The purpose of this project is to continue to produce outstanding drinking water for the community and to continue to meet all federal and state drinking water regulations. The United States Environmental Protection Agency (EPA) has proposed Stage 2 Disinfection Byproduct regulations that amend some of the drinking water requirements to further restrict the byproducts in water that can be allowed from the necessary disinfection of water. Following significant public input in 2012, to include a symposium and a public hearing, the Board of Directors of the Rivanna Water and Sewer Authority (RWSA), in consultation with elected officials, selected granular activated carbon as the treatment method for consistently achieving the new regulations.
This narrative provides some background about what disinfection byproducts are, how granular activated carbon, (GAC) as an addition to current treatment processes, will achieve the new requirements, and option on how GAC can be implemented.
By way of background, there are two types of disinfection processes for drinking water. Primary disinfection occurs within the water treatment facility to kill or inactivate harmful viruses, bacteria, and microbial matter that may be in the water when it is pumped from the environment (stream or reservoir) to the treatment plant. Secondary disinfection is a trace residual disinfectant that remains in the water to prevent re-infection as it moves through the RWSA transmission pipelines and City or the ACSA distribution pipelines on the way to service connections to the homes and businesses served. Several chemicals or processes that are approved by the Environmental Protection Agency (EPA) for primary disinfection (e.g., ozone, ultraviolet light) are not approved for secondary disinfection because those chemicals or processes do not maintain a long lasting residual suitable for distribution systems. EPA recognizes both free chlorine and chloramines as acceptable secondary disinfectants provided that the concentration of either disinfectant in drinking water does not exceed four milligrams per liter (or four parts per million). EPA and Virginia Department of Health (VDH) regulations require the continuous presence of a secondary disinfectant throughout water distribution systems.
RWSA is presently using free chlorine for both the primary and secondary disinfectant, and proposes to continue to use free chlorine as both the primary and secondary disinfectant. This is an important consideration as it is both necessary for compliance with EPA regulations and it is a key feature of a multi-barrier approach to ensuring the safety of water we supply as a wholesaler to the City and ACSA. The capital project presently under design would add granular activated carbon filtration to the existing treatment facilities at all RWSA water treatment plants, including the Urban Water System (all of the City and the surrounding urbanized areas of Albemarle County, including areas surrounding the North Fork Business Park, and the Glenmore County Club area), the community of Crozet, and the Town of Scottsville. GAC removes trace organic matter remaining in the water after conventional filtration, thereby providing less matter for the free chlorine to react with to form disinfection byproducts.
Regulations regarding the requirements for disinfection of drinking water, and the limits on the presence of the byproducts of disinfection that can be present in drinking water, are both set at the federal level in regulations issued by the EPA. In developing drinking water regulations, EPA performs extensive scientific research of health effects, including extensive risk analysis, as well as evaluating and determining acceptable water treatment practices, to assure their regulations both protect public health and can be achieved. All EPA draft regulations are subject to public comment periods before they are promulgated as well as subject to appellate judicial procedures after promulgation.
EPA initially developed regulations for disinfection byproducts in 1979, at a time when most water utilities were using free chlorine. EPA has modified the rules several times since 1979, consistently tightening the standards, and each time the rules were tightened, more water utilities found themselves unable to maintain compliance with byproduct regulations except by making capital improvements to their water treatment process. Most water utilities across the country that have made capital improvements to account for more stringent byproduct regulations have chosen to convert their secondary disinfectant to chloramines, which is known to produce less regulated disinfection byproducts than free chlorine, with the cost of water being among the significant factors considered in selecting chloramines.
Each time EPA has tightened the disinfection byproduct regulations, RWSA's goal has been to attempt to maintain continuous compliance as long as possible by optimizing the chemical use and performance of existing treatment facilities while retaining free chlorine for both primary and secondary disinfection. In so doing, RWSA has not made water plant capital improvements specific to stricter disinfection byproduct regulations before now even as many utilities across the country already have.
Development of the Local Plan to Address EPA Stage 2 Regulations
The most recent changes in disinfection byproduct regulations by EPA have been called the Stage 2 rules. RWSA retained Hazen and Sawyer, consulting engineer, to audit RWSA's present treatment practices and identify the extent to which changes would be needed to assure compliance with the Stage 2 regulations, with priority given to operating practices and other non-capital related changes. An extensive amount of data was collected. In the end, Hazen and Sawyer concluded that continuous compliance with the Stage 2 regulations could not be assured without capital construction upgrades to the treatment facilities. Hazen and Sawyer's conclusions are summarized in a technical report dated July 2011.
Multiple capital upgrade options were then considered, to include: (1) constructing and operating new granular activated carbon filtration facilities; (2) constructing and operating new magnetic ion exchange facilities; (3) constructing additional water storage and chemical storage and feed facilities to convert the secondary disinfectant to chloramines; (4) constructing and operating new membrane nanofiltration facilities; and (5) converting primary disinfection to the use of ultraviolet light.
Literature within the industry readily recognized magnetic ion exchange as a more expensive capital investment than conversion to chloramines, but Hazen and Sawyer and RWSA recognized there was little history in the industry, or published information, on the extent to which adding magnetic ion exchange on the front end of a water plant would reduce the cost of operating subsequent plant processes and the extent to which such reductions over time might offset the higher capital cost. To assure this alternative received fair consideration, RWSA co-sponsored a research study using a "pilot plant" at the South Fork Rivanna and Scottsville WTPs that resulted in the world wide publication of a research paper by the Water Research Foundation. The findings however, were that magnetic ion exchange will consistently meet the Stage 2
regulations, but the operating savings were still significantly insufficient, leaving the magnetic ion exchange process as a more expensive way to meet Stage 2.
Likewise, Hazen and Sawyer confirmed through evaluation that the granular activated carbon filtration option and the membrane filtration option will consistently meet Stage 2 requirements but either option if operated consistently for all water treated would be significantly more expensive for the Urban Water System. Hazen and Sawyer also determined that the use of ultraviolet light for primary disinfection was more costly yet would not avoid the need to convert secondary disinfection to chloramines, thereby offering little advantage compared to the present process with chloramine addition. A summary of the consultant's estimated capital costs and additional annual operation and maintenance costs for these alternatives are summarized in Table 1 below:
RWSA sponsored a Safe Water Symposium on June 21, 2012 which allowed citizens to ask questions to a panel of eight individuals who provided a wide range of viewpoints and expertise. A joint meeting of the "four boards" with a public hearing followed on July 25, 2012, where approximately 50-60 citizens spoke, all in support of GAC filtration over chloramines. Several of the citizens speaking recognized the higher cost of GAC but expressed the viewpoint that the importance of public health necessitated the greater expense associated with removing organic precursors from the water (GAC) as opposed to slowing the byproduct reaction through the addition of trace ammonia to water (chloramines). Following the public hearing all four boards, including the RWSA Board, voted unanimously to take chloramines "off the table" and advocate some form of GAC filtration for Stage 2 compliance.
A few local citizens appealed to elected officials that no action by RWSA was required to remain in compliance with EPA rules. To the contrary, following detailed technical studies by experts, it is very conclusive that additional measures are required. Our drinking water regulations come from the federal government through EPA and the federal law does not allow compliance or non-compliance with those regulations to be at the discretion of local officials. EPA can impose penalties of up to
GAC Pilot Plant Operations and "Hybrid" Alternatives Analysis
The July 2012 RWSA Board decision to choose GAC also recognized the high costs associated with this technology, and the Board further agreed to look at some partial-GAC treatment options that could comply with Stage 2 regulations but reduce the cost of providing GAC treatment. In all cases the existing treatment process would remain in service, meaning at no time would the drinking water be of lower quality than it has been historically. Partial GAC treatment options came to be referred to in this community as "Hybrid GAC" options, and included seasonal GAC treatment, blending of GAC treated water with conventionally treated water that by-passes GAC, and "TOC trigger". TOC is an abbreviation for Total Organic Carbon and is an indicator of the organic matter in the water which can combine with free chlorine to form byproducts. Under the "TOC trigger" Hybrid, GAC treatment would be activated only when the organic matter indicated reached a defined threshold.
In November 2012 a "GAC pilot plant" was set up at each of the Urban water treatment plants to receive a continuous sample of the conventionally treated water and operate it through miniature (laboratory-scale) GAC columns. Seasonal data was collected between November 2012 and July 2013 to determine how well the GAC treated the specific water at each plant, and to estimate the rate of exhaustion of the GAC media. This data is fundamental to determining how well the various Hybrid options would perform. Because every source water has unique chemistry, based upon the nature of its watershed drainage area, it was essential to have site specific data. Further, GAC performs by adsorbing organic matter through its porous structure, but much like a sponge, as it adsorbs matter its effectiveness to adsorb further matter diminishes until its capability is exhausted. Exhausted GAC can be regenerated, but the operating costs of regeneration are very high, so the life of the GAC between regenerations becomes very important.
Results of the Hybrid alternatives evaluation were published in a technical memorandum in September 2013 and edited in October 2013, the current version can be viewed here. The Project Documents page of this project web site also includes detailed component cost estimates for each Hybrid option as well as the Full-Scale option, and other documents related to the alternatives analysis.
RWSA is presently receiving public input on the public preference between Full-Scale GAC treatment and Hybrid treatment. The Preliminary Opinion of Project Cost for Full-Scale is $19.5 million. RWSA staff has suggested the best Hybrid option is to install 9 MGD of GAC capacity at the South Fork Rivanna plant, 3 MGD at the Observatory plant, and 2 MGD at the North Fork Rivanna plant, at an estimated cost of $17.3 million. A decision by the RWSA Board is scheduled for November 26, 2013.
Public input can be provided by any of the following options: