STATE OF CALIFORNIA

STATE WATER RESOURCES CONTROL BOARD

ORDER: WQ 98 - 04 UST

In the Matter of the Petition of MATTHEW WALKER

for Review of Denial of Petroleum Underground Storage Tank Site Closure at

818 Jackson Street, Napa, California.

BY THE BOARD:

Matthew Walker (petitioner) seeks review of the decision of the Napa County Department of Environmental Management (County) not to close petitioner's case involving an unauthorized release from a petroleum underground storage tank (UST) located at 818 Jackson Street, Napa, 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.

I. STATUTORY, REGULATORY, AND FACTUAL BACKGROUND

Tank owners and operators who are eligible for reimbursement from the UST 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), 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 92-49, Policies and Procedures for Investigation and Cleanup and Abatement of Discharges Under Water Code section 13304 also applies to petroleum UST cases. Resolution 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 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 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 92-49, III.A).

The San Francisco Bay RWQCB Basin plan designates existing and potential beneficial uses of groundwater in the Napa Valley basin as municipal and domestic (MUN) supply, industrial supply, agricultural supply, and as freshwater replenishment to surface waters. (SFBRWQCB & SWRCB, Water Quality Control Plan, San Francisco Bay Basin (1995) at p. 2-5). The Basin plan specifies a narrative taste and odor water quality objective as follows: "Groundwaters designated for use as domestic or municipal supply (MUN) shall not contain taste- or odor-producing substances in concentrations that cause a nuisance or adversely affect beneficial uses." (Id. at p. 3-7.) The basin plan also contains the following narrative water quality objective for toxic substances as follows: "...groundwaters designated for beneficial use as domestic or municipal supply (MUN) shall not contain concentrations of constituents in excess of the maximum (MCLs)...specified in...Title 22 of the California Code of Regulations...." (Id. at 3-6.)

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 of 1 ppb for benzene, 100 ppb for toluene, 680 ppb for ethylbenzene, and 1,750 ppb for xylene. (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 total petroleum hydrocarbon gasoline, or TPH-g) in water is commonly accepted to be 5 ppb, with 10 ppb giving a strong odor. The threshold odor concentration of commercial diesel (measured as TPH-d) in water is commonly accepted to be 100 ppb. (SWRCB, Water Quality Criteria (2d ed. 1963) p. 230.)

The following is a brief historical summary of petitioner's site at 818 Jackson Street in the City of Napa. The site is located in an industrial and commericial area about one-half mile west/northwest of the Napa River. The two USTs at the site ceased operating some time during the 1950's. Both were reported to have had "mixed" use, storing diesel, gasoline, and motor oil. According to County inspector records regarding the tank removal, UST #1 had a 600 gallon storage capacity and UST #2 (located in a separate area of petitioner's site approximately 100 feet south of UST #1) had a capacity of 1,100 gallons. When removed in September 1995, both USTs were described as rusted and with multiple holes, consistent with their pre-1950-vintage. According to the County inspector, the pit for UST #2 "smelled of diesel" and, during removal of the tank, a "black oily sludge" spilled into the pit. The inspector also noted an area of "obvious contamination" in the southeast corner of the pit.

The native soil immediately underlying petitioner's site consists predominantly of low permeability clay, with groundwater as shallow as about 5-6 feet below ground surface (bgs). The uppermost fine-grained deposits apparently grade into coarser materials below these depths. Groundwater monitoring wells at a nearby UST site at 1865 Tanen Street indicate shallow groundwater at similar depths and a generally southeasterly hydraulic gradient (e.g., toward the Napa River about one-half mile east-southeast of petitioner's site). No drinking water wells have been identified within about one half-mile of petitioner's site.

After removal of the two USTs, up to 40 cubic yards of petroleum-affected soil were removed to a depth of about eight feet from the two separate pits. During the tank removal, one soil sample was collected from a sidewall of the UST #1 excavation area, five soil samples were collected from the sidewalls of the UST #2 excavation area (where the diesel odor and the sludge spillage had been reported during tank removal), and a "grab" water sample was collected from each of the tank pits. One soil sample was also collected from the stockpile of excavated soils from each UST pit.

UST #1 soil and water samples both indicated "non-detect" diesel (reported as TPH-d), "non-detect" gasoline (reported as TPH-g), "non-detect" motor oil (reported as TPH-mo), and "non detect" for benzene, toluene, ethylbenzene, and xylene (BTEX). Residual petroleum hydrocarbons were detected in two of five soil samples from the sidewalls of the UST #2 excavation area. Concentrations were reported as 29 parts per million (ppm) TPH-d and 250 ppm TPH-mo (all other constituents were "non-detect") in the sample from the east wall of the pit and 1,200 ppm TPH-d (with all other constituents "non-detect") in the sample from the southeast wall, where the inspector had earlier observed "obvious contamination." Three of five soil samples (south, north, and west) were "non-detects" for all constituents. The only constituent detected in the stockpiled soil samples from each overexcavation was TPH-mo at 27 ppm and 28 ppm in UST #1 and UST #2 , respectively. These stockpiled soils were disposed of at an offsite landfill.

Analysis of the "grab" water samples collected from the excavation at UST #2 indicated the following concentrations of total petroleum hydrocarbons: 94 ,000 ppb (TPH-d), 140,000 ppb (TPH-mo) and "non-detect" (TPH-g). In addition, the following gasoline constituents were detected: 21 ppb (benzene), 33 ppb (toluene), 110 ppb (ethylbenzene), and 156 ppb (xylene). A similar "grab" water sample from UST #1 indicated "non-detect" for all petroleum hydrocarbon constituents. Based on these results, the County requested additional soil and groundwater investigation in the area of UST #2, but no additional work in the vicinity of UST #1.

Subsequent investigations near UST #2 in July 1996 included four soil borings (B1 through B4). Six soil samples ranging from 3.0 to 6.5 feet bgs were analyzed, in addition to two "grab" groundwater samples (one from B1 and one from B3). No soil discoloration or petroleum odors were noted during drilling. All six soil samples and "grab" water samples were "non-detect" for benzene and MTBE (the primary constituents of concern) and for toluene and ethylbenzene.

Out of six soil samples recovered from the four borings, the two collected from Boring B3 (three feet and six feet bgs) had the only "hits" of TPH-d (15 ppm and 29 ppm, respectively) and TPH-g (1.1 ppm and 1.9 ppm, respectively). TPH-mo (9.5 ppm) and xylene (0.013 ppm) were detected in B3 at six feet bgs, only. Boring B3 is located within 10 feet of the southeast pit sidewall where the County inspector had noted "obvious contamination." The only other detection of residual petroleum constituents in soil borings was at 5.5 feet bgs in B4 (about 10 feet south of the pit) which indicated 130 ppb xylene in soil (the MCL for xylene in groundwater is 1,750 ppb) with all other petroleum constituents "non-detect."

The "grab" groundwater sample collected from the open borehole in B3 (i.e., within 10 feet down-gradient of the pit) only detected the same constituents that were also detected in the soil samples for that boring (i.e., TPH-d at 8,600 ppb, TPH-g at 140 ppb, TPH-mo at 1,900 ppb, and xylene at less than one part per billion) while the "grab" groundwater sample from B1 was (like the soil samples from that boring) "non-detect" for all petroleum constituents, including benzene and MTBE.

Despite the low levels of residual petroleum constituents detected and the universal "non-detects" of the principal constituents of concern (i.e., benzene and MTBE), the County declined to classify the site as "low risk" citing reported concentrations of TPH-d, TPH-g, TPH-mo in the B-3 "grab" water sample. In a December 2, 1996 letter to petitioner, the County stated its conditions for closure as (1) a demonstration that "contamination" is of limited extent, (2) that pollutants in soil and groundwater are being treated or degraded, and (3) that the beneficial use of groundwater will be restored within a reasonable period of time. To this end, the County requested additional investigation.

On June 3, 1997, after petitioner again requested closure, County staff reiterated its opinion that the impact to groundwater from the petroleum hydrocarbon release was not adequately investigated and that additional investigation was necessary. In October 1997, petitioner requested review of his case by the UST Cleanup Fund manager pursuant to Health and Safety Code section 25299.39.2, subdivision (b). On February 5, 1998, County staff approved petitioner's request to suspend its requirements for a subsurface investigation pending the decision of the SWRCB. In a April 20, 1998 letter to the Fund manager, the County provided the record for review and restated its contention that the site is "not suitable for closure."

II. CONTENTIONS AND FINDINGS

Contention: The petitioner contends his case should be closed because the limited, localized, and diminishing impacts of residual petroleum constituents pose a "low risk" to current or probable future beneficial uses of water.

Findings: Petitioner's contention has merit. As explained below, the facts in the record support the finding that additional soil and groundwater investigation is not necessary and that residual petroleum constituents at petitioner's site 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 site cleanup is consistent with the maximum benefit to the people of the state and will meet the applicable objectives in the San Francisco Bay RWQCB Basin Plan within a reasonable time frame.

The primary source (two USTs located about 100 feet apart which were not active for many decades prior to tank removal and overexcavation in 1995) as well as substantially affected soils from the immediate vicinity of the USTs have been removed. Residual petroleum constituents have been effectively removed, eliminated through natural attenuation processes to "non-detect" levels, or degraded to detectable but immobile concentrations adsorbed to soil. These weathered residuals have such low solubility that they are not contributing dissolved petroleum constituents to groundwater in concentrations which would impair existing or probable future beneficial use. Four soil borings installed at the County's request in the immediate vicinity of UST #2 indicate low concentrations of lingering residual petroleum (TPH-d, TPH-g, TPH-mo, and xylene) detected within about ten feet down-gradient of the former tank pit (i.e., in B3) that diminish to "non-detect" in soil and "grab" groundwater samples within 15 feet (i.e., in B1) down-gradient of the former tank pit.

The reported presence of detectable, low level "hits" of benzene, toluene, ethylbenzene, and xylene in the "grab" groundwater sample from the UST #2 pit appears to reflect adsorbed chemicals mobilized from disturbed suspended sediments which were introduced during overexcavation of the pit. Because these samples were "grabbed" from a highly disturbed, suspended-sediment-rich environment of an excavated pit they cannot be relied upon as quantitative indicators of ambient, dissolved groundwater quality. Although laboratory analyses of such "grab" water samples certainly include any dissolved constituents (if present) in the reported total, they will also include constituents adsorbed to soil particles dislodged from surrounding soils that are not representative of the underlying water-bearing zone under ambient, undisturbed conditions. At best, such "grab" samples can provide evidence of the absence of constituents (either dissolved or adsorbed to suspended sediments) or a qualitative indication that constituents are present in the sample, although not necessarily dissolved in ambient groundwater. Such analyses can be overwhelmed by the presence of even minute quantities of adsorbed concentrations loosened from the excavation sidewalls of the pit (or boring) even when dissolved concentrations in groundwater are truly "non-detect." In these instances, soil samples analyses will give the best quantitative picture of the magnitude and extent of the release while "grab" water samples will, at best, provide a simple qualitative indicator of the presence or absence of petroleum constituents at a particular location.

Of the five soil samples taken from the soils immediately surrounding the UST #2 excavated area, none detected benzene, toluene, ethylbenzene, or xylene. The only constituents detected (TPH-d, TPH-g, and TPH-mo) indicated very old, highly attenuated, immobile residual petroleum adsorbed to soil. The "grab" groundwater sample from this pit was the only sample at the site that detected benzene (29 ppb). None of the four borings in the immediate vicinity of this pit, including B3 and B1, which are within 10 feet and 15 feet down-gradient of the pit, detected benzene, toluene, or ethylbenzene (the most soluble and mobile petroleum hydrocarbons of concern). These facts indicate a very localized area of impacted soils and well-advanced degradation of immobile residual petroleum constituents which is consistent with a 1950's release.

The County contends that the extent of contamination has not been defined and that the stability of the presumed groundwater plume has not been demonstrated. We disagree. The soil borings and "grab" water samples provide sufficient information to conclude that (1) there is no "contamination" (e.g., "an impairment of the quality of the waters of the state . . . to a degree which creates a hazard to the public health . . . ." as defined in Wat. Code, § 13050, subd. (k)), and (2) there is no dissolved "plume" to define and the extent of soil affected by immobile residuals has been shown to be localized within just a few feet east and southeast of former UST #2.

Furthermore, MTBE was not found in any of the six soil boring samples or in the two "grab" groundwater samples collected from borings within 10-15 feet down-gradient of former UST #2. These findings, too, are consistent with the 1950's operation of the tanks.

The absence of detectable benzene, toluene, ethylbenzene, or xylene from all samples except one "grab" groundwater sample from the pit, which included disturbed soil from the east and southeast sidewalls (which had detectable concentrations of TPH-d and TPH-mo) provides substantial evidence of very limited, very localized soil impacts from a very old release of petroleum. The "grab" groundwater sample did not measure ambient, dissolved groundwater quality, but rather reflected contribution from the limited, localized residual petroleum constituents adsorbed to soils exposed during excavation. (It should be noted that even assuming no contribution from detectable petroleum constituents adsorbed to soils, the reported concentrations of toluene, ethylbenzene, and xylene in "water" were all less than their respective MCL.) Evidence that detectable, residual petroleum constituents are limited to the immediate vicinity of the former UST (and that petitioner's case should be, for all practical purposes, considered one of localized impact to a limited volume of petroleum-affected soil) is also strengthened by the fact that in boring B1 (15 feet down-gradient of the former UST #2) all petroleum constituents are "non-detect" in both soil and "grab" groundwater samples.

Thus, the available facts indicate the absence of a "dissolved" plume of soluble, mobile constituents and do not support the County's request for additional groundwater investigation to determine plume extent. The facts in the record indicate that with no further regulatory action, residual detectable concentrations of TPH-g, TPH-d, TPH-mo, and xylene adsorbed to shallow, fine-grained soils will remain localized and continue to attenuate naturally over time.

The lingering, but diminishing residual concentrations of petroleum constituents will not affect beneficial uses of groundwater. According to Department of Water Resources well records and 1990 Census data, there are no drinking water wells within 2,500 feet of petitioner's site. The nearest is a domestic well installed more than thirty years ago at 2217 Soscol Avenue, about 2,500 feet to the north. This well encountered the first water-bearing zone at depth of 43 feet, is screened from 30-85 feet bgs and has a surface sanitary seal to 30 feet bgs. Drilling logs further indicate that groundwater produced in this well was first encountered at a depth of 43 feet but rose to 7 feet bgs, which indicates confined conditions that preclude significant recharge from shallower groundwater such as encountered at petitioner's site at six feet bgs. Nevertheless, concentrations of TPH-g in that shallow groundwater in immediate contact with (albeit limited) residual TPH-g adsorbed to soils will likely remain above 5 ppb (the commonly accepted odor threshold for water, which is more stringent than the 100 ppb threshold for TPH-d) in a localized volume of surrounding groundwater for a significant period of time. Considering the absence of existing wells in close proximity to petitioner's site, the local hydrogeologic considerations, and standard well construction practices, such a limited, isolated scenario will not unreasonably affect existing or probable future beneficial uses.

To remove all traces of residual petroleum constituents at petitioner's site would require additional, but feasible, excavation of soil between the former southeast corner of the UST#2 pit and the "non-detect" boring B1, about 15 feet away and perhaps to a depth of 6-8 feet. Removal of 50 cubic yards or less would eliminate residual, detectable petroleum concentrations. However, if complete removal of detectable traces of petroleum constituents becomes the standard for UST corrective actions, the statewide technical and economic implications will be enormous. For example, disposal of soils from comparable areas of excavation throughout the state would greatly impact already limited landfill space. In light of the precedent that would be set by requiring additional excavation at this site and the fact that beneficial uses are not threatened, attaining background water quality at petitioner's site is not feasible. It is impossible to determine the precise level of water quality that will be attained given the limited residual TPH-g that remains at the site, but in light of all the factors discussed above, a level of water quality will be attained that is consistent with the maximum benefit to the people of the state. Footnote2

The final step in determining whether cleanup to a level of water quality less stringent then background is appropriate for this site requires a determination that the alternative level of water quality will not result in water quality less than that prescribed in the relevant basin plan. Pursuant to SWRCB Resolution 92-49, a site may be closed if the basin plan requirements will be met within a reasonable time frame.

In the instant case, as discussed above, TPH-g in the shallow groundwater in immediate contact with the limited residual TPH-g adsorbed to soils will likely remain above 5 ppb (the commonly accepted odor threshold for water) and thus violate the basin plan's narrative odor objective in a localized volume of surrounding groundwater for a significant period of time. This time period could be anywhere from a couple of decades to hundreds of years.

Nonetheless, during this time these residual concentrations above 5 ppb TPH-g will not pose a threat to current or future beneficial uses. It is highly unlikely that TPH-g detected in localized areas in the immediate area of the UST's discharge will migrate substantially beyond current limited spatial extent. Though the longer chain hydrocarbons comprising TPH-g biodegrade more slowly than certain petroleum constituents, such as benzene, they are also more recalcitrant (i.e., less volatile, less soluble and highly absorbent) and much less mobile. It is also highly unlikely that this particular very limited pocket of shallow groundwater will be used directly as a source of drinking water. Thus, the significant period of time that it will take for water quality in this limited area to meet all Basin Plan objectives is a reasonable time frame. Closure of the site, given the facts in this particular case, is appropriate.

III. SUMMARY AND CONCLUSION

1. There is no evidence of MTBE at this site. Residual concentrations of petroleum hydrocarbons at petitioner's site have degraded to detectable but immobile concentrations strongly adsorbed to fine-grained soil particles in contact with shallow groundwater. This limited volume of soil is localized within a few feet immediately east and southeast of the location of one of the former USTs.

2. Petitioner's site is located in an industrial and commercial area. According to drilling logs, the nearest nearest well (about 2,500 feet to the north) has a surface sanitary seal to 30 feet bgs and is screened from 30-85 feet bgs in a confined groundwater bearing zone. These data indicate that shallower groundwater such as that observed at petitioner's site is effectively precluded from adversely affecting the deeper, confined groundwater zone.

3. Given the low permeability and shallowness of the affected water-bearing soils at petitioner's site and the standard practice of installing surface sanitary seals to depths of 30 feet or more in water supply wells, the residual, detectable concentrations of highly weathered petroleum hydrocarbons 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.

4. Additional soil and water investigation at petitioner's site is not necessary.

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

6. Given the adverse technical and economic implications statewide if further corrective action was required, and the minimal benefits, if any, that would be gained by further corrective action, it is not feasible to attain background water quality at petitioner's site.

7. Detectable TPH-g in shallow groundwater in immediate contact with the limited, weathered residual TPH-g adsorbed to soil particles will likely remain above 5 ppb (the commonly accepted odor threshold for drinking water) and thus violate the basin plan's narrative odor objective in a very localized, small volume of surrounding groundwater for anywhere from decades to hundreds of years.

8. The determination as to what constitutes a reasonable period must be based on evaluation of all relevant factors, including but not limited to the extent and gravity of any threat to public health and the environment during the period require to meet basin plan objectives. Although the time required to attain objectives in this case is lengthy, it is a reasonable period considering the facts of this particular case, including that there are no known drinking wells within 2,500 feet of the site, it is highly unlikely that TPH-g detected in localized areas in the immediate area of the UST's discharge will migrate substantially beyond the current limited spatial extent, it is highly unlikely that this particular very limited pocket of shallow groundwater will be used directly as a source of drinking water, and that even if the affected groundwater were used as a source of drinking water the TPH-g in that water would not pose any threat to public health.

9. Therefore, no further corrective action is necessary.

10. The above conclusions are based on the site-specific information relative to this particular case.

IV. ORDER

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 uniform closure letter pursuant to Health and Safety Code section 25299.37, subdivision (h).

CERTIFICATION

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 August 26, 1998.

AYE: Mary Jane Forster

James M. Stubchaer

John W. Brown

John P. Caffrey

NO: Mark Del Piero

ABSENT: None

ABSTAIN: None

/s/

Maureen Marché

Administrative Assistant to the Board

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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

In approving an alternative level of water quality less stringent than background, the SWRCB has also considered the factors contained in California Code of Regulations, title 23, section 2550.4, subdivision (d). As discussed earlier, the adverse effect on shallow groundwater will be minimal and localized, and there will be no adverse effect on the groundwater contained in deeper aquifers, given the physical and chemical characteristics of petroleum constituents; the hydrogeological characteristics of the site and surrounding land; and the quantity of the groundwater and direction of the groundwater flow. In addition, the potential for adverse effects on beneficial uses of groundwater is low, in light of the proximity of groundwater supply wells; the current and potential future uses of groundwater in the area; the existing quality of groundwater; the potential for health risks caused by human exposure; the potential damage to wildlife, crops, vegetation, and physical structures; and the persistence and permanence of potential effects.

Finally, a level of water quality less stringent than background is unlikely to have any impact on surface water quality, in light of the volume and physical and chemical characteristics of petroleum constituents; the hydrogeological characteristics of the site and surrounding land; the quantity and quality of groundwater and the direction of groundwater flow; the patterns of precipitation in the region, and the proximity of residual petroleum to surface waters.