United States
Environmental Protection Agency
Office of Water (4203)
Washington, DC 20460
EPA-841-B-00-005A
October 2000
Bioretention Applications
Inglewood Demonstration Project, Largo,
Maryland
Florida Aquarium, Tampa, Florida
Introduction
Two case studies demonstrate the potential to use
integrated management plans (IMPs) in the design
of new parking facilities and as retrofits for
existing parking facilities. The Inglewood study
in Largo, Maryland, compared the pollutant
removal efficiency of a bioretention cell in a
laboratory setting to that of a comparable facility
constructed in a parking lot. The Florida
Aquarium study in Tampa, Florida, included
monitoring of several storm events for volume
and water quality control.
Inglewood Project Area
The project area is an existing 5-acre outdoor
parking area located in a highly urbanized office
park adjacent to Interstate 95. Runoff from
adjacent areas does not flow across the lot. The
slope of the parking area is approximately 3
percent. Parking stalls are aligned at 90-degree
angles, and there are approximately 30 cars in
each row of an aisle. At the end of each aisle are
planting areas surrounded by curbs and gutters.
Curb drainage inlets have been placed in some of
the islands to intercept and collect runoff as sheet
flow, which is piped to a downstream regional
storm water management facility.
Inglewood Project Description
The Inglewood project consisted of a laboratory
segment and a field segment. The laboratory
segment involved construction of a planter box
filled with a typical bioretention facility soil
mixture (50 percent construction sand, 20 to 30
percent topsoil, and 20 to 30 percent compost).
This facility is approximately half the size in
volume of the Inglewood facility. The box was
planted with representative plants and mulched.
A synthetic stormwater mixture was applied and
the pollutant removal efficiency, temperature, and
runoff volume rate were measured. The pollutant
Key Concepts:
> Retrofits
> Structural Controls
> Source Controls
LOW-IMPACT
DEVELOPMENT
CENTER
Project Benefits:
> Retrofit Opportunity
> Pollutant Removal
> Volume Reduction
> Cost-Effectiveness
mix included metals (copper, lead, and zinc),
phosphorus, organic nitrogen, and nitrate.
A landscaped island measuring approximately 38
feet by 12 feet was chosen as the retrofit area.
The island contains a curb inlet that drains into the
municipal storm drain system. Almost the entire
drainage area is impervious. A 4-foot slot was cut
into the curb immediately before the inlet. The
landscaped island was then excavated to a depth
of 4 feet. An underdrain was installed and tied
into the bottom of the existing inlet to completely
drain the planting soil to avoid over saturation.
The underdrain was covered with 8 inches of 1- to
2-inch gravel and backfilled with typical
bioretention soil mix. The backfill extended to a
depth of about 12 inches below the top of the
curb, which allows for a ponding depth of
approximately 6 inches of water in the island
Figure 1. Bioretention landscaping at the Inglewood
demonstration project site.
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Table 1. Summary of bioretention pollutant removal results for the Inglewood demonstration project.
Pollutant
Cu dissolved (u.g/L)
Cu total (ug/L)
Pb dissolved (u.g/L)
Pb total (ug/L)
Zn dissolved (mg/L)
Zn total (mg/L)
Ca (mg/L)
Cr (mg/L)
Na (mg/L)
P (mg/L)
TKN (mg/L as N)
NCV (mg/L as N)
Input mean ±
standard deviation
120 ± 27
120 ± 27
54 ± 9.4
54 ± 9.4
1.1 ± 0.021
1.1 ± 0.021
44 ± 6.4
5.1 ± 0.48
3.1
0.83
6.9 ± 0.81
1.3 ± 0.05
Output mean ±
standard deviation
63 ± 6.5
69 ± 9.4
11 ±6
16 ±7
0.24 ± 0.44
0.39 ± 0.44
32 ± 6.1
162 ± 80
359 ± 170
0.11 ± 0.017
2.3 ± 0.64
1.1 ±0.15
Output range
55-75
55-85
6.7-25
6.7-26
0.11-0.56
0.12-1.4
24-41
74-228
68-497
0.10-0.13
1.7-3.0
0.94-1.2
Output percent
removal mean ±
standard deviation
48 ± 12
43 ± 11
79 ±26
70 ±23
78 ±29
64 ±42
27 ± 14
3,000a
ll,000a
87 ±2
67 ±9
15 ± 12
aShows percent production.
before a backwater is created at the curb opening.
Subsequently the area was planted and covered
with 3 inches of shredded hardwood mulch.
Figure 1 shows the bioretention area after
vegetation was established.
The stormwater mixture was applied to a 50-
square-foot area in the field facility at a rate of 1.6
inches per hour for 6 hours. The removal rates for
several pollutants are shown in Table 1. In
addition to pollutant removal, the runoff
temperature was lowered approximately 12 °C as
the runoff was processed and filtered through the
soil mixture. Most of the pollutant removal
process occurred in the mulch layer.
A similar field investigation was conducted on an
8-year-old facility, and the metals removal rate
was much higher (Davis et al., 1998). This effect
might be attributed to slower flow rates through
the soil, which has higher clay content, as well as
greater pollutant uptake by vegetation.
Inglewood Project Summary and
Benefits
This study showed the feasibility of retrofitting an
existing parking facility and demonstrated the
consistency of laboratory and field pollutant
removal performance. The retrofit cost
approximately $4,500 to construct and treats
approximately one-half acre of impervious
surface. The bioretention retrofit was a more cost-
effective way to filter pollutants than many
proprietary devices designed to treat the same
volume of runoff. These proprietary devices
could cost $15,000 to $20,000, would be more
expensive to maintain, and would not significantly
decrease runoff volume or temperature. Also,
bioretention areas offer the ancillary benefit of
aesthetic enhancement. It is interesting to note
that a drought occurred after the installation of the
plants, and although many of the other plants in
the parking lot died or experienced severe drought
stress, the plants in the bioretention facility
survived because of the retained water supply.
Florida Aquarium Project Area
The Florida Aquarium site is an 11.5-acre, asphalt
and concrete parking area that serves
approximately 700,000 visitors per year. Runoff
was controlled using the following EVIPs:
- End-of-island bioretention cells
- Bioretention swales located around the
parking perimeter
- Permeable paving
- Bioretention strips between parking stalls
- A small pond to supplement storage and
pollutant removal
Figure 2 is an illustration of the site that details
the type and location of runoff controls.
Florida Aquarium Project Description
A total of 30 storm events were monitored for one
year at the Florida Aquarium site during 1998-
1999. The Southwest Florida Water Management
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THE FLORIDA AQUARIUM SITE PLAN
District measured rainfall
and flow from eight of
the subcatchments in the
parking area and
collected water quality
samples on a flow-
weighted basis.
Comparisons between
pavement areas controlled
by IMPs and uncontrolled
asphalt areas were made
for peak runoff rate,
runoff volume, runoff
coefficients, and water
quality. Sediment cores
from swales also were
collected and analyzed.
Florida Aquarium
Project Summary
and Benefits Figure 2. Layout of the Florida Aquarium site with IMPs. The eight basins outlined
with dotted lines were evaluated in this part of the study.
The parking areas
controlled by IMPs showed a significant reduction
in runoff volume and peak runoff rate. Table 2
shows pollutant load reductions for three
pavement types; reduction is compared to
pollutant loads in runoff from a basin without a
swale. Much of the pollutant reduction is
attributed to the reduced runoff in basins with
swales. Because the swales are only the first
to Underground Pipe
^ Out of Underground Pipe
O Sample Location
element in the treatment train, even better removal
efficiencies should be seen when data are
analyzed for the entire system.
References
Table 2. Load efficiency of pollutants expressed as
percent reduction for three types of pavement at
the Florida Aquarium site.
Davis, A., M. Shokouhian, H. Sharma, and C.
Minami, 1998. Optimization of Bioretention
Design for Water Quality and Hydrologic
Characteristics. Report 01-04-31032. Final
report to Prince George's County, Maryland.
Constituents
Ammonia
Nitrate
Total Nitrogen
Orthophosphorus
Total Phosphorus
Suspended Solids
Copper
Iron
Lead
Manganese
Zinc
Percent pollutant reduction3
Asphalt
w/swale
45
44
9
-180
-94
46
23
52
59
40
46
Cement
w/swale
73
41
16
-180
-62
78
72
84
78
68
62
Porous
w/swale
85
66
42
-74
3
91
81
92
85
92
75
aThe basins with swales were compared to a basin without a
swale to determine the amount of reduction in pollutant loads
possible using these small alterations. Notice that the
efficiencies for phosphorus are negative, indicating an increase
in phosphorus load in the basins with a swale.
Rushton, B. 1999. Low Impact Parking Lot
Design Reduces Runoff and Pollutant Loads:
Annual Report #1. Southwest Florida Watershed
Management District, Brooksville, Florida.
Contact Information
Larry Coffman
Prince George's County, Maryland, Department of
Environmental Resources
Largo, Maryland 20774
(301)833-5834
Betty Rushton
Resource Management Department
Southwest Florida Water Management District
Brooksville, Florida 34609
(352)796-7211
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