The fury over slurry

Wet concrete cutting creates a water/slurry cocktail that government agencies are finding increasingly objectionable. Here are ways to manage it.

Water/slurry collection, disposal and recycling for concrete sawing and drilling is becoming more of an issue across the country, report sources at the Concrete Sawing and Drilling Association (CSDA).

Government entities are creating a patchwork of regulations and means to enforce them.

Since there is no single standard to deal with water and concrete slurry, the CSDA has become involved with the issue. It now offers advice and guidance on tool use, techniques and procedures to deal with the growing list of regulations and enforcement groups that want to oversee them.

Slurry experts who are members of the CSDA recently banded together to develop a best practice guideline (CSDA-BP-001) to provide the industry a base from which to develop and improve processes to handle slurry from concrete sawing and drilling.

“With this understanding, concrete sawing and drilling contractors will be able to use the right tools and techniques to improve slurry collection, recycling and proper disposal,” says Pat O’Brien, CSDA executive director.

Before the bid
The slurry experts encourage contractors to ask the following questions before submitting a bid:

1. What do the prime contractor and/or owner require for slurry containment and disposal?

2. Are criteria documented in the specifications or proposed contract? What regulations are in force for this project? Is there an approved dump site? Who is responsible for collection, handling and disposal?

3. Will you need to add tools, materials and labor to your bid to handle slurry?

4. Is there construction water available and can you let slurry/water run off the site?

Job planning
Once on the job, planning can greatly reduce the challenges of dealing with slurry. The experts suggest considering:

1. Does your firm and the prime/owner agree on a slurry control method or plan?

2. Do your operators know what is required and will the slurry controls interfere with other work?

3. Will slurry controls also improve worker safety?

4. What special tools and supplies do you need for the job?

5. Can you set up your collection system prior to sawing or drilling?

Collection and control device setup
This is where your planning pays off in fast, efficient setup so you can get to work quickly. The following hands-on tips can greatly improve your slurry control:

1. Locate the low point of the work area and let gravity help control and direct the slurry runoff.

2. Enclose work areas with a polyethylene or waterproof barrier. Make sure it meets local or environmental rule requirements, if any. Clearly mark wet areas with caution tape and restrict access. Use gutters or other channeling equipment to direct slurry to the collection point.

3. Have squeegees, mops and brooms available to move slurry runoff, especially when sawing.

4. Vacuums, such as a 55-gal. drum system, can be used to collect the slurry so it can settle into sludge. Vacuum hose attachments can greatly simplify the collection of water/slurry during core drilling.

For example, circular plastic devices can develop suction against the wall or floor while sending effluent to a wet-vacuum drum.

Some plastic containers can be modified to aid in core drilling collection. For sawing, a variety of systems are available or under development.

5. You may want to consider dry sawing or drilling, but be aware of the need for dust control. Large vacuum trucks and other mobile devices can handle road jobs.

6. When wire sawing, gutters around cut lines can reduce water needs and make wetting the wire easier. It also helps control the spray and makes collection more efficient.

Making the cut/controlling slurry
When you’re set up to make the cut and control the slurry runoff, the experts recommend keeping the following tips in mind:

1. Minimize water input to the tool as much as possible, yet make sure you meet the manufacturer operating guidelines. Use a water spray instead of a constant flow; water delivered at the blade flange can reduce water needs.

2. Limit water to the blade’s point of contact in the cut and use the full blade guard to maximize water use and minimize water/slurry spray.

3. Additives can help. Surfactants make water “wetter,” reducing the water flow required. Softeners and soap improve water tension and reduce water volume needed.

If your system recirculates or recycles slurry water, alkalinity must be controlled. High pH or highly alkaline solutions will irritate skin the more it recirculates and creates a higher pH.

Slurry storage
The experts recommend setting up a temporary onsite storage system to collect slurry and allow sludge to settle.

1. Using 55-gal. drums can work well because they can be handled relatively easily with drum dollies. Water may be decanted after the sludge settles out of the slurry.

2. Large (200 to 500-plus gal.) plastic containers also work well on larger jobs. If located correctly, gravity can move slurry into them. Some contractors first collect the slurry with drum-vacuums, then pump it into a larger container for settling and future disposal. For-hire vacuum trucks are also an effective option.

3. Some contractors use 20 and 40 cu. yd. dumpsters that are divided into up to four sections. The sections allow slurry water to move from one end to the other as solids settle out of the slurry. Spoil areas may be provided by the owner for temporary or permanent storage.

Slurry disposal
Regardless of how you collect or store the slurry, you need a plan for proper disposal, report the experts.

1. Before hauling, decant the water. A large truck-mounted container or plastic tank can work well, or you may want to subcontract a waste hauler or super-sucker truck for slurry disposal.

2. Solidify the slurry before disposal. Minimize the amount of material you are disposing by first removing as much water from it as possible.

Use weirs in a large container, or drain from one barrel to the next, until enough solids settle out. After settling, suck off clear water with a vacuum. Don’t use a pump; it may stir up the slurry.

3. Protect streams, lakes or drain systems from runoff. Many types of filter cloths and screens are available to protect drains. Hay bales or absorptive pigs or blankets can be used in the runoff area or even within a large container to collect some of the slurry. Flocculants can also accelerate solids settling.

4. Dry out the slurry. There are several methods that can be used. Evaporation can work if you have if a large area and time is not an issue. Fly ash, which is readily available from coal power plants and some stores, or SP400 water crystals can be used. Cement can also be used, but it’s more expensive than fly ash. Heated drum evaporators work well and can be found on some sites such as nuclear facilities.

5. Be considerate when you dispose of slurry. Ask before dumping on your client’s site or anywhere else. Locate and use a regulated landfill or dispose of the slurry on your own property, if local regulations allow.

It’s a good idea to treat slurry for high alkalinity (low pH) prior to disposal. Some concrete batch plants will accept the slurry.

6. The list of local, county, state and federal regulations is growing, but enforcement is currently limited. Western states are becoming stricter.

Additional resources
The EPA has set strict standards for disposing of potential pollutants that could end up on land or in waterways.

The complete text of the National Pollutant Discharge Elimination System (NPDES) standard can be found at: http://cfpub.epa.gov/npdes/index.cfm.

The CSDA offers the publication, Chemical Characterization of Concrete Slurry Samples and Development of Guidelines for Slurry Management. This 62-page document contains the results from a study conducted by a private engineering firm which sets baseline criteria to assist in the establishment of guidelines for management of slurry as hazardous or non-hazardous waste material. Contact the concrete Sawing and Drilling Association for copies at www.csda.org.

Published in the May/June 2007 issue of Contractor Tools and Supplies magazine.

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