Preparing to Maintain

June 9, 2015

By Mark Harrison

The word of the week in Chattanooga during the first week of May was “Infiltration”. If you have been following stormwater news for the Chattanooga/Hamilton County area for the past few months, you know that the word infiltration has been a hot topic for a while. However, during this week in particular, I heard a lot about estimating or maintaining infiltration rates. This past December, in order to comply with the provisions of the newest version of their NPDES MS4 Permit, the City of Chattanooga passed new ordinances that require stormwater management measures and methods intended to help minimize CSO overflows using green infrastructure. Basically, new developments will have to capture and infiltrate more rain on site than ever before.

The City is one of the first communities to come under this latest version of the MS4 permits. Hamilton County is not far behind. The hope is that promoting the use of green infrastructure will serve as a means for community revitalization. In addition, it will establish the Chattanooga/Hamilton County area as a leader in sustainable water quality management. It also means that we have new courses and workshops to attend. Makes it easy to meet my continuing education requirements.

On Tuesday May 5th, Lee Gentry and I attended the Pervious Concrete Maintenance, Demonstration, and Workshop sponsored by the City and the Tennessee Concrete Association (TCA). Then on Thursday May 7th we attended the City of Chattanooga Stormwater Regulations Seminar, Sponsored by the Chattanooga Branch of ASCE‐ TN EWRI Chapter.

At these two events, we learned that the City is going to require As-Builts of newly constructed stormwater management structures. Additionally, the City will require verification of infiltration rates for these structures annually beginning shortly after construction. Meaning that the owner will only receive credit for the verifiable infiltration rates achieved and maintained, not just those estimated during design. The infiltration rates will be measured and documented by a Landscape Architect or Engineer.

Pervious Pavement

Infiltration testing at Finley Stadium.

The accepted testing method for estimating infiltration rates for pervious pavement is ASTM C1701 Pervious Concrete Infiltration Test. An overview to this method can be reviewed at:

Vacuuming of pavement

Brent Rollins using a vacuum unit. In addition, the area was swept with a broom to remove large debris and lose gravel.


Pervious Pavement 1

Alan Sparkman pressure washing and vacuuming pervious pavement.

The photos show the work performed to treat two sections of the pervious pavement. The infiltration rates for the two sections, treated during the workshop, increased from 0 before treatment to 54 in/hour after treatment and 108 in/hour before treatment to 705 in/hour after treatment, respectively.

Alan Sparkman mentioned that he will be working with Dr. Heather Brown at MTSU to test at least 3 different types of cleaning equipment to gather data on the effectiveness of each. Each method of cleaning will be evaluated based on productivity and effectiveness of removing debris from pervious concrete. They will also gather information about the types of material removed from the pervious pavement including size, composition, and other data.