Gorgas Wetlands RevitalizationAlabama Power

CompanyEnvironmental AffairsField Services

Gerson Pickett

Background

Recirculating Reducing and Alkalinity Producing System

(ReRAPS) ReRAPS was designed and

built by APC as a EPRI TC in the late 1990’s

Purpose is to treat acidic coal pile runoff

Treatment system is a series of constructed wetland cells

Where it Begins Chemical process begins at the coal pile Pyrite oxidation process occurs:

Pyrite + Bacteria + Moisture acid2FeS2(s)+7O2+2H2O 2Fe2++4SO4

2-+4H+

Water produced is high in dissolved metals Aluminum

Iron

Acidic CPR is harmful to aquatic life

Runoff is routed to a detention basin Coal pile runoff pH ranges between

2.5 and 5.5

ReRAPSReRAPS (Recirculating Reducing and

Alkalinity Producing System)Treats runoff using an alternative constructed

wetland design Provides improved wetland performance Based on partial recirculation of treated water into

detention pond (pH >4.25)Set to 20 to 40 gpm, <6”- 24hr rainSemi-passive RAPS based system

Combined pump/gravity generated systemRecirculation moderate pH in detention pond

Minimize potential Al hydroxide plugging (armoring) of RAPS substrate

11 acre coal pile

Constructed Wetland

Coal Pile

RunoffCollection

DetentionBasin

CattailFilter

OxidationPrecipitation

Basin

RAPS & Stilling Basin

WetlandStorage Basin

Aeration

VegetativeCell

Flow Diagram

RiverDischarge

Coal Pile

RunoffCollection

DetentionBasin

CattailFilter

OxidationPrecipitation

Basin

RAPS & Stilling Basin

WetlandStorage Basin

Aeration

VegetativeCell

Flow Diagram

RiverDischarge

RAPS or Vertical Flow Component

Organic matter is composed of wood chips, also cow, horse , and chicken manure.

Pooled WaterPooled WaterPooled Water

Coal Pile RunoffLow pH

D-FeD-Al

(avoided)Neutral pHLow ORP

D-Fe passes throughOrganicMatter

Pooled Water

Alkalinity productionMetal sulfide precipitation

Limestone

RAPS Chemistry Alkalinity Production

Limestone Dissolution CaCO3 (s)+H+ Ca2+ +HCO3

-

Organic Decomposition 2CH2O+SO4

2- H2S+2HCO3-

Metal sulfide precipitation Me2+

(ag) +S- (ag) MeS2(s)

Background2 acre ReRAPS has

successfully treated coal pile runoff for over 10 yrs. Neutralize acidity Reduce toxicity to aquatic life

0.1 acre RAPS or vertical flow component (VFC) RAPS cell is the heart of the

wetland Performance has

diminished due to decomposition and reduced porosity (plugging).

Waste Characteristics and Disposal•Toxicity Characteristics Leaching Potential (TCLP)

• TCLP results determined that the materials were non hazardous

•Disposal option chosen was off-site landfill•Greenhouse Gas (GHG) Rule reporting avoided

•Cost effectiveness

Hazardous Waste Identification

Test Results Found (mg/l)

TCLP Regulatory

Level (mg/L)

Silver ND (<0.006) 5.0

Arsenic ND (<0.009) 5.0Barium 0.103 100.0

Cadmium 0.003 1.0

Chromium ND (<0.01) 5.0

Mercury ND (<0.0002) 0.2Lead ND (<0.01) 5.0

Selenium ND (<0.02) 1.0

Majority of the decomposed

materials was replaced Through joint efforts between

EA Field Services and Plant Gorgas, the old organics/limestone have been removed and replaced Process was accomplished

by allowing the system to completely dry

Material was removed in layers to assure thorough drying

Dried product then hauled to a off-site landfill.

Waste removal process

Quantity of Material Removed/Replaced-“Revitalizing” the Wetland

• Organic Material• 220 tons • 4 ft in depth•125 ft long• wood chip/manure mixture

•Limestone• 30 tons •1 ft of the original 3 ft• 3 to 4 inch stone

Back In BusinessThe wetland is in full operation mode.With recent rain events, there is now CPR

water to be treated Testing and pH monitoring has confirmed

optimal performance Annual compliance test are TSS, pH and

oil & grease

Questions?