GENERAL45949 - Laserfiche WebLink

Home Browse Search

Page 2 • ,~ compared to many waters but does not present a problem as a contaminate of drinking water. Coliforms range from a low of 5800 MPN (most probable number) per 100 ml to 6.2 million MPN per 100 ml; the safe upper limit for drinking water is 10,000 MPN per 100 ml. Nitrogen in the South Platte occurs mainly as ammonia (NH4) and nitrate (N03); NH4 is the major occuring nitrogen form. During low flows occurring during cold weather, NH4 can reach levels of 14 mg/1, while NO3 will be typically less than 1.0 mg/1. During the warmest month Nki4 levels drop to levels as low as 2.0 mg/1 while N03 levels rise to between 2.0 and 3.0 mg/1. June of 1977 saw N03 levels between .5 - .6 mg/1; the highest recorded N03 level occurred in 1965 and was 7.8 mg/1 of NO3. N03 can be a problem in drinking water if levels rise above 10 mg/1. NH4 is not considered a problem, but the Dept. of Health is concerned with high levels because NH4 will complex with chlorine in treated water supplies. Dissolved Oxygen (DO) varies at Henderson from 3.7 to 7.6 mg/1. The major source of NH4, P04, and coliforns to the South Platte is upstream sewage treatment plants. The quality of the ground water system at Henderson according to Dept. of Health and the Statewide 208 Program is much worse than that of the South Platte where N03, D0, and Total Dissolved Solids (TDS) are concerned. NH generally does not occur in ground water as it is used by a variety of microrganisms before it reaches the ground water system, P04 is usually not measured in ground water as it is generally very low. TDS at Henderson is about 1300 mg/1, DO is close to 0 mg/1 and N03 is about 36 - 37 mg/1. Coliforms are not measured. The reasons cited for high TDS and high N03 is irrigation practices associated with farming. The only real potential pollution problem is with excessive coliform populations. Coliforms in the South Platte have three possible avenues of entry to the lakes created by Hazeltine: 1) overbank flows during flooding, 2) through the river bottom and banks, and 3) in irrigation water should it be directly delivered to the lakes. During overbank flows enough dilution has taken place so as to render col iform populations to safe levels (5 yr. avg. of 5800 MPN per 100 ml). According to the Dept. of Health, effluent from drain fields associated with septic tanks is probably safe relative to colifonns after the effluent has passed through 40 - 50 ft. of soil. The minimum distance water would have to flow from the South Platte through soils to the Lazeltine Lakes is approximately 100 ft. Coliform populations while high in the South Platte are very much lower than those which would occur in effluent from a septic tank; on this basis Dept. of Health personel felt that coliform populations delivered to the lakes by this method were not worth considering as a potential problem. Irrigation water delivered to the lakes would be greatly diluted but coliforms could still be a problem during the irrigation season. Again, the major concern expressed was with nutrient concentrations; as P04 is not considered a problem, the remaining constituents of concern are NH4 and N03. NH4 which finds its way to the lakes will more than likely be fully utilized by algeas; subsequent decay of algea will release nitrogen but not entirely as NH4.