NATURAL WATERS 



Data already given in the tables, Figure 7, and the text show how chloride 

 buildup occurs in large rivers and one large lake. A potential problem is that 

 small streams and ponds or partially closed bays, may reach much higher 

 chloride levels which can impair biologic activity or even prevent an annual 

 overturn.'^^ Figures 3 through 6 and 8 through 9 shpw buildup in various 

 groundwater reservoirs or aquifers, but little can be added because of the 

 absence of information about physical properties, volume, and residence times. 

 Some useful insights can be obtained, however, by consideration of what might 

 be expected as shown by a mathematical model for dispersion from a highway. 



Computer simulations of a modified form of a model developed at Colorado 

 State University'*^ have been performed at the University of New Hampshire for 

 thin, narrow acquifers overlying bedrock. The results show that chloride will 

 buildup and fluctuate seasonally close to a highway. This has been observed from 

 measurements in many wells and concentrations may reach 1000 mg/£. chloride 

 or more. Away from the highway, however, the model indicates that lower but 

 more or less steady state values will prevail once chloride outflow to a nearby 

 water body equals inflow from the highway. This ha§ not been commonly 

 observed because most monitoring programs emphasize wells close to highways. 

 This steady state situation should occur after a few years of appHcation of salt, 

 and the chloride should flush out a few years after cessation of salting. 



The implication is that in small, thin aquifers intersected by streams such as 

 are commonly found in much of New England, buildup of chloride may not be a 

 serious problem except close to highways. Chloride from septic tanks may act in 

 much the same way but for the special case of a point source. This optimistic 

 view must be tempered somewhat, however, by the fact that ecologic problems 

 from increased chloride may develop in ponds, streams, and wetlands draining 

 the aquifers. This aspect does not seem to have received much attention. 



If the same computer model is applied to larger aquifers such as for the 

 supplies shown in Figures 3 through 6 and 8 through 9, then the same general 

 pattern develops except buildup away from the highway will likely be greater. 

 Also, the aquifer will flush much more slowly because of volume and if salting 

 ceases the impact of chloride is more serious than in the thinner aquifers. 



CORROSION 



The corrosion associated with road deicing salt of automobile bodies, 

 concrete pavement and structures, metal manhole covers and so on, is discussed 

 well in the literature'*^ -44 but the potential toxicity of the corrosion products 



'^^ PROCEEDINGS, STREET SALTING - URBAN WATER QUALITY WORKSHOP AT 

 STATE UNIVERSITY COLLEGE OF FORESTRY, SYRACUSE UNIVERSITY 74-79 

 (R. H. Hawkins ed, 1971) 



'^^D. L. REDDELL & D. K. SUNADA, NUMERICAL SIMULATION OF DISPERSION IN 

 GROUNDWATER AQUIFERS (Colorado State University Hydrology Papers 41, 1970). 



"^^ FIELD 34. 



''"'^STRUZESKI 77-80. 



23 



