Otter Tail Water Management District Septic System Use and Maintenance Evaluation October 23, 2017 Dr. Sara Heger sheger@umn.edu septic.umn.edu
1. Professional Training Designers, Inspectors, Maintainers, Installers 2. Research and Demonstration 3. Homeowner Operation & Maintenance 4. Small Community Wastewater Solutions
Failures are a result of: Improper maintenance Overuse of water Improper design/installation Introduction Septic systems recycle wastewater back into the natural environment Proper operation and maintenance of systems ensures: wastewater is treated efficiently and thoroughly prevents costly repairs and replacement
Otter Tail Water Management District 55-square mile area with 1,700 septic systems District is responsible for maintaining septic systems Formed in 1981 to ensure proper sewage treatment at an affordable long-term cost for the community US-EPA initiated and funded large portion of project in 1984 to upgrade and inspect the existing 1,250 septic system Of the 1,250 inspected, 850 new individual onsite & cluster systems were installed
Why was District formed? Residents noticed reduced water quality Identified several inputs/impacts to lake Wastewater Agricultural runoff Reduction in native shore land GOAL: Properly managed wastewater treatment at an affordable long term cost which would maintain the rural character of the community
Why upgrades needed? Small lakeshore properties Sandy soils with rapid transmissivity to lake Many existing septic systems installed: Too close to lake Too deep in regard to elevation of lake
District powers and responsibilities Set fee structure to support District activities Levy taxes to property tax statements Needed 10% of the time Write and enforce ordinance Inspection and monitoring program Issue compliance orders Including interest and penalties
Project history 1978 -- Studies started Education program which led to 85% acceptance of project 1981 -- District formed 7 member board appointed by County board 1981-82 -- Environmental Impact Study completed 1982-84 -- Final project design & public hearings 1984 -- Construction started 1985 -- Installations completed
Determined status of all systems High % non-complying 250 300 "couldn t comply" 200 "not as bad" Identified potential cluster sites
1984 & 1985 Upgraded 850 sites 16 cluster systems - 260 cluster hook ups 590 Individual systems 350 other systems: Tanks pumped Inspected New tank covers installed
Passive maintenance program System is under District jurisdiction HO responsible for all maintenance & repairs District inspects tanks for pumping, drain field failures, lift pump operation District notifies HO to pump & provides reply form when completed Can switch to active plan criteria to meet Maintain records/history of system Information/education on user best management practices
Active maintenance program District maintains from the tank & beyond Pumping & repairs to drain field and lift Unless HO is negligent excessive water use, modifying/damaging system Changes other than normal maintenance & repairs are at owner s expense Cannot switch to passive plan Clusters must be on active plan
Fees for management Passive Administrative fee only Dwelling $40 $50 Cluster or business user $60 + $5 per additional tank and duplex unit Business $40-$300 Active System type Dwelling with and without a pump Cluster versus dwelling Seasonal versus permanent Dwelling versus business
Annual cost of active plan Type of Active Facility Permanent residence with tank, pump & soil treatment system Annual Cost $239 Permanent residence with tank & soil treatment $179 Seasonal residence (based on 3 months average) 30% of permanent Permanent cluster system (single or multiple units) $207-267 Seasonal cluster system $253 Resorts and businesses $170 - $2200
Preventative maintenance inspections Includes tanks, lifts, drain fields Measurement of sludge and scum and pumping if needed. Permanent residences every 2 years Seasonal residences every 3 years
Number of Bedrooms Septic tank capacity: dwellings Septic Tank Capacity (GPD) With Garbage Disposal (GD)* (GPD) With GD & Pumping from Basement* (GPD) 3 or less 1000 1500 1500 4-5 1500 2250 2250 6-7 2000 3000 3000 8 or 9 2500 3750 3750 * Must have multiple tanks or compartments
Cleaning frequency impacted by many factors: 1. Household size 2. Total wastewater generated 3. Volume of solids in wastewater 4. Septic tank size Need further analysis of the impact that household practices have on maintenance needs How do household practices impact longevity and function of septic system?
When do tanks need maintenance? 1. Greater than ¼ of the initial liquid capacity is occupied by floating and settled solids OR 2. The top of the sludge layer reaches 12 inches below the outlet baffle OR 3. Scum is 3 inches above the bottom of the outlet baffle Must be evaluated every three years or cleaned (Minnesota Rules definition)
Dual Chamber Septic Tank Scum Hydraulic Retention Time Sludge Clear Zone
Devices for measuring sludge Sim/Tech TruCore Draw string closes the opening Dipstick - with ball valve Sludge Judge - check valve on the end
Financing Initial capital investment Grant expenditures for the installation of the initial systems were $5,621,700 $4700 per connection $244,660 paid by county and landowners On-going operational costs Annual operating budget is approximately $140,000 $40- $2,200 per property depending upon system/use
Types of systems Most systems consist of 1,000-gallon first compartment followed by 500-gallon second compartment Types of septic systems found throughout the district: On-site mounds, pressure beds, gravity trenches, gravity beds, and community cluster drainfields
A success story Since 1986, only 40 of the 1,680 septic system have been replaced Failure rate of only 2.4% Majority gravity beds An additional 120 older pre-district systems have been replaced or upgraded Effective inspection and maintenance program Lift stations cleaned every 3 years Septic tanks inspected every 2-3 years, depending on residence type
Ground & water quality impacts Groundwater monitoring wells Originally 120 were required Reduced to less then 30 due to no noticeable impacts MPCA is considering dropping permit/wells all together due to lack of impacts Lake water quality monitoring Phosphorus levels Water clarity
Nitrate Data for Cluster Drainfield 73 Nitrate (mg/l) 1 0.8 0.6 0.4 0.2 0 12/4/1986 5/26/1992 11/16/1997 5/9/2003 Date Nitrate Up Gradient Nitrate Down Gradient
Secchi Disk Reading (ft.) 20 Change in Water Clarity in Otter Tail Lake 18 16 14 12 10 8 6 4 2 0 1980 1985 1990 1995 2000 2005 2010 2015 Year Formation of District
Growth? More development? Development has been minimal, which was one of the goals Amount of seasonal versus permanent has not changed Overall total connections have increased ~10% over 30 years
Research project Looked for correlations between household practices and the function of septic system to identify factors that impact septic tank cleaning frequency Homeowner surveys were coupled with septic tank cleaning records from the District Cleaning categories: 1. Septic tank cleaning frequency # of years the tank was cleaned; e.g., 2 (pumped in 1992 & 2001) 2. Average time between septic tank cleanings # of years between tank cleanings; e.g., 3 years (pumped in 2000 & 2003) Kruskal-Wallis H statistical test for data set that is not normally distributed Ranks data based on averages so the different groups can be compared
Questions included: property use frequency average number of visitors Homeowner Survey the presence and use of water-related household appliances (garbage disposal, dishwasher, etc.) the presence of water-related activities and/or equipment (hot tub, sump pump, outdoor drains, etc.) discharge to the septic tank antibacterial products use of medications Survey response rate: 27% (443/1618)
Maintenance records Obtained from district Management plan type (active vs. passive) Residence type (permanent vs. seasonal) Scum measurement Sludge measurement Years tank cleaned Installation date System type Drainfield size Years lift station cleaned
Results District Composition 440 permanent residents (26%) 1260 seasonal residents (74%) 28 household factors * 2 cleaning factors 56 tested factors 17 factors found to have an impact Full-time 34% Residence Type of Respondents All Seasons Part-time 5% N/A 1% Warm Months Part-time 60%
Household Factor (response options) Use (permanent/seasonalsummer/seasonal-all year) Property Use Septic Tank Cleaning Frequency Average Time Between Septic Tank Cleanings Average Number of Septic Tank Cleanings Warm-month part-time residents: 2.4 Full time residents: 3.2 All season part-time: 2.7 Average Time Between Septic Tank Cleanings Warm-month part-time residents: 8.9 years Full time residents: 4.9 years All season part-time: 7.9 years Results Significant impact from a factor on septic tank cleaning is indicated by The number listed is the p- value, which signifies a statistically significant factor is less than 0.05. Large p-values mean the factor was not significant on tank cleaning frequency
Can you pump a tank too much? Yes, BUT this is not typically our problem After cleaning tank it can take several months for tank microbes to get fully established Affected by temperature For every 50 o F increase in temperature the microbial activity doubles Become dormant from 35-39 F. Since tanks are buried, septic tank effluent on average is approximately 10-20 F warmer than the ambient ground temperature Cleaning recommended late spring early fall
Household Factor (response options) Occupancy Septic Tank Cleaning Frequency Average Time Between Septic Tank Cleanings Adults* (#) 0.08 Children* (#) 0.07 Bedrooms (#) 0.78 0.79 Household Factor (response options) Well Water (yes/no) Water Quality Test (yes/no) Sewer Backups (yes/no) Home Characteristics Septic Tank Cleaning Frequency 0.26 Average Time Between Septic Tank Cleanings 0.09 0.71 0.20 0.99
Household Factor (response options) Garbage Disposal (yes/no) Standard Household Appliances Septic Tank Cleaning Frequency Average Time Between Septic Tank Cleanings 0.90 0.31 Garbage Disposal Use (often/rare/never) 0.13 0.38 Dishwasher (yes/no) Dishwasher Weekly Loads* (#) 0.51 0.74 Washing Machine (yes/no) Washing Machine Weekly Loads* (#) 0.57 0.91 Detergent Type (liquid/powder/both) Household Factor (response options) Additives to Septic (yes/no) Antibacterial Products (yes/no) Long Term Prescription Medications (yes/no) 0.90 0.62 Household Chemical Use Septic Tank Cleaning Frequency Average Time Between Septic Tank Cleanings 0.58 0.34 0.40 0.26 0.20
Household Factor (response options) Water Softener (yes/no) Water Softener to Septic (yes/no) Hot Tub (yes/no) Extra Household Appliances Septic Tank Cleaning Frequency Average Time Between Septic Tank Cleanings 0.94 0.78 Hot Tub to Septic (yes/no) 0.14 0.71 Sump Pump (yes/no) 0.92 Sump Pump to Septic (yes/no) 0.59 0.72 Floor/Roof Drains (yes/no) 0.09 0.25 Floor/Roof Drains to Septic (yes/no) Other Water Treatment Device (yes/no) Other Water Treatment Device to Septic (yes/no) Fixture Leaks (yes/no) 0.64 0.41 0.07 0.10 0.79 0.90
Factors that had an impact Water softener Adds additional water to the system Potential for impact from the amount of salt in recharge Use Permanent vs. seasonal home use Washing machine Additional water and lint Fixture leaks Additional water Dishwasher Additional water and solids (many organics that do not break down easily)
Factors that had an impact Hot tub - hydrologic surges leading to tank turbulence Well water - those paying for city water may have higher awareness of water usage compared to those who have well water Adults - more people, more solids Sump pump - extra water to the septic system
Factors that had an impact Long term prescription medications Disturbs bacteriological balance in the tank, resulting in decreased solid breakdown Children More people, more solids
Characteristics with little data When few homes have a certain practice there is no real way to determine influence For example: In home businesses - N = 9 Water softener NOT to septic - N =9 Additives N= 16
Garbage disposal - effluent quality increase? TSS 33% and BOD 24% an increase Wastewater Engineering Treatment and Resource Recovery
What does all this mean? Managing systems will increase longevity Evaluating conventional systems every 2-4 year is valuable: Find problems in the tank missing baffles, cracks, corrosion, missing caps, broken lids Confirm alarm is working in the pump tank Confirm soil treatment area is still working as designed Identify problems related to use: products in the home, vegetation/compaction, surges, etc. More jurisdictions are moving towards measuring sludge/scum versus mandatory pumping Particularly with increasing dumping fees and challenges with land application
QUESTIONS & MORE INFORMATION Paper posted on NOWRA website septic.umn.edu H2OandM.com sheger@umn.edu