Specifying and Permitting Alternative MTDs
This article is an update to a previous one I wrote in the July/August 2004 issue of Stormwater . Recent advances and changes in the approval and use of manufactured treatment devices (MTDs), particularly in New Jersey, warrant a revisit and further discussion of their use. MTDs are generally defined as prefabricated stormwater treatment structures that utilize settling, filtration, absorptive/adsorptive materials, vortex separation, vegetative components, or other appropriate technology to remove pollutants from stormwater runoff. Compliance with the EPA’s National Pollutant Discharge Elimination System Phase II rule is having an impact on the MTD market.
Many state and local regulatory agencies, such as those in New Jersey, have been implementing and continue to implement and enforce the use of new stormwater management regulations to provide for increased water-quality control, particularly for new developments. Limited developable property, rights of way, and other site constraints are making the use of such conventional best management practices (BMPs) as aboveground basins, bioretention, infiltration, and stormwater treatment wetlands difficult or not cost-effective. In the last year alone, this has resulted in a substantial increase in the use of MTDs. To meet the increasing need to provide alternatives for removal of floatables, total suspended solids (TSS), and dissolved pollutants, innovative BMP devices are being developed and marketed by various vendors. A quick count of the MTDs in just one issue of Stormwater revealed approximately 20 MTDs in use.
In New Jersey, the evaluation and certification is performed by the New Jersey Department of Environmental Protection (NJDEP) Division of Science, Research & Technology (DSRT) in coordination with the New Jersey Corporation for Advanced Technology (NJCAT). The DSRT is ultimately responsible for certifying final pollutant-removal rates for all manufactured treatment devices. All conditional interim certifications are effective only for a limited time period, as determined on a case-by-case basis by the NJDEP. In addition, the NJDEP has typically attached certain conditions for use of BMPs that have interim certifications, such as that they be used only as part of a “treatment train” or where it is proven that no other conventional water-quality BMP can be incorporated into the design. It is important to note that devices may be “NJCAT Verified” but have not received full certification from the NJDEP.
An overview of the process currently in place in New Jersey for evaluating and certifying MTDs was also presented in the previous article. Providing uniform design and review standards for the use of these MTDs is continually needed to facilitate a level playing field of equity and fairness. In addition, specifying multiple MTDs avoids proprietary issues, particularly on state and federally funded public projects. The reader is encouraged to visit the NJCAT Web site (http://www.njcat.org/verification) and the NJDEP Web site (http://www.state.nj.us/dep/dsr) for detailed information and the specific conditions on the use of these structures.
MTDs are designed to capture sediments, metals, hydrocarbons, floatables, and/or other pollutants in stormwater runoff before the runoff is conveyed to a storm sewer system, additional stormwater-quality treatment measure, or water body.
It is important to note that federally funded projects restrict the use of proprietary products. State agencies, such as the New Jersey Department of Transportation, also require that the designer provide justification for a product’s use. If an item uses a non-standard detail or specification, the designer must submit the justification for its use. If a proprietary device is used that is not an approved standard item, the designer must try to provide at least three approved equals.
Sometimes during construction, the contractor proposes an alternative and the designers and owners are confronted with trying to determine if the substitute is an equal, or whether the different MTD complies with the approved permits. Typically, there is insufficient time or it is not practical to go back to the regulatory agencies to get approval or a revised permit.
As outlined before, the NJDEP has a procedure in place for evaluations and certifications of manufactured treatment devices. At the time of this writing, six MTDs have received conditional interim certification from the NJDEP. There were only two approved MTDs a year ago. Currently, there are also another four MTDs that are candidates for NJCAT verification that will most likely receive NJDEP conditional interim certification. The NJDEP also requires field-testing as a condition of the interim conditional approval. Perhaps after testing is complete, the TSS removal rates and storage and maintenance issues may be clarified, which will help provide for a more robust design and approval selection process.
The filtration-type MTDs are currently approved for an 80% TSS removal rate, and the gravity-separation-type MTDs are approved for a 50% TSS removal rate. It is important to note that the NJDEP has provided all the gravity-separation-type MTDs with an equal TSS removal rate. On one hand, providing a uniform TSS removal rate has somewhat neutralized any perceived superior performance aspect (from a regulatory/permit approval standpoint) of a specific product being promoted by each vendor. On the other hand, it has simplified the selection process. Selection can now be made based on site conditions, cost, and which product provides the greatest ease of maintenance. There are positives and negatives to this policy decision.
Having several approved MTDs to select from has presented another issue to discuss and consider, particularly related to preparing permit documents. Each unit is of different size and shape. Inverts in and out of the structure vary, and the head required to efficiently operate the MTDs also varies. The frictional and structural losses through the units vary as well, which could impact the drainage design and upstream hydraulic grade line evaluation.
The goal of the design by the engineer, if practical and within the scope of services, is to allow for the multiple selections of the approved units by the contractor to encourage competition and facilitate a cost-effective product. The role of the design engineer is also one of providing benchmarks to facilitate an equitable review and approval of alternatives. The NJDEP states in its approved permit documents that “no change in the plans or specifications shall be made except with the prior written permission of the NJDEP.”
The contractor sometimes looks for cost-effective alternatives that may not be specifically detailed in the design or permit documents. Certain economic and regional factors also dictate which MTD can be the most cost-effective at the specific time of the bid. Relationships and/or reduced time for ordering, fabrication, and delivery may make one unit more desirable than another, despite the lower purchase price. Most often, time is money for the contractor.
With the above in mind, outlined as follows are some issues to consider for owners and designers of MTDs:
- Plan ahead and provide for a design, if possible, that allows for a change in invert elevations. Some MTDs have the same invert in and out, and some MTDs require a change in elevation between the invert and outlet.
- Consider specifying that any alternative MTDs must maintain the same amount of storage volume (e.g., for sediment and oil). This will prevent a substitution that may result in additional maintenance requirements for the owner. It is recognized that this can be somewhat subjective, because each MTD captures TSS at different rates and different particle sizes.
- Consider in the hydraulic design of the drainage facilities that different MTDs have different head losses. It should be recognized that certain site constraints and limited hydraulic depth might eliminate some feasible alternatives.
- Provide enough design information in the contract documents that the contractor can evaluate and demonstrate that all alternatives meet the design objectives. Depending on the vendor and economic factors, it might be possible to upsize a unit to reduce head losses, but still provide an alternative that is competitive with a smaller and less expensive product under other circumstances.
- Format the design, details, specifications, and permit applications to specify at least several approved MTDs. This range of choices might avoid the need to modify the permit documents during construction. This will save time and project costs for both the contractor and owner and could also avoid potential delays and claims. It should be recognized that this practice would result in additional design costs.
- If applicable, clarify in the design and construction documents that the contractor will be responsible for obtaining regulatory approval for any changes that violate the approved permit plans or conditions.
If the contract documents or information submitted by the contractor is not clear, it may result in confusion on what is an “approved equal.” This could lead to problems modifying permits or getting regulatory or owner approval of an alternative MTD. It should be recognized that different approaches to the design and specification of alternative MTDs might be needed between privately and publicly funded projects.
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Figure 1 outlines a typical design and approval process of MTDs in New Jersey.
The ongoing development of standards and approval methods of multiple MTDs will clarify selection options for designers, regulatory reviewers, owners, and contractors, while protecting the environment and improving water-quality treatment and control. Never before has providing cost-effective MTDs required such a highly coordinated team effort between the owners, designers, regulatory agencies, and contractors.
January-February 2006
Specifying and Permitting Alternative MTDs
This article is an update to a previous one I wrote in the July/August 2004 issue of Stormwater . Recent advances and changes in the approval and use of manufactured treatment devices (MTDs), particularly in New Jersey, warrant a revisit and further discussion of their use. MTDs are generally defined as prefabricated stormwater treatment structures that utilize settling, filtration, absorptive/adsorptive materials, vortex separation, vegetative components, or other appropriate technology to remove pollutants from stormwater runoff. Compliance with the EPA’s National Pollutant Discharge Elimination System Phase II rule is having an impact on the MTD market.Many state and local regulatory agencies, such as those in New Jersey, have been implementing and continue to implement and enforce the use of new stormwater management regulations to provide for increased water-quality control, particularly for new developments. Limited developable property, rights of way, and other site constraints are making the use of such conventional best management practices (BMPs) as aboveground basins, bioretention, infiltration, and stormwater treatment wetlands difficult or not cost-effective. In the last year alone, this has resulted in a substantial increase in the use of MTDs. To meet the increasing need to provide alternatives for removal of floatables, total suspended solids (TSS), and dissolved pollutants, innovative BMP devices are being developed and marketed by various vendors. A quick count of the MTDs in just one issue of Stormwater revealed approximately 20 MTDs in use.
In New Jersey, the evaluation and certification is performed by the New Jersey Department of Environmental Protection (NJDEP) Division of Science, Research & Technology (DSRT) in coordination with the New Jersey Corporation for Advanced Technology (NJCAT). The DSRT is ultimately responsible for certifying final pollutant-removal rates for all manufactured treatment devices. All conditional interim certifications are effective only for a limited time period, as determined on a case-by-case basis by the NJDEP. In addition, the NJDEP has typically attached certain conditions for use of BMPs that have interim certifications, such as that they be used only as part of a “treatment train” or where it is proven that no other conventional water-quality BMP can be incorporated into the design. It is important to note that devices may be “NJCAT Verified” but have not received full certification from the NJDEP.
An overview of the process currently in place in New Jersey for evaluating and certifying MTDs was also presented in the previous article. Providing uniform design and review standards for the use of these MTDs is continually needed to facilitate a level playing field of equity and fairness. In addition, specifying multiple MTDs avoids proprietary issues, particularly on state and federally funded public projects. The reader is encouraged to visit the NJCAT Web site (http://www.njcat.org/verification) and the NJDEP Web site (http://www.state.nj.us/dep/dsr) for detailed information and the specific conditions on the use of these structures.
MTDs are designed to capture sediments, metals, hydrocarbons, floatables, and/or other pollutants in stormwater runoff before the runoff is conveyed to a storm sewer system, additional stormwater-quality treatment measure, or water body.
It is important to note that federally funded projects restrict the use of proprietary products. State agencies, such as the New Jersey Department of Transportation, also require that the designer provide justification for a product’s use. If an item uses a non-standard detail or specification, the designer must submit the justification for its use. If a proprietary device is used that is not an approved standard item, the designer must try to provide at least three approved equals.
Sometimes during construction, the contractor proposes an alternative and the designers and owners are confronted with trying to determine if the substitute is an equal, or whether the different MTD complies with the approved permits. Typically, there is insufficient time or it is not practical to go back to the regulatory agencies to get approval or a revised permit.
As outlined before, the NJDEP has a procedure in place for evaluations and certifications of manufactured treatment devices. At the time of this writing, six MTDs have received conditional interim certification from the NJDEP. There were only two approved MTDs a year ago. Currently, there are also another four MTDs that are candidates for NJCAT verification that will most likely receive NJDEP conditional interim certification. The NJDEP also requires field-testing as a condition of the interim conditional approval. Perhaps after testing is complete, the TSS removal rates and storage and maintenance issues may be clarified, which will help provide for a more robust design and approval selection process.
The filtration-type MTDs are currently approved for an 80% TSS removal rate, and the gravity-separation-type MTDs are approved for a 50% TSS removal rate. It is important to note that the NJDEP has provided all the gravity-separation-type MTDs with an equal TSS removal rate. On one hand, providing a uniform TSS removal rate has somewhat neutralized any perceived superior performance aspect (from a regulatory/permit approval standpoint) of a specific product being promoted by each vendor. On the other hand, it has simplified the selection process. Selection can now be made based on site conditions, cost, and which product provides the greatest ease of maintenance. There are positives and negatives to this policy decision.
Having several approved MTDs to select from has presented another issue to discuss and consider, particularly related to preparing permit documents. Each unit is of different size and shape. Inverts in and out of the structure vary, and the head required to efficiently operate the MTDs also varies. The frictional and structural losses through the units vary as well, which could impact the drainage design and upstream hydraulic grade line evaluation.
The goal of the design by the engineer, if practical and within the scope of services, is to allow for the multiple selections of the approved units by the contractor to encourage competition and facilitate a cost-effective product. The role of the design engineer is also one of providing benchmarks to facilitate an equitable review and approval of alternatives. The NJDEP states in its approved permit documents that “no change in the plans or specifications shall be made except with the prior written permission of the NJDEP.”
The contractor sometimes looks for cost-effective alternatives that may not be specifically detailed in the design or permit documents. Certain economic and regional factors also dictate which MTD can be the most cost-effective at the specific time of the bid. Relationships and/or reduced time for ordering, fabrication, and delivery may make one unit more desirable than another, despite the lower purchase price. Most often, time is money for the contractor.
With the above in mind, outlined as follows are some issues to consider for owners and designers of MTDs:
- Plan ahead and provide for a design, if possible, that allows for a change in invert elevations. Some MTDs have the same invert in and out, and some MTDs require a change in elevation between the invert and outlet.
- Consider specifying that any alternative MTDs must maintain the same amount of storage volume (e.g., for sediment and oil). This will prevent a substitution that may result in additional maintenance requirements for the owner. It is recognized that this can be somewhat subjective, because each MTD captures TSS at different rates and different particle sizes.
- Consider in the hydraulic design of the drainage facilities that different MTDs have different head losses. It should be recognized that certain site constraints and limited hydraulic depth might eliminate some feasible alternatives.
- Provide enough design information in the contract documents that the contractor can evaluate and demonstrate that all alternatives meet the design objectives. Depending on the vendor and economic factors, it might be possible to upsize a unit to reduce head losses, but still provide an alternative that is competitive with a smaller and less expensive product under other circumstances.
- Format the design, details, specifications, and permit applications to specify at least several approved MTDs. This range of choices might avoid the need to modify the permit documents during construction. This will save time and project costs for both the contractor and owner and could also avoid potential delays and claims. It should be recognized that this practice would result in additional design costs.
- If applicable, clarify in the design and construction documents that the contractor will be responsible for obtaining regulatory approval for any changes that violate the approved permit plans or conditions.
If the contract documents or information submitted by the contractor is not clear, it may result in confusion on what is an “approved equal.” This could lead to problems modifying permits or getting regulatory or owner approval of an alternative MTD. It should be recognized that different approaches to the design and specification of alternative MTDs might be needed between privately and publicly funded projects.
Figure 1 outlines a typical design and approval process of MTDs in New Jersey.
The ongoing development of standards and approval methods of multiple MTDs will clarify selection options for designers, regulatory reviewers, owners, and contractors, while protecting the environment and improving water-quality treatment and control. Never before has providing cost-effective MTDs required such a highly coordinated team effort between the owners, designers, regulatory agencies, and contractors.