HYDRO27256

• Permit No: C1980006
• IBM Index Class Name: Hydrology
• Doc Date: 7/12/1993
• Doc Name: REQUEST OFR STORMWATER EXEMPTION
• From: KERR COAL CO
• To: WQCD
• Permit Index Doc Type: NPDES Permit
• Media Type: D
• Archive: No

~_
III 1111111111111 III
999
kerr coal company
box 487 ~ Walden, Colorado 80480 ~ [phone]
RFCEIVEC
Date• JUL 121993
Ms. Anne lltlenfeldt Divisron of none~ats a heoloyy
Colorado Department of Health
Water Quality Control Division
4210 East 11th Avenue
Denver, Colorado 80220
Re: Kerr Coal Company - M?~r Mine (Permit No, COG8500211, Reaues< for Stormwater
Exemption
Dear Ms. lltlenfeldt:
Kerr Coal Company (Kerr) operates the Mazr Mine, loated approximately founeen miles east
of the town of Walden, Colorado. Drainage and sediment control for the mining related
disturbance is provided by a number of engineered sedimentation ponds, collection/diversion
ditches, and associated drainage structures. Discharge from the sedimentation ponds is
controlled and regulated under applicable provisions of Permit COG850021. Discharge for the
twelve individual outfalls under this permit comes eadusively from either preapitation or
snowmelt runoff, with no process water discharge.
All sedimentation ponds are designed and maintained to provide a minimum detention time of
at least 24 hours for retained runoff resulting from the 10 year, 24 hour storm event. While [he
ponds are designed to provide adequate detention time to allow settlement of suspended solids,
due [o the characteristics of the dominant soil types in this area both undisrurbed and disrurbed
area runoff typically have relatively high levels of suspended solids. In addition, a relatively high
percen[age of the suspended solids in Stormwater runoff aze fine colloidal materials which do
not readily settle ou[ of suspension.
During periods of high flow due to either snowmelt or preupitation runoff, the acted factors
combine to limit the trapping efficiencq of the existing sedimentation ponds with the result that n
Total Suspended Solids (I'SS) and Settleable Solids concentrations in pond discharge ma ex ~o,.eX D~
applicable effluent limitations. The accompanying monitoring report(s) for pond(s) 30~
indiate eaceedance of TSS and/or Settleable Solids limitations for the corresponding
monitoring period. Eaceedance of applicable permit effluent limitations resulted from:
^ Discharge from rainfall runoff occurring within 48 hours after measurable
predpita[ion has stopped
Discharge from snowmelt runoff occurring within 48 hours after runoff inflows
to the pond(s) have stopped
Documentation of preapitation and snowmelt occurrence and snowmelt inflows to the ponds
is retained at the minesite and is available for inspection by authorized agenry representatives.