MEMORANPUM UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460



## NOY 5 

## 1997 OFFICE Of' WATER

SUBJECT: Establishing Site Specific Aquatic Life Criteria


### TudorT. Davies, Director

# ~~ Ito Natural Background ) FROM: Office ofScience and

# Techn~1A TO: WaterManagement Division Directors, Regions 1-10 State and Tribal WaterQuality Management Program Directors

In the course ofreviewing State and Tribal water quality standards (WQS), EPA has identified several issues pertaining to the establishment ofsite specific numeric criteriaon the basis ofnatural background conditions. EPA is issuing this policy to provide greaterclarity and direction for States and Tribes who are considering establishing site specific criteria equal to natural background conditions, and for EPA Regional Offices reviewing State and Tribal water quality managementprograms.
BacklW>und
Site specific criteria are allowed by regulation and are subject to EPA review and approval. The Federal water quality standards regulation at 40 CFR 131.11(b)(I) requires States and authorized Tribesto adopt numeric water quality criteria that are based on section 304(a) criteria, section 304(a) criteriamodified to reflect site-specific conditions, or otherscientifically defensible methods. Under 40 CFR 131.5(a)(2), EPA reviews State WQS to determine whether
a State has adopted criteriato protect the designated uses. Existing guidance and practice are that EPA will approve site specific criteria developed on the basis ofsound scientific rationales. Currently, EPA guidance has specified three procedures for States and Tribes to follow in deriving site specific criteria. ·These are the Recalculation Procedure, the Water-Effect Ratio Procedure and the Resident Species Procedure. These procedures can be found in the Water 

### QualityStandards Handbook (EPA-823-B940005a, 1994). EPA also recognizes there may be naturally occurring concentrations ofpollutants which may exceed the national criteria published under section 304(a) ofthe Clean Water Act.Policy
This policy applies only to site specific numeric aquatic life criteria based on natural background. States and Tribes may establish site specific numeric aquatic life water quality criteria by settingthe criteria value 

### equal to 

### natural background. Natura) background is defined
asbackground concentration due

### only to non-anthropogenic sources, i.e., non-manmade sources. In setting criteria

### equal to 

### natural background the State orTribe should, at a minimum, include 

### in their waterquality standards:
(1) a definition of natural background consistent with the above; (2) a provision that site specific criteria may be set equal to natural background; (3) a procedure for determining natural background, oralternatively, a reference intheir water

### quality standardsto another documentdescribing the binding procedure that will be 

### used.

Discussion

A State orTribal procedure for detennining natural background will need to be specific enough to establish natural background concentration accurately and reproducibly. States and Tribes should also provide for public notice and commenton the definition, the provision, the procedure and the site specific numeric criteriaderived from the procedure. The State orTribe will need to document the resulting site specific numeric criteria in the State orTribal water 

### quality standards, including specifying the waterbody segment to which the site specific criteria apply. This can be accomplished through adopting the site specific criteria into the State or Tribal WQS, or, alternatively, by appending the site specific criteria to the WQS. In either case, the StateorTribe must comply with the public participation requirements of40 CFR 131.20 and 40 CFR Part25, and State and Tribal citizens should be able to readily detennine the water 

### quality criteria applicable to specific waterbodies.

For aquatic life uses, where the natural background concentration for a specific parameter isdocumented, by definition thatconcentration is sufficient to support the level ofaquatic life expectedto occur naturally at the site absent any interference by humans. The State orTribe should considerrefining the designateduse for the water body to more precisely define the existing aquatic life use.
This policy does not apply to human health uses. For human health uses, where the natural background concentration is documented, this new information should result in. at a minimum, a re-evaluation ofthe human

### health use designation. Where the newbackground informationdocuments that the natural background concentration does not support a human health use previously believed attained, it may be prudent for the State orTribe to change the human health use to one 'he natural baclcground concentration will support (e.g., from drinking water supply to drinking water supply only aftertreatment).



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### Conclusion
This policy explains and clarifies the use ofnatural background conditions in establishing site specific criteria for protectionofaquatic life uses. In addition to the three procedures 

### listed above for deriving site specific 

### criteriaas discussed above. States and Tribes 

### can address natural background conditions through refining the designated use 

### to more accurately reflect the aquatic communitypresent within the stream 

### segment. EPA

### recognizes that there are other options available

### to StateslTribes to account for otherambient conditions (e.g.• concentrations due to non-naturaI. man-made conditions) which exceed the national criteria. One such option is for a State orTribe

### to conduct

### aUse Attainability Analysis. consistent with the requirements of40 

### CFR 131.10, and adopt a 

### use which 

### is less than the 101(a) goal 

### uses ofthe CleanWater Act, e.g., 

### less than ufishablelswimmable", ormodify a 101(a) goal 

### use such that less stringentcriteria

### are required. 

### In any 

### case, the existing 

### uses ofthe waterbody segment must be maintained and protected.
Ifyouhave any questions orconcerns regarding 

### this policy, please contactme or have yourstaff

### contact Elizabeth Southerland, Acting Director, Standards and Applied Science Division, at 202-260-3966.

cc: Lepow, OGC Wayland, OWOW Cook,OWM Dougherty, OGWDW



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