Correspondence (8) CleanWater Services
MEMORANDUM
DATE: April 29, 2019 RECEIVED
TO: City of Tigard—Permits Department APR 2 9 2019
CITY OF TIGARD
FROM: Michael Idehara, Clean Water Services BUILDING DIVISION
SUBJECT: Durham TPS Building Landscape & Irrigation Project No. 6788.20
Durham AWWTF Plan District Narrative
The District would like to make improvements the landscaping surrounding the recently remodeled
Durham Treatment Plant Services (TPS) Building at the Durham Advanced Wastewater Treatment
Facility(AWWTF) located at 16060 SW 85th Ave,Tigard, Oregon 97224.
This memorandum is being submitted at the request of the City of Tigard as part of the Site Work permit
application,which will summarize the proposed improvements and how they meet the criteria set forth
in Chapters 18.630.040 Development Standards and 18.630.050 Landscaping and Screening Standards of
the Durham AWWTF Plan District Development Code.The area of proposed work falls within the limits
of the Administrative Subdistrict.
The District proposes to make improvements to the existing landscaping and impervious areas
surrounding the Durham TPS Building to provide the following:
1. Improve drainage, reducing the potential of water ponding around the perimeter of the existing
planter areas on the west and north sides of the TPS building.
2. Re-direct public access away from inaccessible areas of the building and provide a continuous,
safe path around the two active water features.This includes replacing existing concrete pavers
with concrete sidewalk to minimize tripping points.
3. Restore and improve the landscape surrounding the TPS building, post building remodel that
was completed in May 2018.This includes the conversion of the west planter area into a shallow
rain garden.
4. Construct two low profile retaining walls around two existing catch basins to improve the
transition in grade to the top of the catch basin.
The improvements include the following:
1. On the west side of building, demolish and remove existing concrete sidewalk and steps.
2. Remove existing planter and construct new shallow rain garden in its place. Connect rain garden
overflow drain to existing storm drain system.
3. At the south side of the west water feature, replace the existing concrete pavers with a concrete
sidewalk.
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CleanWater Services
4. At the existing north planter, construct a new concrete sidewalk at the east and west ends of
the planter and place shoulder drain rock around the perimeter. Connect a new drain pipe from
the shoulder drain rock to the existing storm drain system.
5. At the northeast side of the building, construct two low profile retaining walls around two
existing catch basins.
6. At the east side of building, across the parking lot, construct a larger concrete pad at the existing
vehicle charging station.
7. Restore all disturbed areas with new plantings. New plantings to include seeded,ground cover,
shrubs, and trees.
The improvements described above are in compliance with the Durham AWWTF Facility Plan District as
the work may be categorized as landscaping work.The improvements will be incorporated into and
compliment the existing landscape.
Per Chapter 18.30.020, Paragraph D.7,the proposed improvements are not a "Development" as they
are not (1)A building or structure; (2) a mining operation; (3) a material change in the use or
appearance of a structure or land; or(4) division of land into two or more units of land.Therefore,the
improvements are exempt from the criteria specified in Chapter 18.630.040 Development Standards.
The proposed improvements comply with Chapter 18.630.050 Landscaping and Screening Standards.
Regarding Screening Standards, since no additional Development is being constructed and all the work is
proposed surrounding the existing Durham TPS building, no additional screening is required at the
eastern boundary of the Subdistrict. Regarding the Landscaping requirements,the proposed
improvements comply with the requirements of Chapter 18.420.040 Landscaping Standards.The
proposed landscaping improvements as shown in the attached landscaping plans will provide the
following:
1. Reduce the area of impermeable surfaces and improve stormwater quality.
2. Create an inviting space for the public around the Durham TPS building.
3. Provide additional screening of the existing Durham TPS building and bike locker storage.
The proposed landscaping plan meets or exceeds the requirements prescribed in Table 18.420.1
Landscaping Standards.
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