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COLORADO DEPARTMENT O~EALTH, Water Quality Control ~ision Permit Number CO-0032751 Page 9 . D. Whole Effluent Toxicity (WET) Testine: (Continued) Chronic Biomonitorine: (Cont.) stream. For this permit, since segment 3 is classified for Class 1 Cold Water Aquatic Life, chronic WE7' testing is required for this permit. Other Considerations for WET Testing Requirements: The permit:tee should read the biomonitoring conditions outlined in the permit careiully and should note that the test methods for the toxicity tests are described in detail in the Division guidance document. This document should be read carefully prior to commencing the required biomonitoring to ensure that the permittee is aware of the various test conditions that could affect the test results (e.g., sample holding time). E. Materials Containment Plan A Materials Containment Plan (or as previously termed, a Spill Prevention Control and Containment Plan) was submitted far Division review in a letter dated November 27, 1985. As described in that letter, there were two 500 gallon diesel storage tanks on site with a small dam a.t the base of the tanks, and an 18 foot wide roadway/dike prevents spills entering Coon Track Creek; also, oil and oil related products other than diesel are kept in a storage facility inside a building on site. Since that time, according to the 1988 permit application, there are now four above ground diesel fuel storage tanks with a 12' X 16' wide dike separatir..g the tanks from the creek. An update of the Materials Containment Plan is required to be filed within 90 days of this permit's effective date. In this update, any changes from the 1985 submittal for any material which is used, processed, or stored at the site which may have a visible or otherwise detectable impact on receiving waters are to be addressed. For specific requirements refer to Part I.E.1. of the permit. F. Change in Definition of Average Limitations The definitions of the 30 day average limitation and the 7 day average limitation have changed. In the past it was necessary to have 3 samples in a 30 day period in order to demonstrate compliance or noncompliance with a 30 day average limitation. The new definition, which satisfies 40 CFR 122.2 and Section 10.1.0 of 5 CCF 1002-3, represents an arithmetic mean of all samples collected in a 30 day period. The arithmetic mean is calculated as the sum of all samples measured during the month, divided by the number of samples measured during the month. The significance of this is that if only one sample is collected during a month the results must satisfy the 30 day average limitation or the permit is violated. If the initial result is high, the permittee is encouraged to perform additional sampling in an effort to lower the arithmetic mean, but the monthly average reported must be based on all sampling results, and must utilize all additional data regardless of the result.