Chapter 2

      POTWs are required to examine their operations in order to determine if local limits are needed to protect against pass through, interference, and treatment plant upset. When PVSC decided that it would beneficially reuse its biosolids (commonly referred to as sewage sludge), the agency began the work necessary to adopt local limits that would allow it to achieve that goal by June 30, 1997.

      PVSC hired a consultant in 1992 to conduct the necessary study so that the limits could be adopted by 1994. At that time, the PVSC biosolids contained high levels of cadmium, copper, lead, molybdenum and zinc, which required additional pretreatment. The levels of four other metals - arsenic, chromium, mercury and nickel - were not of concern due to their low levels.

      At PVSC, the effluent trading concept arose during the process of developing these local limits. Trading was initially intended to address a specific, and seemingly unique, problem with a large leather tanner in the PVSC district. This facility had previously installed a pretreatment system that met the 1985 compliance date for the federal categorical limits for chromium. In fact, by using this system it was able to consistently produce effluent with a chromium concentration half the 8 mg/l federal limit for the tanning industry.

      The first draft of the local pretreatment limits included a chromium limit of about 3 mg/l, which was below the effluent concentration emanating from the tanner. If this had become the final limit for chromium, the company would not have been able to meet it without extensive and costly renovations to its existing pretreatment equipment. PVSC was very reluctant to require the company to further reduce its chromium levels for two reasons: 1) the leather tanner had already installed pretreatment equipment that decreased the chromium concentration in its wastewater discharge to levels well below the applicable federal categorical limit; and 2) the total amount of chromium contained in the wastewater flowing into the PVSC treatment plant could have been increased by a factor of three and PVSC would still have been able to meet the chromium limit for beneficial reuse of its biosolids.

      At one of the Pretreatment Advisory Committee meetings, a representative of the tanner, who was a member of the Committee, asked if PVSC could develop an approach that would allow some flexibility in establishing the facility's local limit. PVSC agreed to examine the issue and concluded that effluent trading could allow flexibility in setting a local limit for a facility as long as the revised limit did not exceed the federal categorical limit.

      The trading concept was included in PVSC's local pretreatment limits rule, but it was only after the rule became effective in 1994 that PVSC recognized this concept had a much wider application. It is important to note that several circumstances in the PVSC case made the decision to include effluent trading in the rule easier. First, chromium levels in PVSC's biosolids were already very low. Second, the company in question was in compliance with a federal categorical limit. Third, the company needed only a small incremental increase in its limit.

      Through its innovative local limit development process, PVSC established two classes of metal dischargers. All dischargers must meet the local limits, but those that discharge a metal at or below a threshold value (set at background levels, which are slightly above the method detection limit) qualify for a non-use certification. (Exhibit 2-1 presents the threshold values and the local limits for the metals regulated by PVSC.) Companies that qualify under the new class of discharger are required to sample their effluent only twice a year to show they remain under the threshold. As part of this process, PVSC recalculated its local limits using a smaller regulated volume for each metal, excluding the volume for companies qualifying for non-use certification.

      This change in the structure of PVSC's limits resulted in a final local limit for chromium of 5.36 mg/l, which happened to be higher than the concentration discharged by the tanner. Thus, after providing the impetus to develop an effluent-trading concept, the company responsible no longer needed to trade.¹ In fact, PVSC has recently withdrawn its local limit for chromium due to the rescission of EPA's chromium biosolids limit based on the outcome of a legal challenge.

      The Pilot Team's ability to facilitate a trade was greatly enhanced because PVSC had already established trading as an accepted approach to meeting local pretreatment limits. The importance of incorporating trading into a POTW's regulations is emphasized further throughout this report.

¹ The impetus for PVSC to establish effluent trading could have come from the local limit for any metal. The role of the chromium limit was simply a function of the specific concerns of a single large tanning company.    GO BACK

TOP OF PAGE

Last Revision: March 9, 2000
http://www.epa.gov/emergingstrategies/njcip/etdoc/chapter2.htm