The Texas Commission on Environmental Quality (TCEQ) has reverted to its previous requirements related to reporting, investigation, and response actions for contaminant releases at petroleum storage tank (PST) facilities. At the inception of the PST Responsible Party Remediation Program, reporting requirements for such releases were covered under Texas Administrative Code (TAC) Chapter 334 regulations. The TCEQ subsequently amended the reporting requirements for sites with reportable releases that occurred after September 1, 2003. This amendment required investigation and response actions using the Texas Risk Reduction Program (TRRP)(TAC Chapter 350).

On March 19, 2009, the TCEQ reverted to using the previous TAC Chapter 334 regulations for current and active leaking petroleum storage tank (LPST) site as well as newly-reported LPST sites. The major differences between the two regulations include the investigation requirements, groundwater classification definitions, response action requirements, and initial reporting levels of contaminant concentration. These major differences are described more fully below.

• Investigation Requirements - PCLs and Action Levels. TRRP defined contamination action levels as Protective Concentration Levels (PCLs) for affected media including surface soil, sub-surface soil, groundwater, air, surface water, and sediment. The PCLs are used to determine if the release is subject to additional actions under TRRP. If no chemicals of concern (COCs) were observed having concentrations exceeding the generic Tier 1 PCLs, then no further action was required at the PST facility. If the concentrations of the COCs were determined to exceed Tier 1 PCLs, then the release was subject to additional actions defined under TRRP. TAC Chapter 334’s reporting regulations listed COCs associated with gasoline or diesel releases and defined the reporting levels as “TCEQ PST Program Action Levels.”

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TAC Chapter 334 regulations required additional action and investigation if the COC concentrations exceeded the PST Program Action Levels. PCLs are derived from toxicity and fate and transport models. PST Program Action Levels are risk-based. Groundwater PCLs cannot be altered to meet site-specific conditions. TAC Chapter 334 allows action levels to be altered using a risk model known as a “Plan B” assessment. Site-specific soil and groundwater-bearing zone conditions (for example, seepage velocity) compared with the exposure pathway distance to the nearest potential receptor can be introduced in the Plan B model (Domenico Equation) in an effort to derive site-specific action levels.

• Groundwater Classification. TRRP includes three classifications of groundwaterbearing units: Class 1, Class 2, and Class 3. TAC Chapter 334 includes four classifications of groundwater-bearing units: Category I, Category II, Category III, and Category IV. Both rules require an assessment of the groundwater that includes the analysis of the total dissolved solids (TDS) concentration and the identification of any water wells within a defined distance from the release that have screened intervals within the known depth of the affected groundwater-bearing unit. TRRP includes an additional requirement which allows for a potential well-yield assessment to be conducted to determine whether the groundwater-bearing unit can produce a sufficient amount of water to be classified as a potential drinking water source. TAC Chapter 334 does not have any provisions allowing groundwater category selection based on maximum daily yield from the affected groundwater-bearing unit.

• Response Action Requirements. Response action requirements are more narrowly defined under TRRP than by TAC Chapter 334. For example, under TRRP, if groundwater is affected above Tier 1 PCLs and no active remediation is desired by the responsible par ty, owner, operator, or lender to complete closure requirements (i.e. the contamination is to be left in place), then a formal Monitored Natural Attenuation (MNA) demonstration would be the typical response action and an institutional control such as a plume management zone would be implemented.

A similar situation under TAC Chapter 334 would require a groundwater monitoring program including a minimum of four groundwater monitoring events to establish contaminant concentration stability or decrease. Under TRRP, MNA requires analysis of the primary indicators (specific contaminants) and secondary indicators (geochemical parameters) to demonstrate that the contaminant plume will eventually decrease to concentrations less than their applicable PCLs. Groundwater monitoring under TAC Chapter 334 requires analysis for primary indicators only and does not require a demonstration that the contaminant plume concentrations will eventually decrease to levels below their respective action levels.

These major differences between the two rules should allow for more expedited closures at open or new LPST sites. Consultants who conduct related PST investigation and response action services both agree and disagree with the changes. The major agreement is that use of TRRP rules was costly, time consuming, and potentially would not allow for case closure if MNA or a related type of response action was not successful. An MNA demonstration could potentially last for five or more years and a final site closure could not be issued without conditions. TCEQ project coordinators do not have the ability to amend TRRP requirements for unique situations. The major disagreement is that TAC Chapter 334 may not protect current or future landowners or operators in situations where an LPST site has received closure without a sufficient amount of investigation or response action.

PST facility owners, operators, and real-estate related entities (financial institutions, brokers and/or real-estate agents) agree with the amendments based on the timeframe, cost, and certainty of closure under TAC Chapter 334. Typically, TAC Chapter 334 investigation and response actions are more cost-effective and less time-consuming than those under TRRP. Additionally, costs and timeframe estimations made by the applicable consulting agencies are more accurate, allowing for real-estate transaction closings. Uncertainties related to cost and timeframe are typically lessened by using TAC Chapter 334 regulations.

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