Effect of septic-tank wastes on quality of water, Ipswich and Shawsheen River basins, Massachusetts

Many housing projects in the metropolitan area of Boston are beyond the reach of municipal sewer systems. Waste water disposed of through septic-tank or cesspool systems percolates to ground-water reservoirs and eventually reaches the streams. The dissolved-solids load in the streams receiving septic-tank effluent is increased by an amount that can be predicted from the housing density. In the study area, highway deicing salts are the only materials other than septic-tank discharge that contribute to water-quality degradation. The effect of these salts on the relationship with housing density is eliminated by subtracting the specific conductance due to sodium chloride from the measured specific conductance of a water sample. The difference is called residual conductance and is proportional to the dissolved-solids content minus the concentration of sodium chloride.