2016-04-29_HYDROLOGY - M1977342 - Laserfiche WebLink

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Water Systems Engineering, Inc. 785.242.6166 http://www.h2osystems.com casing or well seal, although an inspection of the well casing and well head should be conducted to confirm this. Recommendations: No information was presented on the performance of the well but considering the high level of biological congestion as indicated by the extreme amount of resuspended iron, extreme ATP cell counts, and heavy amounts of iron oxide and biofilm identified within the sample, well rehabilitation should be considered. The process should begin with pulling the pump and mechanically scrubbing the interior of the well using a surge block or brush. This will help remove loose scale, rust deposits, and biofilm which can provide a protective environment for microorganisms. Once the entire column has been scoured, bail or pump the disrupted material and any fill from the well, starting at the bottom. Once clear, a combined chemical and mechanical treatment can continue. Chemical treatment should begin by placing a solution of 6% phosphoric acid combined with 2% dispersion polymer such as Layne's QC-21 or Johnson Screen's NW-310 biodispersant below the static water level and aggressively swabbing or surging it into the producing zones for approximately four minutes per foot of screen. The recommended biodispersant is NSF approved for use in potable wells and is recommended to enhance the activity of the acid in cleaning biomass and extending the efficiency of the acid in attacking mineral scale. The use of phosphoric acid is recommended over hydrochloric acid since phosphoric acid is less aggressive than hydrochloric acid but will achieve the same level of reaction. This produces less reaction with the steel well and pump components resulting in fewer iron ions being released which can provide a food source for iron oxidizing organisms. Also, phosphoric acid will have a less violent reaction than hydrochloric acid with any carbonates that may be present in the well. The acid and biodispersant solution will aid in breaking down the biofilm that surrounds and protects the organisms, allowing for better penetration of the disinfection solution as well as removing any mineral scale present. If possible, leave the acid solution in the well overnight while maintaining a pH of 3 or less. Once the well has been effectively purged of all acid residue and is pumping clear of visible turbidity, disinfection should be carried out utilizing a pH adjusted chlorination at a 300 ppm chlorine level with a targeted pH range of 6.5 to 7.0. The treatment volume of the disinfection solution should be equivalent to 3 times the well volume and evenly distributed throughout the producing zones. This larger volume is utilized to flood the borehole with the disinfection solution in order to increase the effectiveness of treatment as well as the effective treatment zone. Utilization of a chlorine enhancing chemistry such as Layne's Oximate or Johnson's NW- 410 for pH control is strongly advised to improve disinfection as well as to increase the treatment zone. The disinfection solution should be surged into the well for approximately four minutes for each foot of producing zone. Monitor the chlorine level during disinfection and add additional chlorine to maintain at least a 100 ppm chlorine level during disinfection. For acid treatments, mix the chemicals in this order: water, acid, biodispersant. Mix lightly. If during acid treatment, the pH rises to a level above 3.0, add additional acid and water at the rate of 2 gallons acid and 1 gallon water. No additional dispersant should be needed. For the chlorine treatment, mix the chemicals in this order: water, chlorine enhancer, check the pH (below 5.5), add chlorine. Mix lightly. During disinfection, if the chlorine residual has dropped 20175.w.pw.p.MLGW-ACR Page 5 of 6