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HomeMy WebLinkAbout7 - "Brown Water" Problem AGENDA NUMBER: PREPARED BY: SUBJECT: DATE: INTRODUCTION: BACKGROUND: ",,'. CENSUS '90 . 7 LARRY J. ANDERSON, DIRECTOR OF PUBLIC WORKS CONSIDER THE USE OF POLYPHOSPHATES IN THE WATER SYSTEM TO OFFSET "BROWN WATER" PROBLEM APRIL 2, 1990 The source of the Municipal Water System is the Jordan Acquifer. The aquifer contains both iron and manganese at levels which are a nuisance. Iron and manganese are picked up by the water flowing to the wells through underground rock strata when the water comes in contact with deposits of these minerals. The problem arises when the minerals in the water oxidize to form precipitates in the drinking water. The use of polyphosphates may help reduce the problem with brown water. The City has had brown water complaints at various levels since the Municipal Water System began. The extent of the problem varies. Some people do not have any problems, and others feel a severe problem exists. The water has been analyzed and the levels of iron and manganese are such that they pose no health risk, but are at a nuisance level, according to the Minnesota Health Department. In 1987, a City wide survey was completed. At that time, it was determined that a water treatment plant could be constructed at a cost of $2,000,000.00 with an average household cost of $67.00 per year. Sixty-one percent (61%) of those responding indicated that they did not favor the construction of an iron/manganese removal plant. At the time the Council acted not to proceed with a removal plant project. 4629 Dakota 51. 5.E., Prior Lake, Minnesota 55372 / Ph. (612) 4474230 / Fax (612) 447-4245 DISCUSSION: Some housen91ds are currently getting a buildup of "tron/manganese in the1r service lines and/or lines in their homes. In some instances, the buildup has been to the point that a significant loss of water pressure occurs and the lines have had to be cleaned. This problem has definitely been pinpointed to the homeowners lines. The problem appears to be getting worse, as can be seen by the evidence of the buildup in the homeowners lines. Staff believes that the problems in the past year have been higher than other years. The construction of the new tower and repainting of the other tower has caused additional interim problems. Presently, two-thirds of the communities in the Metropolitan area are using polyphosphates to control this problem. Depending on the specific location of the community, the levels of iron and manganese vary. If the levels are concentrated at twice the City's current level, a treatment plant is required to address the problem. There is no exact method to determine the required level of polyphosphates needed to address the problem. This is due to the fact that each water system has significant variables in its construction. However, based upon the "experience" of other communities, Staff strongly believes that the polyphosphates can reduce our problem. The pol~hosphates will sequester (provide a coat1ng for) the iron and manganese to prevent the precipitation of the two minerals into the water, in the form of brown or black sediments. The exact level needed can be best determined by a combination of two methods. One,is the testing of the water at the end of the system to determine if all the iron and manganese is sequestered. The second, is by the amount of phone calls received from complaints. Since there is a cost involved in addin9 the chemical to the system, we will be adJusting the feed rate to minimize the amount required. Based upon the experience of other communities, the initial level will be 5 parts per million. Initiall~, the chemical may remove some of the buildup 1n the lines and the problem may be worse than what we currently have. On a long term basis, the cleaning of the lines will be a benefit if it occurs. On the short term ALTERNATIVES: RECOMMENDATION: I \ basls. it will probably take a year to determine if we have reduced the problem, thereafter the results should be obvious based upon citizen complaints. From a health standpoint, the Minnesota Department of Health doesn't have any objections to the use of polyphosphates. Their only requirement is that they be notified when a municipality uses the chemicals. From an operational standpoint, the chemical is a source of nutrient and the City's residual chlorine must be maintained to eliminate the growth of bacteria. This does not change our current requirement as the City is mandated to chlorinate the water system. The optimum time to initiate this is after the spring flushing of the water system and prior to peak watering demands. The spring flushing will start on April 9, 1990 and will be completed in approximately one month. The initial level of polyphos~hates to be is five (5) parts per mil110n and is enough not to affect the environment when water system is flushed. The initial cost of the equipment to feed the chemical is $5,000.00 and an estimated annual cost of the chemical is $18,000.00 per year. used low the The alternatives are as follows: 1. Authorize the use of polyphosphates in the Municipal Water System. 2. Table this item for further discussion with specific direction. 3. Take no action on this Agenda item. The recommendation is to add polyphosphates to the potential benefits appear the negative aspects. The recommendation is based upon the experiences of other communities, our level of the two minerals in the water, and our belief that the addition of polyphosphates will, in all likelihood, produce ~ositive results. Even if we were to put up w1th the brown water complaints, the problem with individual water lines closing off cannot be ignored. authorize staff to water system. The to greatly outweigh BUDGET IMPACT: ACTION REQUIRED: Initially, we mayor may not have more problems, but in the long term this should be a benefit to the community. This item was not budgeted for and will be paid from the water utility budget. Revenues are expected to offset this expenditure. The amount for 1990 would be $19,000.00. We are three months into 1990 and the chemical costs have been correspondingly reduced. utility revenues are predicted to be higher than estimated and the $19,000.00 cost will have no major impact on the utility Fund. utility Fund revenues and expenses are not related to property taxes. Depending on the action may vary. If use polyphosphates, a to direct Staff to do Council discussion, the the Council chooses to motion would be in order so.