Cynthia,

I apologize for my lack of input on this. Things have been quite hectic recently.

I think I mentioned this concern to you by phone some time ago, but I am still struggling with the selection of

only D4 and D5 for this evaluation. Really my concern is the justification for selecting only D4 and D5. Is there

any evidence that D4 and D5 are the predominant siloxanes discharged in sewage, either domestic sewage or

industrial waste from facilities producing or using Si

‐ containing chemicals? Based on everything I have read,

there are a wide range of siloxane compounds that are discharged to and found in domestic sewage.

Of those compounds, it appears that D4 and D5 have just the right set of physical characteristics in terms of

sorbability and volatility versus temperature to be the predominant siloxanes in digester gas for most POTWs. I

am concerned that this observation has suggested to EPA that these siloxanes must also be the predominant

compounds in sewage. I am not at all convinced that this is the case. 

## RE: NACWA Comments on Si loxane ECA Proposals

Bott, Charles

to:

'Cynthia Finley', Marcus Aguilar, Robert Jones

09/20/2012 08:59 AM

Cc:

"kthomas@sehsc.com", "pgriffith @lacsd.org", "Feltner, Mark"

Hide Details

From: "Bott, Charles" <CBOTT@hrsd.com>

To: 'Cynthia Finley' <CFinl ey@NACWA.ORG>, Marcus

Aguilar/DC/USEPA/US@EPA, Robe rt Jones/DC/USEPA/US@EPA

Cc: "kthomas@sehsc.com" <kthomas@s ehsc.com>, "pgrif fith@lacsd.org"

<pgriffith@lacsd.org>, "Feltn er, Mark" <MFELTNER@HRSD.COM>

History: This message has been forwarded. Pa g e 1 of 2

11/28/2012 file://C:\Documents and Settin g s\ma g uil01\Local Settin g s\Tem p \notes879

...I do agree that D4 and D5 represent a large cost to POTW in terms of digester gas treatment, but there are

certainly other compounds present. If the concern for this effort is water quality and environmental protection

from potentially harmful recalcitrant compounds such as siloxanes, I am worried that the justification for

choosing D4 and D5, simply because these are the predominant compounds in digester gas (vs sewage), is

misplaced. Is undue focus being placed on D4 and D5 when there could be other much more important

compounds from an environmental perspective?

I understand that this comment is somewhat outside the scope of what you were asking from us.

Regards,

Charles

Charles B. Bott, Ph.D., P.E., BCEE

Chief of Special Projects

Hampton Roads Sanitation District

cbott@hrsd.com

o: 757-460-4228

m: 757-646-7923

f: 757-464-6912

http://www.hrsd.com/

Adjunct Professor

Charles E. Via, Jr. Department of Civil and Environmental Engineering

Virginia Tech

Blacksburg, Virginia

Adjunct Professor

Department of Civil and Environmental Engineering

Old Dominion University

Norfolk, Virginia

From: Cynthia Finley [ mailto:CFinley@NACWA.ORG ]

Sent: Tuesday, September 18, 2012 11:03 PM

To: Marcus Aguilar; jones.robert@epa.gov

Cc: kthomas@sehsc.com; pgriffith@ lacsd.org; Bott, Charles

Subject: NACWA Comments on Siloxane ECA Proposals

I have attached the comments of the National Association of Clean Water Agencies (NACWA) on the siloxane

Enforceable Consent Agreement proposals. Please contact me if you have any questions about these

comments. I plan to join the discussion on Thursday afternoon by phone.

Thank you,

Cynthia

Cynthia A. Finley, Ph.D.

Director, Regulatory Affairs

National Association of Clean Water Agencies

1816 Jefferson Place, NW

Washington, DC 20036

‐ 2505

202

‐ 533

‐ 1836

www.nacwa.org 

## Pa g e 2 of 2

11/28/2012 file://C:\Documents and Settin g s\ma g uil01\Local Settin g s\Tem p \notes879

...