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Home My WebLink AboutCT 81-04; Laguna Vista; Drainage Siltation Water Quality; 1981-03-10DRAINAGE SILTATION WATER QUALITY LACUNA VISTA CARLSBAD TRACT CT 81-4 § CONDOMINIUM PERMIT NO. 150 CARLSBAD TRACT CT 81-4 /CP 150 DRAINAGE The subject site is approximately .83 acres in size. The entire size drains into the Buena Vista Lagoon. Run-off from a 50-year storm, if the site is fully developed, will peak at 2.5 cubic feet per second in a sheet flow condition. . • Drainage from the site into the Buena Vista Lagoon could impact the lagoon adversely due to siltation, either during the construction phase or afterwards; and by discharging urban pollutants into the lagoon. Urban pollutants such as hydro-carbons, rubber, and metal particles from parking areas, fertilizers from landscape areas would have an adverse effect on the life sustaining capability i of the lagoon. SILTATION•• " "•"—'" ""'L * Grading Phase and Building Construction Phase: During this phase of the development of the project the site will be most susceptable to siltation if the work is done during the rainy season, which is defined as being between the months of October and April. To reduce sands and silts from being carried into the Lagoon during construction sand bagging along the limits of grading is proposed. A stilling basin or basins can be created for drainage large enough to provide storage for a period exceeding three (3) minutes, in the event of a 50-year storm. This will allow sufficient time for sands and silts to settle to the bottom of the stilling basin or basins and allow a sheet flow condition to be maintained to permit storm run-off into the lagoon as previously existed. Permanent De-Silting Improvements: After completion of the project, a portion of the site will be covered with impervious improvements. Less than half of the site will be earth with ground cover or grass, and will not have been disturbed by grading. The area of the s'ite to be left as earth with either grass or ground cover will not generate an amount of silt worthy of consideration. WATER QUALITY Water quality of the lagoon could be adversely affected by this development if urban pollutants generated on the site were allowed to drain into the lagoon. Two sources for these urban pollutants would be fertilizer from landscaped areas or hydrocarbons, rubber, metal particles or other items from parking areas. As regards fertili?ors for landscaped areas, it is the developers intent to use wherever possible ground covers which will have a low requirement for fertilizers. What small amount of fertilizers reach the lagoon from the small area to be landscaped will be negligible regarding the water quality of the i lagoon. CONCLUSION ' ' . From the above discussion it is evident that there will be insignificant or no adverse environmental effects on the Buena Vista Lagoon from the development of this project. -2- CG ENGINEERING Planning and Engineering Received W L l 10, 1981^.p. CITY OR CARLSBAD Mr. Michael G. Howes City of Carlsbad Planning Department 1200 Elm Avenue Carlsbad, California 92008 Re: Laguna Vista Tentative Tract No. CT-81-4 Addendum #1 to Drainage, Siltation, and Water Quality Report Gentlemen: With reference to the discussion under the water quality section of the above referenced report, this addendum addresses mitigation measures proposed for urban pollutants. As described in the report, urban pollutants may consist of hydrocarbons, rubber, metal particles or other items from parking areas. During dry weather conditions, the method by which the maintenance of the parking areas for this project will be carried-out by mechanical dry sweeping. Mechanical dry sweeping will permit gathering of extraneous materials which should include urban pollutants thence, disposing them offsite. For the occasion where storm runoff would wash down the relatively small ramp area to the parking garage, drainage facilities with piping of the runoff to a desilting basin will be constructed. The desilting basin or basins, as maybe determined during final design, will be designed to accomplish the following functions: (1) Reduce relocities of flow to permit the storm runoff to be outlet into the Lagoon thereby reducing erosion, and (2) to permit the urban pollutants to settle out in the desilting basin without entering the Lagoon. Respefictfu 11 y Surbmi tted John A. Starner, P.E, 'Vice President JASbh 2551 STATE STREET, SUITE 107 • CARLSBAD, CALIFORNIA 92008 • (714)