SENTINEL SITE METHOD UPDATES
EPA Region I has indicated that it is intent on establishing “limits of technology” nutrient reduction requirements for all Taunton Estuary communities. EPA is basing its mandate on simplified analyses, called the “sentinel method,” that presume nitrogen is causing periodic decreases in dissolved oxygen (DO) levels in the estuary. In this approach, EPA chooses an estuary location with no DO violations and asserts that the nitrogen level occurring at this location is required to be attained throughout the estuary. No analysis of any physical, chemical or hydrological factors affecting nutrient impact dynamics are considered. The method does not even seek to confirm the degree to which plant growth is controlling DO regime responses; it simply presumes attaining the nutrient concentration will result in attainment of the DO objective.
CRR discovered through FOIA that 1) the use of the sentinel method in nutrient permit limits or numeric nutrient criteria was never open to public comment, 2) the sentinel method was never subject to a SAB review or peer review, and 3) the sentinel method was never determined to be scientifically defensible. As such, the sentinel method should not and cannot be used to derive nutrient permit limits. Nevertheless, EPA asserted that it plans to continue using the sentinel method in permitting.
CRR requested a Science Advisory Board (SAB) review of the “sentinel method” to ensure that this approach is properly evaluated and confirmed to be “scientifically defensible”. However, EPA declined the SAB review request. Instead, CRR is considering organizing an independent expert peer review to determine the appropriateness of using the sentinel method in numeric nutrient permit limit derivations. Based on prior peer reviews of other similar simplified methods, one may expect this latest approach in Agency decision making to be heavily criticized and require major technical revisions.