Page 1 of 28 Memorandum to Record

Date: J anuary 13 , 201 4 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 Available monitoring data from published and unpublished studies is summarized, and a discussion of each dataset is provided.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 descr iption of variability in performance of passive treatment systems is provided for some select datasets.

Data Sources Used for 2007 P roposal EPA used several datasets at the time of the 2007 proposed rule to calculate a limitation based on the performance o f 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 E PA 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 dat a 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 Categor y, EPA

- 821

- R

- 08

- 007. November 21, 2008 ).

Data S ources U sed for C alculating 280 NTU L imitation for 2009 F inal R ule
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 pretreat ment 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 ).Page 2 of 28 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

.Page 3 of 28 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 dat a. 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 memorandu m 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 treatme nt 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 so me 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 (s ee Tabl e 4 ).Page 4 of 28 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 co nfigurations. 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 throu gh 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 c an 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 the se 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.Page 5 of 28 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

s ample bottle collect ion 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.1 A 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

.Page 6 of 28 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 re moved 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 s ystem 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 rainfall

proportional dosing, or that a solid form of coagulant/flocculant is pl aced 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 no t 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 whereb y 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 re ported 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

- hou r 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 fourPage 7 of 28 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 s ubsequent 24

- hour period (which would constitute the beginning of the next da ily 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 th ese 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 samp led 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 4 4 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 minu tes. 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 (c ollected 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 700 64.3). 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.Page 8 of 28 Sampling for the 9/29/2010 event began at 4:53 PM on 9/29/2010 a nd 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 v ery 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. Examinat ion 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 b egan on 10/14/2010. Figure 2 1 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.Page 9 of 28 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 triggeri ng 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 col lected 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 on e 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 e vent. The hydrograph illustrates two peaks, indicating that two events occurred back

- to

- back.Page 10 of 28 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 fi rst 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 start ing 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 even t

.Page 11 of 28Page 12 of 28 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.Page 13 of 28 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 t his 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 o f 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 th e 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 Dat a 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 fir st 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, EPAPage 14 of 28 only used the first two sample bottles to characterize the turbidity for this event. This thi rd 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 th e 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 colle cted 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. Fi gure 11 is plotted with a logarithmic scale on the vertical axis for flowrate due to the large range in flowrates present.Page 15 of 28Page 16 of 28 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 minute s 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 aliq uots 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.Page 17 of 28 Sam ples 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 emergenc y 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 peri ods from the start of the event and calculated separate average daily turbidity. After the first 24 hour period, ten full bottles were collected. The 11 th bottle contained two aliquots collected within 24 hours of the start of the event, while the second t wo aliquots were collected more than 24 hours after the start of the event . The last aliquot of the 11 th 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.Page 18 of 28 During the next 24

- hour period (5:35 PM on 2/5/2011 throu gh 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.Page 19 of 28 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 3/1 6/2011 at 10:42 AM when the sampler was full. Figure 17 shows the flow and turbidity data for this event.Page 20 of 28 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.Page 21 of 28 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, sin ce 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

T able 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 andPage 22 of 28 representativeness of these datasets for characterizing performance of the passive treatment systems. Based on a de tailed 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 a liquots in some cases exceeded 40,000 NTU, which was the upper range of th e 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, t he large range in observed performance may complicate establishment of a numeric effluent limitation for turbidi ty 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 incomple te. Without dat a 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

.
• Int r a
- 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 t urbidity 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 effect ive 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 esta blishing 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 inPage 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 0.0 3 in (11/16) 0.44 in (11/17) NCR. 2 A 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.2 A 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.2 A 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 NC R.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 int o 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 informationPage 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 NCPage 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

- 01 95 Comment letter from California Coastkeeper Alliance et al