Interactive Nitrogen Loading Calculators

Interactive Nitrogen Loading Calculators

We have created this webpage and subpages of interactive nitrogen calculators so that town officials, managers, scientists, engineers, and the public can quickly estimate and nitrogen loading contributions from various sources. You may have to tell your web browser to allow scripts to allow this page to work correctly. Please report errors or send comments about this page to Joe Costa.

The detailed calculators on the subpages are just unprotected spreadsheets where you can enter data, and if you want, save them to your computer. Refresh your browser to start again if you accidentally delete a formula cell.

Javascripts / ActiveX must be allowed on your web browser for this page to work correctly.

Where you looking for the Wareham Board of Health N-Calculators? The values obtained with those calculators differ somewhat from these calculators to better match draft regulations being considered by a Wareham Board of Health workgroup.

Wastewater Facility (or septic system) Nitrogen Loading

Important: Enter the properties water use that is presumed to discharge to the septic system. For example, in the MEP model, 90% of residential water use is presumed, on average, to discharge to the wastewater system.

STF Load Calculator (use no commas, just enter values in volume and concentration)
Volume: gallons per day Concentration: ppm or mg/l tip
Total Load: kg per yr Total Load: lbs per yr
Total Load: kg per day Total Load: lbs per day

Use this quick calculator, or use the more detailed Wastewater Facility N Loading calculator. For septic systems, the MEP assumes that 90% of the residential water use is discharged at a TN concentration of 26.25 ppm.

Residential and Commercial Parcel Nitrogen Loading Calculator

For commercial properties, use one-half of design flow of the system to estimate loadings. If you do not know design flows, you can estimate them with our Title 5 Design Flow Calculator.

Parcel Size: acres Calc. Method:
MEP method is based on flow, but you can approximate with occupancy. Septic System ppm:
Winter Occupancy: persons Summer Occupancy: persons Wastewater Flow: gpd avg MEP assumes 90% of annual water use goes to septic system.
Lawn Area: sq. ft Roof Area: sq. ft Paved Area: sq. ft
Septic Load: lbs per year % of total
Lawn Load: lbs per year % of total
Impervious Load: lbs per year % of total
Natural Landscape load: lbs per year % of total
Total Load: lbs per year

Use this quick calculator, or use the more detailed Single Parcel Loading Calculator. The values preloaded into this calculator are typical for residential parcels. For Commercial Parcels, the biggest uncertainty is wastewater flow. See discussion below for guidance.

Subdivision Nitrogen Loading Calculator

Subdivision Calc. Method:
Just enter subdivision size and zoning, we'll estimate the rest. After you populate fields with defaults, you can change scenarios.
Wastewater Calc. Method:
MEP method is based on flow, but you can approximate with occupancy. Septic System ppm:
Subdivsion Size: acres Zoning: min lot size (ac) Just enter subdivision size and
minimum lot size for a quick estimate.
Winter Occupancy: persons Summer Occupancy: persons Wastewater Flow: gpd avg Total Lots: lots
Total Lawn Area: sq. ft. Total Roof Area: sq. ft. Total Road and Lot Paved: sq. ft.
Septic Load: lbs per year % of total
Lawn Load: lbs per year % of total
Impervious Load: lbs per year % of total
Natural Landscape load: lbs per year % of total
Total Load: lbs per year

The values preloaded into this calculator are typical for subdivisions (10% area for roads, 1500 sq. ft. paved per lot, 1500 sq. ft. roof per lot, and 5000 sq ft lawn per lot).

Commercial and Residential Parcel Flow Estimation

When scientists are estimating watershed nitrogen loads to establish TMDLs, to the maximum extent possible, they want to use actual site-specific information. In the calculation of residential wastewater loads, water use records, or actual seasonal occupancy, are the best basis for estimating loads. For example, average water use per person discharging to the sewer line typically averages about 50 to 60 gpd, and the average water use of a single family home is typically ranges between 130 and 180 gpd. This volume reflects the fact that in most watersheds around Buzzards bay, occupancy typically ranges between 1.9 and 2.5 persons per home.

When managers are trying to regulate nitrogen through the permitting process, regulations are adopted that include either a “margin of safety” adopt a worse case design. For example, in the case of Title 5 onsite wastewater system design, each person is assumed to discharge 55 gpd, and each bedroom is assumed to have up to 2 persons in it. Therefore, a 4-bedroom home in Massachusetts is required to have a leach field and tank sized appropriately for 440 gpd. Of course, the occupancy of most homes will seldom reach two persons per bedroom, but when they do, a system designed under Title 5 will handle that flow. Some properties, like restaurants, may only approach design flows during summer tourism periods, or their busiest days.

For any class or type of property, it is difficult to predict future actual flows. In the case of nitrogen management regulations, nitrogen loading worksheets employed by regulators typically employ a wastewater flow volume for loading calculations somewhere between actual typical existing flows and Title 5 design limits (the Cape Cod Commission does this). This approach gives a suitable margin of safety for future potential increases. This approach is justifiable because for decades, many areas in the Buzzards Bay watershed have shifted from seasonal to year round occupancy (an more tourism related commercial establishments have become year round).

For many commercial and institutional properties, using one-half of design flows will give a reasonable estimate of average actual flows, with a margin of safety. If you do not know the design flow of the system, consult your municipal board of health, or use our Title 5 Flow Calculator. Generally, wastewater discharges from private properties are under 10,000 gpd, otherwise a state groundwater discharge permit is required.