Environmental Investigations in Dry Cleaning Operations
Contaminant Source Areas – Where to Sample III
Sanitary Sewer - Septic Tank/Drainfield
The sanitary sewer and septic tank/drainfield have historically been popular disposal points for contact water. Some older drycleaning machine service manuals even prescribed discharging contact water to drains.
Sewer lines in urban areas can be constructed from a wide variety of materials. Within a city, many different kinds of sewer piping may be utilized depending on the time period the sewer lines were installed. Older sewer lines are made of cast iron and vitrified clay and newer lines have been constructed from concrete or more recently thermoplastic.
Manholes were typically constructed of brick/mortar and concrete.
Early sewer line joints were sealed with mortar and bituminous compounds. Neither of these materials is watertight and subsequent settling and cracking have provided pathways for contaminant migration.
Many local sewer authorities specify permissible leakage rates for newly-constructed sewer lines “of approximately 500 gallons per inch diameter per day per mile.”
Contact water, free-phase solvent and solvent vapors can leak from sewer lines through cracks, joints or breaks. Contact water and free-phase solvent can also leach through sewer piping.
Soil-gas sampling along sewer lines can be used to delineate contamination associated with leaking sewer lines.
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