ARTICLE 5  RELEASE RESPONSE AND CORRECTIVE ACTION
5-1  General.
(a)  Effective February 1, 1999, the owner/operator of a regulated substance system must, in response to a confirmed release, comply with the requirements of these regulations, which incorporate a risk-based corrective action (RBCA) approach.
(b)  Any and all reports required to be submitted by the owner/operator to the Director under these regulations must be submitted in duplicate and in the format specified by the Director unless otherwise determined by the Director.  Guidance documents and required report formats are available on the OPS website.
(c)  Any work performed or required under these regulations does not automatically qualify for reimbursement from the State Fund.  Fund reimbursement requirements are located in Article 8 of these regulations.
5-2  Initial Response 
(a)  Upon confirmation and reporting of a release in accordance with Article 4 of these regulations, or after a release from a regulated substance system is identified in any other manner, the owner/operator must perform the following initial response actions within 24 hours:
(1)  Take immediate action to prevent any further release of the regulated substance into the environment; and
(2)  Identify and mitigate fire, explosion, vapor hazards, and acute health hazards; and
(3)  Initiate containment and removal of any free product observed on the ground or water surface; and
(4)  Report the release to the Director by telephone or facsimile.

(b)  Unless directed to do otherwise by the Director, the owner/operator must perform the following abatement measures as soon as possible after a release:
(1)  Prevent further migration of the released substance into surrounding soils and groundwater; and
(2)  Monitor and mitigate any additional fire, safety hazards, and acute health hazards posed by vapors or free product that have entered into subsurface structures (such as sewers or basements); and
(3)  Remedy hazards posed by contaminated media that are excavated or exposed as a result of release confirmation, site investigation, abatement, or corrective action activities. If these remedies include treatment or disposal of media, the owner/operator must comply with applicable state and local requirements.
(c)  Investigate to determine the possible presence of subsurface free product. At sites where there is subsurface free product, the owner/operator must report the presence of free product to the Director within 24 hours of detection by telephone or facsimile; and remove the free product to the maximum extent practicable as determined by the Director, while continuing as necessary any actions required under this Article. In meeting the requirements of free product removal, the owner/operator must:
(1)  Conduct subsurface free product removal in a manner that minimizes the spread of contamination into previously uncontaminated zones by using recovery and disposal techniques appropriate to the hydrogeologic conditions at the site; and
(2)  Properly treat, discharge or dispose of recovered byproducts in compliance with applicable local, state and federal regulations, and handle any flammable products in a safe and competent manner to prevent fires or explosions. 
(d)  Soil samples must be collected to identify the presence and source of a release. If groundwater is encountered during the investigation it must also be sampled. Information regarding soil and groundwater sample collection procedures is presented in the Petroleum Storage Tank Owner/Operator Guidance Document.  The document also provides owners/operators with factors that must be considered in sample location selection.  Although these factors may vary widely among sites, the following scenarios have been identified as common, and required sampling locations have been defined:
(1)  If site investigation activities are being performed in conjunction with the removal or permanent closure in place of a petroleum storage system, the owner/operator must collect samples from beneath each tank,beneath each dispenser island, beneath areas of piping, and beneath any loading racks.  Soil samples must also be collected from any other location where contamination is suspected based on either visual or olfactory evidence.  The results from the tank closure investigation must be submitted to the Director within 30 days of the tank closure whether contamination is encountered or not.  Tank owner/operators must still comply with the requirements stated in section 4-4(a) and (b).
(2)  If site investigation activities are being performed due to the failure of any approved method of leak detection (including tank and/or product piping testing), the owner/operator must collect samples from any areas the tests indicate may have been impacted by a release of a regulated product.
(e)  Samples collected at all sites must be analyzed for each individual chemical of concern (COC) including: benzene, toluene, ethylbenzene, xylenes, and methyl-tertiary butyl ether (MTBE); and for total petroleum hydrocarbons (TPH).  The nature of the product must be considered when selecting the analyses to be performed for TPH. The Petroleum Storage Tank Owner/Operator Guidance Document contains additional information regarding COCs, the required sampling protocols, and procedures for the sampling and analysis of certain poly-nuclear aromatic hydrocarbons (PAHs) in the event that TPH exceeds the Tier 1 screening level (500 mg/Kg)..
5-3  Site Classification and the Site Summary Form (SSF)
(a)  A limited site assessment must be conducted onsite to establish an acceptable site classification and determine the potential for impacts to receptors.  The site classification proposed in the Site Summary Form (SSF) must receive the Director’s  approval. The assessment activities, described below, must be conducted within 60 days of release discovery and the results must be included with the SSF.
 (1) Collect and analyze soil samples in an effort to identify the source of the release.  If the soil contamination is vertically defined (based on the analytical data) before encountering groundwater, an accurate site classification may be established for the site without conducting further assessment. 
(2)  If soil contamination is not vertically defined as described above, owner/operators will be required to conduct additional assessment activities to establish an accurate site classification.  The following information concerning plume concentration, location and migration must be acquired and submitted to the Director within 60 days of the release discovery date.  
(A)	 Collect soil and groundwater samples from a minimum of three (3) groundwater monitoring wells installed in a non-linear pattern.  At least two of the wells must be installed in the following locations: the presumed source area; and at the (topographically) downgradient property boundary.  The third well should be located to facilitate obtaining a groundwater flow direction. 
(B)	 Following well completion and surveying of the groundwater monitoring wells, calculate groundwater elevations to determine the general groundwater flow direction and establish a hydraulic gradient for the site.
(C)	 Estimate a site specific hydraulic conductivity by one of the following methods: performing a slug test or pumping test, using a reference value based on site lithology, or using data from another site in close proximity with similar lithology.
(D)	 Conduct preliminary modeling of groundwater contaminants to estimate the length of the contaminant plume and the potential for the plume to impact potential points of exposure (POEs).  Where modeling input values are unknown, use Colorado default values provided in the Petroleum Storage Tank Owner/Operator Guidance Document.  
(E)	 Based on the modeling results, identify offsite properties including rights of way that may need to be assessed to complete the site characterization and remediation activities.  Access request efforts shall be initiated immediately and copies of the access request letters sent shall be included as an attachment to the SSF. 
(F)	Identify POEs on the POE Location figure in the SSF. This figure must identify each property in the vicinity of the site which could potentially be affected by the release.  Determine the distance and direction from the source to the nearest POE.  For each property provide the address, the property use (e.g., single family residential, vacant land, retail, gas station, etc.), and current occupancy status. POEs for benzene, toluene, ethylbenzene and xylenes are: property boundaries, surficial soils, subsurface utilities, structures, groundwater wells, surface water, and sensitive environments.
(G)	Based on the site data collected and completion of the Site Classification Checklist, a site classification for the site can be proposed.  The proposed site classification must receive approval from the Director. 
(b)  The owner/operator must submit all information collected about the site, as required  under section 5-2 and section 5-3(a) of these regulations, and as specified on the SSF, within 60 days of the release date.  The SSF must include a brief outline of the site conditions, the required limited assessment data and a complete Site Classification Checklist, to aid in determining a date for submittal of a Site Characterization Report (SCR). 
(1)  The due date for submission of the SCR will be based on threats to human health and the environment identified in the Site Classification Checklist.   Risk-based due dates will require that high risk sites submit an SCR on a shorter timeframe.  High risk sites may be assigned interim deadlines for securing access, obtaining permits, and evaluating multiple receptors. 
(2)  In lieu of the SSF, the owner/operator may submit a complete SCR, or a No Further Action Request Report (NFAR), as defined in Section 5-4, as appropriate for the site, within 60 days of the release date.
(3)  A quarterly groundwater monitoring program must be established and remain ongoing throughout the investigation and remediation phases of the project, unless an alternate schedule is approved by the Director.  Monitoring data must be submitted on a quarterly basis, unless an alternate schedule is approved by the Director, in the Monitoring and Remediation Report (MRR) format.
5-4  Site Characterization
(a)  During the site characterization activities, the owner/operator must determine the full extent of contamination in soil and groundwater resulting from the release of a regulated substance as described below:
(1)  At all sites, the extent of soil contamination must be defined to the Tier 1 Risk-Based Screening Levels (RBSLs) for the Soil Leaching to Groundwater Exposure Pathway, as presented in Table 5-1, and to 500 mg/Kg for total petroleum hydrocarbons;
(2)  At all sites where groundwater contamination is suspected, groundwater contamination must be defined to the Tier 1 RBSLs for the Groundwater Ingestion Exposure pathway. These levels are presented in Table 5-1;
(b)  The owner/operator must determine the hydrogeologic and geologic characteristics of the site and the surrounding area, as appropriate for the site conditions. See the Petroleum Storage Tank Owner/ Operator Guidance Document for more information regarding the list of site parameters to be collected;
(c)  During site characterization activities, the owner/operator must note any POEs not previously identified, including the distance from the source area to each POE.  The owner/operator must also indicate which POEs have been impacted by the release;
(d)  The owner/operator must evaluate each exposure pathway, listed in Table 5-1, and determine if each pathway is completed between the source of contamination and any POE, or if any pathway may potentially be eliminated from further consideration.  Refer to the Petroleum Storage Tank Owner/Operator Guidance Document for further information on evaluating exposure pathways;
(e)  The owner/operator may evaluate land use criteria, and provide a recommendation of land use classification (residential or industrial).  Unless all properties impacted by the release are currently zoned industrial, the Director shall consider all land use to be classified as residential.  See the Owner/Operator Guidance document for further information regarding the industrial land use classification;
(f)  The owner/operator must determine the appropriate RBSLs for every site by using the Tier 1 RBSL Table (Table 5-1). Compare the highest levels of contamination remaining on the site with the Tier 1 RBSLs. Each completed exposure pathway must be evaluated. The completed exposure pathway with the lowest RBSLs will determine the cleanup goals for the site. If the Director determines that the Tier 1 RBSLs are not sufficiently protective of human health and/or the environment due to site specific conditions, the owner/operator may be required to perform a Tier 1A or Tier 2 evaluation, incorporating site specific data.

Table 5-1 - Tier 1 Risk-Based Screening Levels (RBSLs)	

Media	
Complete Exposure
Pathway	
Land
Use	
Benzene	
Toluene	
Ethyl-benzene	Xylenes	MTBE	

Surficial
Soil
[mg/kg]	
Ingestion/
Dermal/
Inhalation	
Residential	
2.8	
4,000	
2,100	10,000	N/A	
		
Industrial	
6.8	
31,000	
16,000	90,000	N/A	

Subsurface 
Soil
[mg/kg]	
Leachate to
Groundwater
Ingestion	
Residential and Industrial	

0.26	
140	
190	>Sat* or
260**	N/A	

Soil
Vapor
[µg/m3]	
Indoor Air
Inhalation	
Residential	
2,900	
>VP	
>VP	>VP	N/A	
		
Industrial	
37,000	
>VP	
>VP	>VP	N/A	

Groundwater
[mg/l]	
Indoor Air
Inhalation	
Residential	
0.016	
10	
26	2.9	N/A	
		
Industrial	
0.41	
490	
>Sol	140	N/A	

Groundwater
[mg/l]	
Groundwater
Ingestion
[MCLs]	Residential and Industrial	

0.005	

1.0
	
0.7	10* or 1.4**	0.020	

>VP	Denotes that even at a concentration equal to the vapor pressure of the chemical, a hazard quotient of 1 is not exceeded.
>Sol	Denotes that even at a concentration equal to the solubility of the chemical, a hazard quotient of 1 is not exceeded.
>Sat	Denotes that even at a concentration equal to the saturation of the chemical, a hazard quotient of 1 is not exceeded.
N/A	Not applicable. No established RBSL.
*	This RBSL will be in effect for releases that occurred prior to September 14, 2004.
**	This RBSL will be in effect for releases that occurred on or after September 14, 2004.
(g)  If concentrations of COCs remaining in soils exceed the site Tier 1 RBSLs, and if the site-specific conditions differ from the assumptions used to create the Tier 1 RBSLs, the owner/operator may consider the preparation of a Tier 1A analysis.  A Tier 1A analysis allows the owner/operator to:
(1)  Substitute actual site-specific data into the ASTM E 1739 equations and the Domenico model (used to create the Tier 1 RBSL Table) to create a Tier 1A Site-specific Risk-Based Screening Level (SS-RBSL) table. This table must be included with the SCR. The substitution of site-specific data is subject to the following restrictions:
(A)	 Collect site-specific data (as appropriate to the site) for the input parameters listed in Table 5-2 below. Only data actually collected from the site may be substituted.   Consult the Owner/Operator guidance document if you would like further assistance regarding site data collection procedures and applications.
(2)  Utilize the SS-RBSLs in the Tier 1A Table to determine site-specific cleanup goals, subject to the approval of the Director.

Table 5-2 - Tier 1A Input Parameters	

Depth to subsurface soil source	
Total porosity of the unsaturated zone	

Depth to groundwater	
Unsaturated zone water content 	

Thickness of the capillary fringe	
Unsaturated zone air content	

Thickness of the unsaturated zone	
Infiltration rate	

Width of source	
Soil bulk density	

Groundwater Darcy velocity 	
Distance to point of exposure in groundwater	

Fraction of organic carbon	
Effective porosity of the saturated zone	
 (h)  Based on the comparison of the highest contaminant concentrations remaining on the site with the Tier 1 RBSLs or the Tier 1A SS-RBSLs the owner/operator may recommend the following options:
(1)  No Further Action Status based upon Tier 1 or Tier 1A screening levels; or,
(2)  A method to remediate to Tier 1 or Tier 1A screening levels; or,
(3)  Preparation of a Tier 2 evaluation.
[Note: If option 2 and/or 3 above are recommended, the owner/operator must refer to Section 5-5 for the requirements for preparing a CAP and performing Tier 2 analyses.]
(i)  The owner/operator must assemble and submit information about the site and the nature of the release,  by the due date established in the SSF, in accordance with 5-3(b), and approved by the Director (see Table 5-3). This information must be submitted on the SCR form which must include all information collected under Article 4, Sections 4-2 through 4-4; and Article 5, Sections 5-2, 5-3, and 5-4 plus an updated Site Classification Checklist.
(j) If MTBE concentrations in groundwater greater than the RBSL exist beyond the limits of the other COCs, time frames for completing the additional assessment activities and reporting to the Director will be extended in accordance with the MTBE Guidance Document.
(k)The owner/operator may submit a NFAR instead of the SCR if no COCs have ever been detected as a result of the release at levels in excess of the Tier 1 RBSLs, and TPH has not been detected above 500 mg/Kg in soils. The NFAR must be submitted in the approved format.

Table 5-3 SCR Due Dates	
Site Classification	High Risk
1.1-1.6	High to Moderate Risk 
2.1-2.5, 2a1-2a.2	Moderate Risk 2.6-2.7, 3.1-3.4	Low Risk
4.1-4.3	
SCR Due Date*	<120 days from release date	<150 days from release date	<180 days from release date	<210 days from release date	
*SCR due dates will be based upon the Maximum Site Classification (i.e. lowest classification number) since the release was discovered.  For example a site that mitigates explosive vapors will retain a “High Risk” classification for SCR reporting purposes.  
5-5  Corrective Actions.
(a)  After reviewing SCR information or at any other time when deemed necessary by the Director, an owner/operator may be required to develop and submit a CAP. If a CAP is required, the owner/operator must submit the CAP, in the format approved by the Director, within 60 days of the request unless an extension is granted by the Director in writing.
(b)  The owner/operator must submit to the Director the names and addresses of any parties or properties known to be impacted by the release, or who may have the potential to be impacted by the release or by the selected remediation method prior to the expected attainment of the site cleanup goals.
(c)  In preparing for corrective action, the owner/operator must evaluate three applicable methods, for the site lithology and contaminant distribution, which will protect human health, safety, and the environment and which will be economically feasible.  This evaluation will consider:
(1)  Three methods of remediation; or
(2)  Two methods of remediation, and a Tier 2 evaluation.  To perform a Tier 2 evaluation:
(A)	 Collect site-specific data (as appropriate to the site) for the input parameters listed in Table 5-4 below (which are specific to the soil leaching to groundwater exposure pathway).  Only data actually collected from the site may be substituted. Consult the Owner/Operator guidance document if you would like further assistance regarding site data collection procedures and applications.
(B)	 Input the parameters collected into an acceptable model such as API DSS VADSAT or BP RISC to create a Tier 2 Site Specific Target Level (SSTL) Table.  Acceptable models for the unsaturated zone will be analytical, transient, capable of modeling one dimensional dispersion and degradation, and calculating effective solubility for individual constituents in a mixture.  Acceptable models for the saturated zone will be analytical or semi analytical, transient, and simulate retardation, degradation, one dimensional flow and three dimensional dispersion.  This table must be included with the CAP.  Utilize the SSTLs in the Tier 2 Table to determine site specific cleanup goals, subject to the approval of the Director.
[Note: For further information on the Tier 2 evaluation and models, consult the Owner/Operator Guidance Document.]

Table 5-4 Tier 2 Input Parameters	

Source Parameters	

Depth to top of contamination	
Width of source	

Length of source	
Thickness of contamination	

Unsaturated Zone Properties	

Soil bulk density	
Saturated conductivity	

Total porosity of the unsaturated zone	
Infiltration rate	

Residual water content	
Van Genuchten’s N	

Fraction of organic carbon	
Thickness of unsaturated zone	

Gradient	
Degradation rate (for each chemical)	

Aquifer Properties	

Effective porosity of saturated zone	
Soil bulk density	

Hydraulic conductivity	
Hydraulic gradient	

Fraction of organic carbon	
Degradation rate (for each chemical)	

Point of Exposure Location	

Distance downgradient	
Well screen interval	

Distance crossgradient 	

Lens parameters (if applicable)	

Total porosity	
Van Genuchten’s N	

Residual water content	
Thickness	

Saturated conductivity	

Source Concentration Parameters	

Source concentration(s)	
TPH Mixture	
(d)  The owner/operator must conduct an economic evaluation which examines the alternative remediation methods.  This study will include the expected total cost of each method, including the cost of remediation to Tier 2 SSTLs, if Tier 2 evaluation is a selected alternative, and the expected length of active operation and monitoring for each method.
(e)  The owner/operator must select the most technologically and economically feasible method of the three evaluated and:
(1)  Prepare a remedial design, which must include, pilot testing results, the remedial system design, a monitoring plan including the location of point of compliance (POC) wells, and a plan to confirm the attainment of site cleanup goals
(2)  Prepare a schedule for the implementation of the CAP.
 (f)  The Director will approve the CAP only after ensuring that implementation of the CAP will adequately protect human health, safety, and the environment.
(g)  Upon approval of the CAP or as directed by the Director, the owner/operator must implement the CAP. The owner/operator must monitor, evaluate, and report the results of implementing the CAP in accordance with a schedule and in a format approved by the Director. Any deviation from the approved CAP, including schedule revisions, must be approved by the Director.
(h)  The owner/operator may, in the interest of minimizing environmental contamination and promoting more effective cleanup, begin cleanup of soil and groundwater before the corrective action plan is approved provided the owner/operator:
(1)  Notifies the Director of an intention to begin cleanup;
(2)  Complies with any conditions imposed by the Director, including halting cleanup or mitigating adverse consequences from cleanup activities; and
(3)  Incorporates these self-initiated cleanup measures in the CAP that is submitted to the Director for approval.
5-6  Public Participation.
(a)  For each confirmed release that requires a CAP, the Director has the responsibility to provide notice to the public by means designed to reach those members of the public directly affected by the release and the planned corrective action. This notice may include, but is not limited to, public notice in local newspapers, block advertisements, public service announcements, publication in a state register, letters to individual households, or personal contacts by field staff, or announcements on the OPS website.