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Discharges to the Sanitary Drains

I. The Issue:

Historically, many have thought of sinks and drains as an ideal spot for disposing of unwanted items... including chemicals. Unfortunately, improper disposal of chemicals via sanitary drains can create a number of health and safety issues. First, using laboratory sinks for chemical preparation and disposal as well as for food preparation and utensil cleaning can result in cross contamination and chemical ingestion. Also, the disposal of chemicals into sanitary drains can adversely impact indoor air quality if the materials collect in drain traps and slowly release emissions. Another point of concern is related to the disposal of water reactive materials to sanitary drains. These substances can react with water to release a gas or heat and energy. Depending upon the material, it may generate a noxious gas (e.g. chlorine based pool cleaners) or be explosive in nature (e.g. aluminum phosphide or sodium metal). A final concern is related to what environmental impact occurs where the drain ultimately discharges. Does the drain discharge to an on-site septic system which may create a local contamination problem or will the discharged material travel a distance and combine with other chemicals at a waste water treatment plant or receiving waters. One Massachusetts high school has been labeled a hazardous waste disposal site as a result of chemical wastes being discharged into laboratory sinks which resulted in the contamination of the sanitary leachfield serving the school. This problem could have been worse if the school had also been using an on site well for drinking water.

In light of these concerns, it is necessary that we prevent the introduction of hazardous chemicals into sanitary drains and that we establish appropriate measures for managing hazardous waste. Otherwise catastrophic environmental or personal injury may occur.

II. The approach taken:

While inspecting the high school science area in 1992 and 1993, I routinely noted that the staff appeared to be using the sinks for solution preparation and chemical disposal. I also noted that much of the science staff used the sink in the central preparation area for both chemical handling and food preparation. These observations suggested that the staff was using improper hazardous waste management practices. In addition, the use of the sink in the central preparation area for both chemical handling and food preparation increased the likelihood of cross contamination and accidental chemical ingestion by the staff.

Routine and repeated observations involving improper chemical handling around the science department sinks prompted the Board of Health to review existing records to determine what disposal procedures and hazardous waste disposal records existed. As a result, we discovered records dating to 1971 suggesting that the high school science department had routinely disposed of its hazardous waste via the sanitary sewer system. In addition, the science department had on occasion contacted several municipal departments regarding the flow rate and outfall of the municipal sewer system with the intent of optimizing the dilution of the materials discharged to the sanitary sewer. No records were available to indicate how the hazardous waste generated by the school or science department had been managed prior to 1993. These findings suggested that the staff may have disposed of chemicals via the sanitary sewer system.

As a suburban community located in close proximity of metropolitan Boston, Burlington is a member of the Massachusetts Water Resource Authority (MWRA). The MWRA is a quasi-governmental regional agency responsible for providing drinking water and treating sewerage for many communities in eastern Massachusetts. In Burlington, the MWRA is responsible solely for the treatment of sewerage. In the 1980's, the treatment and inspection methods of the MWRA were deemed inadequate and antiquated when the Boston Harbor was identified as one of the most heavily polluted harbors in America. Much of the contamination discovered in the harbor was believed to be the result of chemical contaminants being discharged into the sanitary sewers and then into Boston Harbor via the MWRA system. In response to these problems, the MWRA has adopted some of the most stringent discharge limitations for organic solvents and heavy metals. Using this information, we established local discharge standards consistent to or more stringent than those established by the MWRA. Next, we trained and informed the staff with regard to the existing discharge requirements. At the same time, we also assisted the school department with the establishment of new hazardous waste management procedures.

During follow up inspections conducted in 1994, we continued to find evidence that the staff might still be using the sanitary drains for chemical disposal. After lengthy discussions, it was learned that the some of the staff learned that the MWRA did not actively permit and regulate schools and as a result a number of the staff members incorrectly believed that the discharge limits established by the MWRA did not apply to the school. In order to end this debate, the Board of Health adopted an active enforcement policy with regard to the local discharge standards. The risk of incurring a $200 fine per violation per day of noncompliance provided the motivation for most teachers to significantly reduce the volume of hazardous waste being discharged via the sanitary drains at the high school.

III. Observations made:

Random inspections of the high school science department conducted between 1992 and 1994 resulted in the routine observation of chemical containers stored in sinks or materials being emptied in sinks. In addition, the laboratory sink located in the central preparation area and adjacent to the department office was frequently found to be used for chemical preparation and food handling. These practices suggest that inappropriate materials may have been discharged via the local sanitary sewer. The possibility also existed that cross contamination could have occurred between chemical containers and eating utensils and resulted in accidental chemical ingestion.

A review of historical records suggested that chemical disposal via the sanitary drains may have been common practice by the high school science department during the 1970's and 1980's. In 1971, the high school science department contacted the Board of Health and the Department of Public Works requesting information regarding local sewer flow rates, volume, treatment methods and discharge points. The intent of the author was to maximize the dilution of the materials discharged via the laboratory drains. In 1986, this practice went awry when one pound of water reactive aluminum phosphide detonated when disposed of via a laboratory sink. The resulting explosion destroyed the laboratory plumbing and created two holes in a cinder block wall. When the aluminum phosphide violently reacted with water it also generated highly toxic phosphine gas, a basic chemical warfare agent. The generation of this material prompted the local hazmat team to evacuate the school.

A survey of local records failed to uncover any documents recording the disposal of hazardous waste prior to 1993. This discovery raised concerns as to how chemical wastes had been historically managed by the school department staff.

Training and informing the staff with regard to proper chemical management practices and local sewer discharge practices initially met with limited success. However, active local enforcement provided the motivation necessary to promote a significant reduction in the amount of hazardous chemicals entering the sanitary sewer at the school.

IV. Problems or concerns noted:

V. Actions taken:

A. Established hazardous waste disposal procedures. Almost at the outset of this review, it became apparent that the lack of guidance regarding the management and disposal of hazardous waste may have played a role in the staff developing their own procedures. As a result, new formal practices and procedures were created to eliminate confusion and to ensure the proper management and disposal of chemical waste generated by the school department.

B. Trained and informed the staff of local discharge requirements established by the regional water and sewer authority. This exercise involved a discussion of the types of materials that could be discharged via the lab sinks as well as a discussion of the materials that could not be discharged and had to be containerized for disposal as hazardous waste. A review of newly established hazardous waste collection and disposal procedures was also provided at this time.

C. Risk of enforcement promoted the adoption of new procedures. Inappropriate chemical handling was noted even after the creation of new hazardous waste disposal procedures and the completion of additional training. This prompted the Board of Health to seek enforcement assistance from the MWRA and the Massachusetts Department of Environmental Protection. Both agencies expressed concern but also indicated that they did not actively review or regulate schools and therefore would not take action. As a result, the Board of Health adopted a local policy of fining personnel caught discharging hazardous waste via sanitary drains. This policy provided the motivation for the staff to alter its chemical handling practices.

Lessons learned:

1. Do not assume that everyone practices good chemical hygiene. We frequently noted that the staff prepared stock solutions and disposed of chemicals in the same sink and bench top areas that they used for preparing their lunches and cleaning eating utensils. Even after being informed of the risk of chemical cross contamination and the possibility of accidental chemical ingestion, the staff still continued to resist changing their practices.

2. If you do not establish procedures for managing hazardous waste then your staff will probably develop their own - legal or not. During discussions many staff members indicated that they had never been formally directed how to manage or dispose of their excess chemistry. As a result, the staff either placed the material in long term storage in the classrooms and laboratories or managed the material as they felt was appropriate. This resulted in the accumulation of a large volume of unlabeled and potentially hazardous substances in the science area as well as the improper disposal of an unknown quantity of materials.

3. The adoption of new procedures and methods does not mean that the problems will automatically be resolved. Training and follow up inspections will be necessary. In addition, disciplinary action may be required to modify entrenched habits and behavior.

Tips and suggestions:

1. Develop a nontoxic or less toxic curriculum to eliminate or alleviate this problem.

2. Establish hazardous waste collection and disposal procedures to ensure the safe and legal handling of these materials.

3. Train and inform your staff with regard to the proper handling and management of chemicals.

4. Post warnings/advisories around sinks and drains prohibiting the disposal of chemicals via the sanitary sewer system.

5. Be prepared to take enforcement or disciplinary action to change old habits.

6. Consult local sewer regulatory authority to determine what discharge standards apply for your location.


The U.S. Environmental Protection Agency and the Massachusetts Department of Environmental Protection provided me with general guidance used during the initial phase of this review. As the local regulatory body with primary jurisdiction over the sanitary sewer system, the Massachusetts Water Resource Authority rapidly became my main source of information and guidance. Prior to initiating a comparable review, I recommend that you consult your local sewer authority or publicly owned waste water treatment plant for guidance and information regarding local discharge requirements, procedures, and assistance programs.

prepared by Todd H. Dresser, Environmental Engineer
(formerly of)
Burlington Board of Health, 29 Center Street, Burlington, MA 01803

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