This is not about diesel or gasoline fuel. "Diesel range organics" are hydrocarbons with 10-28 carbon atoms, "gasoline range organics" have 6-10 carbon atoms.

Data:

"To address this research gap, we sampled 64 private residential
groundwater wells, ranging from 9–213 m deep, over a 3-y period
(2012–2014) in northeastern Pennsylvania (n = 62) and in southern
New York (n = 2) for analyses of GC-amenable organic
compounds. Fifty-nine samples were analyzed for volatile
organic compounds (VOCs) and gasoline range organic compounds
(GRO; defined as the hydrocarbons eluting between
2-methylpentane and 1,2,4-trimethylbenzene; approximately between
nC_6 and nC_10), and 41 were also analyzed for diesel range
organic compounds (DRO; defined as the hydrocarbons eluting
between nC_10 and nC_28)"

Results:

"Trace levels of GRO and DRO compounds were detected in 9 of
59 (0–8.8 ppb total GRO) and 23 of 41 (0–157.6 ppb total DRO)
groundwater samples, respectively. Although the highest concentrations
of GRO and DRO were always detected within 1 km
of active shale gas operations, this difference in concentration
within 1 km (n = 21) and beyond 1 km (n = 20) from shale gas
wells was only significantly higher in the case of DRO"

Discussion:

"In this region, there are multiple potential sources of elevated
DRO in groundwater, including (i) upward migration of naturally
occurring, formation-derived organic compounds over
geologic time; (ii) lateral transport of drilling muds, flowback, or
produced fluids from faulty wells; (iii) leaking oil and gas waste
containment ponds; (iv) input of organic contaminants from
surface spills of either raw chemicals or residual fracturing fluids;
and (v) leaking underground storage containers or local traffic.
To evaluate these sources systematically, we used geochemical
fingerprinting of inorganic constituents (i.e., Br/Cl ratios),
groundwater residence times (i.e., 4
He concentration),
and dissolved methane concentrations, coupled with our
GRO, DRO, and geospatial analysis."

1) Upward migration: should result in higher levels of 4He in shallow groundwater. Highest DRO and GRO concentrations occur in young groundwater and with low 4He levels.

2) Lateral transport from wells: should result in higher GRO concentration but relatively low levels of DRO (because GROs spread faster), and higher levels of methane. Samples with high methane levels show no correlation with GRO or DRO.

3) Leaking waste containment ponds from fracturing operations: They don't have any data to correlate pond locations with DRO/GRO measurements. Leaks should result in higher DRO than GRO levels, because GROs evaporate, and also elevated chloride and bromide levels. They didn't observe these chloride and bromide levels in high-DRO-samples.

4) Surface spills of fracturing chemicals: should lead to higher DRO and somewhat lower GRO concentration (again because GROs evaporate). This is what they observed in some of their samples: DROs vs. distance to active fracturing wells has "significant" Spearman rank correlation (P=0.03, rho is not given). They have a graph showing that their samples either have elevated GRO or DRO levels, but not both at the same time, so the high-GRO-samples are not explained.

5) Leaking underground fuel tanks, local traffic: the chemicals found are not usually stored in underground tanks and are distinct from gasoline or diesel fuels.