Minutes 10-14-2014 Late - Laserfiche WebLink

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• TM1: Comparison of Flow Estimation Methods • TM2: Evaluation of the Sensitivity of the Falls Lake Nutrient Response Model Water Quality Sampling During July 2014, CardnoEntrix received approval from DWR for three required technical memoranda that had been prepared and submitted for DWR review that describe in detail the watershed sampling project that will form the foundation of the re-examination process: • Quality Assurance Project Plan (QAPP) • Falls Lake Watershed Monitoring Plan • Modeling Framework The QAPP and the Monitoring Plan describe the three-to five-year watershed sampling effort that was initiated in August 2014. The water quality sampling program will provide information for the following purposes: • Determination of nutrient source allocation and jurisdictional nutrient loading to Falls Lake; • Falls Lake response modeling; • Development of data for consideration of additional regulatory options; and • Linkage of water quality conditions in Falls Lake to the designated Attachment C illustrates the locations that will be sampled in the Falls Lake watershed for the determination of jurisdictional loading, as well as the stations that are designed to provide information about nutrient loading to the lake. Attachment D illustrates additional water quality sampling locations that other organizations are monitoring within Falls Lake. Modeling Data Gaps UNRBA re-modeling of Falls Lake is expected to start in approximately two years, and is intended to update the lake response model that DWQ utilized in the development of the Falls Lake Rules. The UNRBA contractor identified several gaps in the data used by DWQ in the modeling completed during the development of the Falls Lake Rules, including: • DWQ held constant the total organic carbon and chlorophyll-a input values assumed for the tributaries feeding into Falls Lake. These concentrations were based on levels measured within the lake, not in the tributaries. It is probable that these concentrations were artificially high to begin with and were unable to decrease at all over the course of the modeling study. • There are no stream gages on any of the streams that flow into Falls Lake east of I-85, thus no flow information was incorporated for any of these 12 streams. • Atmospheric deposition of nitrogen in the lake or watershed was not accounted for by DWQ. • Streambank erosion, possibly a significant source of phosphorus in the watershed, was not considered as a possible source by DWQ. • Internal lake processes, such as sediment re-suspension, were also not accounted for by DWQ. BMP Credit Review and Nutrient Trappinq Analysis CardnoEntrix is also currently working on a nutrient reduction BMP credit literature review and the analysis of nutrient trapping that occurs within the larger impoundments in the watershed. While the nutrient trapping analysis will be important for the remodeling of the watershed, the BMP credit determination project will be beneficial to entities, including UNRBA member governments, which must use BMPs to meet required nutrient reduction goals. DWR approval of additional BMP credits is expected to take nearly a year per each additional BMP as a result of the stringent credit determination process currently proposed by DWR. With several measures in need of credit determination, the process of developing a thorough BMP "tool kit" for regulated entities to employ may take a decade or more.