BALTIMORE CITY DPW
Baltimore City, MD
Throughout our half century of existence, Balter has provided a wealth of projects for Baltimore City DPW. These projects range from pipeline design, to construction management, as well as dam evaluations and tank construction. Some highlights of work we have recently performed, or are currently performing for Baltimore City are provided below.
Druid Lake Dam
Druid Lake Dam construction started in 1863 with a $300,000 loan by Baltimore City to construct a billion gallon reservoir to provide suitable drinking water. Completed in 1871, the dam supported a reservoir 750 feet long with a width of 600 feet at the base tapering to 60 feet at the top and covers over 55 acres. Reconfigured over the years to construct I-83 and the 28th Street exit, the dam still measures 30’ at the top.
The Robert B. Balter Company (Balter) performed a geotechnical evaluation on the existing Druid Hill Lake Dam located west of Interstate 83 in Baltimore, Maryland. A significant settlement event occurred on I-83 in the outflow pipes for the dam. Concerned that the settlement was due to a leak in the dam, the Maryland Department of the Environment (MDE) requested that the City of Baltimore perform a study on the dam to confirm that it was still in good working order.
To perform this study a multiple-phased approach was taken, with Phase 1 consisting of a records research program and a site reconnaissance. The records research included reviewing all city documentation, and in-house Balter documents, including boring logs, from the surrounding area. This data provided an understanding of how the dam was constructed and how it has changed over the years. A detailed site reconnaissance was performed which included traversing the entire slope from top to bottom and the full length of the slope. Observations included minor settlements and localized slope failures throughout the slope.
Phase 2 of the study was to perform a geophysical evaluation to identify potential areas of concern (ie, potential water seeps, low density zone, etc.). The study included an electromagnetic survey, a microgravity survey, a spontaneous potential survey, and MASW. The advantage of this study was that it identified areas of potential concern which we focused on and conversely eliminated previously believed areas of concern.
Phase 3 consisted of geotechnical borings at the top, middle, and toe of the existing dam. Significant coordination with MDE and the City of Baltimore to obtain both ROW and Joint Environmental Permits was needed. MOT was required along I-83. The borings were drilled through the entire dam into the underlying rock. The borings were converted into ground water monitoring wells and vibrating wire piezometers for a long-term monitoring program. Soil samples collected were tested for engineering index tests, flex wall permeability, and pin hole flow tests all of which to evaluate the seepage conditions of the dam. Extensive seepage and slope stability analyses using Slide 6.0 by Rocscience were performed which indicated this historic earthen dam is still working properly after over 140 years of use. The piezometer data was evaluated using an in-house developed computer program. Once the study was completed, Balter provided the City with directions and specifications to continue to provide MDE with routine monitoring results of the monitoring wells and vibrating wire piezometers.
Balter’s continual involvement in the Dam has extended to other area projects, including the Vernon Pumping Station which is a part of the Druid Lake system, located just east of the dam. As part of the station upgrades, new water lines will be installed within the toe of the dam, which is not routinely performed in the Mid-Atlantic region. Balter corresponded with various Corp of Engineer and MDE dam experts on the issue and performed additional significant stability evaluations specifically addressing the temporary excavation at the toe. Developed Plans and Specifications addressing required construction slope monitoring equipment and trench support methods.
Ashburton Pumping Station
The City of Baltimore is planning a significant renovation and upgrade to the historic Ashburton Pumping Station. Inside the pumping station, new pumps, HVAC, and electrical systems will be installed. Outside a new generator building will be constructed along with new above-ground fuel tanks. The new generator building was designed to conform to local historical requirements such that the new building will match the style of the historic pumping station.
The Robert B. Balter Company (Balter) performed an extensive geotechnical evaluation to provide detailed geotechnical recommendations for design of the new generator building. The challenge to the site was identifying the subsurface materials which were comprised of fills up to 50 feet that were placed in the early 1900s during the original construction of the pumping station and Ashburton Lake Dam. The area was a large ravine that was filled in with boulder fills in an uncontrolled manner. The sensitive nature of the new generator building warranted the use of a deep foundation system to bypass the load to the underlying bedrock. A detailed network of underground utilities is present in the proposed generator building area; therefore, Balter performed Ground Penetrating Radar (GPR) to locate all of the utilities prior to drilling. Multiple borings were drilled across the site to fully evaluate the subsurface conditions. Significant soil and rock laboratory tests were performed in our AASHTO-accredited and Corps of Engineers validated laboratory. Using the field and laboratory data, detailed recommendations were developed addressing a micropile foundation system for support of the generator building. Balter developed the earthwork and micropile specifications for the project as well as assisted the client in development of the final plans. Participated in all design meetings and in meetings with the City of Baltimore. Once construction begins, Balter will remain active in the project providing Quality Assurance and Special Inspection services during construction of the generator building.
Balter has provided a wide range of professional services for Dundalk Sewershed. These services have included everything from Geotechnical Support to Asset Location in the field for the City of Baltimore.
Geotechnical Support - The Robert B. Balter Company (Balter) provided geotechnical services for the Dundalk Sewershed (SC902) located in Baltimore, Maryland. The purpose of our services was to provide a summary of the anticipated geologic conditions anticipated within the sewershed. The study was performed using in-house data, including data collected from our extensive library, public information, and information provided by the client. Geologic maps, topographic maps, and in-house boring logs were reviewed to provide a summary of the anticipated subsurface conditions. In addition to review, each proposed replacement location was visited by one of our engineers to make observations regarding the existing site conditions. A report was developed that provided the summary of the research findings, as well as recommendations for future subsurface evaluations.
Access Requirements - Balter was also responsible for detailed research and oversight of property assessments to prepare construction access documents for the Dundalk Sewershed which has been undergoing significant infrastructure upgrades. As part of this process Balter reviewed plans provided by the client regarding the sewershed to develop a detailed database which provided property owners along with any special access conditions or permit requirements. Balter’s scope included field reconnaissance to confirm field conditions and access locations.
Asset Location - During subsequent field visits, Balter also assisted in maintaining databases that documents asset location, and highlighted discrepancies with the existing documentation. This included, but was not limited to, location manholes and outfall structures, as well as highlighting manholes which may have been buried during paving operations. These data was used to update the City inventory of Wastewater assets to later be incorporated into GIS layers.
Construction Document Development - Balter also assisted the client with development of the final plans and specifications. This consisted of detailed site visit to accurately locate existing features, including manholes, and light poles, as well as evaluating the site conditions at all of the residential properties that could be impacted by future construction. Transferred all documented items to the final AutoCad drawings as well as making modifications to the drawings as requested by the client. Condition Assessment – Finally, Balter was responsible for reviewing both pre- and post-rehabilitation Closed Circuit Television (CCTV) Videos for improvements to the Dundalk Sewershed. As part of the work, Cured in Place Plastic (CIPP) was used to line the existing sewers. Prior to the CIPP lining, the pipes were inspected with CCTV to locate any necessary point repairs or locations that may not be lined. Balter provided comments on the contractor’s claims for point repairs as well as identifying other potential issues during lining. During the asset location operations, Balter also performed condition assessments of existing manholes within the sewershed using both visual and CCTV methods. Following the lining procedures, the pipe segments were inspected again to confirm that the CIPP was adequate. Balter was responsible for reviewing the post-lining videos to identify any discrepancies and aide the City of Baltimore in accepting the CIPP.