Engineers Inc. has worked in the design and construction of Wastewater Treatment Plants, including recent work experience in writing feasibility reports for plant owners investigating upgrades and/or process adjustments, including the performance of site investigations, review of operating data and research on new techniques and equipment. Engineers Inc. has designed the construction of new and the rehabilitation of existing lined ponds for wastewater treatment and process water storage and developed hydraulic profiles of plant liquid flow systems. We have designed the rehabilitation of headworks facilities, including replacement of bar screen devices and the design and construction of a septage pre-treatment facility, the replacement and upgrade of aeration systems in both raceway and lagoon type secondary treatment facilities, the rehabilitation of tank-type clarifiers, the design of sand filter and ultraviolet light tertiary treatment facilities, and the design of improvements to sludge transfer plumbing and pumping systems.
Wastewater Collection System
Client: San Pablo MDWCA
San Pablo is located in the Rio Grande Valley adjacent to the municipalities of Las Cruces and Mesilla. San Pablo is designated a Colonia. Groundwater is within six to eight feet of the surface in the densely developed community. There was no collection and/or treatment system; many residences used wastewater holding tanks that had to be pumped monthly. With financial assistance from BECC, RUS, NMED, the City of Las Cruces, and Doña Ana County, Engineers Inc. developed a wastewater master plan and preliminary engineering report for San Pablo. An extensive evaluation revealed that a new treatment facility for San Pablo was not economically, or environmentally prudent. Instead, the community was connected to the Las Cruces wastewater system. The community now operates its collection system and pays a bulk rate for treatment as metered at the central lift station connecting the community to the Las Cruces System.
The connection to the City of Las Cruces included almost 10,000 feet of force-main from the vacuum station to the Las Cruces collection system. Because of high groundwater and narrow congested rights-of-way, conventional gravity sewers were not feasible. A vacuum sewer collection system was the most practical alternative for the community. Another technically and administratively challenging aspect of the project was the in-situ rehabilitation of an older sewer main within the Las Cruces system to carry San Pablo wastewater. The rehabilitation was also negotiated in the joint agreement and completed as part of the San Pablo project. This was a multiphase project.
Wagon Mound Sewer Improvements
Client: Village of Wagon Mound
The Village of Wagon Mound is a small community located in the north central portion of New Mexico just off of I-25 along the Old Santa Fe Trail. The Village's aged sewer collection system consisted of a variety of materials from vitrified clay to replaced sections of PVC. The manholes were of brick construction with large portions of the transmission lines passing through a seasonally high water table. Overloading at the 3-pond lined lagoon treatment plant caused concerns reported against their discharge permit. Other design improvements to the effluent land application system were required at the plant.
The most critical correction was to determine cause of system overloading. Down-hole cleaning and video of the trunk lines indicated pipe failures and sources of infiltration. Phase 1 of the project was the design of the new sewer lines and manholes to correct the infiltration issues. Phase 2 design at the plant included a tablet chlorination system, irrigation sprinkler heads, replacement of actuator valves, and sealing of manholes. A third emergency project has been added to provide a backup pump for the land application lift station.
RUS Wastewater System Improvements
Client: Tyrone Property Owner's Association
The Tyrone Townsite was developed in the mid-1960's as housing for the employees of the new Tyrone Mine. Wastewater was collected through clay tile pipe gravity lines and transported to a two-stage lagoon system for treatment. The designed capacity and the quality of the initial construction was very good. At this point in time, the primary lagoon had been filled to capacity and the treatment system needed reconstruction/rehabilitation. The Property Owners Association, through Engineers Inc., investigated the feasibility of construction of new treatment lagoons, a stand-alone activated sludge treatment plant or the connection to the Silver City municipal system were investigated. By piggy-backing upon a separate wastewater collection project, the construction costs of connecting to the Silver City system were favorable and the Association chose to advance that project.
The design concept to overcome was to develop a wastewater pumping and transmission system appropriate for the relatively low wastewater flow rates (100 gpm) and high pumping heads (240 ft TDH). To make that work, a triplex system of positive displacement pumps was specified and installed. The 8,600 feet long force main pipeline was constructed of 6-inch SDR 11 HDPE pipe. Pipeline isolation valves, cleanouts and sewage air relief valves were installed along the length of the pipeline to improve operation and serviceability. A propane fired emergency generator was installed at the lift station to provide clean site power, when needed.
There were a number of locations within the Townsite where the clay tile pipes had failed, primarily because of root intrusion, and the rehabilitation of these areas was included into the original construction project. A portion of the construction contingency funds was utilized to rehabilitate additional lengths of sewer pipe, lengthening the working life of a nearly 50 year old collection system.
Wastewater System Improvements
Client:Town of Hurley, NM
The Town of Hurley was initially developed and settled in 1910 as a company town for the employees of the concentrator and smelter operations of Chino Mines Company. Fresh water was provided to the residences and sewage was collected from the residences by the Company. The residential sewage was added to the industrial wastewater stream where it was greatly diluted and eventually recovered as industrial make-up water. As the result of a recent requirement for the sanitary treatment of the sewage, the Town is joining the Regional Wastewater Treatment plant in Bayard. In order to deliver its sewage to the plant, Engineers Inc. has provided to the Town of Hurley design and construction services for a duplex lift station and 25,000 foot long, 10-inch diameter, force main pipeline that will deliver the sewage stream into the existing Bayard gravity main approximately 300 feet upstream of the plant.
Wastewater Treatment Plant Aerators
Client: Town of Silver City, NM
The original construction of the Silver City WWTP was in 1968. Concrete structures and operating machinery had been utilized with only required maintenance since that time. A number of components had deteriorated to the point that their structural integrity was compromised, their operating efficiency was unacceptable or the original operating concept was inappropriate for the purpose. A project was developed to address the rehabilitation or replacement of components that were most greatly affecting plant performance. The design and construction of the project were completed at a time when construction costs were rising and bidding results were unpredictable.
The four gravity clarifiers/thickeners were constructed with reinforced concrete tanks, steel truss walkway bridges and center hub drives. The aeration basin was constructed with a reinforced concrete tank and steel truss walkway bridges above each of the four rotor assemblies. The outboard bearings for the walkway bridges were constructed as steel slide plates. The daily cycle of differential thermal expansion and contraction between the steel bridges and the concrete tanks had caused the tank walls to fail at the bearings. Repairs were designed and constructed to the concrete tank walls and the bearings were replaced with slide plates that included boxed-in Teflon slides.
The process aeration was performed by four paddle rotors constructed upon an oval raceway. The loss of paddles due to corrosion and the long term wear of the rotating components had reduced the reliability and performance of the aeration system to unacceptable levels. Replacement of all of the structural and rotating components with new components of greater efficiency and increased corrosion resistance was designed. The project funding was not adequate to allow the construction of the complete project. Working with the Owner, a phased replacement plan was devised where the worst three rotors were replaced as part of the project, the best unit of the original four was kept in operation and the replacement of the 4th rotor was deferred until additional funding became available. The replacement of the 4th rotor was funded and constructed three years later. The aeration rotor motors were subsequently equipped with new motor controls with soft starts and clock timers to allow timed shut down of surplus aeration capacity and energy savings during the cooler off-hours of the operation and to reduce high amperage draw and associated demand penalties at the time of motor start-up.
Plant operations efficiencies were also hampered by the inability to effectively dewater the contents of the aerobic digester basin prior to transferring process sludge to the drying beds for final dewatering. The digester basin was originally designed and constructed with decant-type valves for dewatering the sludge. Dewatering the sludge through the use of theses valves was slow and the effectiveness of the dewatering was poor, causing material handling problems at the plant. Working with an equipment vendor, EI personnel developed a conceptual design that would allow dewatering of any desired depth of the basin. The construction of other improvements in the aerobic digester process precluded the construction of this dewatering concept.
South Side Sewer (Trunk Line Project)
Client: City of Deming, NM
The purpose of the project was to extend the City of Deming's existing water and wastewater collection systems to the south side of town. The area is rapidly developing and there are multiple planned subdivisions. The City wants to promote growth by installing trunk lines that will ensure that the City's infrastructure can keep up with the demand. The project cost was estimated to be $3.9 million. Funding was provided by multiple sources including the Army Corp of Engineers and the New Mexico Finance Authority. The work consisted of a Preliminary Engineering Report, an Environmental Assessment, the design and construction of approximately 5.7 miles of new 18-inch wastewater collection piping, 65 manholes, 1.2 miles of 10 force main and approximately 6.3 miles of new 12-inch water distribution piping. In addition a new lift station with variable frequency drive pumps was connected to the City's existing SCADA (Supervisory Control and Data Acquisition) system. The SCADA system was designed in a previous project by Engineers Inc.