The purpose of the Dry Weather Monitoring (DWM) Program is to identify and address pollutant discharges through the sampling of dry weather flow in urban areas to prevent contaminant entry into the storm drain system and the subsequent degradation of water quality in receiving waterbodies. The DWM sample site CYPB0178 VL, located in the basin of Nature Park, remains on the targeted list for the city of Cypress due to repeated nitrate-nitrogen exceedances over a 4-year sampling period. A direct source for the exceedances has yet to be identified by stormwater officials and is presumed to be the result of nonpoint source urban runoff originating from the adjacent residential neighborhoods. In an effort to better understand the potential nitrate-nitrogen exceedance source, this study analyzes dry weather sample data collected from May 2016 to September 2020 as well as the site's hydrogeologic setting and past and present land use pressures. Analysis shows a strong correlation between nitrate-nitrogen, electrical conductivity, and selenium concentrations at the Nature Park sample site. These relationships suggest that the nitrate-nitrogen exceedance source may be due to groundwater seepage within the storm drain system rather than nonpoint source urban runoff. This is further supported by the area's shallow depth to groundwater and intense history of agricultural and husbandry land use. Given these factors, it is likely that primary source for the nitrate-nitrogen exceedances is contaminated groundwater resulting from past surface contamination pressures and an overall lack of water quality regulations.
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