From: Brenda Reiner

Sent: Fri Mar 16 12:32:29 2018

To: george Snegirev

Subject: RE: 600 Rivers Lane

Importance: Normal

George,

These will be onsite private systems that will be submitted to and reviewed by the Clackamas County Building Department. If they (County) and the engineer determine that they cannot do an onsite private system then the developer will have to connect to and upsize the public system to accommodate flows.

The sizing of the system is based on the total impervious area which includes paved parking areas, driveways, and the house footprint.

25year storm event- design max water surface for the 2-year, 10-year, and 25-year design storms.

I doubt that the infiltration trench will work for class D soils. But the min infiltration rate seems reasonable for your calcs.

Let me know if I missed anything.

Thanks,

Brenda Reiner | Senior Engineering Technician

City of Molalla

117 N Molalla Ave. | PO Box 248 |Molalla, OR 97038

Office: 503.759.0243 I Fax: 503.829.3676

From: george Snegirev [mailto:avalonengineering@wavecable.com]

Sent: Thursday, March 15, 2018 5:00 PM

To: breiner@cityofmolalla.com

Subject: 600 Rivers Lane

Brenda

I will be working on the storm water management plan for Peter Burkoff for his new residence at 600 Rivers Lane.

Do you mind answering a few questions on how this needs to be done.

To connect into the storm drainage system out in Toliver Rd seems to be not an option, so an on-site storm water facility is what will be required in this instance.

The NRCS Soil Survey shows this area to be Dayton silt loam which belongs in hydrologic soil group D, this soil group has a very slow infiltration rate.

Table 3.12 Infiltration Trench Requirements show Soils requirements (NRCS classification) of A or B for publicly maintained facilities; C soils may be used for privately owned facilities if drawdown standards are met.

Can we still have an infiltration trench in class D soils; and if possible can we use the minimum rate of 0.5 inches per hour for our design or is an infiltration test needed to be done to verify the infiltration rate.

Is this infiltration facility required for the roof runoff only or it needs to be designed for all the runoff on this site.

What storm event does this facility need to manage.

If you could provide me answers for these questions then this will first determine if the infiltration trench is feasible and then the criteria for design.

Thank you very much and I look forward to your response.

George Snegirev P.E.

103 S. First Street, Suite 205

Silverton, OR 97381

(Office) 503-874-4433

(Cell) 503-807-5048