  Pacific Northwest National Laboratory has recently opened a shallow
underground laboratory intended for measurement of low-concentration levels of
radioactive isotopes in samples collected from the environment. The development
of a low-background liquid scintillation counter is currently underway to
further augment the measurement capabilities within this underground
laboratory. Liquid scintillation counting is especially useful for measuring
charged particle (e.g., $\beta$, $\alpha$) emitting isotopes with no (or very
weak) gamma-ray yields. The combination of high-efficiency detection of charged
particle emission in a liquid scintillation cocktail coupled with the
low-background environment of an appropriately-designed shield located in a
clean underground laboratory provides the opportunity for increased-sensitivity
measurements of a range of isotopes. To take advantage of the 35
meters-water-equivalent overburden of the underground laboratory, a series of
simulations have evaluated the scintillation counter's shield design
requirements to assess the possible background rate achievable. This report
presents the design and background evaluation for a shallow underground, low
background liquid scintillation counter design for sample measurements.
