Research Idea Details

Research Idea Scope

Background:

Many Departments of Transportation (DOTs) are
being required to retrofit existing highways to comply with Total Maximum Daily
Loads (TMDLs) to improve the quality of runoff discharged from highways. This
retrofit is a particular challenge given the limited right-of-way (ROW)
available in urban areas. Recent research[1]
sponsored by California DOT (Caltrans), Texas DOT (TxDOT), and North Carolina
DOT (NCDOT) has documented substantially better runoff water quality from
highways paved with Permeable Friction Course (PFC) and Open Graded Friction
Course (OGFC), with up to a 90% reduction of the solids discharged in runoff.
By incorporating stormwater treatment within the pavement itself, a number of
difficulties related to highway retrofit can be overcome. No additional ROW is
required for installation. No special maintenance is needed for the pavement to
reduce pollutants over its structural life and many states already have
standard specifications for PFC (or OGFC) and use it widely without recognition
of its environmental benefit. Consequently, PFC is the one truly highway specific
Best Management Practice (BMP).

The processes that improve the quality of
runoff within PFC appear to be primarily sedimentation and filtration. These
are processes that remove sediment and the associated pollutants. The problem
with retrofitting highways with PFC to address many TMDL requirements is that
the constituents of concern are frequently dissolved. The three most common
causes of impairment are pathogens, metals, and nutrients, accounting for about
27,000 listings. All three of these are difficult to remove in conventional
BMPs, and metals and nutrients have a substantial dissolved phase, which makes
treatment even more difficult. Consequently, what is needed now is research on
additives to PFC to improve its pollutant removal for these problem
constituents.

Researchers[2]
have already demonstrated that addition of granular activated carbon to PFC
reduces the concentration of total organic carbon in runoff. We also know
already that there are a number of candidate materials that successfully remove
bacteria, nutrients, and dissolved metals. For instance, iron oxides have
demonstrated substantial removal of both dissolved metals and dissolved
phosphorus. There are also a variety of commercial antimicrobial coatings
available.

The benefits resulting from this research
include:

Providing treatment within the pavement
itself for the primary causes of receiving water impairment;
Improving the removal of dissolved
constituents in stormwater runoff; and
Eliminating the need for large,
conventional BMPs that require additional ROW.

Research
Objective:

The general goal of this research is to begin an investigation
into how PFC could be modified to improve the removal of bacteria, nutrients,
and dissolved metals. The objectives include identifying candidate materials
for testing, incorporating these materials into PFC cores, and then dosing the
cores with simulated highway runoff to determine removal efficiency.

Specific Tasks:

Task 1 –
Literature Review and Background

The main goal of the literature review is to identify materials
that reduce the concentrations of bacteria, nutrient, and dissolved metals in
runoff. The review will include a comprehensive analysis of published reports
in peer-reviewed technical journals to determine the materials previous research
suggests can remove the targeted constituents in highway runoff. Examples of
these materials include metal oxides (dissolved metals and phosphorus removal)
and titanium dioxide (a catalyst for reducing bacteria as well as ozone
concentrations).

Task 2 – Laboratory Evaluation

The laboratory evaluation will determine the effectiveness of the
materials identified in Task 1 for pollutant reduction. The candidate materials
will be added to the cores, which will then be dosed with synthetic stormwater
runoff at rates comparable to those observed during typical rainfall events.
Influent and effluent concentrations will be recorded to determine the
pollutant removal effectiveness. The most promising materials will be
identified for a future field testing program as described in Task 3.

Task 3 – Future Research

A research plan will be developed describing a field prototype testing
program. The research plan shall be developed to thoroughly investigate how to
incorporate additives to PFC as both a stormwater quantity control and a water
quality control BMP that will be developed for further implementation by DOTs.

[1] Eck, Bradley, Winston, R., and Hunt, W., Barrett, M., Water quality of drainage from permeable friction course, American
Society of Civil Engineers Journal of Environmental Engineering, Vol. 138, No.
2, pp. 174 – 181, February 2012.

[2] Wang et al., 2011, Development and
Evaluation of Functional Open Graded Friction Courses (FOGFC) Mixtures for In
Situ Highway Runoff Treatment, in Geo-Frontiers 2011, Dallas, TX March 13-16,
2011.