40W201 Wasco Road, Suite D • St. Charles, IL 60175• Ph: 630.587.0470 • Fax: 630.587.0475
 

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Water Engineering

As communities with aging infrastructure continue to grow, there is a need to address the quality, quantity, and efficiency of delivering potable water. Driven by the 1986 Safe Drinking Water Act (SDWA) Amendments, water systems are being affected by a new emphasis on microbiological safety, disinfection requirements, reduction of disinfection by-products (DBPs), new maximum contaminant levels (MCLs) for arsenic, organic contaminants and radionuclides and minimization of lead and copper concentrations "at the tap." Today’s water system operators must find new supply sources, better and more efficient treatment technologies, and the ability to maintain and expand existing distribution systems. TAI provides its clients with a comprehensive suite of water system engineering services including:

 

Master Planning Water Treatment Design

Distribution System Modeling

Distribution System Engineering
Water Supply Development Water Storage

 

The potable water system is one of the most important services a community can provide. Most systems are designed and operated in such a manner that interruption of service is an unusual event. As a result, the public water supply is commonly taken for granted by the general public. The easiest way to avoid any problems is to anticipate problem scenarios and then develop the water supply and distribution contingencies. This will help to minimize the effects of main breaks and/or peak demands.

Public Water Supplies are typically revenue-producing utilities supported by user fees (not the community's General Fund). As a result, improvements required by aging infrastructure, increased demand, or regulatory changes are financed through replacement funds, revenue bonds or the newly created Illinois Low Interest Loan Program.

Master Planning

Part of a public official's charge is to invest their communities’ limited resources wisely. That serious responsibility includes decisions regarding improvements to the community's water system, which is the lifeblood of the community. TAI excels in the development and updating of water facilities plans for communities. This enables staff and elected officials to make informed decisions concerning the improvements to be implemented. These decisions should be made with the full understanding of the cost and benefits of the improvements. If the community is seeking Low Interest Loan Funding for improvements, the Illinois EPA requires an updated Water Planning Report. The Water Planning Report should include the following:

· Review of existing usage
· Estimate of future usage
· Rate structure analysis and comparison
· Review of existing distribution, supply, storage, and treatment
· Review of pending and future regulatory requirements
· Analysis of alternative solutions including rehabilitation, extension and expansion, projects .
· Recommendations, cost estimates and schedule.

Once completed and adopted by the community, the report is forwarded to the Illinois EPA for review and approval as part of the loan process. In addition, the report becomes a very useful tool for the five and ten year budgeting processes. The community may adjust their rate structure in anticipation of future needs, thus limiting its reliance on external funding sources for the pending improvements.
Water Distribution Modeling and Design

Distribution System Modeling

The TAI staff has completed numerous water distribution system modeling and design projects. Both new distribution systems and older, dual pressure zoned systems have been modeled with WaterCAD® software. Distribution system models have proven to be valuable tools for determining the performance of the distribution system under normal conditions, as well as during emergency situations or stressed conditions. The WaterCAD® software allows for distribution system characteristics to be modeled for several unique scenarios, some of which include:

· Fire Flow Protection
· Watermain Breaks
· Wells and Towers Out of Service
· System Dynamics During a Contamination Event
· Computing Water Age
· Analyzing Constituent Concentrations
· Performing a Trace Analysis

If properly calibrated, the model can be used to quickly determine the affect of modifications to the distribution system. Through the model, TAI has evaluated proposed watermain within pending developments, rehabilitation projects within existing service areas, transmission main improvements, as well as the addition of wells and water storage facilities. The resulting analysis has allowed our clients to better understand the impact of each alternative. Owners can then make educated decisions on where to invest the community’s resources.

Distribution System Design

TAI has designed and inspected projects that range from transmission mains to small distribution systems. Design and construction phase engineering requires experience, attention to detail, and open communications with the owner to ensure that the finished product meets the owner’s expectations. The clarity and accuracy of TAI’s construction documents result in tighter bids and minimal change orders. As a result, TAI is able to assure its clients projects that will remain within budget and be completed on schedule.

Water Supply and Storage

The TAI staff is experienced in water supply projects. Through close working relationships with local drilling companies and State agencies, TAI is able to readily identify potential sources for water. Through the use of historic data, TAI is able to predict both water quality and quantity from each source. The TAI staff can assist an owner in identifying, designing and constructing a viable public water supply system, which will meet state standards. As part of the preliminary investigation, the staff reviews water quality and treatment requirements. Once these standards have been identified, the total cost can be estimated including the operation and maintenance requirements associated with each source. The importance of operation and maintenance costs is commonly more significant in the evaluation than the original construction cost. As a result, the project will meet the client’s needs and expectations.

TAI’s staff has experience in the design, specification and construction management of water storage improvements including ground storage reservoirs, booster stations and elevated storage tanks. The water facilities plan and distribution system model provide the basis for decisions on sizing of storage facilities. The water facilities plan will define the maximum hourly usage, which is utilized in formulating the balance between water system supply and storage. In addition, the distribution system model will identify the hydraulic gradeline to be maintained. From this information, storage volume and configuration can be established.

Ground storage reservoirs are typically located at well or treatment sites. One of the major advantages of ground storage reservoirs is the flexibility they provide operators to maximize cycle time for well pumps or treatment units. For example with a ground storage reservoir, an operator can elect to run the wells and treatment facilities at night when electrical demand charges are lowest and meet the systems demand during the day with the booster pumps only.

Elevated storage size and location are dependent on the characteristics of the distribution system as well. Once the storage volume and site are selected, the style and configuration of the tower must be determined. The options include the older style multiple leg tanks, spheroids, standpipes and pillars. Each alternative generally has a volume range in which it is economical to construct. Therefore, the style of elevated storage tank may be determined by a combination of factors including systems storage needs, aesthetics and site constraints. Once the style is selected of the elevated storage is selected, several decisions need to be made regarding SCADA configuration, yard piping, controls, maintenance and painting access and security. Trotter and Associates, Inc.’s staff is experienced in and can guide its clients through the selection and design process as well as provide construction supervision services for the required water storage improvements.

Water Treatment

TAI’s professional staff participates in postgraduate studies, technical seminars and continuing education programs to acquire the latest and most advanced information in the rapidly changing field of water treatment. This ongoing training enables staff to make recommendations based on the most current technology -- a clear advantage to clients. TAI recognizes the importance of incorporating provisions into the design for modifications to accommodate pending regulation or expansions in the future.

TAI’s water treatment experience includes barium, radium, radon, iron and manganese removal, as well as removal of organic and inorganic compounds. The staff works closely with manufacturer's representatives to fully understand the requirements of each piece of equipment. By incorporating the manufacturer into the design team, each entity understands the project's objectives and constraints.

TAI’s process engineers have experience designing ion-exchange systems. Ion exchange is the same process used by most home water softening systems. Ion exchange units contain a medium or resin bed, which is charged with a cation or anion depending on the inorganic to be removed. For example, radium is a positively charged ion and therefore a positive or cation exchange will be used. In the ion exchange process, ionic contaminants (Radium, Barium, Calcium etc.) are removed through adsorption onto a resin exchange medium. As the name implies, one ion is substituted for another by passing the water through the medium. During ion exchange, the contaminant ions replace the regenerate ions on the resin because the exchange medium is designed to selectively prefer the contaminant to the regenerate ion. Therefore, the medium releases the regenerate ion such as sodium in exchange for a contaminant ion. The resin exchange capacity is expressed in terms of weight per unit volume of the resin. When the regenerate ions on the medium have been nearly exhausted, the resin needs to be recharged or the contaminant ions will begin to pass through the unit. This condition is commonly referred to as breakthrough. The calculation of the breakthrough time for an ion exchange unit requires knowledge of the resin exchange capacity, the influent contaminant concentration, and the desired effluent quality. The resin is regenerated by backwashing at a high flow rate, which physically flushes the contaminant ions off the medium. Then the resin is saturated in brine, salt solution, which allows the regenerate ion in the solution to attach to the resin. Following the brine step, the resin is rinsed to remove excess brine, which did not attach to the resin from the unit. Once the excess salt has been rinsed from the resin, the unit is returned to service and begins the ion exchange process again. The regeneration time is typically about an hour and a half. Because of the required regeneration cycle, the water treatment facility should have multiple units and only allow one unit to regenerate at a time. Therefore, the water treatment facility can operate on continuous basis without any reduction in capacity during regeneration cycle. Typical ion exchange units consist of pre-filtration, ion exchange, and distribution elements. Sodium chloride is often used to regenerate the exchange medium in ion exchange systems because of the low cost of the chemical. However, this can result in high sodium residual in the finished water, which may be unacceptable for individuals with salt restricted diets. This problem can be avoided by using other regenerate materials, such as potassium chloride

TAI has recently completed an analysis considering various water treatment alternatives. One of the alternatives considered was membrane filtration. One of the advantages of using membrane filtration is objectionable constituents like radium are removed from raw water without replacing the ions with a less objectionable substance like salt.

There are four commercially used membrane processes: microfiltration, ultrafiltration, nanofiltration and reverse osmosis. The processes are distinguished by the size of the openings in the membrane and the amount of pressure applied to pass the solution through the membrane. Reveres osmosis has the smallest openings and requires the highest amount of pressure for treatment. Nanofiltration has slightly larger openings and requires less pressure. Both processes are capable of removing the Radium ion, but nanofiltration has the advantage of requiring less pressure (approximately 100 psi verses 300 psi). The lower pressure reduces the electrical consumption of the process and makes it inherently more cost effective. The operational cost of membrane treatment systems is predominately related to the cost electricity. In addition, the membranes have a relatively short operational life, four to 6 years and are rather expensive to replace.

TAI also recently completed the design and construction of a 2.2 MGD iron and manganese removal facility for the City of St. Charles. The selection of the media is dependent on the raw water quality and should include jar and possibly pilot testing. This project included both. During the jar testing varying media’s were analyzed for their effectiveness of removal, estimated operational cycle time and estimated cost. Based n the results of the laboratory testing, a two-week pilot test of the preferred media, manganese greensand, was performed to provide field data which corresponded to the laboratory results. The final configuration of the new water treatment facility included two 750 gpm pressure filters; chemical feed equipment, SCADA improvements and a new well.