Roadway in PG County Solves Stormwater Problem Instead of Creating One

Aaron Fisher | January 22, 2022

The PaveDrain permeable pavement system is a next generation permeable surface. The presence of open joints in the system leads to higher water infiltration rates, and reduced maintenance compared to other permeable pavements.

The Site

A 2,350 ft² PaveDrain system was installed at the intersection of 40^th Avenue and Newark Road in the right-of way. This intersection is property of the Town of Colmar Manor (MD). This area is part of the Anacostia River basin, which is subject to a TMDL (Total Maximum Daily Limit) for TSS (total suspended solids).

Stormwater Permitting

Permit drawings show that this stormwater management structure will receive drainage from 8,705 ft² —a run-on ratio of 2.7:1. The site was excavated to ~4 feet below grade. The base was then placed from the bottom: 12” clean sand, 24” of #2 stone, 4” of #57 stone, with a PaveDrain surface (Figure 2). A mid-drain was installed in the system, which is converted to an overdrain at its outfall within the manhole. Details on the site are provided in Table 1.

Table 1. Stormwater BMP Summary Table as per Approved Permit

SWM Area (ft²)	Drainage Area (ft²)	Run-On Ratio	Target P_E (in)	Target Vol (ft³)	Design Vol (ft³) using ESD practices	Max ESD Vol (ESD max) (ft³)	RCN
2,350	8,705	2.7:1	1.00	214	376	376	89

Soil Characterization

After excavation was completed, three soil samples were taken (Figure 3) to characterize the soil into which the water will infiltrate. The three samples showed a variable soil base, characterized as 1) Gray SILT [ML] {USDA – LOAM} 2) Brown silty SAND [SM] {USDA – SAND}, and 3) Gray lean CLAY [CL] {USDA – SILTY CLAY LOAM}. These samples fall into Hydrologic Soil Groups (HSG) A, B, and D, respectively. This agrees with permitting, as per Prince George’s County Department of Permitting, Inspection and Enforcement, which classified the soil per the lowest HSG of D.

Sensoring

The installation was completed in April 2021. After construction was completed, an INFIL-Tracker system (in-situ water-level monitoring) from P4 Infrastructure, Inc. was placed vertically in the base to collect the water level point several times a minute, with data reported to the cloud every 10 minutes (Figure 3). A rainfall and environmental monitoring system was also placed nearby to get a granular report of rainfall that would match to the data collected by the water sensor. The sensors are connected via cellular signal, and regularly report measurements to the cloud.

Performance

20″+ of stormwater was captured and exfiltrated through a stone and sand media permeable pavement gallery in each of three rain events in September through November (see image below). Sure looks like a stormwater infiltration device to me. Data doesn’t lie.