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[[Category:Level 2 - General information, reference, tables, images, and archives/Reference]]

Revision as of 18:54, 3 December 2022

TP and TSS credits and guidance for manufactured treatment devices (mtds)

test This page provides pollutant removal credits guidance on determining credits for manufactured treatment devices (mtds).

Overview

Credits are provided for total phosphorus and total suspended solids. Credits refer to the amount of pollutant reduced by treatment with a stormwater best management practice (BMP). For more information on credits, link here.

Abbreviations

  • TP – total phosphorus
  • DP – dissolved phosphorus
  • OP – orthophosphorus
  • TSS – total suspended solids
  • TAPE - Technology Assessment Program – Ecology
  • TER – Technical Evaluation Report
  • GULD - General Use Level Designation
  • LCL – Lower confidence limit of the mean (usually the 95% LCL)
  • MTD (mtd) – manufactured treatment device

What manufactured treatment devices are credited?

Only Washington State Technology Assessment Protocol - Ecology (TAPE) devices that received General Use Level Designation (GULD) are credited for pollutant reductions. TAPE-approved devices include devices that are considered pretreatment devices in Minnesota, as well as permanent structural practices not designed specifically for pretreatment. In Minnesota, pretreatment is required for permanent treatment practices and therefore pretreatment devices are not credited for pollutant removal.

Pollutant removal credits are provided for the following devices.

Device name Manufacturer TAPE approval date Total suspended solids Total phosphorus
BayFilter w/EMC Media BaySaver Technologies, Inc. 7/10/19 Basic Basic
BioPod Biofilter with Curb Inlet Oldcastle Infrastructure, Inc. 10/28/19 Basic Basic
Compost-Amended Biofiltration Swale WSDOT 8/26/13 Basic
ecoStorm plus Watertectonics, Inc. 1/9/13 Basic
Filterra Bioscape CONTECH Engineered Solutions, LLC. 9/16/19 Basic Basic
Filterra System CONTECH Engineered Solutions, LLC. 6/11/20 Basic Tiered
FloGard Perk Filter Oldcastle Infrastructure, Inc. 8/9/18 Basic Basic
Media Filter Drain WSDOT 5/22/14 Basic Basic
Media Filtration System CONTECH Engineered Solutions, LLC. 11/15/16 Basic
MWS-Linear Modular Wetland Bio Clean Environmental Services, Inc. (A Forterra Company) 12/16/19 Basic Tiered
StormFilter using PhosphoSorb Media CONTECH Engineered Solutions, LLC. 1/2/20 Basic Tiered
Stormfilter using ZPG Media CONTECH Engineered Solutions, LLC. 4/14/17 Basic
StormGarden Modular Stormwater Bio-filtration System Environmental Solutions 8/28/19 Basic Basic
The Kraken Bio Clean Environmental Services, Inc. (A Forterra Company) 12/16/19 Basic Basic
Up-Flo Filter w/Filter Ribbons Hydro International 3/5/19 Basic Basic

Data analysis

Data were compiled from Technical Evaluation Reports (TERs) for Washington State’s Technology Assessment Program – Ecology (TAPE). We compiled data for all storm events for each device. Not all data are included in TAPE’s analysis. For example, inflow concentrations for TP must be 0.1 mg/L or greater. In our assessment, we included both TAPE-generated values and values for all data. A summary of the analysis is provided in the adjacent table. The LCL was derived using Washington State’s bootstrap calculator. Detailed discussions for each practice are provided below.

Summary statistics for data collected for Washington State TAPE GULD certification. NOTE: These data are not to be applied to crediting for mtds in Minnesota. For mtd credits, link here
Link to this table

Manufactured treatment device Median inflow TP (mg/L) Median inflow TSS (mg/L) TP Removal (%) TSS removal (%)
Number samples Data with influent > 0.05 mg/L TP TAPE analysis All data TAPE analysis
Data with influent > 0.05 mg/L TP Meeting TAPE criteria Median Mean LCL TAPE median TAPE LCL Median Mean LCL TAPE median
Filterra System 0.090 43.5 17 10 69.0 66.8 59.0 78.5 69.2 89.5 86.2 82.8 89.3
Filterra Bioscape - see Filterra System
StormFilter using PhosphoSorb Media 0.280 389 17 16 81.5 77.4 69.9 78.7 63.6 91.6 88.1 84.8 89.0
Up-Flo Filter w/Filter Ribbons 0.109 29 20 13 50.3 41.5 31.0 57.1 49.9 75 67.6 59.9 77.5
MWS-Linear Modular Wetland 0.103 44 24 16 61.3 60.6 52.5 63.3 54.0 81.9 76.6 71.2 82.9
BayFilter w/EMC Media1 0.160 53 12 11 68.6 64.0 59.8 68.6 58.5 89.3 86.1 81.12 89.3
StormGarden Modular Stormwater Bio-filtration System 0.078 29 20 15 58.9 57.4 52.9 58.9 43.2 89.2 86.0 82.8 91.9
BioPod Biofilter 0.104 40 13 7 71.7 66.7 59.4 75.4 62.4 83.3 86.5 82.1 91.9
BoxlessBioPod Biofilter - see BioPod Biofilter
FloGard Perk Filter 0.123 62.5 21 15 66.5 62.3 53.0; 58.6 without outlier 70.7 48.8 (60.6 without outlier) 80.6 74.7 68.5 81.1
The Kraken 0.142 53 14 10 74.5 71.9 63.9 83.6 71.3 90.6 87.4 77.5 90.7
Jellyfish Filter 0.338 134 23 18 75.2 73.6 68.2 71.0 66.8 86.2 80.0 74.1 78.4
StormTree biofiltration 0.118 38 27 29 62 57 51 68 61 93 92 90 92
Media Filtration System Though this device is GULD certified, it is not used in Minnesota. We therefore did not analyze the data.
Stormfilter using ZPG Media Though this device is GULD certified, it is not used in Minnesota. We therefore did not analyze the data.
ecoStorm plus We have not received data for this device
1 Only data meeting TAPE inflow requirements was available.
2 Six outflow concentrations were at the reporting level of 2.5 mg/L; we used half the reporting limit in our analysis


Total phosphorus credits

The adjacent table provides phosphorus removal credits for mtds. This credit only applies to the water treated by the device. To calculate annual pollutant mass removal, the removal credit must be multiplied by the volume treated.

Caution: Total phosphorus credits only apply to the volume of water being treated by a device
Manufactured treatment device Total phosphorus Total suspended solids
Tier 1 Tier 2 Tier 3
Filterra 50 58 65 90
Phosphosorb 50 65 75 88
UpFlo 50 - - 75
Modular wetland 50 54 60 82

Methodology for phosphorus credits

A tiered approach to crediting allows flexibility in selecting practices and associated conditions that may affect performance, such as influent water quality, and operation and maintenance. However, data from the TERs indicate differing performance levels for each device. It is therefore not possible to develop uniform credits across all devices. It is not desirable to conduct an in depth analysis of each device. We therefore chose the following approach to crediting.

  • Tier 1 applies a 50 percent reduction for TP. This is the TAPE-approved value. Basic conditions required to receive this credit are provided in the support documents for each device. These base conditions are generally the same as in the Washington State approval document, tailored for Minnesota.
  • Tier 2 is based on an assessment of 95% lower confidence limits (LCLs) for the device. Since the LCL varies when all data are considered compared to just data used by TAPE, we typically select the more conservative value, though this may be adjusted based on additional analysis and professional judgement. The credit is based on specific conditions in addition to conditions described for the Tier 1 credit.
  • Tier 3 is based on an assessment of medians for the device. Since the medians vary when all data are considered compared to just data used by TAPE, we typically select the more conservative value, though this may be adjusted based on additional analysis and professional judgement. The credit is based on specific conditions in addition to conditions described for the Tier 1 credit.

Phosphorus analysis

Phosphorus may generally be divided into particulate phosphorus (PP) and dissolved phosphorus (DP). Dissolved phosphorus is typically identified as phosphorus passing through a 0.45 micron filter. For more information on the forms of phosphorus in water, link here.

TP removal rates are affected by the type of device. MTDs that utilize filtration or settling as the treatment mechanism treat only PP, while some devices may have amendments or other mechanisms that can also treat DP. For devices that do not treat DP, the treatment effectiveness, as a percent removal rate, will decrease as the DP fraction of TP increases. This is illustrated in the adjacent figure for two mtds.

graph of TP removal vs OP:TP ratio
TP removal as a function of DP:TP ratio for two mtds.

The adjacent table summarizes data from two MTDs, from the Minnesota Stormwater Manual, from Capitol Region Watershed District in Minnesota, and from a study by Fairbairn. The data show that DP:TP ratios vary from 0.14 for the Capitol Region data to about 0.4 for residential land use. The data also show that DP concentrations in the data collected for mtds is low compared to Minnesota data.

We observed that TP removal efficiency decreased as inflow TP concentrations decreased below about 0.15 mg/L. This is illustrated in the adjacent plot. The adjacent table indicates that typical TP concentrations in Minnesota runoff are above this 0.15 mg/L threshold.

plot of TP removal vs inflow TP
TP removal as a function of inflow TP concentration

Concentrations of TP, OP, and DP for four mtds and Minnesota runoff
Link to this table

Data source Rainfall type TP (mg/L) OP (mg/L) DP (mg/L) DP:TP1
Filterra I 0.09 0.01 0.16
UpFlo I 0.11 0.01 0.13
Modular wetland I ND
Phosphosorb II 0.28
Manual - residential II 0.325 0.20 0.43
Manual - commercial II 0.200 0.07 0.25
CRWD II 0.304 0.042 0.053 0.23
Fairbairn II 0.16 0.68 0.78 0.43

1When only OP data was available, we estimated DP assuming OP is 70 percent of DP


Particle size analysis

Calculating annual volume treated by a device

Devices tested and approved in Washington State are required to treat 91% or more of the average annual runoff. Because climatic conditions differ between Washington State and Minnesota, the annual average volume to which the credit applies must be determined. The following are acceptable methods for calculating the average annual volume treated by a device.

  • Translators
  • Modeling
  • Monitoring
  • Devices approved in similar climatic conditions
  • The device is downstream of a retention device that ensures a specified volume is treated by the device

Credits

Credits for manufactured treatment devices

Credit support documents

Although specific guidance and methods for crediting are provided on individual device support documents, an overview of information in these documents is provided here. All devices must meet the following conditions for credit.

  1. The device must be designed, assembled, installed, operated, and maintained following manufacturers specifications.
  2. All systems must meet specified

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