E-6 C15-2022-0013 ADV PACKET FEB 14 — original pdf

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BOA GENERAL REVIEW COVERSHEET CASE: C15-2022-0013 BOA DATE: February 14th, 2022 ADDRESS: 3300 Blue Jay Ln OWNER: Dana & Lenn Sellers COUNCIL DISTRICT: 6 AGENT: Janis J. Smith, P.E. ZONING: LA LEGAL DESCRIPTION: LOT 1 BLK 2 HIDDEN VALLEY SEC NO 1 VARIANCE REQUEST: a) increase the dock length from the shoreline of 30 feet (allowed) to 53.1 feet (requested) b) increase the dock width parallel to the shoreline from 14 feet (allowed) to 16.4 feet (requested) SUMMARY: erect a boat dock ISSUES: shallow water and lake bed impossible to dredge ZONING LAND USES Site North South East West LA SF-2 LA LA LA Single-Family Single-Family Single-Family Single-Family Lake Austin NEIGHBORHOOD ORGANIZATIONS: 2222 Coalition of Neighborhood Association Inc. Austin Lost and Found Pets Friends of Austin Neighborhoods Leander ISD Population and Survey Analysts Long Canyon Homeowners Assn Sierra Club, Austin Regional Group Steiner Ranch Community Association Steiner Ranch Neighborhood Association TNR BCP Travis County Natural Resources E-6/1C15-2022-0013 12853356 0147530119 E-6/2E-6/3E-6/4E-6/5E-6/6E-6/7E-6/8E-6/9E-6/10E-6/11Figure 8. DDE concentrations in Lake Austin sediment, 1985-2009. Horizontal line represents TEC value for DDE of 3.16 ug/kg. Figure 9. Total PAH concentrations in Lake Austin sediment, 1985-2009. Horizontal line represents TEC value for PAH of 1610 µg/kg. Conclusions The following conclusions were derived from the analyses of Lake Austin sediment data: Sediment quality on Lake Austin does not show significant degradation over the entire period of record, with many parameters showing no change, and some metals and herbicides significantly decreasing over time. While many pesticides, herbicides, and PCBs had detectable values during the study, only seven parameters showed any lake-wide significant temporal trend. All lake-wide trends were decreasing, and all but chlordane produced this trend as a result of data collected prior to 1990. At least in the case of chromium and mercury, this may indicate an improvement in analysis techniques in the past 20 years, as SR-10-14 Page 13 of 30 September 2010 E-6/12non-detects were set to one-half the detection limit, and detection limits have improved (decreased) over time. Since 2001, no parameters have shown any lake-wide change except for chlordane. Chlordane was detected in 2003 and 2004 and has been below detection from 2005-2009. This most recent period of non-detects may be due to scouring floods (two significant floods have occurred since 2001) removing sediment from the lake. Site specific analysis shows a similar pattern, with only five metals showing any temporal trend. Of these, only copper and zinc trends are a result of more recent data, other trends appear to be from data collected prior to 1990. Copper and zinc are both increasing over time, and only at Tom Miller. The reasons for this increase are not clear, although copper could be a result of a possible (but not documented) increase in copper-based herbicide use since 1999, when hydrilla was first documented in the lake. It is important to note that even with this increase the maximum value reported is well below the TEC for both parameters. Spatially, concentrations of parameters generally increased with downstream location, as the most downstream site, Tom Miller had the significantly highest mean for most parameters showing spatial differences. This is to be expected, as there is increasing, and more long-established, residential increasing, and more long-established, residential development towards the downstream end of the lake. In addition, sediment (and associated In addition, sediment (and associated development towards the downstream end of the In addition, sediment (and associated contaminants) is transported downstream during high flow events and deposited in deeper, slower water contaminants) is transported downstream during high flow events and deposited in deeper, slower contaminants) is transported downstream during high flow events and deposited in deeper, slower water near the dam, so the most downstream site becomes the repository for contaminants. near the dam, so the most downstream site becomes the repository for contaminants. The Bull Creek site, located between the upper and the lower sites, was often a ‘transition’ site, either sharing significant means with the upper sites or with Tom Miller, except for PAHs. This fits with the pattern of longitudinal increase noted above. The upper sites, Selma Hughes and Emma Long, were not significantly different from each other, and not significantly different from each other, and always had means well below the other two more downstream sites. This could be in part due to their This could be in part due to their always had means well below the other two more downstr This could be in part due to their location in the upper, less developed portion of the watershed, but also a function of the sediment location in the upper, less developed portion of the watershed, but also a function of the sediment location in the upper, less developed portion of the watershed, but also a function of the sediment characteristics. Both these sites were dominated by sand, with very little clay or silt, providing little characteristics. Both these sites were dominated by sand, with very little clay or silt, providing little characteristics. Both these sites were dominated by characteristics. Both these sites were dominated by sand, with very little clay or silt, providing little substrate for contaminant adherence. In addition, the upper end of the watershed typically experiences In addition, the upper end of the watershed typically experiences substrate for contaminant adherence. In addition, the upper end of the watershed typically experiences more scouring flows during flood events, as extremely high velocity water moves in from the upstream more scouring flows during flood events, as extremely high velocity water moves in from the upstream more scouring flows during flood events, as extremely high velocity water moves in from the upstream dam, and less sediment was available at these sites during many sampling events. dam, and less sediment was available at these sites during many sampling events. PAHs show a unique pattern from other parameters, with Bull Creek having a significantly higher mean than all other sites, and a single exceedance of the TEC. The site is located at the confluence with the lake’s only major tributary (Bull Creek), which has a large drainage area with ongoing urban development, possibly a contributing factor in these higher PAH values. Sediment toxicity is generally low on Lake Austin, with only four parameters (arsenic, DDD, DDE, and PAH) showing any exceedences of TEC. None of these parameters were shown to be increasing over time. Recommendations Drop parameters that have no detectable data during the study: o All data from silver, aldrin, alpha-chlordane, gamma chlordane and technical chlordane and diazinon were below detection limits during the period of record, and should be considered for deletion from future parameter lists, unless detection limits improve or conditions change that may increase these parameters. o Consider dropping other parameters with detected, but very low values (i.e., DDT, PCBs) Drop sites that show no significant trends or provide limited information o Upper sites (Selma Hughes, Emma Long) show no significant difference from each other and were always lower in value than the lower end sites. Bull Creek only showed a significant difference from all other sites for PAHs, while Tom Miller Dam consistently showed higher levels of detected constituents, and was significantly different from all other sites. It is recommended that only Tom Miller Dam be included in future monitoring efforts. Any changes in Bull Creek sediment quality can be addressed by the Environmental Integrity Index creek SR-10-14 Page 14 of 30 September 2010 E-6/13E-6/14