The bioretention are that replaced two grass-covered parking lot islands in the parking lot between Memorial Chapel and Old Post Chapel. Photo by EMD

Stormwater management practices reduce pollutants

While people make their way around the base, they may have noticed several new landscaping and hardscaping features. While they may just look like gardens, these new additions were actually designed and constructed to help reduce stormwater pollution.

Stormwater is rain that runs off hard surfaces such as buildings and pavement, and it can carry pollutants to nearby streams. Joint Base Myer-Henderson Hall is located within the Chesapeake Bay watershed, which means that all of the water and pollutants that enter JBM-HH’s storm drains have the potential to end up in the Chesapeake Bay.

Unfortunately, for many years now the health of the bay has been suffering due to stormwater pollution. This negatively affects the communities in the Chesapeake Bay watershed, which rely heavily on the bay to help support the economy, human and wildlife health, tourism, recreation and food supply chains.

To prevent further decline of the health of the Bay and protect communities in the watershed, the U.S. Environmental Protection Agency established limits for three major contributors to the Bay’s poor health — nitrogen, phosphorus, and sediment. The goal is reduce the amount of these pollutants entering the Bay 20-25% by the year 2025 in order to meet federal water quality standards. The resulting allowable pollutant amounts are divided up among the states with streams that discharge to the bay. The states then use stormwater permits to require municipalities, state facilities, industries and military bases, such as JBM-HH, to reduce the amount of pollution going into their storm drains.

JBM-HH is required by its stormwater permit to reduce the amount of nitrogen, phosphorus and sediment in the stormwater runoff on base incrementally through 2028. In order to meet the installation’s required pollutant reductions, the Environmental Management Division has been working with the U.S. Army Corps of Engineers to identify possible methods of reducing pollutants.

Methods used to reduce pollutants in stormwater runoff are called stormwater best management practices for short. Stormwater BMPs can be structural facilities, such as ponds and filter boxes that are constructed to collect and filter stormwater, or nonstructural practices, such as street sweeping or preserving land in its natural state.

Due to the small size of the installation, space is at a premium and any available space is highly sought after by various installation organizations. Therefore, EMD and USACE identified locations on base where several small-scale BMPs could be constructed. The BMPs selected included bioretention areas, two types of bio-swales and permeable pavement and pavers.

Possibly the most noticeable of the new BMPs, two bioretention areas were constructed in the center of JBM-HH’s largest paved area — the parking lot between Old Post Chapel and Memorial Chapel. A bioretention area is generally a vegetated depression that is designed to capture stormwater. Curb cuts allow rainwater to flow into the depressed area, where it is held and allowed to infiltrate the ground rather than flow directly into stormwater drains. As the water infiltrates the ground, pollutants in the stormwater are naturally filtered out by soil, sand, vegetation and organic matter. Bioretention areas often have drains underneath the soil that allow the cleaner, filtered stormwater to flow to nearby streams.

Vegetation is an essential part of bioretention systems and plant species are specifically chosen for their ability to live in wet and dry conditions, keep the soil loose enough to allow water to infiltrate, and absorb water and nutrients such as nitrogen and phosphorus (two of the three Chesapeake Bay pollutants of concern). The stones near the curb cuts that you see in these bioretention areas are used to slow the flow of incoming rainwater, which helps to prevent erosion and sedimentation issues.

 Two areas of bioswales were also constructed on base. A two-tiered bioswale was installed in the grassy area next to the Army and Air Force Mutual Aid Association building along Sheridan Avenue, and long narrow bioswales replaced the grassed islands in the fitness center parking lot. Bioswales are similar to bioretention areas, as they are also designed to capture and filter polluted stormwater. Bioswales tend to be shallower than bioretention areas and have denser vegetation, relying more on the vegetation to slow the flow of water and absorb pollutants. The remaining water then flows through layers of soil and gravel that provide additional filtering and allow water to infiltrate the ground more quickly than in bioretention areas, preventing flooding in these smaller areas.

Because the bioswales in the fitness center parking lot island replaced areas that people are used to seeing as trimmed grass, some may assume the natural vegetation of the bioswales is simply overgrown and unkempt. However, as with bioretention areas, these plant species were chosen specifically for the designed function of the bioswales and are expected to differ in appearance when compared to simple grassed islands. Due to the importance of this vegetation, it is also essential that users of the parking lot avoid walking through the bioswales, as this will damage the plants and compact the soils.

An area of permeable pavement replaced an area of regular pavement in the center of the parking lot near the bioretention areas. Normal asphalt pavement used for parking lots and roadways is impermeable, meaning that water cannot pass through it and will instead flow over it, allowing the water to collect sediment, oils and other pollutants before entering storm drains and nearby streams. Permeable pavement is a specially engineered porous material that allows water to flow through it and infiltrate the ground, while maintaining the strength required to support vehicles. By allowing rainwater to flow through to the ground, it does not have the opportunity to flow across large areas of pavement and pick up pollutants, and any polluted water that does flow through will be naturally filtered by the soils underneath the pavement.

Additionally, an area of permeable pavers replaced the deteriorating overflow lot across from the gas station on Pershing Drive and now provides additional parking for the public. The pavers’ purpose is similar to the permeable pavement — to allow water to infiltrate the ground, rather than pick up pollutants and carry them to nearby waterways. However, pavers are individual bricks laid with gaps in between, which are filled with small stones. This design allows water to flow to the ground through the gaps between bricks. The added advantage to permeable pavers is the aesthetics, as they have a more decorative appearance.