12/9/2004; Page 19 1

Page 19 L.L.C. 

(Previously the United Salad Co. Garage) 

939 SE Alder St.

Project Summary 

Overview of the Stormwater System 

The existing 10,000 sq. ft. asphalt parking lot was replaced with a smaller, re-graded asphalt parking lot, a 

gravel courtyard, a landscape infiltration basin, and perimeter landscape areas. 

• Runoff from the asphalt parking lot (7,000 sq. ft.) drains into the infiltration basin.

• The gravel courtyard (1,825 sq. ft.) captures and infiltrates rainfall. If it reaches capacity, it will 

overflow into the landscape infiltration basin. 

• The infiltration basin fills to a depth of about 6 in. (deepest point) before it overflows into a 

standpipe. The standpipe is located at the lowest point in the basin; it drains to the combined sewer. 

 

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 by July 1, 2003 

Project Type: Light industrial retrofit (parking lot) - demonstration project 

Technologies: Landscape infiltration basin and porous gravel courtyard 

Major Benefits: • Runoff from the modified parking lot, including the gravel courtyard, drains to a landscape 

infiltration basin. The basin reduces stormwater and pollutants draining to the combined sewer. 

• Over 1,000 sq. ft. of native and sustainable landscaping was added, improving the urban 

environment and the aesthetic appeal of the property. 

Cost: $37,080 (unit cost of $3.80/ sq. ft. of impervious area managed). BES provided a $30,000 grant1

for the project. 

Constructed: Summer 2002 

Aerial view of the Page 19 property before 

the project – the parking lot where the 

project was implemented is outlined in red; 

2002. 
12/9/2004; Page 19 2

Stormwater Capacity and System Components 

Stormwater Management Goal

The overall stormwater management goal was to meet the sizing 

and design standards of the “Simplified Approach” of the City’s 

Stormwater Management Manual (SWMM). These standards do 

not typically provide for complete stormwater disposal; actual 

performance is dependent on soil infiltration rates. All design 

standards used for reference in this report were current in the year 

2002. 

Geotechnical Evaluation / Infiltration Test 

The property owners contracted with a geotechnical firm in 1998 to 

perform a field investigation of the property. A soil probe 

encountered 4 to 7 ft. of fill material on top of a base of silt and 

clay-silt. 

The Natural Resources Conservation Service (NRCS) soil survey 

for Multnomah County classifies the soils as 50C-Urban Land: 

highly developed lands atop stratified soils and sometimes fill. 

Because the soils are variable and not typically native, NRCS does 

not provide a typical infiltration rate. 

System Components

Landscape Infiltration Basin

(See Site Plan for details; Figure 1, pg.10)

Catchment Area: 7,000 sq. ft. of asphalt (parking lot) 

Facility footprint2: 400 sq. ft. (within the confines of the basin)

Internal Volume: 105 cu. ft. (volume in the basin to the level of overflow) 

Overflow: The overflow standpipe connects to the city sewer system. 

Capacity: Within the basin itself, there is substantially less storage capacity than would be provided by 

a standard soakage trench – a catchment of 7,000 sq. ft. would require a soakage trench3 with a 

footprint of 420 sq. ft. and a volume of 441 cu. ft. However, there is substantial additional storage 

volume in the asphalt parking lot; prior to overflowing into the standpipe, the area of ponding 

expands beyond the basin into the adjacent areas of the parking lot. The volume of this additional 

capacity is unknown.

 

2

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. 3 The standard eastside soakage trench meets the City’s standard for complete stormwater disposal in soils which infiltrate at least 2 in. per 

hour. The City requires 24 ft. of trench per 1000 sq. ft. of impervious area (drainage catchment). The trench is 3 ft. deep, 2.5 ft. 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 cu. ft. per 1000 sq. ft. of catchment.

Overview of the retrofitted parking 

lot

L-shaped infiltration basin with 

emergency overflow ( see arrow) and 

gravel courtyard 
12/9/2004; Page 19 3

Additional Information: 

• The L-shaped infiltration basin has a total length of 60 ft.. It is 

11 ft. wide and it has 2:1 side slopes. Although it is 6 in. deep 

(ponding depth) at the standpipe, the average depth is just 3 in. – 

the basin is very shallow at its ends. 

• Evenly-spaced curbstones border the basin along the edge of the 

parking lot. In addition to serving as attractive tire stops, the 

spaces between the stones allow runoff to enter the basin. 

• During large storm events runoff ponds on adjacent asphalt areas 

prior to overflowing via the standpipe. 

 

Pervious Courtyard 

Catchment Area: 1,825 sq. ft. of gravel

Internal Volume: 365 cu. ft. (total void space in the gravel and 

rock). 

Overflow: The courtyard slopes gently toward the landscape 

infiltration basin; any overflow will drain into the basin. 

Capacity: The gravel courtyard provides substantially more internal 

capacity than the standard soakage trench3

 that would be 

required for the same catchment – a 1,825 sq. ft. catchment 

would require a soakage trench with a footprint of 153 sq. ft. and 

a volume of 161 cu. ft.. 

Additional Information:

• There is 3 in. of quarter-inch minus gravel above 3 in. of crushed 

rock (the sub base).

• The courtyard is bordered on the south and west sides by the 

infiltration basin; perimeter landscaping borders its east and 

north sides.

• The courtyard is sometimes used by building tenants for 

overflow parking. 

Emergency Overflow 

The overflow inlet (standpipe) is approximately 6 in. above the 

basin floor. The standpipe is located at the elbow of the L-shaped 

landscape basin. The standpipe is a modification to the old parking 

lot catch basin, which was removed and re-plumbed to the location 

of the standpipe. 

Landscaping 

The vegetation within the basin is predominantly native plants such as Gaultheria Shallon (salal), Fragaria 

Chiloensis (Coastal Strawberry), and Juncus Effusus (Common Rush). These species are adaptable to 

both moist and dry soil conditions. 

New subsurface irrigation pipe for 

hose bib, looking north.

Removal of parking lot asphalt 

during project construction, 

summer 2002

L-shaped basin under construction, 

2002
12/9/2004; Page 19 4

Perimeter landscaping includes a variety of native and sustainable 

(edible or harvestable) plants such as Evergreen Huckleberry, 

which produces an edible berry (and also fulfills city code 

requirements for a parking lot hedge). The Clumping Bamboo can 

be harvested for a multitude of uses, and the Serviceberry provides 

food and habitat for wildlife. 

All of the soils in the landscape areas were amended with a mix of 

topsoil and compost (total average thickness of 5 in.). 

Pavement Replacement 

The new 7,000 sq. ft. parking lot slopes toward the landscape 

infiltration basin. The job required much more than simply regrading the surface with additional layers of asphalt; the asphalt 

contractor recommended complete removal of the old asphalt 

surface, including the gravel sub-grade, in order to ensure the 

integrity of the new asphalt surface. About two-thirds of the 

surface was excavated to an average depth of one foot; in some 

areas excavation was as deep as 3 ft. below grade. 

The new asphalt layer is 3 in. thick, on average, to accommodate 

commercial trucks. 

Irrigation 

Four temporary soaker hoses were installed to irrigate the new 

plantings during the 2-year establishment period. A new hose bib at 

the north end of the landscape infiltration basin supplies the hoses. 

Water service for the bib required a new water line from the 

building. The pipe work included the installation of a backflow 

prevention device. 

 

Repaved asphalt parking lot, graded to 

drain into infiltration basin; 2002

Flow paths draining to the location of 

the landscape infiltration basin (yet to 

be built; 2002

Landscape infiltration basin in a rain 

event; 2003
12/9/2004; Page 19 5

Budget 

Page 19 L.L.C. submitted a final project budget of $37,080, including management, design, and 

construction. BES contributed $30,000 in grant funding to the project. The final budget is shown below 

in Table 1. 

Item Item Cost Total Cost

Design $2,000 $2,000

Project and Construction Management $2,000 $2,000

Demolition, grading, site prep $5,971

Mobilization $250

Asphalt (10,000 sq. ft.) - removal, disposal $3,100

Excavate swale and planting areas $1,631

Excavate water line (irrigation) $840

Sawcut concrete slab $150

Construction $18,906

Piping Work

Move existing drain and install new drain $950

piping $1,101

Install new overflow $100

Paving - earthwork

Mobilization of grading crew $400

Mobilization of paving crew $600

Backfill 6in. sub-grade (gravel) $4,039

Paving - construction

Install asphalt (7,036 sq. ft; 3 in. thick) $7,036

Install curbstones and concrete pavers $3,955

Striping $200

Install 3 in. gravel (1/4 in. minus). Includes courtyard. $525

Landscaping (1,147 sq.ft) $6,913

Install topsoil/compost (1350 sq ft, 4 in.deep) $2,241

Install river rock (to 2 in. depth in swale) $150

Plants & trees (installed) $3,525

Three street trees (installed) $600

Irrigation System (soaker hoses) $400

Miscellaneous $1,290

Permit fees $1,165

Core drilling $125

TOTAL $37,080

Page 19 Parking Lot Retrofit Project 

Budget Summary
12/9/2004; Page 19 6

*These costs are subsets from the total budget and reflect only those costs pertaining to the area of 

asphalt that was replaced. 

I. Budget Components

Non-construction Activities 

The total estimated cost for management, design, and permitting was $5,290, comprising approximately 

14% of the total budget. 

 

• Management (Project and Construction Management) 

The total for project and construction management was $2,000, comprising approximately 5% of the 

total budget. The owners managed all phases of the project; they hired contractors and oversaw 

construction. 

• Design 

The landscape architect (one of the property owners) designed the project at a cost of $2,000, 

comprising approximately 5% of the total budget. 

• Permitting 

The cost of the site development permit was $1,165, comprising 4% of the total budget. 

Construction Activities 

Demolition, excavation, construction, and landscaping costs amounted to $31,790, comprising 86% of the 

total budget. 

• Demolition, Excavation, and Grading 

The total for these activities was $5,971, comprising about 16% of the total project budget. The effort 

included demolition and removal of 10,000 sq. ft. of existing asphalt and subgrade (excavation depth 

of up to 3 ft.), import of topsoil, re-grading, and excavation. 

Summary of pavement removal and replacement costs (7,000 sq. ft.) * 

Paving - earthwork: 

 

 Asphalt/fill demo, removal, and disposal $ 2,170.00 

 Mobilization of grading crew $ 400.00 

 Mobilization of paving crew $ 600.00 

 Backfill sub-grade (gravel) $ 4,039.00 

Paving - construction: 

Install asphaltic concrete (7000 sq. ft.; 3 in. thick) $ 7,036.00 

Striping $ 200.00 

Total $ 14,445.00 

Cost per sq. ft. $ 2.06 
12/9/2004; Page 19 7

• Construction 

Construction activities, including installation of more than 7,000 sq. ft. of new asphalt surface and 

relocation of the drain, totaled $18,906. The total is approximately 51% of the total project budget. 

• Landscaping 

The project included a total of 1,147 sq. ft. of landscaping (includes the infiltration basin and the 

landscape around the perimeter of the parking lot). The cost was $6,913, comprising about 19% of the 

total project budget. The total unit cost was approximately $5.76 per sq. ft. of landscape. The unit cost 

for the imported topsoil/compost was $1.66 per sq. ft. Other elements included material and labor for 

planting, river rock, and irrigation. 

II. Cost Elements 

Asphalt work 

Asphalt removal and construction dominated the project budget, accounting for almost 45% of the total 

budget. Activities included removing the existing parking lot (including the sub-base) and installation of a 

new smaller asphalt lot. The contractor recommended replacement of the asphalt and sub grade (rather 

than simple resurfacing) because of use by commercial trucks. 

Landscaping 

The project incurred higher unit landscaping costs than is typical for stormwater projects. Almost a third 

of the landscaping costs were attributed to imported compost and topsoil necessary to improve growing 

conditions. Part of the increased cost is also explained by installation of more expensive plant species 

such as Bamboo. 

 

Plumbing 

The project required limited pipe work compared to other retrofit projects. The work included removing 

the existing catch basin, extending the existing storm line 20 ft. to serve the stormwater basin, and 

installing a hose bib and new water connection to the building. 

Gravel Courtyard 

The gravel courtyard was a cost-effective alternative to re-paving the entire parking lot. It required less 

paving and therefore reduced the size of the stormwater facility. In addition to providing an outdoor 

recreation area (picnicking, etc.), the courtyard is occasionally used as an overflow parking area.
12/9/2004; Page 19 8

III. Cost Comparisons 

This retrofit project required replacement of much of the asphalt 

surface, making it an example of the most intensive type of parking lot 

retrofit. Many parking lot retrofits do not require removal (and 

replacement) of the existing surface; re-grading can be achieved by 

applying new asphalt in local areas. There were other components of 

the project, such as the plants and the curbstones that were also more 

expensive than typical for many stormwater projects. While there may 

have been some savings in the pipe work, the costs for the project 

should probably be viewed as the upper end of parking lot retrofit 

costs, particularly because of the small size of the project – larger 

projects would realize economies of scale. 

Maintenance and Monitoring 

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

of the facilities at Page 19 L.L.C. for at least five years, and perhaps longer. Confirming the hydraulic 

performance of the facility will be a primary concern. BES will also regularly evaluate the level of effort 

required to maintain the facility, the success of the planting regime, and comments from the owner. 

Successes and Lessons Learned

Design - The project is an important example of how a landscape infiltration area can be used as an 

attractive design element in the interior space of a parking lot (as opposed to shedding the runoff to the 

exterior or perimeter landscaping). The design was very successful in terms of preserving the existing 

parking spaces – it resulted in the loss of just two parking spaces. 

 

Pavement Removal - The project demonstrates what is involved in retrofit projects that require asphalt 

replacement. Replacing asphalt can be more expensive than other options, but it opens a number of 

options for managing runoff. 

Spaced Curbstones – The curbstones are an attractive option for bringing runoff into the landscape 

infiltration basin: they provide an effective curb stop and spread flows during large storms. 

Gravel Courtyard – The courtyard provides a number of benefits: it absorbs much of the stormwater that 

falls onto it, provides a recreational (picnic) area, and is periodically used for extra parking spaces. 

Stormwater Capacity - The internal volume of the landscape infiltration basin is smaller than typical for 

its size (footprint) – it has an average depth of just 3 inches. However, additional capacity is provided by 

the parking lot surface: runoff fills the landscape infiltration basin and then temporarily ponds in the 

parking area before overflowing to the sewer system. 

Landscape infiltration basin after a 

storm, 2003. Note damp pavement 

where runoff recently ponded on 

asphalt surface.
12/9/2004; Page 19 9

Site plan of parking lot with infiltration basins (highlighted in green) 

and gravel courtyard.