Photo Placeholder Bloedel Donovan Park Stormwater Retrofit Alternatives and Analysis May 31 st 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.

WE FIND A BETTER WAY TM Meeting Purpose and Plan 1.Review preliminary findings 2.Identify treatment and design considerations 3.Identify site constraints 4.Overview of concepts 5.Determine preferred approach 6.Site walk

WE FIND A BETTER WAY TM Preliminary Findings Topographic Survey of North Park – Complete NAVD88 – Assume OHWM 314.5’, Max ’ (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

WE FIND A BETTER WAY TM 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)

WE FIND A BETTER WAY TM 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

WE FIND A BETTER WAY TM Site Constraints High groundwater table OHWM delineation High volume Park usage

WE FIND A BETTER WAY TM 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 Treatment If 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 Treatment If 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.

WE FIND A BETTER WAY TM 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

WE FIND A BETTER WAY TM Basin A – Concepts (~140,500 SF/3.2 AC) 1.Large Sand Filter (100%) Infiltration Fill ~2.5 foot 20,000 SF Cost ~ $255,000

WE FIND A BETTER WAY TM Basin A – Concepts (~140,500 SF/3.2 AC) 2.Large Sand Filter (91%) Infiltration Fill ~1.5 10,200 SF Cost ~ $175,000

WE FIND A BETTER WAY TM Basin A – Concepts (~140,500 SF/3.2 AC) 3.Large Sand Filter (95%) Infiltration W/ Underdrain Fill ~1.5 foot 2,100 SF Cost ~ $140,000

WE FIND A BETTER WAY TM Basin A – Concepts (~140,500 SF/3.2 AC) 4.Linear Sand Filter (91%) Infiltration W/ Underdrain Fill ~1.5 foot 1,590 SF Cost ~ $115,000

WE FIND A BETTER WAY TM Basin B,C & D – Concepts 1.Regrade with Berm and Large Sand Filter (95%) Infiltration w/ Underdrain Fill ~1.5’ w X 1.5’ 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’ 1,250 SF Cost ~ $95,000

WE FIND A BETTER WAY TM

Emerging Stormwater Treatment Technologies Stormwater Treatment Vault – Contech – Route underdrain through 3 rd level of treatment Sorbtive Media – Blend into sand filters or trenches to increase dissolved phosphorus uptake

WE FIND A BETTER WAY TM Emerging Stormwater Treatment Technologies (Continued) Size and Cost Vaults Sorbtive Media – Removes >90% Total Dissolved Phosphorus – 10 to 50yr service life – $16/LF of infiltration trench ~$50,000 total project Basin Drainage Area ACREStructure Type # of cartridgesInitial Cost*Annual Cost A3.28x11 SF Vault16 $ 40,000 $ 300 B1.272" Manhole6 $ 25,000 $ 120 C0.760" Manhole4 $ 20,000 $ 80 D0.972" Manhole5 $ 23,000 $ 100 Total Costs $ 108,000 $ 600 This accounts for 1/2 of the total flows, assuming the other half is infiltrated

WE FIND A BETTER WAY TM 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

WE FIND A BETTER WAY TM Basin A – Cost Benefit Risks Matrix Option1234 Cost Stormwater Park Usage Constructability Maintenance Total

WE FIND A BETTER WAY TM Where do we go from here? Questions? Discussion?