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AQUIFER STORAGE RECOVERY This continuing education unit has been created to acquaint the reader with the topic of Aquifer Storage Recovery. The International School of Well Drilling gratefully acknowledges the use of the (edited) material below courtesy of R. David G. Pyne, P.E., President ASR Systems LLC, coiner of the term "aquifer storage recovery" and author of "Groundwater Recharge and Wells-A Guide to Aquifer Storage Recovery." Aquifer Storage Recovery (ASR) is the storage of water in a well during times when water is available, and recovery of the water from the same well during times when it is needed. ASR provides a cost-effective solution to many of the world's water management needs, storing water during times of flood or when water quality is good, and recovering it later during emergencies or times of water shortage, or when water quality from the source may be poor. Large water volumes are stored deep underground, reducing or eliminating the need to construct large and expensive surface reservoirs. In many cases, the storage zones are aquifers that have experienced long-term declines in water levels due to heavy pumping to meet increasing urban and agricultural water needs. Groundwater levels can then be restored if adequate water is recharged. The main driving force behind the current rapid implementation of ASR technology around the world is water supply economics. ASR systems can usually meet water management needs at less than half the capital cost of other water supply alternatives. When compared to alternatives requiring construction of water treatment plants and surface reservoirs to meet increasing peak demands, potential cost savings have been known to exceed 90%. A second important driving force has been the increased recognition of this technology as being good for the environment, aquatic and terrestrial ecosystems. By reducing or eliminating the need for construction of dams, and by providing reliable water supplies through diversions of flood flows instead of low flows, ASR systems are usually considered to be environmentally friendly.
(Stored water typically forms a large bubble deep underground extending
Storage zones range in depth from as shallow as about 200 ft. to as deep as 2,700 ft. Groundwater levels in the storage zones range from as much as 30 ft above land surface to more than 900 ft. below land surface. Natural water quality in the storage zone ranges from fresh, suitable for drinking without treatment, to brackish, including total dissolved solids concentrations up to about 5000 mg/I. Most sites have one or more natural water quality constituents that are unsuitable for direct potable use except following treatment. Such constituents may include iron, manganese, fluoride, hydrogen sulfide, sulfate, chloride, radium, gross alpha radioactivity, and other elements which are typically displaced by the stored water as the "bubble" is formed underground. At one site, not currently in operation, ASR was shown to be feasible and highly cost-effective, storing drinking water in an aquifer containing seawater. For most of these sites, it is first necessary to properly develop the storage zone around the well, after which it is possible to recover the same volume as that stored. At a few more challenging sites, water quality, hydraulic or geochemical constraints may limit recovery to somewhat less than the volume stored. Water is stored deep underground in water-bearing geologic formations, or "aquifers," that may be in sand, clayey sand, sandstone, gravel, limestone, dolomite, glacial drift, basalt and other types of geologic settings. Stored water displaces the water naturally present in the aquifer, creating a very large bubble around the well. The bubble is usually confined by overlying and underlying geologic formations that do not produce water. However, at several sites, the aquifer is unconfined. Storage volumes in these bubbles range from as small as about 13 million gallons in individual ASR wells, to as much as 2.5 billion gallons or more in large ASR wellfields. ASR Applications Most ASR systems provide seasonal water storage, storing water during the wet season and recovering it during the following dry season. Many also use ASR for water banking, storing water during wet years and recovering it years later during extended droughts. Increasingly, many water managers are constructing ASR systems to ensure reliability during emergencies, whether severe floods, earthquakes, contamination incidents, pipeline breaks, or potential damage due to warfare or sabotage. Increasingly, ASR is being considered for development of Strategic Water Reserves to provide water supply security from terrorism or warfare. Actually, there are at least 22 ASR applications, and others will undoubtedly follow.
Most operating ASR sites are storing treated drinking water. When In the Tampa Bay area of Florida, which is an area with tremendous growth in water demand and limited available supplies, treated wastewater is reclaimed and piped to golf courses, parks, gardens and other areas requiring irrigation to reduce the demand for potable water. When the rains begin and irrigation demand ceases, reclaimed water is stored in ASR wells in deep brackish aquifers, from which it is recovered when needed to meet irrigation demands during dry periods. Reclaimed water ASR is therefore beginning to be a booming application of the ASR technology. A 24" ASR well at West Palm Beach, Florida was initially tested with drinking water from the adjacent water treatment plant and has been retrofitted to recharge and recover partially treated surface water from Clear Lake at rates of 8 million gallons/day. Storage zone is a brackish limestone artesian aquifer at a depth exceeding 1,000 ft. Several sites are storing untreated groundwater pumped from overlying or underlying aquifers, or from well fields located at great distances from the ASR site. When needed, this water is recovered from the storage zone and combined with whatever flows are then available from the primary water sources, to help meet peak or emergency water demands. In coastal areas subject to salt water intrusion, or other areas subject to contamination or overpumping, ASR is being used to achieve the full water supply benefits of local aquifers, which are then used for water storage more than for water production. Groundwater ASR is increasingly viewed as a desirable application of ASR technology. The newest ASR application is for storage of partially treated surface water. Prior to recharge, water is treated sufficiently to ensure that the aquifer does not plug with particulates or organic material, and to ensure that the aquifer is not contaminated. Generally, it is anticipated that the level of treatment will be less than that required for production of drinking water. Stored water is recovered to help meet peak demands for supplemental untreated water, whether for urban needs, ecosystem protection, low streamflow maintenance, agricultural irrigation, industrial water requirements, power plant cooling make-up water, or other needs. ASR is a unique technology, different than for production wells or injection wells. Understanding ASR technology ensures success almost all situations, whereas misunderstanding the unique aspects of this technology can lead to failure, lost investment and disappointment. The term "aquifer storage recovery" was coined by David Pyne, P.E. (see first paragraph of text) in 1983, when the first ASR system at Manatee County, Florida, began successful operation. Development of this system had been underway since 1978. Manatee County is completing construction of its third phase of ASR expansion to include four wells with a combined nominal capacity of 10 million gallons/day. Where is ASR? ASR systems are known to be operating in the United States, United Kingdom, Canada, Australia, South Africa and Israel. ASR development programs are underway in several other countries, including the Netherlands, New Zealand, Thailand, Taiwan and Kuwait. Operating systems are defined as those for which construction is completed, facilities are fully permitted and in operation. This is a relatively new technology. In the U. S., the U.S. Geological Survey conducted small tests of well recharge systems beginning in the late 1940s, but none of these test sites were placed into operation. The first ASR well began operation at Wildwood, New Jersey in 1969, and this system is still in operation, having been expanded to four wells. Most subsequent ASR wells have been constructed since 1983, when the Manatee County, Florida, ASR system began operation. Currently, about 69 ASR sites are in operation around the United States, ranging from a single well to 30 wells, with recovery capacities ranging from 0.5 million gallons/day from single wells to 100 million gallons/day from wellfields. In the planning stages is a very large ASR program for South Florida to restore the Everglades. At such time as this program is completed, it is expected to have over 300 ASR wells storing and recovering water at combined rates of up to 2 billion gallons/day. Looking at topics of public concern During the past two years, several public interest groups have expressed concerns regarding whether ASR technology has been adequately proven in Florida. Concerns have focused on whether proposed applications for storage of drinking water, treated surface water, reclaimed water and fresh groundwater in Florida's brackish aquifers may create unacceptable water quality and environmental problems. Specifically, concerns have focused on potential leaching of metals such as arsenic, mercury and uranium from the limestone into the recovered water or into the surrounding aquifer; potential contamination of the aquifer with disinfection byproducts (DBPs); potential contamination with pathogenic microbiota such as bacteria, viruses and protozoa; and mixing with surrounding brackish water so that recovery efficiency is reduced to below acceptable levels. Similarly concerns have been expressed by the United States Geological Survey (USGS) related to the potential for ASR to alter native ground water quality to the extent that it may affect the potential future use of that resource. Scientific literature is substantial and consistent in showing that, under hydrogeologic conditions prevalent in Florida and almost all other ASR sites nationwide, DBP constituents are reduced or eliminated rapidly through natural processes during ASR storage, if these constituents are present in the recharge water. The principal mechanism for the reduction in the DBP's is microbial degradation. Several proven approaches are currently utilized at various Florida water treatment plants to control or eliminate the presence of DBPs in the recharge water, if needed. As such, DBP's should not be an issue for Florida ASR sites. Metals occur naturally at low concentrations in the limestone of the Floridan aquifer. During ASR storage, these metals may tend to dissolve out of the limestone and create elevated concentrations in the recovered water. Metal concentrations typically decline with time, with distance from the ASR well, and with successive operating cycles. No long-term operating ASR sites in Florida are known to have elevated concentrations of metals such as arsenic, uranium or mercury, although metals data is sparse in many of the data sets. During initial cycle testing at a new ASR well, elevated concentrations of arsenic may occur at some ASR sites, particularly at those sites recharging treated surface water due to the generally higher oxidation-reduction potential (Eh) of this water. This is of some concern since in January, 2005, drinking water standards for arsenic will decrease from 50 micrograms per liter (pg/I) to 10 pg/I, which is within the range of concentrations observed during initial cycle testing at some Florida ASR sites.
Typically, it is anticipated that after four to eight ASR cycles at
the same Pathogenic microbiota are not present in recharge water to ASR wells in Florida, reflecting regulations and policies by Florida Department of Environmental Protection (FDEP) and the SJRWMD to recharge only water that meets drinking water standards for storage in our brackish aquifers. Scientific laboratory investigations and, to a lesser degree, field investigations in Florida, have shown that bacteria, viruses and some protozoa attenuate naturally and rapidly during ASR storage, and under controlled conditions approximating ASR storage. This natural attenuation serves as an additional barrier to protect groundwater quality and public health. No Florida data are currently available regarding the fate of Cryptosporidium and algal toxins during ASR storage; however, such data are available from sources outside Florida. This is not an issue for recharge water meeting drinking water standards.
Utah Water Systems Work to Meet New Arsenic RuleThe vast majority of Utah’s drinking water systems comply with the U.S. Environmental Protection Agency’s new regulations for arsenic levels. And the water utilities that don’t have been getting a helping hand from state environmental regulators, who are working with them to meet the tougher standard that went into effect on January 23, 2006. In recent months, the Drinking Water Board has granted three-year extensions to 32 water utilities to allow them more time to meet the new standard of 10 parts per billion (ppb) arsenic in drinking water – much lower than the 50 ppb once considered safe to drink. The utilities are required to submit semi-annual reports so the Board can monitor their progress. “We recognize the need to grant additional time to help those water utilities potentially faced with a huge capital expense,” said Kevin Brown, director of the Department of Environmental Quality’s Division of Drinking Water (DDW). For the past two years, the Division has been working with water utilities outlining strategies to enable them to meet the new standard. The options include abandoning the high-arsenic sources, or blending water from low-arsenic wells with water from those with higher readings. The Division also has worked with utilities to allow them to purchase filtration devices that fit on the homeowners’ faucet or develop alternative sources of water. Some districts have installed source water treatment systems. EPA did find evidence to suggest that high levels of arsenic were making people sick, said Ken Bousfield, compliance manager for DDW. “This evidence came from studies of water users in Taiwan and Chile and showed increased levels of bladder and skin cancers.” A 1999 study in Utah’s Millard County showed exposures to high levels of arsenic did not produce those health impacts. “Higher rates of bladder and skin cancers were not found in the western Millard County study,” Bousfield said. “Nor were high rates of hypertension or prostate cancers found in the Taiwan and Chile studies.” Arsenic is a naturally occurring contaminant that leaches into the groundwater from the surrounding rock. Although high concentrations of arsenic in drinking water are most often found associated with higher concentrations of metals, such as near past or present mining operations, arsenic concentrations can vary greatly from well to well in the same area. It can even change in the same well over time, according to Don Lore, an environmental scientist with DDW. In 2001, when EPA proposed the new 10 ppb standard, DDW identified 86 water systems that would be impacted. The standard was put on hold when President Bush took office to enable additional review of the science behind the new standard. Eventually that hold was lifted and water systems were ordered to be in compliance by January 2006. “In anticipation of this rule, we identified systems that could have problems and invited them to a number of training events,” Bousfield said. “We tried to direct water systems to the least-costly alternatives, and we have been aggressive in doing that. But there is the nagging issue of the cost ultimately being passed onto the customers.” Magna really got serious about its arsenic problem, developing a central treatment facility that addresses not only arsenic but other contaminants as well. In order to pay for it, voters approved an $18 million bond. “Magna found a silver bullet,” Bousfield said. “The city is able to treat for arsenic, reduce total dissolved solids and address a future regulatory issue of perchlorate in a single treatment scheme.” Park City, which had some of the highest arsenic in the state, opted to install a $3.7 million treatment technology that now has reduced the arsenic to one of the lowest levels in the state, at measurements of 2 ppb. “Water utilities have taken different approaches,” Brown noted. “We tried to be flexible enough to allow them to develop their own solutions to meeting the new rule.” They said that we couldn’t do this in California. Why not? Wonder why they didn’t do the studies in the U.S.
We were told that wherever they went they could not
find wells to meet the arsenic standard
Case Study Contact Information
Jesse Dutcher
Many of the
production wells for
Lessons Learned System Description
The
City of McCook is
located in the southwestern portion of
The City of
Under the
terms of a consent decree, the City of
Many of the City’s production wells have elevated levels of nitrate, uranium, and/or arsenic. Arsenic has been detected in City wells at levels of 10-15 ppb. Results of water sampling conducted in 2003 show that arsenate (As(V)) comprises 70 to 90 percent of the arsenic in two City wells. The City has been dealing with high nitrate levels for 17 years. Nitrate levels at the point-of-entry to the distribution system were greater than 10 mg/L in two of four samples collected in 2005. Based on water sampling results from 2005, the average uranium level in the distribution system is 32 ppb. Nitrate levels drive the selection and combination of production wells used on a particular day. City personnel carefully plan the combination of wells in service at any one time to assure that the treatment system can remove nitrate, uranium, and arsenic to safe levels. Maximum Contaminant Levels (MCLs) Allowed by Drinking Water Regulations
Arsenic
10 ppb Water Treatment Selection The City selected an ion exchange treatment system to remove arsenic, nitrate, and uranium from the drinking water supplies. The treatment process includes a cation exchange reaction for water softening, and an anion exchange reaction to remove the contaminants. The treatment plant, rated at a 6.8 MGD production capacity, was built in about 14 months and put into service February 7, 2006. Depending on which sources of supply are being used, the treatment system is set up to treat 50 to 55 percent of the water, and the remaining water bypasses the treatment process and is blended with the treated water. The finished water contains nitrate levels less than 8 mg/L, arsenic levels less than 8 ppb, and uranium levels of 25 ppb. (McCook Community Profile ) Water Treatment Options The ion exchange resin is periodically regenerated on-site, producing a liquid waste stream that includes backwash water, brine solution, and rinse water. The brine solution may contain high levels of arsenic, nitrate, and uranium. As an interim measure, the City is currently discharging this waste stream to the wastewater treatment plant, located two miles from the water treatment plant. For the February to June 2006 period, an average of 2.6 percent of the water produced was wasted in the treatment process.
The City
has identified a deep earth injection well as the only viable long-term
solution for waste stream disposal. The City considered discharging the
waste stream directly to the
The deep earth injection well will cost an estimated $1 million to construct and cost about $50,000 a year to maintain. The cost per user will be around 14 cents per 1,000 gallons. The City has drilled a test well and conducted necessary tests and expects to receive the final decision and permit in early Spring 2007. Alternatives Considered Before deciding on the ion exchange treatment option, the City also considered reverse osmosis (RO) treatment and development of a new well field in another aquifer. The City rejected the RO treatment alternative because 25 percent of the water would be wasted, requiring disposal either to a water body or to a wastewater treatment plant. In comparison, the ion exchange process only wastes 1.5 percent of treated water. The City engineers discussed the possibility of obtaining an NPDES permit to discharge the RO waste stream to the Republican River but learned from the DEQ that the permit most likely would not be allowed due to the waste stream’s expected arsenic level and lower than normal river levels due to the current regional drought. The RO process also requires a high energy cost because of the high pressure required to move the water through the filters. Over a 13-year period, the City evaluated the possibility of abandoning the existing wells and developing a new well field in the Ogallala (High Plains) aquifer, one of the world's largest aquifers. The City purchased land that provided access to this aquifer and drilled test wells to evaluate water quality and production capability. Preliminary test results showed that water quality was acceptable. However, because this land was located adjacent to a former U.S. Air Force Base, many water system customers were concerned about possible contamination of the new drinking water supply. For this reason, the City withdrew plans for this new well field.
McCook’s new water treatment facility including a new 4 MG water storage tank. Funding Process Capital spending amounted to $12.3 million for the new treatment facilities including the ion exchange treatment system, a waste disposal system for the water treatment waste stream, and a 4-million gallon water storage tank. The project was funded by water system revenues. A rate increase was originally anticipated but was not needed because of higher than expected water consumption that generated additional revenues.
The City of
Arsenic is a Regional Problem
Three
communities located 20 miles east of McCook have taken a different approach
to arsenic compliance. The towns of Bartley, Indianola, and
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