Call Before You Dig!

1. Call Before You Dig!

2. Method for Estimating Attenuation of Nutrients from Septic Systems (MEANSS) (OR THE ARTIST FORMERLY KNOWN AS “SNoRES”) Eric Regensburger Montana DEQ eregensburger@mt.gov

3. WHY MEANSS?? • Estimate septic loading for TMDL’s • Estimate septic loading for Nutrient Trading (DEQ-13) • Need for a simple method that uses site-specific info known to control denitrification • Lack of available tools for estimating septic contributions to surface water……

4. OTHER TOOLS • ArcNLET: GIS based, ground water travel time, user-defined denitrification • STUMOD: Spreadsheet, detailed chemical/physical process, can use all default or site-specific parameter, N reduction below drainfield only • SWAT: Complex model with biozone function (N reduction below drainfield only), can add user defined denit. rate • WAG – Wild A#% Guess (my favorite)

6. PARAMETERS • Three Variables: • Hydrologic Soil Group (HSG) at drainfield • Distance to nearest perennial surface water • HSG in 100 foot riparian buffer • Variables receive %N reduction score • Add up the 3 values for total reduction • Assumes the complete volume of effluent reaches surface water (SW) • Assumes simple flow direction to SW

7. DATA SOURCES • Drainfield location from GIS: search “Montana Structures Framework” (drainfield location ~ residence) • HSG is from NRCS STATSGO(2) OR SSURGO • HSG used to classify runoff potential • 4 HSGs – A,B,C,D: low to high clay content (<10, 10-20, 20-40, >40 %). • Distance to receiving/perennial SW is from GIS

8. A LITTLE MORE DETAIL….. • Denitrification occurs in soils with high organic content, anoxic, and time for reaction to occur >>> HSG best commonly available data to estimate that. • Travel distance easier to measure than travel time. • Improve MEANSS accuracy: • Measure soil carbon content • Measure travel time instead of distance • Accurate flow direction for distance

10. Stream 100 ft 450 ft C soil @ d.f. = 20% B soil @ riparian =20% 450 ft. to stream = 10% Reduction: 20+20+10=50% Group B Soil Group C Soil Drainfield

11. COMPARISONS/VALIDATION • Compared to 5 studies that measured N in ground water • Montana(2), Wisconsin(2), Nevada(1) • MEANSS estimated N load was 68%, 74%, 82%, 83% and 120% of the comparable loads measured in studies. • In process of validating to a SWAT model for Prickly Pear drainage south of Montana City

12. MEANSS RESULTS

13. THE END ….