Natarajan, PoornimaIncrease in stream temperature by heated stormwater runoff from impervious surfaces is a serious environmental problem. An underground storage/slow release facility is a versatile stormwater best management practice (BMP) for buffering high flows. Temperature reductions in underground storage BMPs, however, have not been quantified. A field study on an underground storage facility was undertaken to characterize its effect on stormwater runoff temperatures. In colder months, when the runoff temperature ranged from 5 and 15○C, small or no temperature change was observed. Runoff produced during summer storm events, with event mean temperatures over 20○C, exhibited mean temperature reductions of 1.6○C through the BMP. While statistically significant, the reductions were not sufficient to cool the summer runoff discharges below the Maryland Class III temperature standard (20○C) 100% of the time. The results indicate that underground facilities can moderate high runoff temperatures, but that a more efficient design is needed.en-USThesisEngineering, EnvironmentalBest management practiceUrban stormwater runoffUnderground storagetemperature