Bates Engineering, Inc. Tank Rehabilitation

Tank Rehabilitation

Bates Engineering designs many new tanks. As a result our clients regularly ask us to review their tanks designed by us and others. The review typically culminates in a report which includes recommendations for improvements and repair. Examples of recent projects that Bates Engineering has completed from review through construction are listed below.

City of Fort Collins 4 MG Reservoir

Completed access house at the
City of Fort Collins 4 MG Reservoir.

Fort Collins Utilities Reservoir Improvements

In 1995, the City of Fort Collins, Colorado contracted with Bates Engineering to review all of their system reservoirs to determine necessary improvements. The reservoir system at that time consisted of two concrete 15 MG "hopper bottom" reservoirs at the Water Treatment Facility constructed in the 1960's and a two-cell rectangular concrete 4 MG reservoir near the Colorado State University stadium constructed in the 1980's. Bates Engineering made observations both from a raft and the dry reservoirs and provided the City with reports including repair and improvement recommendations. Bates prepared bid documents to carry out these recommendations.

In 1996, the City approached Lillard and Clark construction about providing construction services in the City's modified design/build process for $600,000. Work was carried out from 1996 to 1998. Work included:

Site access improvements including regarding, placement of base course and new concrete stairways
Doubling the size of one access house to provide a disinfection clean room
Providing new doors, recoating of steel surfaces, halogen lighting and a fall protection system in all access houses
Valve vault improvements including an enlarged hatch, lighting and heating
Installing 10 new 5'x 8' aluminum hatches on concrete risers through the roofs for light, ventilation and access
Installing one-half mile of 4-inch PVC washdown piping to facilitate annual cleaning of the reservoirs
Various concrete repairs including polyurethane injection of leaking joints and sealant replacement. Due to the difficult floor geometry, roof repairs were made by the contractor from a floating platform inside the tank

At this time, Bates Engineering was also asked to make a recommendation for coating the 4 MG Reservoir roof which has experienced significant structural cracking. Bates researched 17 coating products for the City and evaluated each product based on nine weighted criteria which were believed to be important to the success of the project including constructibility, serviceability, durability and cost. Three of these products were selected for further evaluation. Bates arranged with three coating contractors to apply test sections to the reservoir roof. After one year in place, Bates evaluated the coatings and made a final coating selection. In 2000, Bates prepared bid documents to complete this work.

Baffle Details City of Fort Collins 15 MG Reservoirs

Baffle details in the City of Fort Collins, Colorado 15 MG Reservoirs

In 1997 the City asked Bates Engineering to perform a hydraulic model study. The study conducted at the Bureau of Reclamation Hydraulics Laboratories in Denver developed efficient baffle systems to increase contact time in the two short-circuiting 15 MG Reservoirs. Bates designed Hypalon baffles that were installed by Lillard and Clark Construction in 1998. The City's subsequent fluoride tracer tests verified the efficacy of the baffle systems. This study was included in an AWWA Research Foundation study report and won the American Consulting Engineers Council of Colorado Excellence Award for Studies in 2000.

Rafter replacement in the City of Longmont 6 MG Tank

City of Longmont 6 MG Steel Reservoir

In 1997 the City of Longmont, Colorado asked Bates Engineering to evaluate two of their reservoirs including their 6 MG steel reservoir. Bates performed both a floating and a dry review. Bates Engineering contracted with a nondestructive testing service to evaluate steel thickness in the floor and roof and a tank testing service to perform magnetic flux testing of the floor. Bates had the interior and exterior coatings tested for lead, chromium and cadmium. Significant levels of lead were found both in the interior and exterior coating systems. A complete report with photographs was presented to the City making repair and improvement recommendations.

Bates prepared bid documents for the work which included the following items:

Site grading and access improvements
Replacement of three 36-inch butterfly valves in the valve vault
Recoating the reservoir including removal or overcoating of lead-based paints
Removing and replacing 30 corroded roof rafters
Lowering the height of the overflow piping to avoid wetting of the roof rafters
Providing safety rails around the inlet pipe and floor drain
Designing a new caged exterior ladder with locking cover and landing
Providing two new 5' x 8' roof access hatches with safety railing
Adding a new 30-inch-diameter manhole including a concrete washdown pad outside the tank and reinforcing the steel floor inside the tank to protect from traffic damage
Verifying the results of the magnetic flux testing by cutting and repairing coupons from the tank floor plate

Bates provided regular field observation during the construction and provided construction administration services to the City.

East Vail Meadow Tank

Completed East Vail Meadow Tank

Eagle River Water and Sanitation District
500,000 Gallon East Vail Meadows Tank

Between 1996 and 1998, Eagle River Water and Sanitation District in Vail, Colorado asked Bates Engineering to review and prepare bid documents to repair three of their system reservoirs including two concrete tanks located on Vail Mountain. The concrete tank repairs included removing a damaged lining from one tank and shotcreting the underside of the roof of the other. Both tanks received new roof hatches and a new ladder. Due to the difficult terrain, Bates reviewed one site by snowmobile. Construction access required the use of track vehicles.

The 500,000 Gallon East Vail Meadows steel tank is located at the east end of Vail in an active avalanche chute. Due to the high value of downhill residences, the City asked Bates Engineering to retrofit the tank to mitigate damage due to the presence of the tank and stored water during a 100-year avalanche event. Because stiffening the tank was believed to exceed the replacement value of the tank, Bates designed retrofit anchor bolts to secure the tank to its concrete foundation for the loads due to this 17-foot-deep avalanche. In addition to specifying the new interior and exterior coatings, Bates also recommended cathodic protection system repairs, designed a new access ladder and helped the District select aluminum clad insulation to replace badly vandalized insulation. Construction was completed in 1999.