Tar pit

A tar pit is a special case of contaminated deposits: it combines historical construction and industrial technology with today’s requirements for environmental, occupational, and plant safety. In the context of deconstruction, remediation, and selective removal, the tar pit touches on topics such as materials science (tar versus bitumen), contaminated sites management, emissions control, as well as the question of which gripping, cutting, or splitting methods are used to properly open concrete coverings, built-in components, or in-situ rock. Especially in concrete demolition and special demolition as well as in building gutting and cutting, tools such as concrete pulverizers or hydraulic rock and concrete splitters are used, supplied by compact hydraulic power units.

Definition: What is meant by a tar pit

A tar pit is an artificially created or subsequently formed cavity or depression in which tar-containing substances have been deposited, temporarily stored, or have seeped. Historically, such pits often originated around gasworks, coking plants, tar furnaces, road depots, or roofing felt production. They typically contain coal tar, tar oil, tar-containing sludges, and mixtures with mineral aggregates. Tar pits are relevant in contaminated sites practice because their contents may include polycyclic aromatic hydrocarbons (PAHs) and other critical constituents that can impact soil, structures, and groundwater. In addition to open pits, there are covered tar deposits encased in concrete or concealed under paving, asphalt, and slabs, which must be selectively exposed during deconstruction.

Origin, construction types, and typical features of tar pits

Tar pits were created partly as simple ground depressions, partly as masonry or concrete basins and shafts. A layered buildup of collected sludge, mixed-in construction materials, tar pitch, sand, brick rubble, and metal parts is common. The top is often sealed with concrete slabs, foundations, screeds, or asphalt surfaces. Odor (phenolic, “tar-like”), dark, viscous to brittle masses, and iridescent films indicate tar-containing substances. In existing structures, built-ins such as steel plates, anchors, old pipe connections, or separator chambers may occur. Such coverings can be selectively removed during deconstruction using concrete pulverizers or opened with hydraulic splitters for stone and concrete with low vibration, in order to provide controlled access to the underlying contents.

Tar, bitumen and related substances: differences with practical relevance

Coal tar is a distillation product from coal processes and, depending on the fraction, contains PAHs, phenols, and other aromatic hydrocarbons. Bitumen, by contrast, derives from petroleum processes and has a different contaminant profile. In practice, the distinction is essential for evaluation, waste separation, and disposal. Clues are provided by odor, UV fluorescence, solubility in organic media—but ultimately analytics provide certainty. For the choice of deconstruction methods, it is relevant whether thermal methods should be avoided and whether low-vibration, cold cutting techniques—such as hydraulic splitting or pulverizer-based methods—offer advantages to reduce emissions and sparks.

Hazardous substances, environmental aspects, and occupational safety

PAHs, BTEX, phenols, sulfur compounds, cyanides (site-specific), heavy metals, and tar oils may occur in tar pits. These entail potential risks for skin contact, inhalation of vapors, and for water bodies and soil. Measures such as low-dust working methods, ventilation, spark avoidance, and suitable personal protective equipment must be considered in planning. In sensitive environments—e.g., near buildings, utilities, or water bodies—methods with low vibration and controllable force transmission are often preferred, including the targeted use of concrete pulverizers and hydraulic splitters for stone and concrete. Regulatory requirements must always be reviewed on a site- and project-specific basis; general standards and authority guidelines serve as a framework.

Investigation and assessment before intervention

Professional investigation is the basis of any measure. It includes historical research, probing, core drilling, sampling, and, if necessary, geophysical methods. The goal is to clarify location, extent, construction, and material inventory. The result determines the access and removal strategy: If the pit lies beneath a reinforced concrete slab, removal by concrete pulverizers followed by hydraulic splitting may be appropriate; if tar-containing masses are directly adjacent to natural rock, selective rock excavation with a rock wedge splitter is an option to comply with blasting prohibitions and keep vibrations low.

Exposure, opening and selective removal

Opening a covered tar pit requires a planned, step-by-step approach to avoid uncontrolled outflows and emissions. In practice, a sequential approach with cold, controlled separation techniques has proven effective:

• Concrete demolition: Covering slabs, bearing elements, and lintels are picked off piece by piece with concrete pulverizers; embedment depths and reinforcement layout are verified by trial exposure and marking.
• Low-vibration approach: Hydraulic splitters generate defined splitting forces in boreholes to release massive components or in-situ rock in a controlled manner, without transmitting impact energy to the surroundings.
• Separating metal: Reinforcement, tabs, or cover plates are cut using steel shears or combination shears; Multi Cutters assist in cutting heterogeneous inserts.
• Power supply and mobility: Hydraulic power packs supply pulverizers, split cylinders, and shears. The choice of output, hose length, and equipment location is oriented toward emission zones and accessibility.

This allows bottlenecks, foundations, and built-ins to be targeted and released. Functional reliability, sealing edges, and emergency sealing must be provided if contents are flowable.

Handling of liquid and solid contents

Tar pits may contain liquid, pasty, or solid fractions. As a rule: do not mix, dilute, or foam without a plan. Instead, separate, secure, and document.

• Separating and recovering: Viscous contents are vacuumed off or recovered by scooping; solid chunks are separated in suitable containers.
• Separating components: Concrete, masonry, steel, wood, and tar-containing materials should be separated on site wherever possible to organize material flows.
• Sealing and leakage control: Temporary dams, absorbent barriers, or containment trays prevent unintended release. Positive and negative pressure zones can control emissions.

Where steel tanks, built-in trays, or vessels are encountered, they require a targeted opening strategy. For cold mechanical opening, steel shears or a Tank Cutter may be considered, provided a risk assessment allows it and protective measures are in place.

Application areas and typical scenarios

Concrete demolition and special demolition

When deconstructing covering structural elements, the focus is on controlled opening and separation. Concrete pulverizers support the stepwise removal of load-bearing and non-load-bearing components, while hydraulic splitters for stone and concrete convert massive blocks into manageable segments. For reinforcement and profiles, steel shears complement the process chain.

Building gutting and cutting

In existing buildings with potentially contaminated areas, exposure is often only possible in sections. Combination shears and Multi Cutters simplify cutting through alternating material layers without having to change tools between operations.

Rock excavation and tunnel construction

Tar-containing deposits may lie in former galleries, shafts, or fills. Rock wedge splitters make it possible to selectively release surrounding rock where blasting vibrations or ignition sources are to be excluded. The targeted splitting process creates working space for safe recovery.

Natural stone extraction

In rare cases, tar-containing substances occur in quarries as legacy deposits at the edges of former operating areas. Selective removal with splitters and pulverizers minimizes impacts on ongoing extraction.

Special deployment

At locations with limited access, sensitive adjacent structures, or emission restrictions, quiet, low-vibration methods are required. Here, hydraulically operated gripping and splitting tools offer advantages in controllability and cut profile—an essential criterion for protecting surrounding structures.

Planning, sequence, and quality assurance

A structured workflow improves safety, ergonomics, and outcome quality. The following steps have proven their worth:

1. Pre-clarification by reviewing historical records, utility plans, and preliminary investigation results.
2. Protection concept for people, environment, and neighbors with defined zones, work equipment, and emergency measures.
3. Selective opening of the covering using concrete pulverizers and—where indicated—hydraulic splitters for stone and concrete; cut steel parts with steel shears or combination shears.
4. Recovery of contents by fraction; tight interim storage, labeling, and documentation.
5. Control of emissions (e.g., odors, volatile constituents) as well as regular visual checks and leakage tests.
6. Aftercare with final inspections and monitoring—such as soil gas, leachate, or component surfaces—in accordance with project specifications.

Practical guidance on tool selection

Tool selection is based on component thickness, reinforcement level, accessibility, and emission targets:

• Concrete pulverizers for controlled nibbling of slab edges, beams, and wall panels; good visibility and finely adjustable force transmission.
• Hydraulic splitters for stone and concrete for low-vibration segmentation of massive components or natural rock; drilling pattern planning controls crack lines and piece sizes.
• Steel shears for reinforcement, profiles, and plates; combination shears and Multi Cutters for changing materials.
• Hydraulic power packs matched to the required flow rate and line length; pay attention to equipment location, ventilation, and hose routing.
• Tank cutters for vessels and closed built-ins, provided the permissible conditions (degassing, gas-free certification, protective measures) are met.

Documentation and verification

Transparent documentation accompanies every phase: photo records before/after opening, sketches of drilling patterns, details of tools and parameters, consignment notes for material flows, and logs of measurement and control values. These documents support the assessment of whether the tar pit was properly exposed, contents were correctly recovered, and adjacent components or soils were protected.

Special aspects in existing structures: building during operations and inner-city locations

Tar pits often occur where areas have been overbuilt multiple times. In densely developed areas, coordination with adjacent trades and operating units is crucial. Tools with low noise emission, controlled force, and without thermal separation facilitate work during operations or at night. This argues for splitting and pulverizer-based methods that can be deployed precisely and in sections.

Material separation, packaging, and transport

A clear separation logic reduces risks and costs. Practical steps include:

• separate containers for tar-containing, mineral, metallic, and organic fractions,
• labeled, tight containers with catch trays,
• careful cleaning of tools and hoses in secured areas,
• transport along predefined routes with minimal reloading.

The specific classification and disposal are based on analytics and applicable requirements. General statements do not replace project-specific evaluation.

Quality characteristics of a successful approach

Success is reflected in cleanly separated material flows, intact edge zones, minimal uncontrolled emissions, and reproducible work steps. In execution, robust, finely controllable tools and a team that coordinates splitting, pulverizer, and shear processes support these outcomes. Especially for tar pits, a combination of precise gripping, targeted splitting, and controlled cutting pays off.