WQCD Response:Biotic Ligand Model Issues

1

Overview• Biotic Ligand Model (BLM) is a relatively new tool from

EPA for developing site-specific criterion-based copper standards. It is the best tool available for the task.

• Hearing process has provided an opportunity to work closely with stakeholders to gain insights regarding acquisition of input data and interpretation of model output. The Division appreciates the cooperative approach.

Status Review

Proponent Segments Status CommentAurora US16i Withdrawn Additional data

neededParker CC01 Temp Mod Additional data

neededPlum Creek US10a Temp Mod Additional data

neededMetro US15 &

MS01aSite-specific stds

Adoption recommended

Centennial US16g & 14 Site-specific stds

Adoption recommended

UTSD BT02 Reviewed stds Let stand

What Makes a Good Proposal?• Metro is a good case study

•Spatial coverage brackets significant hydrologic features and extends far enough to support proposal

•Temporal coverage spans enough years to incorporate seasonal and hydrologic variability

•Large sample size improves precision of result

•Longevity plan will support review of standards at next basin hearing

South Platte, Denver to Platteville (9 sites, 42 mi)

Results with Confidence Intervals

0

10

20

30

40

50

60

70

0 10 20 30 40

Acu

te FM

B, u

g/L

River Miles below Metro

Wrap-up• Expecting more copper proposals based on BLM

• Process should be easier to navigate next time because there is greater clarity regarding expectations for data collection and analysis

• Future proposals to benefit from:

•Revised guidance from Division

•Revised documentation and expanded model output from EPA

Significant Hydrologic Features

0

20

40

60

80

100

120

0 5 10 15 20

Acu

te FM

B, u

g/L

River Miles below Chatfield