The NJDEP is developing a re-suspension test
procedure for those manufactured treatment devices (MTDs) used as an online
water-quality device. Until the test procedures are developed, all approved MTDs
shall be used in an offline configuration for all storms that exceed the water
article is a related update to previous articles I wrote on MTDs that appeared
in the January/February 2006 and the July/August 2004 issues of Stormwater.
Recent changes in the approval and
use of manufactured treatment devices (MTDs), particularly in New Jersey, warranted a
quick overview and highlight of a recent decision by the New Jersey Department
of Environmental Protection (NJDEP) on the use of MTDs.
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. In New Jersey, the evaluation and certification
is performed by the NJDEP Division of Science, Research & Technology (DSRT)
in coordination with the New Jersey Corporation for Advanced Technology (NJCAT).
The NJDEP 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, NJDEP has typically attached
certain conditions for use of MTDs that have interim certifications, such that
they only are used as part of a “treatment train” or where it is proven that no
other conventional water-quality best management practice (BMP) can be
incorporated into the design. It is important to note that devices may be “NJCAT
Verified” but not receive full certification from NJDEP.
overview of the process currently in place in New Jersey for evaluating and certifying MTDs
was also presented in the previous articles. The reader is encouraged to visit
the NJCAT Web site and the
NJDEP Website for detailed information and the
specific conditions on the use of these structures.
time of the writing of this article, 12 MTDs have received conditional interim
certification from NJDEP. Six were approved in 2006 and only two approved in
2005. The filtration-type MTDs are
currently approved for an 80% total suspended solids (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 the same TSS removal rate.
NJDEP is currently developing a resuspension test protocol for those MTDs that
seek approval for use as an online water-quality device. Until such protocol is
developed and testing has been submitted and deemed acceptable under that
protocol, all MTDs approved by NJDEP shall be used offline for all storms that
exceed the NJDEP water-quality design storm effective April 11, 2008. Once the
new protocol is in place, vendors may complete testing, and if the results
justify doing so the MTDs may be approved for online use.
Figures 1 and 2 show a typical
offline drainage system layout and a typical configuration of a diversion
Placement of offline MTDs will require additional space and hydraulic evaluations to model the diversion structure and friction and structural losses as a result of the additional pipe and structures. A few vendors have prefabricated diversion structures they market with their MTDs and provide technical guidance on the hydraulic design of the diversion structure.
has been a lot of work performed to date related to the ongoing development of
standards and approval methods of MTDs.
There is an American Society of Civil Engineers (ASCE)/Environmental and
Water Resources Institute (EWRI) task force committee currently studying the
certifications of manufactured stormwater BMPs. The task force committee is
reviewing existing certification programs for various manufactured stormwater
BMPs nationwide. This review and input will be used to help develop new
guidelines. Additional information can be found at the Rutgers University-based
Water Technology Website.
development and use of MTDs continues to increase in order to meet escalating
water-quality requirements and as the available land to develop becomes
limited. This will focus the need
to continue to evaluate and measure the performance of the various MTDs in the
Corporation for Advanced Technology, Verification Process Website. Accessed May 2008.
Department of Environmental Protection, Division of Science, Research &
Technology Website. Accessed May 2008.
Rutgers University, School of Engineering, Water Technology Website
. Accessed May 2008.