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Memorandum to Record

Date: January 13, 2014

Subject: Construction and Development Effluent Guidelines - Numeric Limitation Data 

Discussion

Prepared By: Jesse W. Pritts, USEPA

Summary

This memo describes some of the data available to EPA on the performance of technologies to control 

turbidity and other pollutants in stormwater discharges from construction activities. Available 

monitoring data from published and unpublished studies is summarized, and a discussion of each 

dataset is provided. Additional description of variability in performance of passive treatment systems is 

provided for some select datasets.

Data Sources Used for 2007 Proposal

EPA used several datasets at the time of the 2007 proposed rule to calculate a limitation based on the 

performance of active treatment systems (ATS), namely chitosan-enhanced sand filtration (CESF). These 

systems generally provided effluent turbidity less than 10 nephelometric turbidity units (NTU). EPA did 

not use effluent from CESF systems for the 2009 final rule as EPA selected passive treatment instead of 

active treatment as the technology basis for the 2009 final rule. However, EPA did use some CESF 

pretreatment data to represent the performance of passive treatment in the 2009 final rule. Table 1 

summarizes the data used for the 2007 proposed rule. Additional discussion of these datasets can be 

found in the development document for the 2007 proposed rule (Development Document for Proposed 

Effluent Guidelines and Standards for the Construction and Development Category, EPA-821-R-08-007. 

November 21, 2008).

Data Sources Used for Calculating 280 NTU Limitation for 2009 Final Rule

For the 2009 final rule, EPA based the numeric turbidity limitation on the performance of passive 

treatment. EPA used pretreatment data from several CESF systems to represent passive treatment. Only 

those systems where data was collected after the pretreatment pond but before the CESF system were 

used. EPA also used data collected by researchers at North Carolina State University to support the 2009 

limitation. Table 2 shows the data used to calculate the 2009 final rule limitation. Additional discussion 

of these datasets can be found in the development document for the 2009 final rule (Development 

Document for Final Effluent Guidelines and Standards for the Construction and Development Category,

EPA-821-R-09-010. November, 2009).
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Table 1

Source Site name or location Abbreviation

Clear Creek Systems, Inc. California, Oregon and Washington 2

3

4

6

8

11

BZR08

SC05

SC08

Cascade EcoSolutions Beacon Hill Reservoir Burying Project BHRBP

Brightwater Waste Water Treatment Plant BWWTP

WSDOT SR-522 Road Improvement Project 

(Elliot Road)

ELLRD

Lakeside LSIDE

Seatac Airport SEAAIR

Sound Transit Central Link Light Rail STCLLR

Oregon Department of Environmental 

Quality

West Linn Corporate Park WLCPO

Hoodview Estates HEO

Table 2

Source Site name or location Abbreviation 

Construction 

type 

Cascade 

EcoSolutions 

Beacon Hill Reservoir Burying Project, 

Seattle, WA BHRBP Other 

Brightwater Waste Water Treatment Plant 

in King County, WA BWWTP Commercial 

Sea-Tac Airport in King County, WA SEAAIR Transportation 

Sound Transit Central Link Light Rail 

Tacoma/Seattle, WA STCLLR Linear 

Clear Water 

Compliance 

Services, Inc. 

Beacon Hill Reservoir Burying Project, 

Seattle, WA 

BHRBP2 * Linear 

Sea-Tac Airport in King County, WA KC-variations Transportation 

Springville, NY highway widening NY Transportation 

Redmond, WA residential project Red.East, 

Red.West Residential 

NCSU Research 

(McLaughlin, et al) 

North Carolina mountain roadway project 

in 2006-7 

NCR.1 NCR.2 Transportation 

North Carolina mountain roadway project 

in 2008 NC.Road Transportation 

* Because BHRBP2 is a more complete data set, it was used to calculate the long-term average and 

variability factor for this site instead of the BHRBP data set for the 2009 final rule.
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Additional Datasets Available to EPA

At the time of the 2009 final rule, EPA had some additional datasets in its possession that were not used. 

These datasets, and the reasons they were not included in calculation of the 2009 final rule, are 

described in Table 3. 

Table 3

Source Site name or location Abbreviation Reason for exclusion

Oregon Department 

of Environmental 

Quality (proposal 

data, Jurries no date)

West Linn Corporate Park WLCPO The effluent data 

represent ATS. The 

influent data were not 

pretreated with EPA’s 

model technology.

Hoodview Estates HEO

Resource Planning 

Associates (DCN 

41107) and Minton 

(DCN 41108)*

Six systems at a commercial 

site in Redmond, CA RED.1-RED.6

These sites used batch 

treatment in cells, which 

is more extensive than 

EPA’s model technology

of passive treatment.

Clear Water 

Compliance Services

Morrisville, NC, was a 

commercial site with a 

runoff area of 82 acres and 

two treatment systems.

not incorporated 

into EPA’s 

databases

Data were provided only 

as minimum and 

maximum values which 

could not be used to 

calculate daily averages.

*DCN (Document Control Numbers) are from the 2009 final rule index.

Subsequent to promulgation of the 2009 final rule, EPA continued to receive data from various sources. 

EPA contacted researchers from North Carolina State University to obtain additional details on the 

studies used for the 2009 final rule as well as to collect additional datasets. EPA published a Federal 

Register notice on January 3, 2012 soliciting data, which yielded some information and data. In addition, 

EPA received additional information and data following publication of the April 1, 2013 proposed 

amendments to the 2009 final rule. Due to the quantity of information available, EPA has not 

summarized all of these datasets in this memorandum but has included a table summarizing many of 

these data (see Table 7). While EPA has not summarized and discussed all available data for this 

memorandum, EPA has prepared the following discussion which highlights some of the passive 

treatment studies and discusses variability of the datasets which illustrates the challenges with respect 

to calculation of a numeric turbidity limitation based on passive treatment systems. EPA has chosen to 

discuss these data in more detail because they are some of the most instructive datasets available to 

EPA because samples and flow data were collected over the course of discharge events. All of the 

information referenced can be found in the dockets for the various rulemakings and actions conducted 

by EPA (see Table 4).
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Table 4 Docket IDs

Action Docket ID

2007 Proposed Rule EPA-HQ-OW-2008-0465

2009 Final Rule EPA-HQ-OW-2008-0465

2102 Federal Register Notice EPA-HQ-OW-2010-0884

Interstate 485 project northwest of Charlotte, North Carolina

This site, described in the paper “Water Quality Improvements Using Modified Sediment Control Systems 

on Construction Sites” by McLaughlin, et al. (see DCN 70063, as well as detailed data for this site in DCN 

70065), utilized polyacrylamide (PAM) blocks as well as granular PAM applied in ditches along with 

various configurations of sediment basin inlets and outlets at a highway construction site in North 

Carolina (Interstate 485). 

This research project studied three sediment capture and treatment system configurations. The first 

type of system consisted of a sediment basin and ditches leading up to them, the second type of system 

added a forebay, porous baffles and PAM treatment in the diversion ditches. PAM was applied at several 

points in the system through the use of solid blocks and through the application of PAM powder to jute 

mesh lined ditches. The third type of system tested was the same design as the second system with the 

addition of a floating outlet or skimmer. A total of six basins utilizing PAM were monitored. The data 

reported in this paper was collected between 2004 and 2006. 

EPA notes that the effluent from both of the passive system configurations that employed polymer 

addition demonstrates wide variability with effluent turbidity ranging from values below 100 NTU to 

several thousand NTU. This indicates that that the PAM blocks may have been providing inadequate 

dosing in order to flocculate the sediment. Other research (see DCN 70067) also noted problems with 

the use of PAM blocks, which can be buried by sediment or can dry out, thus rendering them ineffective

in dosing. McLaughlin notes that there was little emphasis or attention paid to the passive systems by 

the construction crews at this site and the researchers were some distance away and frequently not 

present prior to or during storm events. Thus, poor construction oversight may have contributed to the 

variability in performance observed at this site.

Steeltown Road, Curley Maple Road, I-540, Unnamed Orange County Site

These construction sites, located in North Carolina, utilized PAM in various forms. Daily average turbidity 

data for three of these sites were available at the time of the December 2009 final rule (see DCNs 70018 

and 70034 for a complete description of these data and the construction sites). Data for a fourth site 

was provided to EPA after promulgation of the December 2009 final rule (see DCN 70004,70053-70060, 

70062 and 70065). Table 5 summarizes these data.
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Table 5

Site 

Name

Site 

location

Abbreviation Construction 

Type

Treatment 

Type

Site 

Size/Drainage 

Area (acres)

Reference 

DCN

Date 

Range of 

Data 

Collection

Steeltown 

Road

Caldwell 

County, 

NC

NCR.1 Transportation Fiber 

check 

dams w/ 

PAM

Not Described 70018, 

70065

6/2006 -

10/2006

Curley 

Maple 

Road

Watauga 

County, 

NC

NCR.2 Transportation Fiber 

check 

dams w/ 

PAM

Not Described 70018, 

70065

7/2006 -

9/2006

Not 

Described

Orange 

County, 

North 

Carolina

NC.Road Institutional Skimmer 

basin w/ 

PAM

Approximately 

1 acre of 

drainage

70034, 

70065

9/2008 -

1/2009

I-540 

Turnpike

Wake 

County, 

North 

Carolina

NCR.1A Transportation Skimmer 

basin w/ 

PAM

1.1 acres 70004, 

70053 

and 

70054

9/2010 -

3/2011

NCR.2A Transportation Skimmer 

basin w/ 

PAM

Varied 

between 

approximately 

2.5 to 3 acres

Steeltown Road and Curley Maple Road (referred to as NCR.1 and NCR.2) were mountain roadway 

construction projects that utilized fiber check dams with polyacrylamide (PAM). The drainage areas for 

each of these projects were not reported. Samples at these sites were collected using automated 

samplers that were triggered by precipitation and runoff. Individual sample bottles collected allows for 

evaluation of performance of the systems over time. DCN 70065 contains additional details on individual 

sample bottle collection times and turbidity values for these sites, which was provided to EPA in 2011. 

The NC.Road project was an institutional construction project in North Carolina that utilized PAM 

addition prior to a sediment basin with a skimmer outlet. NCR.1A and NCR.2A are located at a North 

Carolina Department of Transportation construction project. Treatment consists of sediment basins with 

skimmer outlets treated with PAM. Additional information on the drainage area of each site and the 

time frame over which samples were collected is contained in Table 5.
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In all of these treatment systems, PAM application was accomplished by either direct application to the 

check dams, application to coir netting or wattles prior to the basin inlet, and/or use of PAM blocks 

placed in drainage ditches or sediment forebays. In all of these cases, the primary removal mechanism 

of turbidity is coagulation/flocculation followed by settling. In the case of fiber check dams, the check 

dams are porous and flocculated material could also be removed by filtration/adhesion. Thus, the 

physical unit process taking place in these passive treatment systems is settling and/or filtration aided 

by the addition of a coagulant/flocculant, such as a polymer (in these cases, polyacrylamide). 

For a dosing system to be effective, there are three main requirements: (1) the coagulant/flocculant is 

added to the turbid stormwater at a sufficient dosage, either by flow-proportional or rainfallproportional dosing, or that a solid form of coagulant/flocculant is placed in a channel, pipe or other 

conveyance in such a manner that the flowing water can come into contact and dissolve/mobilize the 

chemical at a sufficient dose rate; (2) that mixing is facilitated, which can be accomplished in many ways 

including, but not limited to, in-channel by a check dam, by placing the chemical in a structure such as a 

riser or a corrugated plastic pipe through which the water flows, or with the case of pumped water 

providing sufficient turbulence either within the pipe or somewhere down-slope of where the pumped 

water is conveyed; and (3) providing an area for the flocculated material to settle, such as a basin or 

trap, or removal through filtration, such as a porous check dam, jute baffle, filter bag, or vegetated area 

(biofilter). Certain flocculated material may also have an affinity for organic material, such as jute, so 

removal may also occur through adhesion or other physical processes.

DATA DISCUSSION

At all of these sites, samples were collected via automated sampler whereby up to four individual 

sample aliquots were combined into one sample bottle. The samplers were programmed to collect 

samples at the beginning of the discharge and to continue sampling until the discharge ends (or until all 

bottles in the sampler have been used). Samples were collected using flow-weighted compositing 

(although the 6/27/2006 event at NCR.1 appears to be time-weighted, since samples were reported to 

be collected at 20-minute increments). In addition, sample bottle collection times were not reported for 

the 10/5/2006 event at NCR.1. 

For this discussion, EPA utilized a definition of a day as the 24-hour period after the first sample aliquot 

was collected. If an event lasted more than 24 hours, then samples collected during a subsequent 24-

hour period were treated as a separate day in some cases, if sufficient samples were collected. There 

were some exceptions to this approach (see, for example, discussion of the 10/28 - 10/29/2010 event at 

NCR.1A discussed below). This approach of using a 24-hour time period, as opposed to a calendar day, is 

appropriate in the context of stormwater discharges, where discharge is related to the occurrence of 

precipitation or runoff (such as snowmelt).

For events where the duration of the discharge lasted for more than 24 hours, EPA separated these 

datasets into individual 24-hour periods which were then used to calculate daily average turbidity (with 

exceptions, noted below). However, in some cases, a sample bottle contained sample aliquots that were 

collected more than 24-hours after the start of the event. Since each bottle is a composite of up to four 
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individual aliquots, EPA was not able to separate the portion of the sample that was collected during a 

given 24-hour period from those that were collected in the subsequent 24-hour period (which would 

constitute the beginning of the next daily period of data). In some cases, if the sample collection time 

was only slightly more than 24 hours, then these samples were averaged with the previous day’s 

turbidity values. In other cases, where these sample aliquots were collected appreciably longer than 24 

hours after the start of the event, EPA did not use the reported turbidity for these bottles in calculating 

the daily average turbidity for that day, but in some cases these samples were treated as a separate day 

and were used to calculate another daily average turbidity if, in EPA’s opinion, sufficient samples were 

collected to adequately characterize discharge during a subsequent day. DCN 70048 summarizes the 

events sampled and the turbidity of the individual sample bottles used in calculating the limitation.

NCR.1 and NCR.2 Data Discussion

The turbidity values reported in DCN 70065 for NCR.1 and NCR.2 differ slightly for some events than the 

values reported in DCN 70018. In these cases, EPA has used the values reported in DCN 70065.

NC.Road Data Discussion

The daily average turbidity for the 11/4/2008 event at the NC.Road site was reported as 43 NTU in DCN 

70034, while the calculated value based on data in DCN 70065 was 44 NTU. EPA used the 44 NTU value 

reported in DCN 70065 for this event.

The 11/25/2008 event at this site began at 2:51 AM, and the last sample was collected at 3:08 AM on 

11/26/2008. This event spanned a time period of 24 hours and 17 minutes. Since this event was only 

slightly longer than 24 hours, all bottles were used to calculate the average turbidity for that day. 

The 1/9/2009 event began at 10:41 AM and the last sample was collected at 13:44 (1:44 PM) on 

1/10/2009. This event was 27 hours and 3 minutes. Since this event was notably longer than 24 hours, 

only sample bottles collected within 24 hours of the start of the event were used to calculate the daily 

average turbidity for this event. As a result, the last two bottles collected for this event (collected at 

12:10 PM and 1:44 PM on 1/10/2009) were excluded from calculating the daily average turbidity for this 

event.

NCR.1A Data Discussion

Detailed flow information was provided to EPA for the NCR.1A and NCR.2A sites (see DCN 70064.1, 

70064.2 and 70064.3). As a result, EPA is able to provide a comparison of sample collection times and 

flowrates for events at these sites. 

The data files provided to EPA include two reported values for turbidity. The first value is the value 

reported by the meter in the laboratory, while the second value accounts for the calibration of the 

instrument (see DCN 70057). EPA has used the values after correction for calculation of the limitation 

for these sites.
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Sampling for the 9/29/2010 event began at 4:53 PM on 9/29/2010 and ended at 1:33 PM on 9/30/2010. 

Sampling ended because all bottles in the sampler were full. A review of the hydrograph and the sample 

collection times and individual sample bottle turbidity reading (see Figure 1) indicates that turbidity was 

initially very low during this event, but increased as the storm progressed. This may indicate that the 

polymer dosing was not as effective or potentially exhausted during the later part of this event. The 

sampler also did not capture the entire storm event. Examination of the turbidity values do indicate a 

downward trend towards the latter part of the storm, which would be expected as the hydrograph 

recedes.

Several samples were collected by the samplers between 10/8/2010 and 10/12/2010, however these 

samples did not coincide with appreciable flows from the system. Therefore, these turbidity values were 

excluded from consideration.

The next significant event began on 10/14/2010. Figure 21 shows the hydrograph and individual sample 

bottle collection times and turbidity for this event. The first sample was collected at 10:19 AM and the 

last was collected at 6:36 PM. The sampler logged additional samples collected after 6:36 PM further out 

on the descending limb of the hydrograph, but turbidity was not reported. The first sample bottle 

collected for this event (reported as Bottle 9 in DCN 70064.1) contained one aliquot collected on 

10/13/2010. Although this aliquot was not collected during this event, since it comprised only one of the 

 1 All figures are plotted using the same scales on the vertical axes for flow and turbidity in order to facilitate direct 

comparison between the magnitude of flows and turbidity readings present during each event.
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four aliquots for this bottle EPA did not exclude this bottle from calculation of the daily average turbidity 

for this event.

A small amount of flow occurred on 10/16/2010 triggering collection of an aliquot, and again on 

10/26/2010. The next appreciable discharge began on 10/28/2010. The sampler collected two aliquots 

(reported as Bottle 14 in DCN 70064.1) beginning on 10/28/2010 at 12:28 AM that were combined with 

the aliquots collected on 10/16 and 10/26/2010. Since two of the aliquots in this bottle were from 

previous days, this bottle was not used to calculate the daily average turbidity for this event. Samples 

for the next bottle were collected starting at 2:21 AM and sampling continued until 5:47 AM on 

10/29/2010. The last aliquot in the last bottle was collected 27 hours and 26 minutes after the start of 

this event. The other three aliquots in this bottle were collected within 24 hours of the start of this 

event. Since only one aliquot in this bottle was collected more than 24 hours after the start of the event, 

EPA included this bottle when calculating the daily average turbidity for this event. Figure 3 shows the 

hydrograph and sample collection times and turbidity for this event. The hydrograph illustrates two 

peaks, indicating that two events occurred back-to-back.
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The next series of discharges began on 11/4/2010, with discharges and sampling continuing through 

11/8/2010. The first sample was collected at 11:51 AM on 11/4/2010. EPA grouped sample bottles into 

24-hour periods from the start of this event, which yielded three separate daily averages.

One sample bottle consisted of two aliquots collected during the first 24-hour period (1:36 AM and 7:45 

AM on 11/5/2010), while the third and fourth aliquots were collected during the second 24-hour period 

(12:57 PM and 1:49 PM on 11/5/2010). EPA chose to exclude this bottle (which had a turbidity of 70.8 

NTU) from consideration as opposed to assigning this bottle to either the first or second 24-hour period.

Figures 4, 5 and 6 show the flow and turbidity and sample collection times for the first, second and third 

of these three events, respectively. The last bottle collected during these series of events, which was 

collected starting at 1:31 on 11/7/2010 was not used for calculating a separate daily limitation. 

EPA did not calculate a daily average turbidity for the 11/6 – 11/7/2010 sampling event, since this event 

was the trailing leg of the previous event and not a separate event.
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The first sample for the 11/16 - 11/17/2010 event was collected at 11:53 PM on 11/16/2010. The last 

sample aliquot was collected at 11:38 AM on 11/17/2010. Figure 7 shows the hydrograph and the 

sample collection times and turbidity values.
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The next event occurred on 12/1/2010. The first sample was collected at 4:59 AM and sampling 

continued until 12:11 PM. There were two bottles collected during this event. However, the second 

bottle only contained two aliquots from this event. The second bottle also contained two aliquots for an 

event that occurred on 12/4/2010. Since this second bottle contained aliquots from an event three days 

later, EPA only used the first bottle (consisting of four aliquots) to characterize the daily average 

turbidity for this event. Figure 8 shows the hydrograph and the sample collection times and turbidity for 

this event.

Samples collected at the NCR.1A site (and at the NCR.2A site) on January 4, 2011 were not used in 

calculating daily average turbidity because these samples were grab samples not collected during the 

corresponding runoff event that occurred during December 16 and 17, 2011 (see DCN 70053). The use 

of grab samples may have been appropriate, had these samples been collected over the course of an 

event. However, a one-time grab sample would not be expected to capture any variability present in 

discharge turbidity and could not be used to calculate a daily average value. In addition, these grab 

samples were not collected during or soon after the corresponding precipitation event (see DCN 70056).

A sample was collected beginning on 1/6/2011 and continuing until 1/11/2011. This bottle was not used 

to calculate a daily average turbidity because this composite sample spanned several days.

NCR.2A Data Discussion

The first sampled event began on 9/26/2010 at 11:55 PM. This event continued through 9/29/2010. EPA 

broke this event up into separate days, with the first event ending at 11:55 PM on 9/27/2010. Two 

sample bottles were collected within this first 24-hour period. A third bottle has two aliquots collected 

during this day while the second two aliquots were collected on the subsequent days. As a result, EPA 
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only used the first two sample bottles to characterize the turbidity for this event. This third bottle 

(collected beginning at 7:51 AM on 9/27/2010 and the last aliquot collected at 4:44 AM on 9/29/2010) 

was not used in any daily turbidity calculations since sample aliquots spanned nearly two days. Figure 9 

shows the flow and turbidity data for the 9/27/2010 event.

The next event began on 9/29/2010 at 4:57 AM, with the first bottle of this event filled at 7:57 AM on 

the same day. Sample bottles in the sampler were changed on this day, so sampling of this event 

continued with the next sample collected at 8:18 AM and the last aliquot collected at 8:23 PM. 

Discharge continued from this event for the next several days, but all bottles in the sampler were full so 

the remainder of this event was not sampled. This event shows a marked increase in runoff rate with 

two large peaks during 9/30/2010. Figure 10 shows the flowrate and turbidity data for the 9/29/2010 

event. Figure 11 shows the data for this event as well as the flow data through 9/30/2010 illustrating the 

large peaks in flowrate not sampled. Figure 11 is plotted with a logarithmic scale on the vertical axis for 

flowrate due to the large range in flowrates present.
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The next event sampled began on 10/14/2010. at 9:31 AM and sampling continued until the sampler 

was full at 1:21 AM on 10/15/2010. Figure 12 shows the flow and turbidity data for this event.

The next event sampled began on 11/16/2010 at 11:59 PM. The last sample aliquot was collected at 

4:12 AM on 11/18/2010. The samples collected for this event spanned a time period of more than 24 

hours. Bottle 17 of this event contains 2 aliquots collected within 24 hours of the start of the event, and 

2 aliquots collected after 24 hours. The last aliquot of this bottle was collected at 1:45 AM on 

11/18/2010, which is 25 hours and 46 minutes after the first sample was collected. EPA used bottles 1 

through 17 to characterize this event, even though the samples spanned more than 24 hours. EPA did 

not use bottle 18 for this event or to calculate a separate daily average turbidity since all aliquots in this 

bottle were collected more than 24 hours after the start of the event. Figure 13 shows the flow and 

turbidity readings for this event. This was the first event sampled after the weir was removed from 

downstream of the emergency spillway.
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Samples collected at the NCR.2A site on January 4, 2011 were not used to calculate a daily turbidity 

value (see discussion above for rationale).

The next series of events began on 2/4/2011. These samples were collected at the weir installed after 

the emergency spillway, capturing any discharge from the skimmer as well as any discharge over the 

spillway. The first sample was collected at 5:35 PM on 2/4/2011 and the last sample was collected at 

2:44 AM on 2/7/2011. EPA split this event into separate 24 hour periods from the start of the event and 

calculated separate average daily turbidity.

After the first 24 hour period, ten full bottles were collected. The 11th bottle contained two aliquots 

collected within 24 hours of the start of the event, while the second two aliquots were collected more 

than 24 hours after the start of the event. The last aliquot of the 11th bottle was collected at 6:23 PM on 

2/5/2011, which was 24 hours and 48 minutes after the start of the event. Since this is only 48 minutes 

longer than 24 hours, EPA used the bottle 11 turbidity results along with the first 10 bottles to 

characterize turbidity for that day. Figure 14 shows the flow and turbidity data for the 2/4 – 2/5/2010 

event.
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During the next 24-hour period (5:35 PM on 2/5/2011 through 5:35 PM on 2/6/2011) a total of eight 

sample bottles were filled. Figure 15 shows the flow and turbidity readings for this event. 

During the next 24 hour period (5:35 PM on 2/6/2011 through 5:35 PM on 2/7/2011), two sample 

bottles were collected. The last sample was collected at 2:44 AM on 2/7/2011. Figure 16 shows the flow 

and turbidity data for this event.
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The next event occurred on 3/15 and 3/16/2011. The first sample was collected on 3/15/2011 at 10:57 

AM and the last sample was collected on 3/16/2011 at 10:42 AM when the sampler was full. Figure 17 

shows the flow and turbidity data for this event.
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The next event occurred on 3/30/2011. The first sample was collected at 11:59 AM and the last sample 

was collected at 10:30 PM. Figure 18 shows the flow and turbidity data for this event.

The next event occurred on 4/9/2011. The first sample was collected at 9:08 PM and the last sample was 

collected at 10:18 PM. This was a short-duration, high-intensity storm event. Figure 19 shows the flow 

and turbidity values for this event.
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The last sampled event at the NCR.2A site occurred on April 16, 2011. This was a very high intensity, 

short-duration storm. Total rainfall over the 45-minute event was 0.39 inches, with a peak 5-minute 

rainfall depth of 0.14 inches, which equates to an hourly intensity of 1.68 inches/hour. Turbidity for 

many of the samples exceeded 40,000 NTU, which is the measurement limit of the instrument used. EPA 

was not able to calculate an average daily turbidity for this event, since many of the measurements 

exceeded the measurement limit of the instrument. Figure 20 shows the flow and turbidity data for this 

event. Samples with turbidity exceeding 40,000 NTU were plotted at 40,000 NTU.

SUMMARY OF DAILY TURBIDITY MEASUREMENTS 

Table 6 summarizes all of the daily average turbidity measurements determined by EPA. Table 6 also 

presents the daily precipitation that occurred at nearby climate stations, as well as the number of 

sample bottles that comprise the daily average turbidity for each day.

DISCUSSION AND OBSERVATIONS

The NCR.1 and NCR.2 datasets are the most instructive of the datasets available to EPA for evaluation of 

the performance of passive treatment because sampling at these sites was conducted using automated 

samplers that collected sample aliquots over the course of storm events and the individual sample 

bottle data was available to EPA. This allows for analysis of performance of the practices over the course 

of a storm event, which can illuminate factors such as the ability of the practices to control differing 

levels of turbidity resulting from changes in storm intensity. In addition, these datasets are the most 

instructive because data on flow was collected, which can be used to evaluate the completeness and 
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representativeness of these datasets for characterizing performance of the passive treatment systems. 

Based on a detailed evaluation of these data, EPA makes the following observations:

• Passive treatment systems exhibit a large range of performance. These data show average

runoff event turbidity ranging from 8.5 to over 28,000 NTU. Individual sample aliquots in some 

cases exceeded 40,000 NTU, which was the upper range of the instrument used. Without 

documentation of the site conditions, in particular the availability of polymer during the 

precipitation events, it is difficult to know whether the performance observed in the data 

represents a well operated and maintained passive system. Furthermore, the large range in

observed performance may complicate establishment of a numeric effluent limitation for 

turbidity based on passive treatment, since EPA's methodology for calculating numeric effluent 

limitations includes a variability factor, which in this case would be very high due to the large 

range in observed turbidity both intra- and inter-event.

• The automated samplers sometimes were not able to collect samples over the entire runoff 

event due to all sample bottles being filled to capacity before the end of the event. Therefore, 

characterization of some events (such as the 2/29/2010 event at NCR.1) was incomplete. 

Without data over the entire runoff event, it is unknown where the limit of performance of the 

passive treatment system may occur (e.g., where available polymer in the system would be 

exhausted and the effect of the polymer in reducing turbidity would be reduced or eliminated)

and how the practice performed over the entire event. 

• Intra-event variability in observed turbidity was high in some cases. The most apparent instance 

was the 4/16/2011 event at NCR.2. The high-intensity nature of rainfall events appears to 

overwhelm the ability of passive treatment systems to effectively reduce turbidity in some 

cases. This would complicate establishment of a numeric effluent limitation because it would be 

desirable to have data representing a range of storm intensities in order to determine the point 

at which passive treatment ceases to be effective in reducing turbidity.

• In sum, factors such as large inter- and intra-event variability in performance, incomplete 

sample collection over the course of entire discharge events, and unknown operation and 

maintenance practices complicates the ability to determine representativeness and adequacy of 

the existing dataset and to establish reasonable and defensible numeric effluent limitations

based on these data. Additional data collection is necessary in this area to further explore the 

feasibility of establishing numeric effluent limitations based on the performance of passive 

treatment at construction sites.
Page 23 of 28

Table 6

Site

Average 

Turbidity 

(NTU)

Sample Event Date(s)

Event Start 

Time

Event End 

Time

Sampled Event 

Duration 

(hours:min)

Number of 

Sample 

Bottles**

Daily 

Precipitation*

NCR.1 109.3 6/27/2006 3:50 AM 10:50 AM 7:00 22 33 mm

NCR.1 335.3 7/25/2006 2:32 AM 3:08 AM 0:36 6 9 mm

NCR.1 24.4 8/9/2006 8:04 PM 9:16 PM 1:12 2 11 mm

NCR.1 23.5 8/11/2006 12:55 AM 11:06 PM 22:11 13 31 mm

NCR.1 40.3 8/12/2006 12:05 AM 4:45 AM 4:49 9 38 mm

NCR.1 40.1 8/30/2006 6:07 PM 10:44 PM 4:37 12 28 mm

NCR.1 41.3 8/31/2006 12:10 PM 10:53 PM 10:43 9 27 mm

NCR.1 39.8 9/4/2006 2:06 AM 3:36 AM 1:30 3 43 mm

NCR.1 15.6 9/7/2006 2:42 PM 6:22 PM 3:40 9 15 mm

NCR.1 8.5 9/13/2006 7:01 AM 10:45 PM 15:44 7 25 mm

NCR.1 77.3 9/23/2006 1:58 PM 4:20 PM 2:22 4 9 mm

NCR.1 17.8 9/24/2006 1:34 AM 1:44 AM 0:10 4 18 mm

NCR.1 15.3 10/5/2006 Not Reported Not Reported Not Reported 11 19 mm

NCR.2 90.2 7/13/2006 1:00 PM 5:30 PM 4:30 4 9 mm

NCR.2 14.6 9/10/2006 3:05 PM 3:05 PM *** 1 11 mm

NCR.2 44.4 9/13/2006 9:12 AM 10:27 AM 1:15 4 30 mm

NCR.2 532.7 9/24/2006 7:10 PM 7:18 PM 0:08 2 12 mm

NC.Road 167.0 9/16/2008 11:27 AM 1:01 PM 1:34 11 0.29 in

NC.Road 44.4 11/4/2008 8:35 AM 11:53 PM 15:18 24 0.37 in

NC.Road 50.2 11/14/2008 3:20 PM 9:37 PM 6:17 24 0.61 in

NC.Road 40.2 11/25/2008 – 11/26/2008 2:51 AM 3:08 AM (next 

day)

24:17 17 0.37 in (11/25);

0.0 inches 

(11/26)

NC.Road 37.4 11/30/2008 2:37 AM 7:04 AM 4:27 7 0.38 in
Page 24 of 28

Site

Average 

Turbidity 

(NTU)

Sample Event Date(s)

Event Start 

Time

Event End 

Time

Sampled Event 

Duration 

(hours:min)

Number of 

Sample 

Bottles**

Daily 

Precipitation*

NC.Road 38.2 12/25/2008 2:13 AM 6:21 AM 4:08 24 0.31 in

NC.Road 10.3 1/9/2009 – 1/10-2009 10:41 AM 8:11 AM (next 

day)

21:30 19 0.0 in

NCR.1A 246.4 9/29/2010 - 9/30/2010 4:53 PM 1:33 PM (next 

day)

20:40 24 0.27 in (9/29)

3.18 in (9/30)

NCR.1A 19.0 10/14/2010 10:19 AM 6:36 PM 8:16 3 0.51 in

NCR.1A 29.4 10/28/2010 - 10/29/2010 2:21 AM 5:47 AM (next 

day)

27:26 3 0.29 in (10/28); 

0.0 in (10/29)

NCR.1A 68.8 11/4/2010 11:51 AM 11:38 PM 11:47 3 0.07 in

NCR.1A 48.1 11/5/2010 - 11/6/2010 2:06 PM 11:35 AM 

(next day)

21:29 4 0.67 in (11/5)

NCR.1A 55.2 11/6/2010 - 11/7/2010 12:40 PM 11:02 AM 

(next day)

22:22 2 0.01 in (11/6)

0.15 in (11/7)

NCR.1A 72.5 11/16/2010 - 11/17/2010 11:53 PM 11:38 AM 

(next day)

11:45 4 0.03 in (11/16)

0.44 in (11/17)

NCR.1A 75.3 12/1/2010 4:59 AM 8:13 AM 3:14 1 0.3 in

NCR.2A 72.0 9/26/2010 - 9/27/2010 11:55 PM 7:42 AM

(next day)

7:47 2 0.93 in (9/26)

2.59 in (9/27)

NCR.2A 27.1 9/29/2010 4:57 AM 8:23 PM 15:26 25 0.27 in

NCR.2A 37.7 10/14/2010 – 10/15/2010 9:31 AM 1:21 AM

(next day)

15:50

24

0.51 in (10/14)

0.60 in (10/15)

NCR.2A 126.1 11/16/2010 - 11/17/2010 11:59 PM 1:45 AM

(next day)

25:46 17 0.03 in (11/16)

0.44 in (11/17)

NCR.2A 164.2 2/4/2011 – 2/5/2011 5:35 PM 6:23 PM

(next day)

24:48 11 0.03 in (2/4)

0.53 in (2/5)

NCR.2A 184.4 2/5/2011 – 2/6/2011 6:54 PM 4:58 PM

(next day)

22:04 8 0.81 in (2/6)

NCR.2A 144.5 2/6/2011 – 2/7/2011 6:01 PM 2:44 AM 8:43 2 0.0 in (2/7)
Page 25 of 28

Site

Average 

Turbidity 

(NTU)

Sample Event Date(s)

Event Start 

Time

Event End 

Time

Sampled Event 

Duration 

(hours:min)

Number of 

Sample 

Bottles**

Daily 

Precipitation*

(next day)

NCR.2A 129.2 3/15/2011 - 3/16/2011 10:57 AM 10:42 AM

(next day)

23:45 24 0.0 in (3/15)

0.15 in (3/16)

NCR.2A 93.4 3/30/2011 11:59 AM 10:30 PM 10:31 5 0.02 in

NCR.2A 456.9 4/9/11 9:08 PM 10:18 PM 1:10 2 1.04 in

NCR.2A 28,731.4 4/16/2011 3:47 PM 5:12 PM 1:25 8 0.39

*Precipitation data for NCR.1A, NCR.2A and NC.Road events is from the Raleigh/Durham Airport, NC station (see DCNs 70061 and 70068), and 

should therefore be considered approximations of precipitation occurring at the actual sites. Precipitation data for NCR.1 and NCR.2 are values 

reported in DCN 70018 by the author.

**This is the number of sample bottles collected for a given event. Up to four individual sample aliquots were composited into each bottle.

***The time each bottle was collected was reported, but not the time of each aliquot contained in the bottle. As a result, the duration of 

sampling for events with only one bottle collected is unknown.
Page 26 of 28

Table 7

DCN FDMS Document ID TITLE/SUBJECT

70000 EPA-HQ-OW-2010-

0884-0007

Water Treatment Assessment Report, Petersburg Airport Culvert 

Replacement

70001 EPA-HQ-OW-2010-

0884-0008

Airport Runway in Alaka Requires Innovative Stormwater Treatment for 

Compliance and Preservation

70002 EPA-HQ-OW-2010-

0884-0009 Stormwater Treatment in Multiple Climates

70003 EPA-HQ-OW-2010-

0884-0010

TYPAR® GEOCELL Sediment-Control Device: A Controlled Ditch Test 

with Polyacrylamide (Final Report)

70005 EPA-HQ-OW-2010-

0884-0012 IECA Southeast Chapter Newsletter August 2010.

70006 EPA-HQ-OW-2010-

0884-0013 NCDOT Biopolymer Field Test

70007 EPA-HQ-OW-2010-

0884-0014 StormKlear dual biopolymer field test site description, Annapolis MD

70008 EPA-HQ-OW-2010-

0884-0015 StormKlear dual biopolymer field test site description, Austin TX

70009 EPA-HQ-OW-2010-

0884-0016 StormKlear dual biopolymer field test site description, Beaverton OR

70010 EPA-HQ-OW-2010-

0884-0017 StormKlear dual biopolymer field test site description, Griffin GA

70011 EPA-HQ-OW-2010-

0884-0018 StormKlear dual biopolymer field test site description, Raleigh NC

70012 EPA-HQ-OW-2010-

0884-0019 StormKlear dual biopolymer field test site description, Tampa FL

70013 EPA-HQ-OW-2010-

0884-0020

StormKlear dual biopolymer field test site description, Tennessee and 

Erosion Control Magazine Article

70018 EPA-HQ-OW-2010-

0884-0024

Improving Construction Site Runoff Quality with Fiber Check Dams and 

Polyacrylamide (Data Report: NCR.1 and NCR.2)

70034 EPA-HQ-OW-2010-

0884-0040 Target Turbidity Limits for Passive Treatment (Data Report: NC.Road)

70035 EPA-HQ-OW-2010-

0884-0041

Technical Engineerinig Evaluation Report for the Chotosan-Enhanced 

Sand Filtration Technology for Flow-Through Operations

70049 EPA-HQ-OW-2010-

0884-0048

Performance of a Sediment Retention Pond Receiving Chemical 

Treatment

70050 EPA-HQ-OW-2010-

0884-0049 Protecting the Chattahoochee River (plus data file)

70052 EPA-HQ-OW-2010-

0884-0051 Erosion Prevention and Sediment Control Computer Modeling Project

70053 EPA-HQ-OW-2010-

0884-0052 Email: Rich McLaughlin to Jesse Pritts, NCR1.A and NCR.2A data

70054 EPA-HQ-OW-2010-

0884-0053 Email: Rich McLaughlin to Jesse Pritts, NCR1.A drainage information
Page 27 of 28

DCN FDMS Document ID TITLE/SUBJECT

70055 EPA-HQ-OW-2010-

0884-0054 Email: Ryan Brown to Jesse Pritts, questions on NCR1.A and NCR2.A

70056 EPA-HQ-OW-2010-

0884-0055 Attachment to DCN 70055

70057 EPA-HQ-OW-2010-

0884-0056

Email: Ryan Brown to Jesse Pritts, questions on NCR1.A and NCR2.A 

5/13/2011

70058 EPA-HQ-OW-2010-

0884-0057

Email: Ryan Brown to Jesse Pritts, questions on NCR1.A and NCR2.A 

5/16/2011 12:58 PM

70059 EPA-HQ-OW-2010-

0884-0058 Attachment to DCN 70058

70060 EPA-HQ-OW-2010-

0884-0059

Email: Ryan Brown to Jesse Pritts, questions on NCR1.A and NCR2.A 

05/16/2011 10:20 PM

70061 EPA-HQ-OW-2010-

0884-0060 Daily Precipitation Records, Raleigh, NC, 7/1/2010 to 3/31/2011

70062 EPA-HQ-OW-2010-

0884-0061 Attachment to DCN 70060

70063 EPA-HQ-OW-2010-

0884-0062

Water Quality Improvements Using Modified Sediment Control Systems 

on Construction Sites

70064.1 EPA-HQ-OW-2010-

0884-0063 11.3csk level&flow1 June30.xlsx

70064.2 EPA-HQ-OW-2010-

0884-0064 11.4 lev&flow Outlet1.xlsx

70064.3 EPA-HQ-OW-2010-

0884-0065 I540 sample data.xlsx

70065 EPA-HQ-OW-2010-

0884-0066 Data Files NC sites

70066 EPA-HQ-OW-2010-

0884-0067

Email: Rich McLaughlin to Jesse Pritts, 6/16/2011 re: I-485 project 

treatment.

70067 EPA-HQ-OW-2010-

0884-0068 The Use of Flocculants and Coagulants to Aid the Settlement of 

Suspended Sediment in Earthworks Runoff : Trials, Methodology and 

Design [draft]

70068 EPA-HQ-OW-2010-

0884-0069 Daily Precipitation Records, Raleigh, NC, 9/1/2008 to 1/31/2009

70069 EPA-HQ-OW-2010-

0884-0070 Polymer-Assisted Clarification of Stormwater from Construction Sites

70070 EPA-HQ-OW-2010-

0884-0071 StormKlear dual biopolymer field test site description, Huntersville NC

70071 EPA-HQ-OW-2010-

0884-0072 StormKlear dual biopolymer field test site description, Hanover MD

70072 EPA-HQ-OW-2010-

0884-0073 StormKlear dual biopolymer field test site description, Apex NC

70073 EPA-HQ-OW-2010-

0884-0074

StormKlear dual biopolymer field test site description, Bonita Springs 

FL

70074 EPA-HQ-OW-2010-

0884-0075 StormKlear dual biopolymer field test site description, Staten Island NY

70075 EPA-HQ-OW-2010-

0884-0076

StormKlear dual biopolymer field test site description, Cabarrus County 

NC
Page 28 of 28

DCN FDMS Document ID TITLE/SUBJECT

70076 EPA-HQ-OW-2010-

0884-0077

StormKlear dual biopolymer field test site description, Anne Arundel 

County MD

70077 EPA-HQ-OW-2010-

0884-0078 StormKlear dual biopolymer field test site description, Cartersville GA

70078 EPA-HQ-OW-2010-

0884-0079 StormKlear dual biopolymer field test site description, Central SC

70079 EPA-HQ-OW-2010-

0884-0080 StormKlear dual biopolymer field test site description, Fairview NC

70080 EPA-HQ-OW-2010-

0884-0081 StormKlear dual biopolymer field test site description, Lavonia GA

70081 EPA-HQ-OW-2010-

0884-0082

Toxicity of Anionic Polyacrylamide Formulations when Used for Erosion 

Control in Agriculture

70082 EPA-HQ-OW-2010-

0884-0083

Overview of the Effects of Residual Flocculants on Aquatic Receiving 

Environments

70085 EPA-HQ-OW-2010-

0884-0086 Cleveland Airport data

N/A

EPA-HQ-OW-2010-

0884-0089 Comments from Kevin H. Wolfe, Civil and Environmental Consultants

N/A

EPA-HQ-OW-2010-

0884-0100 Effluent Turbidity Performance from Various Construction Passive 

Sediment-Control Best Management Practices (BMPs)

N/A

EPA-HQ-OW-2010-

0884-0105 Comment letter from Atwell, LLC

N/A

EPA-HQ-OW-2010-

0884-0111 Comment letter from Tennessee DOT

N/A

EPA-HQ-OW-2010-

0884-0116

Comment letter from James Spotts, Southeast Environmental 

Consultants

N/A

EPA-HQ-OW-2010-

0884-0133 Comment letter from AASHTO

N/A

EPA-HQ-OW-2010-

0884-0142 Comment letter from Harris County, Texas

N/A

EPA-HQ-OW-2010-

0884-0156 Comment letter from HaloSource

N/A

EPA-HQ-OW-2010-

0884-0157 Comment letter from Harris County Flood Control District, Texas

N/A

EPA-HQ-OW-2010-

0884-0195 Comment letter from California Coastkeeper Alliance et al