Developing Offset Banking Systems in Georgia

Offset banking involves a public or private entity investing in a project that has the effect of substantially reducing a targeted pollutant(s), such as sediment runoff, phosphorus, heavy metals, etc. This project is referred to as "the bank." The entity creating the bank receives "credits" for the associated reduction in pollutants, which it can then sell to publically-owned treatment works (POTWs) or other point source polluters facing high costs of meeting discharge standards. Trades can be allowed on a 1-to-1 basis: the buyer obtains one credit for each creditequivalent increase in pollution associated with his/her activities; or higher trading ratios can be required, e.g., 3:1, where the buyer must acquire (in this example) three credits for each creditequivalent increase in pollution associated with his/her activities. In this latter case trades result in actual environmental improvements.This paper addresses two major issues. The first refers to the steps required to establish a pilot project for one or more offset banking projects in Georgia. These steps are: identifying entities with incentives to purchase offset credits; identifying one or more entities that might establish a bank, and potential bank sites; establishing trading rules with appropriate local water quality management authorities; and obtaining approval of the proposed trading program from the U.S. EPA.The second major issue addressed in the paper is means by which an offset bank might be created. For this purpose, a brief survey is offered of existing water quality trading projects in the U.S.. Buyers of offset credits are virtually always point-source polluters (POTWs or industries). Point and non-point projects have been used as "banks" -- as a source for offset banking credits. Attention in this paper is focused on non-point sources that might serve as banks for pilot offset banking projects in Georgia. Both low- and high-technology alternatives that might be used for such projects are discussed.Notwithstanding incentive-related limitations on the number of point source polluters that might constitute the "demand" for offset credits discussed in section II, the authors have identified one entity (Fulton County) that may represent significant demand for credits, and they expect to identify others. Moreover, the authors argue that continued growth in Georgia, particularly in the Atlanta and Coastal areas of the State, will give rise to sufficient numbers of point source entities seeking new discharge permits to warrant interest in offset banking as a means of meeting increasingly stringent discharge restrictions at minimum cost. If or when enforcement of TMDLs gains strength in the State, needs for systems like offset banking will increase accordingly. These considerations, and the associated benefits to Georgians that might attend the establishment of offset banking programs in the State, serve as the rationale for the author's continued interest in exploring means by which pilot offset banking projects can be established in Georgia. Working Paper # 2003-00

Superficial femoral artery eversion endarterectomy: A useful adjunct for infrainguinal bypass in the presence of limited autogenous vein

AbstractPurpose: To evaluate, in a group of technically high-risk patients, the results of infrainguinal revascularization using a conduit constructed with endarterectomized superficial femoral artery (SFA) and available arm or saphenous vein.Methods: Of 237 consecutive lower extremity vein graft bypass procedures performed in 195 patients from July 1992 through August 1996, 15 SFA eversion endarterectomies (in 10 men and five women; median age, 70 years) were performed and used as a composite bypass conduit with available autogenous vein for the treatment of limb-threatening ischemia. In each case, an occluded SFA was divided 8 to 15 cm distal to its origin, proximally endarterectomized, and sewn end-to-end to a segment of vein to provide adequate conduit length for bypass grafting. Indications for this technique were unavailability of vein as a result of failed previous bypass grafting (n = 10) or previous coronary artery bypass grafting (n = 5). Veins were sewn distally to a below-knee popliteal artery (n = 4; 27%) or tibial artery (n = 11; 73%).Results: Primary patency, secondary patency, and limb salvage rates at 36 months by life table analyses for the 237 grafts were 62.3%, 81.0%, and 77.2%, respectively. The 15 composite SFA-vein bypass grafts had 36-month primary patency, secondary patency, and limb salvage rates of 60.0%, 72.0%, and 65.9%, respectively (mean follow-up, 15 months). Currently, eight of these patients (53%) have patent bypass grafts; two (13%) died at 4 and 18 months after the operation with patent grafts; two (13%) underwent amputations for progressive foot gangrene despite a patent bypass graft; and three (20%) had grafts that thrombosed at 4, 5, and 10 months. Typical hyperplastic intrinsic graft-threatening stenoses developed in two patients (13%) in the SFA segment at 4 and 8 months; they were discovered by routine duplex scan surveillance.Conclusion: Composite SFA eversion endarterectomy/vein graft conduits yield acceptable results, behave similarly to other autogenous conduits used for technically high-risk infrainguinal revascularization, and are beneficial when autogenous vein is limited

High Temperature Evaluation of an Active Clearance Control System Concept

A mechanically actuated blade tip clearance control concept was evaluated in a nonrotating test rig to quantify secondary seal leakage at elevated temperatures. These tests were conducted to further investigate the feasibility of actively controlling the clearance between the rotor blade tips and the surrounding shroud seal in the high pressure turbine (HPT) section of a turbine engine. The test environment simulates the state of the back side of the HPT shroud seal with pressure differentials as high as 120 psig and temperatures up to 1000 F. As expected, static secondary seal leakage decreased with increasing temperature. At 1000 F, the test rig's calculated effective clearance (at 120 psig test pressure) was 0.0003 in., well within the industry specified effective clearance goal

Further Characterization of an Active Clearance Control Concept

A new test chamber and precision hydraulic actuation system were incorporated into an active clearance control (ACC) test rig at NASA Glenn Research Center. Using the improved system, a fast-acting, mechanically-actuated, ACC concept was evaluated at engine simulated temperatures and pressure differentials up to 1140 F and 120 psig, on the basis of secondary seal leakage and kinematic controllability. During testing, the ACC concept tracked a simulated flight clearance transient profile at 1140 F, 120 psig, with a maximum error of only 0.0012 in. Comparison of average dynamic leakage of the system with average static leakage did not show significant differences between the two operating conditions. Calculated effective clearance values for the rig were approximately 0.0002 in. at 120 psig, well below the industry specified effective clearance threshold of 0.001 in

Seal Investigations of an Active Clearance Control System Concept

In an effort to improve upon current thermal active clearance control methods, a first generation, fast-acting mechanically actuated, active clearance control system has been designed and installed into a non-rotating test rig. In order to harvest the benefit of tighter blade tip clearances, low-leakage seals are required for the actuated carrier segments of the seal shroud to prevent excessive leakage of compressor discharge (P3) cooling air. The test rig was designed and fabricated to facilitate the evaluation of these types of seals, identify seal leakage sources, and test other active clearance control system concepts. The objective of this paper is to present both experimental and analytical investigations into the nature of the face-seal to seal-carrier interface. Finite element analyses were used to examine face seal contact pressures and edge-loading under multiple loading conditions, varied E-seal positions and two new face seal heights. The analyses indicated that moving the E-seal inward radially and reducing face seal height would lead to more uniform contact conditions between the face seal and the carriers. Lab testing confirmed that moving the balance diameter inward radially caused a decrease in overall system leakage

A response to “Likelihood ratio as weight of evidence: a closer look” by Lund and Iyer

Recently, Lund and Iyer (L&I) raised an argument regarding the use of likelihood ratios in court. In our view, their argument is based on a lack of understanding of the paradigm. L&I argue that the decision maker should not accept the expert’s likelihood ratio without further consideration. This is agreed by all parties. In normal practice, there is often considerable and proper exploration in court of the basis for any probabilistic statement. We conclude that L&I argue against a practice that does not exist and which no one advocates. Further we conclude that the most informative summary of evidential weight is the likelihood ratio. We state that this is the summary that should be presented to a court in every scientific assessment of evidential weight with supporting information about how it was constructed and on what it was based