INTEGRATION OF CONCRETE LINED STORM DRAINS IN STUDIES OF STREAM/AQUIFER INTERACTIONS IN URBAN SETTINGS - MORE DYNAMIC THAN YOU MIGHT AT FIRST THINK

Concrete lined storm drains are used all over the world to convey storm runoff away from urban areas. They also convey dry weather flows such as car wash runoff, lawn runoff, and other “nuisance flows” away from urban centers. Areas in southern California and elsewhere have shallow water tables and dry weather flows in concrete lined channels often consist primarily of perennial groundwater seepage flows. In these areas, groundwater leaks through cracks, joints, weepholes, and intentional dewatering structures into storm drains, with flows eventually discharging into natural riverine channels, coastal wetlands, and estuaries. The “lined” sections of these channels are hardly impervious; in fact, the lining of channels often affords excellent opportunities to collect groundwater samples at discrete points that are usually not present along unlined channels where well control is sparse or where technical or legal issues prevent installation of piezometers. Frequently, as much as 95% of the nutrient and trace element loading in urban catchments during dry weather is from seepage of groundwater that is laden with pollutants. Pollutants then impact the ecology and water quality of receiving waters. This project presents several examples of our experiences in conducting stream/aquifer studies in lined and semi-lined channels in Southern California. Sub-projects include evolution of groundwater quality along flowpaths oriented sub-parallel to the transect of lined channels, detection of unwanted recharge mounds in shallow groundwater systems due to leaky water main pipes, and geologic factors in water quantity and water quality fluxes in urban catchments. Tools that are utilized and described include application of isotopic tracers (O-H-S-N stable isotopes); trace element speciation analysis; and innovative sampling methods.