ITEM 4: PETITION OF MOBIL OIL CORPORATION FOR REVIEW OF DENIAL OF PETROLEUM UNDERGROUND STORAGE TANK SITE CLOSURE AT 5599 MISSION BOULEVARD, RUBIDOUX, CALIFORNIA.

DISCUSSION: Health and Safety Code section 25299.39.2, subdivision (b) provides that a petroleum underground storage tank (UST) owner or operator who believes that the corrective action plan for the owner's or operator's site has been satisfactorily implemented may petition the manager of the UST Cleanup Fund (Fund) for review of the owner's or operator's case. Mobil Oil Corporation (petitioner) filed a petition pursuant to this provision for review of the decision of the Riverside County Health Services Agency not to close this case.

Petitioner contends that its case should be closed because the concentrations of petroleum hydrocarbons at its site do not pose a threat to human health and safety, or the environment.

The Fund manager has reviewed petitioner's case and has concluded that petitioner's contention has merit. Accordingly, the proposed order finds that background water quality has been attained at the site, basin plan objectives are met, no further action on this matter is warranted and residual concentrations of petroleum hydrocarbons sorbed to fine-grained soil above the water table do not pose a threat to human health and safety, or the environment, and do not threaten to adversely affect current or probable future beneficial uses of water. Therefore, the proposed order requires petitioner's case to be closed.

POLICY ISSUE: Should the State Water Resources Control Board adopt the proposed order?

RWQCB IMPACT: Santa Ana RWQCB

FISCAL IMPACT: None

STAFF RECOMMENDATION: Adopt the proposed order.

BY THE BOARD:

Mobil Oil Corporation (petitioner) seeks review of the decision of the Riverside County Health Services Agency (County) not to close petitioner's case involving an unauthorized release of petroleum from underground storage tanks (USTs) formerly located at 5599 Mission Boulevard, Rubidoux, California. For the reasons set forth below, this order determines that petitioner's case should be closed and no further action related to the release should be required. Low concentrations of MTBE detected in groundwater samples from a monitor well adjacent to the site's new up-graded USTs do not relate to the release considered in this order and are the subject of a separate investigation.

Tank owners and operators who are eligible for reimbursement from the Underground Storage Tank Cleanup Fund can petition the Fund Manager for a review of their case if they feel the corrective action plan for their site has been satisfactorily implemented, but closure has not been granted (Health and Saf. Code, § 25299.39.2, subd. (b)). Footnote1

Several statutory and regulatory provisions provide the State Water Resources Control Board (SWRCB), Regional Water Quality Control Boards (RWQCBs), and local agencies with broad authority to require responsible parties to clean up a release from a petroleum UST. (e.g., Health & Saf. Code, § 25299.37; Wat. Code, § 13304, subd. (a).) The County has been designated as an agency to participate in the local oversight program for the abatement of, and oversight of the abatement of, unauthorized releases of hazardous substances from USTs. (Health & Saf. Code, § 25297.1) The SWRCB has promulgated regulations specifying corrective action requirements for petroleum UST cases. (Cal. Code of Regs., tit. 23, §§ 2720-2728.) The regulations define corrective action as "any activity necessary to investigate and analyze the effects of an unauthorized release, propose a cost-effective plan to adequately protect human health, safety and the environment and to restore or protect current and potential beneficial uses of water, and implement and evaluate the effectiveness of the activity(ies)." (Cal. Code Regs., tit. 23, § 2720.). Corrective action consists of one or more of the following phases: (1) preliminary site investigation, (2) soil and water investigation, (3) corrective action plan implementation, and (4) verification monitoring. (Cal. Code Regs., tit. 23, § 2722, subd. (a)).

The preliminary site assessment phase includes initial site investigation, initial abatement actions, initial site characterization and any interim remedial action. (Cal. Code Regs., tit. 23, § 2723, subd. (a)). Corrective action is complete at the conclusion of the preliminary site assessment phase, unless conditions warrant a soil and water investigation. A soil and water investigation is required if any of the following conditions exists: (1) There is evidence that surface water or ground water has been or may be affected by the unauthorized release; (2) Free product is found at the site where the unauthorized release occurred or in the surrounding area; (3) There is evidence that contaminated soils are or may be in contact with surface water or ground water; or (4) The regulatory agency requests an investigation, based on the actual or potential effects of contaminated soil or ground water on nearby surface water or ground water resources or based on the increased risk of fire or explosion. (Cal. Code Regs., tit. 23, § 2724).

The purpose of a soil and water investigation is "to assess the nature and vertical and lateral extent of the unauthorized release and to determine a cost-effective method of cleanup." (Cal. Code of Regs., tit. 23, § 2725, subd. (a)).

SWRCB Resolution No. 92-49, Policies and Procedures for Investigation and Cleanup and Abatement of Discharges Under Water Code Section 13304 also applies to petroleum cases. Resolution No. 92-49 directs the RWQCBs to ensure that water affected by an unauthorized release attains either background water quality or the best water quality which is reasonable if background water quality cannot be restored. (SWRCB Resolution No. 92-49, III.G.) Any alternative level of water quality less stringent than background must be consistent with the maximum benefit to the people of the state, not unreasonably affect current and probable future beneficial use of affected water, and not result in water quality less than that prescribed in the water quality control plan for the basin within which the site is located (hereafter basin plan). (Ibid.)

Resolution No. 92-49 does not require, however, that the requisite level of water quality be met at the time of site closure. Even if the requisite level of water quality has not yet been attained, a site may be closed if the level will be attained within a reasonable period. (SWRCB Resolution No. 92-49, III.A.)

The Santa Ana RWQCB Basin Plan for the Santa Ana River basin (Basin Plan) designates existing and potential beneficial uses of groundwater in the Riverside I groundwater subbasin as municipal and domestic supply (MUN), agricultural supply (AGR), industrial service supply (IND), and industrial process supply (PROC) (SARWQCB & SWRCB, Water Quality Control Plan, Santa Ana River Basin (1995) at p. 3-26). However, the Basin Plan contains an exception to the municipal supply beneficial use designation for surface waters in that reach of the Santa Ana River where groundwater, which flows beneath the subject site, discharges (Id. at p. 3-12). The exception is made in accordance with criteria specified in the "Sources of Drinking Water Policy". (Ibid.) Footnote2

The Basin Plan specifies the following taste and odor narrative water quality objective: "The groundwaters of the region shall not contain, as a result of controllable water quality factors, taste- or odor-producing substances at concentrations which cause a nuisance or adversely affect beneficial uses" (Id. at p. 4-14). The Basin Plan also contains the following narrative water quality objective for toxic substances: "All waters of the region shall be maintained free of substances in concentrations which are toxic, or that produce detrimental physiological responses in human, plant, animal or aquatic life" (Ibid).

With regard to the water quality objective for toxicity, the State Department of Health Services (DHS) has set a maximum contaminant level (MCL) for drinking water for benzene, toluene, ethylbenzene, and xylene (BTEX) in drinking water of 1 ppb, 100 ppb, 680 ppb, and 1,750 ppb, respectively (Cal. Code of Regs., tit. 22, § 64444). Although DHS has not yet set an MCL for methyl-tertiary-butyl-ether (MTBE), DHS has set an interim action level of 35 ppb. (DHS Memorandum from Joseph P. Brown, Ph.D., Acting Chief, Water Toxicology Unit to Alexis M. Milea, P.E., Acting Supervisor, Standards and Technology Unit, Office of Drinking Water (February 19, 1991) at p. 2.) DHS has more recently proposed a 5 ppb MTBE concentration as a secondary drinking water standard for taste and odor. The threshold odor concentration of commercial gasoline (measured as TPH-g) in water is commonly accepted to be 5 ppb, with 10 ppb giving a strong odor. (SWRCB, Water Quality Criteria (2d ed. 1963) p. 230.).

The following is a brief historical summary of petitioner's site at 5599 Mission Blvd. in the city of Rubidoux. The site is an active gasoline service station located in the Riverside I groundwater basin and about 4,000 feet northwest of the Santa Ana River on the river's historic flood plain. Shallow soil underlying the site consists predominantly of low permeability silty sand, silt, and clay to a depth of approximately ten feet. Groundwater at the site is encountered at a depth of about 15 feet in coarse-grained, highly permeable sand and gravelly sand alluvial sediments. Groundwater beneath the site is unconfined, exhibits a moderate southwesterly hydraulic gradient of about 0.007, and a groundwater flow velocity of about 750 feet per year. The groundwater discharges to the Santa Ana River as surface water about one to two miles southwest of the site.

In April 1989, three soil borings were drilled in the vicinity of the site's USTs and a gasoline sheen was observed on groundwater obtained from one. In May 1989, a hydro-probe survey indicated that shallow groundwater was affected by petroleum hydrocarbon compounds in all directions from the site's USTs. In August 1989, the site's three single-walled gasoline USTs were removed and approximately 500 cubic yards of soil excavated. Soil samples obtained from the bottom and sidewalls of the excavation contained concentrations of TPH-g ranging from less than 1 to 3,430 ppm. In September 1989, during the installation of two doubled-walled fiberglass USTs and attendant piping and dispensers, gasoline affected soil was discovered in the vicinity of each of the site's former pump islands. An additional volume of affected soil (estimated to be about 350 cubic yards) was subsequently excavated.

In April 1991, six monitor wells were installed at and adjacent to the site. Groundwater sampling of these wells revealed a sheen on the water surface in the well installed at the location of the former USTs and low concentrations of benzene (4 to 6 ppb) in two other wells. In September 1991, six additional monitor wells were installed and groundwater samples collected and analyzed from all site wells. These analyses revealed low concentrations of benzene (less than 1 ppb) in groundwater from two wells and low concentrations of toluene and xylene (1 to 2.4 ppb) in one well; concentrations of TPH-g were not detected (the detection limit was 50 ppb) in any of the groundwater samples. Analyses of groundwater samples collected from site wells in September 1992 and March 1993 did not detect any concentrations of dissolve phase petroleum hydrocarbons. Based on these sample analytical results, petitioner requested closure of the site in a letter dated May 5, 1993.

By letter dated June 9, 1993, the County denied petitioner's closure request citing a concern that a plume of dissolve phase petroleum hydrocarbons may be present between the locations of "...widely spaced down-gradient monitor wells..." and requested that petitioner submit a workplan to address this concern. Petitioner complied and in November 1993, obtained a shallow "Hydropunch" groundwater sample in the area of concern. Analysis of the water sample indicated a TPH-g concentration of 2,000,000 ppb and BTEX concentrations ranging from 2,700 to 46,000 ppb.

In February 1994, petitioner proposed to collect seven additional "Hydropunch" groundwater samples in the area down-gradient of the site and in April, mobilized personnel and equipment to the site. However, due to subsurface conditions and equipment problems, no samples were collected.

In March 1995, petitioner proposed to monitor groundwater down-gradient of the site for a period of one year using five wells and to abandon the seven wells at and up-gradient of the site. In its April 4, 1995 response, the County rejected the well abandonment proposal but agreed to allow semi-annual groundwater sampling of those wells. The County also requested additional investigation.

In a workplan dated October 2, 1995, petitioner proposed the installation of two monitor wells in the vicinity of the November 1993 "Hydropunch" sample location. The County approved the workplan with the following stipulations: 1) the wells should be developed a minimum of 72 hours, 2) groundwater sampling should be performed within 72 hours after well development, and 3) the wells should be constructed with 4-inch well casing and screen.

Beginning in March 1996, MTBE was added to the list of analytes tested for in groundwater samples collected at the site. Only well MW-3, which is located about ten feet down-gradient of the currently operating, new up-graded USTs installed in 1989, has consistently tested positive for MTBE (55 to 380 ppb in four out of five samples). The sample analyses also show that TPH-g and BTEX are not present.

By letter dated July 31, 1996, petitioner submitted to the County a "Request For No Further Action." Petitioner stated that it considered the site a "low risk groundwater case" and that passive bioremediation was the most reasonable corrective action alternative. Petitioner noted that 1) the source of the release had been removed (the USTs and approximately 850 cubic yards of affected soil); 2) groundwater samples from down-gradient monitor wells have never detected gasoline constituents (six sampling events between October 1991 and March 1996); 3) the "Hydropunch" sample collected in November 1993 is anomalous because groundwater samples from nearby monitor wells have never contained detectable concentrations of any gasoline constituents; and 4) groundwater occurs at a depth of less than 50 feet and there are no production wells within 250 feet of the site.

By letter dated September 17, 1997, the County denied petitioner's request for no further action citing the following reasons: 1) source removal was not complete because "free product", i.e., a sheen had been observed in 1989; 2) all affected soil was not removed from the site; 3) the November 1993 "Hydropunch" groundwater sample results cannot be discounted; 4) groundwater in the Riverside I groundwater basin has designated beneficial uses; and 5) the groundwater "plume" was never defined. The County then directed petitioner to install the two down-gradient monitor wells proposed in the October 2, 1995 workplan.

By letter dated October 16, 1996, petitioner proposed that in lieu of installing the two wells, it would rather perform a "feasibility study." The objective of the study was to quantify the remaining residual hydrocarbons in site soil, groundwater impacts and migration, and subsurface attenuation. In a November 12, 1995 response, the County turned down petitioner's proposal and directed that the wells be installed.

By letter dated March 27, 1997, petitioner again requested site closure. The County, in a letter dated April 10, 1997, denied petitioner's request for closure on the basis that further site assessment was necessary. In June 1997, petitioner requested review of its case by the UST Cleanup Fund manager pursuant to Health and Safety Code section 25299.39.2, subdivision (b).

Contention: Petitioner contends its case should be closed because the source of gasoline release has been removed and analyses of groundwater samples from wells at and down-gradient of the former USTs demonstrate an absence of groundwater impacts. Hence, current site conditions do not pose a risk to current or probable future beneficial uses of groundwater.

Findings: Petitioner's contention has merit. The facts in the record support the finding that residual petroleum constituents at petitioner's site, as they relate to the release reported in 1989, do not pose a threat to human health and safety, or the environment, and do not adversely affect current or probable future beneficial uses of water. In addition, the level of corrective action taken at the site is consistent with the maximum benefit to the people of the state.

The record indicates that removal of the USTs and approximately 850 cubic yards of affected soil in 1989 was successful in effectively eliminating any potential risk to current or probable future beneficial uses of groundwater. The primary source of the release as well as a substantial volume of affected soil which could contribute to further groundwater degradation were removed. Furthermore, as discussed below, geologic and hydrogeologic conditions at and in the vicinity of the site are conducive to enhanced attenuation (biodegradation and dispersion). The County declined to close petitioner's case because it believed that source removal was not complete, that the groundwater plume was never defined, and that the Basin Plan designates groundwater in the area as municipal supply.

We are confident, however, that site conditions for the purpose of evaluating potential risks associated with the release can be understood from the current record. Based on our interpretation of the geology and hydrogeology in the vicinity of the site, any residual gasoline which may still be present in shallow soil does not represent a threat to beneficial uses. Furthermore, a detectable plume of dissolved petroleum constituents from the former USTs no longer exists. A high velocity groundwater flow regime and relatively clean sand and gravel aquifer material have contributed substantially to an absence of a measurable thickness of free product in any of the site wells and a plume of dissolved phase constituents in groundwater. The coarse character and high permeability of the aquifer sediments would not contribute to a mounding of free product above the capillary zone but rather would promote rapid lateral dispersion. The high groundwater flow velocity (estimated to range from 2 and 3.5 feet per day, depending on the gradient) would readily transport dissolved phase constituents, aid in their diffusion, and be conducive to rapid biodegradation. Thus, once the source (the USTs) was removed in 1989 and in the absence of a substantial mass of sorbed phase constituents Footnote3, groundwater beneath the site quickly achieved Basin Plan water quality objectives.

A review of groundwater analytical data from site wells demonstrate the capacity of the aquifer composition (i.e., sand and gravel with little or no silt and clay) and its flow regime to minimize short term water quality impairment and long term impacts. The initial sampling of well MW-5 (located at the source of the release) in February 1991 revealed a sheen to be present. A second sampling in October 1991 revealed no sheen and a benzene concentration of only 0.8 ppb. All subsequent groundwater samples collected from the well between September 1992 and September 1997 (12 sampling events) did not detect any gasoline constituents. Thus, within two years of the UST removal, the concentration of benzene in groundwater at the source of the release was less than the drinking water standard and in three years was not detectable. Groundwater data for down-gradient well MW-9 (nine sampling events between October 1991 and September 1997) show that the dissolved phase plume stabilized at a distance less than 400 feet from the site (groundwater samples from MW-9 consistently tested "ND" for all constituents including MTBE).

With regard to the "Hydropunch" water sample collected in November 1993, its validity is questionable. The sample's reported TPH-g concentration of 2,000,000 ppb is more than ten times the water solubility of gasoline. If the results of the analysis were valid, it would indicate that either free product was present in the sample vial or that the sample contained an excessive amount of fine sediment (i.e., high turbidity and a substantial fraction of sorbed gasoline). Given standard sampling procedures and methods, it is unlikely that a sample vial with free product would go unnoticed by either the sampling or laboratory personnel. In the event that the sample may have been turbid, the sample results are clearly not valid. Moreover, a sample with a reported TPH-g concentration of 2,000,000 ppb would have to undergo at least a 500 fold dilution to bring it into the normal operating range of the laboratory equipment. However, the report shows a standard detection limit (TPH = 50 ppb, BTEX = 0.3 ppb) for the sample indicating no dilution. Given these facts and the understanding that groundwater samples from site wells in all directions from the origin of the sample in question tested "not detected" prior to and after its collection, the anomalous 2,000,000 ppb value can not be relied upon as accurate or representative of subsurface conditions.

With regard to the detection of MTBE in groundwater samples from the well adjacent to the operating, upgraded USTs that were installed in 1989, the detections may be related to these upgraded USTs. Because the concentrations of MTBE detected are relatively low and the sample analyses do not demonstrate the presence of other constituents (TPH-g and BTEX) commonly associated with a release of liquid petroleum into groundwater, the detections may be a consequence of a vapor leak from the dispenser's vapor recovery system. We have informed the County of this possibility, the County has requested that the petitioner investigate this possibility, and the petitioner is preparing a workplan to comply with that request.

Data contained in the record indicate that a plume of dissolved phase gasoline constituents does not currently exist in the vicinity of the former UST complex and that residual petroleum constituents remaining in shallow fine-grained soil above the water table as a consequence of the former release do not pose a threat to current or probable future beneficial groundwater uses. Background water quality has been attained, Basin Plan objectives have been met Footnote4, and no further action on this matter is required. The occurrence of low concentrations of MTBE in groundwater in the vicinity of the new up-graded USTs has been noted and will be addressed as an issue separate from the UST release and corrective action which are the subject of this petition.

1. Background water quality has been attained, Basin Plan objectives are met, and no further action on this matter is warranted.

2. Residual concentrations of petroleum hydrocarbons sorbed to fine-grained soil above the water table at petitioner's site do not pose a threat to human health and safety, or the environment, and do not threaten to adversely affect current or probable future beneficial uses of water.

3. The level of site cleanup is consistent with the maximum benefit to the people of the state.

4. Concentrations of MTBE detected in groundwater samples from the well adjacent to the operating, upgraded USTs that were installed in 1989 are not related to the case at hand and will be addressed by the County and petitioner as a separate issue.

IT IS THEREFORE ORDERED that petitioner's case be closed, and no further action related to the release be required. The UST Cleanup Fund Manager is directed to issue petitioner a closure letter consistent with Health and Safety Code section 25299.37, subdivision (h).

The undersigned, Administrative Assistant to the Board, does hereby certify that the foregoing is a full, true, and correct copy of a resolution duly and regularly adopted at a meeting of the State Water Resources Control Board held on November 19, 1998.

AYE:

NO:

ABSENT:

ABSTAIN:

______________________________

Maureen Marché

Administrative Assistant to the Board

Footnote1

To the extent that the SWRCB may lack authority to review this petition pursuant to Health and Safety Code section 25299.39.2, subdivision (b) because the petitioner did not submit a corrective action plan for the site, the petition is being reviewed on the SWRCB's own motion pursuant to Health and Safety Code section 25297.1, subdivision (d) and SWRCB Resolution 88-23.

Footnote2

SWRCB Resolution 88-63 provides that "all surface and ground waters of the State are considered to be suitable, or potentially suitable, for municipal or domestic water supply . . . with the exception of . . . [s]urface and ground waters where . . . [t]here is contamination, either by natural processes or by human activity (unrelated to a specific pollution incident), that cannot be reasonably treated for domestic use using either best management practices or best economically achievable treatment practices." Resolution 88-63 has been incorporated into the basin plan. (SARWQCB Resolution 89-42 and approved by SWRCB Resolution 89-75.)

Footnote3

The sorbtive capacity of clean sand and gravel is virtually nil.

Footnote4

The Basin Plan's taste and odor water quality objective for TPH-g is 5 ppb. The detection limit for the groundwater sample analyses is 50 ppb. However, because concentrations of BTEX are also "non detect" (less than 0.3 to 0.5 ppb) in the samples, it is reasonable to infer that the taste and odor water quality objective for TPH-g has been achieved.