As the Town of Cramerton completed a stormwater master plan, the Town’s parking lot and adjacent roadways were identified as top priorities for infrastructure improvements.
pROJECT OWNER
Town of Cramerton, NC
Town of Cramerton, NC
Permeable Pavers
for Parking Lot
Case Study
Project Background
Due to the deterioration of the existing parking lot and localized street flooding, and with support from LaBella consultation, the Town decided to replace and expand the parking lot while incorporating necessary infrastructure upgrades into the area.
Location
Cramerton, NC
Project Size
17,371
Square Feet
Green Infrastructure
Permeable Pavers
Status
Completed 2022
Benefits
Improved water quality & drainage
Enhanced landscape aesthetics Reduced maintenance Increased parking
ADA-compliant safety features
Planning & Financing
Project
Design
Site Evaluation
& Permitting
Construction
Process
Planning efforts for the Town’s parking lot improvements involved evaluating core samples of the existing pavement and considering different alternatives, including asphalt and Low Impact Development (LID) techniques such as permeable pavers.
ARPA Funding/Credit for Stormwater with Permeable Interlocking Concrete Pavement (PICP) was used:
SCM Credit Table
Other SCM Benefits
Benching
Baffles
Paver Placement
Planning & Financing
LaBella Associates, in collaboration with the Town of Cramerton, proposed several potential solutions, including the use of asphalt or LID techniques such as permeable pavers.
After leveraging the ARPA stormwater credit and considering aspects such as street flood reduction and direct runoff into the South Fork Catawba River, the Town opted to safeguard the river through LID techniques. These methods not only enhance stormwater quality and detention but also improve street drainage and provide localized flood protection.
Ultimately, permeable pavers were chosen for their numerous benefits. These concrete pavers are interlocking bricks laid over layers of stone or gravel. Stormwater filters down between the pavers and through the stone, allowing runoff to soak into the gravel layers beneath during rainstorms. These gravel layers provide space to filter and store runoff from parking lots.
In addition, permeable pavers provide better traction compared to asphalt, which can be slippery for tires. The pavers also save valuable real estate for stormwater control measures by housing the drainage system beneath the pavers, unlike asphalt, which requires a separate location for water collection. This feature is particularly critical in downtown settings where space is limited.
Furthermore, maintenance is less frequent with permeable pavers compared to asphalt. Asphalt requires seal coating, crack sealing, and striping every two years, along with remedial maintenance and patching during the 10th year, with a life expectancy of 20 years.
In contrast, permeable pavers only need sweeping a few times a year, if necessary, and remedial maintenance every 10 years, with an estimated life expectancy of 50 years.
The design also incorporated a concrete curb, improved storm drainage systems, and the addition of a Plaza Market area with shade sails along the east side of the parking lot. This design aims to minimize flooding in the adjacent street and meet stormwater quantity and quality requirements before discharging into the river.
Project Design
Survey and demolition plans were developed for the area, including the removal of the existing, deteriorated pavement.
Subsurface exploration revealed that the gas line was not beneath the proposed paver area, the sewer line was deep enough, the underground electric line was situated in front of the area, and only the waterline required relocation.
In addition to relocating the waterline and electrical engineering for lighting, the project also involved completing a structural review of the shade sail pole foundations. A floodplain permit for grading and various other agency permits and approvals were also obtained.
Technical Brief Testing at several locations showed dry results after 72 hours with the seasonal high-water table deeper than 52 inches from the existing grade.
The required water quality volume (1”) equals 2,135 cubic feet. Provided #2 Washed Stone to baffle equals 3,294 cubic feet (accounting for the void ratio n of the stone of 0.4), not accounting for the volume from the benches. Therefore, the 1 foot of storage provided was more than sufficient.
The minimum depth of washed stone calculated from the permeable paver area (15,310 square feet) equals 0.74. When the additional paver sidewalk (2,061 square feet) was included, this depth was reduced to 0.70 feet, providing an additional 30 feet of storage in the 1-foot-deep section.
The design included a 1.0-foot minimum depth of stone to the top of the baffle, excluding the benches, which provided additional storage. From the outfall, 2.8 feet were provided for underdrain outfall, with a tier of benches sloped at less than 2% up to the top of the parking lot (as shown below).
Site Evaluation & Permitting
The contractor first added a 12-inch-thick subbase layer of 2- to 3-inch crushed stone, along with the bench, to the excavated area to create space for water storage and help filter stormwater as it travels downward. Next, a 4-inch base layer of 3/4-inch crushed stone was spread over the entire parking and driving areas. Concrete curbs were then built to contain the stone. After the curbs were installed, a thin layer of small stone, known as the setting bed, was placed over the previous layers and screened to create a flat surface on which to lay the pavers.
Construction Process
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Outcome
The new parking lot has significantly reduced the rate at which stormwater runoff leaves the site, increased parking capacity without expanding the site’s footprint, provided a great covered area for events, and enhanced the aesthetics for Town patrons.
The permeable pavers and layers of crushed stone filter and store stormwater, allowing it to drain off the site gradually over a span of two to five days. Previously, the gravel parking lot did not store stormwater, and any rain that fell on the site would run off within minutes.
This extended drainage time reduces erosion and impervious area effluent compared to asphalt, releasing water as a small trickle over several days.
The site can now manage the runoff from a 100-year storm event, which has a one percent chance of occurring each year and generates approximately seven inches of rainfall in a 24-hour period.
The prolonged drainage through the crushed stone beds under the pavers also helps remove sediment and debris from the stormwater.
The parking lot is now more accessible and user-friendly, featuring two access points, level grading, pedestrian-friendly walkways, and ADA compliance. In addition, the previously worn and disheveled parking lot is now visually enhanced with higher durability due to the new pavers.
Results
Parking Lot
Improvements
Increased parking capacity to a total of 34 parking spaces
Shade sails and additional seating
Improved landscaping and enhanced aesthetics
Increased usability, access, and ADA-compliant safety features
Stormwater
Management
Improved street drainage and flood protection without sacrificing additional real estate
Enhanced stormwater quality/detention and river protection through the use of LID techniques
Utilized ARPA/NCDEQ stormwater credit
Life Cycle
Cost Analysis
The selected pavement solution provides durability and longevity with minimal maintenance requirements.
Permeable pavers are projected to last at least 50 years, with maintenance twice a year, compared to asphalt’s typical 20-year lifespan.
Cost
Effectiveness
Although permeable pavers have higher upfront material and labor costs, they save 25% in the long run (not accounting for savings from no undercut required of soft soils or storm structures required for impervious pavement) through reduced maintenance and increased durability, along with the added benefits of improved drainage and pollutant removal without additional real estate.
Funding opportunities from the American Rescue Plan Act (ARPA) and the North Carolina Department of Environmental Quality (NCDEQ) for stormwater credits aimed at improving stormwater quality were also explored.
Infiltration testing revealed that drainage occurred in the subsoils, with water infiltrating into the ground within 72 hours. This qualifies the pavers for 100% credit for infiltration according to NCDEQ guidelines, as shown in the Credit Table.
The entire parking lot qualified for stormwater funding because the whole pavement system functions as a stormwater control measure (SCM), unlike asphalt, which does not qualify for such funding.
The design also incorporated a concrete curb, improved storm drainage systems, and the addition of a Plaza Market area with shade sails along the east side of the parking lot. This design aims to minimize flooding in the adjacent street and meet stormwater quantity and quality requirements before discharging into the river
LaBella Associates, in collaboration with the Town of Cramerton, proposed several potential solutions, including the use of asphalt or LID techniques such as permeable pavers.
After leveraging the ARPA stormwater credit and considering aspects such as street flood reduction and direct runoff into the South Fork Catawba River, the Town opted to safeguard the river through LID techniques. These methods not only enhance stormwater quality and detention but also improve street drainage and provide localized flood protection.
Ultimately, permeable pavers were chosen for their numerous benefits. These concrete pavers are interlocking bricks laid over layers of stone or gravel. Stormwater filters down between the pavers and through the stone, allowing runoff to soak into the gravel layers beneath during rainstorms. These gravel layers provide space to filter and store runoff from parking lots.
In addition, permeable pavers provide better traction compared to asphalt, which can be slippery for tires. The pavers also save valuable real estate for stormwater control measures by housing the drainage system beneath the pavers, unlike asphalt, which requires a separate location for water collection. This feature is particularly critical in downtown settings where space is limite
Furthermore, maintenance is less frequent with permeable pavers compared to asphalt. Asphalt requires seal coating, crack sealing, and striping every two years, along with remedial maintenance and patching during the 10th year, with a life expectancy of 20 years.
In contrast, permeable pavers only need sweeping a few times a year, if necessary, and remedial maintenance every 10 years, with an estimated life expectancy of 50 years.
The design included a 1.0-foot minimum depth of stone to the top of the baffle, excluding the benches, which provided additional storage. From the outfall, 2.8 feet were provided for underdrain outfall, with a tier of benches sloped at less than 2% up to the top of the parking lot (as shown below).
Survey and demolition plans were developed for the area, including the removal of the existing, deteriorated pavement.
Subsurface exploration revealed that the gas line was not beneath the proposed paver area, the sewer line was deep enough, the underground electric line was situated in front of the area, and only the waterline required relocation.
In addition to relocating the waterline and electrical engineering for lighting, the project also involved completing a structural review of the shade sail pole foundations. A floodplain permit for grading and various other agency permits and approvals were also obtained.
Technical Brief Testing at several locations showed dry results after 72 hours with the seasonal high-water table deeper than 52 inches from the existing grade.
The required water quality volume (1”) equals 2,135 cubic feet. Provided #2 Washed Stone to baffle equals 3,294 cubic feet (accounting for the void ratio n of the stone of 0.4), not accounting for the volume from the benches. Therefore, the 1 foot of storage provided was more than sufficient.
The minimum depth of washed stone calculated from the permeable paver area (15,310 square feet) equals 0.74. When the additional paver sidewalk (2,061 square feet) was included, this depth was reduced to 0.70 feet, providing an additional 30 feet of storage in the 1-foot-deep section.
To complete the parking lot, the contractor used a specialized machine to place 4-foot square pallets of pavers in the parking lot and driveway areas. Finally, small stone chips were compacted into the spaces between pavers. This prevents dirt and debris from clogging the drainage system while allowing runoff to soak into the gravel layers below. Additionally, sidewalk permeable pavers were installed over the area outside the concrete curbs to connect the parking lot to the sidewalk
The parking lot is now more accessible and user-friendly, featuring two access points, level grading, pedestrian-friendly walkways, and ADA compliance. In addition, the previously worn and disheveled parking lot is now visually enhanced with higher durability due to the new pavers.
The new parking lot has significantly reduced the rate at which stormwater runoff leaves the site, increased parking capacity without expanding the site’s footprint, provided a great covered area for events, and enhanced the aesthetics for Town patrons.
The permeable pavers and layers of crushed stone filter and store stormwater, allowing it to drain off the site gradually over a span of two to five days. Previously, the gravel parking lot did not store stormwater, and any rain that fell on the site would run off within minutes.
This extended drainage time reduces erosion and impervious area effluent compared to asphalt, releasing water as a small trickle over several days.
The site can now manage the runoff from a 100-year storm event, which has a one percent chance of occurring each year and generates approximately seven inches of rainfall in a 24-hour period.
The prolonged drainage through the crushed stone beds under the pavers also helps remove sediment and debris from the stormwater.
