Presented to the 2018 MN Water Resources Conference Oct 16 - 17, 2018

Regional Progress in Water Quality ---- A Trend Analysis for Three Major Rivers in the

Twin Cities Metro Area (1976 – 2015)

Hong Wang, Erik Herberg, Judy Sventek, Kent Johnson and John Barland

Metropolitan Council Environmental Services, St Paul, MN

Outline

• Project objectives and scope

• Method

• Select water quality trends across region

• Conclusions and recommendations

• Assess how the river water quality has changed during the last 40 years

• Understand if these changes occurred in response to pollution reduction efforts

• Identifies current water quality issues and needs for improvement

• Make conclusions and recommendations for decision-making and future actions

ObjectivesObjectives

• River monitoring program and sites−Started in 1976−Monitors various

variables−Covers 150 river

miles

• Select parameters− TSS, BOD5

− TP, TN, nitrate, ammonia

− Chl-a, fecal coliform, − Chloride

Study Scope

• Non-Flow-Adjusted Trends ---- The overall trends resulting from both natural and

human factors

• Flow-Adjusted Trends ---- The trends without impact of natural flow variabilities

• Non-monotonic Trend Model ---- QWTREND:

Log C(t) = M + SEAS + SRA + TND + PRDEV + NOISE

Flow-Adjusted Water Quality Trend

• Akaike Information Criteria (AIC)

AIC = (-2lnL) + (2*Parameters)

• p-value

p =1-pchisq((-2lnL)initial - (-2ln L)linear, Trends)

• Critical p-value: 0.1 - 0.01

Tests for Trend Significance

Total Suspended Solids Trend

Changes in water quality• Decreased significantly across

the region− Miss R: 34% - 74%− MN R: 37%-51%− St. Croix R: 48% - 75%

Influencing Factors• Better farming practices and

land management • Improvements in stormwater

management• TMDLs and BMP

implementations• Reduced discharges from

WWTPs

The Metro WWTP Discharge Flow and TSS

• Secondary treatment Applied in 1966

• TSS Reduced by 98%

− 128 to 3 mg/L during 1966-2015

− 60 mg/L to 3 mg/L during 1976-2015

Changes in water quality• Decreased significantly across

the region− Miss R: 36% - 59%− MN R: 44% - 51%− St. Croix R: 26% - 32%

Influencing Factors• P bans in detergents and lawn

fertilizers• Better farming and land

management practices• TMDLs and BMP

implementations• Bio-P removal technology in

WWTPs

Total Phosphorus Trend

The Metro WWTP Discharge TP

• Bio-P removal technology started to apply in 2000

• TP reduced by more than 90% during 2000 - 2015

− Concentrations: 3.4 to 0.3 mg/L

− Loads: 1,067 to 90 tons/year

Changes in water quality• Decreased significantly across

the region− Miss R: 66% - 98%− MN R: 88% - 61%− St. Croix R: 59% - BRL

Influencing Factors• Better management of feedlots

and manure uses in agricultural areas

• Improved urban stormwater management (such as CSO, MS4)

• TMDLs and BMP implementations

• Advanced treatment technologies in WWTPs

Fecal Coliform Trend

Changes in water Quality• Increased significantly across

the region except in the MN R at Jordan − Miss R: 181% - 302%− MN R: PT - 21%− St. Croix R: 24% - 67%

Influencing Factors• Change in land use• Increases in fertilizer use• Expansion in livestock and

poultry production• Growth in population• Increase in industrial activities• Conversion of harmful

ammonia in WWTPs to nitrate

Nitrate Trend

Changes in water Quality• Increase significantly across

the region except in the MN R at Ft. Snelling − Miss R: 45% - 86%− MN R: 8% - NT− St. Croix R: 110% - 143%

Influencing Factors• Runoff from winter de-icing

salt use• KCl fertilizer uses• Livestock production• WWTP discharges (water

softening, disinfection, human excreta)

• Septic systems• Ground water contribution

Chloride Trend

• Decreased trends found for TSS,TP, ammonia, fecal coliform and BOD5 over assessment period

• Increased trends for nitrate, TN and chloride

• Mixed trends for Chl-a

Conclusions

• Establish a water quality standard by state to reduce N loads

• Educate on efficient chloride and fertilizer uses

• Maintain working relationships with citizens, local WMOs, state and federal agencies to control water pollution

• Continue monitoring and assessing river water quality to determine if observed improvements can be sustainable, and if improvement goals can be achieved for parameters with declining WQ

Recommendations

Question?

Dr. Hong WangPrincipal Environmental Scientist

Metropolitan Council Environmental Services hong.wang@metc.state.mn.us

P. 651.602.1079 | F. 651.602.1130390 North Robert Street, St. Paul, MN55101

www.metrocouncil.org

You can find the river report at: www.metrocouncil.org/river-assessment

Thank You!