CPWG Evaluated Runoff Discharging Into Lake Holden.
CPWG Environmental and Water Resources Team
- Installed Autosamplers
- Collected Runoff Samples
- Compared Watershed Loadings
- Evaluated Water Quality Trends
- Reviewed Impact of Previous Changes
CPWG Analyzed Trophic State Indicators
- Total Nitrogen
- Total Phosphorus
- Secchi Disk Depth
CPWG’s Final Report
- Compared New Loadings with Previous Loading
- Evaluated Previous BMPs Effectiveness
- Ranked Estimates of Overall Runoff Loadings
- Made Recommendations to Reduce Pollution
Lake Holden Runoff Evaluation
Orange County contracted Cribb Philbeck Weaver Group (CPWG) Environmental and Water Resources team to evaluate runoff loadings and impacts from currently untreated drainage sub-basins discharging to Lake Holden. A total of 10 sub-basins were selected which currently discharge into Lake Holden with little or no stormwater treatment. Autosamplers were installed at each of the 10 selected locations, and a minimum of five runoff samples were collected at each site and analyzed for nutrients and general runoff parameters. The results of the stormwater monitoring were used to estimate runoff generated loadings from the untreated watersheds and to prioritize recommendations for future retrofit projects for sub-basins with significant runoff inputs. An updated water quality database was developed, and trend analyses were conducted for significant water quality parameters. Draft and Final Reports were prepared which outline the results of the field monitoring program and provided specific recommendations for projects to maintain and improve water quality in Lake Holden.
CPWG developed an updated water quality database of available surface water quality data for Lake Holden to identify water quality trends for significant trophic state indicators (such as total nitrogen, total phosphorus, chlorophyll-a, and Secchi disk depth) were summarized in a graphical format, and statistical trend analyses were conducted. This information was used to evaluate the success of previous water quality improvement projects conducted for Lake Holden.
CPWG personnel installed stormwater autosamplers at each of the 10 locations selected during the kick-off meeting. Each of the autosamplers included a flow probe which allowed collection of runoff samples on a flow-proportioned basis. The equipment was housed in insulated aluminum shelters for security. CPWG personnel collected a minimum of 5 composite runoff samples at each of the 10 monitoring locations. The runoff samples were collected to represent a wide range of rainfall depths and antecedent dry period conditions. The collected samples were analyzed in the laboratory for the following parameters:
- Specific Conductivity
- NOx (nitrite + nitrate)
- Particulate Nitrogen)
- Total Nitrogen
- Orthophosphorus (SRP)
- Particulate Phosphorus)
- Total Phosphorus
- Total Suspended Solids (TSS)
CPWG’s Environmental and Water Resources team used the chemical characteristics of the collected runoff samples to estimate mass loadings discharging from each of the evaluated watersheds. Revised watershed loadings were calculated for each of the sub-basin areas discharging to Lake Holden based on the results of the field monitoring program and new BMPs installed in recent years. Drainage well modifications had recently been completed on the two drainage wells located on Lake Holden. The as-built conditions of the drainage well structures were reviewed by CPWG and evaluated for potential impacts on water levels within the lake. The revised loadings were compared with previous loading estimates. Estimates of overall runoff loadings to Lake Holden from all watershed areas were ranked, and recommendations were provided for sub-basins which required additional BMPs.