In the summer of 2014, the City of Columbia,

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1 Maintaining the Next Generation of Permeable Pavement This is a unique perspective of the lot, 70% completed. In the summer of 2014, the City of Columbia, MO completed a project where they transformed an above-ground, large flood volume, detention basin on city property into an underground stormwater quality detention facility with a permeable pavement parking lot on top. The result was more employee parking, a more appropriately functioning detention system and treatment of stormwater runoff. As the city grew, the city s workforce also grew and needed additional parking. The city received project funding from Boone County, the recipient of an EPA Clean Water Act 319 grant through the Missouri Department of Natural Resources, to retrofit the City s Public Works operations facility with stormwater treatment practices in an effort to reduce non-point source pollution. Hinkson Creek, in Columbia, Missouri, is an impaired waterway as defined by the EPA 303(d) list where no one pollutant or condition could be identified as the source of the impairment (TMDL Information sheet-mdnr rev. 9/2009). The 319 grant was an effort to address the required TMDL-to reduce storm water runoff volume. The EPA made it clear, the impairment/pollutant was runoff volume. By reducing this pollutant, the result would be to reduce the impact of storm water on the stream channel, raise the water table and restore the in-stream habitat and reduce pollutant loads associated with storm water ( Total Maximum Daily Load Information Sheet: Hinkson Creek MO Dept. of Natural Resources). Clearly, increasing the volume of stormwater detained and improving the treatment of the runoff by increasing the time of concentration on a mostly impervious site would work towards directly achieving these goals. Although the City portion of the project is located in the Bear Creek watershed, the goal of the grant was to show the efficacy of these treatment practices in the mid-missouri area to improve water quality which is certainly transferrable to projects in the Green Infrastructure s key goal is to mimic natural processes of dealing with stormwater and attempt to return an area s hydrology to pre-development levels through infiltration and a variety of other practices. neighboring Hinkson Creek watershed. One key element of the project was how to do it in a manner that would showcase Green Infrastructure practices and reduce or eliminate the concern as to their effectiveness and long term viability in Missouri, the Show-Me state. Green Infrastructure s key goal is to mimic natural processes of dealing with stormwater and attempt to return an area s hydrology to pre-development levels through infiltration and a variety of other practices. Erin Keys, an engineer with the Columbia Public Works Department, decided that while she was going to increase the parking space area, improving the detention mechanism and treating the water quality volume was imperative to achieving the long term goals of improving water quality of the site stormwater runoff. As a result, one of the 20 July/August 2015

2 additional design features was a detention system that drains over 48 hours instead of the traditional 24 hours. This made a significant reduction in the peak flow while improving infiltration. By allowing additional contact time of the stormwater to the ground below, infiltration will be increased. What made this underground system unique for the region was utilizing a permeable pavement solution to drain the water into the underground detention system. There are no catch basins or surface inlets of any kind on this project. All roof drains and surface water enter the system through the joints of the 6200 square foot permeable pavement system. The stormwater will filter through the gravel layer and geotextile fabric, flow into the void space PERMEABLE PAVERS of the tank system, then flow through the outlet structure in a controlled flow. The designed cross section consisted of installing over 1000 Atlantis Flo-Tank modules in the Triple Tank configuration, wrapped in geotextile fabric, on a 6 inch compacted base, two feet of clean one-inch stone on top of the wrapped tanks, and then installing the Permeable PaveDrain Articulating Concrete Block Mat System on top of the compacted rock. (See insert on bottom of page 22 for cross section) The existing control structure for the detention basin was retrofitted to accommodate the new underground tank system. The manhole in the outlet control structure, located at the lower end of the tanks, can monitor the water coming out of the tank system. Inspection ports in other locations were installed to monitor any sediment in the tanks and to monitor the water height. Long term monitoring will include a yearly inspection to determine any maintenance needs. Since the only way the stormwater runoff gets into the tanks is by filtering through the rock and the geotextile layer, no significant sediment should be observed inside the tank system and stormwater quality will be achieved exiting the system. 21

3 Installing the Atlantis Flo-tanks. Final cost of the underground detention and installation was approximately $10 per cubic foot of tank storage. In the original plan, all of this work was to be performed by city personnel but after reviewing the available work schedules, the installation of the Flo-Tanks, rock and permeable pavement were completed by Seth Paul Excavating. A vital preconstruction meeting was first completed on January 17th, 2014 to make sure all parties understood the installation process, equipment requirements, staging of materials in a very tight construction area and the key elements of installation that were critical to the long term success of the project. Seth Paul was up for the challenge and brought a critical perspective to the process. One of the key elements valued by Keys was that the permeable pavement system was shipping in finished mats so that the installation involved equipment and not a high amount of labor. Installation of the permeable pavement was achieved with 3 laborers and one equipment operator with a 46,000 pound hydraulic excavator (Case CX-210) and a skid steer. The first load of mats arrived on May 28, 2014 and included a spreader bar to be used to lift the mats off of the truck and set them in place. Care was taken in fine grading the one-inch clean stone and surface finishing with a plate compactor to flatten the surface. The mats were lifted and placed in their proper location. After several mats were laid, a bump bar was used to tighten the space between the blocks so the joint spacing was uniform across the entire parking area and the project stayed in compliance with ADA requirements. The bump bar was nudged with a skid steer to complete this aspect of the installation. In approximately 3 days, all mats were laid and the edging and final hand-placed edge blocks were installed. In reviewing the installation after completion, one aspect that would have been done differently would have been the staging and laying of mats. During the preconstruction meeting, significant time was taken to evaluate the different layout possibilities for efficiency. While necessary for the limited working and staging area that was available, the final plan that was chosen resulted in the equipment being driven over the graded, compacted gravel for each mat placement. Therefore, the finished grade had to be reworked each time an additional mat was to be installed. On future installations, it would be beneficial to keep this in mind so mats can be laid in such a way that equipment would not have to run on the compacted areas ready for mats. Driving on the installed mats is another option and is now a frequent occurrence because of this valuable lesson. Another consider- 22 July/August 2015

4 ation to improve placement efficiency and reduce installation time would be to use a crane to set the permeable pavement mats instead of the hydraulic excavator. As with many decisions, it is a matter of time and money. Final installed cost of the permeable pavement was approximately $10 per square foot. As with most new products, Keys and others with the city, were concerned about the long-term maintenance needs. As stated earlier, a critical element of this pavement design is that the blocks properly infiltrate so that the water can drain into the tanks below. One of the challenges in this particular installation is that on most days, the city s multiple street sweepers are cleaned and washed out immediately upstream of the permeable pavement. Large amounts of sediment and debris drain from the washout area to a small pretreatment area, but noticeable amounts of debris are still deposited with the runoff right on to the blocks. In a 6 month period, not only was there close to 1800 square feet of block that was clogged with sediment, there was a 40 square foot area that had two to four inches of sediment on top of the blocks at the furthest downhill section of the parking The PaveDrain mats being zippered into the adjoining mat. lot. Besides its ability to infiltrate at over 3000 inches per hour, one of the great values of this system is that PaveDrain, LLC also developed a vacuum head capable of cleaning the pavement with the use of a basic combination sewer and vacuum truck most municipalities have. This vac-head can spray water up to 3500 psi through 16 Genesis Nursery, Inc. What does your pavement do for you?

5 Above: 6 months later, while other areas had some sediment, 2-4 of sediment completed plugged access to the block. Inset: The PaveDrain, LLC Vac-head completely cleaning the void space to return the infiltration rate to over 2000 inches per hour. spinning nozzles directly on the permeable block, while also utilizing 3400 cfm from the vacuum truck to remove debris from the open joints. On April 1, 2015, (no joke), ASP Enterprises demonstrated this vac-head for the City of Columbia and several of its key people. The city s vacuum equipment was utilized and cleaned the 1800 square feet in 90 minutes. Prior to cleaning, Todd Noble from ASP Enterprises completed the ASTM C1781 Standard Test Method for Surface Infiltration Rate of Permeable Unit Pavement Systems. That test consists of placing an 8 inch tall piece of 12 inch diameter pipe, sealed with plumber s putty directly on a representative sample of the pavement. The initial test was performed on one of the clogged areas. Per the ASTM test, 40 pounds of water (approximately 5 gallons) was poured into the pipe without exceeding a one half inch water height and the process was timed from the start of water being poured until standing water no longer exists. The initial pre-cleaned pavement test was performed and the ASTM calculation resulted in an infiltration rate of 141 inches per hour in a highly, almost fully, plugged state. Over the course of the next 90 minutes, the vac-head was utilized over all the sediment laden areas. While it felt like a slow process, the effectiveness was monitored to make sure that the sediment was getting removed all the way down to the bottom of the block and the rock was being opened back up for infiltration. In most cases, we were able to clean down to 5.25 inches (the thickness of the block) in two passes of the vac-head. One back and forth pass in all areas removed most of the sediment. With the vac-head being on good quality wheels, it was fairly simple to use and move around with little effort. After the cleaning was finished, the The 40 pounds of water drained through the permeable pavement system in seconds! The ASTM calculation was done and the infiltration rate of the pavement was calculated to be 2,188 inches per hour, a 15- fold improvement. ASTM Infiltration test was performed again. The 40 pounds of water drained through the permeable pavement system in seconds! The ASTM calculation was done and the infiltration rate of the pavement was calculated to be 2,188 inches per hour, a 15-fold improvement. The test was performed in other areas of the pavement with similar results. A YouTube video highlighting this maintenance can be found at com/watch?v=y8rp3axs378. Erin Keys stated her elation with the result: It was a HUGE relief to see what a great job the Pave- Drain cleaning head does. The purpose of the pavement is to allow for stormwater to effectively enter into the gravel layer that will filter the runoff from the Grissum site, So seeing the effectiveness of cleaning the pavement allays my concerns. Over the next two weeks, two additional sites were cleaned as maintenance demonstration projects in Omaha, NE and Ankeny, IA. The same permeable pavement system and vac-head performed well and with similar before and after infiltration rates observed. This system is truly maintainable. L&W by Donald Thieman, CPESC, LEED Green Associate Donald Thieman, CPESC, LEED Green Associate, is the Vice President of Sales and Operations for ASP Enterprises and Quick Supply Co. serving Nebraska, Iowa, Illinois, Missouri, Kansas and Oklahoma with a wide range of stormwater solutions. Over the last 20 years, he has gained a great deal of handson experience working with new products and new techniques to come up with better, long term solutions creating demonstration projects like this. For more information, he can be contacted at dthieman@aspent.com. Don would like to thank the Cities of Columbia, Omaha and Ankeny for their participation in these demonstrations and their commitment to understanding stormwater solutions better by supporting these efforts. 24 July/August 2015