Proposed Rules

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Proposed Administrative Rules (Posted December 18, 2007)

Amendments to Chapter 135, "Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks"

The Department proposes amendments to revise the current Risk Based Corrective Action (RBCA) Tier 2 software model, the evaluation of public water supply wells, codify changes to the planning process for corrective action at high risk leaking underground storage tank (LUST) sites, enforcement, and transitional rules.  These proposed amendments were derived from previous Informational Notice of Intended Actions, several stakeholder meetings, and written comments.

Based on observations during the first decade’s use of the existing RBCA Tier 2 model, there was a perception the length of contaminant plumes generated by the model, in many cases, significantly over-estimated the extent of contaminant migration.  A committee was formed to discuss how to recalibrate the Tier 2 software model to make the modeled groundwater plumes more closely match the actual groundwater plumes.  The proposed RBCA Tier 2 model changes are the result of the committee’s work.

The Department looked at the potential impact of the RBCA Tier 2 model (Tier 2 software version 2.51) revision on sites with respect to public water supply wells in consideration of research indicating these wells may induce groundwater contaminant plume movement.  For situations where there is a potential for plumes to be drawn into the water supply, the revised RBCA Tier 2 model (Tier 2 software version 3.1) alone could be an inappropriate tool for their risk evaluation.

The Department developed an internal screening process to determine if the leaking underground storage tank site is within a sensitive area of a public water supply well.  This is determined based on the leaking underground storage tank site being located within the five-year capture zone, or within the 2500-foot fixed radius as determined by the Geological Survey Bureau in the Source Water Protection Area, or within 1000 feet of a public water supply well, whichever is larger and having a Source Water Protection Aquifer designation of highly susceptible or susceptible.

If the leaking underground storage tank site is located within the sensitive area of a public water well receptor, the public water supply well receptor will be evaluated with Tier 2 software version 2.51, which generates a larger modeled plume (‘buffer area’) than the proposed Tier 2 software, version 3.1.

As a result of a business process improvement event held by the Department in 2004, a modified approach to processing and planning activities for high risk LUST sites was implemented. The proposed rules incorporate these changes in the processing of high risk sites.

Attached are the Notice of Intended Action and the stakeholder comments and DNR responses received while developing the Notice of Intended Action Ch 135 Comments-Responses.  The Notice of Intended Action will be discussed at the 01/15/08 Environmental Protection Commission meeting. Please contact tammy.vander_bloemen@dnr.iowa.gov with questions or concerns.