Foundry Sand Reuse in Idaho

Planning to reuse spent foundry sand in Idaho? This guide covers the rules that apply, the tests that decide how the sand can be managed, and what to check with DEQ before the sand is reused.

Key terms

Spent foundry sand

Foundries bond silica sand into molds and cores for casting metal. The sand is reused many times in the plant. Spent foundry sand is molding and core sand that can no longer make molds or cores.

Green sand and chemically bonded sand

Green sand is bonded with clay, usually bentonite, plus water and additives such as carbon. Chemically bonded sand uses resin binders. Most cores are chemically bonded. The binder system affects what the spent sand contains.

Beneficial reuse

Beneficial reuse puts a waste material to productive use instead of disposing of it. Idaho’s Solid Waste Management Rules use other terms. For waste reuse, the rules define “recyclables” and “recycling.”

TCLP

The Toxicity Characteristic Leaching Procedure (EPA Method 1311) measures how much of certain contaminants can leach from a sample. It is one part of deciding whether a waste is hazardous.

What’s in your spent sand?

Spent sand carries what the casting process added: binder residue, metal fines, and burnt core material. The alloy matters most. Sand from iron, steel, and aluminum foundries is the most commonly reused. Sand from leaded brass and bronze foundries is often regulated as hazardous waste.

Keep each stream separate. Baghouse dust, shotblast fines, cupola slag, broken cores, and core room sweepings need their own evaluation. Mixing them into spent sand can change how the whole load is managed. Track the alloys cast, the binder system, and any process changes.

Idaho’s solid waste rules

Idaho regulates solid waste under the Solid Waste Management Rules, IDAPA 58.01.06. The rules have no separate reuse approval and no provision written for foundry sand. These provisions shape how spent sand can be reused:

1. Recyclables and recycling. Recyclables are used, end, or waste products with useful properties that can be reused. Recycling means reclaiming solid waste for an industrial process that turns it into a new product. The material loses its original identity (IDAPA 58.01.06.005.28–29).
2. Recycling centers. The rules do not apply to recycling centers (001.02.b). A recycling center receives recyclables, then sorts, bales, loads, or physically alters them and sends them to markets (005.30).
3. Inert waste. The rules do not apply to inert waste unless it is mixed with more than incidental quantities of regulated waste (001.01.b). Inert waste is noncombustible, nonhazardous, and non-putrescible. It is likely to keep its physical and chemical structure and has a de minimis potential to generate leachate under expected conditions of disposal (005.14). Confirm with DEQ before relying on this exclusion.
4. Solid waste facilities. The rules classify facilities as below regulatory concern (BRC), Tier I, Tier II, or Tier III (009). Tier II and Tier III facilities need DEQ approval before construction and again before accepting waste (012, 013).

Stockpiles have a limit. Speculative accumulation covers stockpiles of materials or recyclables awaiting reuse or disposal (005.37). It applies when half the material is not reused or disposed of by the end of the calendar year after first receipt, and the stockpile may create a nuisance or public health impact. DEQ says recycling facilities must operate within this limit. A facility that fails it is deemed an unauthorized solid waste facility. An authorized facility may instead face a citation and monetary penalty.

Working with DEQ

• Waste determination: waste from an industrial or commercial process requires the generator to make a waste determination. It ensures the waste is not hazardous.
• Before you ship: describe the sand, the receiving site, and the proposed use to your DEQ regional office.
• Receiving sites: Tier I facilities must notify DEQ before operating (011). Tier II and Tier III facilities submit applications and plans to DEQ for review and approval (032). A Tier II or Tier III operating plan describes the wastes the facility will accept (012, 013).
• Landfills: municipal landfills cannot accept hazardous waste. They may refuse nonhazardous industrial waste that does not meet their waste acceptance criteria.
• Liquids and sludge: impoundment of pumpable waste that is solid waste, and not covered by a discharge or land application permit, is regulated under IDAPA 58.01.06.

DEQ Hazardous Waste Bureau: (208) 373-0502. For local questions, contact your DEQ regional office.

Hazardous waste determination

Idaho adopts the federal hazardous waste rules (40 CFR Parts 124, 260–268, 270, 271, 273, 278, and 279, revised to July 1, 2025) by reference in IDAPA 58.01.05.002.

Idaho adds state steps for hazardous loads. A transporter carrying manifested hazardous waste must avoid municipalities and population centers, even when that adds miles (IDAPA 58.01.05.500). When federal rules require a generator emergency report, the emergency coordinator must also call the Idaho Office of Emergency Management at 1-800-632-8000 (006).

Under 40 CFR 262.11, the foundry must decide whether its spent sand is hazardous:

1. Make the determination at the point of generation, before mixing or dilution. Repeat it if the waste may have changed.
2. Check whether the waste is excluded from the hazardous waste rules.
3. Check whether it matches a listed hazardous waste.
4. Check for hazardous characteristics, including toxicity. Use knowledge of the materials and process, testing, or both. Test when knowledge alone is not enough.

Small and large quantity generators must keep records supporting the determination for at least three years after the waste was last sent for treatment, storage, or disposal.

TCLP testing and limits

Tell the lab the alloys cast, the binder system, and which streams the sample includes. Use representative samples. Agree on the sampling plan with the lab, DEQ, and the receiving site before collecting.

A waste is hazardous for toxicity if its TCLP extract meets or exceeds any limit in 40 CFR 261.24. The limits for the RCRA metals are:

Passing TCLP addresses toxicity for the substances tested. It does not approve reuse or rule out other reasons a waste may be hazardous. See material testing for sampling basics.

DEQ notes that you can run a totals metals test first, but you may still need TCLP if levels could exceed TCLP limits.

Finding a reuse destination

EPA’s 2014 risk assessment found three uses protective of health and the environment for silica-based spent sand from iron, steel, and aluminum foundries: manufactured soil, soil-less potting media, and road subbase. EPA and USDA support those uses. The finding does not cover sand from brass or bronze foundries, olivine sand, or sand mixed with other foundry wastes such as baghouse dust or cupola slag. EPA defers to state programs, so the state rules on this page still decide each use.

Idaho has no separate reuse approval. DEQ looks at each use case by case. Check any destination and proposed use with DEQ before scheduling delivery.

When you talk to DEQ, describe the proposal using the terms in IDAPA 58.01.06. For example, will the sand go into an industrial process that makes a new product, such as concrete? Is the receiving site a recycling center, or a facility that needs DEQ approval? Get the receiving site’s specifications and written acceptance. If reuse is not cleared, arrange disposal that fits the waste determination.

Worker protection

• Silica: foundry sand is mostly crystalline silica. OSHA’s general industry standard, 29 CFR 1910.1053, sets a permissible exposure limit of 50 µg/m³ of respirable crystalline silica as an 8-hour average. Exposure assessment starts at the 25 µg/m³ action level.
• Construction use: crews placing sand as fill or subbase fall under the construction silica standard, 29 CFR 1926.1153.
• Lead: brass and bronze foundries that cast leaded alloys also follow OSHA’s lead standard, 29 CFR 1910.1025.
• Dust: control dust during shakeout, storage, and loading.

Storage and records

Store spent sand on a defined pad or in bins, control dust and runoff, and keep other foundry wastes out. Plan volumes so at least half of any stockpile is reused or disposed of by the end of the calendar year after first receipt (IDAPA 58.01.06.005.37).

Keep the waste determination, lab reports, DEQ correspondence, and the receiving site’s acceptance together. Record tonnage shipped, dates, and destinations. Keep determination records for at least three years.

Before pickup

1. Identify the alloys cast, sand and binder systems, separate streams, monthly volume, and plant location.
2. Make the hazardous waste determination and complete the required tests.
3. Choose a destination and get its material specifications.
4. Confirm the destination, proposed use, and any facility approval with your DEQ regional office.
5. Get written acceptance and arrange pickup.

Common questions

Rules and guidance

• IDAPA 58.01.06: Solid Waste Management Rules
• Idaho DEQ: Recycling, Reuse, and Composting
• Idaho DEQ: Commercial Industrial Waste
• IDAPA 58.01.05: Rules and Standards for Hazardous Waste
• Idaho DEQ: Hazardous Waste Determinations
• Idaho DEQ: Regional Offices
• 40 CFR 262.11: Hazardous waste determination
• 40 CFR 261.24: Toxicity characteristic
• EPA Method 1311: TCLP
• EPA: Beneficial Uses of Spent Foundry Sands
• EPA: Risk Assessment of Spent Foundry Sands in Soil-Related Applications
• 29 CFR 1910.1053: Respirable crystalline silica
• 29 CFR 1926.1153: Respirable crystalline silica in construction