12/9/2004; Barrington Square Retrofit 1

Barrington Apartment Complex, 2001

Barrington Square Apartments 

7123 SE Powell Boulevard, Portland

Project Summary 

Project Type: Commercial stormwater retrofit – demonstration project 

Technologies: Landscape infiltration basin; mini soakage trenches; simple downspout disconnections (to splash 

blocks). 

Major Benefits: • Runoff from more than 16,500 sq. ft. of roof (5 apartment buildings) has been removed from the 

combined sewer. 

• The stormwater facilities remove more than 350,000 gallons of runoff from the sewer in a typical 

year, with corresponding reductions in runoff pollutants. 

• Approximately 5,600 sq. ft. of native landscaping was added, improving the urban environment and 

the aesthetic appeal of the property. 

Cost: $71,200 (unit cost of $4.30/sq. ft. of impervious area managed). Adjusting for a project component that 

was not essential – replacement of the entire gutter and downspout system - the estimated total cost was 

$54,200 or $3.25/sq. ft. BES provided a $30,000 grant for the project. 

Constructed: Spring 2002 

Project Background 

The owner of the Barrington Square Apartments 

was making plans to replace the gutters and 

downspouts at the complex when he received a 

brochure regarding the Willamette Stormwater 

Control Program1. He subsequently hired a 

landscape architect to develop a proposal to 

disconnect the apartment roofs from the 

combined sewer. He viewed the project as an 

opportunity to increase the aesthetic appeal and 

commercial value of his property while reducing 

impacts on the combined sewer system. He also 

anticipated potential savings on his stormwater 

rates. BES accepted his project proposal in May 

2001.

 

1

 Portland’s Bureau of Environmental Services implemented the Willamette Stormwater Control Program in 2001. The 

Program offered financial grants and technical support for a series of projects to retrofit existing commercial properties with

stormwater controls incorporating green technologies. The Program recruited these demonstration projects in order to research 

the feasibility, cost and performance of commercial stormwater retrofits in the area served by the combined sewer. The 

Program provided grant funds for a total of eleven projects. The projects were completed July 1, 2003. 

 

 

 

 

 
12/9/2004; Barrington Square Retrofit 2

Project Scope 

• Replaced all of the gutters and downspouts. 

• Disconnected the downspouts from the combined sewer system.

• Hand dug approximately 350 linear ft. of mini soakage trench (this 

eliminated potential damage to the property by heavy equipment).

• Constructed 3 landscaped infiltration basins.

• Installed 13 subsurface mini catch basins.

• Installed subsurface ABS pipes to link all of the stormwater 

management facilities.

Notable Features 

• The designer did an excellent job of integrating the landscape 

facilities into the existing layout of the property, taking advantage 

of the space around the pool deck and stairwells. 

• The design successfully provides complete on-site disposal 

(infiltration) of runoff by linking a number of stormwater facilities, 

some of which are too small by themselves to serve the area that 

drains to them. 

Project Design

The property owner hired Landesign Associates, a local landscape 

architecture firm, to design the project. The firm was responsible for 

all phases of the project including design, layout, and construction 

management. 

Overview of the Stormwater System

(See site plan for drainage details, page 10) 

• Approximately 6,780 sq. ft. of roof surface from buildings on the 

north half of the property drain to a system of mini soakage 

trenches surrounding the swimming pool (Area I). 

• Runoff from an estimated 4,700 sq. ft. from buildings on the south 

side of the courtyard drain to two linked landscape infiltration 

basins (Area II). 

• The southern halves of the two buildings along Powell Boulevard, 

approximately 2,300 sq. ft. of roof, drain to mini soakage trenches 

in the landscape (Area III). 

• Runoff from over 2,700 sq. ft. of roof area drains to a combination 

infiltration basin/trench on the east side of the property (Area IV). 

This area also serves as the terminus for the entire linked system 

around the courtyard and pool. 

Mini soakage trench surrounding 

the pool (note plantings along 

edge); 2004

Landscape infiltration basin under 

stairs; 2004

Courtyard with landscape 

infiltration basins around edges 

and under stairs; 2004
12/9/2004; Barrington Square Retrofit 3

Capacity and System Components 

I. Introduction

The overall stormwater management goal was to meet the Bureau of 

Development Services (BDS)2 standards for stormwater disposal. 

When BDS approved the project in 2002, the disposal standard was to 

infiltrate at least 3 in. of runoff in 24 hours (approximately the size of 

the 10 year design storm). All design standards cited in in this report 

were current in the year 2002.

A site-specific infiltration test was not required for this particular 

project; local drainage characteristics had already been documented 

by other projects in the vicinity 3. The Natural Resource Conservation 

Service (NRCS) Soil Survey for Multnomah County classifies the 

local soils as moderately well-draining silty loams (type B hydrologic 

group). The Survey lists an expected infiltration range of 0.6 – 2.0 

in. per hour. 

City staff collaborated with the designer to develop a stormwater 

management system that would meet capacity standards. At one 

point the designer considered adding drywells in order to extend the 

capacity of the system. However, installing drywells would have 

required heavy equipment with a substantial risk of damage to the 

walkways and other structures. To avoid this risk and provide 

adequate capacity, the designer successfully modified the 

configurations of the soakage trenches and landscape infiltration 

basins (from the 2002 Stormwater Management Manual) to fit the 

space constraints of the site. 

II. Facility Components

Gutter System 

The property owner replaced all of the gutters with a covered gutter 

system which should substantially reduce the amount of debris 

entering the mini-soakage trenches and landscape infiltration basins. 

 

2 BDS is responsible for developing standards for stormwater disposal and inspecting projects to confirm compliance with those standards. 3

 It is common for the Bureau of Development Services to require infiltration tests prior to approving plans for infiltration facilities. 

Designers should contact the Bureau prior to submitting plans in order to determine the type of documentation required. 

Installation of Mini soakage 

trench next to the pool.

East side of the pool deck prior to to 

construction of the project; 2001

East side of the pool deck just after 

construction of soakage trench; 2002
12/9/2004; Barrington Square Retrofit 4

Linked Soakage Trenches and Infiltration Basins (manages runoff 

from all roof surfaces except those along Powell Blvd.) 

 (See Site Plan for drainage details, pg.10)

Catchment Area: 16,585 sq. ft. of roof 

Facility footprint4

: 282 sq. ft.

Estimated Internal Volume: 395 cu. ft. 

Overflow: The linked stormwater system - excluding the soakage 

trenches along Powell Boulevard (Area III) - overflows to a 

landscape infiltration basin on the east side of the property. There 

is no pipe overflow for this landscape basin; if the system ever 

crests it will flow overland to Powell Boulevard. 

Capacity: The measured volume of the facility )to the elevation of the 

pipes linking the different sections) is about 40% of the volume of 

the standard eastside soakage trench5

 that would be required (the 

trench would have a footprint of 995 sq. ft. and an internal volume 

of 1045 cu. ft.). In larger storms, this capacity would be 

substantially augmented by the “freeboard” on the facilities, which 

would allow them to fill well above the level of the pipes. The 

freeboard is the vertical distance between the surface grade and the 

overflow pipe elevations (that link the facilities). The volume of 

that additional capacity is unknown. 

Additional Information: 

Mini Soakage Trenches

• The bottoms of the trenches are 8 to 15 in. wide, widening at ground level (see drawing). They 

average 22 in. deep. 

• They are filled with 3-in. diameter river rock. 

• Roof runoff enters via subsurface downspout extension pipes. 

• There is a 4-in. perforated pipe that travels the length of the bottom of each trench to distribute flows. 

• The trenches are linked by 3-in. ABS pipes. The pipes are approximately 6 in. below grade, allowing 

up to fourteen inches of ponding within the trenches. 

Landscape Infiltration Basins

• The two basins under the stairs are each approximately 50 sq. ft. in area, with a ponding depth of 14 

in. and 2:1 side slopes. 

• The basin on the southeast edge of the property is approximately 65 sq. ft. in area with a ponding 

depth of 12 in. and 2:1 side slopes. 

• They receive runoff from adjacent roofs and overflows from the soakage trenches. 

• Runoff enters approximately 12 to 14 in. below grade through 3-in. ABS pipes. 

 

4

For the purpose of comparing the capacity of the facility with the standard eastside soakage trench, the footprint has been calculated as the 

wetted (ponded) surface area when the facility reaches maximum capacity. 5 The standard eastside soakage trench meets the City’s standard for complete stormwater disposal in soils which infiltrate at least 2 inches 

per hour. The City requires 24 feet of trench per 1000 ft2

 of impervious area (drainage catchment). The trench is 3 feet deep, 2.5 feet wide, 

and filled with drainage rock. Flow enters the trench through a pervious pipe that travels the length of the top of the trench. Assuming a 

porosity of 35%, the trench provides an internal volume of approximately 63 cubic feet per 1000 ft2

 of catchment.

Excavation of mini soakage trench 

along SE edge of property; 2002

The trench filled with gravel and 

planted along the edges; 2002
12/9/2004; Barrington Square Retrofit 5

• The basins are lined with 3-in. diameter river 

rock. 

• Filter fabric was not installed in order to 

create better rooting conditions for the plants. 

Mini Catch Basins 

• Mini catch basins were installed at points 

where the subsurface downspout extensions 

enter the stormwater facilities. 

• City plumbing code requires the catch basins 

to prevent the passage of debris and sediment. 

• A removable screen captures debris and 

allows easy cleaning. 

Emergency Overflow Point 

The linked stormwater system serving most of the 

roofs - excluding the south side of the roofs along 

Powell Boulevard - flows to a landscape 

infiltration basin on the east side of the property. 

There is no piped overflow for this landscape 

basin; if the system ever crests it will flow 

overland to Powell Boulevard.

Landscaping 

• Approximately 5,600 sq. ft. of landscaping was added, more than half of which was previously turf 

grass. 

• Plants are native species selected from the plant list in the BES 2002 Stormwater Management 

Manual (SWMM). The plants also include flowering perennials. 

• The planting plan for the landscape infiltration basins does not fully meet BES’ standards for 

inclusion of trees and grass or grass-like plants. The project did not formally trigger the requirements 

of the SWMM - it did not create or redevelop impervious surface. 

• River rock was used as a mulch to suppress weeds, reduce erosion, and diminish the slope of the sides. 

The river rock also creates a more formal appearance (drawing on the aesthetic appeal of the Buckman 

Heights Apartment courtyard in NE Portland). 

Irrigation 

The project expanded the existing irrigation system to serve the newly planted areas. 

Cross section for mini soakage trench 

DEQ requires simple registration of all 

subsurface stormwater disposal systems. See the 

following web-site for current information: 

:http://www.deq.state.or.us/wq/groundwa/uicho

me.htm 

. 
12/9/2004; Barrington Square Retrofit 6

Budget 

The total budget for the project was $71,200 including design and construction. BES contributed $30,000 

in grant funding from the Willamette Stormwater Control Program; the owner contributed the remaining 

amount. The following table lists the budget elements. 

I. Budget Elements 

Non-Construction Activities 

The total estimated cost for management, design, and permitting was $13,300, comprising approximately 

19% of the total budget. 

• Management 

The total for construction management was $5,600, comprising 8% of the total budget. The 

overall project management effort is incorporated into this figure. 

• Design 

The landscape architect’s cost for designing the project was $7,600, comprising 11% of the 

total budget. Although the design costs are not out-of-scale with the total project costs, they 

reflect the complex design process for retrofitting an existing developed site with stormwater 

management facilities. 

• Permitting 

The cost of permitting was reported as just $100, the cost of the plumbing permit. However, 

this is not representative of typical costs for permits; the City will ordinarily require a site 

development permit. 

Task Item Cost Total Cost 

Design $7,600.00 

Construction Management $5,600.00 

Excavation $19,600.00 

Landscaping $19,000.00 

Plant material $7,700.00 

Plant installation $4,300.00 

River rock $4,600.00 

Irrigation $2,400.00 

Miscellaneous $19,400.00 

Permitting $100.00 

New gutters and downspouts$17,000.00 

Small catch basin $2,300.00 

Total $71,200.00 
12/9/2004; Barrington Square Retrofit 7

Construction Activities 

Excavation, construction, and landscaping costs totaled $57,900, 

comprising 81% of the total budget. 

• Grading and Construction 

The cost of construction (including grading) was $38,900 

comprising 57% of the total budget. Components included: 

o Replacement of the gutter and downspout system, which 

was about 41% of total construction costs. 

o Installation of the 13 small catch basins, which were 

integral components of the management system (cost: 

$2,300). 

o Excavation of the site, which was performed manually 

(with shovels) to reduce damage to existing structures and 

to reduce disruption for the residents. 

• Landscaping 

The cost to landscape approximately 5,600 sq. ft. was 

$19,000, comprising 27% of the total budget. 

o The total unit cost for landscaping was approximately 

$4.22 per sq ft. 

o Installation costs ranged from $2.75 to $ 3.00 per sq. ft., 

reflecting a relatively intensive planting of larger plants. 

o Installing river rock in the landscape facilities added 

approximately $1.00 per sq. ft.. 

II. Cost Efficiencies

Demolition 

Many retrofit projects incur substantial costs for removing or 

modifying existing structures such as pavement or walkways. The designer of the Barrington Project 

avoided substantial demolition costs by minimizing alterations to existing structures in the courtyard. 

This benefit may have been offset by the cost of some of the subsurface piping required, particularly in 

the case of installing downspout extensions under the walkways. 

III. Cost Comparisons with Other Projects

The project is a great example of what it takes to retrofit an existing apartment complex with landscape 

facilities that have sub-surface downspout connections. The project is fairly complex relative to some 

other roof disconnection projects because of the replacement of the gutter and downspout systems as 

well as the extensive sub-surface piping. 

It is important to note that the cost for this type of project could be substantially reduced if replacement 

of the gutters and downspouts was not a component – in this case the cost would be reduced by almost 

Excavation of mini soakage trench 

along south side of the property; 

2002

The same trench in 2004
12/9/2004; Barrington Square Retrofit 8

25% (to approximately $54,200). While many similar projects 

would require re-locating some downspouts, completely replacing 

the gutter and downspout systems would probably not be 

required. 

Bidding and Permitting

I. Bidding

The landscape architect contracted directly with Seven Dees 

Landscaping for all phases of construction. 

II. Permits

Plumbing Permit

A plumbing permit was required for replacement of the 

downspouts, installation of the sub-surface piping, and expansion 

of the existing irrigation system. 

Building Permit 

The City did not require a building permit project since the 

project did not create or alter any structures. 

Site Development Permit (SD) Permit 

The City typically requires a site development permit for any stormwater project entailing excavation. 

The process includes three reviews: for the adequacy of erosion control and grading plans; for compliance 

with the BES Stormwater Management Manual (for water quality and flow control requirements); and for 

the capacity of the system if the goal is to provide complete on-site disposal. 

Planning and Zoning Review 

The project did not trigger any requirements related to conditional uses, non-conforming uses, or overlay 

districts (trails, e-zones, plan districts, etc.). No reviews were required for transportation or pedestrian 

issues, ADA, or seismic issues. 

III. Permitting Issues

Setbacks – The City normally requires that infiltration facilities be at last 10 feet from foundations and 5 

ft. from property lines (“safety setbacks”). Along the SE edge of the property, where there is just 10 ft. 

between the apartment and the property edge, the project designer filed a permit appeal to construct the 

trench closer to the building and property line than allowed by code. The City accepted the designer’s 

appeal based on the low risk associated with the project - the building does not have a basement, the 

grades are flat, and the soils drain well. 

Beginning hand excavation of 

landscape infiltration basin - east 

side of property

One of 13 cleanouts installed where 

subsurface downspout extensions 

enter the trenches and basins
12/9/2004; Barrington Square Retrofit 9

Construction 

Seven Dees Landscaping constructed the project in May and June of 2002. The landscape architect 

provided oversight during construction. Construction proceeded on schedule with no significant issues to 

report. Minimizing disruption to the residents was a primary concern during construction; excavating the 

facilities by hand (with shovels) helped reduce construction disturbance. The workers used part of the 

parking lot as a staging area for excavated soil and construction materials. 

Maintenance and Monitoring 

The property owner is responsible for all maintenance activities. BES will monitor the performance of the 

facilities at Barrington Square for at least five years, and perhaps longer. Confirming the hydraulic 

performance of the facility will be a primary focus; BES will also regularly evaluate the level of effort 

required for maintenance, the success of the planting regime, and the comments of the owner. 

Successes and Lessons Learned

Good Design – The design process started with an intensive evaluation of the existing functions and uses 

of the property. The designer integrated the new stormwater systems into areas surrounding existing 

structures such as the pool deck and the outdoor stairways. The result is a visual enhancement of the 

existing landscape that does not impact usable space in the courtyard commons. 

Stormwater Capacity – The linked stormwater system is key to providing substantial on-site capacity. The 

additional capacity provided by the landscape infiltration areas, coupled with the capacity of the mini 

soakage trenches, proved adequate to handle runoff from the north side of the property. 

Landscaping – The project is a great example of how landscape stormwater systems can be incorporated 

into more formal (manicured) settings. 

Owner Motivation – The fact that the gutters were old and needed replacement was a factor in the 

owner’s willingness to undertake the project – he already needed to replace a part of the existing 

stormwater system. The project also afforded the property owner an opportunity to aesthetically upgrade 

the courtyard. 
12/9/2004; Barrington Square Retrofit 

Mini Soakage Trench Landscape Infiltration Basin 

NORTH Barrington Apartment Site P

■— Drainage from Downspout