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## Major Factors Impacting E nvironmental L evels of S iloxanes (D4/D5) at POTWs without Industrial Siloxane Sources and Selection of Si tes for M onitoring
Charge: Build on the SEHSC proposal to develop a science

- based, rational proposal for monitoring of Publicly Owned Treatment Works (POTW) sites which provides sufficient information and data on the presence and concentrations of D4 and D5 in the environment near POTWs, to support a national risk assessment. Monitoring that establishes the contribution of siloxanes to POTW loadings from manufacturing, formulating and processing facilities will be addressed separately. Monitoring Objective : A s ampling strategy should collect monitoring data that scans a variety of POTWs that have attributes that could be used to characterize the likely range of siloxane environmental concentrations around POTWs. With these data , an understand ing of how populati on size, receiving water body flow and other factors contribute to the environmental loading of siloxanes near POTWs would be developed

. Approach
The major factors in site selection likely to affect the measured levels of siloxanes in the sediment at
o utfalls from POTWs outside of SEHSC control would be established

. T hese factors w ould then be used as input to an optimization process to develop a monitoring program design . This optimization method, D

- Optimal design , coupled with the relevant major facto rs established, would provide a scientific basis for a monitoring prog r am design to understand how the various factors contribute to siloxane measured result s without testing the entire set of possible permutations. Additional sampling considerations such as air monitoring and seasonal variability would be considered in the future, but do not impact site selection and are not included here. Major Factors R elevant to the E nvironmental P resence of S iloxanes
Below is a list of major factors related to site selection that EPA believes most strongly impact the siloxane levels in the sediment and water at POTW outfalls.
Influent sources

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. Population size served by the POTW (High/Medium/Low)
This factor could provide information on how consumer or household use of siloxanes contribute s to POTW silo x ane loadings.

POTW characteristics

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. Treatment types ( activated sludge , other secondary treatment types)

. Other secondary treatment types could include trickling filter, oxidation ditch or lagoons.2 A focus would be placed on POTWs that use secondary treatment because this would represent the vast majority of POTWs across the nation

T ertiary treatment is not included because it is assumed there would be very low siloxane concentrations in effluent

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. High Total S uspended S olids ( TSS ) in effluent.
Indications of high TSS in effluent from the POTW could be important as we know that siloxanes partition to solids.

R eceiving body characteristics

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. Geography (North, South) Geography could be important as c older temperatures likely decrease the amount of siloxanes that partitions to the air and will increase the amount that remains in the water and that reaches the sediment.

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. Receiving body flow (lake/ low flow stream /high flow river)
Receiving b ody flow d irectly impacts the degree of dilution and probably the turbulence in the water . B oth could impact the partitioning behavior of siloxanes

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. Organic content of receiving body (high/low) High organic content in the receiving body could increase the amount of siloxa nes that partition to the sediment

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