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Drainage is the most important design factor when building any asphalt or concrete pavement. The industry standard for minimum slope for drainage is 1% in any direction. PLM whenever possible designs and plans for 1.5% slope to ensure that there are no areas of standing water upon completion of asphalt construction. Over time, asphalt pavements will move, shift, heave and settle and when we have a greater starting slope, there is more likelihood that drainage will be maintained over time.

water running down storm basin

Storm Basins and Curb Inlets

Storm basins (manholes) and curb inlets allow water to drain from within the area of the parking lot into storm sewers. Over time these structures will move or settle differently than the adjacent pavement causing drainage challenges. When the elevations of these structures shift it reduce the effectiveness of the drainage by not allowing water to enter the sewers and instead seep into the underlying asphalt structure. Periodic maintenance should be completed to ensure that the elevations of storm drains are flushed with the asphalt for drainage as well as snow removal concerns.



Sinkholes will develop adjacent to storm sewers where water seeps into the asphalt pavement through openings and cracks and burrows its way down towards the lowest elevations but NOT through the sewer openings. When this happens, the water erodes the underlying areas and the pavement creates an air pocket to develop. When the pocket collapses a sinkhole is formed very similarly to a pothole in a roadway. A sinkhole left unattended can become a substantially more expensive repair if deferred and pose a significant safety liability.


Drain Tile and French Drains

Sub-surface drainage is important when groundwater or surface drainage challenges are present at your property. Drain tile functions by being placed 12-24″ below the top of the pavement allowing water that gets trapped below the pavement the means to fall downward into a trench to collect the water. Water is the greatest enemy an asphalt pavement faces, and by installing drain tile or French drains we can collect the water below the parking lot, convey it into the sewer structures and preserve the expected life of the pavement.


PLM is continuously looking for new team members to strengthen our company regardless of experience.


Waukesha 262-691-3964
Racine/Kenosha 262-654-1214
Madison 608-251-3565
Milwaukee 262-691-3964


Duplainville Road
Pewaukee, WI 53072

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