ENVIRONMENTAL TECHNOLOGY VERIFICATION
PROGRAM
U.S. Environmental Protection Agency
NSF International
ETV Joint Verification Statement
TECHNOLOGY TYPE:
APPLICATION:
TECHNOLOGY NAME:
TEST LOCATION:
COMPANY:
ADDRESS:
WEB SITE:
EMAIL:
STORMWATER TREATMENT TECHNOLOGY
SUSPENDED SOLIDS TREATMENT
DOWNSTREAM DEFENDER®, 6-ft DIAMETER
MADISON, WISCONSIN
HYDRO INTERNATIONAL
94 Hutchins Drive
Portland, Maine 04102
http://www.hydrointernational.biz/us/
stormwaterinquiries@hil-tech.com
PHONE: (207)756-6200
FAX: (207)756-6212
NSF International (NSF), in cooperation with the U.S. Environmental Protection Agency (EPA), operates
the Water Quality Protection Center (WQPC), one of six centers under the Environmental Technology
Verification (ETV) Program. The WQPC recently evaluated the performance of a 6-ft Downstream
Defender®, manufactured by Hydro International. The Downstream Defender® was installed at the
Madison Water Utility in Madison, Wisconsin. Earth Tech, Inc. and the United States Geologic Survey
(USGS) performed the testing.
EPA created ETV to facilitate the deployment of innovative or improved environmental technologies
through performance verification and dissemination of information. The ETV program's goal is to further
environmental protection by accelerating the acceptance and use of improved and more cost-effective
technologies. ETV seeks to achieve this goal by providing high quality, peer-reviewed data on technology
performance to those involved in the design, distribution, permitting, purchase, and use of environmental
technologies.
ETV works in partnership with recognized standards and testing organizations; stakeholder groups, which
consist of buyers, vendor organizations, and permitters; and with the full participation of individual
technology developers. The program evaluates the performance of innovative technologies by developing
test plans that are responsive to the needs of stakeholders, conducting field or laboratory tests (as
appropriate), collecting and analyzing data, and preparing peer-reviewed reports. All evaluations are
conducted in accordance with rigorous quality assurance protocols to ensure that data of known and
adequate quality are generated and that the results are defensible.
07/31/WQPC-WWF
The accompanying notice is an integral part of this verification statement.
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TECHNOLOGY DESCRIPTION
The following description of the Downstream Defender® was provided by the vendor and does not
represent verified information.
The Downstream Defender® is a hydrodynamic vortex separator designed to remove settleable solids (and
their associated pollutants), oil, and floatables from stormwater runoff. It consists of a cylindrical
concrete vessel, with plastic internal components and a 304 stainless steel support frame and connecting
hardware. The concrete vessel is a standard pre-cast cylindrical manhole with a tangential inlet pipe
installed below ground. Two ports at ground level provide access for inspection and clean out of stored
floatables and sediment. The internal components consist of two concentric hollow cylinders (the dip
plate and center shaft), an inverted cone (the center cone), a benching skirt, and a floatables lid.
The Downstream Defender® is self-activating, and operates on simple fluid dynamics. The geometry of
the internal components and placement of the inlet and outlet pipes are designed to direct the flow in a
pre-determined path through the vessel. Stormwater is introduced tangentially into the side of the vessel,
initially spiraling around the perimeter in the outer annular space between the dip plate cylinder and
manhole wall. Oil and floatables rise to the water surface and are trapped by the dip plate in the outer
annular space. As the flow continues to rotate about the vertical axis, it travels down towards the bottom
of the dip plate. Low energy vortex motion directs sediment toward the center and base of the vessel.
Flow passes under the dip plate and up through the inner annular space, between the dip plate and center
shaft, as a narrower spiraling column rotating at a slower velocity than the outer downward flow. The
outlet of the Downstream Defender® is a single central discharge from the top water level in the inner
annulus.
Performance of the Downstream Defender®, in terms of sediment removals, depends on the incoming
flow rate, particle size distribution, specific gravity, and runoff temperature. According to Hydro
International, for runoff at 15 C°, the Downstream Defender® will remove over 80% of settleable solids
with a specific gravity of 2.65 and a particle size distribution similar to Maine DOT road sand at flow
rates up to 3 cfs. Flows exceeding the design capacity (3 cfs for the tested system) would be bypassed by
a weir system installed upstream of the Downstream Defender®.
VERIFICATION TESTING DESCRIPTION
Methods and Procedures
The test methods and procedures used during the study are described in the Test Plan for the Verification
of. Downstream Defender® "Madison Water Utility Administration Building Site" Madison, Wisconsin
September 30, 2005. The Downstream Defender® was installed to treat runoff collected from a paved
parking area at the Madison Water Utility in Madison, Wisconsin. Madison receives an average annual
precipitation of nearly 33 in., with an average snowfall of 44 in.
Verification testing consisted of collecting data during a minimum of 15 qualified events that met the
following criteria:
• The total rainfall depth for the event, measured at the site, was 0.2 in. (5 mm) or greater;
• Flow through the treatment device was successfully measured and recorded over the duration of
the runoff period;
• A flow-proportional composite sample was successfully collected for both the inlet and the outlet
over the duration of the runoff event;
• Each composite sample was comprised of a minimum of five aliquots, including at least two
aliquots on the rising limb of the runoff hydrograph, at least one aliquot near the peak, and at least
two aliquots on the falling limb of the runoff hydrograph; and
• There was a minimum of six hours between qualified sampling events.
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Automated sample monitoring and collection devices were installed and programmed to collect composite
samples from the inlet, system outlet, bypass, and combined discharge (system plus bypass) during
qualified flow events. In addition to the flow and analytical data, operation and maintenance (O&M) data
were recorded. Samples were analyzed for total suspended solids (TSS), suspended sediment
concentration (SSC), total dissolved solids (TDS), volatile suspended solids (VSS), and particle size
distribution. The TSS analytical method was modified for samples with a heavy settleable sediment load
using a procedure developed by USGS. The adjusted TSS method was designed to provide an improved
methodology for measuring large, dense sediment particles in samples. Refer to the verification report for
additional details about the modified TSS method.
VERIFICATION OF PERFORMANCE
Verification testing of the Downstream Defender® lasted approximately 17 months, and coincided with
testing conducted by USGS and the Wisconsin Department of Natural Resources. A total of 20 storm
events were sampled.
Test Results
The precipitation data for the rain events are summarized in Table 1. Peak flow rates exceeded the rated
treatment capacity of the Downstream Defender® during events 5, 6, 19 and 20. These events were large
and intense, and it appeared that runoff from an adjacent drainage area may have contributed additional
flow and organic solids loading to the unit during these events.
The monitoring results were evaluated using event mean concentration (EMC) and sum of loads (SOL)
comparisons. The EMC evaluates treatment efficiency on a percentage basis by dividing the outlet
concentration by the inlet concentration and multiplying the quotient by 100. The EMC was calculated
for each analytical parameter and each storm event. The SOL comparison evaluates the treatment
efficiency on a percentage basis by comparing the sum of the inlet and outlet loads (the parameter
concentration multiplied by the runoff volume) for all storm events. The calculation is made by
subtracting from one the quotient of the total outlet load divided by the total inlet load, and multiplying by
100. SOL results can be summarized on an overall basis since the loading calculation takes into account
both the concentration and volume of runoff from each event. The analytical data ranges, EMC range,
and SOL reduction values are shown in Table 2.
The ratio of organic sediment to total sediment was measured by evaluating the ratio of VSS to TSS or
SSC. This ratio showed a median organic sediment loading of 21% over all events, with a range of 4.7%
to 67% during individual events. Organic materials, which include grass or leaf debris, are less dense
than inorganic sediments, such as soil. The vendor claims that the Downstream Defender® is not as
effective at removing lower-density organic solids from runoff.
A particle size gradation was conducted to quantify percentage (by weight) of particles ranging from
>500 um to <2 um, and the SOL was recalculated based on particle sizes. The particle size distribution of
the sediments encountered at this site was significantly finer than the Maine DOT road sand and F-110
Silica Sand which formed the basis of product claims. For the range of solids encountered at this site, the
Downstream Defender® removed 90% of particles larger than 250 um on a cumulative basis. As shown in
Table 3, the Downstream Defender® removed 78% of the particles greater than 125 um and 67% of the
particles greater than 63 um on a cumulative basis.
System Operation
The Downstream Defender® was installed prior to verification, so verification of installation procedures
on the system was not documented. It was thoroughly cleaned prior to the start of verification testing.
The Downstream Defender® was inspected periodically during verification, and no significant issues were
noted. By the end of the verification test, the sediment chamber contained sediment at an approximate
average depth of 0.35 ft. A particle size distribution analysis conducted on the retained solids showed
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that approximately 93% of the retained solids were 125 um or larger. No specific gravity analysis was
conducted for the captured solids; however, visual inspections suggested significant organic content. The
dry weight of the retained solids was 416 pounds.
Table 1. Rainfall Data Summary
Rainfall Rainfall Runoff
Event Start Amount Duration Volume
Number Date Time (in.) (hr:min)
1.
2.
3.
4.
1 3/8/06 18:03 0.71 4:36
2 3/12/06 18:34 0.43 9:25
3 4/2/06 20:41 1.01 10:01
4 4/12/06 5:07 0.37 2:56
51 4/16/06 4:15 1.13 12:44
6 4/29/06 17:18 1.65 25:38
7 5/1/06 21:16 0.25 0:26
8 5/9/06 12:01 0.37 6:50
9 5/11/06 6:59 0.86 23:55
10 5/17/06 15:36 0.23 2:02
11 6/25/06 17:34 0.79 15:41
12 7/9/06 19:45 0.36 0:08
13 7/11/06 8:44 1.87 8:51
14 7/19/06 21:43 0.96 9:44
15 7/22/06 16:51 0.36 0:30
161 7/27/06 12:27 2.16 1:30
17 8/6/06 6:53 0.71 5:08
18 8/17/06 16:27 0.29 1:45
191 8/23/06 23:06 1.60 8:17
201 8/24/06 13:30 1.35 2:13
(ft3)2
1,880
1,370
5,910
1,980
6,230
8,480
1,570
2,090
5,040
1,310
4,250
1,430
10,990
4,680
1,860
7,150
3,630
1,300
13,450
17,180
Peak Flow
Rate (cfs) 2
1.0
0.42
0.38
0.63
5.81
0.66
2.0
0.35
0.18
0.85
0.67
2.6
1.5
2.5
1.9
6.51
0.50
1.3
4.41
4.61
Water
Temp.
(°C)
3.5
4.6
15.5
3
3
3
3
15.44
10.54
14.84
19.04
24.84
20.74
22.84
23.04
24.04
23.44
22.44
22.44
22.84
Peak flow capacity was exceeded and bypass flows were sampled.
Runoff volume and peak discharge rate measured at the inlet
report for further details.
Temperature not recorded due to equipment malfunction.
Water temperature recorded at a nearby stormwater sampling
Department of Natural Resources.
monitoring point. See the verification
site monitored by Wisconsin
Table 2. Analytical Data, EMC Range, and SOL Reduction Results
SOL SOL reduction
Inlet Outlet reduction all events inc.
range range EMC range w/o bypass bypass
Parameter (mg/L) (mg/L) (%) (%) (%)
TSS
ssc
TDS
vss
23 - 700
22 - 904
<50 - 260
9-76
19-584
21-662
<50 - 238
10-76
-51-62
-47 - 70
-163-55
-82 - 19
27
42
1
-7
22
33
1
-6
07/31/WQPC-WWF
The accompanying notice is an integral part of this verification statement.
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September 2007
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Table 3. Sediment Sum of Load Results by Particle Size Category
Individual
Particle Size Load
DD System
Cumulative
Particle Size Load
DD System
Particle Size
Category (um)
>500
250-500
125-250
63-125
32-63
14-32
DD Inlet
Ob)
453
449
150
128
122
517
DD Outlet
Ob)
39
49
146
156
122
550
Bypass
Ob)
32
58
49
56
31
164
Efficiency
91
89
3
-2
0
-6
Efficiency
85
79
2
-15
0
-5
Efficiency
91
90
78
67
61
42
Efficiency
85
82
69
58
52
34
Quality Assurance/Quality Control
NSF personnel completed a technical systems audit during testing to ensure that the testing was in
compliance with the test plan. NSF also completed a data quality audit of at least 10% of the test data to
ensure that the reported data represented the data generated during testing. In addition to QA/QC audits
performed by NSF, EPA personnel conducted an audit of NSF's QA Management Program.
Original signed by
Sally Gutierrez
October 15, 2007
Sally Gutierrez Date
Director
National Risk Management Research Laboratory
Office of Research and Development
United States Environmental Protection Agency
Original signed by
Robert Ferguson
October 3, 2007
Robert Ferguson
Vice President
Water Systems
NSF International
Date
NOTICE: Verifications are based on an evaluation of technology performance under specific,
predetermined criteria and the appropriate quality assurance procedures. EPA and NSF make no expressed
or implied warranties as to the performance of the technology and do not certify that a technology will
always operate as verified. The end user is solely responsible for complying with any and all applicable
federal, state, and local requirements. Mention of corporate names, trade names, or commercial products
does not constitute endorsement or recommendation for use of specific products. This report is not an NSF
Certification of the specific product mentioned herein.
Availability of Supporting Documents
Copies of the ETV Verification Protocol, Stormwater Source Area Treatment Technologies Draft
4.1, March 2002, the verification statement, and the verification report (NSF Report Number
07/31/WQPC-WWF) are available from:
ETV Water Quality Protection Center Program Manager (hard copy)
NSF International
P.O. Box 130140
Ann Arbor, Michigan 48113-0140
NSF website: http://www.nsf.org/etv (electronic copy)
EPA website: https://www.epa.gov/etv (electronic copy)
Appendices are not included in the verification report, but are available from NSF upon request.
07/31/WQPC-WWF
The accompanying notice is an integral part of this verification statement.
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September 2007
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