Attenuation Factors for Hydrocarbons Associated With a Diesel Spill

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1 Attenuation Factors for Hydrocarbons Associated With a Diesel Spill By Lindsay Breyer, CIH and James B. Cowart, PE Walsh Environmental Scientists and Engineers, Boulder, Colorado

2 Site Location: Mandan, North Dakota Project Location

3 Site Characteristics Million gallon diesel LNAPL Smear Zone around LNAPL Contaminated soil and groundwater Commercial and residential buildings above impacted area

4 Conceptual Model Approx. 20 ft. Contaminants from soil, groundwater, or free product

5 Project Description Screening level investigation Install soil gas monitoring wells Sample free product, groundwater, soil, soil gas, indoor air, and outdoor air Identify COCs for vapor intrusion pathway Evaluate completeness of vapor intrusion pathway

6 Field Investigation COCs: Diesel-related contaminants (e.g. BTEX, naphthalene, trimethylbenzenes, etc. Media Sampled: Soil (Deep and Shallow), Free Product, Groundwater, Soil Gas (Deep and Shallow), Indoor Air, Outdoor Air Single Sampling Event, October 2002

7 Sampling Locations 12 Indoor Air Locations Above Contamination 1 Indoor Air Location Outside Known Contamination 3 Outdoor Air Locations 5 Shallow Soil Gas, 5 Deep Soil Gas 5 Shallow Soil, 5 Deep Soil 4 Groundwater 2 Free Product

8 Analytical Methods Analysis Soil Groundwater Soil Gas Indoor/ Outdoor Air Volatile Organic EPA 8260B EPA 8260B EPA TO-15 EPA TO-15 Compounds (VOCs) Semivolatile Organic Compounds (SVOCs) EPA 8270C EPA 8270C EPA TO-13 1 EPA TO-13 1 Diesel Range Organics (DRO) EPA 8015M EPA 8015M EPA TO-13 Mod. EPA TO-13 Mod. C2 to C10 Hydrocarbons NA NA EPA TO-3 EPA TO-3 Fixed Gases 2 NA NA ASTM D1946 ASTM D Includes only the polynuclear aromatic hydrocarbons (PAHs) 2 Methane, nitrogen, oxygen, carbon dioxide, carbon monoxide

9 Additional Information Gathered Soil grain size, bulk density, moisture content Field screening for O 2, LEL, CO, H 2 S, VOCs Groundwater/LNAPL elevation, ph, conductance, temperature, dissolved oxygen Building inspections and interviews

10 Efforts to quantify background Comprehensive questionnaire, building inspection Collection of outdoor air samples Sampling in location outside of known contaminant plume

11 Results - Compounds Detected Diesel-Related Contaminants: Methane Benzene Toluene Ethylbenzene Xylenes 1,2,3-TMB 1,2,4-TMB 1,3,5-TMB n-propylbenzene Isopropyltoluene 2-Ethyltoluene 4-Isopropyltoluene n-butylbenzene sec-butylbenzene Naphthalene Other aliphatic, aromatic hydrocarbons Non-Diesel Compounds: PCE, TCE, others

12 Results - Concentrations Above LNAPL Compound Average LNAPL ug/l Deep Soil ug/kg Shallow Soil ug/kg Deep Soil Gas ug/m 3 Shallow Soil Gas ug/m 3 Average Indoor Air ug/m 3 Average Outdoor Air ug/m 3 "Background" Indoor Air ug/m 3 n=2 n=1 n=1 n=1 n=1 n=6 n=3 n=1 1,2,4-Trimethylbenzene 7,500, , ,3,5-Trimethylbenzene 1,545, , < Isopropyltoluene NA , < Benzene <200, , Ethylbenzene 666, , Isopropylbenzene 228, , < Naphthalene 2,655, , <2.6 <2.6 n-butylbenzene NA , < n-propylbenzene 952, , sec-butylbenzene 296, , < Toluene <200, , Xylenes (total) 2,780, , ,2,3-Trimethylbenzene NA NA NA 36, < Ethyltoluene NA NA NA 25,000 1, Ethyltoluene NA NA NA 89, Methane NA NA NA 23% 2.00% % % % Averages exclude non-detects

13 Results - Concentrations In Smear Zone Compound Average Groundwater ug/l Average Deep Soil ug/kg Average Shallow Soil ug/kg Average Deep Soil Gas ug/m 3 Average Shallow Soil Gas ug/m 3 Average Inside Air ug/m 3 Average Outside Air ug/m 3 "Background" Indoor Air ug/m 3 n=3 n=3 n=3 n=3 n=3 n=6 n=3 n=1 1,2,4-Trimethylbenzene ,333 2, ,3,5-Trimethylbenzene < <6.7 29,667 1, Isopropyltoluene NA 735 <6.7 3, Benzene <6.7 15, Ethylbenzene <6.7 61, Isopropylbenzene <6.7 7, Naphthalene ,000 1, <2.6 n-butylbenzene NA 2333 <6.7 15, n-propylbenzene <6.7 24, sec-butylbenzene < <6.7 4, Toluene <10 <1300 < Xylenes (total) <6.7 69,687 1, ,2,3-Trimethylbenzene NA NA NA 41,333 1, Ethyltoluene NA NA NA 25, Ethyltoluene NA NA NA 45,667 1, Methane NA NA NA 17% 0.85% % % % Averages exclude non-detects

14 Results - Summary Compound Soil* Groundwater Deep Soil Gas Shallow Soil Gas Indoor Air Background Indoor Air Benzene X X X X X X X Toluene X X X X X X X Ethylbenzene X X X X X X X Xylenes (total) X X X X X X X 1,2,3-Trimethylbenzene NA NA X X X X 1,2,4-Trimethylbenzene X X X X X X X 1,3,5-Trimethylbenzene X X X X X X n-propylbenzene X X X X X X X Isopropylbenzene X X X X X X 2-Ethyltoluene NA NA X X X X X 4-Ethyltoluene NA NA X X X X X n-butylbenzene X X X X X Sec-butylbenzene X X X X X X p-isopropyltoluene X X X X X X Naphthalene X X X X X 2-Methylnaphthalene X X NA NA NA NA NA Acenaphthene X X X X Fluorene X X Phenanthrene X X Anthracene X X = Compound detected in one or more samples from this medium NA = Compound not included in analyte list *Screening levels not available for soil samples Highlighting indicates one or more samples exceeds EPA screening level Outdoor Air

15 Observed Attenuation Factors Compound LNAPL to Deep Soil Gas Locations Above LNAPL Deep Soil Gas to Shallow Soil Gas Shallow Soil Gas to Indoor Air Locations Outside LNAPL But Above Contaminated Soil Deep Soil to Deep Soil Shallow Soil Deep Soil Gas to Gas to Gas Shallow Soil Indoor Air Gas 1,2,4-Trimethylbenzene ,3,5-Trimethylbenzene Isopropyltoluene NA Benzene NA Ethylbenzene Isopropylbenzene Naphthalene n-butylbenzene NA n-propylbenzene sec-butylbenzene Toluene NA NA Xylenes (total) ,2,3-Trimethylbenzene NA NA Ethyltoluene NA NA Ethyltoluene NA NA Methane NA NA Average Minimum Maximum

16 Difficulties and Limitations Cold and wet during sampling event Difficulties in sampling soil gas Single event, limited number of samples Low groundwater elevation Background sources

17 Conclusions The observed attenuation factors of diesel-related compounds for deep soil gas to shallow soil gas averaged about 0.03 to For shallow soil gas to indoor air, the attenuation factors were 0.03 to Attenuation factors for individual compounds varied by an order of magnitude or more. Methane was found in potentially explosive concentrations in the subsurface at this site. Methane has the potential to accumulate to hazardous concentrations in underground structures such as sewers and utility vaults. The concentrations of diesel-related compounds in indoor air were relatively low, although several compounds exceeded the screening level established in the EPA vapor intrusion guidance. Further evaluation of the site is recommended to more fully evaluate the impacts of subsurface diesel contamination on indoor air.

18 Contact Information Contact: (303)