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3.e Anderson Erickson Memo Updated April 2019= BO ETON 8#- NA P= N K , Consulting Engineers & Surveyors � 12224 Nicollet Avenue • Burnsville, MN 55337 Phone (952) 890-0509 • Fax (952) 890-8065 www.bolton-menk.com MEMORANDUM Date: 04/03/19 To: Ryan Goodman, P.E. From: Jacob Humburg, P.E. Subject: A/E Lift Station and Drain field Scandia, MN NC® The Anderson/Erickson drain field was designed to treat up to 6,700 gallons per day. A Scandia City ordinance states that new connections to this treatment system are not allowed without sufficient capacity. Sufficient capacity is defined as 90% or less of the 6,700 gallons per day flow as measured over a peak 3 -day period, and peak flow on a monthly basis being less than 90% of a target monthly limit of 5,300 gallons per day. Evaluation is done over a minimum 12 - month period. The lift station contains two — 5 HP grinder pumps designed to deliver 50 gallons per minute. Based on drawdown testing, pump no. 1 can produce 62.6 gpm and pump no. 2 can produce 70.5 gpm. Analysis of historic pump run data show is shown in Table 1 below. Table 1: Historic Pump Run Times Year Peak Day Flow (gal/day) 2017 6,592 2018 6,921 2019 10,413* *Data only available through March Typically, the highest flows occurred between April and July for each year, with peak flows occasionally exceeding the design capacity of 6,700 gallons per day of the system. Peak flows for each year were determined by first finding the peak day flow for the entire year. The peak flow was then determined by taking the three-day average which included the peak day and both the day prior to and after the peak. The calculated peak flows in 2017 and 2018 do not exceed the Anderson Erickson Drain field Evaluation DESIGNING FOR A BETTER TOMORROW Bolton & Menk is an equal opportunity employer. treatment facility's capacity, while that in 2019 does. This is presumed to be due to excessive precipitation and snow melt during a short time period in March of 2019. On a day-to-day and month -by -month basis, it was not a common occurrence for flows to exceed the design capacity over the last two years. Using the historic flows, an estimate of how many houses can be connected to the system can be determined. Septic systems are designed based on volume of water per person per bedroom in a house. The design standard for Minnesota is 150 gpd/bedroom. This assumes that there are two people per bedroom. Using this criteria, and assuming each house has four bedrooms, the total flow from each house would be 600 gpd into the system. Based on the City ordinance, sufficient capacity would not be available if peak flow over a 3 -day period averaged over 90% of the 6,700 gallons per day design flow (over 6,030 gallons per day). There have been a number of instances in recent years when this value has been surpassed. Additionally, there is at least one home still being constructed which has been approved for connection to the system, and multiple other homes on the system which only have single occupants, meaning that greater flows from them should be expected in the future. Taking all of this information into account, it is not recommended that additional new residences be approved for connection to the Anderson/Erickson drainfield system at this time. Anderson Erickson Drain field Evaluation DESIGNING FOR A BETTER TOMORROW Bolton & Menk is an equal opportunity employer. • = BO ETON 8L M F= N K Consulting Engineers & Surveyors 12224 Nicollet Avenue • Burnsville, MN 55337 Phone (952) 890-0509 • Fax (952) 890-8065 www.bolton-menk.com Table 3: 2017 A/E Flow Month Avg. (gal/day) Peak (gal/day) January 2243 3567 February 2977 7986 March 2156 4416 April 2293 3461 May 3338 7187 June 2391 3053 July 3163 5355 August 2610 4525 September 2463 5827 October 2047 3570 November 2080 3617 December 2646 4416 Average/Max 2534 7986 Table 4: 2018 A/E Flow Month Avg. (gal/day) Peak (gal/day) January 2727 3990 February 2697 3993 March 2530 18791 April 3702 7140 May 3362 5590 June 2826 3993 July 2661 5922 August 2214 3194 September 1988 7939 October 1673 2819 November 1759 3194 December 1845 2803 Average/Max 2499 18791 Anderson Erickson Drain field Evaluation DESIGNING FOR A BETTER TOMORROW Bolton & Menk is an equal opportunity employer. NCS Table 5: 2019 A/E Flow Month Avg. (gal/day) Peak (gal/day) January 2754 3390 February 2409 3194 March 4966 18182 Average/Max 3376 18182 Anderson Erickson Drain field Evaluation DESIGNING FOR A BETTER TOMORROW Bolton & Menk is an equal opportunity employer.