Document ID: EPA-HQ-OW-2017-0303-0019
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2018-01-30T05:00Z

From: Fleck, Diane 
Sent: Wednesday, January 17, 2018 3:01 PM
To: 'John Kenny' <kennyjd@gmail.com>
Subject: RE: Proposed EPA Withdrawal of Certain Federal Criteria for California

Hello Mr. Kenny,
Thank you for your interest.  The method of determining MCLs under the Safe Drinking Water Act and the method used to calculate human health ambient water quality criteria under the Clean Water Act consider different factors.  These differences can sometimes result in quite different values.  Below are some bullets to consider:

 EPA's human health Clean Water Act section 304(a) criteria recommendations are designed to minimize the risk of adverse effects occurring to humans from chronic (i.e., lifetime) exposure to pollutants through the ingestion of drinking water and consumption of fish and shellfish obtained from ambient surface water, while also protecting against adverse effects that may reasonably be expected to occur as a result of elevated acute or short-term exposures. In contrast, the Safe Drinking Water Act (SDWA) controls the presence of contaminants in finished drinking water ("at-the-tap").
 Because exposure through the ingestion of drinking water and consumption of fish and shellfish are considered, the criteria are typically expressed as "water + organism" criteria.
 MCLs, on the other hand, are developed with consideration given to the costs and technological feasibility of reducing contaminant levels in water to meet those standards.  In addition, MCLs do not consider exposure pathways beyond drinking water, e.g., exposures via fish consumption.

In answer to your second question:  we are proposing to remove criteria for lead and the two trihalomethanes only for the waters (and associated uses) for which the State adopted site-specific objectives.  

I hope this information answers your questions.  If you have any additional questions, please do not hesitate to contact me.

Diane Fleck

Diane E. Fleck, P.E., Esq.
U.S. EPA Region 9 WTR-2-1
75 Hawthorne Street
San Francisco, CA 94105
P: 415 972-3527 Tuesday/Thursday
P: 408 243-9835 Monday/Wednesday
Fax: 415 947-3537

From: John Kenny [mailto:kennyjd@gmail.com] 
Sent: Friday, January 12, 2018 5:39 PM
To: Fleck, Diane <Fleck.Diane@epa.gov>
Subject: Proposed EPA Withdrawal of Certain Federal Criteria for California

Hi Diane, 

I don't understand why the CTR water & organisms DCBM and DCBM goals are so low (0.4 ug/L and 0.56 ug/L), compared to the drinking water TTHM MCLs (80 ug/L). Is it because the TTHM MCL is an MCL, which takes economics, etc. into account, whereas the CTR is more like a goal? They both are trying to achieve 10^-6 risk, I believe; do they make different assumptions? 

Also, why does this change only apply to certain water bodies and not others? 

Best, 

John