Low water on the Noatak River may be the reason behind changes in the water quality in community wells. The water quality began to change in the plant as measured (eventually) by the need for twice as much chlorine and Naclo polymer in order to get an acceptable residual of chlorine. The change indicates that the well recharge had been depleted and the that wells began operating on stored water in the aquifer. This water would have been older, likely anaerobic and higher in organics and in inorganics such as iron and manganese.
Observation by Paul Walton:
I am the water operator for Noatak. I have been doing this job since 1992. Our water comes from two shallow wells at about 40 feet along the side of the Noatak River drainage. It is a located between the drainage of our creek.The Noatak River has been very low this fall. The channel has moved further east then ever before. I am thinking the low river level has resulted in our primary water source becoming lake water rather then the river. The water has an earthy taste to it makes me think lake water. On about the 18th of October the water quality began to change in the plant as measured (eventually) by the need for twice as much chlorine and Naclo polymer in order to get an acceptable residual of chlorine. I am thinking I am getting a lot of lake water with related dead fish etc as normally there would be a lot more river water in the wells. The river is coming up now because we have been getting rain. I am comfortable with the water quality but concerned about the amount (double or quadruple) of chlorine and Nalco that I am having to add to get a residual. It might be spring time before the water level is up to normal.
System Details:
On October 11th, a normal day, running two pumps at 21 gallons per hour, the Nalco injection rate was 0.0086 gallon / hr. The chlorine was 0.145 gallons per hour. My SCD reader was 20.2 and the SP was a constant rate at 20.0. My turbidity on that day was 0.022 ntu. My chlorine residual was 0.55 mg/ L out of the filter. The manganese was only 0.021. On the 18th it began to change and on the 23rd, running two pumps at 21.9 gallons per hour, the Nalco injection rate was 0.0910 gallon / hr. And I change that on manual to 0.160 gal/hr. The chlorine was 0.275 gallons per hour. My SCD reader was -38.0 and the SP was a constant rate at 20.0. My turbidity on that day was 0.028. My chlorine residual in the tank was 0.38 mg/ L, and after the filter was 0.69 mg/ L. The manganese was 0.013 ppm. I took the auto off and put it on manual. And have the Nalco at 0.160 and still got a negative reading on my SCD (-28.5), and my injection rate today is 0.280 gal/hr on the chlorine. This has never happened before in my 28 years as an operator. Paul Walton, Water Operator
Paul writes in a follow up comment:
Very cold today -3 F lakes, streams creeks freezing less run-off. Water at the river change back to normal clarity. Amazing how the hydrologic cycle can alter do to unusual warmer weather. October is the month when lakes and streams would be frozen, On the 28th of October a high of 42 degree F was recorded and rain all day, run-off from lakes streams became more acidic do to decayed vegetation on the tundra, in lakes and stream run-off. Today's temp. is -3 F Nov 6. lakes and streams freezing now. The clarity of the river water has changed back to normal. Using less Cl and Nalco to treat the water. 11-6-19
Comments from LEO Editors:
The best weather data available for the region is from the NWS station in Kotzebue, 47 miles to the south of Noatak. For the period from May 1 to October 31 the temperatures recorded in Kotzebue were higher then at any time since records began in 1897 (see graph). Precipitation was a little higher then normal for the same period, in comparison with other years. This is the first observation posted in LEO Network about measurable changes in well water quality, as a possible outcome for changes in local environmental conditions. Mike Brubaker
John Warren with Alaska Native Tribal Health Consortium writes:
The wells are shallow and are under the influence of surface water based on the treatment that is being provided. The treatment system provides for the removal of surface water contaminants including particulates and dissolved organics.A cationic polymer is being used to provide charge neutralization and subsequent coagulation of organic acids and other negatively charged contaminants.A streaming current detector (SCD) is being used to control the feed rate of the cationic polymer based on the net charge density in the coagulated water. The set point (SP) on the SCD is set to provide a very positive charge meaning the system is likely overdosing polymer (a positive SP means excess polymer and a negative SP means an under dose of polymer).Chlorine demand is fluctuating substantially because the coagulation system is not efficiently removing organics.
My comments are as follows:
The change in water quality in the wells indicates that the well recharge had been depleted and the that wells began operating on stored water in the aquifer. This water would have been older, likely anaerobic and higher in organics and in inorganics such as iron and manganese. The SCD should be set to seek a charge set point somewhere near zero. This is where optimum coagulation and removal of contaminants (such as organics that impart a chlorine demand) occurs. A negative reading on the SCD indicates that the system cannot inject enough cationic polymer to neutralize the negative charges in the water (usually associated with organic acids).
My Recommendations:
- Review SCD operation and set points. Provide thorough maintenance on the SCD including cleaning both the probe and contacts.
- Adjust the set point to near zero net charge. This will improve removal of organics and reduce chlorine demand, chlorine fluctuations and DBP production.
- Ensure the polymer feed system has the range to satisfy coagulant demand. You may be able to just increase or decrease the solution strength. Solution strength should be in the range of 1-10%. Below 1 and it degrades too rapidly and above 10% and you do not get good dispersion. Either way you are wasting costly chemical.
- If taste & odor and or inorganics is an issue, consider feeding a little permanganate when this happens.
John Monville with ANTHC writes:
After reading John Warren’s response and coordinating with Chris Cox (who previously had worked with the local RMW and operator to address the issue) I contacted the operator Paul Walton. Paul was always able to produce water within the acceptable ranges for SMCLs and MCLs, and with the recent colder weather things have returned to normal. He has no water treatment concerns currently but will keep in touch in case adjustments are needed next spring/summer when temperatures rise. 11-6-19
