Call Before You Dig!

Eric Regensburger

Montana DEQ

eregensburger@mt.gov

Method for EstimatingAttenuation of Nutrients

from Septic Systems(MEANSS)

(OR THE ARTIST FORMERLY KNOWN AS “SNoRES”)

Method for EstimatingAttenuation of Nutrients

from Septic Systems(MEANSS)

(OR THE ARTIST FORMERLY KNOWN AS “SNoRES”)

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……

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)

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

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

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

Percent Nitrogen Load

Reduction

Soil Type @ Drainfield

Soil Type within 100’ of surface

water

Distance to surface water

(ft)

0 A A 0 – 100

10 B   101 – 500

20 C B 501 – 5,000

30 D C 5,001 – 20,000

50   D 20,001+

Stream

Drainfield

Group B Soil

Group C Soil

450 ft

100 ft

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

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

MEANSS RESULTS

Watershed

# Septics Used in Analysis

% TN entering surface water

Lower Gallatin 15,871 56Bitterroot 15,934 33Little Blackfoot 326 47Flint Creek 1,623 36Helena 9,090 48Bison Creek 74 29Dayton Area 390 66

THE END ….