POST-CONSTRUCTION INFILTRATION TESTING TECHNIQUES FOR POROUS ASPHALT AND INFILTRATION BMPS Methodology and Lesson s Learned

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1 POST-CONSTRUCTION INFILTRATION TESTING TECHNIQUES FOR POROUS ASPHALT AND INFILTRATION BMPS Methodology and Lesson s Learned James Hook, Andrew Oster City of San Diego Storm Water Division San Diego, CA INTRODUCTION The field of storm water treatment devices and methods is a constantly growing and evolving one. Inspecting, testing, and maintaining these BMPs needs to grow and evolve as well. The City of San Diego, and many other jurisdictions, have an ever growing inventory of Post-Construction BMPs that they are required to inspect and maintain. Many of these BMPs are of the infiltration type by means of permeable pavements or soil infiltration. In the past, The City of San Diego (San Diego) only performed a visual check and very rudimentary drainage test (i.e. dump some water on it and see if it drains) of these BMPs. Something felt lacking for more objective evidence that a BMP needed maintenance or wasn t functioning properly. So, San Diego adopted a soils infiltration test from the USDA and a permeable pavement infiltration test from the ASTM to add to their inspection tool-kit. We want to share with you the techniques and methodologies used along with some of our lessons learned implementing these new inspection tools. Figure 1: Porous pavement test site in San Diego.

2 METHODOLOGY The permeable pavements testing procedure was adapted from The ASTM s Standard Test Method for Infiltration Rate of In-Place Pervious Concrete (C1701/C1701M). Figure 2: Permeable pavement testing in a parking lot. The basic outline of our test is as follows: 1) Apply plumbers putty to bottom of 12 ring, and press firmly down on surface area to be tested. 2) Pre-wetting stage: a. Using 1 gallon of water, pour into test ring and record time in seconds. b. If pre-wetting test takes longer than 30 seconds: Use 1 gallon of water for Main Test c. If pre-wetting test takes less than 30 seconds: Use 5 gallons of water for Main Test 3) Main Test: a. Using either 1 or 5 gallons, pour into test ring at an even rate.

3 b. Record time the water takes to infiltrate, in seconds. c. For a more accurate reading, perform a second Main Test and average the two times together. 4) Calculate infiltration rates using the ASTM formula. 5) Lower limit for maintenance needs: 10 in/hr Standard infiltration rates of effective pervious pavements vary from in/hr. UNCLOGGING POROUS ASPHALT WITH A POWER WASHER Previous to the pilot study, the parking lot we targeted for the test was severely clogged with sediment. The method we used to unclog the porous asphalt was with a high pressure power washer. In the pictures you can probably notice some cleaning lines on the parking lot. Lessons learned and Notes: - Conduct a pre-site visit in order to configure logistics of catching all run-off from the process. - Reclaim wash water and properly dispose of. - Use a jet-type nozzle or setting, not a fan-type setting. Needs the more forceful stream. - Go slow. - Overlap or get tight cleaning lines with each pass. Like mowing a lawn, don t leave portions of un-cut grass in between mowed areas. o These portions of your pavement/asphalt will not get un-clogged and will negatively affect BMP performance. - In the parking lot that we power washed one half was done more sloppily and left gaps in between each pass of the power washer. o This was evident in the infiltration tests, as that portion of the parking lot had a much higher variance in infiltration rates, compared to the more carefully unclogged other portion. o See Figure 9, South Site Infiltration Tests

4 Figure 3: Power washing to unclog porous asphalt in a parking lot, with vac-truck to capture wash-water. PILOT STUDY: MECHANICAL VS REGENERATIVE-AIR SWEEPER There are two main types of mechanized sweepers out there: mechanical broom (mechanical) and regenerative-air (regen-air). Forgive us if we are excluding other sweeper types, but for most publicworks and large facility fleets, these are the most common. Also, these two types are the ones used by San Diego, so these are the focus of our study. We wanted to test which type of sweeper more effectively can maintain permeable pavements. The mechanical sweepers utilize a giant broom wheel and vacuum. Pretty much like an extra-large version of your standard household vacuum cleaner. Regen-air sweepers utilized a forced-air injection onto the surface, which agitates dust and dirt, followed by a vacuum pump which attempts to suck up the agitated dust and dirt.

5 Figure 4: Infiltration testing discussions, with sweeper watching. Figure 5: Mechanical broom sweeper.

6 Infiltration Rate (in/hr) Figure 6: Regenerative Air sweeper. 110 Mechanical vs Air Re-Gen Sweeper Test Initial After 1 Pass After 3 Passes Mechanical Air Re-Gen Number of Sweeper "Passes" Figure 7: Graph comparing infiltration rates of sweepers during the great Sweep-off

7 Infiltration Rate (in/hr) The regenerative-air sweeper demonstrated that it was more effective than the mechanical broom sweeper in this study. The main reason for this is probably that the air-injection penetrates further into the asphalt pores compared to a broom sweeper. Talking with our sweeper drivers, they echoed that sentiment and added that the regen-air is better for finer particles and sediments, where the broom sweeper is better at larger pieces of debris. In light of these findings, we moved forward with a regenerative-air sweeper in order to test sweeping frequencies. Finding an ideal and effective sweeping frequency would allow us to find an adequate maintenance schedule. SWEEPING FREQUENCY TESTING A critical part of proper BMP maintenance is an effective maintenance schedule. The benefit of finding a sweet-spot in maintenance frequency is that you re not wasting resources over-sweeping nor are you under-sweeping where you risk clogging the BMP, in which you have to power-wash or replace the surface. After putting in the costly and laborious task of installing (or unclogging) porous pavements, one would want to properly maintain the BMP to ensure its functionality in treating run-off. We started out scheduling monthly lot sweeping with a regen-air sweeper and performed infiltration testing to monitor the newly unclogged parking lot. We chose two testing sites; a North site and a South site. We performed infiltration testing before and after scheduled monthly sweeping for six months. 'North' Site Infiltration Tests /15/2017 8/5/2017 9/2/ /4/ /2/2017 1/6/2018 2/3/2018 Regen-Air Sweep Date Before Sweeping Before Power Washing After Sweeping N/A Figure 8: Graph of Before/After Infiltration Testing on North testing site.

8 Infiltration Rate (in/hr) Before Power Washing N/A /15/2017 8/5/2017 9/2/ /4/ /2/2017 1/6/2018 2/3/2018 Before Sweeping Regen-Air Sweep Date After Sweeping 'South' Site Infiltration Tests Figure 9: Graph of Before/After Infiltration Testing on South testing site. Monthly testing demonstrated that the regen-air sweeper was effectively maintaining the porous asphalt, per the results of infiltration tests. We then decided to do bi-monthly sweeping and monitor the before and after infiltration rates of the asphalt. As of the time of this paper, only one before and after test has been performed. The initial results were lower than usual infiltration rates, compared to monthly sweeping tests. However, more testing is needed, and we will have two more data points of this test by August. CONCLUSIONS AND LESSONS LEARNED Adding infiltration testing of permeable pavements to our inspection tool kit has helped our program in numerous ways. First off, it gave us a means to objectively test and measure the Sweeper Efficiency Pilot Study. From that, we ve been able to identify a way to unclog permeable pavements that have become ineffective. On top of that, we ve also determined an ideal maintenance frequency with the best type of sweeper, to help keep permeable pavement performing as it should. On the macro scale, infiltration testing allows us to have a much more comprehensive evaluation in determining functionality of these types of BMPs when compared to standard visual observations. Infiltration testing is an objective, replicable method to measure the performance of these types of BMPs. Over time and with recurring inspections, we can better gauge the health and maintenance

9 needs of these types of BMPs. We can make much more informed decisions whether these BMPs need maintenance rather than an expensive retrofit or rebuild, if they have become too far gone. This helps the BMP owners, public and private, save money and resources in efficiently maintaining their storm water treatment systems. This helps property managers, taxpayers, and the environment in ensuring these treatment systems are performing and being maintained effectively. We also do infiltration testing on soils in flow-through planters, bioretention BMPs, and engineered soil mixtures. This test is adapted from the USDA s method for testing soils. The procedure is similar to that of the test of permeable pavements, where we pour a known quantity of water into a test ring, time the drainage, and calculate an infiltration rate from there. The current City of San Diego Storm Water Standards Manual requires BMPs to have a 5 in/hr soils infiltration rate or greater. Figure 10: Soil infiltration test for a bio-retention swale. Testing the infiltration rate of soils has given us a good repeatable, objective tool to measure BMP performance and maintenance needs in those BMPs that utilize flow-through treatment. Currently, we are refining the methodology of this test to make it more accurate as there are a number of variables that we have encountered. Stay tuned for next year s presentation for an update.