Worksheet Grade 9 Math

Holloway Creek Plant: Nutrient Loading and Load Limits

A grade 9 worksheet at the fictional Holloway Creek plant, using the pounds formula to find nutrient loads and solving for a concentration that meets a permit.

Grade: Grade 9
Subject: Math
Material: Worksheet
Time: 40 min
Prep: No prep
Materials: Calculator

Standards

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Items 1, 2, and 6 carry mg/L, MGD, and the 8.34 constant through the pounds formula so the answer lands in pounds per day.

All materials for HSN-Q.A.1 →

HSA-CED.A.1 Common Core Math

Create equations and inequalities in one variable and use them to solve problems. Include equations arising from linear and quadratic functions, and simple rational and exponential functions.

How this material aligns: Item 5 has students set the pounds formula equal to a permit limit and solve the one-variable equation for the allowed effluent concentration.

All materials for HSA-CED.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will calculate nutrient load in pounds per day using the pounds formula.
Students will solve for the effluent concentration that keeps a load within a permit limit.
Students will explain why nutrients act as both a resource and a pollutant.

Vocabulary

Biosolids: Biosolids are the nutrient-rich solid material left over after sewage sludge has been treated and made safe. Many farms use treated biosolids as fertilizer for their fields.

Also: pounds formula, total nitrogen, total phosphorus, load, removal efficiency

Teacher overview

The fictional Holloway Creek plant cleans wastewater before returning it to the creek. Nitrogen and phosphorus play two roles: they fertilize crops on a farm, yet the same nutrients feed algae blooms in a stream. This worksheet has students find nutrient loads in pounds per day with the operator pounds formula, solve for the concentration that meets a permit limit, and reason about why a useful nutrient is still a pollutant here.

Holloway Creek Plant: Nutrient Loading and Load Limits — Grade 9 Math

Name: ____________________________ Date: ______________

Student Worksheet

Holloway Creek (a fictional plant) treats 4 MGD of wastewater. Use these facts:

Load in pounds per day = concentration in mg/L, times flow in MGD, times 8.34.
Removal efficiency, in percent, = (influent minus effluent) divided by influent, times 100.
One MGD equals 694 gallons per minute.

The effluent total nitrogen is 8 mg/L at the 4 MGD flow. Find the nitrogen load in pounds per day.
The effluent total phosphorus is 1.5 mg/L at the 4 MGD flow. Find the phosphorus load in pounds per day.
Influent nitrogen is 35 mg/L and effluent nitrogen is 8 mg/L. Find the removal efficiency as a percent. Round to the nearest whole percent.
The permit caps nitrogen at 250 pounds per day. Does the item-1 load meet the cap, and if not, by how much is it over?
Find the effluent nitrogen concentration that gives exactly 250 pounds per day at 4 MGD. Round to the nearest tenth.
During a storm the flow rises to 6 MGD while effluent nitrogen stays at 8 mg/L. Find the new nitrogen load in pounds per day.
Convert the plant's 4 MGD design flow to gallons per minute.
Explain why nutrients that help a farm's crops grow become a problem once they reach the creek.
A farm buys the plant's biosolids, which carry 40 pounds of nitrogen per ton. How many pounds of nitrogen are in 12 tons?
Explain why the operator and the regulator track load in pounds per day instead of only the concentration in mg/L.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: 266.88 lb/day. 8 mg/L times 4 MGD times 8.34 = 266.88 pounds per day. (8 times 4 = 32; 32 times 8.34 = 266.88.)
Answer: 50.04 lb/day. 1.5 times 4 times 8.34 = 50.04 pounds per day.
Answer: 77 %. (35 minus 8) divided by 35, times 100 = 27 divided by 35, times 100 = 77.14, about 77 percent.
Answer: No, over by 16.88 lb/day. The load is 266.88; 266.88 minus 250 = 16.88 pounds per day over the cap.
Answer: 7.5 mg/L. Solve 250 = C times 4 times 8.34, so C = 250 divided by 33.36 = 7.49, about 7.5 mg/L.
Answer: 400.32 lb/day. 8 times 6 times 8.34 = 400.32 pounds per day.
Answer: 2,776 gpm. 4 MGD times 694 = 2,776 gallons per minute.
Answer: In the creek the nutrients feed algae blooms. When the algae die and decay, that decay uses up dissolved oxygen, which can drop below what fish need.
Answer: 480 lb. 40 pounds per ton times 12 tons = 480 pounds of nitrogen.
Answer: Load combines both concentration and flow. A low concentration at a high flow can still send a large mass of nutrient to the creek, so pounds per day is the more complete measure.

Differentiation

Support

Give students the pounds formula on a reference card with the flow and the 8.34 constant already filled in, so they multiply one factor at a time. Provide the subtraction for item 3 already set up.

Extension

Ask students to write a general equation for the allowed effluent nitrogen concentration at any flow that still meets the 250-pounds-per-day cap, then use it to find the limit if the flow grows to 5 MGD.

ELL supports

Pre-teach "nutrient," "load," "permit," and "biosolids" with a two-picture card: fertilizer helping a field on one side, green algae covering a stream on the other. Provide a sentence frame for item 8: "Nutrients help ___, but in the creek they cause ___."