12/9/2004; Barrington Square Retrofit 1 Barrin g ton A p artment Com p lex
, 2001 

# Barrington Square Apartments

7123 SE Powell Boulevard, Portland

Project Summary

Project Type: Commercial stormwater retrofit – demonstration project

Technologies: Landscape infiltration basin; mini soakage trench es; 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 350,0 00 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 an d 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 re place the gutters and downspouts at the comple x when he received a brochure regarding the Willamette Stormwater Control Program 1 . 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 th e aesthetic appeal and commercial value of his property while reducing impacts on the combined sewer system. He also anticipated potential sa vings on his stormwater rates. BES accepted his project proposal in May

2001.

1 Portland’s Bureau of Environmental Services implemente d the Willamette Stormwater Control Program in 2001. The Program offered financial grants and technical support for a seri es of projects to retrofit ex isting commercial properties with stormwater controls incorporating green technologies. The Program recruited these demonstration projects in order to research the feasibility, cost and performance of co mmercial stormwater retrofits in the ar ea served by the combined sewer. The Program provided grant funds for a total of eleven projects. The proj ects 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 jo b of integrating the landscape

facilities into the exis ting 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 them selves 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 includi ng 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 drai n 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 tw o 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; 200412/9/2004; 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 characteri stics had already been documented by other projects in the vicinity 3 . The Natural Resource Conservation Service (NRCS) Soil Survey for Mu ltnomah County classifies the local soils as moderately well-dr aining silty loams (type B hydrologic group). The Survey lists an expect ed 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 subs tantial risk of damage to the walkways and other structures. To avoid this risk and provide adequate capacity, the designe r successfully modified the configurations of the soakage tr enches 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 infilt ration basins.

2 BDS is responsible for developing standards for stormwater disposal and inspecting proj ects to confirm compliance with those st andards.

3 It is common for the Bureau of Development Services to requi re infiltration tests prior to approving plans for infiltration fa cilities. 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; 200212/9/2004; Barrington Square Retrofit 4 Linked Soakage Trenches and Infi ltration 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 footprint 4 : 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 lands cape basin; if the system ever

crests it will flow overl and to Powell Boulevard. Capacity : The measured volume of the fac ility )to the elevation of the pipes linking the different sections ) is about 40% of the volume of the standard eastside soakage trench 5 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 distan ce between the surface grade and the overflow pipe elevations (that li nk 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 subsurf ace 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. AB S 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 ar e 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 a nd overflows from the soakage trenches.

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

4 For the purpose of comparing the capacity of the facility with th e standard eastside soakage trench, the footprint has been cal culated as the wetted (ponded) surface area when the facility reaches ma ximum capacity.

5 The standard eastside soakage trench meets the City’s standard fo r complete stormwater disposal in soils which infiltrate at le ast 2 inches per hour. The City requires 24 feet of trench per 1000 ft 2 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 vo lume of approximately 63 cubic feet per 1000 ft 2 of catchment. Excavation of mini soakage trench

along SE edge of property; 2002

The trench filled with gravel and

planted along the edges; 200212/9/2004; 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 co nditions 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 ove rflow 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, mo re than half of whic h was previously turf

grass.

• Plants are native species selected from the pl ant 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 gr ass-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, re duce erosion, and diminish the slope of the sides. The river rock also creates a more formal appear ance (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 projec t was $71,200 including design and c onstruction. BES contributed $30,000 in grant funding from the Willamette Stormwater C ontrol 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 designi ng the project was $7,600, comprising 11% of the total budget. Although the design co sts are not out-of-scale with th e total project costs, they reflect the complex design proces s for retrofitting an existing developed site with stormwater management facilities.

• Permitting The cost of permitting was reported as just $1 00, 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

N ew gutters and downspouts$17,000.00 Small catch basin $2,300.00

Total $71,200.0012/9/2004; 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 (i ncluding 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 sma ll 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 appr oximately 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 fr om $2.75 to $ 3.00 per sq. ft., reflecting a relatively intensiv e planting of larger plants. o Installing river rock in th e landscape facilities added approximately $1.00 per sq. ft..

II. Cost Efficiencies

Demolition Many retrofit projects incur subs tantial costs for removing or modifying existing structures such as pavement or walkways. The designer of the Ba rrington Project

avoided substantial demolition costs by minimizing alterations to existin g structures in the courtyard. This benefit may have been offset by the cost of so me of the subsurface pipi ng required, part icularly in the case of installing downspout extensions under the walkways.

III. Cost Comparisons with Other Projects

The project is a great example of wh at it takes to retrofit an existin g apartment complex with landscape

facilities that have sub-surface downs pout connections. The project is fa irly 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 substan tially reduced if replacement of the gutters and downspouts was not a component – in this case the co st would be reduced by almost Excavation of mini soakage trench
along south side of the property;

2002

The same trench in 200412/9/2004; Barrington Square Retrofit 8 25% (to approximately $54,200). While many similar projects would require re-locat ing some downspouts, co mpletely replacing the gutter and downspout systems would probably not be required.



### Bidding and Permitting

I. Bidding

The landscape architect contract ed 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 s ub-surface piping, and expansion of the existing irrigation system.

Building Permit The City did not require a bu ilding permit project since the project did not create or alter any structures.

Site Development Permit (SD) Permit The City typically requires a site development perm it for any stormwater project entailing excavation. The process includes three reviews: for the adequacy of erosion contro l and grading plans; for compliance with the BES Stormwater Management Manual (for water quality and fl ow 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 requi rements related to conditional uses , non-conforming uses, or overlay districts (trails, e-zones, plan districts, etc.). No reviews were required for tr ansportation 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 setb acks”). Along the SE edge of the property, where ther e is just 10 ft. between the apartment and the property edge, the proj ect designer filed a permit appeal to construct the

trench closer to the buil ding 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 basins12/9/2004; Barrington Square Retrofit 9 

### Construction

Seven Dees Landscaping constructed the project in May and June of 2002. The landscape architect provided oversight during constructi on. Construction proceeded on schedule with no significant issues to report. Minimizing disruption to th e residents was a primary concern during construction; excavating the facilities by hand (with shovels) helped reduce constr uction disturbance. The workers used part of the parking lot as a staging area for exca vated soil and constr uction materials.



### Maintenance and Monitoring

The property owner is responsible for all maintenance activities. BES will monito r the performance of the facilities at Barrington Square for at least five years, and perhap s 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 pl anting regime, and the comments of the owner.



### Successes and Lessons Learned

Good Design – The design process started with an intensive evaluation of the existi ng functions and uses of the property. The designer integrated the new stormwater systems into areas surrounding existing structures such as the pool deck a nd the outdoor stairways. The resu lt 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 substantia l 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 r unoff from the north side of the property.

Landscaping – The project is a great exam ple of how landscape stormwater systems can be incorporated into more formal (manicured) settings.

Owner Motivation – The fact that the gutters were old an d needed replacement was a factor in the owner’s willingness to undertake th e 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 Retrofit10Mini Soakage TrenchLandscape Infiltration BasinNORTHBarrington Apartment Site Plan■— Drainage from Downspout