Caltrans Headquarters - Stormwater Quality Monitoring Program - Open/Gap Graded Asphalt Pavements (OGGAP) Stormwater Quality

The Open and/or Gap Graded Asphalt Pavements (OGGAP) Stormwater Quality Project pilot study was planned to evaluate stormwater runoff water quality by comparing open-graded and gap-graded pavements to that of conventional (dense-graded) pavements. The overall objective of this project was to investigate the impacts of various types of asphalt pavement on water quality from:

• Rubberized Hot Mix Asphalt - Open Graded (RHMA-O)
• Open-Graded Friction Course (OGFC)
• Dense-Graded Hot Mix Asphalt (DGHMA)

The project included eleven pilot study sites located statewide. Nine of the pilot study sites consisted of two paired monitoring stations each: one overlay test station, and one control station. For the paired sites, the test stations consisted of a freeway section with a relatively new pavement overlay (RHMA-O or OGFC), up to 5 years old. The test station was paired with a control station consisting of a nearby section of the same road, paved with conventional dense-graded pavement (DGHMA). An additional two pilot study sites consisted of one test station of recently applied dense-graded pavement.

For this water quality monitoring pilot study, ADH, as a subcontractor, was responsible for three paired site stations and one single control site station within Caltrans Districts 1 and 5. ADH monitored sites in Willits, Boonville, Salinas and Atascadero. After site selections were performed in 2006, up to twenty-one storm events have been monitored at each paired site.