How does the District deal with odors from the plant?
GLSD controls odors in two ways:
First, as summer progresses, incoming wastewater to the District becomes more odorous. These odors are then released at different points in the District's treatment process. To control these incoming odors, the District adds odor neutralizing chemicals (known as "oxidants") to the incoming wastewater. These chemicals are added into the wastewater initially as the wastewater passes through the District's interceptor sewers. Chemicals are also added at the Riverside Pump Station and at various points in the wastewater treatment plant itself.
Second, with the completion of the Biosolids Improvement Project, all sludge treatment processes at the treatment plant has been covered or enclosed. Odorous air from each of these processes is now sent through a biofilter that removes the odor from the air prior to its release into the atmosphere.(Previously, odorous air from the District's sludge processes were not captured and treated.)How does GLSD plan for how much wastewater it will treat?
For planning purposes, the District assumes that the average household produces roughly 75,000 gallons of wastewater per year. This number is only an average usage. Actual usage may vary considerably from household to household.How does GLSD operate financially?
The District collects an annual "assessment" from each of its member communities, and does not charge directly to the individual users. GLSD currently charges 99 cents per thousand gallons of wastewater treated. For fiscal year 2007, the member communities will pay the following assessments:
- Lawrence: $5,910,906
- Methuen: $2,682,328
- Andover: $1,380,568
- No. Andover: $1,269,820
- Salem: $1,129,366What does “treatment” mean?
The GLSD wastewater treatment plant provides two types of treatment: wastewater treatment and sludge/solids treatment. These two types of treatment are described as follows:
Wastewater Treatment: Virtually all the wastewater entering the GLSD plant passes through the main pumping station known as the Riverside Pump Station. This station has the capacity to pump up to 120 million gallons per day of wastewater. At the treatment plant, the wastewater passes through four stages of treatment:
- Primary Clarification for removal of solids in the wastewater;
- Aeration Treatment for removal of organics remaining in the wastewater after primary clarification;
- Disinfection to destroy harmful pathogenic organisms in the treated wastewater;
- Discharge back to the Merrimack River.
Sludge/Solids Treatment: Both the primary clarification and aeration treatment processes produce sludge, which also must be treated. The "Biosolids Improvement Project" completely revamped the treatment of sludge at the GLSD. The following summarizes the new sludge treatment system:
- Gravity Thickening for initial removal of water from sludge produced by the Primary Clarification process. Covers have been added to these tanks for odor control.
- Gravity Belt Thickening for initial removal of water from sludge produced by the Aeration Treatment process.
- Anaerobic Digestion: This process receives the sludge from the two thickening processes. Anaerobic Digestion is a biological process that performs several functions:
- Breaking down organic matter into simple compounds thereby stabilizing the sludge and reducing its odor potential;
- Reducing the concentration of pathogenic organisms present in the sludge, and producing methane gas that can be utilized as a fuel.
- Centrifuge Dewatering removes additional water from the sludge transforming it into a solid material that is then sent to the onsite drying facility where it is processed and converted into dry pellets that can be utilized as a fertilizer and soil conditioner.
- Although not part of the sludge treatment process, the Biosolids Improvement Project also includes a new "Biofilter" for control of odors produced during sludge processing.How many commissioners oversee the GLSD and how are they determined?
The number of GLSD commissioners (for Massachusetts communities) is set forth in the enabling legislation that established the District Chapter 750 of the Acts of 1968. Section 2 of that legislation states that the commission "shall consist of three members from the City of Lawrence, two members from the Town of Methuen, one member from the Town of Andover, and one member from the Town of North Andover". The legislation generally indicates that number of commissioners for each community is established on a population basis.
Salem, NH joined the District in 1982 through a formal agreement between the District and the town. Section 11 of this agreement provides that Salem shall have one non-voting representative to the commission.
Population* of District:
Location 1977 Now Andover 25,600 31,500 Lawrence 64,300 72,200 Methuen 36,300 44,200 No. Andover 19,000 27,700 Salem Not Applicable 28,300 TOTAL 145,200 203,900
*Please note that some of the population shown for each of the communities is not yet served by public sewers.
What are the findings today?
Although water quality problems (notably wet weather discharges) still exist, the conditions on the Merrimack are greatly improved since the plant began operation. Bacterial counts are lower by orders of magnitude. The river now generally meets water quality standards for dissolved oxygen. Also, except during wet weather conditions, discharges of solids and grease have ceased.
Documented pollution levels:
1. "Coliform": Coliform refers to a group of related bacteria that are often used as an indicator of the degree to which a waterbody is contaminated by pathogenic organisms. Although Massachusetts no longer has a standard for (total) coliform levels in rivers and streams, New Hampshire's standard is "no sample greater than 406 counts per 100 milliliters".
Coliform counts in the Merrimack River below Lawrence:
- 1963 Data: Average of all samples = 4,850,000 counts per 100 milliliters.
- 1994 Sample: Result = 190 counts per 100 milliliters.
2. "Dissolved Oxygen": The dissolved oxygen level in a waterbody is one measure of its level of pollution by organic substances, such as contaminants in sewage. For a river body such as the Merrimack, the Massachusetts standard for dissolved oxygen level is "not less than 5.0 milligrams per liter". Levels below the standard are evidence of significant contamination and could be toxic to fish.
Dissolved Oxygen Levels in River below Lawrence:
- 1963 Data: Average of all samples = 2.4 milligrams per liter (Some samples showed complete depletion (i.e. Ð 0) of dissolved oxygen.
- 1994 Sample: Result = 7.97 milligrams per literWhat were the findings that led to the creation of the plant?
A 1963 study by Camp, Dresser & McKee (before treatment plants) summarized then prevailing conditions as follows:
"Our investigations and studies indicate that the Merrimack River is polluted from the New Hampshire state line down to the Atlantic Ocean. The pollution resulting from excessive bacterial counts makes any type of recreational use of the river hazardous to the public health. This bacterial pollution results almost entirely from the discharge of untreated sanitary sewage into the river. The pollution resulting from excessive decomposable organic matter causes depletion of oxygen content of the river water during dry weather and is sufficient to cause odor nuisances and be dangerous to fish life. In addition to bacterial and organic pollution, the discharge of floating solids and grease causes unsightly nuisance conditions on the river and its banks."Is GLSD the only treatment plant on the Merrimack River and in Massachusetts?
GLSD is one of several wastewater treatment plants along the Merrimack River that collectively protect the quality of Merrimack River waters. There are roughly 135 treatment plants in Massachusetts.What is the history of expansion for the plant?
Prior to the Biosolids Contracts 1 and 2, the plant had one other expansion project, completed in 1989.How much revenue does the plant receive from septage treatment?
Septage revenue for fiscal year 2003 totaled $1,048,672. This represents roughly 14% of the total revenues received by the District (from all sources) for wastewater treatment plant operations in fiscal year 2003.How much septage does the plant treat?
GLSD processes approximately 50,000 gallons of septage per day. Approximately one-third of the septage received is from the five District communities. The balance is received from other communities. Septage represents less than 0.2 percent of the flow to the wastewater treatment facility and approximately three percent of the loading of solids to the facility.How much wastewater does the plant treat?
In a typical year, the plant treats approximately 30 million gallons per day of wastewater, 900 million gallons per month, 11 billion gallons per year.What communities does the District serve?
The GLSD treatment plant receives wastewater from five communities: Lawrence, Methuen, Andover, North Andover, MA, and Salem, NH.When did GLSD open its facility?
The Greater Lawrence Sanitary District plant opened in 1977.