Monday, February 8, 2010

TCEQ Nutrient Criteria and Screening Levels

The Texas Commission on Environmental Quality (TCEQ) is proposing a methodology to calculate site-specific Nutrient Criteria and Screening Levels for reservoirs, is as a new addition to the standards rule. The result will be chlorophyll a criteria and supplemental screening values for total phosphorus and transparency which will be used to confirm if a water body is attaining the nutrient criteria. TCEQ is soliciting comments on this draft approach to derivation of criteria and screening levels in comparison to other alternative criteria, such as stand-alone criteria for chlorophyll a without supplemental screening levels.

If selected as the preferred method, TCEQ intends to use a stand-alone chlorophyll a criteria that is adjusted to be equivalent to chlorophyll a criteria with supplemental screening levels. If stand-alone chlorophyll a criteria were to be adopted, then references to supplemental screening levels for total phosphorus and transparency would be omitted in draft language in §307.2, §307.7, §307.9, and §307.10, and only the statistically adjusted stand-alone chlorophyll a criteria would appear in the final methodology.

Criteria for chlorophyll a are planned to be assessed with long-term medians of sampling data. Criteria for chlorophyll a are attained when they are not exceeded by the median of monitoring data results.

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