Radiation Safety

Sewer Disposal

Very limited amounts of aqueous liquid waste in microcurie amounts, including biodegradable scintillation cocktails may be discarded down designated sink drains. Sink disposal must be approve in advance by the RSC. Guidelines for disposal are provided below:

  1. Liquid radioactive waste must be soluble and readily disbursable in water.
  2. Identify all other constituents such as flammable solvents, heavy metals or biohazards in the solution that may be restricted from sewer discharge.
  3. Sewer disposal concentrations must be within regulatory limits. First, calculate the amount of each isotope that can be discharged, then make sure that the amount does not exceed the university’s monthly discharge limit. Waste limits are discussed in 10 CFR 20.2003(a)(4) which states:

“The total quantity of licensed and other radioactive material that the licensee releases into the sanitary sewerage system in a year does not exceed 5 curies (185 GBq) of hydrogen-3, 1 curie (37 GBq) of carbon-14, and 1 curie (37 GBq) of all other radioactive materials combined.”

Table 3 of 10 CFR 20 provides the monthly average concentrations for release to sanitary sewers. Some common radionuclides and their limits are provided below:



Concentration (uCi/ml)


1 x 10-2


3 x 10-4


9 x 10-5


8 x 10-4


1 x 10-3


6 x 10-5

4.Discharge the liquid into a designated and labeled sink with water running from the faucet. Survey the sink and surrounding surfaces following disposal

5.Record the date, isotope, activity, location discharged, and the individual discharging waste.

6.Scintillation waste – Most biodegradable scintillation fluids meet the sink disposal criteria. Traditional flammable organic solvents such as toluene or xylene must be disposed as hazardous waste, regardless of radioactivity. Organic liquid waste shall segregated by isotope in safety containers provided by the RSO. All containers must be labeled as to which specific isotopes should be discarded therein; strict compliance with these labels is essential. Contact the RSO for Off-site disposal.

Page last modified May 19, 2011