DEEP: P2 Case Study: New Parts Cleaning Systems Eliminate Hazardous Waste

New Parts Cleaning Systems Eliminate Hazardous Wastes
A Pollution Prevention Case Study

Environmental Assessment
Screening Alternatives
Evaluating Costs
Results – Aqueous Sink-Over-Drum Units
Unanticipated Costs
Revisiting Alternatives
Results – Automatic Parts Washer (Dishwasher Style Unit)
Pollution Prevention Works


A vehicle maintenance facility in Hartford had used solvents in three sink-over-drum units to manually clean parts. In 1995 they eliminated the use of solvents and the associated environmental and health and safety hazards by switching to two aqueous-based sink-over-drum units. Subsequently, in 2001 they switched to a single automatic dishwasher type unit and realized further operational cost savings. Through these changes they have dramatically reduced costs, eliminated associated hazardous wastes, freed up manpower formerly needed to clean parts by hand and eliminated worker exposure to solvents.


The United States Postal Service (USPS) has made a commitment to achieving environmental compliance and becoming an environmental leader. The USPS operates a fleet of approximately 1,400 vehicles in north central Connecticut for use by area post offices. These vehicles are serviced at the Hartford Vehicle Maintenance Facility (VMF). The facility has nine bays for mechanical repairs, a body shop and a paint spray booth. Work performed at this VMF consists of everything from replacing tires, changing oil and performing tune-ups, to swapping engines and transmissions. There are approximately 3,850 vehicle servicings performed per year. The facility employs 23 mechanics working six days per week, two shifts per day. The facility was built in the 1960s, and operated by the USPS as a VMF since then.

Environmental Assessment

In 1992, the facility operated three sink-over-drum units to support all repair work. All parts cleaning was done manually using solvents. The first step taken to justify changing out these units was to measure the types and amounts of wastes generated. Of the “hazardous” liquid wastes, parts cleaning solvent was the biggest contributor (3,480 gallons). Based on the overall rate of hazardous wastes generated, the facility should have been classified as a “Large Quantity Generator” (over 1,000 Kg hazardous waste per month). This classification under federal RCRA regulations means the facility was required to undertake substantial hazardous waste management, reporting, and employee training. The costs to the facility were significant.

The goal was therefore proposed to significantly decrease or eliminate the generation of hazardous wastes from these operations. It was also necessary to maintain quality and productivity and hold the line on costs. Management added an additional requirement to eliminate or significantly reduce worker exposures from the use of any OSHA regulated hazardous or toxic chemicals during cleaning. It was quickly realized that only aqueous-based cleaners would fit these requirements.

Screening Alternatives

The three criteria used to evaluate the alternatives in both evaluations were (in order): performance, potential environmental and health and safety liabilities, and cost. For the first evaluation (1992), various vendors and suppliers were asked to supply Material Safety Data Sheets (MSDS) for the solutions used in their parts cleaners. These were checked by the facility supervisor for the presence of any chemicals targeted for elimination by the USPS or the EPA. Only parts cleaner solutions without these chemicals were admitted into the shop for the mechanics to test.

The mechanics were then asked to evaluate these finalists. The sink/solutions combinations were used in the normal course of work for an average of two weeks. The existing solvent unit was used for comparison in the performance evaluation, even though it did not meet the screening criteria. Only those washers that were rated “good” or better by the mechanics for performance were evaluated further. For consistency, the same mechanics were asked to evaluate each alternative.

Evaluating Costs

The systems that passed the initial screening and performance evaluations were then evaluated for costs. All quantifiable costs were considered, including equipment purchase, materials, operating, waste handling and disposal, labor, environmental compliance, and health and safety compliance. Some less quantifiable costs were included such as administrative (filling out manifest forms, training, etc.), potential rejection (waste shipment rejection due to contamination), and the potential liability for spills. The costs evaluation showed only minor variation among the units evaluated. All were approximately $1,011 per year per sink unit to own and maintain in house. This compared favorably with the $1,272 cost for the existing service contract for each of the existing solvent-based units. At the same time, the number of sinks needed for the facility was evaluated, and the decision was made that two sink units would be sufficient for this facility.

Results - Aqueous Sink-Over-Drum Units

After a choice was made among the acceptable sink units there was an initial period of adjustment, primarily related to the change in cleaning agent. The aqueous-based cleaner left a slight visible residue, which was disconcerting at first, but was proven to be acceptable with a “white glove” test. There were no problems with parts rusting, and a noticeable improvement in shop air quality. The mechanics were also pleased about the reduced exposure to harsh chemicals. After three years of use, the mechanics were satisfied with the performance of the aqueous parts washer. As shown by detailed analytical testing, the generation of hazardous waste (per federal regulations) from this operation was completely eliminated. The waste sludge and filters were still required to be handled as a (less costly) Connecticut regulated waste.

Unanticipated Costs

The change to aqueous based sink-over-drum units provided real benefits but did not yield the expected cost savings. This was due to a variety of factors. The new units still required manual labor to operate, so the mechanic was still unavailable to work on vehicles. After a few months of use, several maintenance issues emerged. The heating elements were "problematic" (burned out), necessitating taking the units out of service to replace them, again using up staff time. The traps and filters were clogging up frequently, which meant taking the unit out of service to clean the trap and replace the filter. Each unit had to be completely drained and cleaned out every two months. These unanticipated costs added up to approximately $2,000 per year for two units. The cleaner was used up at a faster than anticipated rate. The facility went through approximately one 55-gallon drum at a cost of $575 per year. The waste disposal (sludge) was approximately three 55-gallon drums at a cost of $800 per year.

Revisiting Alternatives

The facility supervisor continued to keep an eye on the parts cleaning equipment marketplace for further potential gains in costs and productivity. By 2001, advertised improvements in automatic dishwasher style units enticed him to search out reputable local dealers to provide details on currently available units. A detailed review along with visits to existing installations provided sufficient information to support the purchase of a single automated unit to replace the two sink-over-drum units. Among the anticipated benefits of these types of units were "hands free" operation, which allowed the mechanics to continue work on the vehicle while the parts were cleaned as well as less waste generation and less maintenance.

Results - Automatic Parts Washer (Dishwasher Style Unit)

After more than one year of service, use of the automatic unit has delivered on the promise of true hands free operation, which frees up the mechanics to continue vehicle repairs. The unit uses standard technology, with no apparent "delicate" components. It is sized to accommodate the smallest to the largest parts in the shop, including transmissions. The unit uses much less soap, partly due to the built-in oil skimmer. The dirty water is periodically evaporated from the unit so there is no wastewater discharge (eliminating wastewater discharge permit issues). The sump is cleaned out approximately once a week and generates significantly less waste than the former units. There is a greater investment required for this unit that for sinks but so far the benefits seem to outweigh the costs.


Acting on a desire to control costs and to eliminate solvents from the shop, management looked into the replacement of a solvent based system. In 1995 two aqueous-based sink type units were purchased which eliminated the solvent hazardous waste stream completely, satisfied the mechanics' need for ease of use and maintained acceptable quality. In 2001 an automatic part washer (dishwasher style unit) was purchased to achieve the desired cost savings and free up the mechanics to continue to work on vehicles while the parts are cleaned automatically.

Pollution Prevention Works!

Materials Tracking and Costs for Selected Years 

Type/Description 1992
3 Solvent Sinks
2 Aqueous Sinks
1 Automatic
Parts Washer
Annual hazardous waste solvent disposal (approx.) 3,478 gallons - cost included in contract 0 0
Annual aqueous sludge disposal (approx.) 0 165 gal./$800

7 gal./$35
water is evaporated

Degreaser solvent purchased annually (approx.) 3,500 gallons - cost included in contract 0 0
Soap/cleaner purchased annually 0 55 gal./$575 5 gal./$105
(appears to last approx. 3 years)
Maintenance by staff None - included in contract "Lots of cleaning traps, replacing filters and repairs" "Very little"
Labor required to clean parts? Yes - totally
"hands on"
Yes - totally
"hands on"
Only to load part(s) and start unit
Total annual cost
(to own and operate)

(leased - includes solvent and service)

(purchased - includes unanticipated repairs)
("lease to own" -
  60 month lease)

The product information in this case study is provided solely as a service to Connecticut businesses. This information may not include all available services and suppliers, and does not represent an endorsement by the USPS or DEP. Use of this information does not in any way lessen one's responsibilities for compliance with applicable state and federal laws.

Prepared by the Connecticut Department of Environmental Protection. For more information, call the Office of Pollution Prevention at 860-424-3297, or Mark Couillard, USPS at 860-524-6240.

Content Last Updated on December 8, 2006