photo placeholder bloedel donovan park stormwater retrofit alternatives and analysis may 31 st 2013

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Bloedel Donovan Park Stormwater Retrofit

Alternatives and AnalysisMay 31st 2013

WE FIND A BETTER WAY TM

Project Goals & Outcomes (Based on Ecology Grant)

• Reduce phosphorus and fecal coliform concentrations in stormwater runoff generated by park surfaces.

• Prevent direct discharge of phosphorus or bacteria-laden runoff.

• Maximize pollutant-removal opportunities at the park.

• Implement engineered stormwater BMP solutions, such as infiltration and media treatment.


Meeting Purpose and Plan

1. Review preliminary findings2. Identify treatment and design considerations3. Identify site constraints4. Overview of concepts5. Determine preferred approach 6. Site walk


Preliminary Findings• Topographic Survey of North Park – Complete

NAVD88– Assume OHWM 314.5’, Max.314.94’ (City

datum)• Geotechnical

– 5 borings, 4 with wells– High groundwater

• 1.5 to 3.0 feet below ground surface• Higher than lake water surface elevation• Groundwater flow towards lake year round

– Existing effective subsurface infiltration rate ~0.13 in/hr


Preliminary Findings (continued)

• Stormwater Modeling– Existing subsurface soils (infiltration rate 0.13

in/hr); could meet required infiltration capacity, but

– Separation to groundwater is 1.5 feet min.• Water Quality – PW Green Team!

– Baseline phosphorus – (pending results)– Baseline fecal –

• surface water sample – 5/21 during heavy rain from a puddle of standing water in the middle of the lawn area in question. There was a lot of goose feces, and the results reflect that in being very high at 21,000 CFU/100 ml (pending groundwater results)


Treatment and Design Considerations

• Avoid focus flows to trench without pre-treatment• Maximize vertical separation from groundwater• Spread over large area and avoid saturation for

biodegradation• Avoid groundwater mounding• Treatment effectiveness is a function of area vs.

volume• Maximize bacterial mat above groundwater for

fecal treatment


Site Constraints

• High groundwater table• OHWM delineation• High volume Park usage


Department of Ecology Manual • 3.3 Phosphorus Treatment

Options: Any one of the following options may be chosen to satisfy the phosphorus treatment requirement.1. Infiltration with appropriate pretreatment If infiltration is through soils meeting the minimum site suitability criteria for infiltration treatment a presettling basin or a basic treatment facility can serve for pretreatment.2. Infiltration preceded by Basic TreatmentIf infiltration is through soils that do not meet the soil suitability criteria for infiltration treatment, treatment must be provided by a basic treatment facility unless the soil and site fit the description in the next option below.3. Infiltration preceded by Phosphorus TreatmentIf the soils do not meet the soil suitability criteria and the infiltration site is within ¼ mile of a phosphorus-sensitive receiving water, or a tributary to that water, treatment must be provided by one of the other treatment facility options listed: Large Sand Filter, Large Wetpond, Emerging Stormwater Treatment Technologies targeted for phosphorus removal; Two-Facility Treatment Trains.


Location of Focus - North Park Basins• A. West - open lawn, including volleyball court

and playground• B. North - tip towards rain garden• C. Internal - sloping into existing vegetated area• D. East – bulkhead, boat launch, and beach

restoration


Basin A – Concepts (~140,500 SF/3.2 AC)

1. Large Sand Filter (100%) Infiltration • Fill ~2.5 foot depth @ 20,000 SF• Cost ~ $255,000



2. Large Sand Filter (91%) Infiltration • Fill ~1.5 foot @ 10,200 SF• Cost ~ $175,000



3. Large Sand Filter (95%) Infiltration W/ Underdrain • Fill ~1.5 foot depth @ 2,100 SF• Cost ~ $140,000



4. Linear Sand Filter (91%) Infiltration W/ Underdrain • Fill ~1.5 foot depth @ 1,590 SF• Cost ~ $115,000


Basin B,C & D – Concepts

1. Regrade with Berm and Large Sand Filter (95%) Infiltration w/ Underdrain

• Fill ~1.5’ w X 1.5’ d @ 1,675 SF• Cost ~ $120,000

2. Regrade with Berm and Linear Sand Filter (91%) Infiltration w/ Underdrain

• Fill ~1.2’ to 2.2’ w X 1.5’ d @ 1,250 SF• Cost ~ $95,000


Emerging Stormwater Treatment Technologies• Stormwater Treatment Vault – Contech

– Route underdrain through 3rd level of treatment• Sorbtive Media

– Blend into sand filters or trenches to increase dissolved phosphorus uptake


Emerging Stormwater Treatment Technologies (Continued)

• Size andCost Vaults

• Sorbtive Media– Removes >90% Total Dissolved Phosphorus– 10 to 50yr service life– $16/LF of infiltration trench ~$50,000 total

project

BasinDrainage Area

ACRE Structure Type

# of cartridge

s Initial Cost *Annual Cost

A 3.28x11 SF

Vault 16 $ 40,000 $

300

B 1.2 72" Manhole 6 $ 25,000 $

120

C 0.7 60" Manhole 4 $ 20,000 $

80

D 0.9 72" Manhole 5 $ 23,000 $

100Total

Costs $ 108,000 $

600 This accounts for 1/2 of the total flows, assuming the other half is infiltrated


Costs, Benefits, Impacts & Risk Rating• Cost – High, moderate, or low • Stormwater – How effective is it at treating fecal

coliform and phosphorus?• Park Usage – Is there an impact to park use?

(reduce area, no change, increase area)• Constructability – Environmental risks and

recovery time (temporary delay in park use)• Maintenance – Long-term costs and effort


Basin A – Cost Benefit Risks MatrixOption 1 2 3 4

Cost

Stormwater

Park Usage

Constructability

Maintenance

Total


Where do we go from here?

Questions? Discussion?

photo placeholder bloedel donovan park stormwater retrofit alternatives and analysis may 31 st 2013

Documents

management of shorelines

stormwater runoff

shoreline management

park surfaces

better way tmmeeting

shoreline buffersb

required infiltration

baseline phosphorus