EXECUTIVE COMMITTEE

PRESIDENT

Suzanne E. Goss Government Relations Specialist JEA (Electric, Water & Sewer) Jacksonville, FL

VICE PRESIDENT Julius Ciaccia, Jr.

Executive Director Northeast Ohio Regional

Sewer District Cleveland, OH

TREASURER
Karen L. Pallansch Chief Executive Officer Alexandria Renew Enterprises Alexandria, VA

SECRETARY Adel H. Hagekhalil

A ssistant Director Bureau of Sanitation City of Los Angeles Los Angeles, CA

PAST PRESIDENT
David R. Williams Director of Wastewater

East Bay Municipal Utility District

Oakland, CA

EXECUTIVE DIRECTOR
Ken Kirk September 18, 2012

Robert Jones
Chemical Control Division
Office of Pollution Prevention and Toxics U.S. Environmental Protection Agency 1200 Pennsylvania Ave, NW Washington, DC 20460
Via Email: jones.robert@epa.gov

Re: Enforceable Consent Agreement Nego tiations for Two Cyclic Siloxanes

Dear Mr. Jones:

The National Association of Clean Wate r Agencies (NACWA) is providing these comments as an interested party in the enforceable consent agreement (ECA) negotiations to collect environmental monitoring data for octamethylcyclotetrasiloxane (D4) an d decamethylcyclopentasiloxane (D5). NACWA has been participating in the EC A discussions about these two siloxanes that began on June 27 and has reviewed th e proposals that have been made for the ECA by the Silicones Environmental, Heal th and Safety Council of North America (SEHSC) and EPA, including EPA’s Septem ber 6 proposal. Our comments address aspects of the proposals’ recommende d sampling efforts for publicly owned treatment works (POTWs), as well as othe r questions that EPA has asked about the
effects of siloxanes at POTWs.

The ECA negotiations on POTW sampling have focused on the number of POTWs
that should be included in the data collect ion effort and the factors that should be used in determining whic h POTWs should be sampled. In its September 6 proposal, EPA recommended 16 POTWs for the study, while SEHSC recommended five in its original proposal. NACWA recommends sampling at seven or eight POTWs, to potentially include two POTWs that use lagoon treatment and five or six POTWs that use activated sludge treatment. NACWA believes that data collected from seven or eight POTWs, when combined with other existing data sources, should provide EPA with sufficient data for an environmental risk assessment of
D4 and D5.

NACWA’s publicly owned wastewater treatment agency members are interested in
this data collection effort because of th e detrimental effects of siloxanes on the exhaust stages of combustion equipment when biogas is used as a renewable fuel

### NACWA Comments on Siloxane ECA September 18, 2012 Page 2 of 5

source, as well as the potentially harmful effects of silo xanes that may be released into the environment from
wastewater effluent or biosolids. While NACWA recognizes that the pr oblems associated with combustion equipment are not part of EPA’s environmental risk assessment, the Association believes that the data collection for the risk assessment will provide useful info rmation for addressing this issue in the future.



## Proposals for the Enforceable Consent Agreement The proposals made by SEHSC and EP A for sampling at POTWs include measurements of D4 and D5 from the POTW influent, effluent, and biosolids, as well as surfac e water, sediment, and biota in the receiving waters. Air monitoring was also proposed for one POTW. The negotiat ions to date have focused on the factors that should be considered for selecting POTWs and determining how many POTWs that should be sampled. NACWA has the following comments on these issues.

Population Size Served by the POTW By sampling POTWs, EPA would like to determine the contribution of siloxanes to POTW loading from domestic sources and has suggested that population size could provid e information about these domestic contributions. NACWA agrees that quantifying domestic sources is important, since D4 and D5 are used in a wide range of consumer products and POTWs have no ability to regulate chemical discharges from domestic sources. However, NACWA disagrees that population size would provide the appropriate information. There is no basis for believing that us e of products containing D4 and D5 will be dependent on the population served by
the POTW. A better measure of the domestic source cont ribution of D4 and D5 wo uld be the proportion of
influent to a POTW that comes from domestic sources. In addition, the type of industrial discharges to the
POTW must be considered. If a POTW has significant influent from industrial sources that do not discharge siloxanes, the domestic sources will be diluted. Conver sely, the influent concentrations of D4 and D5 will be increased over what is expected from domestic sources if there is a significant contribution from industrial

sources.

EPA’s September 6 proposal states th at “All monitored POTWs should have a low industrial contribution to influent (<10%).” NACWA agrees th at the industrial contribution shou ld be as low as possible, and the maximum 10 percent value for industrial contribu tion is a realistic goal for selecting POTWs.

For POTWs with combined sewers, which convey both wast ewater and stormwater, the influent will also be affected after precipitation events, and potentially much longer if the POTW stores stormwater to treat over time. This should be taken into account for any samplin g that occurs at POTWs with combined sewer systems. Also, even separate sewer systems, which are not meant to collect stormwater, can have infiltration of groundwater into the sewer pipes and inflow of stormw ater from illegal connections to the sewer. This infiltration and inflow from precipitati on events dilutes the wastewater befo re it reaches the treatment plant. These factors must also be considered when determining th e amount of influe nt from domestic sources.

Treatment Method Used by the POTW NACWA agrees with EPA that the focus of the sampling should be on POTWs that use secondary treatment. Furthermore, NACWA recommends that the proportion of treatment processes used by the POTWs sampled for the ECA be similar to the proportion of the amount of wastewater treated with these processes in the U.S. SEHSC’s original ECA proposal included sampling at fi ve POTWs: two with activated sludge treatment, one with oxidation ditch treatment, one with trickling filt er treatment, and one with lagoon treatment. This sampling would not reflect the proportion of wastewat er treated with these methods in the U.S. EPA’s

### NACWA Comments on Siloxane ECA September 18, 2012 Page 3 of 5

September 6 proposal, with sampling at 12 POTWs using activated sludge and four POTWs using lagoons, is a more realistic proportion of the treatment types used in the U.S.

Flow Rate of the Receiving Waterbody Predicting the receiving body flow rate for a POTW may be difficult in some cases, since the flow rate may depend on recent events and the time of the year that the sampling occurs. Receiving body flow may depend on the amount of precipitation, any runoff from snowfall me lt, and use of the water for other purposes, such as irrigation. Based on the chemical properties of silo xanes and previous studies of siloxanes at POTWs (e.g., Wang et al., 2012), the removal rates of siloxanes at POTWs are expected to be very high, with the majority of influent siloxanes expected to partition to the biosolids. The concentrations of s iloxanes in the effluent are expected to be very low. While the flow rate of the re ceiving waterbody should be considered in the analysis of the sampling results, its unpredictabilit y and the likely low discharges of s iloxanes to the receiving water body mean that it should not be used as a deciding factor in choosing POTWs for sampli ng. Evaluating the impacts of this factor would be best accomp lished by conducting sampling at the same POTW at different times of the year, as EPA has recommended in its September 6 proposal.

Additional Factors of Interest EPA states in the September 6 proposal that “there would be value in samp ling at several POTWs that discharge to a receiving water body with high organic content,” but “it would be difficult to identify POTWs for potential monitoring based on this factor.” NACWA agrees that organic content of the receiving water body should be used in the analysis of sampling results, but should not be used as a basis for choosing POTWs for sampling.

NACWA also agrees with EPA that “env ironmental conditions in different pa rts of the country could affect the partitioning and sedimentation of siloxanes.” The POTWs chosen for sampling should be geographically diverse, but it is not necessary to determine a specifi c number of POTWs in different regions of the country.

Sampling Details NACWA agrees that two sampling events at each site are sufficient for this study. In addition to sampling of POTW influent, effluent, biosolids, sediment at outfall, and surface water, biogas produced at the POTW should also be sampled.

EPA has proposed sampling at 16 POTWs, while SEHSC has proposed sampling at five POTWs. EPA’s sampling plan matrix includes population served and dilu tion level (based on flow rate of the receiving water body). However, as explained above, NACWA does not be lieve that these factors are relevant. Furthermore, there is no justification given in the EPA proposal for th e four-by-three size of this matrix. Sampling at only five POTWs, as proposed by SEHSC, would not provide su fficient data to evaluate unusual or outlying results, especially with only two of the five sites using activated sludge treatment.

NACWA recommends using available data when determin ing the number and type of POTWs that should be used for sampling. Sampling at four POTWs with lagoon treatment, as recommended by EPA, is excessive due the small proportion of U.S. population served by POTWs with this treatmen t type and the available data in the Wang et al. (2012) study of Canadian POTWs. In th is study, seven POTWs with lagoon treatment were sampled. EPA states in its September 6 proposal that “it is likely that the Canadian sites are not representative of U.S. POTWs.” NACWA disagrees with this assessment and believes that the Canadian data for lagoons are

### NACWA Comments on Siloxane ECA September 18, 2012 Page 4 of 5

consistent with other studies of silo xane behavior at POTWs. The numbe r of lagoons sampled for EPA’s risk
assessment should therefore be reduced.

NACWA recommends sampling at seven or eight POTWs to provide enough data to evaluate the behavior of
siloxanes at POTWs and the factors in fluencing this behavior. This numbe r could include two POTWs that use lagoon treatment if EPA believes that it is necessary to verify the Canadian data. Five or six POTWs that use activated sludge treatment would allow evaluation of the variability of the data.

Additional Comments Neither the EPA nor SEHSC proposals consider septic tanks. Since approximately 20 percent of the U.S. population uses septic tanks for their wastewater treatm ent, and this method of treatment is vastly different from treatment at POTWs, EPA’s risk assessment should consider environmental exposure to siloxanes from septic system treatment.



## Costs Associated with Siloxane Removal at POTWs EPA asked NACWA to provide more information about th e costs incurred by POTWs that use biogas as a
renewable fuel source and must remove siloxanes fr om the biogas to prevent damage to combustion equipment. The following information on co sts has been provided by NACWA members.

• The Great Neck Water Pollution Control District in New York is installing two 65 kW microturbines that will convert methane gas from the anaerobic dige sters to electricity with the by-product of hot water. As part of the microturbine system, the ut ility must install a siloxane stripping unit which is approximately 30 percent of the cost ($285,000) of the microturbine project and will require the majority of the maintenance costs.

• Metro Wastewater Reclamation District in Denver st ruggles with heavy siloxane deposition on the heat exchangers that are located in the exhaust stacks of its combustion turbines. Rather than assume the expense of gas treatment to remove siloxane, the ut ility shuts down its cogeneration facility about once every three to four months to physically remove th e siloxane from the heat exchanger coils using a highpressure water spray. The shutdown takes about 6-7 hours. The shutdowns are inconvenient, but currently cost less than gas treatment.

• The Hampton Roads Sanitation Distri ct (HRSD) in Virginia has designed a project with construction completion expected in 2013. The Atlantic CHP (combined heat and power) project has two 1100 kW Cummins gas fired engines that will burn treated di gester gas and includes A pplied Filter Technology, Inc.’s SAG Pack System for siloxane remo val. Moisture and hydrogen sulfide (H 2 S) removal is also done to protect both the engine and the siloxane removal media. The entire CHP project construction cost is $7.6 million. The construction cost of the siloxane removal system itself is $300,000 (4% of total). HRSD is removing H 2 S and moisture in order to protect the siloxane removal media and estimates that in total, $800K of the construction costs can be attr ibuted to costs associated with siloxane removal.

• In early 2004, the City of Eugene, Oregon, installed th e SAG Pack biogas filter system by Applied Filter Technology, Inc., which consists of two filters. Th e total project cost was $343,000. Eugene produces an average of 350,000 ft 3 /day of digester gas, requiring the silo xane filter media to be changed every 18 months at a cost of $3,500.

### NACWA Comments on Siloxane ECA September 18, 2012 Page 5 of 5

• A NACWA member installed siloxane removal in 2011 as part of a larger project which included the addition of cogeneration equipment to utilize onsite biogas for power generation. Removal is achieved by passing the gas through a carbon media engineered spec ifically to remove siloxanes . It is part of a gas cleaning system which also includes H 2 S removal as well as moisture remo val. The gas cleaning system is installed ahead of two 1059 kW engines. The cost of the siloxane removal system alone was about $310,000 and about $580,000 for the entire biogas cleani ng system. These are roughly 12% and 23% of the cost of the cogeneration portion of the project, re spectively. Since the project has been operating for less than a year, the utility does not have optimized operation and maintenance costs yet. In particular, the siloxane media has not been change d yet, and this is expected to be a large maintenance cost. This year, the H 2 S media was replaced for about $115,000, and th e siloxane media is expected to cost more
than the H 2 S media. Labor, power, and maintenance were estimated at $120,000/yea r for the entire gas cleaning system.

• A NACWA member conducted a full-scale pilot of a reciprocating internal co mbustion engine exhaust treatment system consisting of digester gas clean- up and two post-combustion catalysts in series to reduce carbon monoxide (CO), oxides of nitrog en (NOx), and volatile organic compound (VOC) emissions. The pilot study was conducted to determ ine whether the challenges of working with biogas (namely, the presence of contaminan ts such as siloxanes and hydrogen sulfide) could be overcome in applying existing catalyst technology to biogas-fired engines. The pilot project’s biogas cleanup system utilized an existing gas dryer (heat exchanger) plus a new fixed-bed gas cleaning vessel with a blend of activated carbon. Only initial cost estimates are ava ilable for this system at this time. It is estimated that the digester gas cleaning vessels capital cost is approximately 20 percent of the capital cost of the two post-combustion catalysts and building improvements to house the catalysts.

Thank you for your consideration of these co mments. Please contact me at 202-533-1836 or cfinley@nacwa.org if you have any questions.

Sincerely,

Cynthia A. Finley, Ph.D. Director, Regulatory Affairs