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

Introduction

Failures are a result of:• Improper maintenance

• Overuse of water

• Improper design/installation

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 Annual CostPermanent residence with tank, pump & soil

treatment system$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

Septic tank capacity: dwellings

Number of

Bedrooms

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)

Sludge

Clear Zone

Scum

Dual Chamber Septic Tank

Hydraulic Retention

Time

Devices for measuring sludge

Sim/Tech TruCore Draw string closes

the openingDipstick - 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 systemsMost 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

0

0.2

0.4

0.6

0.8

1

12/4/1986 5/26/1992 11/16/1997 5/9/2003

Date

Nit

ra

te (

mg

/l)

Nitrate Up Gradient

Nitrate Down

Gradient

0

2

4

6

8

10

12

14

16

18

20

1980 1985 1990 1995 2000 2005 2010 2015

Secc

hi D

isk

Rea

din

g (f

t.)

Year

Change in Water Clarity in Otter Tail Lake

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 projectLooked 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

Homeowner Survey

Questions included: • property use frequency

• average number of visitors

• 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)

• 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

Maintenance recordsObtained from district

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

All Seasons Part-time5%

N/A1%

Warm Months Part-time

60%

Full-time34%

Residence Typeof Respondents

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

ResultsProperty Use

Household Factor(response options)

Septic Tank Cleaning Frequency

Average Time Between Septic Tank Cleanings

Use (permanent/seasonal-summer/seasonal-all

year)

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

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 50oF 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

Occupancy

Household Factor(response options)

Septic Tank Cleaning Frequency

Average Time Between Septic Tank Cleanings

Adults* (#) 0.08

Children* (#) 0.07

Bedrooms (#) 0.78 0.79

Home Characteristics

Household Factor(response options)

Septic Tank Cleaning Frequency

Average Time Between Septic Tank Cleanings

Well Water (yes/no)

0.26

Water Quality Test (yes/no)

0.09 0.71

Sewer Backups (yes/no)

0.20 0.99

Standard Household AppliancesHousehold Factor(response options)

Septic Tank Cleaning FrequencyAverage Time Between Septic Tank

CleaningsGarbage Disposal

(yes/no)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)0.90 0.62

Household Chemical UseHousehold Factor(response options)

Septic Tank Cleaning FrequencyAverage Time Between Septic Tank

Cleanings

Additives to Septic(yes/no)

0.58 0.34

Antibacterial Products(yes/no)

0.40 0.26

Long Term Prescription Medications

(yes/no)0.20

Extra Household AppliancesHousehold Factor(response options)

Septic Tank Cleaning Frequency

Average Time Between Septic Tank Cleanings

Water Softener

(yes/no)Water Softener to Septic

(yes/no)0.94 0.78

Hot Tub (yes/no)

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)0.64 0.41

Other Water Treatment Device

(yes/no)0.07 0.10

Other Water Treatment Device to

Septic (yes/no)0.79 0.90

Fixture Leaks

(yes/no)

Factors that had an impactWater 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?

Wastewater Engineering – Treatment and Resource Recovery

TSS 33% and BOD 24% an increase

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