Updated: 2 May 2019 Print version Lecture #53 Redox Chemistry: Arsenic II, Geochemistry (Stumm & Morgan, Chapt.8 ) Benjamin; Chapter 9 David Reckhow CEE 680 #53 1
Arsenic Geology 20th in Abundance in Earth’s Crust Typically Associated with Igneous or Sedimentary Rocks Arsenic Concentrations Tend to be High in Igneous Rocks Containing Iron Oxides Often Associated with Sulfidic Ores From presentation by Philip Brandhuber (2001) David Reckhow CEE 680 #53 2
Geology (cont.) Approximately 245 Arsenic Bearing Minerals have been Identified Some Common Arsenic Bearing Minerals Realgar (AsS) Orpinent (As 2 O 3 ) Arsenopyrite (FeAsS) . H 2 O) Scorodite (FeAsO 4 From presentation by Philip Brandhuber (2001) David Reckhow CEE 680 #53 3
National Distribution of Arsenic in Groundwater From presentation by Philip Brandhuber (2001) Welsh et al. 2000 David Reckhow CEE 680 #53 4
Arsenic Mobility Theoretically As(III) tends to be more Mobile than As(V) As(V) will Strongly Sorb to Iron Oxides To a lesser Extent, As(V) will Sorb to Manganese Oxides However, As(VI) Associated with Iron Oxides may be Transported (Colloidal As) Changes in Redox Conditions may Mobilize Arsenic From presentation by Philip Brandhuber (2001) David Reckhow CEE 680 #53 5
Arsenic Size Distribution Size < 3K Dalton 0.45u > Size > 3K Dalton Size > 0.45u 100 100 80 % of Total As 80 % of Total As 60 60 40 40 20 20 0 0 S1 S2 S3 S4 S5 S6 S7 S8 G1 G2 G3 G4 G5 G6 G7 G8 Surface Water Ground Water From presentation by Philip Brandhuber (2001) Reference: Brandhuber and Amy 1998 David Reckhow CEE 680 #53 6
From: Hering & Elimelech, 1996; AWWARF Report David Reckhow CEE 680 #53 7
Arsenic E h - pH Diagram in Pure Water From presentation by Philip Brandhuber (2001) Arsenate H2 O Unstable 1.000 H O2 (g) H3 AsO4 O .750 - H2 AsO4 .500 O = As - OH 2- HAsO 4 .250 O 3- H AsO 4 E h H 3 AsO 3 0 (V) -.250 Arsenite As AsH 3 - H 2 AsO 3 -.500 H H 2 (g) O -.750 H 2 O Unstable 2- HAsO 3 -1.00 0 As 8 0 2 4 6 10 12 14 O O p H H H Reference: Ferguson and Garvis (1972) David Reckhow CEE 680 #53 8
As and S Ferguson & Gavis, 1972 [Wat. Res. 6:1259] As T = 10 -5 M S T = 10 -3 M Solids in () From: Evangelou, 1998, Environmental Soil and Water Chemistry, Wily Publ. David Reckhow CEE 680 #53 9
Regulatory Dates I 1942, Public Health Service Establishes 50 ppb Standard 1975, EPA formalizes 50 ppb Standard 1989, EPA misses the First of Several Deadlines for Revising Rule June 22, 2000, EPA Proposes MCL of 5 ppb January 22, 2001, EPA Publishes Final Rule, MCL of 10 ppb From presentation by Philip Brandhuber (2001) David Reckhow CEE 680 #52 10
Regulatory Dates II March 20, 2001, EPA Announces it will “Reassess” Costs and Scientific Issues, Delay Rule 60 Days April 23, 2001, EPA Announces Additional Delay of Nine Months May 22, 2001, EPA Announces Delay Until February 22, 2002 July 19, 2001, EPA Request Comment on MCL’s of 20, 5 and 3 as Alternative to 10 ppb October 31, 2001, EPA announces that As standard will be 10 ppb (effective 2006?) From presentations by Brandhuber (2001) & Kempic (2001) David Reckhow CEE 680 #52 11
New regulated Possible Extension contaminants UCMR: 12 months of sampling within window Initial Final List List Health CCL1 CCL2 CCL3 50 42 106 chemicals 10 9 12 microbials Preliminary Final Proposed Final Not actual Rulemaking Process Regulatory Regulatory Schedule Rule Rule Determination Determination Occurrence UCMR1 UCMR2 UCMR3 Monitoring Monitoring Monitoring L1: 12 & 0 L1: 10 & 0 28 & 2 L2: 15 & 1 L2: 15 & 0 98 03 99 00 01 02 04 05 06 07 08 09 10 11 12 13 14 15 12 Year 12
Other new or revised rules expected Revised TCR E. coli in; fecal coliforms out <5% positive for TC as before Published: Feb 13, 2013 with Apr 1, 2016 effective date http://water.epa.gov/lawsregs/rulesregs/sdwa/tcr/regulation_revisions.cfm Revised Pb/Cu Rule Revised LCR: New site selection criteria & sampling procedures not before 2020 no flushing or removal or aerators Same 0.015 mg/L & 1.3 mg/L action levels (in 10% of samples) Perchlorate (ClO 4 - ) Peer review in 1/2017; Proposed rule is delayed States: MA @ 2µg/L; CA @6µg/L; others advisory @1-18µg/L Chlorate (ClO 3 - ) Could be a problem for on-site hypochlorite generation (Stanford, 2014) Hexavalent Chromium Currently regulated as total Cr Likely carcinogen: Final health assessment: end of 2011 Late addition to UCMR 3 (2013-2015) 13
A “simple” view of what’s happening Carcinogenic Carcinogenic Six-Year 2 Six-Year 3 Proposal Six-Year 3 VOCs Final VOCs Proposal (3/ 2010) (<3/ 2014) (3/ 2016) (2/ 2018) (10/ 2013) (not required) RTCR Final RTCR (S ummer, Effective 2012) (S ummer, 2015) CCR Review (12 – 16 months) UCMR3 UCMR3 Monitoring Proposal (1/ 2013 – 12/ 2015) (3/ 2011) LT2ESWTR Review Round 2 LT2ESWTR LT2ESWTR Meetings Method Monitoring - ClO 4 (4/ 2015 – 5/ 2021) Meeting - LT-LCR Proposal LT-LCR ClO 4 (in 2011) Proposal (3/ 2013) Final Final (10/ 2012) (10/ 2014) (3/ 2017) 2012 2015 2016 2013 2014 2017 Reg Det 3 CCL3 Final Reg Det 3 CCL4 Proposal CCL4 Final Final Proposal (<10/ 2013) (10/ 2009) (<10/ 2014) (<7/ 2013) 1 (<7/ 2012) Key Final Rule(s) Proposed Rule(s) Proposal – no fill (<7/ 2015) 1 (<1/ 2017) 1 Final –filled Uncertain – cross hatched Not e: As yet unassigned (fluoride, acrylamide, epichlorohydrin, t ot al chromium / Cr(VI)) Modified from: Steve Via, AWWA Unique color for related regulatory actions 14
Impact to Utilities, Alternative MCL’s 10 9 # CWS I mpacted (1000s) 8 7 6 5 4 GW SW 3 2 1 0 3 5 10 20 Alternative MCL (ug/ L) EPA: Federal Register From presentation by Philip Brandhuber (2001) 65(121):38888 David Reckhow CEE 680 #52 15
Key Features of Arsenic’s Chemistry in Water Present in two Oxidation States Behaves as an Acid Arsenate (As(V)) - = > HAsO 4 2- = > AsO 4 3- H 3 AsO 4 = > H 2 AsO 4 Arsenite (As(III)) - = > HAsO 3 2- H 3 AsO 3 = > H 2 AsO 3 From presentation by Philip Brandhuber (2001) David Reckhow CEE 680 #52 16
Coagulation As(V) is much better removed than As(III) From: Hering & Elimelech, 1996; AWWARF Report David Reckhow CEE 680 #52 17
Coagulation Alum vs Ferric Fe(III) is clearly better Why? From: Hering & Elimelech, 1996; AWWARF Report David Reckhow CEE 680 #52 18
Oxidize - - O 3 - Cl 2 - MnO 4 Treat - RO/NF - Coagulation/MF - Activated Alumina - Ion Exchange - Greensand - Iron media (GFH) Dispose of Residual - POTW - Dewater - Landfill From presentation by Philip Brandhuber (2001) David Reckhow CEE 680 #52 19
Ferrous Arsenite Initial Arsenite:Fe ratio of 1:1 From GEO-CHEM-PC From: Evangelou, 1998, Environmental Soil and Water Chemistry, Wily Publ. David Reckhow CEE 680 #53 20
To next lecture DAR David Reckhow CEE 680 #53 21
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