The project site is one of the last isolated islands of Ada County and will be annexed into Garden City.

The site is surrounded by residential development with stub roads to the north and east that will be extended/connected as part of the project. Proposed construction includes ACHD roadways, Garden City water and sewer main extensions, and a private pressure irrigation system.

Stormwater runoff from all internal roadways and the front yards of all buildable lots will drain to a central pond via sheet flow, concrete gutter, pipe, and vegetated channel flow. Concentrated runoff will flow through two Aqua Swirl treatment manholes (or other treatment devices allowed by ACHD) prior to being discharged to vegetated swales that lead to the central pond. Sub-basins are identified on the drainage basin map.

The pond is planned to be about 10-feet deep to allow the colder deeper groundwater to circulate and reduce algae growth. Our surface irrigation water is also planned to discharge to the central pond. An overflow discharge from our project site is requested by the southern neighbors to help them maintain their rear yard pond amenity levels. Instead of the surface water discharging directly to the Dry Creek Canal at our northwest corner, it will be routed through the southern neighbors’ ponds before overflowing to the same canal near our southwest corner. During rain events, all stormwater from the internal public streets will discharge to the pond after treatment. A freeboard amount of approximately 2-feet will remain above the overflow outlet to account for stormwater storage. An orifice plate is planned at the outlet and is sized for the surface irrigation inlet flow, therefore restricting stormwater discharge to the southern neighbors. The water level will drop to the outlet elevation overtime as the pond hydraulically stabilizes with the groundwater table via permeation through the exposed native sands and gravels beneath the pond.

A design infiltration rate of 8 in/hr will be calculated across the wet footprint of the pond, and groundwater depth was encountered at less than 3 feet BGS (for further details see soils report by Natural Resource Solutions, Dated: August 6, 2019). Onsite groundwater was found to fluctuate between 2 to 5-feet deep Final groundwater readings were taken in the month of August 2019. The central pond was sized for the 100-year event.

10,900

Estate

9,413

Estate

8,195

Estate

8,335

Estate

8,335

Estate

9,489

Estate

8,979

Estate

7,134

Creekside

6,509

Creekside

6,907

Creekside

6,217

Creekside

6,001

Creekside

7,839

Creekside

8,186

Standard

6,668

Standard

6,668

Standard

7,372

Standard

7,432

Standard

5,914

Pond

5,402

Standard

6,512

Standard

6,380

Pond

7,894

Pond

7,848

Pond