1. Case Studies
    2. Case Study 1: Penn State University - Centre County Visitor Center, Centre County
    3. Porous Asphalt Parking Lots underlain with Subsurface Infiltration Beds
    4. Porous Concrete Sidewalks
    5. Subsurface Infiltration Trenches
    6. Vegetated Infiltration Bed
    7. Several Rain Gardens / Bioretention areas
    8. Project Background
      1. _
        1. _
          1. _

Pennsylvania Stormwater
Best Management Practices
Chapter 9
Case Studies: Innovative Stormwater Management
Approaches and Practices
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Chapter 9
Case Studies: Innovative Stormwater Management
Approaches and Practices
Outline of Information Needed for Case Studies…………………………..…..2
Case Studies……………………………………………………………………….…3
1: Penn State University - Centre County Visitor Center, Centre County...3
2: Dennis Creek Streambank Restoration, Franklin County………….……10
3: Commerce Plaza III, Lehigh County…………………………………………11
4: Flying J. Truck Plaza for Welsh Oil of Indiana……………………………..13
5: Ephrata Performing Arts Center, Lancaster County………………………16
6: Lebanon Valley Agricultural Center, Lebanon County……………………18
7: Penn State University Berks County Campus, Berks County……..…….19
8: Warm Season Meadows at Williams Transco, Chester County………….22
9: Hills of Sullivan Residential Subdivision, Chester County……………….24
10: Applebrook Golf Course Community, Chester County…………………..28
11: Swan Lake Drive Development, Delaware County…………………….…..30
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Case Studies: Innovative Stormwater Management Approaches and Practices
9.1 Introduction
Although examples of BMPs have been included throughout all chapters of this manual with a
considerable number of illustrations, in most cases these examples have been necessarily condensed
and highly summarized. Most examples have not been able to do justice to all aspects of the site
development program and the site design and stormwater management plans that have been
developed. Consequently, early in the process of developing this new manual, the decision was made
to include a chapter that highlights functioning projects in Pennsylvania communities that have
successfully incorporated many of the Non-Structural and Structural BMPs that are described in this
manual. Clearly, seeing is believing – there is great value in being able to visit and view firsthand
successful applications of the many different BMPs which have been presented.
This chapter is a work in progress, where PADEP hopes to increase its file of successful case studies
over time. In particular, the hope is to add many more successful applications from all regions of the
state. Many of the innovative projects that have been undertaken have occurred in projects in
southeastern and southcentral Pennsylvania, to some extent reflecting the greater amount of land
development activity occurring in that region of Pennsylvania.
A Self-Guided Stormwater Best Management Practices Tour has been developed recently by the
Chester County Conservation District and funded by the PADEP Growing Greener Grant Program. The
Tour ingeniously features 21 different sites that include a variety of both non-structural and structural
BMPs applied in residential, commercial, and recreational land use settings. The entire Tour and all of
the written and photographic material which describes the sites and stormwater practices is available
on line through the Chester County Conservation District website. Several of the BMPs included in the
tour are featured in this chapter. Many other County Conservation Districts have also installed
demonstration BMPs at their office locations, including Westmoreland, Adams, Dauphin and Erie
The case studies that have been included in this chapter are designed to focus on successful BMP
application - what works. Over time, this case study discussion will be expanded to include lists of what
to avoid – what doesn’t work – as well. PADEP invites all interested stormwater stakeholders to submit
case study information in the future for additional projects. Section 9.2 is a list of information and data
items that case study descriptions should address, although it is recognized that some data gaps may
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9.2 Outline of Information Needed for Case Studies
PADEP Stormwater Manual Case Study
Outline of Needed Information/Data
Name of Project:
Address of Project:
Year constructed
Developer/builder/owner (name and contact information, if available)
Natural Site Features:
Water Resources
Major Watershed/minor watershed
Stream classification
Special: water supply source? TMDL? Impaired streams?
Streams, ponds, lakes?
Drainage features on the site
Wetlands? Floodplains? Riparian areas?
Wells (existing and future)? Zone of contribution? Zone of influence? Groundwater protected
Rock/aquifer type?
Special? Limestone? Subsidence potential? Fracture/fault traces? Lineaments?
Soils Hydrologic Soil Group A thru D?
Soil testing performed?
Existing at site?
Extent of vegetation disturbed/removed?
Proposed Use/Building Program
How much?
Of what?
Total site area?
Total disturbed area?
Total impervious area?
Costs of development?
Proposed Stormwater BMPs
Design specs, calculations, etc.
Design specs, calculations, etc.
Maintenance issues?
Other special issues?
Costs of site work and stormwater elements?
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9.3 Case Studies
The following case studies present examples of a range of structural and nonstructural BMPs that have
been successfully implemented across the state. The information provided has been assembled from
contributing Conservation Districts within Pennsylvania. Each case study has been developed to
include a high level of detail from the information provided, however data gaps do exist. For further
information, the reader is encouraged to contact the conservation district in the county where the
project is located.
Case Study 1: Penn State University - Centre County Visitor Center, Centre County
Porous Asphalt Parking Lots underlain with Subsurface Infiltration Beds
Porous Concrete Sidewalks
Subsurface Infiltration Trenches
Vegetated Infiltration Bed
Several Rain Gardens / Bioretention areas
Project Background
The Penn State University/Centre County Visitor Center in State College was constructed in 1999 on a
site underlain by the Nittany Formation. The Visitor’s Center incorporates a number of stormwater
infiltration techniques, shown in Figure 9-1, and was designed to imitate the natural hydrologic system
that existed at the site before development.
Figure 9-1. Stormwater Management System at PSU Visitor’s Center in Centre County, PA.
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According to the soil survey, the soil at this site was classified as the Hagerstown Series, well-drained
soils that formed in limestone residuum. Typically, the surface layer was dark-brown silt loam about
eight (8) inches thick. The subsoil consisted of yellowish-red and reddish-brown silty clay, clay, and
silty-clay loam approximately 37 inches thick. The substratum was generally yellowish-brown clay loam
to a depth of about 75 inches. The entire 5-acre site was underlain by the same soil series.
This information indicated several important characteristics of this site, even before detailed testing was
completed. The soil was well-drained with probably at least 5 to 6 feet of soil above the weathered
bedrock. Some clay was contained in the soils, which was a positive element since some mix of clay
would prevent water from draining excessively rapidly and would serve to remove pollutants.
The underlying geology was classified as the Nittany Formation according to the Department of
Environmental Resources, Bureau of Topographic and Geologic Survey (1982). This formation
consists of light to dark gray, finely to coarsely crystalline dolomite with alternating beds of sandy,
cherty dolomite. The rock is moderately resistant to weathering and is slightly weathered to a shallow
depth. The development of joint and solution channel openings in the rock is common. Bedrock
pinnacles are also common in the interface between the rock and soil mantle, which can make
excavation of the rock difficult. No specific geologic features (i.e. fracture traces) are indicated for this
Again, this information was crucial to developing a more detailed site investigation program. The
presence of pinnacles required a field investigation that can provide a site-specific understanding of the
pinnacle locations. In addition, the tendency for joint and solution channel openings to form indicates a
strong need to disperse stormwater and avoid concentrated points of storage or infiltration.
One additional piece of important information is that several University water supply wells are located
approximately 1/2-mile downstream of this site, indicating the importance of maintaining groundwater
recharge and water quality.
Site Testing: Geotechnical Investigation for Building Structure
The initial field investigation involved the excavation of five test borings, two groundwater-monitoring
wells, and four test pits. The initial tests were all installed as part of the geotechnical investigation for
the proposed building (independent of SWM), but provided useful and valid information for the
stormwater system as well. In other words, the stormwater design engineer should make use of all
available data developed at the site.
This information included the following findings:
Groundwater was not encountered in any of the borings or test pits.
Auger refusals were encountered at depths ranging from 2 feet to 8.7 feet – very shallow.
Refusal materials were encountered in three of the four test pits ranging from 3.1 to 4.8 feet.
The dolomitic limestone rock cores were weathered and fractured near the surface.
The rock contained interbedded clay seams.
No evidence of subsurface activity associated with sinkholes was encountered.
Site Testing: Geotechnical Investigation for Stormwater Management
The information from the building geotechnical investigation confirmed that bedrock depth was variable
and could be quite shallow. Based on this information, a more detailed geotechnical investigation was
developed that included a grid of shallow core borings, to a depth of ten feet or refusal, approximately
25 feet on-center. The shallow augers confirmed that there was considerable variation in the top of
rock reflecting the pinnacle nature of the underlying bedrock.
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Seven additional test pits were also excavated at the same time that the borings were undertaken.
These test pits were a critical part of the investigation and provided direct physical observation of the
soil layers and geology, confirming the soil survey series designations (which may or may not be
correct for the site). In this situation the test pits indicated the considerable variability in the top of rock;
even within a distance of eight feet (the length of the test pit), the surface of the bedrock could vary by
two to three feet. At the same time, simple percolation tests were also conducted at the test pits to
provide an estimate of the infiltration capabilities of the soil.
Compilation of Data: Cross Section Development
Before any design of the site and stormwater system takes place, the engineer should understand the
data in relation to the proposed use of the site. The most effective way to understand this information is
to incorporate it into the site plans. The location of the test borings and test pits is indicated on
Figure 9-2, which also indicates the proposed site layout. Next to each test boring, the depth to
bedrock is indicated. This is the first step in laying out the stormwater components. The engineer
should strive to integrate the information on a single sheet that helps the engineer visualize and
determine feasible areas for infiltration systems. At the Penn State Visitor Center, the area of the
parking lots had been generally proposed. The next step in design was to develop a profile of this
information. Several cross sections of the site were developed in the area of the proposed parking lots.
On each profile, the existing surface topography, the depth to bedrock and any other relevant
information was plotted.
Stormwater Management Design: Fit to Site and Close to Source
Using these profiles, the parking bays and infiltration beds were “fit” into the hillside, stepping down the
hillside with two parking bays, and adjusting the bottoms of the infiltration beds to “step down” as well.
This is shown in Figure 9-3.
Several items in design should be noted. Because the rock was shallow in places, the existing soil was
not excavated. Instead, the beds were “built up” using berms to avoid soil excavation, and only the
organic layer was removed. Where rock was very shallow, infiltration was limited to what would
naturally fall or drain to the area before development, and no attempt was made to convey additional
stormwater to the area. Instead, the pre-development balance (or Loading Rate) was carefully
Development of cross sections can be an extremely useful element in design of infiltration systems on
carbonate rock. Because the beds must be carefully set with adequate soil mantle, the cross sections
provide the design engineer with the information necessary for the layout. Additionally, cross sections
provide the Contractor with the necessary information to build the system. In the same manner that
profiles are required for utility pipe design (i.e., water, wastewater, and stormwater pipes), profiles are
an important component of design of infiltration BMPs in carbonate rock.
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Figure 9-2. Core Boring and Soil Test Pit Locations at the PSU Visitor’s Center, Centre County.
Figure 9-3. Cross-section view showing bedrock pinnacles, existing grade, and proposed stormwater
infiltration beds with elevations.
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Finally, and most importantly, it was recognized at the Visitor Center that any attempt to convey
stormwater from one portion of the site to another would result in stormwater pipes that would be
placed in the bedrock. Given the pinnacled nature of the site, it would be inevitable that any length of
pipe would be forced to traverse bedrock. To avoid this situation, stormwater is managed as close to
the source as possible and a variety of measures are incorporated:
Runoff from the roof of the eastern side of the building is conveyed to a Rain Garden and then to a
subsurface Infiltration Trench located on contour.
The Infiltration Trench (Figure 9-4) intercepts a portion of the entrance road runoff. To compensate for
the remainder, a vegetated subsurface Infiltration Bed (Figure 9-5) was located immediately adjacent to
an existing, uncontrolled parking lot.
The runoff from the western portion of the building is conveyed to the parking lot immediately adjacent
to the building where the soil mantle is suitable and the top of bedrock was much deeper (Figure 9-6).
In several key locations where stormwater management was needed, small Rain Gardens (Figure 9-7),
designed to infiltrate, were incorporated to avoid installing stormwater pipes.
Porous concrete sidewalks were constructed to manage the rainfall incident to them (Figure 9-8).
Figure 9-4. Infiltration trench located on contour, State College, Centre County.
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Figure 9-5. Vegetated infiltration bed, State College, Centre County.
Figure 9-6. Porous asphalt parking lot, State College, Centre County.
Figure 9-7. Rain Garden, State College, Centre County.
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Figure 9-8. Porous concrete sidewalks, State College, Centre County.
Engineering Plans
The final and critical element to stormwater infiltration system design was to provide the Contractor the
required information to build the systems. The subsurface grading of the stormwater infiltration beds
was critical to their success. In addition to the cross sections provided, each system should indicate
the subsurface contours. An example from the Visitor Center is provided in Figure 9-9. This grading
information allowed the earthwork contractor to construct the bed as designed. Because this
information is “sub-surface,” it would not normally be part of a site-grading plan. However, adding this
grading information to the stormwater plan was critical.
Figure 9-9. Subsurface contours and grading for the infiltration beds at PSU Visitor’s Center, Centre County.
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Case Study 2: Dennis Creek Streambank Restoration, Franklin County
Riparian Buffer Reestablishment
Wetland Restoration
Partnership began with the Franklin County Watershed Association, an informal cooperative group of
landowners, farmers, municipal authorities, and other local officials
Part of the Potomac River Basin, the watershed originates in Hamilton Township, Franklin County, near
Chambersburg, PA in the pristine headwaters in of the Kittatinny Mountain Ridge. However, nutrient
runoff and the presence of cattle in the stream have degraded both the macro-invertebrate life living
within the stream as well as the streambanks themselves.
Historically, the watershed and forestland was cleared as fuel for the iron industries, causing severe
erosion problems. As the iron industry gave way to the agricultural industry, erosion problems
continued and were exacerbated by overgrazing, cattle waste pollution, and unprotected streambanks.
A first step to restore Dennis Creek was to install several miles of streambank fencing
to keep cattle out
of the stream itself and allow for revegetation of the riparian buffer. This practice alone provided
immediate water quality and macro-invertebrate community improvements. Fences are maintained
through the local partnership
Because many riparian areas had no trees or vegetation, another task in this project included the
streambank planting
of trees and native warm season grasses, as well as the restoration of wetlands
for stormwater runoff quality control. A newly restored marsh provides animal habitat and water quality
improvement in the intensely farmed watershed
A water quality-monitoring program involving government agencies, school students and others has
been implemented to measure the project success.
Important project points:
Total watershed area is 14 square miles
Resulted in improved hunting and fishing opportunities for community and an educational
opportunity for students
Video located on the web:
Figure 9-10. Dennis Creek Watershed in Franklin County, PA.
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Case Study 3: Commerce Plaza III, Lehigh County
Vegetated infiltration basin
Concrete level spreader
Vegetated swale
Project Background
Commerce Plaza III, in Upper Macungie Township and South Whitehall Township in Lehigh County, PA
is a mid-rise office complex that was proposed for a 49-acre site. A major concern during the design
phase was to locate elements of the site stormwater management system away from limestone
formations to avoid potential sinkhole problems. The site, historically in agricultural use before
subdivision, had a pre-existing sinkhole located near the area slated for stormwater management.
Figure 9-11. Vegetated infiltration basin in Lehigh County.
BMP Description
The vegetated infiltration basin
(Figure 9-11)
collects stormwater runoff from one parking lot
and one building, and mitigates runoff from two
additional buildings nearby. The basin was
designed with a high loading rate of impervious
surface runoff to BMP area. Stormwater runoff
sheet flows from the inlet to a concrete level
spreader (Figure 9-12) into the infiltration basin.
The surface of the infiltration basin was graded
with extreme care, creating an even basin
surface elevation to receive stormwater. Figure
9-13 shows the vegetated swale
inflow to the
infiltration basin.
Figure 9-12. Level spreader distributes stormwater
Figure 9-13. Vegetated swale
into the infiltration basin.
: Figure 9-14 shows the Commerce Plaza office location along with the corresponding soil series.
The infiltration basin at Commerce Plaza III is located within the Washington soil series. Washington
soils found in Lehigh County are deep, well-drained soils, whose underlying material is glacial till, or
frost-churned material weathered from limestone.
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Figure 9-14. Commerce Plaza soils, NRCS.
: Figure 9-15 shows the BMP location along with the corresponding surficial geologic
formations. The site is located on the Epler Formation of the Beekmantown Group. The Epler
Formation dates from the Lower Ordovician and is a medium to dark-medium gray, finely crystalline,
silty limestone interbedded with some thin- to thick-bedded cryptocrystalline dolomite.
Figure 9-15. Commerce Plaza in Lehigh County is located on limestone geology.
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Case Study 4: Flying J. Truck Plaza for Welsh Oil of Indiana Truck Refueling Terminal,
Cumberland County
Subsurface Infiltration Bed
Perimeter Trench Drain
Treatment Wetlands
Vegetated Infiltration Filters
Curb Cuts with Filter Strips
Project Background
In 1993, Flying J Truck Plaza, a truck refueling facility in Middlesex Township, Cumberland County,
Pennsylvania, was faced with complying with municipal open space requirements and the site area
needed for their development program. Conventional stormwater detention basins exceeded site area
limits required, and as a result, the use of groundwater recharge beds for stormwater management was
proposed. Subsurface infiltration beds, located beneath the truck parking facility itself, provided
additional space for parking.
Situated over a carbonate formation, the possibility of sinkholes was thoroughly investigated utilizing
ground-penetrating radar to map the underlying bedrock. By designing recharge beds to distribute the
infiltrating stormwater over a large area where the soil mantle was sufficiently thick, the development of
solution channels in the carbonate was minimized. Use of a recharge design for stormwater
management for a facility serving as many as 1,500 heavy trucks per day in a sensitive carbonate
context had to be coupled with special water quality measures. A two-stage pretreatment system was
designed, including a settling unit and vegetated filtration system to remove first flush pollutants from
stormwater runoff before entering the groundwater.
Figure 9-16. Perimeter trench drain.
Figure 9-17. Vegetated infiltration filters.
Site Description
: The primary soils found on the site include Duffield silt loam (DuA and DuB), Hagerstown silt
loam (HaB), and Huntington silt loam (HuA); with Berks shaley silt loam and Blairton silt loam found
primarily around the site perimeter.
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Design Images and Details
Figure 9-18. Stormwater flow path for the Travel Plaza stormwater management system.
Figure 9-19. Shows the construction design detail for the filter station at the Truck Plaza.
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Figure 9-20. Shows the construction design detail for the perimeter channel section.
Figure 9-21. Illustrates the peat infiltration bed that is adjacent to the truck parking lot
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Case Study 5: Ephrata Performing Arts Center, Lancaster County
Porous Asphalt parking lot
Vegetated Swale
Site Address
Ephrata Performing Arts Center
Cocalico Road
Ephrata, PA 17522
Project Background
The Ephrata Performing Arts Center is located in the existing Grater Park, and includes the Ephrata
Playhouse, American Legion, other miscellaneous buildings and associated parking facilities. The
project was proposed in coordination with a planned expansion and remodeling of the existing
playhouse that required new parking facilities to support the additional use.
The new porous parking lot consists of two rows on each end of the existing lot. A total of 9,200 square
feet of porous parking area was installed, providing 40 new parking spaces on the site. The new
parking was installed in an existing lawn area and vegetated bioretention swales were included in the
design. The project was completed in September 2004.
Site Description
The site is located within the Cocalico Creek Watershed. The stream is classified WWF (Warm Water
Fishery) and is on the 303(d) list of impaired streams for siltation/sediment. The site is bordered to the
north by Cocalico Creek.
The site is underlain by the Snitz Creek (CsC) Formation, which is a Cambrian Age Dolomite and
Sandstone. All BMPs were installed within the Hagerstown Urban Soil Complex, which is classified as
Hydrologic Soil Group “C”. Percolation tests were conducted on the underlying soils and infiltration
rates observed were ½ inch per hour or greater. There was no disturbance of steep slopes involved in
the project; all construction occurred on slopes of 6 percent or less.
BMP Description
The porous parking is underlain by a stone infiltration bed with various benches ranging in depth from
18 to 48 inches and receives runoff from surrounding impervious driveways and parking areas. The
bed connected to the northernmost parking row is designed to overflow to a flat grassed area, and the
bed under the southern row discharges to a vegetated bioretention swale. As part of the design, a
portion of the existing impervious parking area was removed and a bioretention bed was installed to
promote the additional infiltration of runoff conveyed by the existing parking areas.
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Figure 9-22. Construction of porous asphalt parking area to compliment building expansion.
Figure 9-23. Completed porous asphalt parking lot at Ephrata Performing Arts Center.
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Case Study 6: Lebanon Valley Agricultural Center, Lebanon County
Porous Asphalt parking lot
Site Address:
Lebanon Valley Agricultural Center
2120 Cornwall Road
Lebanon, PA 17042
Project Background
The porous parking lot at the Lebanon Valley Agricultural Center was installed to provide additional
parking at the existing site. The completed lot provides 58 new spaces, 40 of which are porous. The
center drive lane is conventional asphalt with porous pavement limited to the parking bays. The porous
parking installation was completed in July 2003.
Site Description
The Lebanon Valley Agricultural Center is located within the Snitz Creek Watershed, which is classified
TSF (Trout Stocking Fishery). The site contains no wetlands, floodplains or riparian zones. Bedrock
on the site belongs to the Richland Formation, a carbonate formation composed primarily of finely
crystalline dolomite and oolitic limestone. Sandstone beds and pinnacles are present throughout the
formation and sinkholes and closed depressions are prevalent. Hydrologic Soil Group (HSG) B and C
soils are found on the site.
BMP Description
The porous pavement parking lot was installed on an existing lawn area and is underlain by a 24 -inch
infiltration bed. The bed was excavated and unwoven geotextile fabric was placed on the undisturbed
subsoil. Clean AASHTO #1 aggregate was placed in the bed in 12-inch lifts and lightly rolled to prevent
settling. Finally, a 3-inch choker course comprised of AASHTO #57 was placed over the larger
aggregate and was finish graded to prepare for the asphalt pavement.
The porous parking receives runoff
from the center drive lane, which was
constructed with conventional asphalt.
The overflow design is comprised of
four 4-inch pipes placed at the top of
the infiltration bed and discharging to
a well-vegetated area. Two 6-inch
pipes, which discharge to an existing
vegetated swale on the site, provide
additional overflow. The project site
has been observed during several
high intensity storms and appears to
be working successfully as there was
little or no discharge apparent from
the overflow pipes.
Figure 9-24. Completed porous asphalt parking lot at Lebanon County
Conservation District.
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Case Study 7: Penn State University Berks County Campus, Berks County
Porous Asphalt Parking Lots underlain with Subsurface Infiltration Beds
Subsurface Infiltration Trench underlying Standard Asphalt Walkway
Minimum Disturbance
Level Spreader Pipe in the Woods
In addition to its Main Campus in State College, Pennsylvania State University maintains several
satellite campus sites throughout the state. Each of these regional campus sites represents a major
investment in educational resources and recently underwent a substantial expansion and development
of additional facilities. In 1999, the PSU campus in Reading developed a dormitory complex to
accommodate some 400 resident students. The dormitory complex, which consisted of seven attached
buildings, was situated in a wooded knoll on the attractive campus. This facility required additional
parking spaces for some 320 cars.
Prior to the new development, the area of the campus in question consisted of existing dormitories, a
parking lot, a soccer field, a wooded hillside, and lower-lying meadow. The site drains to Tulpehocken
Creek, a pristine tailwater fishery that provides habitat to numerous trout species. The soils on the site
were mostly well-draining Hydrologic Soil Group ‘B’ classification. The campus had historically been
hindered by the formation of sinkholes in the carbonate bedrock formation underlying it at shallow
elevations. In fact, one of the two existing on-site detention basins (Figure 9-25) had suffered from
severe sinkhole problems. This particular basin experienced at least two major sinkholes during its
lifespan, which required massive (and expensive) remediation efforts involving concrete plugging and
lining. The goal of the stormwater management for the new development was thus twofold: mitigation
of newly generated site runoff and reduction of existing runoff to the existing basins.
Figure 9-25. Existing sinkhole-plagued detention basin.
The original development plan called for the construction of a new, standard asphalt parking lot in an
area of existing woodlands, which would be drained by a new detention basin. The new dormitory
complex was going to be located in a highly disruptive fashion in the wooded knoll. The original plan
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was eventually discarded in favor of a more sustainable approach involving minimum disturbance,
volume reduction, water quality improvement, and groundwater recharge. The first major improvement
to the plan was the repositioning of the new
dormitories in a more organic fashion along the
contours in the woods. This sensitive positioning
preserved healthy trees and minimized earth
disturbance, which was limited to within 15ft of the
new structures. Another major improvement was
relocating the new parking lot away from existing
woods and into the meadow. Also, this parking lot
was constructed with porous asphalt and underlain
by an aggregate infiltration bed.
The stormwater management plan for the developed
site was a great improvement over the existing
condition. Stormwater management for new
dormitories consisted of an aggregate infiltration
trench beneath a standard asphalt walkway “interior”
of the complex and “exterior” level spreader
perforated pipes along contours in the woods. Roof
leaders on the interior halves of the dormitories were
connected to the aggregate trench/walkway. (These
walkways were stabilized beyond the standard
asphalt by a “grass pavement” for fire truck access.)
Likewise, roof leaders on the exterior halves were
directly connected to the level spreader perforated
pipes in the woods. These laterally extending pipes
were designed to maintain soil moisture for the
Figure 9-26. Example of minimum disturbance and
prevent erosion or disturbance on the hillside
Figure 9-27. Level spreader pipe/infiltration trench in woods.
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The new porous asphalt parking lot was designed to
mitigate incident rainfall and direct runoff from the nearby
access road and existing dormitories. The porous
parking lot has so far effectively discouraged the
concentration of stormwater runoff downhill and allowed
the incident rainfall to pass directly through the parking
bays, slowly percolating into the soil and recharging the
aquifer system. This system has also dramatically
reduced discharges to the existing sinkhole-plagued
basins. To date, neither the porous parking lot nor the
existing basins have experienced additional sinkhole
problems. Furthermore, polluted runoff from the site,
usually described as nonpoint source pollution (NPS),
was significantly removed by the overall plan. The new
improvements at the PSU Berks County campus have
had virtually zero impact on regional water resources.
The cost of the new porous asphalt parking lot with
subsurface aggregate infiltration bed came to around
$1100 per space, in 1999 dollars. When all related site
work (lighting, landscaping, erosion and sedimentation
control, etc.) was considered, the final cost per space
Figure 9-28. Standard asphalt walkway
was around $2200, also in 1999 dollars
w/ subsurface infiltration trench
Figure 9-29. Porous asphalt parking lot with subsurface infiltration bed.
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Case Study 8: Warm Season Meadows at Williams Transco, East Whiteland Township,
Chester County
Re-Vegetation as Natural Open Space Meadow, Using Native Plants and
Replacing Maintained Lawn
Project Background
This site is largely unpaved land consisting of fields interspersed with an office building, an employee
parking area, and utility structures and right-of-way areas, all previously maintained as conventional
lawn area. Utility line areas consist primarily of poles, towers, and guidelines that disturb minimum
earth once in place.
At this utility company corporate office and utility right-of-way site in the Valley Creek Watershed
(classified as Exceptional Value, EV), a re-landscaping plan was developed for the site, which included
use of native warm season meadow grasses well suited to the local climate. Re-landscaping included
switch grass and native blue stem, planted on about 25 acres of land that had previously been fields of
relatively conventional turf grass that was subject to fertilizer and herbicide/pesticide applications as
well as regular mowing. Prior to this planting of meadow grasses, herbicide was carefully applied to kill
existing vegetation including undesirable invasive plants; this herbicide application was timed so that it
wouldn’t harm an existing stand of native blue stem. The native meadow grasses were planted using
no-till planting practices to prevent excessive earth disturbance. The new grasses grow during the
middle of the growing season and are dormant in the spring and fall. They are best harvested after the
spring nesting season, but require no mowing.
Stormwater Management Functional Benefits
Establishing warm season meadow of native grasses is included in this manual as a BMP because the
overall environmental performance of unmowed, unmaintained native grass meadows is superior to
that of mowed and maintained turf grass fields, both in terms of stormwater quantity and stormwater
quality. Meadows promote stormwater infiltration into the ground; through interception of any
stormwater flow (sheet or channelized), rate of flow is slowed. Periodic application of fertilizers and
herbicides is eliminated; therefore chemical pollution to surface runoff as well as to the groundwater is
reduced. Native grasses also have a greater potential to uptake any pollutants present in stormwater
runoff, in contrast to conventional turf grass, although no pollutant reduction analysis specifically has
been performed for this BMP project. To a large extent, sediment and grit, oil and grease, as well as
nutrients present in site stormwater runoff will be filtered by the natural biological and physical filtration
processes provided by native meadow grasses prior to being discharged into receiving waters or being
percolated deeper into the groundwater. Additionally, established warm season grassy meadows
provide natural open space habitat and are especially attractive to wildlife, including birds.
Operation and Maintenance:
The Chester County Conservation District considers planted meadows
to be a “low maintenance” BMP. Warm season native meadow grasses should be burned every 3 to 4
years to invigorate stem growth, remove thatch, and eliminate growth of invasive plants. At this site,
burning is not an acceptable management option due to the nature of current site activities and
proximity to residential areas; however, as an alternative to burning, the site owner can harvest cut on a
3-4 year cycle. The new meadow grasses with their low nutrient requirements, do not require
fertilization above and beyond available soil nutrients. Meadow grass does need to be periodically cut
around guide wires, structures and buildings to permit inspection and maintenance of structures. To
ensure that this BMP is maintained properly, procedures and specifications for meadow maintenance
should be documented and maintained on the site.
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Cost Issues
The cost of establishing native meadows is low, relative to many other types of stormwater
management practices, and is typically not significantly more expensive than installation of a
conventional landscape. Operating and maintenance costs usually are less than conventional
landscaping. For example, at this site, the warm season meadow offers the site owner cost savings
conservatively estimated at $350 per acre per year through avoidance of mowing, without including the
added costs of fertilization and herbicide applications. Additionally, the meadow grasses can be
harvested annually and sold at current market value. Other factors that may affect cost of establishing
a warm season grass meadow include site conditions, such as the cost of land, local topography, rocky
or highly permeable soil, and bedrock.
For More Information
For more information about this BMP site, contact the site owner, Williams Transco, at 610-644-7373
(Robert Hill, Assistant District Manager). Although this site is part of the Chester County BMP Tour,
site visits should be individually arranged. Also, Tim Smail at the Chester County office of the USDA-
Natural Resource Conservation Service assisted in the BMP design.
Figures 9-30 & 9-31. Warm season native grassy meadows established at this site provide greater stormwater
infiltration opportunities than maintained turf grass fields. Low maintenance meadows enhance wildlife habitat.
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Case Study 9: Hills of Sullivan Residential Subdivision, London Grove Township,
Chester County
Infiltration Trenches
Project Background
This sizable single-family development was constructed over 15 years ago and is located in the White
Clay Creek watershed (classified CWF, TSF). London Grove Township at that time was one of the few
municipalities in Chester County, as well as the state, to require in its stormwater regulations that runoff
volumes for up to the 2-year storm not be increased, pre- to post-development. The site can be
reached from Rose Hill Road south, left onto Avondale Road, right onto Clay Creek Road, left onto
Angelica Drive and then best accessed via the trail located in HOA-owned open space (follow a narrow
trail from Angelica Drive just above a bridge and above the creek).
Project Description
At the encouragement of the Township and its Municipal Engineer, an integrated system of berms and
infiltration trenches was constructed. The typical berm/trench consisted of narrow, elongated, surface
depressions created by built up earthen embankments, or berms, that promote stormwater infiltration.
At this site, the infiltration trenches are elongated, shallow trenches on the surface that collect and
temporarily store stormwater runoff from the upslope residential lots and streets and promote its
infiltration (in contrast to sub-surface, excavated, fabric-wrapped, stone-filled trenches as described in
Chapter 6). Stormwater that collects in these narrow depressions on the hillside gradually seeps
through the soil into the ground and eventually into the creek and water table below. These
berms/trenches follow the contours of the land in a parallel sequence. There are three 400 foot-long
trenches terraced, or stepped, down the slope with one below another.
When the uphill trench is filled to capacity, stormwater overflows into the trench below. There is also a
single 1,000 foot-long trench that functions independently of the three terraced trenches. This large
trench receives stormwater through a subsurface pipe. Because stormwater entering this trench is
conveyed through a pipe with a steep slope and has high velocity, a concrete chamber is used to
dissipate its energy before discharging into the trench. When this trench overflows, stormwater spills
over its downslope berm and flows down the bank into the stream below. For an infiltration trench to
properly function, the bottom soil must be permeable and remain uncompacted for the life of the
structure. Soil percolation tests performed prior to trench construction and at the conclusion of earth
disturbance are used to ensure soil infiltration capacity. Vegetation has naturally established itself in
the trenches. The berms, which double as a walking path, consist of a gravel and grassy base and are
wide enough to permit access for future maintenance of these structures.
Stormwater Function
Infiltration trenches replenish the water table, recharge groundwater supplies, and stabilize base flow in
streams. They provide efficient recharge because the infiltration occurs relatively close to where the
runoff is generated, thus limiting evaporative loss and infiltrating more rainfall. Infiltration trenches
provide an opportunity for physical filtration of pollutants in stormwater runoff removing suspended
solids including dirt and sand particles (solids accumulate in vegetation and bottom soils). Oil and
grease bound to suspended particles, and their heavy metal constituents, may also be filtered from
runoff. These structures also provide naturally vegetated open space for wildlife. The trenches/berms
function as a walking trail for the community and provide maintenance access.
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This BMP is not advisable for use in drainage areas that have extensive stormwater pollution sources
(i.e., “hotspots”), because by itself such a system has limited pollutant removal capabilities.
Functioning as designed, infiltration structures can approximate the following pollutant removal
efficiencies for non-excessive nonpoint source pollutant loadings as would be expected from single-
family residential land uses:
Total Suspended Solids (TSS):
95 %
Total Phosphorus:
70 %
Total Nitrogen:
51 %
Metals (copper and zinc):
99 %
Not Applicable
Operation and Maintenance:
The Chester County Conservation District considers infiltration trenches
to have moderate maintenance requirements. Operation and maintenance requirements include the
following (provided in this case by the Homeowners’ Association):
Regularly inspect to ensure adequate infiltration
Regularly inspect structural components (i.e. energy dissipater, inlet structure) to ensure
they are functioning properly
Periodically trim plants to ensure their growth does not impede the flow of water through
the structure
Remove invasive plants as necessary (remove shoots and roots)
Routinely remove accumulated trash and debris
Avoid running heavy equipment in the trenches to prevent soil compaction
At the completion of construction, scrape soils to remove accumulated sediment and
conduct soil percolation test
Do not apply chemical pesticides or fertilizers to turf in and around infiltration structures
Cost Factors
In general, the cost to construct and maintain infiltration trenches is usually comparable to the cost of
constructing and maintaining large stormwater basins, which would have otherwise been necessary.
Given the age of this project, specific cost data have not been available. Soil percolation tests
performed before and after construction, as well as measures taken to protect the infiltration basin from
sediment inundation during construction add moderately to project costs, but are essential in order to
ensure proper function of the infiltration trenches/berms.
For More Information
Contact London Grove Township at 610-345-0100 or the Township Engineer, Larry Walker (URS) at
302-791-0700. London Grove Township has worked to apply this and other infiltration-oriented BMPs
in other developments, such as Ashland Woods, located near the intersection of Sullivan Road and
New Garden Station Road on Jack Reynolds Way, where infiltration basins are located on individual
lots owned by individual homeowners.
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Figure 9-32. View from Clay Creek Rd: trenches/berms at the base of the grassy hill in background;
trenches/berms barely visible through trees as horizontal undulations.
Figure 9-33. This grassy path is an embankment, or berm, creating depressions for recharge trenches located to
the left of the path.
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Figure 9-34. Narrow, vegetated infiltration trenches/berms follow land contours and take on a naturalized
Figure 9-35. This trench/berm has a subsurface energy dissipater to reduce the velocity of entering stormwater.
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Case Study 10: Applebrook Golf Course Community, Chester County
Constructed Treatment Wetland
Two Wet Ponds
Grass Swales
Cold Water Discharge
Open Storage
In the spring of 2002, stormwater management improvements were constructed at Applebrook Golf
Course Community in East Goshen, Chester County. These improvements were intended to
substantially improve the quality of site runoff, reduce the peak runoff rates, stabilize flow to adjacent
natural wetlands and streams, and provide stable habitat for plants and wildlife, including sensitive and
native endangered species. As the site is within the Ridley Creek watershed, which is deemed
Exceptional Value by the state, these goals were especially important.
The most significant BMPs constructed as part of the
strategy were a constructed treatment wetland and two
wet ponds. Other stormwater measures at the golf c
included grass swales, fertigation (fertilization and
irrigation), cold-water discharges, and open space
donation. The constructed treatment wetland at the site
was designed primarily with water quality objectives in
mind. It was constructed in a low-lying area near natural
wetlands in the Ridley Creek floodplain. This allowed it to
take advantage of inflows of water between storm events
and to maintain sufficient soil moisture. Through physical,
biological, and chemical processes, constructed wetlands
can efficiently remove a great many contaminants
commonly found in runoff (suspended solids, nutrients
(nitrogen and phosphorus), heavy metals, toxic organics,
and petroleum compounds). Wetland vegetation, algae,
and bacteria allow for the biological uptake of
contaminants. Wetland vegetation also provides physical
and chemical pollutant filtering mechanisms, which g
enhance the quality of the runoff from the golf course,
well nearby residential development. Constructed
wetlands also play a role in reducing peak rates from a
site, stabilize flow, and
Figure 9-36. Constructed wetland in background.
provide valuable habitat opportunities.
A wet pond is a stormwater management feature that maintains a permanent pool of water (retention)
and has additional capacity for stormwater detention. Two wet ponds were constructed at the golf
course as part of the improvements. The smaller of these two wet ponds has the preferable elongated
shape, while the larger is comprised of two cells. When the first cell has reached capacity, water spills
over into the second cell. The larger pond receives treated wastewater from a nearby, township-owned
wastewater treatment facility. Water is pumped from this pond and used in the site’s fertigation system.
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Constructed wetlands are considered to be a low to moderate stormwater BMP. Typical operation and
maintenance requirements include: manual adjustment of the water level (especially during plant
establishment), manual removal of invasive plant species, and cleaning out of outlet structures when
excessive amounts of sediment have accumulated.
Other BMPs constructed at the
golf course include grass swales,
fertigation, cold-water discharges,
and open space donation. The
various grass swales at the golf
course provide a sustainable
alternative to concrete-lined
channels or conventional storm
sewers. Their many benefits
include the filtering out of runoff
pollutants, large storm
conveyance, enhanced infiltration
opportunities, and peak rate
Figure 9-37. Large pond, constructed wetland, managed and naturalized
areas of golf course.
The site’s fertigation system provides a sustainable alternative to conventional fertilization. The system
uses water from the larger of the two wet ponds, which receives wastewater effluent from the
Township’s nearby sewage treatment plant. Water from this wet pond is
pumped for use in golf course irrigation and fertilization. This system
allows fertilizers to be introduced to the irrigation water in solution form, a
technique that allows 100% fertilizer use, as opposed to only 20% when
dry fertilizer application is employed.
Water from the wet pond is pumped at or near the bottom so that the
coldest water is returned to Ridley Creek. This is an important
consideration for the trout in the exceptional value creek. The
development includes an area of wetlands of approximately 70 acres that
was donated by the developer to the Township as open space. There is
a conservation easement on this land, which restricts the cutting/mowing
of vegetation to permit wetland plants to mature. The eased land
includes the constructed wetland, the natural wetland, the stream, and its
adjacent floodplains.
Figure 9-38. Pond water is
pumped up to a waterfall and
returns to pond through grass
swales enhancing aeration.
Chester County Stormwater BMP Tour Guide
. Published by Chester
County Conservation District.
Center for Watershed Protection.
A Review of Stormwater Treatment Practices
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Pennsylvania Handbook of Best Management Practices for Developing Areas. Spring 1988.
Case Study 11: Swan Lake Drive Development, Delaware County
Vegetated Infiltration Beds
Site Address
Swan Lake Drive
Concord, PA 19061
Delaware County
Project Background
This project consists of the development of eight single-family dwellings on approximately 12 acres
near the intersection of Mattson and Concord Roads in Delaware County. Stormwater on the site is
managed with on-lot vegetated infiltration beds which reduce runoff volume and help protect water
quality within an existing spring fed pond and associated wetlands.
Site Description
The Swan Lake Drive Development is located within the Greens Creek Watershed, which drains to the
West Branch of Chester Creek. Predevelopment conditions on the site consisted of rolling farmland
with woodlands located on the northern third of the property. Three small streams traverse through the
parcel from west to east. Adjacent to the streams are floodplains with some associated wetland areas.
Existing soils on the property consist of the Glenville, Glenelg, Brandywine and Worsham Series. All
soils are classified as silt loams and range in permeability from moderate to low permeability.
Infiltration testing was conducted on the site and the soils were found to be suitable for infiltration.
BMP Description
Vegetated infiltration beds were constructed to manage the rooftop runoff from each individual lot as
well as runoff generated by driveway and road areas from a large portion of the development. The
remaining runoff on site was conveyed to the existing pond. Shallow subsurface infiltration beds (no
greater than 2.5 feet deep) were installed on all eight lots and rooftop runoff from each home is
conveyed to the onsite infiltration bed. A larger infiltration bed was constructed to manage the runoff
from driveways and Swan Lake Drive. Stormwater overflow and some overland flow are directed into
the existing pond at the bottom of the site. The infiltration systems on the site provide capacity to
store/infiltrate approximately 11,000 cubic feet of runoff over a 24-hour period.

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