September 14, 2012

Mr. Marcus Aguilar

Chemical Control Division (7405M)

Office of Pollution Prevention and Toxics

Environmental Protection Agency

East Building

1200 Pennsylvania Avenue NW

Washington, DC 20460–0001

(via e-mail: Aguilar.Marcus@epamail.epa.gov) 

Re: Enforceable Consent Agreement Development for Two Cyclic Siloxanes (EPA Docket

Number: EPA–HQ–OPPT–2012–0209)

Dear Mr. Aguilar:

The American Cleaning Institute (ACI) is pleased to provide the following comments with 

respect to the proposed Enforceable Consent Agreement (ECA) for two cyclic siloxanes:

octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5; EPA Docket 

Number: EPA–HQ–OPPT–2012–0209). ACI is an Interested Party to the development of the

ECA. 

We have reviewed the documents available in the docket including the recent EPA Siloxane 

Monitoring Proposal (September 6, 2012) and the August 3, 2012 letter from the Silicones 

Environmental, Health and Safety Council (SEHSC) including the July 2012 Final Report 

entitled Recommendation of Number of Sites to Sample for Validation of the D4 and D5 

Publicly-Owned Treatment Works Conceptual Site Model.

The agency indicated in its September 6, 2012 proposal that the ECA “should support a risk 

assessment that will allow EPA to make a determination on whether or not risk management 

action is needed to address the release of siloxanes in the environment.” Further, the agency has 

concluded that the SEHSC proposal would not provide adequate information for the agency to 

conduct a risk assessment. It is not possible to confirm the agency’s conclusions based on the 

information available. EPA has not indicated what approach is will use in conducting its risk 

assessment and it has not reported what data it has at its disposal or where gaps exist. 

It is our observation from the several public meetings on the ECA and related discussion and 

documents in the docket that the scope of the ECA is solely with respect to environmental 

concentrations of D4 and D5, with an emphasis on freshwater streams receiving treated 

municipal and industrial wastewater effluent and associated sediments. In order to characterize 
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September 14, 2012

environmental concentrations efficiently across the entire United States, we recommend that a 

modeling approach be used initially and that environmental monitoring be conducted to confirm 

the modeled results are similar or, at a minimum, conservative in their estimation. Use of 

environmental exposure models allows for insights as to where highest concentrations may occur 

and where the greatest risks may be. Moreover, if conservative environmental monitoring does 

not reveal an unacceptable environmental risk and there is a wide margin of safety, additional 

environmental monitoring may not be necessary at all.

We note that the SEHSC proposal included a conceptual site model and their monitoring 

approach is predicated on collecting data to support that model. We believe their monitoring 

approach is well conceived to achieve that objective. In addition, in a March 2012 presentation 

to the agency, SEHSC stated that they used EPA’s E-FAST model to predict surface water 

concentration distributions and subsequently predicted distribution of surface water 

concentrations of D4 and D5 across the US via ACI’s iSTREEM® model. While they did not 

include the results of their modeling in their documents, such results combined with existing 

publicly available occurrence data might render additional monitoring completely unnecessary.

The agency’s proposal of September 6, 2012 does not contain a conceptual model which would 

incorporate the data it proposes to collect. We recommend that the agency provide such 

information so that the benefit of its proposed sampling plan is readily apparent.

With respect to the parameters that the agency has chosen in order to populate its sampling plan 

matrix for municipal wastewater treatment sites, we agree that in-stream dilution and wastewater 

treatment technology are important. We agree that sites should be selected based on a variety of 

dilution rates for municipal wastewater effluent and that the three tiers proposed by the agency 

may be appropriate. Likewise, we believe a focus on activated sludge treatment is most 

appropriate as 80% of municipal wastewater is treated by this method. However, while we agree 

that lagoons are a very common treatment technology, they present the poorest type of treatment 

– often being associated with increased levels of total suspended solids, biological oxygen 

demand (BOD) and ammonia in treated effluent when compared to other treatment technologies. 

Further, discharge at lagoon treatment facilities is often flow-dependent. That is, it is common 

during low flow months for lagoons not to discharge to receiving surface waters. Hence, if 

lagoons are to be included in a monitoring program, an understanding of where continuous-flow,

well-operated (no significant non-compliance events) facilities occur will be necessary. 

The agency also has proposed a population-POTW flow parameter that appears to be indicative 

of wastewater influent concentration. Based on recent field experience, we have observed that 

the design flow of wastewater treatment plants correlates very closely to the population served 

by a facility (Mudge, 2012, Figure 35, page 47).

1

 Notwithstanding that correlation, it is prudent 

to expect that wastewater influent concentration may vary significantly. However, there are a 

number of parameters that might affect influent concentration including geographical use 

patterns of consumer products, consumer use patterns, daily water use patterns, seasonal weather 

patterns and local infrastructure among others. In fact, we observed during the same research1

that there may be a correlation between influent concentration and effluent dilution based on 

 1 http://www.aciscience.org/docs/Fatty%20Alcohols%20by%20WWTP%20and%20Ecoregion-FINAL.pdf
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September 14, 2012

local meteorology – we observed high influent concentrations in Oklahoma during a prolonged 

drought (and low stream flows), and low influent concentrations in Oregon during a period of 

excessive rain (and high stream flows). Any attempt to predict influent concentration based on 

these and other variables would likely not lead to meaningful results, but more to the point, the 

single parameter that the agency has chosen (population-POTW flow) is not likely to be 

informative. Further, many wastewater treatment plants are specifically designed to dampen 

spikes of influent chemicals through the use of flow equalization basins. We recommend that 

this parameter not be used in the site selection process but that the focus of site selection remains 

on wastewater treatment technology and effluent dilution. 

We appreciate EPA’s consideration of our comments and request that they be included in the 

docket (EPA–HQ–OPPT–2012–0209) and that they be circulated to all interested parties in 

advance of the next meeting scheduled for Thursday, September 20, 2012.

Sincerely,

Paul C. DeLeo, Ph.D.

Senior Director, Environmental Safety

cc: Robert Jones, USEPA (jones.robert@epa.gov)

Karluss Thomas, Silicone Environmental Health and Safety Council (kthomas@sehsc.com)