appeals for the Seventh Circuit
C. EPA's Unopposed Motion
D. Stay of the Numeric Limitation
III. Review of Treatment Data in EPA's Current Dataset
A. Approach to Calculating the December 2009 Turbidity
Limitation
B. Passive and Semi-Passive Treatment Datasets
C. Additional Data
IV. Solicitation of Data and Comments on Numeric Effluent
Limitations for Turbidity
A. Control of Turbidity--Effectiveness, Cost and Feasibility of
Different Technologies
B. Sampling and Data Collection--Procedures and Protocols To
Ensure Representativeness of Data; Differences in Analytical
Equipment
C. Effect of Storm Size, Intensity and Duration of Precipitation
on Performance of Passive Treatment
D. Exemptions--Design Storm Depth vs. Intensity
E. Use of Treatment Chemicals, Disposal and Toxicity Concerns
F. Cold Weather Considerations
G. Small Sites That Are Part of a Larger Common Plan of
Development or Sale
H. Electric Utility Transmission Line Construction
I. Overview
EPA promulgated Effluent Limitations Guidelines and Standards for
the Construction and Development Point Source Category (hereafter
referred to as the ``C&D rule'') on December 1, 2009 (74 FR 62995). The
final rule established requirements based on Best Practicable Control
Technology Currently Available, Best Available Technology Economically
Achievable, Best Conventional Pollutant Control Technology, and New
Source Performance Standards based on Best Available Demonstrated
Control Technology.
The rule included non-numeric requirements to:
Implement erosion and sediment controls;
Stabilize soils;
Manage dewatering activities;
Implement pollution prevention measures;
Prohibit certain discharges; and
Utilize surface outlets for discharges from basins and
impoundments.
The December 2009 final rule also established a numeric limitation
on the allowable level of turbidity in discharges from certain
construction sites. The technology basis for the final numeric
limitation was passive treatment controls including polymer-aided
settling to reduce the turbidity in discharges.
Since issuing the final rule, an error in EPA's interpretation of
the data used to establish the numeric limitation was identified in
petitions from the U.S. Small Business Administration and the National
Association of Home Builders (NAHB). Today's notice seeks comment in
the form of data and information on several of the issues raised in the
petitions, as well as other topics.
II. Background
A. NPDES Regulations, Construction General Permits and Applicability of
40 CFR Part 450 Requirements
EPA promulgated the Phase I National Pollutant Discharge
Elimination System (NPDES) stormwater regulations (55 FR 47990) on
November 16, 1990. The Phase I regulations require that dischargers
must apply for and obtain authorization to discharge (or ``permit
coverage''). One of the categories of dischargers that must obtain
permits is discharges associated with construction activity, including
clearing, grading, and excavation, if the construction activity:
Will result in the disturbance of five acres or greater;
or
Will result in the disturbance of less than five acres of
total land area that is a part of a larger common plan of development
or sale if the larger common plan will ultimately disturb five acres or
greater.
See 40 CFR 122.26(b)(14)(x).
The Phase II stormwater regulations, promulgated on December 8,
1999 (64 FR 68722) extended permit coverage to construction activity
that:
Will result in land disturbance of equal to or greater
than one acre and less than five acres; or
Will result in disturbance of less than one acre of total
land area that is part of a larger common plan of development or sale
if the larger common plan will ultimately disturb equal to or greater
than one and less than five acres.
See 40 CFR 122.26(b)(15).
Since 1992, EPA has issued a series of Construction General Permits
(CGPs) that cover areas where EPA is the NPDES permitting authority. At
present, EPA is the permitting authority in four states (Idaho,
Massachusetts, New Hampshire, and New Mexico), the District of
Columbia, Puerto Rico, all other U.S. territories with the exception of
the Virgin Islands, Federal facilities in four states (Colorado,
Delaware, Vermont, and Washington), most Indian lands and other
specifically designated activities in specific states (e.g., oil and
gas activities in Texas and Oklahoma).
In areas where EPA is not the NPDES permitting authority, states
issue general permits for construction activity. Many state permits
contain requirements similar to those contained in the EPA CGP. In
addition, a few state permits contain monitoring requirements and/or
requirements to comply with numeric effluent limitations. For example,
California's, Washington's, Oregon's, Georgia's and Vermont's current
CGPs include discharge monitoring requirements. In addition,
California's current CGP contains numeric effluent limitations for a
subset of construction sites within the State.
EPA issued new regulations at 40 CFR part 450 on December 1, 2009
(the C&D Rule). The C&D Rule applies to all construction stormwater
discharges required to obtain NPDES permit coverage. The C&D rule
applies to the entire country, not just the areas where EPA is the
permitting authority. Any permit issued by a state or EPA after the
effective date of the rule (which was February 1, 2010) must include
the requirements contained in that rule. The requirements include BMPs
but do not include a numeric limitation which was stayed on January 4,
2011.
B. Petitions for Administrative Reconsideration and Petitions for
Review of the Final Construction and Development Regulation in the U.S.
Circuit Court of Appeals for the Seventh Circuit
Following promulgation of the December 2009 final C&D rule, the
Wisconsin Home Builders Association
[[Page 114]]
and the National Association of Home Builders (NAHB) filed petitions
for review in the U.S. Circuit Courts of Appeals for the Fifth,
Seventh, and DC Circuits. The petitions were consolidated in the
Seventh Circuit. Subsequently, the Utility Water Act Group (UWAG) also
filed suit in the Seventh Circuit. On July 8, 2010, the petitioners
filed their briefs.
In April 2010, the Small Business Administration (SBA) filed with
EPA a petition for administrative reconsideration of several technical
aspects of the C&D Rule. SBA identified potential deficiencies with the
dataset that EPA used to support its decision to adopt the numeric
turbidity limitation. In June 2010, the National Association of
Homebuilders also filed a petition for administrative reconsideration
with EPA incorporating by reference SBA's argument regarding the
deficiencies in the data.
C. EPA's Unopposed Motion
On August 12, 2010, EPA filed an unopposed motion with the Court
seeking to hold the litigation in abeyance until February 15, 2012 (see
DCN 70084) and asking the Court to remand the record to EPA and vacate
the numeric limitation portion of the rule. In addition, EPA agreed to
reconsider the numeric limitation and to solicit site-specific
information regarding the applicability of the numeric effluent
limitation to cold weather sites and to small sites that are part of a
larger project.
On August 24, 2010, the Court issued its decision remanding the
matter to the Agency but without vacating the numeric limitation.
Subsequently on September 9, 2010, the petitioners filed an unopposed
motion asking the Court to reinstate the litigation, hold it in
abeyance until February 15, 2012, and vacate the numeric limitation. On
September 20, 2010 the Court reinstated the litigation and held it in
abeyance until February 15, 2012, but did not vacate the numeric
limitation.
D. Stay of the Numeric Limitation
On November 5, 2010, EPA issued a direct final regulation and a
companion proposed regulation to stay the numeric limitation at 40 CFR
450.22 indefinitely. The proposed rule solicited comment due no later
than December 6, 2010. Since no adverse comments were received, the
direct final rule took effect on January 4, 2011.
Since the numeric portion of the rule was stayed, states are no
longer required to incorporate the numeric turbidity limitation and
monitoring requirements found at Sec. 450.22(a) and Sec. 450.22(b).
However, the remainder of the regulation is still in effect and must be
incorporated into newly issued permits. The purpose of this notice is
to solicit new data from the public and request comment on a number of
issues that EPA would like to consider in the context of establishing
numeric effluent limitations for construction site stormwater
discharges.
III. Review of Treatment Data in EPA's Current Dataset
A. Approach To Calculating the December 2009 Turbidity Limitation
The December 2009 C&D rule established a numeric limitation for
discharges of turbidity from construction sites. The final limitation
was set at 280 nephelometric turbidity units (NTU) based on the
application of polymer-aided settling, or passive treatment. The data
used in the derivation of this limitation came from several
construction sites that were using polymer-aided settling in
impoundments or in channel applications. EPA's data represented
treatment at eight separate construction sites located in Washington
State, New York, and North Carolina.
The data used in the calculation of the December 2009 numeric
limitation included data from ponds that were used to pre-treat
stormwater prior to chitosan-enhanced sand filtration (CESF) active
treatment systems (ATS). Data representing the final effluent leaving
CESF had been used in the calculation of the November 28, 2008 proposed
C&D rule numeric limitation (73 FR 72562), which was based on the
performance of full CESF.
EPA considered effluent from the CESF pretreatment ponds as
representing passive treatment, and used some such data in the
calculation of the December 2009 limitation. An integral part of CESF
and ATS is the ability to recirculate pretreated water or effluent from
the filters back to the pretreatment ponds if turbidity levels are
above pre-established thresholds. Although this recirculated water is
above these thresholds, it may be lower in turbidity than the untreated
stormwater entering the ponds, and/or water that is already in the
ponds. The effect of recirculating water that is lower in turbidity
than water contained in the pretreatment ponds would be to reduce the
turbidity of the water in the pretreatment ponds. Concerns have been
raised that such recirculation represents an additional level of
``treatment'' that goes beyond what is otherwise understood as
``passive'' treatment.
B. Passive and Semi-Passive Treatment Dataset
If EPA excludes data from the ATS pretreatment ponds, the remainder
of EPA's passive treatment dataset used in the December 2009 final rule
consists of data from three passive treatment systems. Since
promulgation of this rule, EPA has received additional information and
data from several sources on the performance of passive and semi-
passive treatment approaches. As discussed below, EPA also had
additional data in the record regarding passive treatment that was not
used in calculating the December 2009 final rule. The following
discussion summarizes the information and data that comprise EPA's
currently reviewed dataset of passive and semi-passive treatment that
is available in the docket. EPA continues to receive and review
additional data as it becomes available. EPA may consider these data
and any data submitted during the public comment period and collected
by EPA in a future rulemaking to correct and remove the stay of the
numeric turbidity limitation. Any data that EPA is considering for use
in this rule making will be placed in the public docket once it has
been reviewed.
Steeltown Road and Curley Maple Road, North Carolina (DCN 70018 and
70065). This study evaluated the performance of fiber check dams with
polyacrylamide (PAM) on two mountain roadway projects in North
Carolina. These data were available at the time of the December 2009
final rule, but additional information on sample collection times and
turbidity were submitted to EPA in 2011 (DCN 70065).
Orange County, North Carolina Skimmer Basin (DCN 70034 and 70065).
This paper evaluated a skimmer sediment basin with PAM at an
institutional construction project. These data were available at the
time of the December 2009 final rule, but additional information on
sample collection times and turbidity were submitted to EPA in 2011
(DCN 70065).
Petersburg airport culvert replacement (DCN 70000). This study
demonstrated the performance of two chitosan lactate biopolymer
formulations in removing turbidity from pumped water at the Petersburg,
Alaska airport. Water was semi-passively treated by pumping turbid
water from one of five culvert locations through a cartridge applicator
and then into sediment traps constructed of filter fabric. Additional
treatment was accomplished by allowing the water to exit the trap and
flow through a vegetated area (called a biofilter).
[[Page 115]]
Testing at this site occurred during March and April of 2009. Reported
air temperatures varied between -1.0 and 10 degrees Celsius and
reported water temperatures varied between -0.1 and 1.0 degrees Celsius
during the study, demonstrating the effectiveness of passive treatment
during cold-weather conditions. The study did note that chitosan
lactate dissolution rates were slower due to the cold temperatures. The
study noted that average daily turbidity of discharge from the sediment
trap was 248 NTU, and discharge from the biofilter was 102 NTU.
Influent turbidities were reported as high as approximately 5,000 NTU.
In order to overcome the slower dissolution rate of the chitosan
lactate due to the cold temperatures, additional cartridges were
installed in order to deliver the appropriate dosage. In addition, the
vendor indicated that a new formulation has been developed that
dissolves at a higher rate specifically for use in colder climates.
This report also provides diagrams showing various forms of passive and
semi-passive dosing that have been developed. Additional references
describing this project are also included in the docket (see DCNs 70001
and 70002). EPA requests comment on whether this dataset should be
considered representative of the BAT technology as described in the
2009 final rule.
Water Quality Improvements Using Modified Sediment Control Systems
on Construction Sites (DCN 70063). This research project studied three
types of sediment capture and treatment systems at a highway
construction project (I-485) between 2003 and 2006 in North Carolina.
The first type of system consisted of unlined diversion ditches with
rock check dams leading to a standard sediment trap with a rock dam
outlet. The second type of system added a forebay, porous baffles and
PAM treatment in the diversion ditches and the forebay. The third type
of system tested was the same design as the second system except the
rock check dam was replaced with a floating outlet or skimmer. The
author reported that the three sediment trapping systems with
modifications including forebays, porous baffles, ditch lining, and PAM
application had storm weighted average turbidity and peak turbidity of
990 and 1,580 NTU, respectively.
North Carolina State University Typar[reg] Field Test (DCN 70003).
North Carolina State University (NCSU) conducted a field test of the
Typar[reg] geotextile product at the university's field laboratory. The
study evaluated the performance of the material in an in-channel
application. The tests incorporated polyacrylamide to aid in sediment
removal. Both total suspended solids and turbidity were evaluated. The
study evaluated varying flow rates as well as varying sediment loading
rates. The report contains a considerable amount of data. The report
indicates that the system is expected to meet a 280 NTU limitation, but
points out that field testing outside of the field laboratory setting,
where turbidity and total suspended solids (TSS) levels may be higher,
would provide additional insights into performance.
Other Research at North Carolina State University (DCN 70004).
Researchers at NCSU have conducted research on a number of passive and
semi-passive treatment approaches. Examples include fiber check dams
with PAM, sediment basins and traps with PAM, PAM applied to erosion
control matting down a slope, PAM application in pipes and geotextile
filter bags with PAM. DCN 70004 contains data from a number of
evaluations. Additional data on one of the projects identified in DCN
70004 is also presented in DCN 70053--70060 and 70062.
North Carolina Department of Transportation (NCDOT) (DCN 70005,
70006). NCDOT conducted a demonstration to evaluate the performance of
a dual biopolymer system in removing turbidity. In this application,
water from culvert sites and caissons at bridge construction sites that
was impounded in a baffled skimmer basin was pumped through a manifold
containing biopolymers. The biopolymers dissolve as water is pumped
through the manifold, and mixing occurs in the manifold, which aids
flocculation. The water then passes through a geotextile filter bag,
which retains the flocculated solids. In this demonstration, turbidity
in the water from the basin was 1,283 NTU, which was reduced to below
100 NTU following the filter bag.
StormKlear[reg] (DCN 70007 through 70013 and 70070 through 70080).
StormKlear[reg]/HaloSource[reg] provided information regarding a number
of sites using both passive and semi-passive dosing of a dual
biopolymer system. Sites described were Annapolis, Maryland (DCN
70007), Austin, Texas (DCN 70008), Beaverton, Oregon (DCN 70009),
Griffin, Georgia (DCN 70010), Raleigh, North Carolina (DCN 70011),
Memphis, Tennessee (DCN 70011), Jacksonville, North Carolina (DCN
70011), Birmingham, Alabama (DCN 70011), Tampa, Florida (DCN 70012),
Tennessee (DCN 70013), Huntersville, North Carolina (DCN 70070),
Hanover, Maryland (DCN 70071), Apex, North Carolina (DCN 70072), Bonita
Springs, Florida (DCN 70073), Staten Island, New York (DCN 70074),
Cabarrus County, North Carolina (DCN 70075), Anne Arundel County,
Maryland (DCN 70076), Cartersville, Georgia (DCN 70077), Central, South
Carolina (DCN 70078), Fairview, North Carolina (DCN 70079) and Lavonia,
Georgia (DCN 70080). The range of turbidity values reported at these
sites is presented in Table 1.
Table 1--Range of Turbidity Values Reported in Dual Biopolymer Field Trials
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Site Untreated NTU Treated NTU
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Annapolis, MD......................... 300-400............................ 15.
Austin, TX............................ 598................................ 10.5-117.
Beaverton, OR......................... 42-44.............................. 14.
Griffin, GA........................... 2,189.............................. 21.1-433.
Raleigh, NC........................... 2,500-3,000........................ 14.
Memphis, TN........................... 1,200.............................. 20.
Jacksonville, NC...................... 300................................ 15.
Birmingham, AL........................ 1,500.............................. 20.
Tampa, FL............................. Not Reported....................... <1.
Huntersville, NC...................... 950................................ 425.
Hanover, MD........................... 570................................ <50.
Apex, NC.............................. 3,787.............................. 297 (1.4 after basin).
Bonita Springs, FL.................... 162-187............................ 3.2-43.
Staten Island, NY..................... 1,057.............................. 5-45.
Cabarrus County, NC................... 1,195.............................. 42.
[[Page 116]]
Anne Arundel County, MD............... 547................................ 120.
Cartersville, GA...................... >4,000............................. 51.
Central, SC........................... 687................................ 32.
Fairview, NC.......................... >4,000............................. 731 (131 after basin).
Lavonia, GA........................... >4,000............................. 32.8.
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ALPURT B2 Motorway Construction Project (DCN 70049). The Auckland,
New Zealand Regional Council evaluated the use of polyaluminum chloride
(PAC) to reduce sediment discharges from a motorway construction
project. A rainfall-activated dosing system was used to deliver PAC
prior to settling in a sediment basin. Samples were analyzed for TSS,
particle size distribution and dissolved aluminum. This study did not
evaluate reductions in turbidity.
ALPURT and Greenhihte Trials (DCN 70067). The Auckland, New Zealand
Regional Council conducted trials using alum, PAC and PAM at several
sites. The study evaluated both rainfall-activated liquid chemical
dosing systems as well as solid forms. This study evaluated reductions
in TSS, but not turbidity.
Bluffs Community Baffle Grid System (DCN 70050). This project,
located in the metropolitan Atlanta, Georgia area, was a residential
construction project. A passive treatment system was utilized
consisting of a grit pit followed by a polymer mixing chamber. The
water then flowed into another grit pit and then into a baffle grid
system. Polymer was dosed using polymer floc logs. Polymer was also
applied to exposed soils up-slope of the treatment system. This system
produced an average treated turbidity of 18 NTU, according to the study
authors. The attached data file shows a range of turbidity after the
baffle grid ranging from 1.0 to 703 NTU.
Cleveland Municipal Airport, Cleveland, Tennessee (DCN 70085). This
site is a multi-year construction project that started in 2009. The
site utilizes passive treatment including ditches lined with jute
matting with PAM and sediment basins. Monitoring is conducted after the
sediment basins as well as in-stream both upstream and downstream of
the construction site. Only limited monitoring data was available for
this site. The turbidity reported in effluent at the outfalls after
implementation of the PAM treatment ranged from 23 to 280 NTU.
C. Additional Data
At the time of this notice, only one state (California) has a
numeric effluent limitation for discharges from construction activities
that applies to a subset of construction sites statewide. Other sites
in the state are subject to monitoring requirements and action
levels.\1\ Between July 1, 2010 and June 20, 2011, permittees reported
735 daily average turbidity values. The range of these daily average
turbidity values was zero to 1,572 NTU with a median value of 42 NTU
(see DCN 70051). EPA did not obtain information about the individual
sites and treatment systems (such as detailed site plans, SWPPPs,
etc.), and has not evaluated the utility of this data in the context of
establishing effluent guidelines. EPA has not evaluated whether any of
these facilities were subject to numeric discharge standards for
turbidity.
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\1\ In December 2011, the California Superior Court invalidated
the California numeric standard of 500 NTU, which applied to a
subset of construction projects, because the state did not evaluate
performance data from available technologies under a variety of site
conditions. Construction projects subject to the standard did not
have ``reasonable assurance that the technologies are capable of
achieving the turbidity NEL (numeric technology based effluent
limitation).'' Decision at 16; California Building Industry
Association v. State Water Resources Control Board, Case No. 34-
2009-800000338 (Sacramento Superior Court) December 2, 2011. See DCN
70086.
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As described in the December 2009 final rule preamble, Warner et
al. evaluated several innovative erosion and sediment controls at a
full-scale demonstration site in Georgia. In this project, polymers or
flocculants were not utilized, but instead a comprehensive system of
erosion and sediment controls were designed and implemented to mimic
pre-developed peak flow and runoff volumes with respect to both
quantity and duration. The system included perimeter controls that were
designed to discharge through multiple outlets to a riparian buffer,
elongated sediment controls (called seep berms) designed to contain
runoff volume from 3- to 4-inch storms and slowly discharge to down-
gradient areas, multi-chambered sediment basins designed with a siphon
outlet that discharged to a sand filter, and various other controls.
Monitoring conducted at the site illustrates the effectiveness of these
controls. For one particularly intense storm event of 1.04 inches (0.7
inches of which occurred during one 27-minute period), the peak
sediment concentration monitored prior to the basin was 160,000 mg/L of
TSS while the peak concentration discharged from the passive sand
filter \2\ after the basin was 168 mg/L. Effluent turbidity values
ranged from approximately 30 to 80 NTU. Using computer modeling, it was
shown that discharge from the sand filter, which flowed to a riparian
buffer, was completely infiltrated for this event. Thus, no sediment
was discharged to waters of the state from the sand filter for this
event. For another storm event, a 25-hour rainfall event of 3.7 inches
occurred over a two-day period. Effluent turbidity from one passive
sand filter during this storm ranged from approximately 50 to 375 NTU,
with 20 of the 24 data points below 200 NTU. For a second passive sand
filter, effluent turbidity ranged from approximately 50 to 330 NTU,
with nine of 11 data points below 200 NTU. In the Warner et al. study
low levels of turbidity in discharges were achieved without relying on
chemical flocculants or polymers or pumping of water. Although these
data were available to EPA at the time, EPA did not use the Warner et
al. data in calculating the limitation contained in the December 2009
final rule because the site did not use polymers. EPA requests comment
on whether the Warner et al. data, data from passive sand filters in
general as described by Warner et al., and data from sites not using
polymers or flocculants should be used in evaluating the feasibility of
a numeric effluent limitation and whether these data should be
considered representative of
[[Page 117]]
the BAT technology as described in the 2009 final rule.
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\2\ The term ``passive sand filter'' in this context is used to
describe an in-ground filter constructed by placing sand and gravel
into an excavated area. The filter receives surface discharge from
up-slope sediment controls which is distributed across the filter
surface using distribution pipes. Water flows down through the
filter bed and is collected by an underdrain system where it is
conveyed down-slope. All flow in this application is by gravity. The
system did not incorporate any pumps or any treatment chemicals. A
passive sand filter differs from the sand filters which are used as
part of CESF, which are operated by a programmable logic controller
or onsite personnel, are pressurized and operate at much higher
flowrates, among other differences.
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IV. Solicitation of Data and Comments on Numeric Effluent Limitations
for Turbidity
The following presents the issues and areas where EPA is soliciting
feedback, data and information.
A. Control of Turbidity--Effectiveness, Costs and Feasibility of
Different Technologies
On November 28, 2008 EPA issued a proposed rule that would have
established a numeric effluent limitation for turbidity based on the
application of what is termed active or advanced treatment, or ATS,
specifically chitosan-enhanced sand filtration (CESF). ATS consists of
a variety of technologies, the two most prevalent being CESF and
electrocoagulation. The basic premise behind CESF is to collect the
stormwater in a pond or basin, withdraw the water from the basin (using
pumps), add a treatment chemical (in this case chitosan, although the
technology is adaptable to other treatment chemicals), and remove the
flocculated solids using filtration. Pretreatment with a treatment
chemical (such as chitosan) is frequently used to reduce the turbidity
of the stormwater withdrawn from the pond or basin to a range that will
allow for efficient filtration. This is frequently done in dedicated
pretreatment cells or tanks, but the configuration can depend on
requirements specified by the regulatory agency or the operator. CESF
typically incorporates a programmable logic controller to monitor
turbidity and pH of the treated water continuously or during some
specified time interval, and valves can be actuated automatically by
the controller to recycle the treated water back to the pretreatment
cells or storage pond if the discharge does not meet pre-established
thresholds. Electrocoagulation does not use a polymer or treatment
chemical, but rather uses an electrical process to destabilize the
particles. Agglomerated particles are removed by settling and/or
filtration. ATS, based on information available to EPA on the
performance of CESF, appears capable of producing very low turbidity
(generally less than 50 NTU, and in many cases less than 5 NTU) in
treated stormwater from construction sites. Performance can be further
enhanced by polishing the filtered water in bag or cartridge filters.
EPA requests comment on this description of ATS.
Costs for ATS systems include equipment rental (pumps, filters,
generators and control equipment), fuel, chemicals, labor, management
of residuals, piping, and miscellaneous consumables (residual polymer
test kits, filtration media, etc.) and data management and reporting. A
stabilized area (such as a gravel pad) may be necessary in some cases.
In colder climates, consideration of measures to prevent freezing of
equipment may also be necessary. The requirement to store water in
ponds and to pretreat water can add costs. Also, managing dewatering of
a series of large impoundments on some sites may be complicated,
particularly during extended periods of precipitation. The costs of
large ponds may be offset to some extent if they are converted to post-
construction stormwater water-quality or flood-control ponds. This is
frequently accomplished by removing the accumulated sediment captured
during the construction phase and altering the outlet structure of the
basin to achieve the water quality and peak discharge rate control
desired for the post-developed condition. This can result in
considerable cost savings for the post-construction ponds, since
significant costs are associated with excavation of the basins.
However, recent trends toward use of decentralized stormwater
management may be a disincentive toward utilizing large ponds (although
the need for flood control ponds and ponds to control stream channel
erosion may still exist). Practices such as bioretention, porous
pavement, infiltration systems and harvest and use systems may replace,
to some extent, centralized conveyance and stormwater detention and
retention ponds. However, if decentralized controls are used for
postconstruction stormwater management, then basins used during the
construction phase may not need to be converted for post-construction
use. In these cases, the construction phase basins may need to be
filled in, at additional expense to the developer. In some instances,
this may provide space where additional structures, parking or other
amenities can be placed, which may provide a benefit to the developer.
Passive treatment systems (PTS) in the context of construction site
stormwater management are practices that do not rely on computerized
systems with pumps, filters and real-time controls but do incorporate a
treatment chemical to aid in sediment and turbidity removal. Passive
treatment could include pumps where they are necessary to move water
around the construction site, and pumping may be integral to properly
dosing the water with treatment chemicals in some cases. When pumps are
utilized to pump the water through a manifold or other apparatus to
dose the chemical, this type of treatment has been characterized by the
industry as semi-passive treatment. In passive treatment, polymer can
be placed in channels that convey water on the construction site, or
they may be used prior to basins or other practices (such as a baffle-
grid, in-ground sand filter or a geotextile filter bag) that allow for
settling and/or filtration of the flocculated material. Treatment
chemicals, either in solid or liquid forms, can be applied at various
locations on the site. Common PTS include fiber check dams with PAM and
sediment basins dosed with PAM as described by McLaughlin (see DCNs
70018, 70034 and 70063). The Auckland, New Zealand Regional Council
also described a PTS that utilized a rainfall-actuated system to
deliver liquid chemical (see DCN 70049 and 70067). Minton (see DCN
70069) described a ``pump and treat'' system whereby water was pumped
from a basin, a treatment chemical was added, and the water was allowed
to settle in dedicated treatment cells. Water can be re-circulated with
the pump and additional chemical added if the settled water does not
meet specifications. As stated above, the term semi-passive treatment
has been used to describe practices that utilize pumped water to dose
the chemical, or applications where the water is first held in a basin
or other impoundment and withdrawn under more controlled conditions for
subsequent treatment. Recent improvements to PTS incorporate the use of
two polymers (see DCNs 70006-70013, 70070-70080), which can be placed
in a manifold or in a channel. The use of baffles and floating outlets
or ``skimmers'' on basins are frequently incorporated as part of PTS,
and directing treated water to vegetated areas or ``biofilters'' can
also provide additional sediment and turbidity removal prior to
discharge. EPA requests comment on these descriptions of ``passive''
and ``semi-passive'' treatment systems and comments on what practices
should be considered representative of the BAT technology as described
in the 2009 final rule.
The performance of PTS varies based on the type of system, the
method used to dose chemicals, as well as other factors. The
performance of simple PTS appears to be sensitive to the type and
frequency of maintenance and system configuration, as well as the
intensity and duration of storm events. An advantage of simple PTS,
such as fiber check dams w/PAM, is that they are
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very inexpensive and can be easily incorporated into sites at multiple
locations and do not require large ponds for storage prior to
treatment. A disadvantage may be that achieving a consistent level of
performance may be more difficult due to variations in storm flows and
sediment loads and little control over dosage rates. The data available
to EPA does show high levels of turbidity in discharges for some
events, indicating that simple passive treatment systems may not
perform well during larger and/or more intense storm events. Data
collected at a construction site in North Carolina that used passive
treatment measured peak turbidity in excess of 40,000 NTU during an
intense storm event (see DCN 70064.3).
Semi-passive approaches, which first hold the water in a basin,
tank or impoundment and then release water either by gravity or with a
pump to provide dosing, appear to be capable of providing lower, and
perhaps more consistent, turbidity levels due to dampening of the storm
flows by the basins. An advantage of semi-passive approaches is that
since the water is withdrawn by pumping (although semi-passive dosing
can be accomplished using gravity flow in certain cases), flowrates and
dosing rates can be more easily controlled, allowing for more
consistent and likely better performance. Since the water is withdrawn
from the storage pond and dosed at a more controlled rate, the large
variability and poorer performance that may occur under some
precipitation conditions with simple passive treatment can potentially
be avoided. A disadvantage may be that the stormwater must first be
stored in ponds, tanks or other impoundments in order to provide a
controlled release. As with ATS, these storage requirements can add
costs and additional operational considerations to address,
particularly during extended periods of precipitation. As described
earlier, these costs may be offset to some extent depending on the
nature of post-construction stormwater requirements in place.
An integral component of ATS and PTS is the use of a treatment
chemical to aid in removal of sediment and turbidity. However, data
presented by Warner and Collins-Camargo (see DCN 70052) indicates that
a comprehensive suite of erosion and sediment controls is also capable
of producing treated stormwater with low levels of turbidity. EPA has
little data on which to base a numeric limitation on these types of
practices as this level of management does not appear to be typical at
most construction sites.
EPA is soliciting data and information on the costs, effectiveness
and feasibility of different technologies to control TSS, settleable
solids, suspended sediment concentration and turbidity in construction
site stormwater discharges. EPA is also soliciting data on other water
quality parameters, such as pH, nutrients and metals. EPA is especially
interested in receiving data on the performance of passive and semi-
passive treatment approaches. Data collected both before the treatment
or management practice (influent data) as well as data after the
treatment or practice (effluent concentration) would be useful. EPA
already has a large dataset on the performance of ATS in removing
turbidity, but additional data on the costs of ATS would potentially be
useful to EPA. To be most useful, EPA requests that treatment
performance data represent multiple discharge events, that samples are
collected over regular intervals over the course of the event (or the
discharge), and that the data contain, if available, the following
descriptive information:
Site information, such as project size, project type
(residential, commercial, road/highway, etc.), location, phase of
construction (e.g., before, during or after grading, site
stabilization, etc), etc.;
Sample date(s) and time(s) of collection and date(s) and
time(s) of analysis;
Sample type (grab sample, flow or time-weighted composite,
continuous turbidity measurement, etc.);
Analytical method and/or type of field instrument used to
measure the parameter; and
Description of the treatment technology, including method
of treatment chemical dosing utilized.
Additional information that would be useful in evaluating these
data includes:
Estimates of the amount and intensity of precipitation for
the time preceding and/or during sampling events;
Drainage characteristics (predominant soil types/textures,
drainage area, estimate of the quantity or percent of the drainage area
that is disturbed);
The ambient air temperature when the data is being
collected;
Date of last calibration if a field instrument was used;
and
Descriptions of any quality assurance/quality control
procedures implemented for the data collection activity.
In order to be most useful, data on costs should include:
Installation costs (both material and labor);
Operation and maintenance burden (in terms of labor hours
and/or costs);
Quantity, cost and frequency of treatment chemical use;
and
Other costs (residuals management, consumables, energy
use, etc.).
EPA requests comment on other factors EPA should consider other
that those listed above in evaluating treatment performance data and
what metadata commenters consider important to consider in the context
of establishing effluent limitations.
B. Sampling and Data Collection--Procedures and Protocols To Ensure
Representativeness of Data; Differences in Analytical Equipment
EPA is aware that there are several issues associated with
collecting turbidity data in the field at construction sites. These
issues are associated with sampling equipment limitations, turbidimeter
limitations, differences between turbidity measuring equipment, and
sample handling and analysis. The following discussion presents
information that EPA is aware of with respect to these issues and
solicits data and comment on these issues. These issues relate both to
collecting samples for the purposes of establishing effluent
limitations as well as collecting samples for compliance determination.
Sampling Equipment Limitations
Collecting samples of stormwater at construction sites can be
accomplished using either automated equipment or by collecting grab
samples. Automated equipment typically requires the use of a flow
measuring device and an automated sampler. Flow measurement devices
require that a weir, flume or other structure be installed in the
conveyance that has a known rating curve (discharge vs. flow depth), or
that a custom rating curve be developed for open channels based on
surveyed channel geometry that can be used to estimate flow as a
function of depth of water. Automated samplers can be set up to collect
samples after a predetermined amount of flow has passed through the
measuring device (flow-weighted) or after a predetermined amount of
time has passed (time-weighted). In either case, the sample collection
interval must be selected such that sufficient samples are collected
over the course of the hydrograph to adequately characterize the
discharge. This is frequently difficult, as it is not known in advance
how much precipitation and flow will occur. If the sample collection
interval is set too low, then the sampler may fill up before the end of
the event. In this
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case, a portion of the hydrograph may not be sampled. If the interval
is set too high, then too few samples may be collected to adequately
characterize the event. Given the variability in stormwater flows, this
may make the use of automated sampling challenging.
Grab samples are easier to collect than automated samples. However,
collecting grab samples requires that someone be physically present on
the site. Given the variable nature of storm events and that those
events can occur during all hours of the day, collecting grab samples
to characterize performance can also be challenging. This is
particularly true when the site is not located in close proximity to
field offices of the sampling personnel.
In the context of characterizing performance for establishing
effluent limitations, both grab samples and automated samples are
potentially useful. Generally, EPA believes that samples used to
characterize performance should be collected regularly over the course
of the event in order to capture variability in flows and associated
pollutant parameters. This is particularly true in the case of passive
treatment, which does not involve capture of the water in a pond or
basin for controlled release, so that one would expect greater
variability in sampled parameters. For treatment of water discharged in
a controlled rate from a pond, one would expect less variability in
flows and performance, so less frequent sample collection would likely
be necessary in order to adequately characterize performance.
Turbidimeter Limitations
Samples collected for turbidity can be measured in the field using
a hand-held turbidimeter, or can be sent to a laboratory for analysis
using a benchtop turbidimeter. Both methods are simple and inexpensive.
However, turbidimeters only operate within specific ranges. The high-
end of the range is typically around 1,000 NTU or more. Samples with
high amounts of turbidity may need to be diluted in order for the
turbidity of the sample to be within the operating range of the
instrument. This is a potential source of error, especially if done in
the field. Another method for measuring turbidity is to use an in-situ
meter coupled to a datalogger. In-situ meters can be programmed to
record turbidity continuously at some specified time interval (such as
every 15 minutes). As with other instruments, in-situ turbidimeters
typically operate within a specific range. With these instruments,
turbidity above the measurement range of the instrument cannot be
determined, since a physical sample is not collected. This is a
potential source of error, particularly during periods of peak flows
where turbidity may be very high. This is a downside of in-situ meters
because an average turbidity for an event cannot be determined if some
of the data exceeds the measurement range of the instrument. In these
cases, the use of both an in-situ meter as well as collection of a
physical sample during peak flow periods may be necessary to accurately
determine the average turbidity for the event. In-situ meters are also
susceptible to failure, such as from battery failure or a piece of
debris obscuring the detector.
Different types of turbidimeters may provide different measurements
of turbidity for the same sample. This is due to differences in light
sources and differences in the orientation of the light source with
respect to the detector. In addition, while turbidity measured in NTUs
is the standard contained in EPA's methods, turbidity can also be
measured in other units, such as formazin turbidity units (FTUs). While
EPA believes that NTUs are the appropriate units in the context of
effluent limitations for construction site stormwater, EPA solicits
comments on the types of equipment that should be allowable and other
considerations related to differences in measurement equipment and
measurement units.
Sample Handling and Analysis
EPA notes that some of the data in EPA's dataset did not follow the
sample preservation protocols contained in EPA's approved analytical
methods. EPA method 180.1 states that turbidity samples should be
immediately refrigerated or iced to 4[deg]C and analyzed within 48
hours. EPA is aware that many of the samples collected by researchers
at North Carolina State University and described in DCNs 70004, 70018,
70034, 70053, 70054 and 70065 were collected using automated samplers,
and that the samples were not analyzed within 48 hours or refrigerated
or iced. In many instances, samples were analyzed several days or weeks
after collection. While EPA notes the deviation from approved methods,
EPA does not believe that this deviation would produce appreciable
changes in measured turbidity in these cases. The sample refrigeration
and analytical timeframe guidelines are intended to minimize changes in
turbidity that would result due to microbial decomposition of solids in
the sample. Since EPA expects little organic material to be present in
samples of stormwater runoff from construction sites since the solids
are primarily composed of inert soil particles, EPA would not expect
biological activity to appreciably change the turbidity of the samples.
EPA does note that since these samples incorporated polyacrylamides,
some additional flocculation could occur in the sample bottles during
the time period between collection and analysis or during transport
from the field to the laboratory, if residual or un-bound
polyacrylamide was present in the sample. EPA solicits comment on the
appropriateness of using data from samples not analyzed within 48 hours
or otherwise not in compliance with established analytical methods in
the context of a future regulation.
EPA also notes that the samples collected by researchers at North
Carolina State University were allowed to settle for approximately 30
seconds after mixing before a subsample was collected and analyzed for
turbidity. EPA understands that this 30-second settling period after
mixing was to allow large flocculated particles to settle, since
analyzing turbidity of a sample that contains large agglomerates may
prevent the turbidity meter from producing a stable reading or may
underestimate turbidity of the sample. The EPA approved sampling method
does not describe an appropriate period of time between mixing of the
sample bottle and collection of the subsample for analysis. As
described in EPA's method 180.1 for measuring turbidity, the approved
analytical procedure is ``Mix the sample to thoroughly disperse the
solids. Wait until air bubbles disappear then pour the sample into the
turbidimeter tube. Read the turbidity directly from the instrument
scale or from the appropriate calibration curve.'' (see DCN 70083), The
method states that ``The presence of floating debris and coarse
sediments which settle out rapidly will give low readings. Finely
divided air bubbles can cause high readings.'' Floating debris and
course sediments and finely divided air bubbles are therefore
considered sources of interference when measuring turbidity. The
practice utilized by researchers at North Carolina State University of
allowing mixed sample bottles to sit for 30 seconds before collecting
the subsample for analysis, which would allow any course sediments to
settle, may be an appropriate means of addressing possible
interferences due to the presence of large particles. EPA also
acknowledges that allowing the sample to settle prior to collecting the
subsample for analysis may result in fewer particles generally being
present in the subsample and thus an artificially low turbidity
reading. EPA solicits
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comment on the appropriateness of using turbidity data where a sample
was allowed to settle for 30 seconds (or some other time period) after
mixing before collection of the subsample for analysis for purposes of
evaluating the performance of technologies and for compliance purposes
and the expected magnitude of the effects of varying settling time on
observed turbidity values.
EPA understands that the subsamples for TSS were collected by the
researchers and analyzed immediately after mixing. As a result, there
are certain cases where particular samples in these data had TSS
concentrations (in mg/L) that would appear inconsistent when compared
to the corresponding turbidity measurements (in NTU) since the large
particles could be present in the TSS subsample. EPA notes that the
ratios of TSS to turbidity for some samples are much higher than for
other samples, which EPA believes can be attributed to the 30-second
settling time prior to collection of the turbidity subsample. EPA
welcomes comments on this topic.
In the context of compliance demonstration, the specifics of a
particular site (such as the location of the site, the number of
discharge points, proximity of discharge points, accessibility of
discharge points, etc.) are important considerations in determining the
type of sample to be collected. Generally, both automated samples and
grab samples are potentially useful for compliance determinations.
However, the inherent limitations with sampling equipment and equipment
malfunctions may be important considerations. With grab samples,
equipment limitations and equipment malfunctions are not of concern.
EPA solicits comment on the appropriate methods for sample
collection in the context of both compliance sampling and analytical
sampling for the purpose of setting limits for a turbidity effluent
limitation for construction site stormwater discharges. EPA recognizes
that logistics and cost are important considerations, and would like to
better understand the potential costs and challenges of sample
collection and analysis in these cases.
C. Effect of Storm Size, Intensity and Duration of Precipitation on
Performance of Passive Treatment
In establishing effluent guidelines and new source performance
standards, proper operation of the candidate best available technology
economically achievable (BAT) and best available demonstrated control
technology (BADCT) should result in meeting the numeric limitation a
very high percentage of the time. In the case of industrial wastewater,
treatment systems typically perform well within a range of flowrates
and influent pollutant concentrations, and systems typically operate
within these ranges. Due to variations in manufacturing production
cycles, the flowrates and pollutant concentrations in wastewater can
vary over the course of a day. Industrial wastewater treatment systems
typically incorporate equalization to dampen these diurnal variations
in flowrates and pollutant concentrations. This dampening assures that
high flows and/or pollutant loads do not overwhelm the treatment
system, or that low flows and/or pollutant loads do not compromise unit
processes.
This same concept applies to stormwater treatment. Since
precipitation is a stochastic process, there can be variation in
stormwater flowrates and sediment loads during the course of a given
precipitation event. Data available to EPA indicates that passive
treatment with limited storage may perform well for some storm events,
but that larger and/or more intense storm events may degrade the
performance of these systems. The likely reasons for a decrease in
performance include inadequate treatment chemical dosing during periods
of higher flows, exhausting the treatment chemical during larger and/or
longer storm events, high sediment loads during intense periods of
precipitation that overwhelm the systems, and short-circuiting/
overtopping of controls. These occurrences are difficult to address as
they occur on construction sites in the context of passive treatment,
which is not based on a high level of operator involvement.
A potential shortcoming of EPA's current dataset on passive
treatment is that much of the data was collected during smaller storm
events. EPA has little data available on the performance of this type
of flow-through passive treatment during larger and/or more intense
storm events, but the limited data available indicate that the
performance of simple passive treatment approaches may not be as good
for these events. The candidate BAT/BADCT should be capable of meeting
the limitation up to whatever cutoff is established for the limitation.
In the 2009 rule, the compliance storm event was the 2-year, 24-hour
storm event (see Section IV.D for additional discussion of storm event
exemptions).
EPA does not expect this concern to arise with treatment that first
holds the water in a pond, basin or impoundment. Impounding the water
has two primary benefits for subsequent treatment--equalization of
flows and reduction/dampening of sediment/turbidity levels. The amount
of sediment and turbidity mobilized during a storm event can vary
greatly, depending on factors such as storm intensity, storm duration,
soil type and composition, slopes of the contributing watershed, extent
of soils exposed, and the extent and nature of construction activities
occurring. When water is held in a basin, a significant portion of the
settleable materials would be expected to be removed. When water is
withdrawn for subsequent treatment, one would expect much lower
variability in the amount of turbidity over the course of the treatment
period.
D. Exemptions--Design Storm Depth vs. Intensity
The December 2009 final rule exempted discharges from compliance
with the turbidity limitation on days where precipitation exceeded the
local 2-year, 24-hour storm depth. The rationale for this exemption was
that large storm events would potentially overwhelm the passive
treatment systems, making compliance with the limitation difficult. If
an impoundment is used to store water prior to treatment, a total storm
depth may be an appropriate compliance threshold since impoundments are
typically designed to store a certain quantity of water. Runoff in
excess of that volume would either bypass storage or be discharged
through an overflow riser or over a spillway. However, both storm depth
and storm intensity may be important drivers for system performance and
appropriate compliance thresholds for simple in-line passive treatment
systems. Total storm depth (and the total volume of stormwater passing
through the passive treatment system) is an important driver of
performance because the amount of treatment chemical available in a
simple passive treatment application is limited (unless more is applied
during the event). At some point, available treatment chemical may be
exhausted and treatment performance would be expected to decline. Storm
intensity may be a much more important driver of performance of in-line
simple passive systems than storm depth. During high intensity rainfall
periods, which occur frequently in many parts of the country, sediment
detachment and mobilization can be significant due to the high energy
of the raindrops. This high level of sediment mobilization, coupled
with flashy flows through conveyances, can deposit large quantities of
sediment in passive treatment systems and flowrates
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can exceed the dosing capacity of these simple systems. Therefore, EPA
solicits data indicating what critical storm intensity would render
simple passive treatment systems ineffective. In addition, any
compliance threshold tied to storm intensity would optimally specify
both storm intensity as well as a duration over which that storm
occurs. For example, a storm may have a peak five-minute intensity of
two inches per hour, but if the storm only lasted for five minutes,
then the total amount of runoff would be small. In addition, optimally,
EPA would specify how long after the intensity threshold has been
exceeded the site would qualify for an exemption from the limitation
(e.g., for the rest of the day, only during the period when the peak
storm intensity had been exceeded, for one hour after the peak storm
intensity had been exceeded, etc.). EPA solicits data and information
on what would be appropriate exemption criteria.
With semi-passive or ATS approaches, storm intensity would likely
not be as critical, given that the water is first held in a basin or
impoundment. Therefore, an exemption based on total storm depth may be
appropriate, since the standard could specify a storage volume and a
drawdown time (e.g., basins must be sized to store runoff from the 2-
year, 24-hour storm and the treatment system sized to dewater the
entire storage volume in 48 hours). Any flow going over the riser or
emergency spillway during that time period could be exempt from the
limitation.
E. Use of Treatment Chemicals, Disposal and Toxicity Concerns
ATS, passive and semi-passive treatment practices on construction
sites utilize a variety of treatment chemicals. Common treatment
chemicals include chitosan, polyacrylamides (PAM), alum, polyaluminum
chloride (PAC), diallydimethyl-ammonium chloride (DADMAC) and gypsum.
These chemicals are used to help destabilize and flocculate soil
particles, allowing for removal by filtration, adhesion or settling.
Additional chemicals may be used to adjust pH or other water chemistry
parameters. Treatment chemicals in use on construction sites have
varying toxicity profiles. EPA has limited data on acute and chronic
toxicity of these treatment chemicals in the context of their use to
treat construction site stormwater; however it is generally known that
unbound cationic chemicals can exhibit mechanical lethality to some
species in some instances. The degree of toxicity of any treatment
chemical is a function of the organism, chemical formulation, charge
density, dose rate, exposure time, and degree of sediment/turbidity in
the receiving environment. Some states have approved specific chemicals
and formulations for use on construction sites. Some stakeholders
raised concerns about the toxicity of the treatment chemicals in
comments received on the November 2008 proposed rule. EPA is also aware
that some states do not currently allow addition of any treatment
chemicals to stormwater on construction sites. In these cases, it is
unclear how permittees would comply with a numeric limitation, although
as stated earlier, a comprehensive suite of conventional practices was
demonstrated to produce low turbidity in discharges at the project
described in Warner et al.
As mentioned above, stakeholders have raised concerns regarding
acute and chronic aquatic toxicity effects due to the use of chemicals
in treatment of construction site stormwater. The concerns are related
to the lack of control of dosage rates in passive treatment, operator
error in passive, semi-passive and ATS applications, and other
accidental or unintended releases. Anionic granular and water-based
PAMs that are used in surface water treatment applications (such as for
managing construction site stormwater and in agricultural applications)
are generally considered to have a low toxicity profile when used
appropriately and within established dosing ranges (see DCN 70081).
Oil-based PAM and cationic PAM are known to exhibit acute and chronic
aquatic toxicity. The Auckland, New Zealand Regional Council evaluated
the ecotoxicological and environmental risk of polyelectrolytes and
inorganic aluminum salts (see DCN 70082) and found that ``there appears
to be a small risk to the natural aquatic environment arising from
potential losses of unbound residual flocculants from treatment ponds
on construction sites. Impacts are likely to be low level and also
likely to not be significant in relation to other factors which govern
the health of aquatic communities. The benefit of reduced sediment
levels in discharges is considered to outweigh the risk of any low
level impacts attributable to residual flocculants.''
There are also concerns related to flocculated material containing
polymers or other treatment chemicals that may pass through passive or
semi-passive treatment systems. Anecdotal information indicates that
PAM bound to soil particles may be discharged to receiving waters in
certain cases in simple passive treatment systems, either due to the
flocculated material not being removed by the practice or previously-
removed material being re-suspended during subsequent storm events. It
is unclear what, if any, downstream effects may be attributable to
these discharges, as sediment-bound PAM is thought to have limited
bioavailability (see DCN 70081). It is also unclear how any detrimental
effects due to discharged chemical would compare to the detrimental
effects of the additional sediment and turbidity that would be
discharged had the chemical not been used. Additional concerns have
been raised regarding the disposal of treatment residuals, which
consist of sediment bound with treatment chemicals. Common practice is
to use treatment residuals as fill material. If fill material is placed
in locations that are not adjacent to surface waters and in areas where
they cannot be re-mobilized, then the potential for subsequent release
may be minimized. However, EPA is not aware of data or studies that
have looked at the fate and transport of treatment chemicals contained
in residuals. It is, however, generally known that components of some
chemicals, such as polysaccharides, will readily degrade into benign
compounds. And, as stated in the previous paragraph, sediment-bound PAM
is thought to have limited bioavailability since there is little or no
desorption from soil particles.
EPA is seeking comment and additional data on the toxicity
associated with the use of chemicals in controlling sediment discharge
in construction stormwater.
F. Cold Weather Considerations
EPA solicits information and data on the performance of polymers as
an aid to reducing turbidity in cold weather. EPA is aware that
temperature may affect dissolution rates of treatment chemicals and
therefore may impact the performance of polymer-aided settling and
filtration (see DCN 70000, 70001 and 70002). Data contained in DCN
70000 indicates that while dissolution rates may be lower, there are
methods available to mitigate detrimental effects on treatment system
performance, such as providing additional application in order to
provide the proper dosing rates and/or use of product formulations
designed specifically for use in colder climates. Directing discharges
to a vegetated buffer (or biofilter) would also be expected to provide
additional removal (see DCN 70000, which illustrates such an
application in a cold climate). This issue was addressed in EPA's
comment response document for the December 2009 final rule (EPA-HQ-OW-
2008-0465-1660, page 507):
[[Page 122]]
EPA expects that NPDES permittees working in cold-climate
regions, such as Alaska, shall be able to comply with the
requirements of the final rule. Very little surface runoff (and
hence discharges) occurs during freezing conditions. As temperatures
warm and snow and ice melt and discharges occur, the limitation
would apply to discharges on those sites that meet the applicability
criteria. In some cases, permittees may need to consider the need
for freeze protection for items such as pumps and polymer dosing
systems, if permittees elect to use these or other items as
components of their treatment systems. Stormwater infiltration may
be limited in cold climates, but the ELGs are flexible enough to
allow permittees to comply with the regulation regardless of frozen
soil/ground conditions.
In addition, comments submitted by the National Association of Home
Builders on the November 29, 2008 proposed rule (EPA-HQ-OW-2008-0465-
1360.2, page 188) indicate that little, if any, runoff would be
expected during the cold months:
In very cold climates, erosion and sediment movement is
nonexistent during the cold months. Once the freeze sets in, the
soil does not move since the freeze penetrates to well below the
surface. Typically builders and contractors do their land disturbing
activities during the summer months. (Home builders line up a number
of home foundations where the building of the houses can proceed
during the winter without the need to move soil.) If digging is done
on site during the winter to put in a foundation, the soil removed
will remain in place until the thaw. Permitting authorities normally
require that sites are stabilized prior to freezing and inspections
take place to ensure stabilization during the spring, including
stabilization for any dirt dug out during the winter.
EPA solicits additional data on the performance of polymer-aided
settling and filtration in colder climates.
G. Small Sites That Are Part of a Larger Common Plan of Development or
Sale
EPA solicits comments on the ability to effectively treat
discharges from small sites that are part of a larger common plan of
development or sale. An example would be a site that is above any
regulatory threshold requiring compliance with a turbidity limitation,
but has a portion of the site (such as an individual lot or small group
of lots) that may not be treated in a common system that treats
discharges for the entire site. These small areas would still be
subject to any numeric limitation because the overall size of the
construction site exceeds the size threshold, and therefore these sites
would need to treat any discharge from their area if there is a
concentrated point of discharge that would be subject to the numeric
limitation. EPA is soliciting data and information on the ability to
apply treatment to small areas within a larger common plan of
development or sale.
Information in the record for the C&D rule indicates polymer-aided
settling and filtration is scalable, and that therefore there are
technologies available that can be used on any size site and any
drainage area. Some of the data used to calculate the December 2009
numeric limitation, such as the North Carolina roadway project and the
North Carolina institutional project, were collected on small drainage
areas. Small drainage areas need only provide a sufficient storage
volume (such as a sediment trap) or a conveyance system (such as a
channel with check dams) to treat stormwater discharges.
For small drainage areas without appreciable slope, or where a
conveyance or impoundment could not be feasibly installed, EPA would
expect that stormwater would be conveyed primarily as overland flow,
once the underlying soil has been saturated, which would be amenable to
treatment through a filter berm, vegetated buffer or other appropriate
control. EPA would not expect stormwater discharges to become
concentrated to such a degree from small, flat drainage areas that
monitoring and compliance with a numeric limitation would be required
since channelization is likely not to occur, except for larger storm
events. In addition, the use of surface covers, tackifiers and other
covers have been shown to be highly effective in preventing
mobilization of soil particles (see the Technical Development Document
for the December 2009 rule for additional information). These practices
can be used on any size area of disturbance and would be particularly
effective on small, flat areas of disturbance. Therefore, EPA believes
that technologies are available for managing any size site or drainage
area.
EPA further believes that decisions the permittee chooses to make
regarding how to grade the site and how to convey stormwater are
important factors to consider during the planning phase of a project,
and that these choices will affect the level of technology needed to
meet a turbidity limitation and the number of discharge points that
will require monitoring, particularly for smaller drainage areas. EPA
solicits comment and data on this issue.
H. Electric Utility Transmission Line Construction
EPA solicits information and data on the costs and feasibility of
implementing controls to achieve a numeric effluent limitation for
turbidity in discharges from electric utility transmission line
construction projects. As discussed below, the length of electric
utility transmission line projects, the multitude of discharge points,
the distance between such discharge points, and the relatively brief
construction period would make it potentially difficult for permittees
to identify all discharge points in advance and monitor at the numerous
points where monitoring would potentially be required.
Since promulgation of the December 2009 C&D rule, EPA has received
information from UWAG (see DCN 70031) regarding several attributes of
construction for electric utility transmission line construction
projects. Information provided to the Agency and the Agency's
understanding of this information indicates that electric utility
transmission line construction projects are different than other types
of linear construction projects, such as roads. Electric utility
transmission line construction projects can span anywhere from a few
dozen miles to hundreds of miles in length and the area of disturbance
is typically non-contiguous. Other linear construction projects, such
as roads, typically do not span the longer distances in this range and
typically have relatively contiguous areas of disturbance. EPA's
understanding of the information provided by UWAG indicates that, given
the considerable length of electric transmission projects and the
number of individual areas where pads and/or poles are installed, the
number of discharge points could run into the hundreds. This number of
discharge points is unique to long, linear electric utility
transmission line construction projects. Further, the distance between
individual areas of disturbance for electric utility transmission line
construction projects can be considerable. This differs from other
linear projects, such as roads, in that other linear projects typically
do not have such distances between areas of disturbance. For example, a
typical road widening project could potentially be up to dozens of
miles long, but the areas of disturbance are generally contiguous or in
close proximity to each other.
Another significant difference between electric utility
transmission line construction projects and other linear construction
projects is that the duration of disturbance for a given piece of land
is typically much shorter and the intensity of disturbance is much less
for electric utility transmission line construction projects than for
other linear construction projects, such as roads. Construction of a
new roadway,
[[Page 123]]
or expansion of an existing roadway to add a new lane or lanes,
typically takes many months and involves intensive land disturbance
(clearing, grading, cut and fill, excavation, etc.), whereas
construction of an individual pad for an electric utility transmission
line tower and/or pole may last a matter of days or weeks.
Based on the length of such electric utility transmission line
construction projects, the multitude of discharge points, the distance
between such discharge points, and the relatively brief construction
period, EPA solicits comments on whether it would be practical to
require such dischargers to identify all discharge points in the notice
of intent to be covered for their permit, for the permitting authority
to determine representative discharge points, and for the discharger to
monitor at the numerous points where monitoring would potentially be
required for these types of projects. EPA solicits comments on the
information provided to EPA by UWAG and additional data on construction
of electric utility transmission lines to support or refute the ability
of these projects to implement controls and monitor discharges.
Dated: December 27, 2011.
Michael H. Shapiro,
Acting Assistant Administrator for Water.
[FR Doc. 2011-33661 Filed 12-30-11; 8:45 am]
BILLING CODE 6560-50-P