Long Creek Monitoring Data Analysis

Challenge

Long Creek is a freshwater urban stream with a watershed area of approximately 3.45 square miles and is located in Portland, South Portland, Westbrook and Scarborough, Maine. The stream currently does not meet State water quality standards due to stormwater runoff which causes elevated concentrations of metals, chloride, phosphorus, nitrogen, polycyclic aromatic hydrocarbons, and reduced DO concentrations. Additional issues include altered hydrological conditions and increased water temperatures from lack of shading in certain areas. Impervious cover such as roads, driveways, parking lots, sidewalks, rooftops, and other constructed surfaces restrict infiltration within the environment. The Long Creek Watershed Management District (LCWMD) desired the services of a qualified consultant to provide monitoring data analysis services to assess the effectiveness of ongoing watershed restoration efforts and help direct future work of LCWMD.
 

Solution

GZA was contracted to provide monitoring data analysis services. These services included a review and statistical analysis of approximately 10 years of water quality monitoring data, which included the following:

• Stream discharge and stage monitoring at the six primary monitoring sites annually
• Continuous water quality monitoring at the six primary sites annually from March to November
• Three to four rounds of spring melt sampling annually at the six primary sites
• One baseflow round of analytical samples in the months of May, July, and September of each year at the six primary and three secondary monitoring sites
• Weather monitoring data, including temperature, and precipitation (rainfall and snowfall) from the National Oceanic and Atmospheric Administration weather station located at the Portland International Jetport
  
   

Benefit

 The Long Creek Watershed water quality monitoring program has accumulated a significant amount of data since the onset of the program in 2010. The dataset holds valuable information for the overall health of the watershed. Key findings and implications are summarized below:

• Daily median, maxima, and minima appeared to be an appropriate reduced (surrogate) dataset in place of the original data for the statistical analyses in this study.
• Water quality data varied noticeably spatially between different monitoring sites; and seasonality appeared to be a major influence factor of water quality and stream flow in the study area.
• Exceedance over the Criterion Maximum Concentration (CMC, or acute) and Criterion Continuous Concentration (CCC, or chronic) criteria were calculated for Chloride (based on the continuous dataset) and metals (from the discrete sampling program). The results showed that there was a significant percentage in time that the Chloride and metals concentration in the stream exceeded the CMC and CCC thresholds.
• Trend analysis was performed on Chloride to examine the effectiveness of the BMPs, using flow weighted monthly averages. The Mann-Kendall and Theil-Sen trend analysis results indicate that there is a downward trend at Site 01 and possibly at Site 17 as well, but no sufficient evidence to make a conclusion for other sites.