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for chemicals in ground waters where these limits are the chemical constituents in ground water at the site of more stringent than MCLS for the same contaminants. your investigation. The Antidegradation Policy requires water quality The next step is to select numerical water quality goals to be set between background and beneficial use limits from the values in the tables of this manual to protective levels when feasible.Multiple waste dis- help you interpret these narrative objectives. Upon chargers in an area and the contribution to degradation examination of the Goss Reference section,you of water quality imposed by each must be considered. discover that listings for the constituents of concern If one discharger is permitted,through the discharge of are found in the Organic Constituents section of this waste,to degrade a water resource to just below the manual. limit where beneficial uses are impaired,then no The second objective from the Basin Plan,stated additional capacity exists for further degradation by above,references California maximum contaminant otherlCdischarges of waste.In addition,our understand- levels(MCLs).These drinking water standards may be ing of the health and environmental effects of chemi- found in the tables of the Organic Constituents section cals and combinations of chemicals is constantly for the chemicals of interest.The applicable California evolving.What is considered to be safe at 10 gg/I MCLs are: today may be found to be harmful at 1 Rg/i tomorrow. Benzene 1 Rg/l An Example of Water Quality Goal Selection Ethylbenzene 680 Xylene(s) 1750 Suppose you are investigating a site where a fuel No California MCLS currently exist for toluene or tank has leaked a petroleum product into the sur- gasoline,but a federal primary MCL has recently been rounding soils.Ground water sampling results indicate established for toluene at 1000µg/l.Since California that benzene,ethyibenzene,toluene,xylene and other .MCLs must be at least as stringent as the federal MCLs, gasoline hydrocarbons have entered ground water. this federal MCL would also be applicable to this case. You wish to know whether the levels detected in that The third water quality objective stated above water are of significant concern. requires that these waters not contain chemicals which The first step would be to look at the Water Quality could impart objectionable tastes or odors_The charts Control Plan(Basin Plan)for the particular Region in in the Organic Constituents section of this manual which your site is located.Upon examination of that contain four types of listings where taste-and odor- docuinent,you determine that the beneficial uses based(organoleptic)levels are found: desigkinated for the ground water are municipal and ❑ California and federal Secondary MCLS; domestic supply. No numerical water quality objet- ❑ California State Action Levels,Taste&Odor; tives are listed in the Basin Plan for benzene,ethyl- ❑ Other Taste&Odor Thresholds;and benzene,toluene,xylene,or gasoline. However,there ❑ U.S.EPA National Ambient Water Quality are three narrative objectives which appear to be Criteria based on Taste&Odor or Welfare. applicable: For the constituents of concern,the most stringent "Ground waters shall not contain chemical con- of these listings are the taste and odor thresholds cited stituents in concentrations that adversely affect benefi- by U.S.EPA in the Federal Register of 1989: cial uses. Ethylbenzene 29 µg/l "Ground waters designated for use as domestic or Toluene 42 municipal supply(M JM shall not contain concentra- Xylene(s) 17 tions of chemical constituents in excess of the maxi- Gasoline 5 murn contaminant levels specified in California Code No listings are found for benzene in these columns. of Regulations,Tide 22,Division 4,Chapter 15. The first applicable water quality objective stated "Ground waters shall not contain taste-or odor- above requires that chemical constituents are not to producing substances in concentrations that cause impair beneficial uses.Since the beneficial uses desig- nuisance or adversely affect beneficial uses." nated in the Basin Plan relate to consumption and other Together,these beneficial uses and water quality uses of water by humans,health-and welfare-related objectives constitute the"water quality standards"for limits would apply.Many of the columns in the tables Selecting Water Quality Goals Page 11