While bulk precipitation has an average value of 0.2 ug/L ClO₄ (n=108), we found that perchlorate in bulk precipitation collected shortly after the Fourth of July increases to a maximum value of 2.8 ug/L, which we believe is due to fireworks. Soil water beneath lawns that are not fertilized or are fertilized with chemical fertilizer have concentrations between <0.1 to 3.0 ug/L. Soil water beneath lawns treated with organic fertilizer has concentrations ranging from 1 to 625 ug/L. Road runoff in stormwater basins has a maximum concentration of 18.5 ug/L, with an average value of 2.2 ug/L (n=35). Recharge basins that receive road runoff have an average value of 3.0 ug/L (n=10). Sewage from cesspool/septic tanks has an average value of 2.9 ug/L (n=38).

The concentrations measured in this study indicate potential sources of contamination to local groundwater supplies, since the sources we measured directly leach to groundwater. The average concentrations measured are below the NY state drinking water planning level of 5 ug/L. Many individual samples, however, are well above this level. As a result, we have to be concerned about the risk of perchlorate concentrations in groundwater increasing to above the New York State planning level and above the potential EPA drinking water standard.